Elaboration of monoarabinofuranosidic building blocks

Article abstract of DOI:10.1002/1099-0690(200211)2002:22<3864::AID-EJOC3864>3.0.CO;2-8

Nucleophilic opening of 1,2,5-orthoesters 1, 2 and 6 of D-arabinose with alcohols, ethanethiol and selenophenol was carried out under very mild conditions with Lewis acid catalysis. The reaction is stereoselective and gave α-D-arabinofuranosides in high yields. Various monoarabinofuranosides, thio-and selenoglycoside donors as well as acceptors were obtained in few steps from the opening products. These building blocks define a comprehensive system of glycosylation for the synthesis of any glycosidic linkage between arabino-furanosides. Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002.

Full text of DOI:10.1002/1099-0690(200211)2002:22<3864::AID-EJOC3864>3.0.CO;2-8

FULL PAPER
Elaboration of Monoarabinofuranosidic Building Blocks[‡]
Sylvie Sanchez,[a] Toufiq Bamhaoud,[b] and Jacques Prandi*[a]
Keywords: Arabinofuranosides / Carbohydrates / Mycobacteria / Orthoesters
Nucleophilic opening of 1,2,5-orthoesters 1, 2 and 6 of D-ara- tained in few steps from the opening products. These build-
binose with alcohols, ethanethiol and selenophenol was car-
ried out under very mild conditions with Lewis acid catalysis.
ing blocks define a comprehensive system of glycosylation
for the synthesis of any glycosidic linkage between arabino-
The reaction is stereoselective and gave α-
ides in high yields. Various monoarabinofuranosides, thio-
and selenoglycoside donors as well as acceptors were ob- 2002)
D-arabinofuranos- furanosides.
( Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany,
Introduction
small motifs called caps, while in AG both terminal units
(᭡ and ᭹) may be esterified with mycolic acids on their 5-
positions.[5] Renewed interest in oligoarabinofuranoside
construction[10Ϫ17] has arisen from the isolation of a myco-
bacterial arabinose donor[18] and the development of an ar-
abinosyl transferase assay that allows in vitro testing
of inhibitors with synthetic oligoarabinofuranosidic ac-
ceptors.[4,11,19]
The mycobacterium genus includes two human patho-
gens, Mycobacterium leprae, responsible for leprosy, and M.
tuberculosis, the causative agent of tuberculosis, a major
worldwide health problem taking millions of lives annually.
The development of new drugs against mycobacterial infec-
tions requires a better understanding of their pathogenicity
and the identification of new therapeutic targets.[1] One
such is the arabinan biosynthetic pathway,[2] already identi-
fied as the site of action of ethambutol, a first-line anti-
tuberculosis drug.[3Ϫ5] Mycobacteria make large use of -
arabinose for the construction of their cell walls, where it is
to be found in arabinogalactan (AG) and lipoglycans: lipo- Figure 1. Schematic structural model of mycobacterial arabinans;
arabinomannan (LAM) and arabinomannan (AM).[6,7] AG
is the major component of the cell wall by weight, is cova-
᭡: attachment points for caps in LAMs; ᭡, ᭹: attachment points
for mycolic acids in AG
lently linked to the peptidoglycan and carries mycolic acids
at its ends. LAM is a major antigen with various biological
properties, depending on the mycobacterial species.[8,9] Al-
though the structural models for AG and LAM show small
differences, -arabinose occurs in all these compounds as
furanoside oligomers. The core of this arabinan domain is
a chain with α-(1Ǟ5)-linked units (᭿, see Figure 1); branch-
ing is found when some of these units (᭜ are also α-glycosyl-
ated with another arabinofuranosyl residue at the 3-posi-
tion. At the end of the domain, β-arabinofuranosides (᭡ are
found, linked on the 2-position of the preceding residue. In
AG, only Ara6 motifs were found, while both Ara4 and
Ara6 have been identified in LAM (Figure 1). In LAM,
these terminal units are substituted on the 5-position by
Although the glycosylation reaction, involving coupling
of a glycosyl donor with an acceptor to give a disaccharide
(Figure 2), is simple in principle, the synthesis of complex
oligosaccharides is still a long and complicated task, owing
to the variety of the linkages between sugar units involved.
Control over the stereochemical outcome of the glycosyl-
ation can be obtained by an appropriate choice of substitu-
ent on the hydroxy group in position 2 in the donor: ester
or similar groups give α-glycosides, while β-glycosides are
obtained by use of the internal aglycon delivery (IAD)
approach[20Ϫ26] (see Figure 2). Major simplification can be
achieved if all the sugar units involved in the synthesis of
an oligosaccharide Ϫ both donors and acceptors Ϫ can be
obtained by the minimum number of steps from a common
advanced synthetic precursor (divergent/convergent ap-
proach) and if some disaccharide blocks obtained from the
first glycosylation, and usually used as acceptors for further
elongation (plain arrow, Figure 2) can also play a donor
role (broken arrow).
