Efficient synthesis of six tri- to hexasaecharide fragments of shigella flexneri serotypes 3a and/or X O-antigen, including a study on acceptors containing N-trichloroacetylglucosamine versus N-acetylglucosamine

Efﬁcient Synthesis of Six Tri- to Hexasaccharide Fragments of

Shigella ﬂexneri Serotypes 3a and/or X O-Antigen, Including a

Study on Acceptors Containing N-Trichloroacetylglucosamine versus

N-Acetylglucosamine

Julien Boutet,^†,‡Catherine Guerreiro, and Laurence A. Mulard*

Institut Pasteur, Unite´ de Chimie des Biomole´cules (URA CNRS 2128), 28 rue du Dr Roux,

F-75015 Paris, France

laurence.mulard@pasteur.fr

ReceiVed September 26, 2008

Six tri- to hexasaccharide fragments of the {2)-[R-D-Glcp-(1f3)]-R-L-Rhap-(1f2)-R-L-Rhap-(1f3)-

[Acf2]-R-L-Rhap-(1f3)-ꢀ-D-GlcpNAc-(1f}_npolymer ([(E)AB_AcCD]_n) were synthesized as their propyl

glycosides. All targets share the (E)AB sequence. Following a thorough investigation on the use of

N-trichloroacetylglucosamine- versus N-acetylglucosamine-containing tri- and tetrasaccharide acceptors,

the successful strategy was based on an efﬁcient combination of the trichloroacetimidate chemistry, a

trichloroacetyl used as permanent N-protection, and an allyl aglycon as temporary and/or permanent

anomeric protection of selected building blocks. Use of an EAB intermediate orthogonally protected at

2_Aprovided both the trisaccharide target and acceptor 12, the condensation of which with a chain terminator

D followed by full deprotection, gave tetrasaccharide D(E)AB. Alternatively, stepwise glycosylation of

12 with a D donor compatible with a selective deblocking at position 3_Dand a 2-O-acetyl C donor

following exposure of OH-3_Dled to a pentasaccharide, which was partially and fully deprotected into

free _AcCD(E)AB and CD(E)AB, respectively. Furthermore, chain elongation of the common D(E)AB

acceptor with a 2_B-O-levulinoyl rhamnobiose donor BC and subsequent partial or total deprotection of

the resulting hexasaccharide provided B_AcCD(E)AB and BCD(E)AB, respectively. All of the synthesized

oligosaccharides are parts of the O-antigen of Shigella ﬂexneri 3a, a prevalent serotype. Moreover, the

non-O-acetylated fragments are also parts of the S. ﬂexneri serotype X O-antigen.

Introduction

infections, which altogether rank third among all causes of

disease burden worldwide.²Shigellosis is a disease of the most

impoverished areas and a major health concern particularly in

the pediatric population between 1 and 5 years. Humans are

the only reservoir of this highly contagious infection associated

with increased antibiotic resistance.^1,3,4The World Health

Organization (WHO) has set it as one of its priorities for the

Shigellosis, also termed bacillary dysentery, is an invasive

infection of the human colon often associated with blood and

mucus in the stools.¹It is one among the many forms of enteric

^†Universite´ Paris Descartes, 12 rue de l’Ecole de Me´decine, F-75006 Paris,

France.

^‡Present address: Glycom A/S, DTU, Building 201, DK-2800 KGs, Lyngby,

Denmark.

(1) Niyogi, S. K. J. Microbiol. 2005, 43, 133–143.

10.1021/jo802127z CCC: $40.75

Published on Web 03/11/2009

2009 American Chemical Society

J. Org. Chem. 2009, 74, 2651–2670 2651

Boutet et al.

FIGURE 1. Repeating units of the O-Ags of S. ﬂexneri serotypes Y (I), X (II), 3a (III), and 2a (IV).

development of a vaccine, and a number of candidates have

undergone clinical trials. However, as an additional complexity,⁴

the large number of pathogens involved seriously hampers the

development of an efﬁcacious vaccine against shigellosis, and

there is yet no broadly distributed vaccine against this disease.⁵

Shigella ﬂexneri, one of the four Shigella species, is the most

frequently isolated causative bacteria worldwide. It is endemic

in developing countries and prevails in children less than 5 years

old.^5,6S. ﬂexneri is divided into 15 serotypes, differentiated on

the basis of the carbohydrate repeating unit of the O-antigen

(O-Ag), which is the speciﬁc polysaccharide part of the bacterial

lipopolysaccharide (LPS),⁷a key player in bacterial virulence

and resistance to innate immunity.⁸As a number of different S.

ﬂexneri serotypes, including serotype 3a, are isolated from

patients, there is an inherent need for a multivalent vaccine in

order to provide a broad protection.^5,6Investigations in the ﬁeld

have shown that an initial infection protects against subsequent

exposure to homologous serotype.^9,10This suggests that S.

ﬂexneri O-Ags are crucial targets used by the host protective

adaptive immunity. Interestingly, all S. ﬂexneri but serotype 6

share a linear tetrasaccharide backbone, made of three R-linked

L-rhamnosyl residues (A, B, C) and a 2-acetamido-2-deoxy-ꢀ-

D-glucopyranosyl residue (D). This tetrasaccharide ABCD (I)

is the basic repeating unit (RU) of serotype Y (Figure 1).

Additional serotype-speciﬁcity is associated with the presence

of branched R-D-glucopyranosyl (E) and O-acetyl decorations.⁷

Noteworthy, the LPS glucosylation affects S. ﬂexneri 5a O-Ag

conformation, resulting in a shortened length.^8,11,12Impact on

bacterial virulence was hypothesized.⁸To our knowledge, the

inﬂuence of the O-acetylation remains yet unknown. Considering

the close resemblance of the O-Ag RUs of the various serotypes,

S. ﬂexneri was selected as an attractive model to investigate

the key role played by bacterial O-Ag decorations in virulence,

resistance to innate immunity and immunodominant epitope

composition. Having initiated our study on S. ﬂexneri 5a^11,13

and S. ﬂexneri 2a,^12,14we focused more recently on additional

serotype-speciﬁc glucosylation and O-acetylation patterns.^15,16

Along this line, we report here the synthesis of fragments of S.

ﬂexneri serotype X and 3a O-Ags, the repeating units of which

are the branched pentasaccharides (E)ABCD (II) and

(E)AB_AcCD (III),⁷respectively (Figure 1). These well-deﬁned

synthetic fragments of the native polymer will serve to probe

O-Ag structure and antibody recognition as previously reported

for serotypes Y,¹⁷5a,¹¹and 2a.¹²Interestingly, the S. ﬂexneri

X O-Ag is the non-O-acetylated form of the S. ﬂexneri 3a O-Ag.

Results and Discussion

The syntheses of all glucosylated di- to pentasaccharide

fragments of S. ﬂexneri 3a and S. ﬂexneri X O-Ags having

residue A, C, or D, at their reducing end have been described

previously.^15,16We report here the synthesis of the tri-, tetra-,

and pentasaccharides EAB (1), D(E)AB (2), _AcCD(E)AB (3),

and CD(E)AB (4). These compounds complete the panel of

frame-shifted glucosylated di- to pentasaccharide fragments of

S. ﬂexneri 3a O-Ag needed for a detailed investigation of the

recognition speciﬁcity of S. ﬂexneri 3a LPS by protective

monoclonal antibodies. In addition, as we are aware of a possible

migration of the acetyl group from position 2 of rhamnose C

to the cis-vicinal hydroxyl in pentasaccharide 3, we also

prepared the 2_C-O-acetylated and non-O-acetylated hexasac-

charides B_AcCD(E)AB (5), and BCD(E)ABC (6), respectively.

Moreover, we propose an optimized protocol for the conversion

of a trichloroacetamide moiety vicinal to an ester into the

corresponding acetamido alcohol product. Taking advantage of

this procedure, two routes to 5 and 6 were studied. The ﬁrst

one involves a 2_D-acetamido D(E)AB acceptor, and the second

one uses a 2_D-trichloroacetamido D(E)AB acceptor. A compara-

tive study was ﬁrst made on the more readily available

2_D-acetamido D(E)A and 2_D-trichloroacetamido D(E)A accep-

tors, respectively.

(2) Girard, M. P.; Steele, D.; Chaignat, C. L.; Kieny, M. P. Vaccine 2006,

24, 2732–2750.

(3) von Seidlein, L.; Kim, D. R.; Ali, M.; Lee, H.; Wang, X.; Thiem, V. D.;

Canh do, G.; Chaicumpa, W.; Agtini, M. D.; Hossain, A.; Bhutta, Z. A.; Mason,

C.; Sethabutr, O.; Talukder, K.; Nair, G. B.; Deen, J. L.; Kotloff, K.; Clemens,

J. PLoS Med. 2006, 3, e353.

(4) Phalipon, A.; Mulard, L. A.; Sansonetti, P. J. Microbes Infect. 2008, 10,

1057–1062.

As for other compounds we synthesized in the S. ﬂexneri 3a

and X series,^15,16the target products 1-6 were obtained as

propyl glycosides. Relying on our previous experience in the

synthesis of S. ﬂexneri 2a and S. ﬂexneri 5a oligosaccharides,^18,19

all glycosylation steps used the efﬁcient trichloroacetimidate

(5) Levine, M. M.; Kotloff, K. L.; Barry, E. M.; Pasetti, M. F.; Sztein, M. B.

Nat. ReV. Microbiol. 2007, 5, 540–553.

(6) Kotloff, K. L.; Winickoff, J. P.; Ivanoff, B.; Clemens, J. D.; Swerdlow,

D. L.; Sansonetti, P. J.; Adak, G. K.; Levine, M. M. Bull. W. H. O. 1999, 77,

651–666.

(7) Lindberg, A. A.; Karnell, A.; Weintraub, A. ReV. Infect. Dis. 1991, 13,

S279–S284.

(8) West, N. P.; Sansonetti, P.; Mounier, J.; Exley, R. M.; Parsot, C.;

Guadagnini, S.; Prevost, M. C.; Prochnicka-Chalufour, A.; Delepierre, M.;

Tanguy, M.; Tang, C. M. Science 2005, 307, 1313–1317.

(9) Ferreccio, C.; Prado, V.; Ojeda, A.; Cayyazo, M.; Abrego, P.; Guers, L.;

Levine, M. M. Am. J. Epidemiol. 1991, 134, 614–627.

(10) Formal, S. B.; Oaks, E. V.; Olsen, R. E.; Wingﬁeld-Eggleston, M.; Snoy,

P. J.; Cogan, J. P. J. Infect. Dis. 1991, 164, 533–537.

(11) Clément, M. J.; Imberty, A.; Phalipon, A.; Perez, S.; Simenel, C.; Mulard,

L. A.; Delepierre, M. J. Biol. Chem. 2003, 278, 47928–47936.

(12) Vulliez-Le Normand, B.; Saul, F. A.; Phalipon, A.; Bélot, F.; Guerreiro,

C.; Mulard, L. A.; Bentley, G. A. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 9976–

9981.

(13) Mulard, L. A.; Ughetto-Monfrin, J. J. Carbohydr. Chem. 1999, 18, 721–

753.

(14) Costachel, C.; Sansonetti, P. J.; Mulard, L. A. J. Carbohydr. Chem.

2000, 19, 1131–1150.

(15) Boutet, J.; Guerreiro, C.; Mulard, L. A. Tetrahedron 2008, 64, 10558–

10572.

(16) Boutet, J.; Mulard, L. A. Eur. J. Org. Chem. 2008, 5526–5542.

(17) Vyas, N. K.; Vyas, M. N.; Chervenak, M. C.; Johnson, M. A.; Pinto,

B. M.; Bundle, D. R.; Quiocho, F. A. Biochemistry 2002, 41, 13575–13586.

(18) Mulard, L. A.; Ughetto-Monfrin, J. J. Carbohydr. Chem. 2000, 19, 193–

220.

2652 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

SCHEME 1. Synthesis of Propyl Glycosides 1 and 2

(TCA) chemistry.²⁰The allyl group, often used in complex

oligosaccharide synthesis,^21,22was selected for temporary

protection at the anomeric position of the various building

blocks. Interestingly, in addition to being orthogonal to a number

of protecting groups, an allyl ether is easily reduced to a propyl

ether upon Pd/C catalyzed hydrogenation. We took advantage

of this property to block the reducing end of the target

oligosaccharides in a form mimicking the anomery found in

the O-Ag.

Synthesis of Trisaccharide EAB (1) and Tetrasaccharide

D(E)AB(2). We ﬁrst undertook the preparation of trisaccharide

1 and tetrasaccharide 2, which did not require chain elongation

at the D residue and did not comprise the 2-O-acetyl C residue.

As depicted in Scheme 1, the allyl rhamnoside 7,^16,23featuring

permanent benzyl groups at O-3 and O-4, was glycosylated with

the known disaccharide trichloroacetimidate 8,²⁴bearing a

benzoyl participating group on position 2_A. The condensation

was run in toluene in the presence of catalytic TfOH to give

the 2_A-O-benzoyl trisaccharide 10 in 93% yield. On the basis

of previous observations, made when working on the corre-

sponding EA methyl glycoside 13, which suggested the partial

masking at OH-2_Aby the vicinal 2,3,4,6-tetra-O-benzyl-D-

glucopyranosyl residue,¹³a steric hindrance surrounding OH-

2_Awas anticipated. Accordingly, debenzoylation of trisaccharide

10 into alcohol 12 (98%) was achieved using a large excess of

sodium methoxide in a 1:2 reﬂuxing mixture of dichloromethane

and methanol. Moreover, the recently reported levulinate

analogue 9¹⁶was investigated as an alternative glycosyl donor.

To our satisfaction, condensation of trichloroacetimidate 9 with

acceptor 7 led to the fully protected 2_A-O-levulinoyl trisaccharide

11 in 92% yield when the reaction was run in toluene. This

solvent was preferred to dichloromethane, in which the reaction

led to a lower isolated yield of levulinate 11 (82%). The NMR

analysis of 11 showed a ¹J_C1A,H1Aof 173.4 Hz, which indicated

an R-AB linkage²⁵and ascertained that the levulinic ester had

played its role of participating group. Interestingly, treatment

of the fully protected 11 in reﬂuxing methanolic sodium

methoxide gave alcohol 12 in a satisfactory 94% yield,

conﬁrming the potential of donor 9 as an alternative to donor

8. As shown previously, this is of special interest when

orthogonality to acetate is required.¹⁶Pd/C mediated hydro-

genolysis and concomitant allyl reduction of alcohol 12 next

provided the linear trisaccharide 1 (77%).

(19) Be´lot, F.; Wright, K.; Costachel, C.; Phalipon, A.; Mulard, L. A. J.

Org. Chem. 2004, 69, 1060–1074.

(20) Schmidt, R. R.; Kinzy, W. AdV. Carbohydr. Chem. Biochem. 1994, 50,

21–123.

(21) Auzanneau, F. I.; Forooghian, F.; Pinto, B. M. Carbohydr. Res. 1996,

291, 21–41.

(22) Be´lot, F.; Guerreiro, C.; Baleux, F.; Mulard, L. A. Chem. Eur. J. 2005,

11, 1625–1635.

(23) Westerduin, P.; de Haan, P. E.; Dees, M. J.; van Boom, J. H. Carbohydr.

Res. 1988, 180, 195–205.

(24) Mulard, L. A.; Clément, M. J.; Segat-Dioury, F.; Delepierre, M.

Tetrahedron 2002, 58, 2593–2604.

(25) Bock, K.; Pedersen, C. M. Acta Chem. Scand., Ser. B 1975, 29, 258–

264.

J. Org. Chem. Vol. 74, No. 7, 2009 2653

Boutet et al.

FIGURE 2. Known methyl glycoside analogues of targets 1 (V) and 2 (VI).

Interestingly, alcohol 12 could serve as an ideal acceptor in

the synthesis of the branched tetrasaccharide 2 (Scheme 1). Thus,

acceptor 12 was reacted with the readily available glucosamine

donor 14^26,27in toluene in the presence of a catalytic amount

of TfOH, to give the tri-O-acetyl tetrasaccharide 15 (87%).

Transesteriﬁcation of the acetates gave triol 16 (79%), which

was next converted to target 2 (68%), following a Pd/C mediated

two-step hydrogenation process allowing hydrogenolysis of the

benzyl ethers, reduction of the allyl into a propyl, and reduction

of the trichloroacetamide into the corresponding acetamide.

Alternatively, target 2 was obtained in 40% overall yield from

alcohol 12 via acetamidotriol 17, issued from concomitant N,O-

transesteriﬁcation and selective N-acetylation of the fully

protected tetrasaccharide 15. Considering the scale on which

the latter transformation was evaluated, both routes appeared

comparable. Noteworthy, the methyl glycoside analogues of

targets 1 and 2, compounds V and VI (Figure 2), respectively,

have been reported before.²⁸Interestingly, the strategy disclosed

here differs quite a lot from the one used previously, in terms

of both the glycosylation chemistry and the protecting group

pattern used for precursors to residues A, B, and D. However,

the use of an EA donor, as reported here, is probably the main

difference between the two disclosed strategies. It was found

advantageous in order to avoid the difﬁcult separation between

the RE- and ꢀE-EAB trisaccharide isomers obtained when

following the formerly reported linear route, which used an AB

acceptor and an E donor.²⁸

Synthesis of Pentasaccharides _AcCD(E)AB (3) and CD(E)-

AB(4) and Hexasaccharides B_AcCD(E)AB (5) and BCD(E)-

AB (6). The retrosynthetic analysis of 3-6 showed that all target

oligosaccharides could derive from a common fully protected

D(E)AB precursor 19. Intermediate 19 is blocked at positions 4_D

and 6_Dvia an isopropylidene acetal, which we found appropriate

on several occasions in the S. ﬂexneri series^18,19following reports

by others²⁹and our own observations¹³on the potential interference

of the more common benzylidene acetal due to anisotropic shielding

of H-6_C(Scheme 2). The use of tetrasaccharide 19 opened the way

to two potential acceptors differentiated at position 2_D, namely, a

2_D-N-trichloroacetyl intermediate 20, bearing a masked acetamido

function at position 2_D, and the 2_D-N-acetyl analogue 21, corre-

sponding to the introduction of the 2_D-acetamido moiety at an early

stage in the synthesis. Indeed, available data suggest that acceptors

containing N-acetylglucosamine are less reactive than their masked

acetamido counterparts and occasionally prone to side reactions^30-32

but can be used successfully in complex oligosaccharide synthe-

sis.²²On one hand, chain elongation with the known trichloroace-

timidate rhamnosyl donor³³22 having the 2_C-O-acetyl in place

would lead to the pentasaccharides 3 and 4. On the other hand,

chain elongation with the newly disclosed rhamnobiosyl trichlo-

roacetimidate 23 would provide both 2_C-O-acetyl hexasaccharide

5 and free hexasaccharide 6. Indeed, as for rhamnose 22, position

2_Cof rhamnobiose 23 is acetylated, whereas position 2_Bis blocked

as a levulinate, selected for its orthogonality to an acetate.

Noteworthy, both acetyl and levulinoyl protecting groups in donors

22 and 23 served as a participating group when required at the

glycosylation stage.

The synthesis of pentasaccharides 3 and 4 was inspired from

that of trisaccharide 1 and tetrasaccharide 2. Thus, trisaccharide

12 was used as an intermediate. Since chain elongation was at

position 3_D, we favored the recently reported, orthogonally

protected glucosamine trichloroacetimidate²⁷18 instead of the

corresponding triacetate 14 to serve as donor. However, the fully

protected tetrasaccharide 19 was isolated in rather low yields,

when the condensation of acceptor 12 and donor 18 was run at

-40 °C in either dichloromethane or toluene (Table 1, entries

1 and 2, respectively), although these conditions had been found

satisfactory for a similar condensation yielding the D(E)ABC

analogue.¹⁶A closer investigation of the reaction showed that

unreacted acceptor remained, whereas the donor was totally

consumed. Other conditions, focusing on temperature, amounts

of catalyst, and amounts of donor were therefore studied (Table

1, entry 4; entries 3 and 4; and entries 5 and 6, respectively).

Since we had previously noticed the degradation of donor 18

at temperatures above -20 °C,¹⁶this temperature was set as a

limit. Indeed, our new data conﬁrmed that the ideal reaction

temperature for compound 18 is closer to -40 °C. Increasing

the amount of catalyst did not improve the outcome of the

condensation; however, increasing the amount of donor 18 up

to 1.7 equiv allowed total consumption of the trisaccharide

acceptor 12, resulting in a 95% isolated yield of tetrasaccharide

19 (Table 1, entry 6). Relying on our ﬁndings made during the

synthesis of the tetrasaccharide 2, the trichloroacetamide 19 was

converted to the acetamido alcohol 21 (77%) via concomitant

N,O-transesteriﬁcation using an excess of sodium methoxide

in a 1:8 dichloromethane/methanol mixture and subsequent

N-acetylation of the resulting aminoalcohol 24. Indeed, early

conversion of the 2_D-N-trichloroacetyl moiety into an acetamide

was favored to prevent, if possible, any unwanted O-acetyl

migration at the ﬁnal Pd/C catalyzed deprotection stage provid-

ing target 3. The TfOH-mediated glycosylation of acceptor 21

with trichloroacetimidate 22 was run in toluene to give the

condensation product 25 in 71% yield. Interestingly, the various

side products observed previously upon glycosylation of the 2_D-

trichloroacetamide D(E)A acceptor¹⁵27 with the same donor

22¹⁵were not isolated. Acidic hydrolysis of the 4,6-O-

isopropylidene acetal gave the intermediate diol 26. Conven-

tional Pd/C catalyzed hydrogenation of the latter gave the mono-

O-acetylated pentasaccharide 3 (67%), which was isolated

following RP-HPLC puriﬁcation in a form of regioisomers

whereby the 2_C- and 3_C-O-acetyl isomers coexisted in a complex

(26) Blatter, G.; Beau, J. M.; Jacquinet, J. C. Carbohydr. Res. 1994, 260,

189–202.

(27) Boutet, J.; Kim, T. H.; Guerreiro, C.; Mulard, L. A. Tetrahedron Lett.

2008, 49, 5339–5342.

(28) Bakinovskii, L. V.; Gomtsyan, A. R.; Bairamova, N. E.; Kochetkov,

N. K. Bioorg. Khim. 1985, 11, 254–263.

(29) Bundle, D. R.; Josephson, S. J. Chem. Soc., Perkin Trans. 1 1979, 2736–

2739.

(30) Crich, D.; Dudkin, V. J. Am. Chem. Soc. 2001, 123, 6819–6825.

(31) Lucas, R.; Hamza, A.; Lubineau, A.; Bonnaffe, D. Eur. J. Org. Chem.

2004, 2107–2117.

(33) Castro-Palomino, J. C.; Hernandez Rensoli, M.; Verez Bencomo, V.

J. Carbohydr. Chem. 1996, 15, 137–146.

(32) Liao, L.; Auzanneau, F. I. J. Org. Chem. 2005, 70, 6265–6273.

2654 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

SCHEME 2. Retrosynthetic Analysis of Propyl Glycosides 3-6

TABLE 1. Study on the Condensation of Acceptor 12 and Donor

18

intermediate. As an alternative to the pathway described using

the D donor 18 and the EAB trisaccharide acceptor 12 (Scheme

3), the condensation of a D(E)A trichloroacetimidate donor

having a levulinoyl protecting group at position 3_D30 and the

rhamnoside acceptor 7 was investigated as a potential inroad

to a more convergent strategy (Scheme 4). Indeed the 3_D-O-

levulinoyl protecting pattern was selected in anticipation to any

requirement for orthogonality to the 2_C-acetate. Trichloroace-

timidate 30 was obtained in three steps from alcohol 27.¹⁵Thus,

treatment of trisaccharide 27 with levulinic acid in the presence

of DCC and DMAP gave the fully protected 28 (90%). Next,

allyl glycoside 28 was converted to hemiacetal 29 (80%)

following a two-step selective deallylation procedure involving

(i) isomerization of the allyl ether into the corresponding prop-

1-enyl ether using a cationic iridium complex³⁵and (ii)

subsequent iodine-mediated hydrolysis.³⁶Finally, the D(E)A

trisaccharide donor 30 was obtained as an anomeric mixture in

85% yield by reacting hemiacetal 29 with trichloroacetonitrile

in the presence of catalytic DBU. Running the condensation of

the latter with the allyl rhamnoside 7 in toluene containing a

catalytic amount of TMSOTf gave mostly unreacted 7 and

hemiacetal 29. When toluene was changed for dichloromethane,

TMSOTf

entry

(equiv)

temp (°C) donor 18 (equiv) solvent yield (%)

1

2

3

4

5

6

0.3

0.4

0.3

-40

-20

-40

1.4

1.5

1.7

CH₂Cl₂

toluene

35

56

77

70

75

95

equilibrium, based on NMR data (δ(H-2_C) ) 4.88 ppm, bs) and

(δ(H-3_C) ) 4.93 ppm, dd), respectively. RP-HPLC analysis also

suggested the presence of a third regioisomer. This result

conﬁrmed our previous observations on the _AcCD(E)A frag-

ment,¹⁵although exceptions do exist.³⁴Subsequent O-deacety-

lation of the propyl glycoside 3, followed by RP-HPLC

puriﬁcation, gave the free pentasaccharide 4 (63%).

