Synthesis of a pentasaccharide fragment of varianose, a cell wall polysaccharide from Penicillium varians

Article abstract of DOI:10.1021/jo061821a

The first synthesis of an oligosaccharide fragment of varianose, a polysaccharide produced by Penicillium varians, is reported. The target pentasaccharide features both α- and β-galactofuranoside residues and the α-galactofuranoside residue is hindered, b

Full text of DOI:10.1021/jo061821a

Synthesis of a Pentasaccharide Fragment of Varianose,
a Cell Wall Polysaccharide from Penicillium Warians
Yu Bai and Todd L. Lowary*
Alberta Ingenuity Centre for Carbohydrate Science and Department of Chemistry, The UniVersity of
Alberta, Gunning-Lemieux Chemistry Centre, Edmonton, Alberta T6G 2G2, Canada
tlowary@ualberta.ca
ReceiVed September 2, 2006
The first synthesis of an oligosaccharide fragment of varianose, a polysaccharide produced by Penicillium
Varians, is reported. The target pentasaccharide features both R- and â-galactofuranoside residues and
the R-galactofuranoside residue is hindered, being substituted on adjacent oxygens (O1 and O2), both of
which are cis to the two-carbon side chain at C4. Key features of the synthesis include a novel method
for the selective protection of the C3 hydroxyl group of galactofuranosyl residues via an epoxide formation/
opening sequence, the introduction of the R-D-galactofuranosyl residue using a 2,3-anhydrosugar donor,
and the use of the 1-benzenesulfinylpiperidine/trifluoromethanesulfonic anhydride activation method for
the addition of an R-D-glucopyranosyl residue to a hindered hydroxyl group in an advanced tetrasaccharide
intermediate.
Introduction
Varianose, a cell wall polysaccharide produced by Penicillium
Varians, was first described in 1935 by Haworth et al., who
demonstrated that this glycan contained D-glucose, D-galactose,
and an unidentified sugar suggested to be either L-altrose or
D-idose.1 Subsequent studies by Jansson and Lindberg showed
that this unidentified sugar was D-mannose and that the major
component of this heterogeneous complex polysaccharide was
a glucogalactan.2 Through the use of methylation analysis, NMR
spectroscopy, and degradation studies, the structure of this
glucogalactan was established to have a backbone of alternating
â-(1f5)- and â-(1f6)-D-galactofuranose (D-Galf) residues.
Attached to the O2 of the â-(1f5)-linked residue of this core
is a disaccharide side chain consisting of D-glucopyranose (D-
Glcp) attached R-(1f2) to an R-D-Galf moiety. Thus, the
repeating unit is that shown in Figure 1. This polysaccharide
has some interesting structural features, for example, the
FIGURE 1. Repeating unit of varianose.
presence of both R- and â-Galf residues as well as a hindered
R-D-Galf residue that is substituted on adjacent oxygens (O1
and O2), both of which are cis to the two-carbon side chain
appended at C4. In the time since this initial structural work,
polysaccharides containing this repeating unit have been identi-
fied in other fungi including additional penicillium species as
well as a number of talaromyces strains.3
(1) Haworth, W. N.; Raistrick, H.; Stacey, M. Biochem. J. 1935, 29,
2668-2678.
(2) Jansson, P.-E.; Lindberg, B. Carbohydr. Res. 1980, 82, 97-102.
Despite the novel structural features present in this glycan
and the occurrence of this structural motif in a range of
10.1021/jo061821a CCC: $33.50 © 2006 American Chemical Society
Published on Web 11/23/2006
9672
J. Org. Chem. 2006, 71, 9672-9680

Pentasaccharide Fragment of Varianose
CHART 1
CHART 2
polysaccharides, to date there have been no reports on the
synthesis of oligosaccharides related to varianose. The absence
of synthetic activity in this area is likely due to the paucity of
methods available for the stereoselective synthesis of R-D-Galf
bonds. These 1,2-cis-furanosides are stereochemically equivalent
to â-arabinofuranosides4 but have received far less synthetic
attention.5-7 Indeed, only very recently have reports appeared
describing the synthesis of naturally occurring glycoconjugates
containing R-D-Galf residues.8,9 Examples include two immu-
nomodulatory glycolipids (1 and 2, Chart 1) that contain single
R-D-Galf moieties8 and a trisaccharide (3)9 produced upon
reductive â-elimination of Bacteroides cellulosolVens glyco-
proteins. Other recent papers have reported studies on the
stereocontrolled synthesis of oligosaccharides containing D-
fucofuranose (6-deoxy-D-galactofuranose) residues.10 In the
course of other investigations, we needed to prepare penta-
saccharide 4, which consists of the repeating unit of varianose,
plus an additional main-chain Galf residue. We describe here
the synthesis of 4 via a route that employs, as a key step,
the 2,3-anhydrosugar methodology developed in our labora-
tory.11,12
The preparation of 5 and 6 is shown in Scheme 1; 7 and 8
were synthesized as previously reported.11,13 Starting from a 1:10
R/â mixture of 9, treatment with sodium methoxide cleaved the
acetate esters yielding a tetrol that was first tritylated and then
benzylated under conventional conditions to afford 10, which
could be separated from its R-glycoside counterpart. The overall
yield for this process was high, giving 10 in 76% yield over
the three steps. A subsequent reaction of 10 with p-toluene-
sulfonic acid in a mixture of dichloromethane and methanol
gave 5 in 85% yield. Thioglycoside 6 was synthesized in two
steps and in 84% overall yield from the known thioglycoside
11,11 first by a reaction with dimethoxypropane and p-toluene-
sulfonic acid in acetone, then followed by acetylation.
Results and Discussion
In designing a route to 4, we envisioned that it could be
synthesized in a stepwise manner starting from the four
monosaccharides shown in Chart 2. Methyl glycoside 5 would
be the precursor to the “reducing” end residue and thioglycoside
6 would serve as the source of the other two â-D-Galf residues.
The remaining two building blocks, glycosyl sulfoxide 7 and
thioglycoside 8, would provide the R-D-Galf and R-D-Glcp
residues, respectively.
Once synthesized, the building blocks could be assembled
into the pentasaccharide. As illustrated in Scheme 2, reaction
of alcohol 5 with thioglycoside 6 in the presence of N-
iodosuccinimide and silver triflate (NIS/AgOTf)14 afforded
disaccharide 12 in 94% yield. Looking ahead to the eventual
need to use a base-promoted opening of a 2,3-anhydrosugar
residue (vide infra), the acetate esters in 12 were exchanged
with benzyl ethers first by deacylation (sodium methoxide in
methanol) and then benzylation (benzyl bromide, sodium
hydride in DMF). The product, 13, was obtained in excellent
overall yield, 96%. The acetal in 13 was then hydrolyzed to
give 14, the primary hydroxyl group of which was protected as
a benzyl ether using a two-step process involving the formation
of a stannylidene acetal and its alkylation with benzyl bromide.15
The desired product, 15, was isolated in 78% yield, together
with 9% of the 5-O-benzyl ether regioisomer. The position of
(3) (a) Parra, E.; Jime´nez-Barbero, J.; Bernabe´, M.; Leal, J. A.; Prieto,
A.; Go´mez-Miranda, B. Carbohydr. Res. 1994, 251, 315-325. (b) Leal, J.
A.; Go´mez-Miranda, B.; Prieto, A.; Domenech, J.; Ahrazem, O.; Bernabe´,
M. Mycol. Res. 1997, 101, 1259-1264.
(4) Lowary, T. L. Curr. Opin. Chem. Biol. 2003, 7, 749-756.
(5) Osumi, K.; Enomoto, M.; Sugimura, H. Carbohydr. Lett. 1996, 2,
35-38.
(6) Gelin, M.; Ferrie`res, V.; Plusquellec, D. Carbohydr. Lett. 1996, 2,
381-388.
(7) Gelin, M.; Ferrie`res, V.; Plusquellec, D. Eur. J. Org. Chem. 2000,
1423-1431.
the benzyl group in 15 could be readily discerned from its 13
C
(8) Lee, Y. J.; Lee, B.-Y.; Jeon, H. B.; Kim, K. S. Org. Lett. 2006, 8,
3971-3974.
NMR spectrum. The signal for C6 of the non-reducing end
(9) Gandolfi-Donad´ıo, L.; Gola, G.; de Lederkremer, R. M.; Gallo-
Rodriguez, C. Carbohydr. Res. 2006, 341, 2487-2497.
(10) Gelin, M.; Ferrie`res, V.; Lefeuvre, M.; Plusquellec, D. Eur. J. Org.
Chem. 2003, 1285-1293.
(11) Bai, Y.; Lowary, T. L. J. Org. Chem. 2006, 71, 9658-9671.
(12) (a) Gadikota, R. R.; Callam, C. S.; Lowary, T. L. Org. Lett. 2001,
3, 607-610. (b) Gadikota, R. R.; Callam, C. S.; Wagner, T.; Del Fraino,
B.; Lowary, T. L. J. Am. Chem. Soc. 2003, 125, 4155-4165.