[‡]
Synthesis of Oligoarabinofuranosides from the Mycobacterial
Cell Wall, I
[a]
Institut de Pharmacologie et de Biologie Structurale du CNRS,
205 route de Narbonne, 31077 Toulouse Cedex 5, France
[b]
´
Laboratoire de Chimie Organique et Bioorganique, Universite
Chouaib Doukkali,
B. P. 20, El Jadida, Moroco
3864
 2002 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1434Ϫ193X/02/1122Ϫ3864 $ 20.00ϩ.50/0 Eur. J. Org. Chem. 2002, 3864Ϫ3873

Elaboration of Monoarabinofuranosidic Building Blocks
FULL PAPER
Figure 2. Schematic representation of a comprehensive system for
the synthesis of oligoarabinofuranosides
We now report the implementation of a strategy based
on this analysis and describe a comprehensive system for
the elaboration of oligoarabinofuranosides capitalizing on
the reactivity of 1,2,5-orthoesters of arabinose towards vari-
ous nucleophiles (see Figure 3).
Scheme 1. a: 10.5 equiv. CH3OCHCl2, 0.8 equiv. SnCl4, CH2Cl2,
room temp., 8 h; b: 2.0 equiv. NEt3, 1.5 equiv. MeOH, 1.0 equiv.
nBu4NBr, 3 A MS, CH2Cl2, room temp., 16 h, 86%, 2 steps; c:
˚
0.01  MeONa, MeOH, room temp., overnight, 92%; d: 0.03 equiv.
˚
camphorsulfonic acid, 4 A MS, CH2Cl2, room temp., 0.5 h, 86%;
e: 1.5 equiv. BnBr, 2 equiv. NaH, DMF, room temp., 1 h, 95%; f:
chloral, H2SO4, reflux, 2 h, 43%; g: 2.0 equiv. tBuOK, tBuOH, 90
°C, 2 h, 78%; h: same as e, 90%; i: 1.5 equiv. BzCl, pyridine, room
temp., 4 h, 86%; j: 5.0 equiv. Bu3SnH, AIBN, toluene, reflux, 7 h,
84%
Figure 3. Divergent/convergent approach to oligoarabinofuranos-
ides from 1,2,5-orthoesters of arabinose
Synthesis of Orthoesters
It has been known for over 30 years that oligomerization
of the 1,2,5-orthobenzoate of -arabinose (the enantiomer
Orthoester 1 was obtained from methyl tri-O-benzoyl-α-
of 1, Scheme 1) can be initiated by treatment with a cata- -arabinofuranoside[30] in four steps (Scheme 1), by apply-
lytic amount of an alcohol under acidic conditions.[27] High ing (with slight modifications) the procedure described by
regio- and stereoselectivities have been observed for the Kochetkov for -arabinose.[31Ϫ34] It was found that, to en-
opening reaction of the orthoester, and stereoregular arabi- sure good and reproducible yields for the final step, the very
nans with high proportions of α-(1Ǟ5)- and α-(1Ǟ3)-glyco- acid-sensitive intermediate 1,2-orthoester 3 had to be puri-
sidic linkages have been obtained.
fied on triethylamine-deactivated silica before use. The clos-
We have now shown that: 1) oligomerization of the or- ing reaction had to be performed in the presence of large
˚
thoester 1 can be avoided under suitable conditions, 2) the quantities of 4 A molecular sieves to trap the released meth-
opening reaction is not restricted to alcohols and can be anol efficiently. With these precautions, an overall yield of
extended to sulfur and selenium nucleophiles, 3) other or- 66% for the four steps could routinely be obtained on a
thoesters of arabinose can be used, and 4) monoarabinofur- multigram scale.
anoside building blocks, ideally suited for construction of
any possible oligoarabinofuranoside, are efficiently ob- dride in DMF gave the protected orthoester 2 in high yield.
tained from the products.
Benzylation of 1 with benzyl bromide and sodium hy-
Although orthodichloroacetate 5 has been mentioned in
Among the numerous methods available for IAD, the the literature,[35] no preparation was available. The proced-
procedure described by Ogawa,[25,26] which uses the 4-me- ure described for the preparation of the corresponding gal-
thoxybenzaldehyde acetal as a temporary tether, seemed to actofuranose derivative[36] was thus investigated and ad-
us to be the most convenient: products are easily prepared, apted. Arabinose was treated with a large excess of anhyd-
they are stable, and this methodology has been shown to rous chloral in acidic medium to give 1,2-trichloroethylid-
work for furanoside synthesis.[12,28,29]
ene acetal 4 in 43% isolated yield after crystallization.