The synthesis of hexasaccharides 5 and 6 was envisioned in

the context of a more ambitious goal, that is, the development

of a synthetic strategy that would open the way to a variety of

larger fragments of S. ﬂexneri 3a O-Ag. For that reason, different

routes to a suitable D(E)AB acceptor were investigated. We

ﬁrst focused on the construction of a fully protected D(E)AB

(35) Oltvoort, J. J.; van Boeckel, C. A. A.; der Koning, J. H.; van Boom,

J. H. Synthesis 1981, 305–308.

(36) Nashed, M. A.; Anderson, L. Chem. Commun. 1982, 1274–1276.

(34) Das, S. K.; Roy, N. Carbohydr. Res. 1995, 271, 177–183.

J. Org. Chem. Vol. 74, No. 7, 2009 2655

Boutet et al.

SCHEME 3. Synthesis of Propyl Glycosides 3 and 4

SCHEME 4. Study on the Synthesis of D(E)AB According to a D(E)A + B Protocol

the acceptor 7 was totally consumed. Two major compounds

31 and 32, both corresponding to condensation products, as seen

by mass spectrometry analysis, were isolated in a 1:1 ratio

(88%). Careful NMR analysis conﬁrmed that 31, the faster

eluting product, was the expected tetrasaccharide having an

R-AB linkage (¹J_C1A,H1A) 171.3 Hz). Interestingly, compound

preventing anchimeric assistance, were developed.³⁷Whether

these protecting groups should be regarded as permanent or

temporary acetamido masking patterns is often deﬁned on a case

by case basis. For example, in the synthesis of a number of

oligosaccharides representative of S. ﬂexneri 2a O-Ag, with

pentasaccharide IV (Figure 1), a regioisomer of II, as a repeating

unit, chain elongation at OH-3_Dwas performed using acceptors

containing N-acetylglucosamine residues.²²However, others

encountered difﬁculties when attempting to glycosylate poorly

reactive hydroxyl groups as part of N-acetylglucosamine-

containing acceptors.^21,31Aiming at reducing the number of

deprotection steps that could potentially interfere with the 2_C-

acetate at the late stage of the synthesis, the next step was thus

to investigate the best protecting group pattern of the amino

group of glucosamine D when involved in building blocks

32 was the stereoisomer having a ꢀ-AB linkage (¹J_C1A,H1A

)

155.1 Hz). Although formation of the latter was anticipated in

the absence of a participating group at position 2_Aof trichlo-

roacetimidate 30, its isolation in such a high yield prevented

any further investigation of this strategy. The D + EAB route

was therefore adopted.

N-Acetyl-ꢀ-D-glucosamine is present in numerous oligosac-

charides of natural origin. However, the acetamido moiety can

hardly be used for anchimeric assistance in complex oligosac-

charide synthesis. For that reason, a number of N-protecting

groups serving as participating groups, or on the contrary

(37) Bongat, A. F.; Demchenko, A. V. Carbohydr. Res. 2007, 342, 374–

406.

2656 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

SCHEME 5. Conversion of the 2_D-Trichloroacetamide 33 into the 2_D-Acetamide 36

CHART 1. Study on the Conversion of 33 into 36^a

^a(A) The initial concentration of 33 in MeOH was 0.4 M (5 equiv of MeONa). (B) The CH₂Cl₂/MeOH ratio (v/v) was constant at 8.

required for chain elongation at position 3_D, such as D(E)AB.

To broaden the analysis, the study was initiated on the more

readily available D(E)A.

23.6 ppm),¹⁵whereas the ﬁrst migrating compound was identi-

ﬁed as the methyl carbamate 37 (HRMS (ESI⁺) for C₅₈H₆₉NO₁₆

([M + Na]⁺, 1058.4514) found m/z 1058.4514, δ_CO) 159.4

ppm, δ_oMe) 52.9 ppm), the formation of which is tentatively

explained via the addition of methanol onto isocyanate 38.⁴⁰

Varying the reaction conditions in terms of dichloromethane/

methanol ratio and amount of sodium methoxide highlighted

the impact of these two parameters on the consumption of the

starting triacetate 33 (Chart 1). Under the best conditions (6

equiv of sodium methoxide in a 8:1 (v/v) mixture of dichlo-

romethane/MeOH), the transformation was completed within

2 h, providing acetamido 36 and carbamate 37 in 90% and 5%

yield post N-acetylation, respectively. Satisfactorily, treatment

of the 3_D-acetate 39¹⁵under the same conditions gave the known

2_D-acetamido acceptor 40¹⁵in 90% yield.¹⁵

This new route to acceptor 40 involving the isopropylidene

donor 18 was compared to the one reported earlier using the

triacetate donor 14.¹⁵The corresponding overall yields of

acetamide 40 from allyl glycoside 41, 81% via isopropylidene

39 and 70% via triacetate 33, respectively, were clearly in favor

of the methodology just disclosed when working below the

millimolar scale (Scheme 6). When working on 2.1 g of acceptor

41²⁴(2.6 mmol), the yield of trisaccharide 40 via route 1 was

86% and involved one puriﬁcation step only.

Finding appropriate conditions to ensure efﬁcient conversion

of the N-trichloroacetyl moiety into the corresponding acetamide

was our ﬁrst goal. Most commonly used methodologies include

basic trichloroacetyl removal and subsequent N-acetylation of

the resulting amine,^24,38,39direct reduction under neutral condi-

tions such as Bu₃SnH-mediated radical hydrodechlorination,^22,26

or often at the ﬁnal stage of the synthesis, nonspeciﬁc palladium-

mediated reductive hydrodechlorination.^19,39Avoiding the tin

methodology, we focused on ﬁnding chemoselective conditions

applicable to nonpolar compounds by taking advantage of

former observations. Indeed, we have reported the high-yielding

transesteriﬁcation of the triacetate 33¹⁵into triol 34¹⁵by use of

a methanolic solution of sodium methoxide under controlled

conditions. However, we also reported O-deacetylation and a

concomitant vicinal N-trichloroacetyl conversion into the cor-

responding amine in the presence of additional Et₃N¹⁴or

dichloromethane.^15,24We now report on a detailed investigation

of the latter conditions resulting in the efﬁcient conversion of

triacetate 33 into acetamidotriol 36¹⁵(Scheme 5).

When running the deprotection step in a mixture of dichlo-

romethane and methanol, two closely migrating compounds

were isolated following subsequent N-acetylation of the ami-

notriol intermediate 35. On the basis of NMR and mass

spectrometry data, the more polar one was the expected

acetamido triol 36 (HRMS (ESI⁺) for C₅₈H₆₉NO₁₅([M + H]⁺,

The new conditions were successfully applied to the synthesis

of the tetrasaccharide acceptor D(E)AB, resulting in an improved

yield of acetamide 21 from intermediate 19, 83% versus 77%.

Alternatively, selective removal of the 3_D-acetate in tetrasac-

charide 19 by use of potassium carbonate in methanol gave

acceptor 20 in 92% yield (Scheme 7).

1020.4745) found m/z 1020.4739, δ_CO) 173.3 ppm, δ_Me

)

(38) Sherman, A. A.; Yudina, O. N.; Mironov, Y. V.; Sukhova, E. V.;

Shashkov, A. S.; Menshov, V. M.; Nifantiev, N. E. Carbohydr. Res. 2001, 336,

13–46.

(39) Donohoe, T. J.; Logan, J. G.; Laffan, D. D. Org. Lett. 2003, 5, 4995–

4998.

(40) Nishikawa, T.; Urabe, D.; Tomita, M.; Tsujimoto, T.; Iwabuchi, T.;

Isobe, M. Org. Lett. 2006, 8, 3263–3265.

J. Org. Chem. Vol. 74, No. 7, 2009 2657

Boutet et al.

SCHEME 6. Access to Acceptor 40 by Condensation of 41 with Donor 14 (Route 1) and Donor 18 (Route 2)

SCHEME 7. Conversion of Fully Protected 19 into

Acceptor 20 or 21

SCHEME 8. Synthesis of Donor 23

tion of the donor was observed, whereas unreacted 40 was

recovered. Turning to TfOH, this time used in larger amounts

(0.9 equiv) was more satisfactory (Scheme 9, route a). Indeed,

running the reaction in toluene at 0 °C resulted in 74% of

isolated pentasaccharide 44. Since the yield of 44 was not higher

when running the condensation between acceptor 40 and donor

23 at 70 °C,²²the TMSOTf-mediated condensation of the same

donor 23 with the tetrasaccharide acceptor 21 was run at 0 °C,

providing hexasaccharide 45 in 65% yield (Scheme 9, route b).

However, careful NMR analysis of the condensation products

44 and 45 suggested, in both cases, the presence of small

amounts of a coeluting contaminant (5-10%). Attempts to

remove this unidentiﬁed side product after cleavage of either

the levuniloyl ester or the isopropylidene acetal failed (not

described). We thus turned to the use of the corresponding 2_D-

trichloroacetamide acceptors 27 and 20.

When applying the reaction conditions found successful for

the condensation of acceptor 27 and the chain-terminator BC

donor 46¹⁵to the glycosylation of 27 and donor 23, we could

conﬁrm the stability of the isopropylidene acetal at -78 °C.

However, the yield of the condensation product 48 (63%) was

lower than expected. Indeed, although the reaction was run for

a longer period (1 h instead of 15 min), some starting acceptor

remained (16%), whereas the donor was degraded (Table 2,

entry 1). Interestingly, when the condensation was run on a 2 g

Having all four different acceptors 20, 21, 27, and 40 in hands,

the next step was to synthesize the rhamnobiose donor 23. This

was easily achieved from the known allyl glycoside 42.¹⁶Indeed,

selective cleavage of the allyl aglycon gave hemiacetal 43

(93%), which was converted into trichloroacetimidate 23 (84%),

when treated with trichloroacetonitrile in the presence of a

catalytic amount of DBU (Scheme 8).

We next focused on the condensation of donor 23 with the

3_D-acetamido acceptor 21 and the subsequent transformation

of the condensation product. Taking into account the fact that

TfOH-mediated glycosylation of acceptor 21 with trichloroace-

timidate 22 in toluene succeeded in providing 25 (Scheme 3),

while conventional TMSOTf-mediated glycosylation of acceptor

40 with the same donor was somewhat unsuccessful,¹⁵we chose

to ﬁrst investigate the use of both catalysts in the condensation

of trisaccharide 40 and donor 23. Running the reaction in the

presence of 0.3 equiv of TMSOTf, at -20 °C, in toluene or

dichloromethane, resulted at best in 25% yield of the pentasac-

charide 44, thus conﬁrming our previous observations. Degrada-

2658 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

SCHEME 9. Condensation of Acceptors 40 (D(E)A) (Route

a) and 21 (D(E)AB) (Route b) with the BC Donor 23

SCHEME 10. Condensation of Acceptor 27 and Donor 23

TABLE 2. Study on the Condensation of Acceptor 27 and Donor

23

entry temp (°C) solvent

time acceptor 27 (%) 48 (%) 49 (%)

1

2

3

4

5

-78

-40

-20

-40

toluene 1 h

CH₂Cl₂1 h

toluene 30 min

toluene 10 min

16

30

no

63

42

66

75

no^a

no

22

13

no

charide acceptor 20 was run in toluene, at -40 °C, for 10 min

in the presence of a catalytic amount of TMSOTf. Under those

conditions, the yield of the condensation was 80%, matching

our expectations. However, two products were isolated, the fully

protected 50 (59%) and a more polar product (21%). Mass

spectrometry and NMR analysis of the latter indicated the

formation of diol 51, corresponding to the 4_D,6_D-O-isopropy-

lidene loss. Treatment of 51 with 2-methoxypropene and CSA

in DMF conﬁrmed this assumption, since the fully protected

50 was isolated in 93% yield. Since diol 51 was a suitable

intermediate in the synthesis targets 5 and 6, preventing acetal

loss was not attempted. To our satisfaction, running the

condensation on larger amounts of acceptor 20 (1.1 mmol

instead of 0.2 mmol) under the same conditions but for longer

time (45 min) to ensure total consumption of the acceptor,

provided 50 and 51 in a 3:1 ratio and 80% total yield.

Subsequent partial and total deprotection of the condensation

product 50 provided hexasaccharides 5 and 6, respectively.

Indeed, TFA-mediated hydrolysis of the 4_D,6_D-O-isopropylidene

of 50 gave diol 51 (89%). The following selective removal of

the levuniloyl protecting group in hexasaccharide 51, using

aqueous hydrazine in pyridine/acetic acid, gave triol 52 (84%).

Alternatively, reacting 51 with sodium methoxide in reﬂuxing

methanol gave tetraol 53 (92%). Conversion of the allyl

glycosides 52 and 53 into the propyl glycosides 5 and 6,

respectively, took advantage of the neutral conditions used

previously for the synthesis of related S. ﬂexneri 3a oligosaccha-

rides.^15,16In practice, treatment of ethanolic solutions of triol

52 and tetraol 53 under a hydrogen atmosphere (50 bar), in the

presence of Pd/C catalyst for 10 days each, allowed concomitant

benzyl removal, allyl reduction into propyl, and trichloroaceta-

mide conversion into the required acetamide. The hexasaccha-

ride targets 5 and 6 were ﬁnally isolated in 64% and 82% yield,

^ano ) not observed.

scale of acceptor 27, the silylated analogue 47 was isolated

(11%) in addition to pentasaccharide 48 (52%). Adding more

donor or increasing the amount of TMSOTf had no impact.

Changing toluene for dichloromethane worsened the outcome

of the glycosylation (Table 2, entry 2), since 30% of unreacted

acceptor was recovered in addition to 48 (42%). The temperature

of the reaction was investigated next in order to overcome this

unexpected outcome. Increasing the reaction temperature to -40

°C was highly satisfactory, since neither the remaining acceptor

27 nor the silylated 47 were apparent. In these conditions (Table

2, entry 3), the overall condensation yield was 88% (Scheme

10, route a). However, the poor stability at this temperature of

the 4_D,6_D-O-isopropylidene resulted in the isolation of two

products, the expected 48 (¹J_C1C,H1C) 167.6 Hz, 66%) together

with the corresponding diol 49 (22%, not described), resulting

from isopropylidene loss post condensation, as ascertained by

mass spectrometry analysis (HRMS (ESI⁺) for C₉₈H₁₁₂Cl₃NO₂₆

([M + Na]⁺1846.643) m/z 1846.6403) and reacetalation.

Additional increase of the temperature had no positive effect

(Table 2, entry 4). Running the condensation in toluene, at -40

°C, for a shorter period of time (10 min), ﬁnally provided

pentasaccharide 48 in 75% yield (Table 2, entry 5). Under these

conditions, the diol 49 was not isolated (Scheme 10, route b).

Having demonstrated the crucial importance of temperature

on the outcome of the condensation between the trisaccharide

acceptor 27 and the disaccharide donor 23, we turned to the

preparation of hexasaccharide 50 (Scheme 11). Taking advan-

tage of the study made for obtaining pentasaccharide 48, the

condensation of the trichloroacetimidate 23 and the tetrasac-

J. Org. Chem. Vol. 74, No. 7, 2009 2659

Boutet et al.

SCHEME 11. Synthesis of Hexasaccharides 5 and 6 from Acceptor 20 (D(E)AB) and Donor 23 (BC)

respectively. Overall, the efﬁciency of the 20 + 23 glycosylation

step along with this one-step conversion fully supported the

selection of trichloroacetamide 20 as the acceptor in the

synthesis of hexasaccharides 5 and 6.

acceptor 20 with donor 23 provided the fully protected hexas-

accharide 50. Conversion of the latter into targets 5 and 6 took

advantage of the feasible concomitant removal and/or transfor-

mation of the protecting groups, including benzyl hydrogenoly-

sis, allyl reduction, and reductive trichloroacetamide conversion

to acetamide. Therefore, partial deprotection of the allyl

glycoside 50 gave monoacetate 5 (3 steps), whereas full

deprotection provided hexasaccharide 6 (3 steps). Data reported

herein provide the chemical tools for further synthesis of larger

fragments of S. ﬂexneri serotypes 3a and/or X O-Ags.

Conclusion

We have described the synthesis of a linear trisaccharide (1)

and ﬁve branched tetra-, penta-, or hexasaccharides (2-6)

representative of fragments of S. ﬂexneri 3a and/or X O-Ags.

All the oligosaccharide targets share the EAB sequence,

whereby residue B is blocked at the anomeric position with a

propyl aglycon. They were synthesized from a common EAB

allyl glycoside 12, obtained in 18 synthetic steps. A one-step

deprotection and concomitant allyl to propyl conversion of

alcohol 12 gave the trisaccharide target 1. Alternatively,

glycosylation of acceptor 12 with D donors 14 (4 steps) and 18

(5 steps) gave tetrasaccharides 15 and 19, respectively. On one

hand, conventional deprotection of the triacetate 15 gave the

tetrasaccharide target 2 (3 steps from intermediate 12). On the

other hand, the 4_D,6_D-O-isopropylidene tetrasaccharide 19 served

as key intermediate to either the N-trichloroacetyl acceptor 20

or the N-acetyl analogue 21. Noteworthy, the one-step basic

conversion of the fully protected 19 into acceptor 21 (83%)

relied on in-house conditions, the optimization of which is also

disclosed here. Acceptors containing N-acetylglucosamine have

some limitations, potentially preventing their use in complex

oligosaccharide synthesis. In the course of this work, two of

such acceptors, trisaccharide 40 and tetrasaccharide 21, were

compared to their N-trichloroacetyl counterparts 27 and 20,

respectively. Independently of the acceptor used, our work

pointed out (i) the lower stability of the 4_D,6_D-O-isopropylidene

acetal when located on the trichloroacetamide derivatives 27

and 20 than when located on the acetamido analogues 40 and

21, (ii) the crucial impact of temperature on the glycosylation

outcome, and (iii) the key input of the condensation duration

in controlling the compromise between glycosylation yield and

isopropylidene loss. Optimizing both parameters resulted in good

yields of glycosylation in all cases. Nevertheless, the presence

of tiny amounts of unidentiﬁed contaminants associated with

the use of the acetamido acceptors 40 and 21 encouraged the

use of the N-trichloroacetyl derivatives 27 and 20, despite their

higher propensity to acetal loss. Finally, chain elongation of

Experimental Section

Allyl (2,3,4,6-Tetra-O-benzyl-r-D-glucopyranosyl)-(1f3)-(2-

O-benzoyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-

benzyl-r-L-rhamnopyranoside (10). TfOH (16 µL, 186 µmol, 0.2

equiv) was added to a solution of acceptor 7^16,23(463 mg, 1.2

mmol, 1.3 equiv) and trichloroacetimidate 8²⁴(953 mg, 0.93 mmol)

in toluene (10 mL) containing 4Å MS (500 mg), stirred at -30

°C. The reaction mixture was stirred for 1 h while slowly coming

back to rt. TLC (CH₂Cl₂/EtOAc, 98:2) showed the complete

disappearance of the acceptor and the presence of a major less polar

product. Et₃N (300 µL) was added. The mixture was ﬁltered and

concentrated to dryness. Chromatography of the residue (Chex/

EtOAc, 100:0 f 80:20) gave the allyl glycoside 10 (1.08 g, 93%)

as a colorless syrup. Trisaccharide 10 had R_f) 0.5 (Chex/EtOAc,

8:2), ¹H NMR (CDCl₃) δ 8.09-8.07 (m, 2H, CH_Bz), 7.59 (m, 1H,

CH_Bz), 7.47-7.08 (m, 37H, CH_Ph), 5.89 (m, 1H, CH)), 5.84 (dd,

1H, J_1,2) 2.1 Hz, H-2_A), 5.37 (d, 1H, J_1,2) 3.4 Hz, H-1_E), 5.28

(m, 1H, J_trans) 17.3 Hz, dCH₂), 5.20 (m_overlapped, 1H, dCH₂), 5.19

(m_overlapped, 1H, H-1_A), 5.00 (d, 1H, J ) 10.2 Hz, H_Bn), 4.96 (d, 1H,

J ) 10.8 Hz, H_Bn), 4.86 (d, 1H, J ) 10.9 Hz, H_Bn), 4.84 (d, 1H, J

) 10.9 Hz, H_Bn), 4.78 (d, 1H, J_1,2) 1.8 Hz, H-1_B), 4.75 (d, 1H, J

) 10.9 Hz, H_Bn), 4.72 (s, 2H, H_Bn), 4.67-4.63 (m, 3H, H_Bn), 4.60

(d, 1H, J ) 12.1 Hz, H_Bn), 4.47-4.44 (m, 2H, H_Bn), 4.39 (dd, 1H,

J_2,3) 3.1 Hz, J_3,4) 9.8 Hz, H-3_A), 4.36 (d, 1H, J ) 12.0 Hz,

H_Bn), 4.15 (m, 1H, H_All), 4.08-4.03 (m, 3H, H-3_E, H-5_E, H-2_B),

3.97-3.90 (m, 3H, H_All, H-5_A, H-3_B), 3.79 (dd, 1H, J_4,5) 9.4 Hz,

J_3,4) 9.7 Hz, H-4_E), 3.76-3.69 (m, 3H, H-5_B, H-6a_E, H-4_A), 3.62

(dd, 1H, J_2,3) 9.7 Hz, H-2_E), 3.59 (m, 1H, J_5,6) 1.7 Hz, H-6b_E),

3.56 (pt, 1H, J_4,5) J_3,4) 9.4 Hz, H-4_B), 1.43 (d, 3H, J_5,6) 6.2

Hz, H-6_A), 1.35 (d, 3H, J_5,6) 6.2 Hz, H-6_B); ¹³C NMR (CDCl₃) δ

166.0 (C_Bz), 139.1-138.0 (C_Ph), 134.2 (CH)), 133.5, 130.4 (3C,

CH_Bz), 129.2-127.7 (CH_Ph, CH_Bz), 117.6 (dCH₂), 99.6 (C-1_A, ¹J_CH

1

) 172.0 Hz), 98.2 (C-1_B, J_CH) 169.5 Hz), 93.1 (C-1_E, J_CH

)

169.2 Hz), 82.4 (C-3_E), 80.9 (C-4_B), 80.3 (C-4_A), 80.1 (C-3_B), 79.3

2660 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

(C-2_E), 77.8 (C-4_E), 76.7, 76.0, 75.9, 75.3, (4C, C_Bn), 75.1 (C-2_B),

73.8 (C_Bn), 72.9 (C-3_A), 72.6, 72.5 (2C, C_Bn), 70.6 (C-5_E), 68.8

(2C, C-2_A, C-5_B*), 68.6 (C-6_E), 68.4 (C-5_A*), 68.0 (C_All), 18.5, 18.4

(2C, C-6_A, C-6_B); HRMS (ESI⁺) for C₇₅H₈₂O₁₅([M + Na]⁺,

1269.5552) found m/z 1269.5563.

J ) 12.0 Hz, H_Bn), 4.54 (d, 1H, J ) 11.0 Hz, H_Bn), 4.36 (d, 1H, J

) 12.0 Hz, H_Bn), 4.19 (m, 1H, H_All), 4.14-4.09 (m, 4H, H-2_A,

H-2_B, H-3_A, H-3_E), 4.04-3.99 (m, 2H, H_All, H-5_E), 3.98 (dd, 1H,

J_2,3) 2.9 Hz, J_3,4) 9.5 Hz, H-3_B), 3.92 (dq, 1H, H-5_A), 3.82 (dd,

1H, J_3,4) 9.4 Hz, J_4,5) 9.8 Hz, H-4_E), 3.75 (dq, 1H, J_4,5) 9.4

Hz, H-5_B), 3.66 (dd, 1H, J_1,2) 3.6 Hz, J_2,3) 9.6 Hz, H-2_E), 3.75

(pt, 1H, J_3,4) J_4,5) 9.3 Hz, H-4_A), 3.55-3.49 (m, 2H, H-6a_E,

H-4_B), 3.45 (dd, 1H, J_5,6a) 1.8 Hz, J_6a,6b) 10.8 Hz, H-6b_E), 1.43

Allyl (2,3,4,6-Tetra-O-benzyl-r-D-glucopyranosyl)-(1f3)-(4-

O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-

benzyl-r-L-rhamnopyranoside (11). TMSOTf (210 µL, 1.2 mmol,

0.3 equiv) was added to a solution of acceptor 7 (1.5 g, 3.9 mmol)

and trichloroacetimidate 9¹⁶(5.1 g, 5.1 mmol, 1.3 equiv) in toluene

(100 mL) containing 4Å MS (3.4 g), stirred at -78 °C. The reaction

mixture was stirred for 15 min while slowly coming back to rt.