(13) Kulkarni, S. S.; Liu, Y.-H.; Hung, S.-C. J. Org. Chem. 2005, 70,
2808-2811.
(14) Konradsson, P.; Udodong, U. E.; Fraser-Reid, B. Tetrahedron Lett.
1990, 31, 4313-4316.
(15) (a) Sugawara, F.; Nakayama, H.; Ogawa, T. Agric. Biol. Chem. 1986,
50, 1557-1561. (b) Gurjar, M. K.; Reddy, L. K.; Hotha, S. J. Org. Chem.
2001, 66, 4657-4660.
J. Org. Chem, Vol. 71, No. 26, 2006 9673

Bai and Lowary
SCHEME 1
SCHEME 2
9674 J. Org. Chem., Vol. 71, No. 26, 2006

Pentasaccharide Fragment of Varianose
SCHEME 3
residue was found at 71.5 ppm, which is shifted downfield from
this resonance in 14 (64.4 ppm), as would be expected upon
alkylation.16
stereochemistry of the epoxide was determined from the 1JC1,H1
of the 2,3-anhydrosugar residue, which was 176 Hz, clearly
indicating the cis orientation of the epoxide and anomeric
hydrogen.11,17 Treatment of 18 with lithium benzylate gave
alcohol 19 in 87% yield. The regioselectivity of the epoxide
opening was established on the basis of the chemical shift of
With alcohol 15 in hand, its NIS/AgOTf-promoted coupling
with thioglycoside 6 afforded trisaccharide 16, which was
subsequently deacylated giving 17 in 81% yield over the two
steps. Next, we needed to selectively protect the O3 of the
terminal Galf residue in 17. While protocols for differentiating
these hydroxyl groups have been reported,10 we explored an
alternate approach in which the diol was first converted to an
epoxide which was, in turn, regioselectively opened with lithium
benzylate. Thus, 17 was subjected to a Mitsunobu reaction with
DIAD and triphenylphosphine, which afforded the correspond-
ing epoxide 18 in excellent (91%) yield. The presence of the
2,3-anhydrosugar residue in 18 was easily discernible by the
presence of two signals in its 13C NMR spectrum, at 55.7 and
53.7 ppm, corresponding to C2 and C3, respectively. The
3
the anomeric carbon resonance (109.0 ppm) and the JH1,H2 (0
Hz), both of which support the â-D-galacto configuration of
the monosaccharide at the non-reducing end of 19.18 The high
selectivity in the opening of the epoxide moiety in 18 is
presumably due to steric hindrance from the anomeric substitu-
ent, which prohibits attack of the nucleophile at C2.19
Having in place a robust method for the synthesis of
trisaccharide 19, the introduction of the R-D-Galf residue was
achieved in two steps using glycosyl sulfoxide 7 (Scheme 3).
(17) Callam, C. S.; Gadikota, R. R.; Lowary, T. L. J. Org. Chem. 2001,
66, 4549-4558.
(18) Cyr, N.; Perlin, A. S. Can. J. Chem. 1979, 57, 2504-2511.
(19) Williams, N. R. AdV. Carbohydr. Chem. Biochem. 1970, 25, 109-
179.
(16) Bock, K.; Pederson, C. AdV. Carbohydr. Chem. Biochem. 1983, 41,
27-66.
J. Org. Chem, Vol. 71, No. 26, 2006 9675

Bai and Lowary
CHART 3
could be achieved in two steps and in 77% overall yield first
by cleavage of the acetal-protecting groups under acidic
conditions (yielding 24) and then by hydrogenolysis of the
benzyl ethers over Pearlman’s catalyst. The NMR data for 4
was in excellent agreement with that reported for the poly-
saccharide from Talaromyces flaVus.3a
In summary, we describe here the first synthesis of an
oligosaccharide fragment of varianose, a polysaccharide pro-
duced by Penicillium Varians; glycans of identical structure have
also been identified in a number of other organisms. Key
features of the synthesis include a novel method for the selective
protection of the C3 hydroxyl group of Galf residues through
an epoxide formation/opening sequence, the introduction of the
R-D-Galf residue using the 2,3-anhydrosugar methodology, and
the use of the BSP/Tf2O activation method for the addition of
an R-D-Glcp residue onto a highly hindered hydroxyl group in
tetrasaccharide 22.
First, glycosylation of 19 with 7 promoted by trifluoromethane-
sulfonic anhydride (Tf2O) yielded the expected tetrasaccharide,
20, in 75% yield. None of the corresponding â-glycoside was
1
detected by TLC. The magnitude of the JC1,H1 for the
2,3-anhydrosugar was 167 Hz, which establishes the R-stereo-
chemistry of this residue.11 Opening of the epoxide ring in 20
using lithium benzylate and (-)-sparteine11,12 proceeded to give
a 67% yield of the expected product, 21, in addition to an 11%
yield of the isomer with the D-idofuranose stereochemistry,
arising from nucleophilic attack at C2. Protection of O5 and
O6 in 21 as an isopropylidene acetal was straightforward, and
an 88% yield of tetrasaccharide alcohol 22 was obtained.
While all of the glycosylations leading to 22 could be carried
out in good yield and without difficulty, the introduction of the
final residue, an R-D-Glcp moiety, was more challenging. The
C2 hydroxyl group of the R-D-Galf residue in 22 is very
hindered, being cis not only to the aglycone on the adjacent
carbon but also to the isopropylidene-protected 1,2-dihydroxy-
ethyl side chain attached at C4. Our initial attempts to
glycosylate the alcohol in 22 with a fully benzylated thiogly-
coside donor (25,20 Chart 3) using NIS/AgOTf activation failed,
yielding only unreacted 22 and hydrolyzed donor together with
the glycosyl-succinimide byproduct 26.21 Similar adducts have
previously been reported in glycosylations promoted by NIS,21,22
and these byproducts are usually observed when acceptors of
low reactivity are used. We also considered the use of imidate
2723 for the introduction of the Glcp residue. However, a series
of model reactions were not promising, and on the basis of
previous studies,11 we had concerns about the stability of the
isopropylidene acetals in 22 to the acidic conditions required
for imidate activation. Finally, we explored the 1-benzenesulfin-
ylpiperidine (BSP)/Tf2O activation method for thioglycosides
reported by Crich and Smith.24 Particularly attractive features
of the method are the basic reaction conditions and the potent
activating power of this reagent combination. With these
considerations in mind, reaction of thioglycoside 8, which had
previously been shown to be a highly R-selective glucosylating
agent,24 with BSP/Tf2O afforded the desired pentasaccharide
23 in 56% yield. While this is not an exceptional yield, it is
respectable considering the highly hindered nature of the
acceptor. The R-stereochemistry of the Glcp residue was
Experimental Section
Methyl R-D-Glucopyranosyl-(1f2)-R-D-galactofuranosyl-
(1f2)-â-D-galactofuranosyl-(1f5)-â-D-galactofuranosyl-(1f6)-
â-D-galactofuranoside (4). To a solution of compound 24 (14 mg,
0.008 mmol) in CH3OH (2 mL) was added 20% Pd(OH)2 on carbon
(5 mg), and the reaction mixture was stirred under a hydrogen
atmosphere for 24 h. The mixture was filtered through Celite and
then concentrated to yield 4 (6.8 mg, 100%) as a white foam. Rf
0.53 (100% CH3OH); [R]D +1.9 (c 0.5, H2O); 1H NMR (600 MHz,
D2O, δH) 5.37 (d, 1H, J ) 4.3 Hz, H-1D), 5.32 (s, 1H, H-1C),
5.01 (s, 1H, H-1B), 4.99 (d, 1H, J ) 3.6 Hz, H-1E), 4.91 (s, 1H,
H-1A), 4.36 (dd, 1H, J ) 8.0, 7.9 Hz), 4.28-4.22 (m, 3H), 4.13-
4.10 (m, 2H), 4.09-4.04 (m, 4H), 3.99-3.93 (m, 3H), 3.88-3.60
(m, 15H), 3.55 (dd, 1H, J ) 10.0, 3.7 Hz), 3.44 (dd, 1H, J ) 9.6,
9.4 Hz), 3.41 (s, 3H, OCH3); 13C NMR (125 MHz, D2O, δC) 109.0
(C-1A), 108.6 (C-1B), 106.7 (C-1C), 99.7 (C-1D), 98.2 (C-1E),
87.8, 83.9, 82.7, 82.3, 81.9 (× 2), 81.6, 80.6, 77.6, 77.55, 77.1,
75.6, 73.7, 73.4, 73.3, 72.9, 72.1, 71.0, 70.5, 70.3, 70.0, 63.7, 63.1,
62.3, 61.3, 55.8 (OCH3). HRMS (ESI): [M + Na] calcd for
C31H54O26Na, 865.2796; found, 865.2795.