This first paper deals with the preparation of arabinofur- Treatment of this acetal with potassium tert-butoxide in re-
anoside building blocks from orthoesters of arabinose, fluxing tert-butyl alcohol gave the crystalline orthoester 5
while applications to the synthesis of various structural mo- in 78% yield. Protection of the 3-hydroxy group was then
tifs of mycobacterial arabinans, including the terminal pen- effected either with benzyl bromide and NaH to give the
tasaccharide of arabinogalactan and the caps of the LAM benzyl ether 6 (90%), or with benzoyl chloride and pyridine
of M. tuberculosis, will be reported in the near future.[13,14] to afford the benzoate 7, isolated in 86% yield.
Eur. J. Org. Chem. 2002, 3864Ϫ3873
3865

S. Sanchez, T. Bamhaoud, J. Prandi
FULL PAPER
Finally, the 1,2,5-orthoacetate of arabinose 8 could be thanesulfonate in dichloromethane (results are summarized
obtained in 84% yield by radical reduction of the orthod- in Table 1). Opening of 6 was more difficult, and the reac-
ichloroacetate 6 with tributyltin hydride and AIBN in re- tions had to be run at room temperature, for a longer
fluxing toluene.[37]
period of time and with significantly larger quantities of
acidic promoter. In this case the major 2-O-dichloroacetate
derivative was always contaminated with a variable amount
of the 5-O-dichloroacetate. The crude reaction mixture
from the opening reactions was treated with catalytic so-
dium methoxide and the 2,5-diols were isolated.
Opening of Orthoesters of -Arabinose
D
Opening with Alcohols
The opening reactions of orthoesters 1, 2, and 6 with
alcohols under Lewis acid catalysis conditions were then
investigated. The conditions described in ref.[27] for the oli-
gomerization of the enantiomer of 1 are very drastic: the
orthoester was heated under reflux in nitromethane with
catalytic amounts of mercuric bromide as Lewis acid for 22
h. As we wanted to isolate monoarabinofuranosides (rather
than to oligomerize the orthoester) and to use much milder
conditions, we looked for different opening conditions.
For 1 and 2, opening reactions were found to be very fast
at 0 °C in acetonitrile or dichloromethane in the presence
of 5Ϫ10% of Lewis acid. α-Glycosides were obtained in
high yields and with complete regiocontrol: only products
with the benzoate group on the 2-position of the ring were
observed (see Figure 4), as determined from the NMR spec-
troscopic data. In the 13C NMR spectra of compounds
9Ϫ16, the observed chemical shifts for C-1 were found be-
Figure 4. Products of opening of orthoesters 1, 2, and 6
Opening with other Nucleophiles
The opening reactions of 2 and 6 with ethanethiol and
tween δ ϭ 104 and 108 ppm, typical values for α-arabinofu- selenophenol, intended to provide glycosyl donors, were
ranosides.[38] Signals for 2-H in the 1H NMR were found as then investigated. These reactions were found to be more
broad doublets between δ ϭ 5.0 and 5.5 ppm, indicating sensitive to the reaction conditions than their alcohol-based
that this position was benzoylated, with the observed small counterparts, with mixtures of 5-O- and 2-O-benzoylated
coupling constant to 1-H (JH1,H2 Յ 1.5 Hz) confirming the compounds being observed when 2 was treated with EtSH
α configuration of the anomeric center.[39]
and BF3·OEt2 in dichloromethane. Tin tetrachloride and
A fivefold excess of alcohol was enough to suppress oli- 1.2 equiv. of EtSH in dichloromethane were found to be
gomerization of the orthoester, whereas treatment with only superior for the synthesis of thioglycosides from 2 and 6.
1 equiv. of alcohol gave 25% of monoarabinofuranoside to- The amounts of thiol and acidic promoter had to be con-
gether with oligomers. No significant influence of the Lewis trolled carefully, the use of a threefold excess of ethanethiol
acid was noted: good to excellent yields of α-glycosides were and a stoichiometric amount of SnCl4 in the opening of 2
obtained with 5Ϫ10% of tin tetrachloride, boron giving the diethyl dithioacetal derivative 19 in 62% yield.
trifluorideϪdiethyl ether, or trimethylsilyl trifluorome- Opening of 2 was complete in 1.5 h at Ϫ15 °C with 0.08
Table 1. Nucleophilic opening of orthoesters
Orthoester
Nucleophile (equiv.)
Promoter (equiv.)