TLC (Tol/EtOAc, 85:15) showed the complete disappearance of

the acceptor and the presence of a major less polar product. Et₃N

(1 mL) was added. The mixture was ﬁltered, and concentrated to

dryness. Chromatography of the residue (Tol/EtOAc, 95:5 f 85:

15) gave 11 (4.5 g, 92%) as a colorless syrup. Trisaccharide 11

had R_f) 0.5 (Chex/EtOAc, 85:15); ¹H NMR (CDCl₃) δ 7.45-7.12

(m, 35H, CH_Ph), 5.87 (m, 1H, CH)), 5.61 (dd, 1H, J_1,2) 2.1 Hz,

H-2_A), 5.32 (d, 1H, J_1,2) 3.4 Hz, H-1_E), 5.31 (m, 1H, J_trans) 17.2

Hz, dCH₂), 5.23 (m, 1H, J_cis) 10.3 Hz, dCH₂), 5.06 (d_po, 1H, J

) 10.5 Hz, H_Bn), 5.05 (d_po, 1H, H-1_A), 5.00-4.89 (m, 5H, H_Bn),

4.82 (d_po, 1H, J ) 12.2 Hz, H_Bn), 4.81 (bs_o, 1H, H-1_B), 4.74-4.64

(m, 5H, H_Bn), 4.53 (d, 1H, J ) 11.0 Hz, H_Bn), 4.38 (d, 1H, J )

12.0 Hz, H_Bn), 4.26 (dd, 1H, J_2,3) 3.2 Hz, J_3,4) 9.6 Hz, H-3_A),

4.20-4.09 (m, 3H, H_All, H-3_E, H-5_E), 4.03 (dd, 1H, J_1,2) 1.9 Hz,

J_2,3) 2.9 Hz, H-2_B), 3.97 (m, 1H, H_All), 3.96-3.90 (m, 2H, H-5_A,

H-3_B), 3.83 (pt, 1H, J_3,4) J_4,5) 9.5 Hz, H-4_E), 3.75 (dq, 1H, J_4,5

) 9.4 Hz, H-5_B), 3.69 (dd_po, 1H, J_5,6a) 2.7 Hz, J_6a,6b) 10.9 Hz,

(d, 3H, J_5,6) 6.3 Hz, H-6_A), 1.39 (d, 3H, J_5,6) 6.2 Hz, H-6_B); ¹³

C

NMR (CDCl₃) δ 138.7-137.6 (C_Ph), 133.9 (CH)), 129.1-127.0

1

(CH _Ph), 117.2 (dCH₂), 101.0 (C-1_A, J_CH) 170.3 Hz), 98.1 (C-

1

1_B, J_CH) 170.3 Hz), 94.0 (C-1_E, J_CH) 166.7 Hz), 82.4 (C-3_E),

80.6 (C-4_B), 80.0 (C-3_B), 79.3 (C-4_A), 79.0 (C-2_E), 77.8 (C-4_E),

76.5 (C-3_A), 75.6, 75.6, 75.5 (3C, C_Bn), 75.0 (C-2_B), 74.9, 74.4,

73.4, 72.5 (4C, C_Bn), 70.7 (C-5_E), 68.1 (C-5_B), 68.0 (C-6_E), 67.7

(C-5_A), 67.7 (C_All), 67.4 (C-2_A), 18.0, 17.9 (2C, C-6_A, C-6_B); HRMS

(ESI⁺) for C₇₀H₇₈O₁₄([M + Na]⁺, 1165.5289) found m/z 1165.5283,

([M + NH₄]⁺, 1160.5735) found m/z 1160.5674.

Propyl r-D-Glucopyranosyl-(1f3)-r-L-rhamnopyranosyl-

(1f2)-r-L-rhamnopyranoside (1). Alcohol 12 (260 mg, 209 µmol)

was dissolved in EtOH (10 mL) containing 1 M aq HCl (155 µL)

and treated with 10% Pd/C catalyst (250 mg), and the suspension

was stirred at rt for 1 night, under a hydrogen atmosphere. TLC

(iPrOH/H₂O/NH₃, 7:1:2) showed the conversion of 12 into a major

polar product. The suspension was ﬁltered on Acrodisc LC 25 mm,

and the ﬁltrate was concentrated. HPLC puriﬁcation of the residue

(0.01 M aq TFA/CH₃CN, 100:0 f 60:40 over 20 min, 5 mL/min,

215 nm, C-18 Kromasil column), followed by freeze-drying, gave

target 1 (83 mg, 77%) as a white powder. Trisaccharide 1 had R_f

) 0.5 (iPrOH/H₂O/NH₃, 4:1:2); ¹H NMR (D₂O) δ 5.09 (d, 1H, J_1,2

) 3.8 Hz, H-1_E), 4.98 (d, 1H, J_1,2) 1.7 Hz, H-1_A), 4.88 (d, 1H,

J_1,2) 1.2 Hz, H-1_B), 4.25 (dd, 1H, J_2,3) 2.7 Hz, H-2_A), 3.94 (ddd,

1H, J_5,6a) 2.5 Hz, J_5,6b) 4.1 Hz, J_4,5) 10.1 Hz, H-5_E), 3.90 (dd,

1H, J_2,3) 3.3 Hz, H-2_B), 3.94 (dd_po, 1H, J_3,4) 9.6 Hz, H-3_A),

3.83 (dd, 1H, J_3,4) 9.6 Hz, H-3_B), 3.79-3.72 (m, 4H, H-3_E, H-6a_E,

H-6b_E, H-5_A), 3.69 (dq, 1H, J_4,5) 9.6 Hz, H-5_B), 3.63 (dt, 1H, J

) 7.0 Hz, J ) 9.8 Hz, H_Pr), 3.56 (dd_po, 1H, J_2,3) 9.9 Hz, H-2_E),

3.54 (pt_po, J_4,5) 9.5 Hz, H-4_A), 3.52 (dt, 1H, J ) 6.3 Hz, H_Pr),

3.44 (pt, 2H, H-4_E, H-4_B), 1.64-1.57 (m, 2H, CH₂), 1.27 (d, 6H,

J_5,6) 6.2 Hz, H-6_A, H-6_B), 0.90 (t, 3H, J ) 7.4 Hz, CH₃); ¹³C

H-6a_E), 3.68 (dd_po, 1H, J_2,3) 9.6 Hz, H-2_E), 3.61 (pt_po, 1H, J_3,4

J_4,5) 9.4 Hz, H-4_A), 3.60 (dd_po, 1H, H-6b_E), 3.53 (pt, 1H, J_3,4

)

9.4 Hz, H-4_B), 2.55 (m, 4H, H_Lev), 2.11 (s, 3H, CH_3Lev), 1.42 (d,

3H, J_5,6) 6.2 Hz, H-6_A), 1.37 (d, 3H, J_5,6) 6.2 Hz, H-6_B); ¹³C

NMR (CDCl₃) δ 206.2 (C_Lev), 171.8 (C_Lev), 138.7-137.7 (C_Ph),

133.9 (CH)), 129.1-127.6 (CH_Ph), 117.2 (dCH₂), 99.2 (C-1_A, ¹J_CH

1

) 173.4 Hz), 97.9 (C-1_B, J_CH) 170.8 Hz), 92.9 (C-1_E, J_CH

)

168.9 Hz), 82.1 (C-3_E), 80.5 (C-4_B), 79.9 (C-4_A), 79.6 (C-3_B), 79.5

(C-2_E), 77.8 (C-4_E), 76.2, 75.6, 75.5 (3C, C_Bn), 75.1 (C-2_B), 75.0,

73.4, 72.8 (3C, C_Bn), 72.3 (C-3_A), 72.2 (C_Bn), 70.3 (C-5_E), 68.4

(C-5_A), 68.3 (C-6_E), 68.1 (C-5_B), 68.0 (C-2_A), 67.7 (C_All), 38.0

(CH_2Lev), 29.7 (CH_3Lev), 28.2 (CH_2Lev), 18.1, 18.0 (2C, C-6_A, C-6_B);

HRMS (ESI⁺) for C₇₅H₈₄O₁₆([M + Na]⁺, 1263.5657) found m/z

1263.5437, ([M + NH₄]⁺, 1258.6104) found m/z 1258.5887.

Allyl (2,3,4,6-Tetra-O-benzyl-r-D-glucopyranosyl)-(1f3)-(4-

O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-r-L-

rhamnopyranoside (12). Route a. Methanolic MeONa (0.5 M,

10 mL, 5 mmol, 6.6 equiv) was added to a solution of benzoylated

10 (935 mg, 750 µmol) in a 1:1 MeOH/CH₂Cl₂(v/v) mixture (12

mL), and the mixture was reﬂuxed for 3 h. TLC (Chex/EtOAc,

7:3) showed the complete disappearance of 10 and the presence of

a single more polar product. The mixture was neutralized by

addition of Dowex X8-200 ion-exchange resin (H⁺) and ﬁltered.

Volatiles were evaporated. The resulting syrup was chromatogra-

phied (Chex/EtOAc, 100:0 f 7:3) to give 12 (845 mg, 98%) as a

colorless oil.

NMR (D₂O) δ 102.4 (C-1_A, ¹J_CH) 169.9 Hz), 99.0 (C-1_B, ¹J_CH

)

170.5 Hz), 95.7 (C-1_E, ¹J_CH) 168.8 Hz), 79.5 (C-2_B), 75.6 (C-3_A),

73.3 (C-3_E), 72.6 (C-4_E*), 72.1 (C-2_E), 71.8 (C-5_E), 70.7 (C-3_B),

70.5 (C-4_A), 70.2(C_Pr), 69.9 (C-4_B*), 69.7 (C-5_A), 69.1 (C-5_B), 67.1

(C-2_A), 60.8 (C-6_E), 22.3 (CH₂), 17.2, 17.0 (2C, C-6_A, C-6_B), 10.3

(CH₃). HRMS (ESI⁺) for C₂₁H₃₈NO₁₄([M + Na]⁺, 537.2159) found

m/z 537.2147.

Allyl (3,4,6-Tri-O-acetyl-2-deoxy-2-trichloroacetamido-ꢀ-D-

glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyra-

nosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-

O-benzyl-r-L-rhamnopyranoside (15). TfOH (4 µL, 45 µmol, 0.3

equiv) was added to a solution of acceptor 12 (163 mg, 143 µmol)

and trichloroacetimidate 14^26,27(110 mg, 185 µmol, 1.3 equiv) in

toluene (5 mL) containing 4Å MS (300 mg), stirred at -40 °C.

The reaction mixture was stirred for 1.5 h at this temperature, then

for 1 h at rt. More donor 14 (20 mg, 34 µmol, 0.23 equiv) was

added, and the reaction mixture was stirred at rt overnight. TLC

(Chex/EtOAc, 7:3) showed the complete disappearance of 12 and

the presence of a major more polar product. Et₃N was added. The

mixture was ﬁltered and concentrated to dryness. Chromatography

of the residue (Chex/EtOAc, 100:0 f 70:30) gave the allyl

glycoside 15 (196 mg, 87%). Tetrasaccharide 15 had R_f) 0.3

(Chex/EtOAc, 7:3). ¹H NMR (CDCl₃) δ 7.42-7.05 (m, 36H, NH,

CH_Ph), 5.87 (m, 1H, CH)), 5.25 (m_overlapped, 1H, dCH₂), 5.22

(d_overlapped, 1H, H-1_E), 5.18 (m, 1H, J_cis) 10.4 Hz, dCH₂), 5.08

(bs, 1H, H-1_A), 5.02 (pt, 1H, J_3,4) J_4,5) 9.7 Hz, H-4_D), 4.93 (d,

1H, J ) 10.8 Hz, H_Bn), 4.87 (d, 1H, J_1,2) 8.5 Hz, H-1_D), 4.82 (dd,

J_2,3) 10.4 Hz, H-3_D), 4.76 (bs_overlapped, 1H, H-1_B), 4.79-4.54 (m,

11H, H_Bn), 4.46 (d, 1H, J ) 11.0 Hz, H_Bn), 4.30 (d, 1H, J ) 12.0

Route b. Methanolic MeONa (0.5 M, 12.2 mL, 6.1 mmol, 1.7

equiv) was added to a solution of fully protected 11 (4.5 g, 3.6

mmol) in MeOH (200 mL), and the mixture was reﬂuxed for 1 h.

TLC (Chex/EtOAc, 7:3) showed the complete disappearance of the

starting material and the presence of a single more polar product.

The mixture was neutralized by addition of Dowex X8-200 ion-

exchange resin (H⁺) and ﬁltered. Volatiles were evaporated. The

resulting syrup was chromatographied (Tol/EtOAc, 98:2 f 9:1) to

give 12 (3.9 g, 94%). Trisaccharide 12 had R_f) 0.6 (Chex/EtOAc,

7:3); ¹H NMR (CDCl₃) δ 7.47-7.19 (m, 35H, CH_Ph), 5.93 (m, 1H,

CH)), 5.32 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.25 (m, 1H, J_cis

)

10.3 Hz, dCH₂), 5.22 (bs, 1H, H-1_A), 5.05-4.99 (m, 3H, H_Bn),

4.97 (d_po, 1H, J_1,2) 3.5 Hz, H-1_E), 4.91-4.88 (m, 2H, H_Bn), 4.84

(d, 1H, J_1,2) 1.6 Hz, H-1_B), 4.83-4.67 (m, 6H, H_Bn), 4.60 (d, 1H,

J. Org. Chem. Vol. 74, No. 7, 2009 2661

Boutet et al.

Hz, H_Bn), 4.21 (ddd, 1H, 1H, J_2,NH) 8.7 Hz, H-2_D), 4.16-4.07

(m, 5H, H-2_A, H-3_A, H-3_E, H_All, H-5_E), 3.95-3.87 (m, 5H, H_All

Pd/C catalyst (100 mg), and the suspension was stirred at rt for 1

night, under a hydrogen atmosphere. TLC (iPrOH/H₂O/NH₃, 7:1:

2) showed reaction completion. The suspension was ﬁltered on a

pad of Celite, and the ﬁltrate was concentrated under vacuum. RP-

HPLC puriﬁcation of the residue (0.01 M aq TFA/CH₃CN, 100:0

f 60:40 over 20 min, 5 mL min^-1, 215 nm, C-18 Kromasil

column), followed by freeze-drying, gave target 2 (36 mg, 68%)

as a white powder.

,

H-2_B, H-2_E, H-6a_D, H-3_B), 3.85-3.79 (m, 3H, H-4_E, H-5_A*, H-6b_D),

3.71 (dq, 1H, J_4,5) 9.4 Hz, H-5_B*), 3.47 (pt, 2H, J_3,4) J_4,5) 9.3

Hz, H-4_A, H-4_B), 3.44-3.39 (m, 2H, H-6a_E, H-6b_E), 2.93 (ddd, 1H,

J_5,6a) 2.7 Hz, J_5,6b) 3.4 Hz, H-5_D), 2.03, 2.00, 1.95 (3s, 9H,

H_Ac), 1.37 (d, 3H, J_5,6) 6.3 Hz, H-6_A*), 1.33 (d, 3H, J_5,6) 6.2

Hz, H-6_B*); ¹³C NMR (CDCl₃) δ 171.0, 170.8, 169.5 (3C, C_Ac),

162.4 (C_NTCA), 138.9-137.9 (C_Ph), 134.2 (CH)), 128.7-127.7

Route b. A 2% TfOH solution in toluene (100 µL, 23 µmol,

0.35 equiv) was added to a solution of acceptor 12 (82 mg, 66

µmol) and trichloroacetimidate 14 (82 mg, 135 µmol, 2.0 equiv)

in toluene (2 mL) containing 4Å MS (200 mg), stirred at -30 °C.

The reaction mixture was stirred for 1 h at this temperature and

then for 1 h at rt. More donor 14 (10 mg, 17 µmol, 0.25 equiv)

was added, and the reaction mixture was stirred for 3 h while slowly

coming back to rt. Et₃N was added. The mixture was ﬁltered and

concentrated to dryness. Chromatography of the residue (Chex/

EtOAc, 100:0 f 70:30) gave contaminated 15 (90 mg). The whole

material was solubilized in CH₂Cl₂(1 mL) and 0.5 M methanolic

sodium methoxide was added (500 µL). The reaction mixture was

stirred for 3 h at rt. TLC (CH₂Cl₂/MeOH, 9:1) showed the presence

of a more polar product that reacted with ninhydrin. The mixture

was neutralized by addition of Dowex X8-200 ion-exchange resin

(H⁺) and ﬁltered. Volatiles were evaporated. The residue was taken

in ethanol (2 mL), and acetic anhydride (1 mL) was added. After

2 h at rt, volatiles were evaporated and coevaporated with toluene.

The crude material was chromatographied (CH₂Cl₂/MeOH, 95:5)

to give the acetamidotriol 17 (54 mg, 56% from 12). The latter

was dissolved in EtOH (5 mL) containing 1 M aq HCl (110 µL)

and treated with 10% Pd/C catalyst (50 mg), and the suspension

was stirred at rt for 1 night, under a hydrogen atmosphere. TLC

(iPrOH/H₂O/NH₃, 7:1:2) showed the conversion of 17 into a more

polar product. The suspension was ﬁltered on a pad of Celite, and

the ﬁltrate was concentrated under vacuum. The residue was puriﬁed

as above to give target 2 as a white powder (19 mg, 40% from

12). Tetrasaccharide 2 had R_f) 0.32 (iPrOH/H₂O/NH₃, 4:1:2);

HPLC (215 nm): t_R) 14.2 min (Kromasil 5 µm C18 100Å 4.6 ×

250 mm analytical column, using a 0-35% linear gradient over

20 min of CH₃CN in 0.01 M aq TFA at 1 mL min^-1ﬂow rate); ¹H

NMR (D₂O) δ 5.15 (d, 1H, J_1,2) 3.7 Hz, H-1_E), 5.07 (d, 1H, J_1,2

) 1.8 Hz, H-1_A), 4.86 (d, 1H, J_1,2) 1.3 Hz, H-1_B), 4.79 (d, 1H,

J_1,2) 8.5 Hz, H-1_D), 4.40 (dd, 1H, J_2,3) 2.3 Hz, H-2_A), 4.02 (ddd,

1H, J_4,5) 10.1 Hz, J_5,6a) 2.5 Hz, J_5,6b) 4.4 Hz, H-5_E), 3.92-3.85

(m, 3H, H-2_B, H-6a_D, H-3_A), 3.84-3.66 (m, 9H, H-3_B, H-6a_E, H-3_E,

H-6b_E, H-6b_D, H-5_A, H-2_D, H-5_B, H-2_E), 3.61 (dt, 1H, J ) 6.9 Hz,

J ) 9.8 Hz, H_Pr), 3.50-3.39 (m, 6H, H-4_E, H_Pr, H-3_D, H-4_B, H-5_D,

H-4_D), 3.34 (pt, 1H, J_3,4) J_4,5) 9.7 Hz, H-4_A), 2.07 (s, 3H, H_NAc),

1.61-1.54 (m, 2H, CH₂), 1.26 (d, 3H, J_5,6) 6.3 Hz, H-6_A*), 1.12

(d, 3H, J_5,6) 6.3 Hz, H-6_B*), 0.80 (t, 3H, J ) 7.4 Hz, CH₃). ¹³C

NMR (D₂O) δ 174.9 (C_NAc), 102.3 (C-1_D, ¹J_CH) 157.0 Hz), 101.7

1

(CH_Ph), 117.5 (dCH₂), 101.4 (C-1_A, J_CH) 175.8 Hz), 101.0 (C-

1

1_D, J_CH) 161.1 Hz), 98.2 (C-1_B, J_CH) 171.0 Hz), 95.0 (C-1_E,

¹J_CH) 166.9 Hz), 93.1 (CCl₃), 83.8 (C-3_E), 81.0, 80.2 (2C, C-4_B,

C-4_A), 79.3, 79.9 (2C, C-2_E, C-3_B), 78.9 (C-4_E), 76.5 (C_Bn), 76.0

(C-2_B), 75.7, 75.6, 75.3 (3C, C_Bn), 75.0 (C-3_A), 74.5 (C-2_A), 74.2,

73.8 (2C, C_Bn), 73.6 (C-3_D), 72.2 (C-5_D), 72.1 (C_Bn), 70.3 (C-5_E),

68.9, 68.2 (2C, C-5_A, C-5_B), 68.1 (2C, C-4_D, C-6_E), 68.0 (C_All),

61.8 (C-6_D), 56.1 (C-2_D), 21.0, 20.9 (3C, C_Ac), 18.4, 18.2 (2C, C-6_B,

C-6_A); HRMS (ESI⁺) for C₈₄H₉₄Cl₃NO₂₂([M + Na]⁺, 1598.5234)

found m/z 1598.5170.

Allyl (2-Deoxy-2-trichloroacetamido-ꢀ-D-glucopyranosyl)-

(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-(4-O-

benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-r-L-rham-

nopyranoside (16). Methanolic MeONa (0.5 M, 1.4 mL, 0.75

mmol, 6 equiv) was added to a solution of triacetate 15 (185 mg,

117 µmol) in MeOH (5 mL), and the mixture was stirred at rt for

3 h. TLC (CH₂Cl₂/MeOH, 95:5) showed the presence of a new

more polar product. The mixture was neutralized by addition of

Dowex X8-200 ion-exchange resin (H⁺) and ﬁltered. Volatiles were

evaporated. The resulting syrup was chromatographied (Chex/

EtOAc, 100:0 f 70:30) to give triol 16 (135 mg, 79%) as a white

1

foam. Tetrasaccharide 16 had R_f) 0.58 (CH₂Cl₂/MeOH, 9:1). H

NMR (CDCl₃) δ 7.52 (d, 1H, J_2,NH) 6.0 Hz, NH), 7.43-7.05 (m,

35H, CH_Ph), 5.87 (m, 1H, CH)), 5.37 (bs, 1H, H-1_A), 5.26 (m,

1H, J_trans) 17.3 Hz, dCH₂), 5.19 (m, 1H, J_cis) 10.4 Hz, dCH₂),

5.15 (d, 1H, J_1,2) 3.6 Hz, H-1_E), 5.10 (d, 1H, J ) 11.1 Hz, H_Bn),

5.05 (d, 1H, J ) 11.1 Hz, H_Bn), 5.00 (d, 1H, J ) 12.2 Hz, H_Bn),

4.92 (d, 1H, J ) 10.8 Hz, H_Bn), 4.90 (d, 1H, J ) 12.3 Hz, H_Bn),

4.79 (d, 1H, J ) 10.9 Hz, H_Bn), 4.73-4.59 (m, 5H, H_Bn), 4.76

(bs_overlapped, 1H, H-1_B), 4.54 (d_overlapped, 1H, J_1,2) 8.3 Hz, H-1_D),

4.53 (d_overlapped, 1H, J ) 10.2 Hz, H_Bn), 4.49 (d, 1H, J ) 10.9 Hz,

H_Bn), 4.35 (d, 1H, J ) 11.9 Hz, H_Bn), 4.17 (dd, 1H, J_1,2) 1.9 Hz,

H-2_B), 4.15-4.07 (m, 5H, H_All, H-3_E, H-2_A, H-3_A, H-5_E), 3.93 (m_po,

1H, H_All), 3.91 (dd_po, 1H, J_2,3) 9.2 Hz, J_3,4) 9.5 Hz, H-3_B), 3.83

(dd_po, 1H, J_3,4) 2.9 Hz, J_4,5) 9.5 Hz, H-4_E), 3.81 (dd, 1H, J_2,3

)

9.8 Hz, H-2_E), 3.76-3.67 (m, 3H, H-2_D, H-5_A, H-5_B), 3.59 (dd,

1H, J_6a,6) 12.2 Hz, J_5,6a) 2.9 Hz, H-6a_D), 3.51-3.44 (m, 4H,

H-4_A, H-4_B, H-6a_E, H-6b_E), 3.11 (dd, 1H, H-4_D), 3.05 (m, 1H, J_4,5

) 9.8 Hz, H-5_D), 2.88 (dd, 1H, J_5,6) 7.7 Hz, H-6b_D), 2.37 (dd,

1H, J_2,3) 10.2 Hz, J_3,4) 8.3 Hz, H-3_D), 1.44 (d, 3H, J_5,6) 6.2

Hz, H-6_A*), 1.36 (d, 3H, J_5,6) 6.2 Hz, H-6_B*); ¹³C NMR (CDCl₃)

δ 164.9 (C_NTCA), 139.0-137.6 (C_Ph), 137.6 (CH)), 129.5-128.1

(CH_Ph), 111.5 (dCH₂), 101.2 (C-1_D), 100.4 (C-1_A), 98.5 (C-1_B),

94.6 (C-1_E), 92.9 (CCl₃), 83.6 (C-3_E), 80.9 (C-3_B), 80.8 (C-4_B), 80.1

(C-4_A), 79.5 (C-2_E), 79.0 (C-4_E), 76.7 (C_Bn), 76.7 (C-3_D), 76.0 (C-

5_D), 75.6, 75.4, 75.3 (4C, C_Bn), 74.5 (C-2_A), 74.3 (C-3_A), 73.9, 73.3

(2C, C_Bn), 73.0 (C-4_D), 71.7 (C-2_B), 70.4 (C-5_E), 69.0, 68.7 (C-5_A,

C-5_B), 68.1 (C-6_E), 68.0 (C_All), 62.8 (C-6_D), 58.3 (C-2_D), 18.3, 18.2

(2C, C-6_B, C-6_A). HRMS (ESI⁺) for C₇₈H₈₈Cl₃NO₁₉([M + Na]⁺,

1472.4913) found m/z 1472.4921.