Methyl 2,3-Di-O-acetyl-5,6-O-isopropylidene-â-D-galactofura-
nosyl-(1f6)-2,3,5-tri-O-benzyl-â-D-galactofuranoside (12). To a
mixture of 5 (790 mg, 1.7 mmol), 6 (770 mg, 1.9 mmol), and 4 Å
molecular sieves (0.5 g) in CH2Cl2 (50 mL) was added NIS (534
mg, 2.25 mmol) followed by AgOTf (146 mg, 0.56 mmol) at 0
°C. After stirring for 20 min at 0 °C, the solution turned dark red,
and Et3N was added. The mixture was then diluted with CH2Cl2
(50 mL) and filtered through Celite. The filtrate was washed with
a saturated aq Na2S2O3 soln (3 × 50 mL), dried (Na2SO4), and
concentrated to give a crude residue that was purified by chroma-
tography (3:1 hexanes/EtOAc) to afford 12 (1.24 g, 94%) as a
colorless oil. Rf 0.25 (2:1 hexanes/EtOAc); [R]D -86.2 (c 1.0,
1
CH2Cl2); H NMR (500 MHz, CDCl3, δH) 7.38-7.21 (m, 15H,
Ar), 5.08 (s, 1H, H-1B), 5.06 (d, 1H, J ) 1.3 Hz, H-2B), 5.02 (dd,
1H, J ) 4.8, 1.3 Hz, H-3B), 4.95 (s, 1H, H-1A), 4.69 (d, 1H, J )
11.7 Hz, PhCH2), 4.56 (d, 1H, J ) 11.9 Hz, PhCH2), 4.51 (d, 1H,
J ) 11.7 Hz, PhCH2), 4.47 (d, 1H, J ) 11.9 Hz, PhCH2), 4.46 (d,
1H, J ) 11.7 Hz, PhCH2), 4.33 (ddd, 1H, J ) 6.7, 6.1, 6.1 Hz,
H-5B), 4.31 (d, 1H, J ) 11.7 Hz, PhCH2), 4.12-4.08 (m, 2H, H-4A,
H-4B), 4.04 (dd, 1H, J ) 8.6, 6.7 Hz, H-6B), 4.01 (dd, 1H, J )
7.2, 3.3 Hz, H-3A), 3.96-3.94 (m, 1H, H-2A), 3.94 (dd, 1H, J )
10.1, 5.2 Hz, H-6A), 3.85 (dd, 1H, J ) 8.6, 6.1 Hz, H-6B), 3.78-
3.74 (m, 1H, H-5A), 3.67 (dd, 1H, J ) 10.1, 7.0 Hz, H-6A), 3.35
(s, 3H, OCH3), 2.08 (s, 3H, acyl CH3), 2.06 (s, 3H, acyl CH3),
1.43 (s, 3H, isopropylidene CH3), 1.37 (s, 3H, isopropylidene CH3);
13C NMR (125 MHz, CDCl3, δC) 170.1 (CdO), 169.6 (CdO), 138.3
(Ar), 137.8 (Ar), 137.7 (Ar), 128.4 (Ar), 128.33 (Ar), 128.3 (Ar),
128.27 (Ar), 128.0 (Ar), 127.9 (Ar), 127.8 (Ar), 127.7 (Ar), 109.9
3
established by the JH1,H2 which was 3.6 Hz. Deprotec-
tion of 23 to provide the target 4 was uneventful and
(20) France, R. R.; Compton, R. G.; Davis, B. G.; Fairbanks, A. J.; Rees,
N. V.; Wadhawan, J. D. Org. Biomol. Chem. 2004, 2, 2195-2202.
(21) Grayson, E. J.; Ward, S. J.; Hall, A. L.; Rendle, P. M.; Gamblin,
D. P.; Batsanov, A. S.; Davis, B. G. J. Org. Chem. 2005, 70, 9740-9754.
(22) (a) Tsukamoto, H.; Kondo, Y. Tetrahedron Lett. 2003, 44, 5247-
5249. (b) Zhang, Z.; Ollman, I. R.; Ye, X.-S.; Wischnat, R.; Baasov, T.;
Wong, C.-H. J. Am. Chem. Soc. 1999, 121, 734-753.
(23) Wegmann, B.; Schmidt, R. R. J. Carbohydr. Chem. 1987, 6, 357-
375.
(24) Crich, D.; Smith, M. J. Am. Chem. Soc. 2001, 123, 9015-9020.
9676 J. Org. Chem., Vol. 71, No. 26, 2006

Pentasaccharide Fragment of Varianose
(isopropylidene C), 107.2 (C-1A), 105.6 (C-1B), 88.4 (C-2A), 82.9
(C-4B), 82.6 (C-3A), 81.3 (C-2B), 80.5 (C-4A), 77.0 (C-3B), 75.9
(C-5A), 75.3 (C-5B), 73.4 (PhCH2), 72.1 (PhCH2), 71.9 (PhCH2),
67.3 (C-6A), 65.5 (C-6B), 54.9 (OCH3), 26.3 (isopropylidene CH3),
25.2 (isopropylidene CH3), 20.8 (acyl CH3 × 2). HRMS (ESI):
[M + Na] calcd for C41H50O13Na, 773.3144; found, 773.3147.
Methyl 2,3-Di-O-benzyl-5,6-O-isopropylidene-â-D-galacto-
furanosyl-(1f6)-2,3,5-tri-O-benzyl-â-D-galactofuranoside (13).
To a solution of 12 (1.2 g, 1.6 mmol) in CH3OH (15 mL) and
CH2Cl2 (15 mL) was added NaOCH3 until the pH of the solution
was ∼10. The mixture was stirred for 12 h, neutralized by the
addition of HOAc, and then concentrated. The crude was dissolved
in DMF (20 mL), and the solution was cooled to 0 °C before NaH
(0.19 g, 4.8 mmol) and BnBr (0.5 mL, 4.0 mmol) were added. The
solution was then stirred for 12 h at rt, and then the reaction was
quenched by the addition of CH3OH. Dilution of the mixture with
CH2Cl2 (50 mL) provided a solution that was then washed with a
saturated aq NaHCO3 solution (3 × 30 mL). The organic layer
was subsequently dried (Na2SO4) and concentrated, and the residue
was purified by chromatography (8:1 hexanes/EtOAc) to give 13
(1.3 g, 96%) as a light yellow oil. Rf 0.29 (8:1 hexanes/EtOAc);
[R]D -63.2 (c 1.7, CH2Cl2); 1H NMR (500 MHz, CDCl3, δH) 7.39-
7.23 (m, 25H, Ar), 5.13 (s, 1H, H-1B), 4.98 (s, 1H, H-1A), 4.78
(d, 1H, J ) 11.7 Hz, PhCH2), 4.60-4.54 (m, 3H, PhCH2), 4.51-
4.44 (m, 5H, PhCH2), 4.33 (d, 1H, J ) 11.7 Hz, PhCH2), 4.22
(ddd, 1H, J ) 6.8, 6.8, 6.7 Hz, H-5B), 4.11-4.07 (m, 2H, H-4A,
H-4B), 4.06-4.04 (m, 1H, H-2B), 4.04 (dd, 1H, J ) 7.2, 3.0 Hz,
H-3A), 4.00 (dd, 1H, J ) 10.4, 3.9 Hz, H-6A), 4.00-3.98 (m, 1H,
H-2A), 3.90 (dd, 1H, J ) 8.2, 6.7 Hz, H-6B), 3.87-3.80 (m, 3H,
H-6B, H-5A, H-3B), 3.75 (dd, 1H, J ) 10.4, 7.7 Hz, H-6A), 3.37
(s, 3H, OCH3), 1.44 (s, 3H, isopropylidene CH3), 1.38 (s, 3H,
isopropylidene CH3); 13C NMR (125 MHz, CDCl3, δC) 138.5 (Ar),
137.8 (Ar), 137.7 (Ar), 137.5 (Ar), 137.4 (Ar), 128.6 (Ar), 128.5
(Ar), 128.4 (Ar), 128.38 (Ar), 128.3 (Ar), 128.25 (Ar), 128.2 (Ar),
128.1 (Ar), 128.0 (Ar), 127.9 (Ar), 127.85 (Ar), 127.8 (Ar), 127.6
(Ar), 109.7 (isopropylidene C), 107.0 (C-1A), 106.6 (C-1B), 88.3
(C-2A), 87.9 (C-2B), 84.1 (C-3B), 82.9 (C-3A), 82.0 (C-4B), 80.8
(C-4A), 76.4 (C-5B), 76.2 (C-5A), 73.6 (PhCH2), 72.2 (PhCH2 ×
2), 72.0 (PhCH2), 71.8 (PhCH2), 68.9 (C-6A), 65.4 (C-6B), 54.8
(OCH3), 26.5 (isopropylidene CH3), 25.4 (isopropylidene CH3).
HRMS (ESI): [M + Na] calcd for C51H58O11Na, 869.3871; found,
869.3876.
(15 mL) were heated at reflux for 6 h, and then n-Bu4NBr (200
mg, 0.62 mmol) and benzyl bromide (90 µL, 0.74 mmol) were
added. The reaction mixture was heated at reflux for another 24 h
and then concentrated. The resulting residue was dissolved in ethyl
acetate (30 mL) and washed with a 10% aq KF solution (30 mL)
and then brine (30 mL) before being dried (Na2SO4) and filtered.