Product[a]
Yield (%)[b]
1
1
1
1
2
2
2
2
6
2
2
6
2
2
methanol (5.0)
4-MeOC6H4CH2OH (5.0)
9-decen-1-ol (5.0)
octanol (5.0)
methanol (5.0)
MeOC(O)[CH2]8OH (5.0)
octanol (5.0)
octanol (5.0)
MeOC(O)[CH2]8OH (5.0)
EtSH (1.2)
EtSH (3.0)
EtSH (1.2)
PhSeH (1.0)
PhSeH (1.0)
SnCl4 (0.1)
SnCl4 (0.1)
SnCl4 (0.1)
SnCl4 (0.1)
SnCl4 (0.1)
SnCl4 (0.1)
BF3·OEt2 (0.1)
TMSOTf (0.1)
SnCl4 (2.0)
SnCl4 (0.1)
SnCl4 (2.1)
SnCl4 (0.2)
SnCl4 (0.1)
HgBr2 (0.1)[c]
12
13
14
15
9
10
11
11
16
17
19
18
20
20
72
77
81
95
86
76
89
90
60
77
62
64
61
78
[a] For structural formulas, see Figure 4. [b] Isolated yields of homogeneous, analytically pure products. [c] Reaction performed in acetonitr-
ile.
3866
Eur. J. Org. Chem. 2002, 3864Ϫ3873

Elaboration of Monoarabinofuranosidic Building Blocks
FULL PAPER
equiv. of SnCl4, while opening of 6 required more acid pro- and afforded alcohol 22, ready for the attachment of the
moter (0.2 equiv.) and a reaction time of 2 h at 0 °C. In this temporary tether required for the IAD procedure.[25,26]
A
case, small amounts (4%) of the β-anomer of 18 were also much better precursor to glycosyl donors (α and β), how-
isolated from the reaction mixture. For unclear reasons and ever, was compound 18, obtained in 64% yield from ortho-
despite numerous experiments, opening of 1 with eth- ester 6. Monoprotection of the primary position of the ring
anethiol was sluggish under any conditions tried (best yields was easily accomplished with TBDPSCl, to give 22 in 80%
25%); this is in sharp contrast with the troublefree reaction yield, or with pivaloyl chloride in pyridine, to give 25 (65%).
between 1 and alcohols.
This left the introduction of the controlling element for
Phenyl selenoglycoside 20 has been obtained in 61% yield the glycosylation on the 2-hydroxy group of the arabinose
by treatment of 2 with phenylselenophenol[40] and 10% ring at the very last stage of the synthesis of the donors.
SnCl4 in dichloromethane.[14] However, the best results Introduction of the 4-methoxybenzyl ether[25,26] was found
(78%) were obtained with a combination of 1.0 equiv. of to be difficult. Under standard benzylation conditions
PhSeH and catalytic quantities of mercuric bromide in ace- (NaH, 4-MeOBnCl, DMF) or with use of phase-transfer
tonitrile, the only case in which acetonitrile proved to be catalysis (4-MeOBnCl, Bu4NHSO4, aqueous NaOH)[43] al-
superior to dichloromethane for opening of the orthoesters. most complete degradation of starting material was ob-
Selenoglycosides are of particular interest, as they might be served, and compound 23 was only isolated in very low
selectively activatable in the presence of thioglycosides[41,42] yields. This problem was eventually solved by use of the
to yield oligosaccharide glycosyl donors (X ϭ SePh, Y ϭ hindered strong base 2-tert-butylimino-2-diethylamino-1,3-
SEt; Figure 2).
dimethylperhydro-1,3,2-diazaphosphorine (BEMP)[44Ϫ46]
and 4-methoxybenzyl bromide[47] in acetonitrile, β-donor 23
being obtained in 70% yield from 22 under these conditions.
From 22, a wide range of α-donors is accessible. The α-
donor 24, for example, was easily obtained in 82% yield by
treatment of 22 with 9-fluorenylmethyl chloroformate
(FMOC-Cl) and pyridine in CH2Cl2. The choice of the
FMOC group as participating group for glycosylation was
based on its easy removal in the presence of other ester
groups (benzoate or pivalate). In an analogous manner, β-
donor 26 was obtained in 67% yield from 25. The use of 18
as a pivotal point to α- and β-donors gives maximum flexib-
ility for the introduction of various protecting group on po-
sition 5 and of different control elements for glycosylation
on position 2. This opens the way to the synthesis of a wide
range of tailor-made thioglycoside donors in only three
steps from orthoester 6.
Elaboration of Donors
The opening products of the orthoesters were then trans-
formed into the required glycosyl donors. As compounds
deriving from the opening of 2 already have a participating
ester group on the 2-position of the ring, silylation of the
5-position with tert-butylchlorodiphenylsilane (TBDPSCl)
was enough to provide α-donors. Thioglycoside 21 and se-
lenoglycoside 27 were thus obtained in 93% and 86% yields,
respectively, from 17 and 20 (Scheme 2). The synthesis of
the β-donor 23 began with the removal of the 2-O-benzoyl
group of 21 with catalytic sodium methoxide in methanol
Another class of α- and β-donors was obtained from se-
lenoglycoside 20. Protection of the primary hydroxy group
of 20 was achieved with TBDPSCl by the use of the same
chemistry as above, and gave α-donor 27 in 86% yield. Basic
removal of the benzoyl group (84%) and introduction of the
p-methoxybenzyl ether with BEMP gave the corresponding
β-donor 29 in 75%.