1

(C-1_B, J_CH) 173.2 Hz), 98.6 (C-1_A, J_CH) 170.6 Hz), 95.0 (C-

1

1_E, J_CH) 167.0 Hz), 79.5 (C-2_B), 76.4, 74.6 (2C, C-4_D, C-4_B),

74.4 (C-2_A), 74.1 (C-3_A), 73.5 (C-3_E), 72.6 (C-3_D), 71.8 (C-5_E),

71.7 (C-2_E), 71.2 (C-4_A), 70.4 (C-3_B), 70.2 (C-5_D), 70.0 (C_Pr), 69.9

(2C, C-4_E, C-5_A), 69.1 (C-5_B), 61.0 (C-6_D), 60.8 (C-6_E), 56.0 (C-

2_D), 23.0 (C_NAc), 22.3 (CH₂), 17.2, 17.0 (2C, C-6_A, C-6_B), 10.2

(CH₃). HRMS (ESI⁺) for C₂₉H₅₁NO₁₉([M + H]⁺, 718.3134) found

m/z 718.3198 ([M + Na]⁺, 740.2953) found m/z 740.3021.

Allyl (3-O-Acetyl-2-deoxy-4,6-O-isopropylidene-2-trichloro-

acetamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-

r-D-glucopyranosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-

(1f2)-3,4-di-O-benzyl-r-L-rhamnopyranoside (19). TMSOTf (69

µL, 380 µmol, 0.3 equiv) was added to a solution of acceptor 12

(1.5 g, 1.3 mmol) and trichloroacetimidate 18²⁷(1.2 g, 2.2 mmol

1.7 equiv) in toluene (30 mL) containing 4Å MS (1.1 g), stirred at

-40 °C. The reaction mixture was stirred for 1 h while slowly

coming back to rt. TLC (Tol/EtOAc, 85:15) showed the complete

disappearance of 12 and the presence of a major less polar product.

Et₃N (1 mL) was added and the mixture was ﬁltered, and

Propyl (2-Acetamido-2-deoxy-ꢀ-D-glucopyranosyl)-(1f2)-[r-

D-glucopyranosyl-(1f3)]-r-L-rhamnopyranosyl-(1f2)-r-L-rham-

nopyranoside (2). Route a. Triol 16 (108 mg, 75 µmol) was

dissolved in EtOH (10 mL) containing 1 M aq HCl (110 µL) and

treated with 10% Pd/C catalyst (108 mg), and the suspension was

stirred at rt for 1 night, under a hydrogen atmosphere. TLC (iPrOH/

H₂O/NH₃, 7:1:2) showed the conversion of 12 into a more polar

product. The suspension was ﬁltered on a pad of Celite, and the

ﬁltrate was concentrated under vacuum. The residue was dissolved

in EtOH (10 mL) containing Et₃N (100 µL) and treated with 10%

2662 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

concentrated to dryness. Chromatography of the residue (Tol/

(C-4_E), 76.3 (C_Bn), 75.9 (C-2_A), 75.7 (C_Bn), 75.5 (C-2_B), 75.4 75.3,

75.0 (3C, C_Bn), 74.2 (C-3_A), 74.1 (C-4_D), 74.0 (C-3_D), 73.5, 72.0 (2C,

C_Bn), 70.1 (C-5_E), 68.8 (C-5_A), 67.9 (2C, C-5_B, C-6_E), 67.7 (C_All), 66.9

(C-5_D), 61.7 (C-6_D), 58.5 (C-2_D), 29.1 (C_iPr), 23.2 (C_NAc), 19.0 (C_iPr),

18.1 (C-6_B), 17.7 (C-6_A); HRMS (ESI⁺) of C₈₁H₉₅NO₁₉([M + H]⁺,

1386.6577) found m/z 1386.6625, ([M + Na]⁺, 1408.6396) found m/z

1408.6478.

EtOAc, 95:5 f 1:1) gave 19 (1.9 g, 95%) as a white foam.

1

Tetrasaccharide 19 had R_f) 0.45 (Tol/EtOAc, 85:15); H NMR

(CDCl₃) δ 7.54-7.09 (m, 36H, NH, CH_Ph), 5.91 (m, 1H, CH)),

5.30 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.23 (m, 1H, J_cis) 10.5 Hz,

dCH₂), 5.23-5.19 (m, 3H, H-1_E, H_Bn), 5.15 (bs, 1H, H-1_A), 5.11

(d, 1H, J ) 10.9 Hz, H_Bn), 5.08 (d, 1H, J ) 11.0 Hz, H_Bn), 4.96 (d,

1H, J ) 10.8 Hz, H_Bn), 4.88-4.84 (m, 2H, J_1,2) 8.5 Hz, J_2,3

)

Allyl (2-O-Acetyl-3,4-di-O-benzyl-r-L-rhamnopyranosyl)-

(1f3)-(2-acetamido-2-deoxy-4,6-O-isopropylidene-ꢀ-D-glucopy-

ranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-

(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-r-L-

rhamnopyranoside (25). TfOH (2 µL, 23 µmol, 0.3 equiv) was

added to a solution of acceptor 21 (128 mg, 94 µmol) and

trichloroacetimidate 22³³(97 mg, 188 µmol, 2 equiv) in toluene

(1.5 mL) containing 4Å MS (200 mg), stirred at -40 °C. The

reaction mixture was stirred for 1 h at this temperature, then for

2 h at rt. TLC (CH₂Cl₂/MeOH, 97.5:2.5) showed the presence of a

major less polar product together with traces of 21. Et₃N (200 µL)

was added. The mixture was ﬁltered, and concentrated to dryness.

Chromatography of the residue (Chex/EtOAc, 100:0 f 50:50) gave

the allyl glycoside 25 (116 mg, 71%) as a white solid. Pentasac-

J_3,4) 9.8 Hz, H-1_D, H-3_D), 4.83 (d, 1H, J ) 11.0 Hz, H_Bn), 4.81

(bs, 1H, H-1_B), 4.79 (d, 1H, J ) 10.3 Hz, H_Bn), 4.74 (d, 1H, J )

11.8 Hz, H_Bn), 4.69 (d, 1H, J ) 10.8 Hz, H_Bn), 4.68 (d, 1H, J )

11.8 Hz, H_Bn), 4.52 (d, 1H, J ) 11.0 Hz, H_Bn), 4.36 (d, 1H, J )

12.0 Hz, H_Bn), 4.25-4.12 (m, 6H, H-2_D, H-3_E, H-2_A, H-3_A, H_All

,

H-5_E), 4.03 (dd, 1H, J_1,2) 1.9 Hz, J_2,3) 2.8 Hz, H-2_B), 4.01-3.92

(m, 3H, H_All, H-2_E, H-3_B), 3.88-3.80 (m, 2H, H-4_E, H-5_A), 3.75

(dq, 1H, J_4,5) 9.4 Hz, H-5_B), 3.68 (pt, 1H, J_3,4) J_4,5) 9.5 Hz,

H-4_D), 3.57-3.46 (m, 5H, H-6a_D, H-4_A, H-4_B, H-6a_E, H-6b_E), 3.43

(pt, 1H, J_5,6a) J_6a,6b) 10.4 Hz, H-6b_D), 2.83 (ddd, 1H, J_5,6b) 5.3

Hz, H-5_D), 2.11 (s, 3H, H_Ac), 1.49 (s, 3H, H_iPr), 1.44 (d, 3H, J_5,6

)

6.2 Hz, H-6_A), 1.41 (s, 3H, H_iPr), 1.36 (d, 3H, J_5,6) 6.2 Hz, H-6_B);

¹³C NMR (CDCl₃) δ 170.8 (C_Ac), 162.2 (C_NTCA), 138.6-137.6 (C_Ph),

133.9 (CH)), 129.1-127.4 (CH_Ph), 117.2 (dCH₂), 101.4 (C-1_D,

¹J_CH) 164.1 Hz), 101.0 (C-1_A, ¹J_CH) 172.5 Hz), 99.7 (C_iPr), 97.9

(C-1_B, ¹J_CH) 167.9 Hz), 94.6 (C-1_E, ¹J_CH) 167.1 Hz), 92.8 (CCl₃),

83.5 (C-3_E), 80.5 (C-4_B), 79.8 (C-4_A), 79.6 (C-3_B), 78.6 (C-4_E),

78.2 (C-2_E), 76.2, 75.3, 75.2, 75.0 (4C, C_Bn), 74.9 (C-2_B), 74.4 (C-

3_A), 74.0 (C_Bn), 73.9 (C-2_A), 73.5 (C_Bn), 72.6 (C-3_D), 72.2 (C_Bn),

71.3 (C-4_D), 70.0 (C-5_E), 68.7 (C-5_A), 68.0 (C-5_B), 67.9 (C-6_E),

67.7 (C_All), 67.4 (C-5_D), 61.8 (C-6_D), 56.6 (C-2_D), 29.0 (C_iPr), 20.9

(C_Ac), 19.1 (C_iPr), 18.0 (C-6_B), 17.9 (C-6_A); HRMS (ESI⁺) for

C₈₃H₉₄Cl₃NO₂₀([M + Na]⁺, 1552.5332) found m/z 1552.5430, ([M

+ NH₄]⁺, 1547.5779) found m/z 1547.5880

1

charide 25 had R_f) 0.58 (CH₂Cl₂/MeOH, 98.5:2.5); H NMR

(CDCl₃) δ 7.44-7.06 (m, 45H, CH_Ph), 6.40 (d, 1H, J_1,2) 8.9 Hz,

NH), 5.85 (m, 1H, CH)), 5.24 (d, 1H, J_trans) 17.2 Hz, dCH₂),

5.17 (m, 2H, H-1_E, dCH₂), 5.13 (dd, 1H, J_1,2) 2.2 Hz, J_2,3) 3.0

Hz, H-2_C), 5.07-5.04 (m, 2H, H_Bn, H-1_A), 5.01-4.97 (m, 5H, H_Bn),

4.81 (d, 1H, J ) 10.8 Hz, H_Bn), 4.76 (d, 1H, J ) 10.1 Hz, H_Bn),

4.72 (bs, 1H, H-1_B), 4.69-4.55 (m, 9H, H-1_C, H_Bn), 4.48 (d, 1H, J

) 10.8 Hz, H_Bn), 4.33 (d, 1H, J ) 12.0 Hz, H_Bn), 4.27 (d, 1H, J_1,2

) 8.6 Hz, H-1_D), 4.19-4.08 (m, 5H, H-3_E, H-5_E, H-2_D, H-3_A, H_All),

3.98-3.87 (m, 8H, H-2_A, H-3_C, H-5_C, H-2_B, H_All, H-3_B, H-2_E, H-4_E),

3.75 (dq, 1H, J_4,5) 9.3 Hz, J_5,6) 6.6 Hz, H-5_A), 3.69 (dq, 1H, J_4,5

) 9.4 Hz, J_5,6) 6.1 Hz, H-5_B), 3.52-3.41 (m, 8H, H-6a_D, H-6b_D,

H-6a_E, H-6b_E, H-4_A, H-4_B, H-4_D, H-4_C), 2.74 (dt, 1H, J_5,6a) 5.3

Hz, J_4,5) J_5,6b) 9.8 Hz, H-5_D), 2.62 (pt, 1H, J_2,3) J_3,4) 9.4 Hz,

H-3_D), 2.28 (s, 3H, H_Ac), 2.08 (s, 3H, H_NAc), 1.39 (s, 6H, H_iPr),

1.33-1.30 (m, 6H, H-6_A, H-6_B), 1.24 (d, 3H, J_5,6) 6.3 Hz, H-6_C).

¹³C NMR (CDCl₃) δ 170.9 (C_Ac), 170.5 (C_NAc), 139.2-18.7 (C_Ph),

134.2 (CH)), 129.7-127.8 (CH_Ph), 117.6 (dCH₂), 103.8 (C-1_D),

101.5 (C-1_A, ¹J_CH) 172.8 Hz), 99.6 (C_iPr), 98.8 (C-1_B, ¹J_CH) 172.9

Hz),), 98.2 (C-1_C), 94.4 (C-1_E), 83.7 (C-3_E), 80.8-78.9 (7C, C-3_D,

C-4_B, C-2_E, C-4_C, C-4_A, C-3_B, C-4_E), 78.1 (C-3_C), 76.6 (C_Bn), 76.4

(C-2_A), 75.6 (C-2_B), 76.0-75.4 (5C, C_Bn), 74.6 (C-3_A), 73.9 (C_Bn),

72.4 (C-4_D), 72.3, 71.8 (2C, C_Bn), 70.3 (2C, C-2_C, C-5_E), 69.2 (C-

5_A), 68.2 (C-5_B), 68.0 (2C, C-6_E, C_All), 67.8 (C-5_C), 67.5 (C-5_D),

62.3 (C-6_D), 55.7 (C-2_D), 29.5 (C_iPr), 24.4 (C_NAc), 21.5 (C_Ac), 19.5

(C_iPr), 18.4, 18.3, 18.0 (3C, C-6_A, C-6_B, C-6_C); HRMS (ESI⁺) for

Allyl (2-Acetamido-2-deoxy-4,6-O-isopropylidene-ꢀ-D-glu-

copyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-

(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-

r-L-rhamnopyranoside (21). Methanolic MeONa (0.5 M, 5.7 mL,

2.8 mmol, 6.9 equiv) was added to a solution of fully protected

tetrasaccharide 19 (630 mg, 412 µmol) in CH₂Cl₂(45 mL), and the

mixture was stirred for 6.5 h. TLC (CH₂Cl₂/MeOH, 98:2 and Tol/

EtOAc, 85:15) showed the complete disappearance of the monoacetate

and the presence of a single more polar product which reacted with

ninhydrin, thus corresponding to intermediate 24 (MS (ESI⁺) of

C₇₉H₉₃NO₁₈([M + H]⁺, 1344.6) found m/z 1344.7). MeOH (91 mL)

and acetic anhydride (400 µL) were added. After 2 h at rt, TLC (Tol/

EtOAc, 85:15) showed the complete disappearance of 24. Evaporation

of the ﬁltrate gave a syrup which was puriﬁed by chromatography

(Tol/EtOAc, 6:4 f 4:6) to give compound 21 (470 mg, 83%) as a

white foam. Tetrasaccharide 21 had R_f) 0.35 (Tol/EtOAc, 6:4); ¹H

NMR (CDCl₃) δ 7.43-7.07 (m, 36H, NH, CH_Ph), 5.89 (m, 1H, CH)),

5.27 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.20 (m, 1H, J_cis) 11.7 Hz,

dCH₂), 5.18 (d, 1H, J_1,2) 3.7 Hz, H-1_E), 5.12 (bs_overlapped, 1H, H-1_A),

5.11 (d_po, 1H, H_Bn), 5.01 (d, 1H, J ) 11.8 Hz, H_Bn), 4.95 (d, 1H, J )

10.8 Hz, H_Bn), 4.91 (d, 1H, J ) 11.0 Hz, H_Bn), 4.89 (d, 1H, J ) 11.7

Hz, H_Bn), 4.82 (d, 1H, J ) 10.8 Hz, H_Bn), 4.80 (d, 1H, J ) 9.9 Hz,

H_Bn), 4.77 (d, 1H, J_1,2) 1.6 Hz, H-1_B), 4.71 (d, 1H, J ) 11.9 Hz,

H_Bn), 4.66-4.63 (m, 3H, H_Bn), 4.60 (d, 1H, J ) 10.1 Hz, H_Bn), 4.55

(d, 1H, J ) 10.9 Hz, H_Bn), 4.40-4.35 (m, 2H, H_Bn, H-1_D), 4.19-4.11

C

₁₀₃H₁₁₉NO₂₄([M + H]⁺, 1754.8201) found m/z 1755.8307.

Propyl (2-O-Acetyl-r-L-rhamnopyranosyl)-(1f3)-(2-aceta-

mido-2-deoxy-ꢀ-D-glucopyranosyl)-(1f2)-[r-D-glucopyranosyl-

(1f3)]-r-L-rhamnopyranosyl-(1f2)-r-L-rhamnopyranoside (3).

TFA (2 mL 50% aq) was added, at 0 °C, to a solution of

pentasaccharide 25 (105 mg, 84 µmol) in CH₂Cl₂(2 mL) at 0 °C,

and the biphasic mixture was stirred vigorously at this temperature

for 1 h. TLC (CH₂Cl₂/MeOH, 95:5) showed the complete disap-

pearance of 25 and the presence of a major more polar product.

Repeated coevaporation with toluene provided crude diol 26 (103

mg). Checking the ¹H NMR spectrum ensured the complete

disappearance of the isopropylidene signals. The crude material was

directly engaged in the next step. Crude diol 26 (102 mg, 60 µmol)

was dissolved in EtOH (4 mL), treated with 10% Pd/C catalyst

(100 mg), and the suspension was stirred at rt for 6 h, under a

hydrogen atmosphere. TLC (iPrOH/H₂O/NH₃, 7:1:2) showed that

the starting material had been transformed into a major polar

product. The suspension was ﬁltered on a pad of Celite, and the

ﬁltrate was concentrated. HPLC puriﬁcation (t_R) 14.6 min, C-18

Kromasil column, 0.01 M aq TFA/CH₃CN, 100:0 f 70:30 over

20 min, 5.5 mL min^-1, 215 nm) of the residue, followed by freeze-

drying, gave the target pentasaccharide 3 (36 mg, 67%) as a white

(m, 4H, H-3_A, H-5_E, H_All, H-3_E), 4.06 (dd, 1H, J_1,2) 2.1 Hz, J_2,3

)

2.4 Hz, H-2_A), 4.02 (dd, 1H, J_2,3) 2.9 Hz, H-2_B), 3.95-3.79 (m, 6H,

H_All, H-4_E, H-3_B, H-2_E, H-2_D, H-5_A), 3.73 (dq, 1H, J_4,5) 9.4 Hz, H-5_B),

3.59-3.46 (m, 7H, H-6a_D, H-6b_D, H-6a_E, H-6b_E, H-4_D, H-4_A, H-4_B),

2.83 (ddd, 1H, J_4,5) 9.9 Hz, J_5,6a) 5.7 Hz, J_5,6b) 9.8 Hz, H-5_D),

2.78 (pt, 1H, J_2,3) J_3,4) 9.2 Hz, H-3_D), 2.40 (s, 3H, H_NAc), 1.50 (s,

3H, H_iPr), 1.48 (s, 3H, H_iPr), 1.40 (d, 3H, J_5,6) 6.2 Hz, H-6_A), 1.35

(d, 3H, J_5,6) 6.2 Hz, H-6_B); ¹³C NMR (CDCl₃) δ 172.9 (C_NAc),

138.5-137.1 (C_Ph), 133.8 (CH)), 129.2-127.4 (CH_Ph), 117.2 (dCH₂),

102.4 (C-1_D, ¹J_CH) 162.8 Hz), 101.0 (C-1_A, ¹J_CH) 177.5 Hz), 99.6

1

(C_iPr), 97.8 (C-1_B, J_CH) 169.0 Hz), 94.1 (C-1_E, J_CH) 167.0 Hz),

83.3 (C-3_E), 80.5 (C-4_B), 80.0 (C-4_A), 79.4 (C-2_E), 79.2 (C-3_B), 78.7

J. Org. Chem. Vol. 74, No. 7, 2009 2663

Boutet et al.

foam. Pentasaccharide 3 was isolated as a mixture of regioisomers

resulting from the migration of the acetyl group. Pentasaccharide

(317 µL, 3.0 mmol, 1.8 equiv) dissolved in CH₂Cl₂(15 mL) was

added to a solution of alcohol 27¹⁵(2.0 g, 1.7 mmol) and DMAP

(420 mg, 3.4 mmol, 2 equiv) in CH₂Cl₂(15 mL). The mixture was

stirred for 1 h at rt. TLC (Tol/EtOAc, 7:3) showed the complete

disappearance of the starting material and the presence of one less

polar product. DCU was ﬁltered and the reaction mixture was

diluted with CH₂Cl₂, then washed with water, saturated aq NaHCO₃

(3 × 20 mL), brine (3 × 20 mL), and water (3 × 20 mL). The

organic layer was dried on Na₂SO₄, ﬁltered, and concentrated under

reduced pressure. Chromatography of the residue (Tol/EtOAc, 85:

15 f 80:20) gave levulinate 28 (1.9 g, 90%) as a colorless syrup.

Compound 28 had R_f) 0.5 (Tol/EtOAc, 7:3); ¹H NMR (CDCl₃) δ

7.47-7.05 (m, 26H, NH, CH_Ph), 5.94 (m, 1H, CH)), 5.29 (m, 1H,

J_trans) 17.2 Hz, dCH₂), 5.21 (m, 1H, J_cis) 10.4 Hz, dCH₂),

5.15-5.09 (m, 3H, H-1_E, H_Bn), 5.07 (s, 2H, H_Bn), 4.80-4.69 (m,

5H, H-1_A, H_Bn, H-3_D, H_Bn, H-1_D), 4.59-4.54 (m, 2H, H_Bn), 4.90

(d, 1H, J ) 11.0 Hz, H_Bn), 4.32 (d, 1H, J ) 12.0 Hz, H_Bn),

3 had R_f) 0.5 (iPrOH/H₂O/NH₃, 7:1:2); HPLC (215 nm): t_R

)

14.7 min (52.3%), 15.4 min (29.4%), 15.9 min (16.9%) (Kromasil

5 µm C-18 100Å 4.6 × 250 mm analytical column, using a 0-35%

linear gradient over 20 min of CH₃CN in 0.01 M aq TFA at 1 mL

1

min^-1ﬂow rate); H NMR (D₂O, selected signals) δ 5.18 (d, 1H,

J_1,2) 3.5 Hz, H-1_E), 5.08 (bs, 1H, H-1_A), 4.93 (dd, 0.3H, J_2,3

)

3.3 Hz, J_3,4) 10.0 Hz, H-3_C), 4.90-4.87 (m, 3H, H-1_C, H-2_C,

H-1_B), 4.84-4.79 (m, 1H, J_1,2) 8.7 Hz, H-1_D), 4.42 (bs, 1H, H-2_A),

4.15-4.00 (m, 2H, H-5_C, H-5_E), 3.94-3.90 (m, 4H, H-3_C, H-3_A,

H-2_B, H-6a_D), 3.87-3.58 (m, 11H, H-2_D, H-3_E, H-3_B, H-6a_E, H-6b_E,

H-5_A, H-6b_D, H-5_B, H-2_E, H-4_C, H_Pr), 3.53-3.38 (m, 7H, H-4_D,

H-4_E, H_Pr, H-4_C, H-4_B, H-3_D, H-5_D), 3.34 (pt, 1H, J_3,4) J_4,5) 9.7

Hz, H-4_A), 2.14, 2.13 (s, 3H, H_NAc), 2.10, 2.07 (s, 3H, H_Ac),

1.64-1.55 (m, 2H, CH₂), 1.27 (d, 3H, J_5,6) 6.2 Hz, H-6_B),

1.25-1.20 (m, 5H, H-6_A, H-6_C), 1.10 (d, 1H, J_5,6) 6.2 Hz, H-6_C),

0.89 (t, 3H, J ) 7.9 Hz, CH₃). ¹³C NMR (D₂O, selected signals) δ

4.18-4.07 (m, 5H, H_All, H-2_D, H-3_E, H-3_A), 4.08 (ddd, 1H, J_4,5)

173.3 (C_NAc), 101.5 (C-1_D,J_CH) 164.0 Hz), 101.2 (C-1_A, ¹J_CH

)

10.2 Hz, H-5_E), 3.99 (dd_po, 1H, J_1,2) 2.3 Hz, H-2_A), 3.94 (m_po,

1H, H_All), 3.90 (dd, 1H, J_1,2) 3.6 Hz, J_2,3) 9.7 Hz, H-2_E), 3.85

(dd, 1H, J_5,6a) 5.4 Hz, J_6a,6b) 10.7 Hz, H-6a_D), 3.79 (dd, 1H, J_3,4

) 9.0 Hz, H-4_E), 3.74-3.69 (m, 2H, H-6b_D, H-5_A), 3.67 (pt, 1H,

J_3,4) J_4,5) 9.6 Hz, H-4_D), 3.45 (pt, 1H, J_3,4) J_4,5) 9.6 Hz,

H-4_A), 3.45-3.39 (m, 2H, H-6a_E, H-6b_E), 2.76-2.63 (m, 5H, H-5_D,

4H_Lev), 2.20 (s, 3H, CH_3Lev), 1.47 (s, 3H, H_iPr), 1.42 (s, 3H, H_iPr),

1.39 (d, 3H, J_5,6) 6.3 Hz, H-6_A); ¹³C NMR (CDCl₃) δ 206.4 (C_Lev),

172.6 (C_Lev), 162.5 (C_NTCA), 139.0-138.5 (C_Ph), 134.2 (CH)),

1

172.8 Hz), 98.5, 98.2 (2C, C-1_B, J

) 172.9 Hz, C-1_C, J

CH

169.8 Hz), 94.3 (C-1_E), 82.3 (C-3_D), 79.1 (C-2_B), 76.1 (C-5_D), 74.3

(C-2_A), 73.6-73.0 (2C, C-3_A, C-3_E), 72.2 (2C, C-2_C, C-4_B), 71.5,

71.4 (2C, C-2_E, C-5_E), 70.8 (C-4_A), 69.3 (C-3_B), 69.8 (C_Pr), 69.6,

69.5 (3C, C-4_C, C-4_E, C-5_A), 68.9-68.3 (4C, C-3_C, C-5_B, C-5_C,

C-4_D), 60.7 (C-6_D), 60.4 (C-6_E), 55.5 (C-2_D), 22.8, 22.5 (C_NAc),

21.9 (CH₂), 20.4, 20.9 (C_Ac), 16.8, 16.6, 16.5, 16.4 (3C, C-6_A, C-6_B,

C-6_C), 9.8 (CH₃); HRMS (ESI⁺) for C₃₇H₆₃NO₂₄([M + Na]⁺,

928.3638) found m/z 928.3660.