The filtrate was concentrated, and the crude product was purified
by column chromatography (3:1 hexanes/EtOAc) to give 15 (432
mg, 78%) as a colorless oil. Rf 0.32 (2:1 hexanes/EtOAc); [R]D
1
-53.5 (c 1.3, CH2Cl2); H NMR (600 MHz, CDCl3, δH) 7.38-
7.22 (m, 30H, Ar), 5.09 (br s, 1H, H-1B), 4.94 (br s, 1H, H-1A),
4.73 (d, 1H, J ) 11.8 Hz, PhCH2), 4.58-4.43 (m, 10H, PhCH2),
4.32 (d, 1H, J ) 11.8 Hz, PhCH2), 4.13 (dd, 1H, J ) 6.4, 3.5 Hz,
H-4B), 4.10-4.07 (m, 2H, H-4A, H-3B), 4.02 (dd, 1H, J ) 2.7,
1.0 Hz, H-2B), 4.01 (dd, 1H, J ) 7.0, 3.1 Hz, H-3A), 3.96 (dd,
1H, J ) 3.1, 1.2 Hz, H-2A), 3.92 (br s, 1H, H-5B), 3.91 (dd, 1H,
J ) 10.4, 4.0 Hz, H-6A), 3.79 (ddd, 1H, J ) 7.7, 4.0, 3.5 Hz,
H-5A), 3.68 (dd, 1H, J ) 10.4, 7.7 Hz, H-6A), 3.56-3.51 (m, 2H,
H-6B × 2), 3.33 (s, 3H, OCH3), 2.40 (br s, 1H, OH); 13C NMR
(125 MHz, CDCl3, δC) 138.5 (Ar), 138.1 (Ar), 137.8 (Ar), 137.78
(Ar), 137.7 (Ar), 137.3 (Ar), 128.5 (Ar), 128.4 (Ar), 128.3 (Ar),
128.26 (Ar), 128.2 (Ar), 128.1 (Ar), 128.09 (Ar), 128.0 (Ar), 127.9
(Ar), 127.88 (Ar), 127.84 (Ar), 127.8 (Ar), 127.79 (Ar), 127.76
(Ar), 127.7 (Ar), 127.68 (Ar), 127.6 (Ar), 107.0 (C-1A), 106.8 (C-
1B), 88.3 (C-2A), 87.6 (C-2B), 83.4 (C-3B), 82.8 (C-3A), 81.6
(C-4B), 80.9 (C-4A), 76.4 (C-5A), 73.6 (PhCH2), 73.4 (PhCH2),
72.3 (PhCH2), 72.1 (PhCH2), 71.9 (PhCH2), 71.8 (PhCH2), 71.6
(C-6B), 70.1 (C-5B), 68.7 (C-6A), 54.8 (OCH3). HRMS (ESI): [M
+ Na] calcd for C55H60O11Na, 919.4028; found, 919.4022.
Methyl 2,3-Di-O-acetyl-5,6-O-isopropylidene-â-D-galactofura-
nosyl-(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-
tri-O-benzyl-â-D-galactofuranoside (16). To a mixture of 6 (61
mg, 0.15 mmol), 15 (102 mg, 0.11 mmol), and 4 Å molecular sieves
(0.2 g) in CH2Cl2 (6 mL) at 0 °C was added NIS (42 mg, 0.18
mmol) followed by AgOTf (12 mg, 0.044 mmol). After stirring
for 20 min at 0 °C, the reaction mixture turned dark red, and Et3N
was added. The solution was diluted with CH2Cl2 (20 mL) and
filtered through Celite. The filtrate was then washed with a saturated
aq Na2S2O3 solution (3 × 10 mL), dried (Na2SO4), and concentrated
to give a crude residue that was purified by chromatography (3:1
hexanes/EtOAc) yielding 16 (119 mg, 89%) as a colorless syrup.
Rf 0.31 (2:1 hexanes/EtOAc); [R]D -57.8 (c 0.8, CH2Cl2); 1H NMR
(500 MHz, CDCl3, δH) 7.38-7.21 (m, 30H, Ar), 5.51 (s, 1H, H-1C),
5.20 (d, 1H, J ) 1.2 Hz, H-2C), 5.09 (d, 1H, J ) 1.4 Hz, H-1B),
5.02 (dd, 1H, J ) 4.6, 1.2 Hz, H-3C), 4.94 (s, 1H, H-1A), 4.75 (d,
1H, J ) 11.8 Hz, PhCH2), 4.60-4.44 (m, 9H, PhCH2), 4.41 (d,
1H, J ) 11.5 Hz, PhCH2), 4.31 (d, 1H, J ) 11.8 Hz, PhCH2), 4.25
(ddd, 1H, J ) 6.2, 6.2, 6.2 Hz, H-5C), 4.22-4.13 (m, 4H, H-5B,
H-3B, H-4B, H-4C), 4.07 (dd, 1H, J ) 7.1, 3.0 Hz, H-4A), 4.03
(dd, 1H, J ) 3.4, 1.4 Hz, H-2B), 4.01 (dd, 1H, J ) 7.1, 3.1 Hz,
H-3A), 3.97-3.92 (m, 2H, H-2A, H-6C), 3.90 (dd, 1H, J ) 10.1,
3.9 Hz, H-6A), 3.81-3.77 (m, 2H, H-6C, H-5A), 3.73 (dd, 1H, J
) 10.2, 7.5 Hz, H-6B), 3.71-3.67 (m, 1H, H-6A), 3.65 (dd, 1H,
J ) 10.2, 4.2 Hz, H-6B), 3.35 (s, 3H, OCH3), 2.04 (s, 3H, acyl
CH3), 1.92 (s, 3H, acyl CH3), 1.35 (s, 3H, isopropylidene CH3),
1.33 (s, 3H, isopropylidene CH3); 13C NMR (125 MHz, CDCl3,
δC) 170.2 (CdO), 169.3 (CdO), 138.4 (Ar), 138.2 (Ar), 138.0 (Ar),
137.8 (Ar), 137.7 (Ar), 137.4 (Ar), 128.4 (Ar), 128.37 (Ar), 128.34
(Ar), 128.3 (Ar), 128.26 (Ar), 128.1 (Ar), 128.0 (Ar), 127.9 (Ar),
127.83 (Ar), 127.8 (Ar), 127.77 (Ar), 127.7 (Ar), 127.67 (Ar), 127.6
(Ar), 127.5 (Ar), 109.8 (isopropylidene C), 107.0 (C-1A), 106.6
(C-1B), 105.5 (C-1C), 88.6 (C-2B), 88.3 (C-2A), 83.5 (C-3B), 83.2
(C-4C), 82.9 (C-3A), 81.2 (C-2C), 80.9 (C-4A), 80.4 (C-4B), 77.0
(C-3C), 76.3 (C-5A), 75.4 (C-5C), 73.6 (PhCH2), 73.4 (PhCH2),
73.2 (C-5B), 72.3 (PhCH2), 72.2 (PhCH2 × 2), 71.9 (PhCH2), 71.2
(C-6B), 68.8 (C-6A), 65.4 (C-6C), 54.8 (OCH3), 26.3 (isopropyl-
idene CH3), 25.2 (isopropylidene CH3), 20.7 (acyl CH3), 20.6 (acyl
CH3). HRMS (ESI): [M + Na] calcd for C68H78O18Na, 1205.5086;
found, 1205.5093.
Methyl 2,3-Di-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-
O-benzyl-â-D-galactofuranoside (14). A solution of compound 13
(190 mg, 0.22 mmol) in 50% HOAc (6 mL, 3:2:1 HOAc/H2O/
THF) was stirred for 10 h at 50 °C. The solution was then
concentrated, and the product was purified by chromatography (3:2
hexanes/EtOAc) to give 14 (153 mg, 85%) as a colorless syrup. Rf
1
0.25 (1:1 hexanes/EtOAc); [R]D -67.5 (c 0.9, CH2Cl2); H NMR
(500 MHz, CDCl3, δH) 7.40-7.25 (m, 25H, Ar), 5.07 (s, 1H, H-1B),
4.97 (s, 1H, H-1A), 4.73 (d, 1H, J ) 11.7 Hz, PhCH2), 4.61-4.45
(m, 8H, PhCH2), 4.34 (d, 1H, J ) 11.7 Hz, PhCH2), 4.14-4.10
(m, 2H, H-4A, H-4B), 4.08 (dd, 1H, J ) 6.6, 2.7 Hz, H-3B), 4.04-
4.02 (m, 1H, H-2B), 4.01 (dd, 1H, J ) 6.9, 3.0 Hz, H-3A), 3.98
(d, 1H, J ) 3.0, H-2A), 3.89 (dd, 1H, J ) 10.4, 4.1 Hz, H-6A),
3.81-3.74 (m, 2H, H-5A, H-5B), 3.69 (dd, 1H, J ) 10.4, 7.5 Hz,
H-6A), 3.70-3.61 (m, 2H, H-6B × 2), 3.38 (s, 3H, OCH3); 13C
NMR (125 MHz, CDCl3, δC) 138.4 (Ar), 137.8 (Ar), 137.6 (Ar),
137.5 (Ar), 137.2 (Ar), 128.5 (Ar), 128.48 (Ar), 128.42 (Ar), 128.4
(Ar), 128.3 (Ar), 128.14 (Ar), 128.1 (Ar), 128.0 (Ar), 127.94 (Ar),
127.9 (Ar), 127.83 (Ar), 127.8 (Ar), 127.6 (Ar), 107.1 (C-1A), 106.9
(C-1B), 88.2 (C-2A), 87.5 (C-2B), 83.6 (C-3B), 82.8 (C-3A), 82.3
(C-4B), 80.9 (C-4A), 76.5 (C-5A), 73.5 (PhCH2), 72.4 (PhCH2),
72.1 (PhCH2), 72.0 (PhCH2), 71.9 (PhCH2), 71.2 (C-5B), 68.6 (C-
6A), 64.4 (C-6B), 54.9 (OCH3). HRMS (ESI): [M + Na] calcd
for C48H54O11Na, 829.3558; found, 829.3550.