Elaboration of Acceptors
One major feature of our system is that many of the ac-
ceptors are the products of opening of the orthoesters and
might be usable directly for elaboration of oligoarabinofur-
anosides. Compounds 12Ϫ15 (Figure 4) are acceptors on
positions 3 and 5, compounds 9Ϫ11 are 5-acceptors. Ac-
ceptors on position 2 were available in a single step from
opening product 16 (Scheme 3), monoprotection of the
primary hydroxy group, as described above for the prepara-
tion of donors, was performed with TBDPSCl to give 30
(69%) and with PivCl to give 31 (80%). The last acceptor
on position 3, although not relevant to the synthesis of my-
cobacterial arabinan fragments, was obtained by monosilyl-
Scheme 2. a :1.5 equiv. tBu(Ph)2SiCl, imidazole, DMF, room temp.,
1 h, 93%; b: 0.01  MeONa, MeOH, room temp., overnight, 80%;
c: 2.5 equiv. 4-MeOBnBr, 2.5 equiv. BEMP, CH3CN, 0 °C to room
temp., 3 h, 67%; d: 1.5 equiv. FMOC-Cl, pyridine, CH2Cl2, room
temp., 1 h, 82%; e: same as a, 80%; f: 1.3 equiv. PivCl, 0.1 equiv.
DMAP, pyridine, 0 °C to room temp., 2.5 h, 65%; g: same as c,
67%; h: same as a, 86%; i: same as b, room temp., overnight, 84%;
j: same as c, 1 h, 75%
Eur. J. Org. Chem. 2002, 3864Ϫ3873
3867

S. Sanchez, T. Bamhaoud, J. Prandi
FULL PAPER
3-O-Benzyl-β-
D
-arabinofuranose 1,2,5-Orthobenzoate (2): Com-
ation of the primary hydroxy group of 15, and gave 32 in
77% isolated yield. Finally, thioglycosides 21, 22, and 25,
which are synthetic intermediates for the preparation of α-
and β-donors (Scheme 2), are also acceptors for selenogly-
cosides donors 27 or 29.
pound 1 (414 mg, 1.69 mmol) in DMF (3 mL) was benzylated with
benzyl bromide (302 µL, 2.54 mmol) and NaH (135 mg of a 60%
suspension in mineral oil, washed twice with petroleum ether,
3.38 mmol) for 30 min at room temperature before quenching with
a few drops of MeOH. CH2Cl2/water extraction and chromato-
graphy (petroleum ether/ethyl acetate, 4:1) gave 2 (543 mg, 95%).
[α]2D5 ϭ Ϫ52 (c ϭ 1.1 in chloroform). 1H NMR (250 MHz, CDCl3,
2
3
25 °C): δ ϭ 3.98 (dd, J5,5Ј ϭ 12.5, J5,4 ϭ 3.5 Hz, 1 H, 5-H), 4.12
2
3
(dd, J5Ј,5 ϭ 12.5, J5Ј,4 ϭ 1.5 Hz, 1 H, 5-H), 4.24 (s, 1 H, 3-H),
4.51 (m, 1 H, 4-H), 4.67 and 4.60 (2 d, 2J ϭ 12.0 Hz, 2 ϫ 1 H,
3
4
CH2-benzyl), 4.82 (dd, J2,1 ϭ 4.0, J2,4 ϭ 1.5 Hz, 1 H, 2-H), 6.12
(d, 3J1,2 ϭ 4.0 Hz, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3,
25 °C): δ ϭ 68.9 (C-5), 71.6 (CH2-benzyl), 81.2 (2), 83.5 (C-2, C-
3, C-4), 104.0 (C-1), 121.0, 125.8, 127.8, 128.0, 128.1, 128.6, 129.5,
135.8, 137.0 ppm. C19H18O5 (326.3): calcd. C 69.93, H 5.56; found
C 70.31, H 5.79.