1

129.6-127.7 (CH_Ph), 117.6 (dCH₂), 101.8 (C-1_D, J_CH) 163.0

1

Hz), 100.1 (C_iPr), 98.7 (C-1_A, J_CH) 171.6 Hz), 95.1 (C-1_E, J_CH

) 165.2 Hz), 93.2 (CCl₃), 83.8 (C-3_E), 80.2 (C-4_A), 79.3 (C-2_E),

79.1 (C-4_E), 76.4, 75.5, 75.3 (3C, C_Bn), 75.0 (C-3_A), 74.7 (C_Bn),

74.6 (C-2_A), 73.8 (C_Bn), 73.3 (C-3_D), 71.6 (C-4_D), 70.3 (C-5_E), 68.7

(C-5_A), 68.3, 68.2 (2C, C_All, C-6_E), 67.5 (C-5_D), 62.4 (C-6_D), 56.9

(C-2_D), 38.4 (CH_2Lev), 30.2 (CH_3Lev), 29.4 (C_iPr), 28.5 (CH_2Lev), 19.3

(C_iPr), 18.3 (C-6_A); HRMS (ESI⁺) for C₆₆H₇₆Cl₃NO₁₇([M + Na]⁺,

1282.4076) found m/z 1282.4189, ([M + NH₄]⁺, 1277.4523) found

m/z 1277.4634.

Propyl r-L-Rhamnopyranosyl-(1f3)-(2-acetamido-2-deoxy-

ꢀ-D-glucopyranosyl)-(1f2)-[r-D-glucopyranosyl-(1f3)]-r-L-

rhamnopyranosyl-(1f2)-r-L-rhamnopyranoside (4). A mixture

of regioisomers 3 (10 mg, 60 µmol) was dissolved in water (1 mL)

and methanolic sodium methoxide (0.5 M, 100 µL) was added.

The reaction mixture was stirred for 3 h at rt. Following RP-HPLC

control (C18 Kromasil column, 4.6 × 150, CH₃CN/0.01 M aq TFA

0 f 30% over 20 min, 215 nm), the reaction mixture was puriﬁed

by preparative RP-HPLC (C18 Kromasil column, 10 × 250) using

the same elution system. Freeze-drying gave the target pentasac-

charide 4 (6 mg, 63%) as a white foam. Pentasaccharide 4 had

HPLC (215 nm): t_R) 14.6 min (Kromasil 5 µm C-18 100Å 4.6 ×

250 mm analytical column, using a 0-40% linear gradient over

20 min of CH₃CN in 0.01 M aq TFA at 1 mL min^-1ﬂow rate); ¹H

NMR (D₂O) δ 5.18 (d, 1H, J_1,2) 3.7 Hz, H-1_E), 5.08 (d, 1H, J_1,2

) 1.7 Hz, H-1_A), 4.88 (d, 1H, J_1,2) 1.2 Hz, H-1_B), 4.85 (d, 1H,

J_1,2) 1.4 Hz, H-1_C), 4.82 (d, 1H, J_1,2) 8.6 Hz, H-1_D), 4.25 (dd,

1H, J_2,3) 2.2 Hz, H-2_A), 4.03 (ddd, 1H, J_4,5) 10.1 Hz, J_5,6a) 2.5

Hz, J_5,6b) 4.4 Hz, H-5_E), 3.96 (dq, 1H, J_4,5) 9.7 Hz, H-5_C),

3.94-3.90 (m, 2H, H-3_A, H-2_B), 3.89 (dd, 1H, J_6a,6b) 12.2 Hz,

J_5,6a) 1.8 Hz, H-6a_D), 3.85-3.76 (m, 5H, H-3_B, H-2_D, H-3_E, H-6a_E,

H-2_C), 3.75-3.69 (m, 6H, H-6b_E, H-5_A, H-6b_D, H-3_C, H-2_E, H-5_B),

3.62 (dt, 1H, J ) 7.0 Hz, J ) 9.8 Hz, H_Pr), 3.51-3.41 (m, 6H, H_Pr,

H-4_D, H-4_E, H-3_D, H-4_B, H-5_D), 3.40 (pt, 1H, J_3,4) 9.7 Hz, H-4_C),

3.35 (pt, 1H, J_3,4) J_4,5) 9.7 Hz, H-4_A), 2.10 (s, 3H, H_NAc),

1.62-1.54 (m, 2H, CH₂), 1.27 (d, 3H, J_5,6) 6.2 Hz, H-6_B), 1.24

(d, 3H, J_5,6) 6.3 Hz, H-6_A), 1.21 (d, 3H, J_5,6) 6.3 Hz, H-6_C),

0.89 (t, 3H, J ) 7.4 Hz, CH₃). ¹³C NMR (D₂O) δ 174.2 (C_NAc),

101.4 (C-1_D), 101.3 (C-1_C), 101.2 (C-1_A), 98.2 (C-1_B, ¹J_CH) 171.8

Hz), 94.4 (C-1_E, ¹J_CH) 171.8 Hz), 81.4 (C-3_D), 79.1 (C-2_B), 76.1

(C-5_D), 74.3 (C-2_A), 73.5 (C-3_A), 73.2 (C-3_E), 72.2 (C-4_B), 71.9

(C-4_C), 71.5, 71.4 (2C, C-2_E, C-5_E), 70.8 (C-2_C), 70.7 (C-4_A), 70.2

(C-3_C), 70.0 (C-3_B), 69.8 (C_Pr), 69.5 (2C, C-5_A, C-4_E), 69.0 (C-5_C),

68.7 (C-5_B), 68.4 (C-4_D), 60.7 (C-6_D), 60.4 (C-6_E), 55.6 (C-2_D),

22.5 (C_NAc), 21.9 (CH₂), 16.8 (C-6_A), 16.6 (C-6_B), 16.5 (C-6_C), 9.8

(CH₃); HRMS (ESI⁺) for C₃₅H₆₁NO₂₃([M + H]⁺, 864.3713) found

m/z 864.3704, ([M + Na]⁺, 886.3532) found m/z 886.3489.

Allyl (2-Deoxy-4,6-O-isopropylidene-3-O-levulinoyl-2-trichlo-

roacetamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-

r-D-glucopyranosyl-(1f3)]-4-O-benzyl-r-L-rhamnopyrano-

side (28). DCC (532 mg, 2.6 mmol, 1.5 equiv) and levulinic acid

(2-Deoxy-4,6-O-isopropylidene-3-O-levulinoyl-2-trichloroac-

etamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-

D-glucopyranosyl-(1f3)]-4-O-benzyl-r/ꢀ-L-rhamnopyranose (29).

1,5-Cyclooctadiene-bis(methyldiphenylphosphine)-iridium hexaﬂu-

orophosphate (30 mg) was dissolved in THF (11 mL) and the

resulting red solution was degassed under an argon stream.

Hydrogen was bubbled through the solution, causing the color to

change to yellow. The solution was then degassed again under an

argon stream. A solution of allyl glycoside 28 (1.8 g, 1.5 mmol) in

THF (15 mL) was added. The mixture was stirred overnight at rt.

TLC (Tol/EtOAc, 8:2) showed the complete disappearance of 28

and the presence of a single less polar product. The mixture was

treated with a solution of iodine (740 mg, 2.9 mmol) in THF/water

(10 mL, 4:1 v/v) for 1 h at rt. TLC (Tol/EtOAc, 8:2 and CH₂Cl₂/

MeOH, 98:2) showed the complete disappearance of the intermedi-

ate and the presence of a single more polar product. Excess iodine

was destroyed by adding a solution of freshly prepared 5% aq

sodium bisulphite (4 mL). CH₂Cl₂(50 mL) was added, and the

organic phase was washed with brine (3 × 30 mL), water (3 × 30

mL), dried on Na₂SO₄, ﬁltered, and concentrated to dryness.

Chromatography of the residue (CH₂Cl₂/MeOH, 99:1 f 90:10) gave

29 (1.4 g, 80%) as a yellow syrup. Hemiacetal 29 had R_f) 0.3

1

(CH₂Cl₂/MeOH, 98:2); H NMR (CDCl₃) δ 7.45-7.05 (m, 26H,

NH, CH_Ph), 5.16 (dd, 1H, J_1,2) 2.2 Hz, H-1_A), 5.15-5.07 (m, 5H,

H-1_E, H_Bn), 4.78-4.68 (m, 4H, H-3_D, H_Bn, H-1_D, H_Bn), 4.58-4.44

(m, 3H, H_Bn), 4.30 (d, 1H, J ) 12.0 Hz, H_Bn), 4.21 (dd, 1H, J_2,3

)

2.9 Hz, J_3,4) 9.6 Hz, H-3_A), 4.16-4.07 (m, 3H, H-2_D, H-3_E, H-5_E),

4.01 (dd, 1H, H-2_A), 3.95 (dq, 1H, J_4,5) 9.4 Hz, H-5_A), 3.90 (dd,

1H, J_1,2) 2.3 Hz, J_2,3) 9.6 Hz, H-2_E), 3.85 (dd, 1H, J_5,6a) 5.1

Hz, J_6a,6b) 10.4 Hz, H-6a_D), 3.76 (dd, 1H, J_3,4) 9.2 Hz, J_4,5

)

9.9 Hz, H-4_E), 3.70 (dd, 1H, J_5,6b) 1.6 Hz, H-6b_D), 3.66 (pt, 1H,

J_3,4) J_4,5) 9.5 Hz, H-4_D), 3.45 (pt, 1H, H-4_A), 3.39 (m, 2H, H-6a_E,

2664 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

H-6b_E), 3.30 (d, 1H, J_1,OH) 3.4 Hz, OH-1_A), 2.77-2.61 (m, 5H,

H-5_D, 4H_Lev), 2.19 (s, 3H, CH_3Lev), 1.47 (s, 3H, H_iPr), 1.42 (s, 3H,

H_iPr), 1.38 (d, 3H, J_5,6) 6.2 Hz, H-6_A); ¹³C NMR (CDCl₃) δ 206.2

(C_Lev), 172.2 (C_Lev), 162.1 (C_NTCA), 138.6-137.6 (C_Ph), 129.3-127.2

H_Bn, H-1_D, H-1_B, H_Bn), 4.71 (d, 1H, J ) 11.8 Hz, H_Bn), 4.67 (d,

1H, J ) 10.8 Hz, H_Bn), 4.66 (d, 1H, J ) 11.8 Hz, H_Bn), 4.60-4.54

(m, 3H, H_Bn), 4.33 (d, 1H, J ) 12.0 Hz, H_Bn), 4.20-4.09 (m, 6H,

H-3_E, H-2_D, H-2_A, H-3_A, H_All, H-5_E), 4.00 (dd, 1H, J_1,2) 2.1 Hz,

J_2,3) 2.9 Hz, H-2_B), 3.98 (m, 1H, H_All), 3.93-3.89 (m, 2H, H-3_B,

H-2_E), 3.85-3.77 (m, 2H, H-4_E, H-5_B), 3.73 (dq, 1H, J_4,5) 9.4

Hz, H-5_A), 3.64 (pt, 1H, J_3,4) J_4,5) 9.5 Hz, H-4_D), 3.54-3.42

1

(CH_Ph), 101.4 (C-1_D, J_CH) 167.7 Hz), 99.7 (C_iPr), 94.6 (C-1_E,

¹J_CH) 167.2 Hz), 93.9 (C-1_A, ¹J_CH) 171.7 Hz), 92.8 (CCl₃), 83.4

(C-3_E), 79.7 (C-4_A), 78.8 (C-2_E), 78.7 (C-4_E), 76.2, 75.9, 75.1 (3C,

C_Bn), 74.5 (C-2_A), 74.4 (C_Bn), 74.1 (C-3_A), 73.3 (C_Bn), 72.8 (C-3_D),

71.2 (C-4_D), 69.9 (C-5_E), 68.3 (C-5_A), 67.8 (C-6_E), 67.1 (C-5_D),

62.0 (C-6_D), 56.4 (C-2_D), 38.0 (CH_2Lev), 29.8 (CH_3Lev), 28.9 (C_iPr),

28.0 (CH_2Lev), 18.9 (C_iPr), 17.9 (C-6_A); HRMS (ESI⁺) for

C₆₃H₇₂Cl₃NO₁₇([M + Na]⁺, 1242.3763) found m/z 1242.3856, ([M

+ NH₄]⁺, 1237.4209) found m/z 1237.4213.

(m, 5H, H-6a_D, H-4_A, H-4_B, H-6a_E, H-6b_E), 3.39 (pt, 1H, J_5,6b

)

J_6a,6b) 10.4 Hz, H-6b_D), 2.80-2.72 (m, 3H, H-5_D, 2H_Lev),

2.68-2.62 (m, 2H, H_Lev), 2.20 (s, 3H, CH_3Lev), 1.44 (s, 3H, H_iPr),

1.40 (d, 3H, J_5,6) 6.3 Hz, H-6_B), 1.39 (s, 3H, H_iPr), 1.32 (d, 3H,

J_5,6) 6.2 Hz, H-6_A); ¹³C NMR (CDCl₃) δ 206.2 (C_Lev), 172.3 (C_Lev),

162.2 (C_NTCA), 138.6-137.5 (C_Ph), 133.8 (CH)), 129.2-127.3

1

(CH_Ph), 117.2 (dCH₂), 101.3 (C-1_D, J_CH) 162.0 Hz), 100.9 (C-

(2-Deoxy-4,6-O-isopropylidene-3-O-levulinoyl-2-trichloroac-

etamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-

D-glucopyranosyl-(1f3)]-4-O-benzyl-r-L-rhamnopyranoseTrichlo-

roacetimidate (30). Hemiacetal 29 (1.3 g, 1.1 mmol) was dissolved

in DCE (10 mL), placed under argon, and cooled to -5 °C.

Trichloroacetonitrile (525 µL, 5.2 mmol, 5 equiv) and DBU (44

µL, 308 µmol, 0.28 equiv) were added. The mixture was stirred at

-5 °C for 10 min. TLC (Chex/EtOAc + Et₃N, 7:3) showed the

complete disappearance of 29 and the presence of a less polar

product. The mixture was directly chromatographied (Chex/EtOAc

+ 5‰ Et₃N, 7:3 f 1:1) to give 30 (1.2 g, 85%) as a yellow syrup.

Trichloroacetimidate 30 (R anomer) had R_f) 0.45 (Chex/EtOAc,

1

1_A, J_CH) 171.3 Hz), 99.7 (C_iPr), 97.9 (C-1_B, J_CH) 170.2 Hz),

1

94.6 (C-1_E, J_CH) 165.1 Hz), 92.8 (CCl₃), 83.4 (C-3_E), 80.4 (C-

4_B), 79.8 (C-4_A), 79.5 (C-2_E), 78.6 (C-4_E), 78.4 (C-3_B), 76.1, 75.3,

75.2, 74.9 (4C, C_Bn), 74.8 (C-2_B), 74.4 (C-3_A), 74.1 (C_Bn), 73.8

(C-2_A), 73.5 (C_Bn), 72.9 (C-3_D), 72.1 (C_Bn), 71.3 (C-4_D), 69.9 (C-

5_E), 68.6 (C-5_B), 68.0 (C-5_A), 67.9 (C-6_E), 67.7 (C_All), 67.2 (C-5_D),

61.7 (C-6_D), 56.6 (C-2_D), 38.0 (CH_2Lev), 29.7 (CH_3Lev), 29.0 (C_iPr),

28.1 (CH_2Lev), 19.0 (C_iPr), 18.0 (C-6_A), 17.9 (C-6_B); HRMS (ESI⁺)

for C₈₆H₉₈Cl₃NO₂₁([M + Na]⁺, 1608.5594) found m/z 1608.5730,

([M + NH₄]⁺, 1603.6041) found m/z 1603.6112.

1

Tetrasaccharide 32 had R_f) 0.6 (Tol/EtOAc, 7:3); H NMR

1

6:4); H NMR (CDCl₃) δ 8.65 (s, 1H, NH), 7.45-7.06 (m, 26H,

(CDCl₃) δ 7.67 (d, 1H, J_NH,2) 8.9 Hz, NH), 7.53-7.05 (m, 35H,

CH_Ph), 5.89 (m, 1H, CH)), 5.31 (m, 1H, J_trans) 17.2 Hz, dCH₂),

5.22 (m, 1H, J_cis) 10.3 Hz, dCH₂), 5.20 (s, 2H, H_Bn), 5.11 (d,

1H, J_1,2) 3.5 Hz, H-1_E), 5.07 (d, 1H, J ) 11.0 Hz, H_Bn), 5.03 (d,

1H, J ) 12.2 Hz, H_Bn), 4.95-4.86 (m, 5H, H-1_D, H-3_D, 2H_Bn, H-1_B),

4.84-4.79 (m, 2H, H_Bn), 4.59-4.48 (m, 5H, 3H_Bn, H-1_A, 2H_Bn),

NH, CH_Ph), 6.22 (s, 1H, H-1_A), 5.11-5.01 (m, 5H, H-1_E, 4H_Bn),

4.82-4.75 (m, 3H, H-3_D, H_Bn) 4.73 (d, 1H, J_1,2) 8.4 Hz, H-1_D),

4.57-4.49 (m, 3H, H_Bn), 4.33 (d, 1H, J ) 12.1 Hz, H_Bn), 4.22-4.07

(m, 5H, H-2_D, H-3_A, H-2_A, H-3_E, H-5_E), 3.92 (dq, 1H, J_4,5) 9.5

Hz, H-5_A), 3.90-3.85 (m, 2H, H-2_E, H-6a_D), 3.82-3.74 (m, 2H,

H-4_E, H-6b_D), 3.71 (pt, 1H, J_3,4) J_4,5) 9.6 Hz, H-4_D), 3.56 (pt,

4.34 (d, 1H, J ) 12.2 Hz, H_Bn), 4.24-4.11 (m, 6H, H-2_D, H_All

,

1H, J_3,4) 9.6 Hz, H-4_A), 3.47 (dd, 1H, J_5,6a) 2.5 Hz, J_6a,6b

)

H-2_B, H-2_A, H-3_E, H-5_E), 4.00 (m, 1H, H_All), 3.98-3.93 (m, 2H,

H-3_B, H-2_E), 3.88 (dd, 1H, J_5,6a) 5.2 Hz, J_6a,6b) 10.6 Hz, H-6a_D),

3.80 (dd, 1H, J_2,3) 2.5 Hz, J_3,4) 9.5 Hz, H-3_A), 3.78-3.67 (m,

3H, H-5_B, H-4_E, H-6b_D), 3.60-3.40 (m, 5H, H-4_D, H-4_A, H-4_B,

H-6a_E, H-6b_E), 3.28 (dq, 1H, J_4,5) 9.2 Hz, J_5,6) 6.2 Hz, H-5_A),

2.83 (ddd, 1H, J_5,6b) 9.8 Hz, H-5_D), 2.78-2.75 (m, 2H, H_Lev),

2.68-2.64 (m, 2H, H_Lev), 2.18 (s, 3H, CH_3Lev), 1.37 (s, 3H, H_iPr),

1.39-1.37 (m, 9H, H_iPr, H-6_A, H-6_B), 1.32 (s, 3H, H_iPr); ¹³C NMR

(CDCl₃) δ 206.1 (C_Lev), 172.2 (C_Lev), 162.0 (C_NTCA), 139.1-137.5

(C_Ph), 134.0 (CH)), 129.1-127.3 (CH_Ph), 117.2 (dCH₂), 100.7

11.0 Hz, H-6a_E), 3.37 (bd, 1H, H-6b_E), 2.85 (ddd, 1H, J_5,6a) 5.2

Hz, H-5_D), 2.77-2.58 (m, 4H, 2CH_2Lev), 2.20 (s, 3H, CH_3Lev), 1.49

(s, 3H, H_iPr), 1.43 (s, 3H, H_iPr), 1.42 (d, 3H, J_5,6) 6.0 Hz, H-6_A);

¹³C NMR (CDCl₃) δ 206.0 (C_Lev), 172.3 (C_Lev), 162.1 (C_NTCA), 160.2

(C)NH), 138.5-137.4 (C_Ph), 129.2-127.4 (CH_Ph), 101.3 (C-1_D,

1

¹J_CH) 159.2 Hz), 99.8 (C_iPr), 96.9 (C-1_A, J_CH) 182.6 Hz), 95.0

1

(C-1_E, J_CH) 165.6 Hz), 92.7 (CCl₃), 91.1 (CCl₃), 83.3 (C-3_E),

79.2 (C-4_A), 78.7 (C-2_E), 78.6 (C-4_E), 76.3, 75.3, 75.0, 74.4 (4C,

C_Bn), 74.3 (C-3_A), 73.3 (C_Bn), 72.7 (C-3_D), 72.2 (C-2_A), 71.2 (C-

4_D), 71.1 (C-5_A), 70.1 (C-5_E), 67.9 (C-6_E), 67.3 (C-5_D), 61.9 (C-

6_D), 56.5 (C-2_D), 38.0 (CH_2Lev), 29.8 (CH_3Lev), 29.0 (C_iPr), 28.1

(CH_2Lev), 18.9 (C_iPr), 17.9 (C-6_A).

1

(C-1_D, J_CH) 163.8 Hz), 99.7 (C_iPr), 97.5 (C-1_A, J_CH) 155.1

Hz), 96.9 (C-1_B, ¹J_CH) 167.2 Hz), 94.1 (C-1_E, ¹J_CH) 167.7 Hz),

92.8 (CCl₃), 83.7 (C-3_E), 81.0 (C-4_B), 79.7 (C-4_A), 78.7 (C-4_E),

77.8 (C-2_E), 77.4 (C-3_B), 76.4 (C-3_A), 76.2, 75.3, 75.1, 74.6, 73.6

(5C, C_Bn), 73.3 (3C, C-2_A, C-2_B, C-3_D), 73.5 (C_Bn), 72.4 (C-5_A),

71.3 (C-4_D), 71.0 (C_Bn), 69.9 (C-5_E), 68.0 (2C, C-5_B, C-6_E), 67.8

(C_All), 67.0 (C-5_D), 62.4 (C-6_D), 56.7 (C-2_D), 38.0 (CH_2Lev), 29.8

(CH_3Lev), 29.0 (C_iPr), 28.1 (CH_2Lev), 19.9 (C_iPr), 18.4 (C-6_A), 18.0

(C-6_B); HRMS (ESI⁺) for C₈₆H₉₈Cl₃NO₂₁([M + Na]⁺, 1608.5594)

found m/z 1608.5914, ([M + NH₄]⁺, 1603.6041) found m/z

1603.6248.

Allyl (2-Deoxy-4,6-O-isopropylidene-3-O-levulinoyl-2-trichlo-

roacetamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-

r-D-glucopyranosyl-(1f3)]-4-O-benzyl-r-L-rhamnopyranosyl)-

(1f2)-3,4-di-O-benzyl-r-L-rhamnopyranoside (31) and Allyl

(2-Deoxy-4,6-O-isopropylidene-3-O-levulinoyl-2-trichloroaceta-

mido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-

glucopyranosyl-(1f3)]-4-O-benzyl-ꢀ-L-rhamnopyranosyl)-(1f2)-

3,4-di-O-benzyl-r-L-rhamnopyranoside (32). TMSOTf (10 µL,

56 µmol, 0.3 equiv) was added to a solution of acceptor 7²³(71

mg, 185 µmol) and trichloroacetimidate 30 (380 mg, 280 µmol

1.5 equiv) in CH₂Cl₂(5 mL) containing 4Å MS (160 mg), stirred

at -78 °C. The reaction mixture was stirred for 15 min while slowly

coming back to rt. TLC (Tol/EtOAc, 7:3) showed the complete

disappearance of the acceptor and the presence of two new

compounds. Et₃N (1 mL) was added and the mixture was ﬁltered,

and concentrated to dryness. Chromatography of the residue (Tol/

EtOAc, 9:1 f 1:1) gave, by order of elution, ﬁrst 31 (130 mg,

44%), and then the ꢀ anomer 32 (130 mg, 44%), both as colorless

Allyl (2-Acetamido-2-deoxy-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-

tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-4-O-benzyl-r-L-rham-

nopyranoside (36) and Allyl (2-Deoxy-2-methylcarbamate-r-D-

glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-

(1f3)]-4-O-benzyl-r-L-rhamnopyranoside (37). Methanolic MeONa

(0.5 M, 4.8 mL, 2.4 mmol, 6 equiv) was added to a solution of

triacetate 33²⁷(0.5 g, 0.4 mmol) in CH₂Cl₂(38 mL), and the mixture

was stirred for 9 h. TLC (CH₂Cl₂/MeOH, 92:8) showed the

complete disappearance of 33 and the presence of a more polar

product. MeOH (77 mL) and acetic anhydride (300 µL) were added.