Methyl 2,3,6-Tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-
tri-O-benzyl-â-D-galactofuranoside (15). Compound 14 (500 mg,
0.62 mmol) and dibutyltin oxide (236 mg, 0.93 mmol) in dry toluene
J. Org. Chem, Vol. 71, No. 26, 2006 9677

Bai and Lowary
Methyl 5,6-O-Isopropylidene-â-D-galactofuranosyl-(1f5)-
2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-O-benz-
yl-â-D-galactofuranoside (17). To a solution of 16 (635 mg, 0.54
mmol) in CH3OH (25 mL) and CH2Cl2 (25 mL) was added
NaOCH3 until the pH of the solution was ∼10. The mixture was
stirred for 12 h, neutralized by the addition of HOAc, and
concentrated. The crude residue was purified by chromatography
(3:2 hexanes/EtOAc) to give 17 (535 mg, 91%) as a colorless syrup.
Rf 0.36 (1:1 hexanes/EtOAc); [R]D -55.9 (c 1.1, CH2Cl2); 1H NMR
(500 MHz, CDCl3, δH) 7.38-7.21 (m, 30H, Ar), 5.36 (s, 1H, H-1C),
5.05 (s, 1H, H-1B), 4.95 (s, 1H, H-1A), 4.73 (dd, 1H, J ) 11.8
Hz, PhCH2), 4.58-4.44 (m, 8H, PhCH2), 4.38 (d, 1H, J ) 12.1
Hz, PhCH2), 4.37 (d, 1H, J ) 11.9 Hz, PhCH2), 4.33 (d, 1H, J )
11.8 Hz, PhCH2), 4.22 (dd, 1H, J ) 7.7, 6.9 Hz, H-5C), 4.16-
4.09 (m, 2H, H-4B, H-5B), 4.08 (dd, 1H, J ) 7.0, 3.2 Hz, H-4A),
4.04-3.84 (m, 10H, H-3A, H-4C, H-3C, H-2B, H-2A, H-2C, H-6C
× 2, H-3B, H-6A), 3.77 (ddd, 1H, J ) 7.7, 3.7, 3.2 Hz, H-5A),
3.75 (br s, 1H, OH), 3.67 (dd, 1H, J ) 10.3, 7.7 Hz, H-6A), 3.61
(dd, 1H, J ) 10.3, 4.0 Hz, H-6B), 3.57 (dd, 1H, J ) 10.3, 6.3 Hz,
H-6B), 3.36 (s, 3H, OCH3), 1.40 (s, 3H, isopropylidene CH3), 1.38
(s, 3H, isopropylidene CH3); 13C NMR (125 MHz, CDCl3, δC) 138.5
(Ar), 137.9 (Ar), 137.8 (Ar), 137.7 (Ar), 137.5 (Ar), 137.1 (Ar),
128.5 (Ar), 128.4 (Ar), 128.3 (Ar), 128.2 (Ar), 128.12 (Ar), 128.1
(Ar), 128.0 (Ar), 127.85 (Ar), 127.8 (Ar), 127.77 (Ar), 127.7 (Ar),
127.68 (Ar), 127.6 (Ar), 127.5 (Ar), 110.0 (isopropylidene C), 107.1
(C-1C), 107.0 (C-1A), 106.1 (C-1B), 88.3 (C-2A), 87.1 (C-2B),
85.4 (C-3A), 84.6 (C-3B), 82.9 (C-4C), 81.4 (C-4B), 80.9 (C-4A),
78.9 (C-2C), 78.6 (C-3C), 76.4 (C-5A), 75.9 (C-5C), 73.6 (C-5B),
73.5 (PhCH2), 73.4 (PhCH2), 72.1 (PhCH2), 72.0 (PhCH2), 71.9
(PhCH2), 71.8 (PhCH2), 69.9 (C-6B), 68.4 (C-6A), 65.7 (C-6C),
54.8 (OCH3), 25.7 (isopropylidene CH3), 25.6 (isopropylidene CH3).
HRMS (ESI): [M + Na] calcd for C64H74O16Na, 1121.4874; found,
1121.4877.
Methyl 3-O-Benzyl-5,6-O-isopropylidene-â-D-galactofurano-
syl-(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-
tri-O-benzyl-â-D-galactofuranoside (19). A prepared solution of
lithium benzylate in benzyl alcohol (2 M, 8 mL) was added to 18
(481 mg, 0.445 mmol). The reaction mixture was heated to 75 °C
and stirred for 12 h; the solution was cooled and then neutralized
with HOAc. The resulting solution was diluted with EtOAc (20
mL) and washed with H2O (10 mL). The organic layer was dried
(Na2SO4) and concentrated to give a crude mixture which was
purified by column chromatography (3:1 hexanes/EtOAc) to yield
19 (458 mg, 87%) as a colorless oil. Rf 0.47 (2:1 hexanes/EtOAc);
[R]D -76.6 (c 0.4, CH2Cl2); 1H NMR (500 MHz, CDCl3, δH) 7.37-
7.20 (m, 35H, Ar), 5.39 (s, 1H, H-1C), 5.08 (d, 1H, J ) 1.6 Hz,
H-1B), 4.94 (s, 1H, H-1A), 4.75 (dd, 1H, J ) 11.8 Hz, PhCH2),
4.66 (d, 1H, J ) 12.3 Hz, PhCH2), 4.57-4.42 (m, 10H, PhCH2),
4.40 (d, 1H, J ) 12.3 Hz, PhCH2), 4.35-4.32 (m, 1H, H-3B), 4.31
(d, 1H, J ) 11.8 Hz, PhCH2), 4.26 (br s, 1H, H-2C), 4.21-4.15
(m, 2H, H-4B, H-5B), 4.10 (dd, 1H, J ) 3.0, 2.8 Hz, H-4C), 4.06
(dd, 1H, J ) 7.1, 3.0 Hz, H-4A), 4.05-3.99 (m, 3H, H-2B, H-5C,
H-3A), 3.96-3.94 (m, 1H, H-2A), 3.90 (dd, 1H, J ) 10.5, 4.0 Hz,
H-6A), 3.86-3.73 (m, 5H, H-3C, H-6C × 2, H-5A, H-6B), 3.70-
3.64 (m, 2H, H-6A, H-6B), 3.33 (s, 3H, OCH3), 1.35 (s, 3H,
isopropylidene CH3), 1.33 (s, 3H, isopropylidene CH3); 13C NMR
(125 MHz, CDCl3, δC) 138.5 (Ar), 138.48 (Ar), 138.2 (Ar), 137.9
(Ar), 137.8 (Ar), 137.7 (Ar), 128.4 (Ar), 128.33 (Ar), 128.3 (Ar),
128.26 (Ar), 128.2 (Ar), 128.17 (Ar), 128.15 (Ar), 128.12 (Ar),
128.1 (Ar), 128.0 (Ar), 127.9 (Ar), 127.8 (Ar), 127.79 (Ar), 127.78
(Ar), 127.73 (Ar), 127.7 (Ar), 127.67 (Ar), 127.6 (Ar), 127.55 (Ar),
127.5 (Ar), 127.4 (Ar), 109.7 (isopropylidene C), 109.0 (C-1C),
107.0 (C-1A), 106.7 (C-1B), 88.6 (C-3A), 88.3 (C-2A), 85.5 (C-
3C), 82.9 (C-2B, C-3B), 82.4 (C-4C), 81.0 (C-4A), 80.6 (C-4B),
78.0 (C-2C), 76.5 (C-5A), 76.4 (C-5C), 73.5 (PhCH2), 73.4
(PhCH2), 73.1 (C-5B), 72.2 (PhCH2), 72.15 (PhCH2), 71.9 (PhCH2),
71.8 (PhCH2), 71.78 (PhCH2), 71.0 (C-6B), 68.8 (C-6A), 65.5 (C-
6C), 54.7 (OCH3), 25.8 (isopropylidene CH3), 25.7 (isopropylidene
CH3). HRMS (ESI): [M + Na] calcd for C71H80O16Na, 1211.5339;
found, 1211.5338.