Scheme 3. a: 1.4 equiv. tBu(Ph)2SiCl, imidazole, DMF, room temp.,
1 h, 69%; b: 1.5 equiv. PivCl, 0.1 equiv. DMAP, pyridine, 0 °C,
1.5 h, 80%; c: same as a, 77%
1,2-O-(2,2,2-Trichloroethylidene)-β-D-arabinofuranose (4): A sus-
pension of -arabinose (100 g, 0.67 mol) in anhydrous chloral
(250 mL) was treated with concentrated H2SO4 (6 mL, 67 mmol)
at reflux for 2 h. Chloroform was added in two portions: one of
130 mL to the hot solution (CAUTION!) and one of 600 mL after
cooling to room temp. The mixture was stirred overnight and the
resulting black solid was filtered and rinsed with CHCl3. This solid
was deposited on Celite and washed with methanol, and the wash-
ings were concentrated. The brown residue was recrystallized from
Conclusion
We have shown that nucleophilic opening of various
1,2,5-orthoesters of -arabinose with alcohols, ethanethiol,
and selenophenol under Lewis acid catalysis conditions oc-
curred with complete regio- and stereoselectivities. α--Ara-
binofuranosides were obtained in every case, in good to ex-
cellent yields. These compounds were then elaborated to boiling methanol, filtered and washed with CH2Cl2 to give a light
brown solid (56 g, 30%). A further crop (24 g, 13%) was obtained
provide a wide range of arabinofuranosidic donors and ac-
ceptors in a very efficient way. From the orthoesters, a max-
imum of two steps was enough to provide any acceptor,
while the longest sequence to donors was only four steps.
Our results on the use of these blocks for the construction
of fragments of mycobacterial arabinans[13,14] will be re-
ported in the near future.
from similar treatment of the mother liquor. M.p. 184 °C (ref.[35]
184Ϫ186 °C). [α]2D5 ϭ ϩ25 (c ϭ 1.06 in methanol) {ref.[35] [α]2D5
ϭ
ϩ30.2 (c ϭ 1.7 in methanol)}. 1H NMR (250 MHz, CD3OD, 25
°C): δ ϭ 3.67 (dd, 2J5,5 ϭ 11.0, 3J5,4 ϭ 6.5 Hz, 1 H, 5-H), 3.72 (dd,
2J5Ј,5 ϭ 11.0, 3J5Ј,4 ϭ 6.5 Hz, 1 H, 5-H), 4.16 (dt, 3J4,5 ϭ 6.5, 3J4,5 ϭ
3
3
6.5, J4,3 ϭ 1.5 Hz, 1 H, 4-H), 4.33 (d, J3,4 ϭ 1.5 Hz, 1 H, 3-H),
3
4.92 (d, J2,1 ϭ 4.0 Hz, 1 H, 2-H), 5.77 (s, 1 H, CHCCl3), 6.33 (d,
3J1,2 ϭ 4.0 Hz, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CD3OD,
25 °C): δ ϭ 63.3 (C-5), 76.6 (C-3), 90.8, 90.9, 101.4, 109.2 (C-1),
110.7 (C-acetal) ppm. C7H9Cl3O5 (279.5): calcd. C 30.08, H 3.24;
found C 30.17, H 2.89.
Experimental Section
General: All reactions were performed under argon in oven-dried
glassware. Anhydrous solvents were distilled before use. Commer-
cial reagents were used as received. Published procedures were ap-
plied for preparation of methyl 9-hydroxynonanoate,[48] seleno-
phenol,[40] and 4-methoxybenzyl bromide.[47] Chromatographic sep-
arations were performed on silica gel (35Ϫ70 µm) obtained from
SDS (Peypin, France). NMR spectra were recorded with a Bruker
AM 250 spectrometer, working at 250 MHz for 1H and 62.89 MHz
for 13C. All chemical shifts are expressed in ppm from internal
tetramethylsilane. Optical rotations were measured at 25 °C with a
PerkinϪElmer 41 polarimeter. Elemental analyses were obtained
from the Laboratoire de Chimie de Coordination du CNRS at
Toulouse (France).
β-D-Arabinofuranose 1,2,5-Orthodichloroacetate (5): Compound 4
(1.33 g, 4.77 mmol) was dissolved in tert-butyl alcohol (48 mL),
and potassium tert-butoxide (1.10 g, 9.80 mmol) was added. The
mixture was heated under reflux for 2 h before cooling and addition
of NH4Cl (300 mg, 5.60 mmol). The solvent was evaporated and
the residue was extracted with EtOAc/water to yield a white solid,
which was recrystallized from EtOAc/petroleum ether (902 mg,
78%). M.p. 123 °C (ref.[35] 117Ϫ119 °C). [α]2D5 ϭ Ϫ37 (c ϭ 1.00 in
methanol) {ref.[35] [α]2D5 ϭ Ϫ41.0 (c ϭ 1.26 in methanol)}. 1H NMR
(250 MHz, CDCl3, 25 °C): δ ϭ 4.04 (m, 2 H, 5-H), 4.39 (m, 2 H,
3
3
3-H, 4-H), 4.66 (dd, J2,1 ϭ 4.0, J2,3 ϭ 1.5 Hz, 1 H, 2-H), 5.76 (s,
1 H, CHCl2), 6.08 (d, J1,2 ϭ 4.0 Hz, 1 H, 1-H) ppm.13C NMR
3
(62.89 MHz, CDCl3, 25 °C): δ ϭ 68.9, 69.2 (C-5, CHCl2), 76.0 (C-
3), 83.6, 83.9 (C-2, C-4), 104.2 (C-1), 119.3 (C-orthoester) ppm.