After 2 h, TLC (CH₂Cl₂/MeOH, 92:8) showed the complete

disappearance of the aminotriol intermediate 35. Evaporation of

the ﬁltrate gave a syrup which was puriﬁed by chromatography

(CH₂Cl₂/MeOH, 98:2 f 95:5) to give, by order of elution, ﬁrst

carbamate 37 (20 mg, 5%), and then acetamide 36¹⁵(371 mg, 90%)

as white foams. Carbamate 37 had R_f) 0.45 (CH₂Cl₂/MeOH, 92:

1

syrups. Tetrasaccharide 31 had R_f) 0.65 (Tol/EtOAc, 7:3); H

NMR (CDCl₃) δ 7.49-7.07 (m, 36H, NH, CH_Ph), 5.89 (m, 1H,

CH)), 5.27 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.21 (m, 1H, J_cis

)

10.3 Hz, dCH₂), 5.16 (d, 1H, J_1,2) 3.6 Hz, H-1_E), 5.12 (bs, 3H,

H-1_A, 2H_Bn), 5.09 (d, 1H, J ) 11.5 Hz, H_Bn), 5.07 (d, 1H, J ) 11.4

Hz, H_Bn), 4.93 (d, 1H, J ) 10.8 Hz, H_Bn), 4.83-4.76 (m, 5H, H-3_D,

J. Org. Chem. Vol. 74, No. 7, 2009 2665

Boutet et al.

1

8); H NMR (CDCl₃) δ 7.42-7.08 (m, 25H, CH_Ph), 6.52 (d, 1H,

J_NH,2) 7.0 Hz, NH), 5.90 (m, 1H, CH)), 5.29 (m, 1H, J_trans

1H, J_4,5) 9.2 Hz, H-5_A), 3.73 (dq, 1H, J_4,5) 9.4 Hz, H-5_B), 3.56

(dd, 1H, J_5,6) 5.3 Hz, J_6a,6b) 10.8 Hz, H-6a_D), 3.52-3.47 (m,

4H, H-6a_E, H-6b_E, H-4_A, H-4_B), 3.41 (pt, 1H, J_3,4) J_4,5) 9.2 Hz,

H-4_D), 3.38 (pt, 1H, J_5,6b) J_6a,6b) 10.0 Hz, H-6b_D), 2.85 (m, 1H,

)

17.2 Hz, dCH₂), 5.20 (m, 1H, J_cis) 10.4 Hz, dCH₂), 5.11-4.96

(m, 4H, 2H_Bn, H-1_E, H_Bn), 4.92 (bs, 1H, H-1_A), 4.83 (d, 1H, J )

10.9 Hz, H_Bn), 4.81 (d, 1H, J ) 11.8 Hz, H_Bn), 4.73 (d, 1H, J )

10.4 Hz, H_Bn), 4.63-4.55 (m, 2H, H_Bn), 4.45-4.42 (m, 2H, H-1_D,

H_Bn), 4.29 (dd, 1H, J_2,3) 9.3 Hz, J_3,4) 9.6 Hz, H-3_E), 4.27 (d,

1H, J ) 12.0 Hz, H_Bn), 4.15 (m, 1H, H_All), 4.12-4.09 (m, 2H,

H-3_A, H-5_E), 3.98 (m, 1H, H_All), 3.87 (bs, 1H, H-2_A), 3.84-3.70

(m, 8H, H-4_E, OMe, H-6a_D, H-6b_D, H-2_E, H-5_A), 3.63 (m, 1H, J_1,2

) 8.1 Hz, H-2_D), 3.51 (pt, 1H, J_3,4) J_4,5) 9.5 Hz, H-4_A), 3.49 (d,

1H, J_3,4) J_4,5) 9.8 Hz, H-4_D), 3.33 (bs, 2H, H-6a_E, H-6b_E), 2.90

(m, 1H, H-5_D), 2.61 (pt, 1H, J_2,3) 9.8 Hz, H-3_D), 1.40 (d, 3H, J_5,6

) 6.2 Hz, H-6_A); ¹³C NMR (CDCl₃) δ 159.4 (C_NOMe), 139.7-137.8

(C_Ph), 134.2 (CH)), 129.4-127.9 (CH_Ph), 117.9 (dCH₂), 103.2

OH), 2.82 (ddd, 1H, J_5,6a) 5.4 Hz, H-5_D), 2.45 (ddd, 1H, J_2,3

)

9.6 Hz, J_3,OH) 2.1 Hz, H-3_D), 1.47 (s, 3H, H_iPr), 1.46 (s, 3H, H_iPr),

1.41 (d, 3H, J_5,6) 6.2 Hz, H-6_A), 1.35 (d, 3H, J_5,6) 6.2 Hz, H-6_B);

¹³C NMR (CDCl₃) δ 163.7 (C_NTCA), 138.6-137.5 (C_Ph), 133.8

(CH)), 129.3-127.4 (CH_Ph), 117.2 (dCH₂), 101.0 (C-1_D, ¹J_CH

)

159.1 Hz), 101.0 (C-1_A, ¹J_CH) 170.3 Hz), 99.7 (C_iPr), 97.9 (C-1_B,

¹J_CH) 168.6 Hz), 94.1 (C-1_E, ¹J_CH) 166.2 Hz), 92.7 (CCl₃), 83.3

(C-3_E), 80.5 (C-4_B), 79.8 (C-4_A), 79.7 (C-2_E), 79.5 (C-3_B), 78.7

(C-4_E), 76.3, 75.4, 75.3, 74.9 (5C, C_Bn), 74.7 (C-2_B), 74.1 (C-3_A),

74.0 (C-4_D), 73.5 (C_Bn), 73.3 (C-2_A), 73.0 (C-3_D), 72.1 (C_Bn), 70.0

(C-5_E), 68.7 (C-5_A), 68.0 (C-5_B), 67.9 (C-6_E), 67.7 (C_All), 67.1 (C-

5_D), 61.4 (C-6_D), 58.8 (C-2_D), 29.1 (C_iPr), 19.0 (C_iPr), 18.0 (C-6_B),

17.8 (C-6_A); HRMS (ESI⁺) for C₈₁H₉₂Cl₃NO₁₉([M + Na]⁺,

1510.5227) found m/z 1510.5243, ([M + NH₄]⁺, 1505.5673) found

m/z 1505.5669.

1

(C-1_D, J_CH) 161.6 Hz), 98.6 (C-1_A, J_CH) 171.5 Hz), 95.8 (C-

1

1_E, J_CH) 170.5 Hz), 83.1 (C-3_E), 80.1 (C-2_E), 79.9 (C-4_A), 78.7

(C-4_E), 78.1 (C-2_A), 77.1 (C-3_D), 76.1 (C_Bn), 76.0 (C-3_A), 75.7, 75.6,

75.4 (3C, C_Bn), 75.2 (C-5_D), 73.8 (C_Bn), 71.5 (C-4_D), 70.6 (C-5_E),

69.0 (C-5_A), 68.3 (C_All), 68.1 (C-6_E), 62.7 (C-6_D), 58.4 (C-2_D), 52.9

(OMe), 18.1 (C-6_A); HRMS (ESI⁺) for C₅₈H₆₉NO₁₆([M + Na]⁺,

1058.4514) found m/z 1058.4514, ([M + NH₄]⁺, 1053.4960) found

m/z 1053.4946.

(3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-(1f3)-

2-O-acetyl-4-O-benzyl-r/ꢀ-L-rhamnopyranose (43). 1,5-Cyclooc-

tadiene-bis(methyldiphenylphosphine)-iridium hexaﬂuorophosphate

(175 mg) was dissolved in THF (90 mL) and the resulting red

solution was degassed under an argon stream. Hydrogen was

bubbled through the solution, causing the color to change to yellow.

The solution was then degassed again under an argon stream. A

solution of 42¹⁶(8.0 g, 10.6 mmol) in THF (15 mL) was added.

The mixture was stirred overnight at rt. TLC (Tol/EtOAc, 8:2)

showed the complete disappearance of 42 and the presence of a

less polar product. The mixture was treated with a solution of iodine

(5.4 g, 21.2 mmol) in THF/water (30 mL, 4:1 v/v), and stirred for

1 h at rt. TLC (Tol/EtOAc, 8:2 and CH₂Cl₂/MeOH, 98:2) showed

the conversion of the intermediate into a more polar product. Excess

iodine was destroyed by adding a solution of freshly prepared 5%

aq sodium bisulphite (25 mL). CH₂Cl₂(200 mL) was added, and

the organic phase was washed with brine (3 × 50 mL), water (3 ×

50 mL), dried on Na₂SO₄, ﬁltered, and concentrated to dryness.

Chromatography of the residue (CH₂Cl₂/MeOH, 99:1 f 90:10) gave

43 (7.1 g, 93%) as a yellow syrup. Hemiacetal 43 had R_f) 0.45

Allyl (2-Acetamido-2-deoxy-4,6-O-isopropylidene-ꢀ-D-glu-

copyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-

(1f3)]-4-O-benzyl-r-L-rhamnopyranoside (40).¹⁵Route a. Meth-

anolic MeONa (0.5 M, 3.7 mL, 1.9 mmol, 6 equiv) was added to

a solution of fully protected trisaccharide 39^15,27(375 mg, 310

µmol) in CH₂Cl₂(30 mL), and the mixture was stirred for 9 h.

TLC (Chex/EtOAc, 1:1) showed the complete disappearance of 39,

and the presence of a single more polar product which reacted with

ninhydrin. MeOH (60 mL) and acetic anhydride (300 µL) were

added. After 2 h, TLC (Chex/EtOAc, 1:1) showed the complete

disappearance of the aminotriol intermediate. Evaporation of the

ﬁltrate gave a syrup which was puriﬁed by chromatography (Chex/

EtOAc, 1:1) to give compound 40 (258 mg, 90%) as a white foam.

Route b. Alternatively, starting from acceptor 41²⁴(2.1 g, 2.6

mmol) and donor 14 (1.8 g, 3.1 mmol, 1.2 equiv), the condensation,

transesteriﬁcation, and acetalation steps were run without any

intermediate puriﬁcation. Column chromatography (Chex/EtOAc,

9:1 f 1:1) of the residue gave the expected 40 (2.4 g, 87%) over

three steps.

1

(CH₂Cl₂/MeOH, 98:2); H NMR (CDCl₃) δ 7.39-7.28 (m, 15H,

CH_Ph), 5.44 (dd, 1H, J_1,2) 1.9 Hz, H-2_B), 5.16 (dd, 1H, J_1,2) 1.8

Hz, H-2_C), 5.12 (dd, 1H, J_1,OH) 3.9 Hz, H-1_C), 5.05 (d, 1H, H-1_B),

4.92 (d, 1H, J ) 11.0 Hz, H_Bn), 4.83 (d, 1H, J ) 10.9 Hz, H_Bn),

4.66 (d, 1H, J ) 11.1 Hz, H_Bn), 4.63-4.60 (m, 2H, H_Bn), 4.45 (d,

1H, J ) 11.3 Hz, H_Bn), 4.20 (dd, 1H, J_2,3) 3.3 Hz, J_3,4) 9.5 Hz,

H-3_C), 3.98 (dq, 1H, J_4,5) 9.5 Hz, H-5_C), 3.89 (dd, 1H, J_2,3) 3.3

Hz, J_3,4) 9.3 Hz, H-3_B), 3.83 (dq, 1H, J_4,5) 9.3 Hz, H-5_B), 3.77

(d, 1H, OH-1_C), 3.47 (pt, 1H, H-4_C), 3.43 (pt, 1H, H-4_B), 2.70 (m,

4H, 4H_Lev), 2.18 (s, 3H, CH_3Lev), 2.14 (s, 3H, H_Ac), 1.29 (d, 3H,

J_5,6) 6.3 Hz, H-6_B), 1.30 (d, 3H, J_5,6) 6.2 Hz, H-6_C); ¹³C NMR

(CDCl₃) δ 206.8 (C_Lev), 172.6 (C_Lev), 171.6 (C_Ac), 138.8-138.4

Route c. Alternatively, starting from acceptor 41 (250 mg, 310

µmol) and donor 18²⁷(220 mg, 400 µmol, 1.3 equiv), the

condensation and transesteriﬁcation steps were run without any

intermediate puriﬁcation. Column chromatography (Chex/EtOAc,

1:1) of the residue gave the expected 40 (258 mg, 80%) over two

steps. Data for alcohol 40 were as described.¹⁵

Allyl (2-Deoxy-4,6-O-isopropylidene-2-trichloroacetamido-ꢀ-

D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyra-

nosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-

O-benzyl-r-L-rhamnopyranoside (20). Anhydrous K₂CO₃(175

mg, 1.3 mmol, 1 equiv) was added to a stirred solution of 19 (1.9

g, 1.3 mmol) in dry MeOH (20 mL). The mixture was stirred at rt

for 1 night, at which time TLC (Tol/EtOAc, 7:3) indicated total

conversion of 19 into a single product. Volatiles were removed

under reduced pressure to give crude alcohol 20 (1.7 g, 92%) as a

white foam. Tetrasaccharide 20 had R_f) 0.45 (Tol/EtOAc, 7:3);

¹H NMR (CDCl₃) δ 7.43-7.08 (m, 36H, NH, CH_Ph), 5.88 (m, 1H,

dCH), 5.29 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.23-5.20 (m, 2H,

H-1_E, dCH₂), 5.13 (d, 1H, J ) 11.0 Hz, H_Bn), 5.12 (bs, 1H, H-1_A),

5.08 (d, 1H, J ) 11.9 Hz, H_Bn), 5.06 (d, 1H, J ) 11.0 Hz, H_Bn),

4.95 (d, 1H, J ) 10.8 Hz, H_Bn), 4.90 (d, 1H, J ) 12.0 Hz, H_Bn),

4.82 (d, 1H, J ) 11.0 Hz, H_Bn), 4.79-4.77 (m, 2H, H_Bn, H-1_B),

4.72 (d, 1H, J ) 11.8 Hz, H_Bn), 4.70-4.61 (m, 4H, 2H_Bn, H-1_D,

H_Bn), 4.56 (d, 1H, J ) 10.2 Hz, H_Bn), 4.53 (d, 1H, J ) 11.0 Hz,

H_Bn), 4.37 (d, 1H, J ) 12.0 Hz, H_Bn), 4.19-4.13 (m, 5H, H-3_A,

H-2_A, H-3_E, H_All, H-5_E), 4.02 (dd, 1H, J_1,2) 2.0 Hz, J_2,3) 2.8 Hz,

H-2_B), 4.01-3.92 (m, 5H, H_All, H-3_B, H-2_D, H-4_E, H-2_E), 3.80 (dq,

1

(C_Ph), 128.9-128.1 (CH_Ph), 99.9 (C-1_B, J_CH) 173.3 Hz), 92.0

1

(C-1_C, J_CH) 170.0 Hz), 80.7 (C-4_C), 80.2 (C-4_B), 78.0 (C-3_B),

77.7 (C-3_C), 75.8, 75.6 (2C, C_Bn), 73.2 (C-2_C), 72.0 (C_Bn), 69.7

(C-2_B), 69.0 (C-5_B), 68.0 (C-5_C), 38.4 (CH_2Lev), 30.2 (CH_3Lev), 28.5

(CH_2Lev), 21.5 (C_Ac), 18.5, 18.4 (2C, C-6_B, C-6_C); HRMS (ESI⁺)

for C₄₀H₄₈O₁₂([M + Na]⁺, 743.3043) found m/z 743.3173, ([M +

NH₄]⁺, 738.3489) found m/z 738.3627.

(3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-(1f3)-

2-O-acetyl-4-O-benzyl-r/ꢀ-L-rhamnopyranose Trichloroacetimi-

date (23). Hemiacetal 43 (8.7 g, 12.1 mmol) was dissolved in DCE

(50 mL), placed under argon, and cooled to -5 °C. Trichloroac-

etonitrile (6.1 mL, 60.7 mmol, 5 equiv) and DBU (508 µL, 3.3

mmol, 0.28 equiv) were added. The mixture was stirred at -5 °C

for 10 min. TLC (Chex/EtOAc + Et₃N, 7:3) showed the complete

disappearance of 43 and the presence of a single less polar product.

The mixture was directly chromatographied (Chex/EtOAc + 5‰

Et₃N, 7:3 f 1:1) to give 23 (8.7 g, 84%) as a yellow syrup.

Trichloroacetimidate 23 (R anomer) had R_f) 0.4 (Chex/EtOAc,

2666 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

1

7:3); H NMR (CDCl₃) δ 8.72 (s, 1H, NH), 7.42-7.29 (m, 15H,

(5 mL) containing 4Å MS (620 mg), stirred at 0 °C. After 45 min,

TLC (Tol/EtOAc, 75:25; Chex/EtOAc, 1:1) showed the presence

of a single less polar product. Et₃N (0.2 mL) was added and the

mixture was ﬁltered, and concentrated to dryness. Chromatography

of the residue (Tol/EtOAc, 75:25 f 1:1) gave 45 (149 mg, 65%)

as a white foam slightly contaminated. Hexasaccharide 45 had R_f

CH_Ph), 6.22 (d, 1H, J_1,2) 1.9 Hz, H-1_C), 5.48 (dd, 1H, J_1,2) 1.8

Hz, H-2_B), 5.31 (dd, 1H, H-2_C), 5.10 (d, 1H, H-1_B), 4.92 (d, 1H, J

) 11.0 Hz, H_Bn), 4.85 (d, 1H, J ) 10.8 Hz, H_Bn), 4.68-4.62 (m,

3H, H_Bn), 4.51 (d, 1H, J ) 11.3 Hz, H_Bn), 4.26 (dd, 1H, J_2,3) 3.3

Hz, J_3,4) 9.5 Hz, H-3_C), 3.96 (dq, 1H, J_4,5) 9.5 Hz, H-5_C), 3.89

1

(dd, 1H, J_2,3) 3.3 Hz, J_3,4) 9.3 Hz, H-3_B), 3.82 (dq, 1H, J_4,5

)

) 0.55 (Chex/EtOAc, 1:1); H NMR (CDCl₃) δ 7.47-7.06 (m,

9.4 Hz, H-5_B), 3.58 (pt, 1H, H-4_C), 3.44 (pt, 1H, H-4_B), 2.72 (m,

4H, 4H_Lev), 2.18 (s, 3H, CH_3Lev), 2.17 (s, 3H, H_Ac), 1.36 (d, 3H,

J_5,6) 6.2 Hz, H-6_C), 1.29 (d, 3H, J_5,6) 6.2 Hz, H-6_B); ¹³C NMR

(CDCl₃) δ 206.5 (C_Lev), 172.3 (C_Lev), 170.3 (C_Ac), 160.5 (C)NH),

138.8-138.0 (C_Ph), 129.2-127.9 (CH_Ph), 99.9 (C-1_B, ¹J_CH) 168.1

Hz), 94.5 (C-1_C, ¹J_CH) 178.7 Hz), 91.2 (CCl₃), 80.2 (C-4_C), 80.1

(C-4_B), 77.9 (C-3_B), 76.5 (C-3_C), 76.1, 75.7, 72.0 (3C, C_Bn), 71.2

(C-2_C), 71.1 (C-5_C), 69.6 (C-2_B), 69.1 (C-5_B), 38.4 (CH_2Lev), 30.2

(CH_3Lev), 28.5 (CH_2Lev), 21.3 (C_Ac), 18.4, 18.3 (2C, C-6_B, C-6_C).

Allyl (3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-

(1f3)-(2-O-acetyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-

acetamido-2-deoxy-4,6-O-isopropylidene-ꢀ-D-glucopyranosyl)-

(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-4-O-

benzyl-r-L-rhamnopyranoside (44). TfOH (23 µL, 263 µmol, 0.9

equiv) was added to a solution of trisaccharide acceptor 40 (310

mg, 290 µmol) and trichloroacetimidate 23 (379 mg, 440 µmol,

1.5 equiv) in toluene (10 mL) containing 4Å MS (1.7 g), stirred at

0 °C. After 15 min, TLC (Chex/EtOAc, 1:1) showed the presence

of a single more polar product. Et₃N (0.2 mL) was added. The

mixture was ﬁltered, and concentrated to dryness. Chromatography

of the residue (Tol/EtOAc, 8:2 f 6:4) gave 44 (383 mg, 74%) as

a white foam slightly contaminated. Pentasaccharide 44 had R_f)

0.35 (Chex/EtOAc, 1:1); ¹H NMR (CDCl₃) δ 7.45-7.07 (m, 40H,

CH_Ph), 6.47 (d, 1H, J_NH,2) 9.0 Hz, NH), 5.90 (m, 1H, CH)), 5.46

(dd, 1H, J_2,3) 3.0 Hz, H-2_B), 5.29 (m, 1H, J_trans) 17.2 Hz, dCH₂),

5.20 (m, 1H, J_cis) 10.4 Hz, dCH₂), 5.15 (d, 1H, J_1,2) 3.5 Hz,

H-1_E), 5.09-4.98 (m, 5H, H-1_B, H_Bn), 4.94 (dd, 1H, J_1,2) 2.1 Hz,

J_2,3) 2.7 Hz, H-2_C), 4.93-4.88 (m, 3H, H_Bn), 4.84 (bs, 1H, H-1_A),

4.79-4.77 (bs, 2H, H-1_C, H_Bn), 4.67-4.60 (m, 5H, H_Bn), 4.52 (d,

1H, J ) 11.0 Hz, H_Bn), 4.42 (d, 1H, J ) 11.4 Hz, H_Bn), 4.35 (d,

1H, J ) 11.9 Hz, H_Bn), 4.28 (d, 1H, J_1,2) 8.6 Hz, H-1_D), 4.21-4.13

50H, CH_Ph), 6.38 (d, 1H, J_NH,2) 9.1 Hz, NH), 5.86 (m, 1H, CH)),

5.44 (dd, 1H, J_2,3) 3.2 Hz, H-2_B′), 5.26 (m, 1H, J_trans) 17.2 Hz,

dCH₂), 5.21-5.17 (m, 2H, dCH₂, H-1_E), 5.07 (d, 1H, J_1,2) 1.6

Hz, H-1_A), 5.05 (d, 1H, J_1,2) 1.8 Hz, H-1_B′), 5.04-4.87 (m, 9H,

4H_Bn, H-2_C, 2H_Bn), 4.84 (d, 2H, J ) 11.2 Hz, H_Bn), 4.78 (d, 1H, J

) 10.2 Hz, H_Bn), 4.75 (d, 1H, J_1,2) 1.4 Hz, H-1_B), 4.70 (bs, 1H,

H-1_C), 4.68-4.57 (m, 9H, H_Bn), 4.50 (d, 1H, J ) 11.0 Hz, H_Bn),

4.41 (d, 1H, J ) 11.3 Hz, H_Bn), 4.35 (d, 1H, J ) 12.0 Hz, H_Bn),

4.28 (d, 1H, J_1,2) 8.6 Hz, H-1_D), 4.21-4.08 (m, 6H, H-3_E, H-5_E,

H-2_D, H-3_A, H_All, H-3_C), 3.99 (dd, 1H, J_2,3) 2.6 Hz, H-2_A),

3.96-3.84 (m, 7H, H-5_C, H-2_B, H_All, H-3_B, H-3_B′, H-2_E, H-4_E),

3.81-3.73 (m, 2H, H-5_A, H-5_B′), 3.71 (dq, 1H, J_4,5) 9.4 Hz, J_5,6

) 6.2 Hz, H-5_B), 3.54-3.38 (m, 8H, H-6a_D, H-6b_D, H-6a_E, H-6b_E,

H-4_A, H-4_B, H-4_D, H-4_C, H-4_B′), 2.75-2.64 (m, 6H, H-5_D, 4H_Lev

,

H-3_D), 2.31 (s, 3H, H_NAc), 2.18 (s, 3H, CH_3Lev), 2.05 (s, 3H, H_Ac),

1.42 (s, 3H, H_iPr), 1.39 (s, 3H, H_iPr), 1.35-1.31 (m, 9H, H-6_A, H-6_B,

H-6_B′), 1.24 (d, 3H, J_5,6) 6.2 Hz, H-6_C); ¹³C NMR (CDCl₃) δ

206.1 (C_Lev), 171.7 (C_Lev), 170.4 (C_Ac), 170.0 (C_NAc), 138.6-137.5

(C_Ph), 133.8 (CH)), 129.3-127.7 (CH_Ph), 117.1 (dCH₂), 103.6

(C-1_D, ¹J_CH) 159.0 Hz), 101.1 (C-1_A, ¹J_CH) 172.8 Hz), 99.5 (C-

1

1_B′, J_CH) 167.8 Hz), 99.2 (C_iPr), 97.9 (C-1_B, J_CH) 172.8 Hz),

97.8 (C-1_C, ¹J_CH) 172.8 Hz), 94.2 (C-1_E, ¹J_CH) 165.3 Hz), 83.4

(C-3_E), 80.5 (C-3_D), 80.4 (C-4_B), 80.2 (C-2_E), 80.1 (C-4_B′), 80.0

(C-4_C), 79.8 (C-4_A), 79.2 (C-3_B), 78.5 (C-4_E), 78.2 (C-3_C), 77.9

(C-3_B′), 76.2 (C-2_A), 76.1, 75.7, 75.4 (3C, C_Bn), 75.3 (C-2_B), 75.2,

75.1, 75.0, 74.5 (4C, C_Bn), 74.5 (C-3_A), 73.5 (C_Bn), 73.2 (C-2_C),

72.1 (C-4_D), 71.9, 71.4 (2C, C_Bn), 70.0 (C-5_E), 69.3 (C-2_B′), 68.9

(C-5_A), 68.5 (C-5_B′), 67.9 (C-6_E), 67.8 (C-5_B), 67.7 (C_All), 67.3 (C-

5_C), 67.2 (C-5_D), 62.0 (C-6_D), 55.0 (C-2_D), 38.1 (CH_2Lev), 29.8

(CH_3Lev), 29.2 (C_iPr), 28.2 (CH_2Lev), 24.1 (C_NAc), 21.0 (C_Ac), 19.1

(C_iPr), 18.0, 17.9, 17.8, 17.7 (4C, C-6_A, C-6_B, C-6_B′, C-6_C); HRMS

(ESI⁺) for C₁₂₁H₁₄₁NO₃₀([M + H]⁺, 2088.9617) found m/z

2088.9619, ([M + Na]⁺, 2110.9436) found m/z 2110.9497.