Methyl 2,3-Anhydro-5,6-O-isopropylidene-â-D-gulofuranosyl-
(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-
O-benzyl-â-D-galactofuranoside (18). To a solution of 17 (535
mg, 0.487 mmol) and PPh3 (383 mg, 1.46 mmol) in THF (25 mL)
at 0 °C was added DIAD (0.30 mL, 1.46 mmol) dropwise. The
reaction mixture was warmed to rt over 30 min, and then stirred
for another 30 min at 40 °C. The resulting mixture was concentrated,
and the residue was purified by chromatography (3:1 hexanes/
EtOAc) to yield 18 (481 mg, 91%) as a colorless syrup. Rf 0.65
Methyl 2,3-Anhydro-5,6-di-O-benzoyl-R-D-gulofuranosyl-
(1f2)-3-O-benzyl-5,6-O-isopropylidene-â-D-galactofuranosyl-
(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-
O-benzyl-â-D-galactofuranoside (20). The sulfoxide donor 7 (381
mg, 0.77 mmol), 2,6-di-tert-butyl-4-methylpyridine (649 mg, 3.1
mmol), and 4 Å molecular sieves (1.0 g) were dried for 3 h under
vacuum in the presence of P2O5. To this mixture was added
CH2Cl2 (30 mL), and the solution was cooled to -78 °C. Tf2O
(156 µL, 0.93 mmol) was added, and the mixture was stirred for
10 min. The solution was then warmed to -40 °C and stirred for
20 min, which was then followed by the addition of trisaccharide
alcohol 19 (368 mg, 0.31 mmol) in CH2Cl2 (10 mL) via a syringe.
After 45 min, the reaction mixture was warmed to rt and stirred
for 24 h before a saturated aq solution of NaHCO3 (2 mL) was
added. The resulting solution was then filtered through Celite, dried
(Na2SO4), filtered, and concentrated. Column chromatography (3:1
hexane/EtOAc) provided 20 (359 mg, 75%) as a colorless syrup.
1
(3:2 hexanes/EtOAc); [R]D -53.6 (c 0.7, CH2Cl2); H NMR (500
MHz, CDCl3, δH) 7.38-7.20 (m, 30H, Ar), 5.47 (s, 1H, H-1C),
5.13 (s, 1H, H-1B), 4.94 (br s, 1H, H-1A), 4.74 (dd, 1H, J ) 11.8
Hz, PhCH2), 4.64 (d, 1H, J ) 11.3 Hz, PhCH2), 4.59-4.40 (m,
9H, PhCH2), 4.31 (d, 1H, J ) 11.8 Hz, PhCH2), 4.21 (ddd, 1H, J
) 6.8, 6.8, 6.8 Hz, H-5C), 4.17 (ddd, 1H, J ) 8.2, 3.8, 2.1 Hz,
H-5B), 4.14 (d, 1H, J ) 7.2 Hz, H-3B), 4.13 (d, 1H, J ) 6.8 Hz,
H-4C), 4.10-3.99 (m, 5H, H-4A, H-4B, H-6C, H-2B, H-3A), 3.96
(dd, 1H, J ) 3.1, 1.2 Hz, H-2A), 3.88 (dd, 1H, J ) 10.4, 4.0 Hz,
H-6A), 3.79-3.70 (m, 3H, H-5A, H-6B H-6C), 3.71 (d, 1H, J )
2.9 Hz, H-2C), 3.68 (dd, 1H, J ) 10.4, 7.7 Hz, H-6A), 3.60 (dd,
1H, J ) 10.1, 3.8 Hz, H-6B), 3.44 (d, 1H, J ) 2.9 Hz, H-3C), 3.32
(s, 3H, OCH3), 1.38 (s, 3H, isopropylidene CH3), 1.34 (s, 3H,
isopropylidene CH3); 13C NMR (125 MHz, CDCl3, δC) 138.4 (Ar),
138.1 (Ar), 138.08 (Ar), 137.8 (Ar), 137.7 (Ar), 137.6 (Ar), 128.42
(Ar), 128.4 (Ar), 128.37 (Ar), 128.34 (Ar), 128.3 (Ar), 128.2 (Ar),
128.1 (Ar), 128.0 (Ar), 127.9 (Ar), 127.84 (Ar), 127.8 (Ar), 127.76
(Ar), 127.7 (Ar), 127.6 (Ar), 127.57 (Ar), 127.5 (Ar), 109.7
(isopropylidene C), 107.0 (C-1A), 106.6 (C-1B), 102.0 (C-1C), 88.2
(C-2A), 88.17 (C-2B), 84.3 (C-3B), 82.9 (C-3A), 81.0 (C-4A), 80.9
(C-4B), 77.3 (C-4C), 76.2 (C-5A), 75.3 (C-5B), 75.1 (C-5C), 73.6
(PhCH2), 73.3 (PhCH2), 72.8 (PhCH2), 72.2 (PhCH2), 71.9 (PhCH2),
71.8 (PhCH2), 71.6 (C-6B), 68.6 (C-6A), 65.6 (C-6C), 55.6
(C-2C), 54.8 (OCH3), 53.6 (C-3C), 26.6 (isopropylidene CH3), 25.2
(isopropylidene CH3). HRMS (ESI): [M + Na] calcd for
C64H72O15Na, 1103.4769; found. 1103.4770.
1
Rf 0.47 (2:1 hexanes/EtOAc); [R]D -29.3 (c 1.45, CH2Cl2); H
NMR (500 MHz, CDCl3, δH) 8.20-7.98 (m, 4H, Ar), 7.58-7.50
(m, 2H, Ar), 7.45-7.17 (m, 39H, Ar), 5.72 (ddd, 1H, J ) 5.8, 5.8,
4.1 Hz, H-5D), 5.42 (s, 1H, H-1C), 5.11 (s, 1H, H-1B), 5.05 (s,
1H, H-1D), 4.94 (s, 1H, H-1A), 4.77-4.65 (m, 5H, PhCH2 × 3,
H-6D × 2), 4.58-4.38 (m, 11H, PhCH2 × 10, H-2C), 4.30 (d,
1H, J ) 11.7 Hz, PhCH2), 4.27 (dd, 1H, J ) 7.0, 3.2 Hz, H-3B),
4.23 (ddd, 1H, J ) 9.2, 2.7, 2.7 Hz, H-5B), 4.19 (dd, 1H, J ) 7.3,
7.3 Hz, H-4C), 4.11-4.04 (m, 4H, H-4B, H-5C, H-4A, H-4D),
4.03-4.00 (m, 2H, H-2B, H-3A), 3.97-3.95 (m, 1H, H-2A), 3.90
(dd, 1H, J ) 10.3, 4.0 Hz, H-6A), 3.85 (dd, 1H, J ) 9.8, 9.2 Hz,
H-6B), 3.80 (dd, 1H, J ) 7.3, 3.5 Hz, H-3C), 3.79-3.75 (m, 2H,
H-5A, H-6C), 3.71-3.65 (m, 2H, H-6A, H-6C), 3.64 (dd, 1H, J )
9.8, 2.7 Hz, H-6B), 3.56 (d, 1H, J ) 2.9 Hz, H-3D), 3.32 (s, 3H,
OCH3), 3.10 (d, 1H, J ) 2.9 Hz, H-2D), 1.26 (s, 3H, isopropylidene
9678 J. Org. Chem., Vol. 71, No. 26, 2006

Pentasaccharide Fragment of Varianose
CH3), 1.24 (s, 3H, isopropylidene CH3); 13C NMR (125 MHz,
CDCl3, δC) 166.0 (CdO), 165.8 (CdO), 138.4 (Ar × 2), 138.3
(Ar), 137.8 (Ar), 137.7 (Ar), 137.6 (Ar), 137.4 (Ar), 133.2 (Ar),
133.1 (Ar), 129.8 (Ar), 129.7 (Ar), 129.66 (Ar), 128.4 (Ar), 128.39
(Ar), 128.33 (Ar), 128.3 (Ar), 128.25 (Ar), 128.22 (Ar), 128.2 (Ar),
128.0 (Ar), 127.9 (Ar), 127.8 (Ar), 127.76 (Ar), 127.74 (Ar), 127.7
(Ar), 127.6 (Ar), 127.58 (Ar), 127.55 (Ar), 127.5 (Ar), 127.48 (Ar),
109.4 (isopropylidene C), 108.2 (C-1C), 107.0 (C-1A), 106.7 (C-
1B), 100.6 (C-1D), 88.3 (C-2A, C-3A), 87.7 (C-2C), 83.9 (C-3B),
83.2 (C-3C), 82.8 (C-2B), 81.8 (C-4C), 81.1 (C-4A), 80.9 (C-4B),
76.2 (C-5A, C-5C), 75.2 (C-4D), 74.9 (C-5B), 73.5 (PhCH2), 73.3
(PhCH2), 72.6 (PhCH2), 72.2 (PhCH2), 71.8 (PhCH2), 71.79 (PhCH2
× 2), 71.7 (C-6B), 71.6 (C-5D), 68.7 (C-6A), 65.3 (C-6C), 63.4
(C-6D), 55.3 (C-2D), 54.7 (OCH3), 54.3 (C-3D), 26.4 (isoprop-
ylidene CH3), 25.5 (isopropylidene CH3). HRMS (ESI): [M + Na]
calcd for C91H96O22Na, 1563.6291; found, 1563.6305.