C7H8Cl2O5 (243.0): calcd. C 34.59, H 3.32; found C 34.82, H 3.04.
β-
in chloroform) {ref.[31] [α]2D5 ϭ ϩ28 (c ϭ 1 in chloroform) for the
enantiomer}. 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.97 (d, 3-O-Benzyl-β-
D
-Arabinofuranose 1,2,5-Orthobenzoate (1): [α]2D5 ϭ Ϫ28 (c ϭ 0.94
D-arabinofuranose 1,2,5-Orthodichloroacetate (6):
2
3
3JOH,3 ϭ 7.5 Hz, 1 H, 3-OH), 4.06 (dd, J5Ј,5 ϭ 13.0, J5Ј,4
ϭ
Compound 5 (902 mg, 3.71 mmol) was dissolved in DMF (12 mL)
and treated with benzyl bromide (530 µL, 4.45 mmol) and NaH
2
3
3.0 Hz, 1 H, 5-H), 4.14 (dd, J5,5Ј ϭ 13.0, J5,4 ϭ 1.0 Hz, 1 H, 5-
3
H), 4.42 (m, 1 H, 4-H), 4.52 (br. d, J3,OH ϭ 7.5 Hz, 1 H, 3-H), (297 mg of a 60% suspension in mineral oil, washed twice with
3
3
3
4.72 (dd, J2,H ϭ 3.5, J2,3 ϭ 1.5 Hz, 1 H, 2-H), 6.13 (d, J1,2
ϭ
petroleum ether, 7.42 mmol). After 1 h at room temp, the reaction
mixture was treated with ethanol and water and extracted with
3.5 Hz, 1 H, 1-H), 7.20Ϫ7.70 (2 m, 5 H, Ar-H) ppm. 13C NMR
(62.89 MHz, CDCl3, 25 °C): δ ϭ 69.3 (C-5), 83.6 (2), 83.7 (C-2, C- CH2Cl2. Recrystallization of the residue from EtOAc/petroleum
3, C-4), 103.7 (C-1), 121.8, 125.8, 128.1, 129.6, 135.8 (Ar) ppm.
ether gave 6 as a white solid (1.11 g, 90%). m.p. 107 °C. [α]2D5
ϭ
3868
Eur. J. Org. Chem. 2002, 3864Ϫ3873

Elaboration of Monoarabinofuranosidic Building Blocks
Ϫ23 (c ϭ 1.04 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): was cooled to 0 °C before addition of the Lewis acid (1 equiv. as a
FULL PAPER
2
3
δ ϭ 3.99 (dd, J5,5Ј ϭ 13.0, J5,4 ϭ 3.0 Hz, 1 H, 5-H), 4.06 (dd,
1  solution in toluene). After completion of the reaction, the mix-
ture was hydrolyzed with 5% NaHCO3 and filtered through Celite.
The filtrate was diluted with EtOAc, the organic phase was washed
with saturated NaHCO3 and dried, and the solvent was evaporated.
The residue was treated for 1 h at room temp with NaOMe (0.01
3
2J5Ј,5 ϭ 13.0, J5Ј,4 ϭ 1.5 Hz, 1 H, 5-H), 4.19 (s, 1 H, 3-H), 4.51
(dd, 3J4,5 ϭ 3.0, 3J4,5 ϭ 1.5 Hz, 1 H, 4-H), 4.59 and 4.65 (2 d, 2J ϭ
3
3
12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 4.81 (dd, J2,1 ϭ 4.0, J2,3
ϭ
3
1.5 Hz, 1 H, 2-H), 5.74 (s, 1 H, CHCl2), 6.09 (d, J1,2 ϭ 4.0 Hz, 1
H, 1-H), 7.30Ϫ7.40 (m, 5 H, Ar-H) ppm. 13C NMR (62.89 MHz,  solution in MeOH). Neutralization with an Hϩ resin, filtration,
CDCl3, 25 °C): δ ϭ 69.3, 69.4 (C-5, CHCl2), 71.7 (CH2-benzyl),.
81.3, 81.7, 83.0 (C-2, C-3, C-4), 104.5 (C-1), 119.5 (C-orthoester),
127.7, 128.2, 128.6, 136.7 (Ar) ppm. C14H14Cl2O5 (333.2): calcd. C
50.47, H 4.23; found C 50.32, H 4.06.
concentration, and chromatographic purification gave the glycos-
ide.