(m, 6H, H-3_E, H-2_D, H-5_E, H-3_C, H_All, H-3_A), 4.00 (dq, 1H, J_4,5

9.6 Hz, H-5_C), 3.97-3.83 (m, 6H, H_All, H-3_B, H-2_E, H-2_A, H-4_E,

H-6a_D), 3.79 (dq, 1H, J_4,5) 9.4 Hz, H-5_B), 3.73 (bd, 1H, J_5,6b

)

Allyl (2-Deoxy-4,6-O-isopropylidene-2-trichloroacetamido-3-

O-trimethylsilyl-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-ben-

zyl-r-D-glucopyranosyl-(1f3)]-4-O-benzyl-r-L-rhamnopyrano-

side (47). TMSOTf (61.0 µL, 340 µmol, 0.3 equiv) was added to a

solution of acceptor 27 (1.3 g, 1.1 mmol) and trichloroacetimidate 23

(1.5 g, 1.7 mmol, 1.5 equiv) in toluene (30 mL) containing 4Å MS

(960 mg), stirred at -78 °C. After 15 min, TLC (Tol/EtOAc, 8:2)

showed the absence of 27. Et₃N (0.2 mL) was added and the mixture

was ﬁltered, and concentrated to dryness. Chromatography of the

residue (Tol/EtOAc, 9:1 f 7:3) gave ﬁrst 47 (233 mg, 11%), and

then pentasaccharide 48 (1.1 g, 52%), both as white foams. Trisac-

10.3 Hz, H-6b_D), 3.70 (dq, 1H, J_4,5) 9.5 Hz, H-5_A), 3.52 (pt, 1H,

J_3,4) J_4,5) 9.3 Hz, H-4_D), 3.58-3.40 (m, 5H, H-4_A, H-6a_E, H-6b_E,

H-4_C, H-4_B), 2.7-2.68 (m, 6H, H-5_D, 4H_Lev, H-3_D), 2.35 (s, 3H,

H_NAc), 2.19 (s, 3H, CH_3Lev), 2.06 (s, 3H, H_Ac), 1.48 (s, 3H, H_iPr),

1.45 (s, 3H, H_iPr), 1.38 (d, 3H, J_5,6) 6.2 Hz, H-6_A), 1.34 (d, 3H,

J_5,6) 6.2 Hz, H-6_B), 1.27 (d, 3H, J_5,6) 6.2 Hz, H-6_C); ¹³C NMR

(CDCl₃) δ 206.1 (C_Lev), 171.8 (C_Lev), 170.5 (C_Ac), 170.1 (C_NAc),

138.7-137.5 (C_Ph), 134.0 (CH)), 129.4-127.8 (CH_Ph), 117.1

(dCH₂), 103.7 (C-1_D, ¹J_CH) 159.9 Hz), 99.5 (C-1_B, ¹J_CH) 169.7

Hz), 99.3 (C_iPr), 98.4 (C-1_A, ¹J_CH) 174.4 Hz), 97.5 (C-1_C, ¹J_CH

)

170.6 Hz), 94.4 (C-1_E, ¹J_CH) 170.1 Hz), 83.5 (C-3_E), 80.7 (C-3_D),

80.4 (C-2_E), 80.1, 80.0 (2C, C-4_B, C-4_C), 79.8 (C-4_A), 78.5 (C-4_E),

78.2 (C-3_C), 77.9 (C-3_B), 76.7 (C-2_A), 76.1, 75.9, 75.5, 75.4, 75.1,

75.0 (6C, C_Bn), 74.8 (C-3_A), 73.4 (C_Bn), 73.3 (C-2_C), 72.4 (C-4_D),

71.3 (C_Bn), 70.0 (C-5_E), 69.3 (C-2_B), 68.6 (C-5_A), 68.5 (C-5_B), 67.9

(C-6_E), 67.8 (C_All), 67.4 (C-5_D), 67.3 (C-5_C), 62.2 (C-6_D), 55.0 (C-

2_D), 38.1 (CH_2Lev), 29.8 (CH_3Lev), 29.2 (C_iPr), 28.3 (CH_2Lev), 24.1

(C_NAc), 21.1 (C_Ac), 19.1 (C_iPr), 17.9, 17.8, 17.7 (3C, C-6_A, C-6_B,

C-6_C); HRMS (ESI⁺) for C₁₀₁H₁₁₉NO₂₆([M + H]⁺, 1762.8098)

found m/z 1762.8198, ([M + Na]⁺, 1784.7917) found m/z 1784.7988.

Allyl (3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-

(1f3)-(2-O-acetyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-

acetamido-2-deoxy-4,6-O-isopropylidene-ꢀ-D-glucopyranosyl)-

(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-(4-O-

benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-r-L-

rhamnopyranoside (45). TMSOTf (18 µL, 100 µmol, 0.9 equiv) was

added to a solution of acceptor 21 (150 mg, 110 µmol) and

trichloroacetimidate 23 (140 mg, 160 µmol, 1.5 equiv) in toluene

1

charide 47 had R_f) 0.5 (Tol/EtOAc, 8:2); H NMR (CDCl₃) δ

7.47-7.08 (m, 26H, NH, CH_Ph), 5.89 (m, 1H, CH)), 5.32 (m, 1H,

J_trans) 17.2 Hz, dCH₂), 5.23 (m, 1H, J_cis) 10.6 Hz, dCH₂), 5.12

(d, 1H, J_1,2) 3.6 Hz, H-1_E), 5.11-5.05 (m, 3H, H_Bn), 4.93 (d, 1H, J

) 12.8 Hz, H_Bn), 4.86 (d, 1H, J_1,2) 1.6 Hz, H-1_A), 4.83-4.76 (m,

3H, H_Bn, H-1_D, H_Bn), 4.61-4.56 (m, 2H, H_Bn), 4.50 (d, 1H, J ) 11.0

Hz, H_Bn), 4.32 (d, 1H, J ) 12.0 Hz, H_Bn), 4.22-4.10 (m, 4H, H-3_E,

H_All, H-3_A, H-5_E), 4.08-3.97 (m, 3H, H-2_A, H-2_D, H_All), 3.90 (dd, 1H,

J_5,6a) 5.3 Hz, J_6a,6b) 10.7 Hz, H-6a_D), 3.83-3.72 (m, 4H, H-2_E,

H-4_E, H-6b_D, H-5_A), 3.58-3.52 (m, 2H, H-4_D, H-4_A), 3.45 (dd, 1H,

J_5,6a) 1.5 Hz, J_6a,6b) 10.8 Hz, H-6a_E), 3.40 (dd, 1H, J_5,6b) 1.5 Hz,

H-6b_E), 3.36 (pt, 1H, J_2,3) J_3,4) 9.2 Hz, H-3_D), 2.96 (ddd, 1H, J_5,6b

) J_4,5) 9.8 Hz, H-5_D), 1.51 (s, 3H, H_iPr), 1.45 (s, 3H, H_iPr), 1.44 (d,

3H, J_5,6) 6.2 Hz, H-6_A), 0.13 (s, 9H, H_Si); ¹³C NMR (CDCl₃) δ 161.7

(C_NTCA), 138.7-137.7 (C_Ph), 134.0 (CH)), 129.1-127.3 (CH_Ph), 117.1

(dCH₂), 101.5 (C-1_D, ¹J_CH) 163.6 Hz), 99.4 (C_iPr), 98.5 (C-1_A, ¹J_CH

) 174.0 Hz), 95.2 (C-1_E, ¹J_CH) 167.5 Hz), 93.3 (CCl₃), 83.3 (C-3_E),

79.8 (C-4_A), 78.7, 78.6 (2C, C-2_E, C-4_E), 75.9 (C_Bn), 75.4 (C-3_A), 75.3,

J. Org. Chem. Vol. 74, No. 7, 2009 2667

Boutet et al.

74.9 (2C, C_Bn), 74.3 (C-3_D), 74.3 (C_Bn), 74.2 (C-4_D), 74.1 (C-2_A), 73.4

(C_Bn), 70.0 (C-5_E), 68.5 (C-5_A), 67.9 (C-6_E), 67.8 (C_All), 67.2 (C-5_D),

62.1 (C-6_D), 58.6 (C-2_D), 29.1 (C_iPr), 19.0 (C_iPr), 18.0 (C-6_A), 0.7 (C_Si);

HRMS (ESI⁺) for C₆₄H₇₈Cl₃NO₁₅Si ([M + Na]⁺, 1256.4104) found

m/z 1256.4188, ([M + NH₄]⁺, 1251.4550) found m/z 1251.4548.

Allyl (3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-

(1f3)-(2-O-acetyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-

deoxy-4,6-O-isopropylidene-2-trichloroacetamido-ꢀ-D-glucopy-

ranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-

4-O-benzyl-r-L-rhamnopyranoside (48). TMSOTf (49 µL, 270

µmol, 0.3 equiv) was added to a solution of acceptor 27 (1.1 g, 0.9

mmol) and trichloroacetimidate 23 (1.2 g, 1.4 mmol, 1.5 equiv) in

toluene (30 mL) containing 4Å MS (1.1 g), stirred at -40 °C. After

15 min, TLC (Tol/EtOAc, 8:2) showed the absence of 27. Et₃N

(0.2 mL) was added. The mixture was ﬁltered, and concentrated to

dryness. Chromatography of the residue (Tol/EtOAc, 9:1 f 7:3)

gave 48 (1.4 g, 75%) as a white foam. Pentasaccharide 48 had R_f

) 0.35 (Tol/EtOAc, 8:2); ¹H NMR (CDCl₃) δ 7.51-7.13 (m, 40H,

CH_Ph), 6.94 (d, 1H, J_NH,2) 8.9 Hz, NH), 5.94 (m, 1H, CH)), 5.48

(dd, 1H, H-2_B), 5.33 (m, 1H, J_trans) 17.2 Hz, dCH₂), 5.24 (m,

1H, J_cis) 10.4 Hz, dCH₂), 5.24 (d, 1H, J_1,2) 3.5 Hz, H-1_E), 5.16

(m, 2H, H_Bn), 5.12 (dd, 1H, J_2,3) 2.8 Hz, H-2_C), 5.11 (d, 1H, J_1,2

) 1.3 Hz, H-1_B), 5.07 (d, 1H, J ) 12.2 Hz, H_Bn), 4.98-4.94 (m,

2H, H_Bn), 4.89 (d, 2H, J ) 11.0 Hz, H_Bn), 4.84 (d, 1H, J_1,2) 1.7

Hz, H-1_A), 4.79 (d, 1H, J_1,2) 1.6 Hz, H-1_C), 4.76 (d, 1H, J ) 10.2

Hz, H_Bn), 4.71 ((d, 1H, J ) 11.2 Hz, H_Bn), 4.67-4.54 (d, 6H, H_Bn,

H-1_D), 4.46 (d, 1H, J ) 11.3 Hz, H_Bn), 4.36 (d, 1H, J ) 12.0 Hz,

H_Bn), 4.24-4.15 (m, 5H, H-3_E, H-3_C, H_All, H-3_A, H-5_E), 4.09-3.96

(m, 5H, H-2_D, H-2_A, H-5_C, H_All, H-5_B), 3.95 (dd, 1H, J_2,3) 3.2

Hz, J_3,4) 9.2 Hz, H-3_B), 3.91-3.85 (m, 3H, H-6a_D, H-2_E, H-4_E),

3.78-3.73 (m, 2H, H-5_A, H-6b_D), 3.57 (pt, 1H, J_3,4) J_4,5) 9.2

Hz, H-4_D), 3.52 (pt, 1H, J_3,4) J_4,5) 9.6 Hz, H-4_A), 3.50-3.44

(m, 4H, H-6a_E, H-6b_E, H-4_C, H-4_B), 2.87 (ddd, 1H, J_5,6a) 5.2 Hz,

J_5,6b) 9.8 Hz, H-5_D), 2.77 (m, 5H, H-3_D, 4H_Lev), 2.21 (s, 3H,

CH_3Lev), 2.16 (s, 3H, H_Ac), 1.52 (s, 3H, H_iPr), 1.50 (s, 3H, H_iPr),

1.46 (d, 3H, J_5,6) 6.2 Hz, H-6_A), 1.40 (d, 3H, J_5,6) 6.2 Hz, H-6_B),

1.31 (d, 3H, J_5,6) 6.2 Hz, H-6_C); ¹³C NMR (CDCl₃) δ 206.5 (C_Lev),

172.1 (C_Lev), 169.9 (C_Ac), 162.4 (C_NTCA), 139.1-138.8 (C_Ph), 134.4

H-1_A, 2H_Bn), 5.11-5.09 (m, 2H, H-1_B′, H-2_C), 5.06 (d, 1H, J )

12.2 Hz, H_Bn), 4.98-4.93 (m, 3H, H_Bn), 4.89-4.83 (m, 3H, H_Bn),

4.81 (d, 1H, J_1,2) 1.4 Hz, H-1_B), 4.72-4.58 (m, 10H, H-1_C, H_Bn,

H-1_D), 4.54 (d, 1H, J ) 11.0 Hz, H_Bn), 4.45 (d, 1H, J ) 11.3 Hz,

H_Bn), 4.37 (d, 1H, J ) 12.0 Hz, H_Bn), 4.24-4.14 (m, 5H, H-3_E,

H-3_C, H_All, H-3_A, H-2_A, H-5_E), 4.07-3.86 (m, 9H, H-2_B, H-2_D, H_All

,

H-5_C, H-5_B′, H-3_B, H-3_B′, H-2_E, H-4_E), 3.80 (dq, 1H, J_4,5) 9.5 Hz,

J_5,6) 6.2 Hz, H-5_A), 3.74 (dq, 1H, J_4,5) 9.4 Hz, H-5_B), 3.58 (dd,

1H, J_5,6a) 5.2 Hz, H-6a_D), 3.56-3.43 (m, 8H, H-4_A, H-4_B, H-6a_E,

H-6b_E, H-4_D, H-4_B′, H-4_C), 3.35 (m, 1H, J_6a,6b) 10.4 Hz, H-6b_D),

2.82 (ddd, 1H, J_5,6b) 1.5 Hz, J_4,5) 9.7 Hz, H-5_D), 2.75-2.69 (m,

5H, 4H_Lev, H-3_D), 2.21 (s, 3H, CH_3Lev), 2.14 (s, 3H, H_Ac), 1.44-1.43

(m, 9H, H_iPr, H-6_A), 1.39 (d_po, 3H, H-6_B′), 1.37 (d_po, 3H, H-6_B),

1.37 (d, 3H, J_5,6) 6.2 Hz, H-6_C); ¹³C NMR (CDCl₃) δ 206.3 (C_Lev),

171.8 (C_Lev), 169.6 (C_Ac), 162.0 (C_NTCA), 138.7-137.6 (C_Ph), 133.9

(CH)), 129.4-127.5 (CH_Ph), 117.2 (dCH₂), 101.2 (C-1_D, ¹J_CH

)

163.9 Hz), 100.9 (C-1_A, ¹J_CH) 172.0 Hz), 99.4 (C_iPr), 99.0 (C-1_B′,

¹J_CH) 168.3 Hz), 98.0 (C-1_B, ¹J_CH) 168.7 Hz), 97.6 (C-1_C, ¹J_CH

) 170.4 Hz), 94.3 (C-1_E, ¹J_CH) 167.5 Hz), 93.1 (CCl₃), 83.1 (C-

3_E), 80.4, 80.1, 79.9, 79.7, 79.6, 79.0 (7C, C-3_B, C-3_B′, C-4_A, C-4_B,

C-4_B′, C-4_C, C-4_E), 78.7 (C-3_D), 77.6 (C-2_E), 76.8 (C-3_C), 76.2, 75.4,

75.3, 75.2, 75.0, 74.9, 74.8 (7C, C_Bn), 74.3 (C-2_B), 74.2 (C-3_A),

73.5 (C_Bn), 73.4 (C-2_A), 72.6 (C-4_D), 72.1 (C-2_C), 72.0, 71.5 (2C,

C_Bn), 69.9 (C-5_E), 69.4 (C-2_B′), 68.7 (C-5_A), 68.5 (C-5_B′), 68.0 (C-

5_B), 67.9 (C-6_E), 67.8 (C-5_C), 67.7 (C_All), 67.0 (C-5_D), 61.8 (C-6_D),

57.4 (C-2_D), 38.2 (CH_2Lev), 29.9 (CH_3Lev), 29.2 (C_iPr), 28.2 (CH_2Lev),

21.2 (C_Ac), 19.1 (C_iPr), 18.3, 18.1, 18.0, 17.9 (4C, C-6_A, C-6_B, C-6_B′,

C-6_C); HRMS (ESI⁺) for C₁₂₁H₁₃₈Cl₃NO₃₀([M + H]⁺, 2190.8447)

found m/z 2190.8403, ([M + Na]⁺, 2212.8267) found m/z 2212.8215.

Allyl (3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-(1f3)-

(2-O-acetyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-deoxy-2-

trichloroacetamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-

r-D-glucopyranosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-

3,4-di-O-benzyl-r-L-rhamnopyranoside (51). TFA (50% aq, 8 mL)

was added, at 0 °C, to a solution of hexasaccharide 50 (1.9 g, 880

µmol) in CH₂Cl₂(30 mL), and the biphasic mixture was stirred

vigorously at rt for 1 h. TLC (Tol/EtOAc, 7:3) showed the complete

disappearance of 50 and the presence of a major more polar product.

Repeated coevaporation with toluene, followed by chromatography

of the residue (Tol/EtOAc, 8:2 f 6:4) provided diol 51 (1.7 g,

89%) as a white foam. The latter had R_f) 0.4 (Tol/EtOAc, 7:3);

¹H NMR (CDCl₃) δ 7.62-7.13 (m, 50H, CH_Ph), 7.04 (d, 1H, J_NH,2

) 8.6 Hz, NH), 5.94 (m, 1H, CH)), 5.53 (dd, 1H, J_1,2) 2.0 Hz,

(CH)), 129.5-127.8 (CH_Ph), 117.5 (dCH₂), 101.7 (C-1_D, ¹J_CH

)

1

163.9 Hz), 99.9 (C_iPr), 99.4 (C-1_B, J_CH) 174.7 Hz), 98.8 (C-1_A,

¹J_CH) 171.5 Hz), 98.1 (C-1_C, ¹J_CH) 167.6 Hz), 94.9 (C-1_E, ¹J_CH

) 165.3 Hz), 93.5 (CCl₃), 83.5 (C-3_E), 80.9 (C-2_E), 80.8 (C-4_B),

80.3 (C-4_C), 80.1 (C-4_A), 79.2 (C-3_D), 79.1 (C-4_E), 78.0 (C-3_B),77.1

(C-3_C), 76.4, 75.8, 75.7, 75.4, 75.3, 75.2 (6C, C_Bn), 75.1 (C-3_A),

74.2 (C-2_A), 73.8 (C_Bn), 73.1 (C-4_D), 72.8 (C-2_C), 71.9 (C_Bn), 70.3

(C-5_E), 69.9 (C-2_B), 69.0 (C-5_B), 68.8 (C-5_A), 68.4 (C-6_E), 68.3

(C-5_C), 68.2 (C_All), 67.4 (C-5_D), 62.5 (C-6_D), 57.8 (C-2_D), 38.6

(CH_2Lev), 30.3 (CH_3Lev), 29.6 (C_iPr), 28.7 (CH_2Lev), 21.5 (C_Ac), 19.4

(C_iPr), 18.5 (C-6_C), 18.4 (C-6_A), 18.3 (C-6_B); HRMS (ESI⁺) for

J_2,3) 3.0 Hz, H-2_B′), 5.44 (bs, 1H, H-1_A), 5.34 (m, 1H, J_trans

)

17.2 Hz, dCH₂), 5.34 (d, 1H, J_1,2) 3.6 Hz, H-1_E), 5.26 (m, 1H,

J_cis) 10.4 Hz, dCH₂), 5.21 (d, 1H, J ) 11.4 Hz, H_Bn), 5.19-5.11

(m, 3H, H_Bn, H-1_B′, H-2_C,), 5.13 (d, 1H, J ) 12.7 Hz, H_Bn),

5.07-4.88 (m, 7H, H_Bn), 4.82-4.78 (m, 3H, 2H_Bn, H-1_B), 4.75-4.58

(m, 9H, H_Bn, H-1_C), 4.56 (d, 1H, J_1,2) 8.8 Hz, H-1_D), 4.45 (d, 1H,

(d, 1H, J ) 11.4 Hz, H_Bn), 4.43 (d, 1H, J ) 11.9 Hz, H_Bn),

4.30-4.18 (m, 7H, H-3_C, H-2_A, H-3_A, H-3_E, H-5_E, H-2_B, H_All),

4.05-3.70 (m, 7H, H_All, H-2_D, H-3_B, H-3_B′, H-5_C, H-4_E, H-2_E), 3.88

(dq, 1H, J_4,5) 9.4 Hz, H-5_B′), 3.81 (dq, 1H, J_4,5) 9.6 Hz, H-5_B),

3.78 (dq, 1H, J_4,5) 10.0 Hz, H-5_A), 3.72 (bd, 1H, J_6a,6b) 11.3

Hz, H-6a_D), 3.61-3.52 (m, 5H, H-4_B, H-6a_E, H-6b_E, H-4_A, H-4_C),

3.48 (pt, 1H, J_3,4) 9.4 Hz, H-4_B′), 3.12-3.08 (m, 2H, H-4_D, H-5_D),

3.05 (m, 1H, H-6b_D), 2.82-2.73 (m, 4H, H_Lev), 2.24 (s, 3H, CH_3Lev),

2.23 (s, 3H, H_Ac), 2.19 (m, 1H, H-3_D), 1.50 (d, 3H, J_5,6) 6.3 Hz,

H-6_A), 1.46 (d, 3H, J_5,6) 6.2 Hz, H-6_B), 1.38 (d, 3H, J_5,6) 6.1

Hz, H-6_B′), 1.37 (d, 3H, J_5,6) 6.1 Hz, H-6_C); ¹³C NMR (CDCl₃) δ

206.1 (C_Lev), 171.7 (C_Lev), 170.0 (C_Ac), 162.2 (C_NTCA), 138.8-137.6

(C_Ph), 133.9 (CH)), 129.4-127.5 (CH_Ph), 117.1 (dCH₂), 101.1

(C-1_D, ¹J_CH) 165.4 Hz), 100.2 (C-1_A, ¹J_CH) 175.4 Hz), 99.1 (C-

C

₁₀₁H₁₁₆Cl₃NO₂₆([M + Na]⁺, 1886.6749) found m/z 1886.6445,

([M + NH₄]⁺, 1881.7195) found m/z 1881.6897.

Allyl (3,4-Di-O-benzyl-2-O-levulinoyl-r-L-rhamnopyranosyl)-

(1f3)-(2-O-acetyl-4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-

deoxy-4,6-O-isopropylidene-2-trichloroacetamido-ꢀ-D-glucopy-

ranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-glucopyranosyl-(1f3)]-

(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-3,4-di-O-benzyl-r-L-

rhamnopyranoside (50). TMSOTf (61 µL, 340 µmol, 0.3 equiv)

was added to a solution of acceptor 20 (1.7 g, 1.1 mmol) and

trichloroacetimidate 23 (1.5 g, 1.7 mmol, 1.5 equiv) in toluene (35

mL) containing 4Å MS (975 mg), stirred at -40 °C. After 1 h,

TLC (Tol/EtOAc, 8:2) showed the absence of 20. Et₃N (0.2 mL)

was added. The mixture was ﬁltered, and concentrated to dryness.