colorless oil. Rf 0.51 (2:1 hexanes/EtOAc); [R]D -36.8 (c 0.6,
1
CH2Cl2); H NMR (500 MHz, CDCl3, δH) 7.40-7.20 (m, 40H,
Ar), 5.42 (s, 1H, H-1C), 5.12 (d, 1H, J ) 4.8 Hz, H-1D), 5.09 (s,
1H, H-1B), 4.95 (s, 1H, H-1A), 4.80 (d, 1H, J ) 11.7 Hz, PhCH2),
4.79 (d, 1H, J ) 11.7 Hz, PhCH2), 4.74 (d, 1H, J ) 11.7 Hz,
PhCH2), 4.61 (d, 1H, J ) 11.2 Hz, PhCH2), 4.60-4.58 (m, 1H,
H-2C), 4.58-4.43 (m, 10H, PhCH2), 4.40 (d, 1H, J ) 11.2 Hz,
PhCH2), 4.31 (d, 1H, J ) 11.7 Hz, PhCH2), 4.23 (dd, 1H, J ) 6.9,
3.5 Hz, H-3B), 4.20-4.06 (m, 6H, H-4C, H-5B, H-4B, H-5C, H-4A,
H-4D), 4.02-3.99 (m, 2H, H-3A, H-2B), 3.97-3.64 (m, 14H,
H-3C, H-2A, H-2D, H-3D, H-5A, H-5D, H-6A × 2, H-6C × 2,
H-6B × 2, H-6D × 2), 3.33 (s, 3H, OCH3), 2.60 (br s, 1H, OH),
1.41 (s, 3H, isopropylidene CH3), 1.31 (s, 3H, isopropylidene CH3),
1.29 (s, 3H, isopropylidene CH3), 1.26 (s, 3H, isopropylidene CH3);
13C NMR (125 MHz, CDCl3, δC) 138.5 (Ar), 138.3 (Ar), 138.0
(Ar), 137.8 (Ar), 137.77 (Ar), 137.7 (Ar), 137.65 (Ar), 137.5 (Ar),
128.5 (Ar), 128.43 (Ar), 128.4 (Ar), 128.33 (Ar), 128.3 (Ar), 128.27
(Ar), 128.25 (Ar), 128.2 (Ar), 128.1 (Ar), 128.0 (Ar), 127.95 (Ar),
127.83 (Ar), 127.8 (Ar), 127.77 (Ar), 127.7 (Ar), 127.68 (Ar),
127.66 (Ar), 127.5 (Ar), 109.8 (isopropylidene C), 109.6 (isopro-
pylidene C), 107.3 (C-1C), 107.0 (C-1A), 106.7 (C-1B), 101.9 (C-
1D), 88.3 (× 2), 86.3, 84.4, 83.6, 83.3, 82.9, 82.3, 82.0, 81.1, 80.9,
78.4, 76.3, 76.2 (× 2), 74.7, 73.5, 73.4, 72.4, 72.2, 72.15, 72.0
71.8 (× 2), 71.6, 68.8, 65.5, 65.2, 54.7 (OCH3), 26.7 (isopropylidene
CH3), 26.3 (isopropylidene CH3), 25.6 (isopropylidene CH3), 25.5
(isopropylideneCH3).HRMS(ESI): [M+Na]calcdforC87H100O21Na,
1503.6655; found, 1503.6651.
Methyl 4,6-O-Benzylidene-2,3-di-O-benzyl-R-D-glucopyrano-
syl-(1f2)-3-O-benzyl-5,6-O-isopropylidene-R-D-galactofurano-
syl-(1f2)-3-O-benzyl-5,6-O-isopropylidene-â-D-galactofuranosyl-
(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-
O-benzyl-â-D-galactofuranoside (23). Thioglycoside 8 (140 mg,
0.25 mmol), BSP (53 mg, 0.25 mmol), 2,4,6-tri-tert-butyl-pyrimi-
dine (130 mg, 0.51 mmol), and 4 Å molecular sieves (500 mg)
were dried for 4 h under vacuum in the presence of P2O5. To this
mixture was added CH2Cl2 (8 mL), and the solution was cooled to
-60 °C. Tf2O (47 µL, 0.28 mmol) was added; the mixture was
allowed to stir for 10 min and was followed by the addition (via a
syringe) of a solution of the vacuum-dried acceptor 22 (75 mg,
0.051 mmol) in CH2Cl2 (7 mL). After 40 min, the reaction mixture
was warmed to rt and was kept stirring for 48 h. A saturated aq
solution of NaHCO3 (2 mL) was added, and the resulting solution
was filtered through Celite, dried (Na2SO4), filtered, and concen-
trated. Column chromatography (7:3 hexane/EtOAc) of this residue
provided 23 (54 mg, 56%) as a colorless syrup. Rf 0.47 (7:3 hexanes/
EtOAc); [R]D -2.7 (c 1.4, CH2Cl2); 1H NMR (600 MHz, CD2Cl2,
δH) 7.50-7.21 (m, 55H, Ar), 5.57 (s, 1H, benzylidene CH), 5.44
(d, 1H, J ) 1.2 Hz, H-1C), 5.40 (d, 1H, J ) 4.2 Hz, H-1D), 5.11
(d, 1H, J ) 3.6 Hz, H-1E), 5.09 (s, 1H, H-1B), 4.89 (s, 1H, H-1A),
4.86-4.79 (m, 4 H), 4.71 (d, 1H, J ) 11.5 Hz), 4.69 (d, 1H, J )
11.5 Hz), 4.63-4.34 (m, 15 H), 4.27 (dd, 1H, J ) 7.5, 4.2 Hz),
4.21 (dd, 1H, J ) 10.2, 4.7 Hz), 4.19 (dd, 1H, J ) 7.0, 3.2 Hz),
4.17-4.12 (m, 4 H), 4.05-3.97 (m, 5 H), 3.93-3.92 (m, 1 H),
3.90-3.82 (m, 5 H), 3.81-3.61 (m, 9 H), 3.58-3.54 (m, 2 H),
3.28 (s, 3H, OCH3), 1.38 (s, 3H, isopropylidene CH3), 1.19 (s, 3H,
isopropylidene CH3), 1.17 (s, 3H, isopropylidene CH3), 1.16 (s,
3H, isopropylidene CH3); 13C NMR (125 MHz, CD2Cl2, δC) 139.2
(Ar), 139.1 (Ar), 138.9 (Ar), 138.8 (Ar), 138.6 (Ar), 138.4 (Ar),
138.3 (Ar), 138.2 (Ar), 138.1 (Ar), 137.5 (Ar), 129.3 (Ar), 129.2
(Ar), 128.9 (Ar), 128.8 (Ar), 128.75 (Ar), 128.7 (Ar), 128.67 (Ar),
128.6 (Ar), 128.58 (Ar), 128.54 (Ar), 128.5 (Ar), 128.44 (Ar), 128.4
(Ar), 128.35 (Ar), 128.33 (Ar), 128.3 (Ar), 128.26 (Ar), 128.2 (Ar),
128.17 (Ar), 128.12 (Ar), 128.1 (Ar), 128.0 (Ar), 127.96 (Ar),
127.83 (Ar), 127.8 (Ar), 127.77 (Ar), 126.6 (Ar), 110.0 (isopro-
pylidene C), 109.6 (isopropylidene C), 107.3 (C-1A), 107.2 (C-
1C), 107.0 (C-1B), 102.0 (benzylidene CH), 99.1 (C-1D), 96.0 (C-
1E), 88.7 (× 2), 85.7, 84.7, 84.3, 83.6, 82.1, 81.7, 81.68, 81.6,
81.5, 80.8, 79.1, 79.0 (× 2), 78.0, 77.1, 76.9, 75.5, 75.2, 73.7, 73.6,
73.3, 72.9, 72.8, 72.6, 72.5, 72.2 (× 3), 69.2, 68.6, 65.5, 65.47,
Methyl 3-O-Benzyl-R-D-galactofuranosyl-(1f2)-3-O-benzyl-
5,6-O-isopropylidene-â-D-galactofuranosyl-(1f5)-2,3,6-tri-O-
benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-tri-O-benzyl-â-D-ga-
lactofuranoside (21). To a solution of 20 (257 mg, 0.167 mmol)
in benzyl alcohol (6.0 mL) was added a prepared solution of lithium
benzylate in benzyl alcohol (1.5 M, 0.9 mL) and (-)-sparteine (0.05
mL, 0.2 mmol). The resulting mixture was subsequently warmed
to 75 °C and stirred until the reaction was complete (∼16 h). After
cooling to rt, the solution was neutralized with HOAc and diluted
with EtOAc (20 mL). The organic layer was washed with water
(15 mL), dried (Na2SO4), filtered, and concentrated to give a crude
residue that was purified by chromatography (1:1 hexane/EtOAc)