Chromatography of the residue (Tol/EtOAc, 95:5 f 70:30) gave,

by order of elution, ﬁrst 50 (1.45 g, 59%), and then diol 51 (505

mg, 21%), both as white foams. Hexasaccharide 50 had R_f) 0.45

(Tol/EtOAc, 8:2); ¹H NMR (CDCl₃) δ 7.47-7.10 (m, 50H, CH_Ph),

6.94 (d, 1H, J_NH,2) 8.8 Hz, NH), 5.92 (m, 1H, CH)), 5.46 (dd,

1H, J_1,2) 1.9 Hz, J_2,3) 3.0 Hz, H-2_B′), 5.30 (m, 1H, J_trans) 17.2

Hz, dCH₂), 5.25-5.22 (m, 2H, H-1_E, dCH₂), 5.15-5.12 (m, 3H,

1

1_B′, J_CH) 171.8 Hz), 98.5 (C-1_C, J_CH) 173.3 Hz), 98.3 (C-1_B,

¹J_CH) 168.3 Hz), 94.1 (C-1_E, ¹J_CH) 166.9 Hz), 93.3 (CCl₃), 87.2

(C-3_D), 83.1 (C-3_E), 80.6 (C-3_B), 80.5 (2C, C-2_E, C-4_B), 80.1 (C-

4_B′), 79.7 (C-4_A), 79.5 (C-4_C), 78.8 (C-4_E), 77.7 (C-3_B′), 77.3 (C-

3_C), 76.3 (C_Bn), 75.6 (C-5_D), 75.5, 75.4, 75.3, 75.0 (6C, C_Bn), 74.1,

74.0 (C-2_B, C-3_A), 73.5, 72.9 (2C, C_Bn), 72.1 (C-2_C), 71.4 (C_Bn),

2668 J. Org. Chem. Vol. 74, No. 7, 2009

Synthesis of Tri- to Hexasaccharide Fragments of Shigella ﬂexneri

71.3 (2C, C-2_A, C-4_D), 70.1 (C-5_E), 69.4 (2C, C-2_B′, C-5_C), 68.9

(C-5_A), 68.7 (C-5_B′), 68.4 (C-5_B), 68.0 (C-6_E), 67.6 (C_All), 62.8 (C-

6_D), 55.5 (C-2_D), 38.2 (CH_2Lev), 29.9 (CH_3Lev), 28.3 (CH_2Lev), 21.1

(C_Ac), 18.1, 18.0, 17.8, 17.9 (4C, C-6_A, C-6_B, C-6_B′, C-6_C); HRMS

(ESI⁺) for C₁₁₈H₁₃₄Cl₃NO₃₀([M + Na]⁺, 2172.7954) found m/z

2172.8081.

(D₂O) δ 5.10 (d, 1H, J_1,2) 3.7 Hz, H-1_E), 5.00 (d, 1H, J_1,2) 1.6

Hz, H-1_A), 4.91 (dd, 1H, J_1,2) 1.9 Hz, J_2,3) 3.1 Hz, H-2_C), 4.89

(d, 1H, J_1,2) 1.4 Hz, H-1_B′), 4.80 (bs, 2H, H-1_B, H-1_C), 4.71 (d,

1H, H-1_D), 4.35 (dd, 1H, J_2,3) 2.6 Hz, H-2_A), 4.00 (dq, 1H, J_4,5

)

9.7 Hz, J_5,6) 6.2 Hz, H-5_C), 3.95 (m, 1H, H-5_E), 3.93 (dd, 1H, J_2,3

) 3.4 Hz, H-2_B′), 3.89-3.51 (m, 14H, H-3_C, H-2_B, H-3_A, H-6a_D,

H-2_D, H-3_B, H-3_E, H-6a_E, H-6b_E, H-5_A, H-6b_D, H-2_E, H-5_B, H-3_B′,

H_Pr), 3.49 (pt, 1H, J_3,4) J_4,5) 9.8 Hz, H-4_C), 3.46-3.30 (m, 8H,

H-4_D, H_Pr, H-5_B′, H-4_E, H-4_B, H-4_B′, H-5_D, H-3_D), 3.26 (pt, 1H, J_3,4

) J_4,5) 9.6 Hz, H-4_A), 2.08 (s, 3H, H_Ac), 2.03 (s, 3H, H_NAc),

1.54-1.47 (m, 2H, CH₂), 1.22-1.13 (m, 12H, H-6_B, H-6_A, H-6_B′,

H-6_C), 0.82 (t, 3H, J ) 7.4 Hz, CH₃); ¹³C NMR (D₂O) δ 174.4

Allyl (3,4-Di-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-O-acetyl-

4-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-deoxy-2-trichloroac-

etamido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-

glucopyranosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-

3,4-di-O-benzyl-r-L-rhamnopyranoside (52). A solution of hydrazine

hydrate (158 µL, 3.2 mmol, 10 equiv) in pyridine/acetic acid (3:2,

v/v, 5 mL) was added to diol 51 (700 mg, 320 µmol) in pyridine

(3 mL). After 25 min at 0 °C, TLC (Tol/EtOAc, 7:3) showed the

complete disappearance of the diol and the presence of a major

more polar product. Water (10 mL) and CH₂Cl₂(50 mL) were

added, and the organic phase was washed with brine (3 × 20 mL),

water (3 × 20 mL), dried on Na₂SO₄, ﬁltered, and concentrated to

dryness. Chromatography of the residue (Tol/EtOAc, 9:1 f 7:3)

gave triol 52 (560 mg, 84%) as a white foam. Hexasaccharide 52

1

(C_NAc), 173.2 (C_Ac), 102.7 (C-1_B′, J_CH) 170.6 Hz), 101.4 (C-1_D,

¹J_CH) 166.0 Hz), 101.2 (C-1_A, ¹J_CH) 173.5 Hz), 98.4 (C-1_C, ¹J_CH

1

) 167.8 Hz), 98.1 (C-1_B, J_CH) 171.5 Hz), 94.2 (C-1_E, J_CH

)

172.8 Hz), 82.6 (C-3_D), 79.1(C-2_B), 77.0 (C-3_C), 76.0 (C-5_D), 74.1

(C-2_A), 73.3 (C-3_A), 73.0 (C-3_E), 72.4 (C-2_C), 71.9 (C-4_B), 71.7

(C-4_B′), 71.3, 71.2, 71.1 (C-5_E, C-2_E, C-4_C), 70.7 (C-4_A), 70.1 (C-

3_B′), 69.9 (2C, C-2_B′, C-3_B), 69.7 (C_Pr), 69.4, 69.3 (3C, C-4_E, C-5_A,

C-5_B′), 68.8 (C-5_C), 68.6 (C-5_B), 68.1 (C-4_D), 60.6 (C-6_D), 60.3 (C-

6_E), 55.3 (C-2_D), 22.7 (C_NAc), 21.9 (CH₂), 20.2 (C_Ac), 16.8, 16.6,

16.5, 16.3 (4C, C-6_A, C-6_B, C-6_B′, C-6_C), 9.8 (CH₃); HRMS (ESI⁺)

for C₄₃H₇₃NO₂₈([M + H]⁺, 1052.4397) found m/z 1052.4360, ([M

+ Na]⁺, 1074.4216) found m/z 1074.4202.

1

had R_f) 0.35 (Tol/EtOAc, 7:3); H NMR (CDCl₃) δ 7.48-7.07

(m, 50H, CH_Ph), 7.02 (d, 1H, J_NH,2) 8.6 Hz, NH), 5.90 (m, 1H,

CH)), 5.40 (bs, 1H, H-1_A), 5.30 (d, 1H, J_1,2) 3.6 Hz, H-1_E), 5.29

(m, 1H, J_trans) 17.2 Hz, dCH₂), 5.22 (m, 1H, J_cis) 10.4 Hz,

dCH₂), 5.17 (d, 1H, J ) 11.0 Hz, H_Bn), 5.16-5.12 (m, 3H, H-1_B′,

H-2_C, H_Bn), 5.10 (d, 1H, J ) 13.0 Hz, H_Bn), 5.04 (d, 1H, J ) 12.8

Hz, H_Bn), 5.01 (d, 1H, J ) 10.4 Hz, H_Bn), 4.93 (d, 1H, J ) 10.9

Hz, H_Bn), 4.85-4.81 (m, 2H, H_Bn), 4.77-4.66 (m, 7H, 3H_Bn, H-1_B,

3H_Bn), 4.62-4.54 (m, 6H, 5H_Bn, H-1_C), 4.51 (d, 1H, J_1,2) 8.4 Hz,

H-1_D), 4.38 (d, 1H, J ) 11.9 Hz, H_Bn), 4.23-4.13 (m, 7H, H-2_B,

H-3_C, H-3_E, H-3_A, H_All, H-5_E, H-2_A), 4.07 (dd, 1H, H-2_B′),

4.00-3.87 (m, 6H, H_All, H-2_D, H-3_B, H-5_C, H-4_E, H-2_E), 3.84-3.81

(m, 1H, H-3_B′, J_2,3) 2.4 Hz, J_3,4) 9.1 Hz, H-5_B′), 3.78-3.69 (m,

2H, H-5_B, H-5_A), 3.65 (bd, 1H, J_6a,6b) 11.2 Hz, H-6a_D), 3.55-3.49

(m, 5H, H-6a_E, H-6b_E, H-4_B, H-4_A, H-4_B′), 3.47 (pt, 1H, J_3,4) J_4,5

) 9.5 Hz, H-4_C), 3.06-3.04 (m, 2H, H-4_D, H-5_D), 2.94 (dd, 1H,

J_5,6b) 5.7 Hz, H-6b_D), 2.20 (s, 3H, H_Ac), 2.15 (m, 1H, H-3_D), 1.46

(d, 3H, J_5,6) 6.2 Hz, H-6_A), 1.42 (d, 3H, J_5,6) 6.2 Hz, H-6_B),

1.33-1.30 (m, 6H, H-6_C, H-6_B′); ¹³C NMR (CDCl₃) δ 170.0 (C_Ac),

162.3 (C_NTCA), 138.7-137.4 (C_Ph), 133.8 (CH)), 129.4-127.4

Allyl (3,4-Di-O-benzyl-r-L-rhamnopyranosyl)-(1f3)-(4-O-

benzyl-r-L-rhamnopyranosyl)-(1f3)-(2-deoxy-2-trichloroaceta-

mido-ꢀ-D-glucopyranosyl)-(1f2)-[2,3,4,6-tetra-O-benzyl-r-D-

glucopyranosyl-(1f3)]-(4-O-benzyl-r-L-rhamnopyranosyl)-(1f2)-

3,4-di-O-benzyl-r-L-rhamnopyranoside (53). Methanolic MeONa

(0.5 M, 745 µL, 370 µmol, 1 equiv) was added to a solution of

diol 51 (800 mg, 370 µmol) in MeOH (20 mL), and the mixture

was reﬂuxed for 1 h. TLC (Tol/EtOAc, 6:4) showed the complete

disappearance of the diol and the presence of a single more polar

product. The mixture was neutralized by addition of Dowex X8-

200 ion-exchange resin (H⁺), and ﬁltered. Evaporation of the ﬁltrate

gave a syrup which was chromatographied (Tol/EtOAc, 8:2 f 7:3)

to give 53 (688 mg, 92%) as a white foam. Hexasaccharide 53 had

1

R_f) 0.45 (Tol/EtOAc, 6:4); H NMR (CDCl₃) δ 7.44-7.05 (m,

50H, CH_Ph), 6.86 (d, 1H, J_NH,2) 8.6 Hz, NH), 5.89 (m, 1H, CH)),

5.36 (bs, 1H, H-1_A), 5.31-5.25 (m, 2H, dCH₂, H-1_E), 5.21 (m,

1H, J_cis) 10.4 Hz, dCH₂), 5.17 (d, 1H, J_1,2) 1.6 Hz, H-1_B′),

5.14 (d, 1H, J ) 11.1 Hz, H_Bn), 5.08 (m, 1H, J ) 11.1 Hz, H_Bn),

5.03-4.90 (m, 4H, H_Bn), 4.82 (d, 1H, J ) 11.0 Hz, H_Bn), 4.74-4.52

(m, 13H, H-1_B, H_Bn), 4.50 (d, 1H, J_1,2) 8.4 Hz, H-1_D), 4.47 (d,

1H, J_1,2) 1.6 Hz, H-1_C), 4.38 (d, 1H, J ) 11.9 Hz, H_Bn), 4.19 (dd,

1

(CH_Ph), 117.1 (dCH₂), 101.1 (C-1_D, J_CH) 161.0 Hz), 100.6 (C-

1_B′, ¹J_CH) 171.0 Hz), 100.1 (C-1_A, ¹J_CH) 174.7 Hz), 98.3 (C-1_C,

¹J_CH) 170.4 Hz), 98.2 (C-1_B, ¹J_CH) 170.4 Hz), 94.0 (C-1_E, ¹J_CH

) 163.1 Hz), 93.1 (CCl₃), 87.1 (C-3_D), 83.1 (C-3_E), 80.5 (C-3_B),

80.4 (C-4_B), 80.3 (C-2_E), 80.0 (C-4_A), 79.7 (2C, C-3_B′, C-4_B′), 79.4

(C-4_C), 78.7 (C-4_E), 77.7 (C-3_C), 76.3 (C_Bn), 75.5 (C-5_D), 75.4, 75.4,

75.3, 75.0, 74.9 (6C, C_Bn), 74.1 (C-2_A), 73.9 (C-3_A), 73.5, 72.8

(2C, C_Bn), 72.0 (C-2_C), 71.7 (C_Bn), 71.3 (C-4_D), 71.0 (C-2_B), 70.0

(C-5_E), 69.1 (C-5_C), 68.8 (2C, C-2_B′, C-5_A), 68.4, 68.3 (2C, C-5_B,

C-5_B′), 67.8 (C-6_E), 67.6 (C_All), 62.7 (C-6_D), 55.3 (C-2_D), 21.2 (C_Ac),

18.0, 17.8 (4C, C-6_A, C-6_B, C-6_B′, C-6_C); HRMS (ESI⁺) for

1H, J_1,2) 2.1 Hz, J_2,3) 2.4 Hz, H-2_B), 4.17-4.12 (m, 5H, H_All

,

H-5_E, H-3_E, H-3_A, H-2_A), 4.06-4.03 (m, 2H, H-3_C, H-2_B′),

3.99-3.82 (m, 9H, H_All, H-2_C, H-2_D, H-3_B, H-5_C, H-5_B′, H-4_E, H-2_E,

H-3_B′), 3.78-3.70 (m, 2H, H-5_B, H-5_A), 3.65 (bd, 1H, J_6a,6b) 11.4

Hz, H-6a_D), 3.59-3.45 (m, 6H, H-4_B′, H-6a_E, H-6b_E, H-4_B, H-4_A,

H-4_C), 3.08-3.03 (m, 2H, H-5_D, H-4_D), 2.94 (m, 1H, H-6b_D), 2.23

(dd, 1H, J_2,3) 9.7 Hz, J_3,4) 7.7 Hz, H-3_D), 1.44 (d, 3H, J_5,6) 6.2

C

₁₁₃H₁₂₈Cl₃NO₂₈([M + Na]⁺, 2074.7585) found m/z 2074.7581,

([M + NH₄]⁺, 2069.8032) found m/z 2069.7925.

Hz, H-6_B′), 1.43 (d, 3H, J_5,6) 6.1 Hz, H-6_A), 1.40 (d, 3H, J_5,6)

6.2 Hz, H-6_B), 1.32 (d, 3H, J_5,6) 6.1 Hz, H-6_C); ¹³C NMR (CDCl₃)

δ 161.9 (C_NTCA), 138.7-137.5 (C_Ph), 133.9 (CH)), 129.1-127.3

Propyl r-L-Rhamnopyranosyl-(1f3)-(2-O-acetyl-r-L-rham-

nopyranosyl)-(1f3)-(2-acetamido-2-deoxy-ꢀ-D-glucopyranosyl)-

(1f2)-[r-D-glucopyranosyl-(1f3)]-r-L-rhamnopyranosyl-(1f2)-

r-L-rhamnopyranoside (5). Hexasaccharide 52 (400 mg, 195

µmol) was dissolved in EtOH (20 mL), treated with 10% Pd/C

catalyst (400 mg), and the suspension was stirred at rt for 10 days,

under a hydrogen atmosphere (45 bar). TLC (iPrOH/H₂O/NH₃, 4:1:

0.5 and Tol/EtOAc, 7:3) showed that 52 had been transformed into

a more polar product. The suspension was ﬁltered on Acrodisc LC

25 mm, and the ﬁltrate was concentrated. Reverse phase chroma-

tography (H₂O/CH₃CN, 100:0 f 70:30) of the residue, followed

by freeze-drying, gave acetate 5 (131 mg, 64%) as a white foam.

Hexasaccharide 5 had R_f) 0.65 (iPrOH/H₂O/NH₃, 4:1:0.5); HPLC

(215 nm): t_R) 13.3 min (Kromasil 5 µm C-18 100Å 4.6 × 250

mm analytical column, using a 0-40% linear gradient over 20 min

1

(CH_Ph), 117.1 (dCH₂), 101.0 (C-1_D, J_CH) 162.7 Hz), 100.8 (C-

1

1_C, J_CH) 169.2 Hz), 100.1 (C-1_A, J_CH) 180.3 Hz), 100.0 (C-

1

1_B′, J_CH) 180.3 Hz), 98.3 (C-1_B, J_CH) 170.3 Hz), 94.0 (C-1_E,

¹J_CH) 168.6 Hz), 93.2 (CCl₃), 86.5 (C-3_D), 83.0 (C-3_E), 80.5 (C-

3_B), 80.4 (2C, C-2_E, C-4_B), 79.8, 79.7, 79.6 (4C, C-4_A, C-3_B′, C-4_B′,

C-4_C), 78.8 (C-4_E), 78.3 (C-3_C), 76.3 (C_Bn), 75.5 (C-5_D), 75.4, 75.3,

75.2, 74.9 (6C, C_Bn), 74.0 (C-3_A), 73.8 (C-2_A), 73.5, 72.8, 72.0

(3C, C_Bn), 71.3 (C-2_B), 71.1 (C-4_D), 70.4 (C-2_C), 70.0 (C-5_E), 68.9

(C-5_C), 68.8 (2C, C-5_A, C-2_B′), 68.7 (C-5_B′), 68.3 (C-5_B), 67.9 (C-

6_E), 67.6 (C_All), 62.7 (C-6_D), 55.8 (C-2_D), 18.1, 18.0, 17.8 (4C, C-6_A,

C-6_B, C-6_B′, C-6_C); HRMS (ESI⁺) for C₁₁₁H₁₂₆Cl₃NO₂₇([M + Na]⁺,

2032.7480) found m/z 2032.7448.

Propyl r-L-Rhamnopyranosyl-(1f3)-r-L-rhamnopyranosyl-

(1f3)-(2-acetamido-2-deoxy-ꢀ-D-glucopyranosyl)-(1f2)-[r-D-

1

of CH₃CN in 0.01 M aq TFA at 1 mL min^-1ﬂow rate); H NMR

J. Org. Chem. Vol. 74, No. 7, 2009 2669

Boutet et al.

glucopyranosyl-(1f3)]-r-L-rhamnopyranosyl-(1f2)-r-L-rham-

nopyranoside (6). Hexasaccharide 53 (580 mg, 289 µmol) was

dissolved in EtOH (15 mL), treated with 10% Pd/C catalyst (340

mg), and the suspension was stirred at rt for 10 days, under a

hydrogen atmosphere (45 bar). TLC (iPrOH/H₂O/NH₃, 4:1:0.5 and

Tol/EtOAc, 6:4) showed that 53 had been transformed into a more

polar product. The suspension was ﬁltered on Acrodisc LC 25 mm,

and the ﬁltrate was concentrated. Reverse phase chromatography

(H₂O/CH₃CN, 100:0 f 70:30) of the residue, followed by freeze-

drying, gave the target 6 (240 mg, 82%) as a white foam.

Hexasaccharide 6 had R_f) 0.2 (iPrOH/H₂O/NH₃, 4:1:0.5); HPLC

(215 nm): t_R) 13.4 min (Kromasil 5 µm C-18 100Å 4.6 × 250

mm analytical column, using a 0-40% linear gradient over 20 min

101.2 (C-1_A, ¹J_CH) 169.8 Hz), 98.2 (C-1_B, ¹J_CH) 170.5 Hz), 94.4

(C-1_E, ¹J_CH) 171.2 Hz), 81.7 (C-3_D), 79.1(C-2_B), 78.1 (C-3_C), 76.0

(C-5_D), 74.2 (C-2_A), 73.5 (C-3_A), 73.2 (C-3_E), 72.2 (C-4_B), 72.0

(C-4_B′), 71.4 (C-5_E), 71.3 (C-2_E) 71.3 (C-4_C), 70.8 (C-4_A), 70.5 (C-

2_C), 70.2 (C-3_B′), 70.2 (C-2_B′), 70.0 (C-3_B), 69.8 (C_Pr), 69.5 (C-4_E),

69.4 (C-5_A), 69.0 (2C, C-5_C, C-5_B), 68.7 (C-5_B′), 68.3 (C-4_D), 60.7

(C-6_D), 60.4 (C-6_E), 55.5 (C-2_D), 22.6 (C_NAc), 21.9 (CH₂), 16.8,

16.7, 16.5 (4C, C-6_A, C-6_B, C-6_B′, C-6_C), 9.9 (CH₃); HRMS (ESI⁺)

for C₄₁H₇₁NO₂₇([M + H]⁺, 1010.4292) found m/z 1010.4295, ([M

+ Na]⁺, 1032.4111) found m/z 1032.4116.

Acknowledgment. The authors thank the Agence Nationale

pour la Recherche (ANR, Grant NT05-1_42479), the Institut

Pasteur, and the Ministe`re de l’Education Nationale, de la

Recherche et de la Technologie (MENRT, fellowship to J.B.)

for ﬁnancial support to this work. The authors also thank F.

Bonhomme (CNRS URA 2128) for running the NMR and mass

spectra. Dr. Yves Janin (CNRS URA 2128) is acknowledged

for proofreading this manuscript.

1

of CH₃CN in 0.01 M aq TFA at 1 mL min^-1ﬂow rate); H NMR

(D₂O) δ 5.20 (d, 1H, J_1,2) 3.7 Hz, H-1_E), 5.10 (d, 1H, J_1,2) 1.6

Hz, H-1_A), 5.01 (d, 1H, J_1,2) 1.2 Hz, H-1_B′), 4.90 (bs, 1H, H-1_B),

4.84 (d, 1H, J_1,2) 1.9 Hz, H-1_C), 4.83 (d, 1H, J_1,2) 9.5 Hz, H-1_D),

4.44 (dd, 1H, J_2,3) 2.1 Hz, H-2_A), 4.07-3.99 (m, 3H, H-2_B′, H-5_E,

H-5_C), 3.96-3.93 (m, 2H, H-2_B, H-3_A), 3.92-3.68 (m, 14H, H-6a_D,

H-2_C, H-2_D, H-3_B, H-3_E, H-3_B′, H-6a_E, H-6b_E, H-3_C, H-5_B, H-5_A,

H-6b_D, H-2_E, H-5_B′), 3.64 (dt, J ) 9.8 Hz, J ) 6.9 Hz, H_Pr),

3.55-3.38 (m, 8H, H_Pr, H-4_C, H-4_D, H-4_E, H-3_D, H-4_B, H-4_B′, H-5_D),

3.35 (pt, 1H, J_3,4) J_4,5) 9.7 Hz, H-4_A), 2.11 (s, 3H, H_NAc),

1.65-1.56 (m, 2H, CH₂), 1.31 (d, 3H, J_5,6) 6.3 Hz, H-6_B), 1.28

(d, 3H, J_5,6) 6.3 Hz, H-6_B′), 1.26 (d, 3H, J_5,6) 6.3 Hz, H-6_A),

1.23 (d, 3H, J_5,6) 6.3 Hz, H-6_C), 0.91 (t, 3H, J ) 7.4 Hz, CH₃);

Supporting Information Available: General experimental

1

procedures, H, ¹³C, and HMBC NMR spectra for compounds

1-6, 10-12, 15, 16, 19-21, 23, 25, 28-32, 37, 44, 45, 47,

48, 50-53. This material is available free of charge via the

Internet at http://pubs.acs.org.

1

¹³C NMR (D₂O) δ 174.0 (C_NAc), 102.4 (C-1_B′, J_CH) 171.2 Hz),

1

101.5 (C-1_D, J_CH) 163.6 Hz), 101.3 (C-1_C, J_CH) 169.8 Hz),

JO802127Z

2670 J. Org. Chem. Vol. 74, No. 7, 2009

Article Doi

Efficient synthesis of six tri- to hexasaecharide fragments of shigella flexneri serotypes 3a and/or X O-antigen, including a study on acceptors containing N-trichloroacetylglucosamine versus N-acetylglucosamine

DOI: 10.1021/jo802127z

Source and publish data:

Authors:

Article abstract of DOI:10.1021/jo802127z

Full text of DOI:10.1021/jo802127z

Products guided by the article

R&D Labs maybe for 1095656-00-0

Relevant to this article

Hot Product