to yield 21 (160 mg, 67%) as a colorless syrup and its corresponding
D-idofuranoside product (27 mg, 11%). Data for 21: Rf 0.41 (1:1
hexanes/EtOAc); [R]D -36.7 (c 2.0, CH2Cl2); 1H NMR (500 MHz,
CDCl3, δH) 7.37-7.20 (m, 40H, Ar), 5.41 (s, 1H, H-1C), 5.11 (d,
1H, J ) 4.8 Hz, H-1D), 5.10 (s, 1H-1B), 4.94 (s, 1H, H-1A), 4.79
(d, 1H, J ) 11.8 Hz, PhCH2), 4.73 (d, 1H, J ) 11.8 Hz, PhCH2),
4.67 (d, 1H, J ) 11.7 Hz, PhCH2), 4.60-4.39 (m, 13H, PhCH2 ×
12, H-2C), 4.30 (d, 1H, J ) 11.7 Hz, PhCH2), 4.24 (dd, 1H, J )
7.1, 3.2 Hz, H-3B), 4.19-4.14 (m, 2H, H-4C, H-5B), 4.11-4.07
(m, 2H, H-4B, H-5C), 4.07 (dd, 1H, J ) 7.2, 3.3 Hz, H-4A), 4.03
(dd, 1H, J ) 6.3, 3.0 Hz, H-3C), 4.02-3.91 (m, 6H, H-3A, H-2B,
H-3D, H-4D, H-2A, H-2D), 3.89 (dd, 1H, J ) 10.3, 4.2 Hz, H-6A),
3.80-3.74 (m, 4H, H-6C × 2, H-5A, H-6B), 3.67 (dd, 1H, J )
10.3, 7.7 Hz, H-6A), 3.66-3.62 (m, 1H, H-5D), 3.61 (dd, 1H, J )
10.2, 3.2 Hz, H-6B), 3.59-3.57 (m, 2H, H-6D × 2), 3.31 (s, 3H,
OCH3), 2.74 (br s, 1H, OH), 2.56 (br s, 1H, OH), 1.33 (s, 3H,
isopropylidene CH3), 1.31 (s, 3H, isopropylidene CH3); 13C NMR
(125 MHz, CDCl3, δC) 138.4 (Ar), 138.2 (Ar), 137.9 (Ar), 137.8
(Ar), 137.7 (Ar), 137.6 (Ar), 128.5 (Ar), 128.46 (Ar), 128.4 (Ar),
128.39 (Ar), 128.33 (Ar), 128.3 (Ar), 128.25 (Ar), 128.1 (Ar), 128.0
(Ar), 127.9 (Ar), 127.84 (Ar), 127.83 (Ar), 127.8 (Ar), 127.77 (Ar),
127.75 (Ar), 127.72 (Ar), 127.7 (Ar), 127.6 (Ar), 127.55 (Ar), 109.6
(isopropylidene C), 107.0 (C-1A), 106.9 (C-1C), 106.6 (C-1B),
101.7 (C-1D), 88.3 (C-2A), 88.2 (C-3A), 86.8 (C-2C), 83.7 (C-
3B), 83.65 (C-3C), 82.84 (C-2B), 82.8 (C-3D), 82.3 (C-4A), 81.4
(C-4C), 81.0 (C-4B), 80.9 (C-5C), 77.2 (C-2D), 76.2 (C-5A), 75.8
(C-4D), 74.8 (C-5B), 73.6 (PhCH2), 73.4 (PhCH2), 72.4 (PhCH2),
72.2 (PhCH2), 72.1 (PhCH2), 72.05 (C-5D), 72.0 (PhCH2 × 2),
71.9 (PhCH2), 71.8 (C-6B), 68.7 (C-6A), 65.4 (C-6C), 64.1 (C-
6D), 54.7 (OCH3), 26.1 (isopropylidene CH3), 25.4 (isopropylidene
CH3). HRMS (ESI): [M + Na] calcd for C84H96O21Na, 1463.6342;
found, 1463.6345.
Methyl 3-O-Benzyl-5,6-O-isopropylidene-R-D-galactofurano-
syl-(1f2)-3-O-benzyl-5,6-O-isopropylidene-â-D-galactofurano-
syl-(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-
tri-O-benzyl-â-D-galactofuranoside (22). To a solution of compound
21 (160 mg, 0.11 mmol) and 2,2-dimethoxypropane (0.11 mL, 0.89
mmol) in acetone (5 mL) was added p-TsOH (0.5 mg), and the
reaction mixture was stirred at rt for 4 h. Two drops of Et3N were
added, and the solution was concentrated. Column chromatography
(3:1 hexanes/EtOAc) of the residue gave 22 (145 mg, 88%) as a
J. Org. Chem, Vol. 71, No. 26, 2006 9679

Bai and Lowary
64.0, 54.8 (OCH3), 27.0 (isopropylidene CH3), 26.6 (isopropylidene
CH3), 25.7 (isopropylidene CH3), 25.6 (isopropylidene CH3). HRMS
(ESI): [M + Na] calcd for C114H126O26Na, 1933.8435; found,
1933.8449.
OCH3); 13C NMR (125 MHz, CDCl3, δC) 138.7 (Ar), 138.4 (Ar),
138.0 (Ar), 137.9 (Ar), 137.8 (Ar), 137.7 (Ar), 137.6 (Ar), 137.5
(Ar), 137.3 (Ar), 128.5 (Ar), 128.45 (Ar), 128.4 (Ar), 128.3 (Ar),
128.2 (Ar), 128.1 (Ar), 128.0 (Ar), 127.98 (Ar), 127.8 (Ar), 127.77
(Ar), 127.7 (Ar), 127.65 (Ar), 127.6 (Ar), 107.0 (C-1A), 106.5 (C-
1C), 106.4 (C-1B), 99.9 (C-1D), 95.9 (C-1E), 88.2 (× 2), 87.8,
85.3, 83.7, 83.5, 82.9, 82.8, 82.5, 80.8 (× 4), 80.3, 79.0, 76.2 (×
2), 75.4, 75.1, 73.5, 73.4, 73.0, 72.3, 72.1 (× 2), 72.0, 71.9, 71.8,
71.3, 71.0, 70.6, 68.5, 64.4, 64.2, 62.5, 54.7 (OCH3). HRMS
(ESI): [M + Na] calcd for C101H114O26Na, 1765.7496; found,
1765.7509.
Methyl
2,3-Di-O-benzyl-R-D-glucopyranosyl-(1f2)-3-O-
benzyl-R-D-galacto-furanosyl-(1f2)-3-O-benzyl-â-D-galactofura-
nosyl-(1f5)-2,3,6-tri-O-benzyl-â-D-galactofuranosyl-(1f6)-2,3,5-
tri-O-benzyl-â-D-galactofuranoside (24). A solution of 23 (40 mg,
0.02 mmol) in 70% HOAc (7 mL, HOAc/H2O/THF 5:1:1) was
stirred at 50 °C for 16 h. The resulting mixture was concentrated
and purified by chromatography (30:1 CH2Cl2/CH3OH) to give 24
(28.1 mg, 77%) as a colorless syrup. Rf 0.36 (20:1 CH2Cl2/CH3OH);
1
[R]D -5.07 (c 0.15, CH2Cl2); H NMR (600 MHz, CDCl3, δH)
Acknowledgment. This work was supported by the Alberta
Ingenuity Centre for Carbohydrate Science, The University of
Alberta, and The Natural Sciences and Engineering Research
Council of Canada.
7.39-7.20 (m, 50H, Ar), 5.44 (s, 1H, H-1C), 5.20 (d, 1H, J ) 4.3
Hz, H-1D), 5.06 (d, 1H, J ) 1.0 Hz, H-1B), 5.00 (d, 1H, J ) 3.3
Hz, H-1E), 4.96 (d, 1H, J ) 11.3 Hz), 4.92 (br s, 1H, H-1A), 4.74-
4.67 (m, 4 H), 4.63 (d, 1H, J ) 11.9 Hz), 4.59 (d, 1H, J ) 11.3
Hz), 4.55-4.38 (m, 13 H), 4.34 (d, 1H, J ) 11.8 Hz), 4.29 (d, 1H,
J ) 11.8 Hz), 4.22 (dd, 1H, J ) 5.9, 2.5 Hz), 4.14 (dd, 1H, J )
5.9, 2.4 Hz), 4.11-4.04 (m, 5H), 4.00-3.98 (m, 2 H), 3.97 (dd,
1H, J ) 3.1, 1.0 Hz), 3.90 (dd, 1H, J ) 3.2, 1.3 Hz), 3.87 (dd, 1H,
J ) 10.2, 4.0 Hz), 3.83 (dd, 1H, J ) 9.2, 9.2 Hz), 3.78-3.70 (m,
3 H), 3.69-3.46 (m, 10 H), 3.44-3.39 (m, 2 H), 3.28 (s, 3H,
Supporting Information Available: Experimental details for
the preparation of 5, 6, and 10, as well as associated characterization
data and 1H and 13C NMR spectra of new compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
JO061821A
9680 J. Org. Chem., Vol. 71, No. 26, 2006