Methyl 2-O-Benzoyl-3-O-benzyl-α-D-arabinofuranoside (9): This
compound was prepared from 2 (43 mg, 0.13 mmol), petroleum
ether/ethyl acetate (2:1), 46 mg, 96%. [α]2D5 ϭ ϩ19 (c ϭ 1.60 in
chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.91 (dd,
3-O-Benzoyl-β-D-arabinofuranose 1,2,5-Orthodichloroacetate (7):
Compound 5 (1.31 g, 5.39 mmol) was dissolved at 0 °C in pyridine
(15 mL) and treated by dropwise addition of benzoyl chloride
(0.94 mL, 8.09 mmol). The mixture was left at room temperature
for 4 h, hydrolyzed with water, and extracted with CH2Cl2. The
organic phase was washed once with water and dried, and the solv-
ent was evaporated. The resulting solid was washed three times
with petroleum ether to give 7 as a white solid (1.37 g, 73%). A
further crop of product (0.24 g, 13%) was obtained from chromato-
graphy (petroleum ether/dichloromethane, 1:1) of the petroleum
ether washings. [α]2D5 ϭ Ϫ76 (c ϭ 1.40 in chloroform). 1H NMR
3
3JOH,5 ϭ 8.0, JOH,5Ј ϭ 4.0 Hz, 1 H, 5-OH), 3.45 (s, 3 H, OCH3),
2
3.64 (m, J5,5Ј ϭ 12.0, 3J5,OH ϭ 8.0, 3J5,4 ϭ 4.0 Hz, 1 H, 5-H), 3.87
2
3
3
(m, J5Ј,5 ϭ 12.0, J5Ј,4 ഠ J5Ј,OH ഠ 3.5 Hz, 1 H, 5-H), 4.07 (m, 1
2
H, 3-H), 4.24 (m, 1 H, 4-H), 4.63 and 4.83 (2 d, J ϭ 13.0 Hz, 2
ϫ 1 H, CH2-benzyl), 5.06 (br. s, 1 H, 1-H), 5.36 (d, 3J2,1 ϭ 1.5 Hz,
1 H, 2-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 54.9
(OMe), 61.9 (C-5), 72.5 (CH2-benzyl), 81.9, 82.6, 83.1 (C-2, C-3,
C-4), 107.3 (C-1), 127.9, 128.0, 128.4, 128.5, 129.7, 133.4, 137.4,
165.4 (CO-benzoyl) ppm. C20H22O6 (358.4): calcd. C 67.02, H 6.18;
found C 67.28, H 5.93.
2
3
(250 MHz, CDCl3, 25 °C): δ ϭ 4.12 (dd, J5,5Ј ϭ 13.0, J5,4
ϭ
2
3
1.5 Hz, 5-H), 4.22 (dd, J5Ј,5 ϭ 13.0, J5Ј,4 ϭ 3.0 Hz, 1 H, 5-H),
8-Methoxycarbonyloctyl 2-O-Benzoyl-3-O-benzyl-α-D-arabinofur-
3
3
4.66 (m, 1 H, 4-H), 4.95 (dd, J2,1 ϭ 3.5, J2,4 ϭ 2.0 Hz, 1 H, 2-
H), 5.50 (s, 1 H, 3-H), 5.81 (s, 1 H, CHCl2), 6.17 (d, 3J1,2 ϭ 3.5 Hz,
1 H, 1-H), 7.46 (td, 3Jortho ϭ 7.5, 3Jmeta ϭ 1.0 Hz, 2 H, Ar-H), 7.61
anoside (10): This compound was prepared from 2 (214 mg,
0.65 mmol), toluene/ethyl acetate (4:1), 256 mg, 76%. [α]2D5 ϭ ϩ101
(c ϭ 1.60 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ
1.26Ϫ1.41 and 1.55Ϫ1.69 (2 m, 4H and 8 H, CH2-octyl), 1.89 (dd,
3
3
3
(td, Jortho ϭ 7.5, Jmeta ϭ 1.0 Hz, 1 H, Ar-H), 8.30 (d, Jortho
ϭ
7.5 Hz, 2 H, Ar-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C):
δ ϭ 68.9, 69.1 (C-5, CHCl2), 76.7 (CH2-benzyl), 78.1, 82.1 (2), 84.1,
104.3 (C-1), 119.9 (C-orthoester), 128.8, 129.8, 133.7 (Ar), 165.4
(CO-benzoyl) ppm. C14H12Cl2O6 (347.1): calcd. C 48.44, H 3.48;
found C 48.50, H 3.10.
3
3
3JOH,5 ϭ 8.5, JOH,5Ј ϭ 4.5 Hz, 1 H, 5-OH), 2.30 (t, J ϭ 6.5 Hz,
2
3
2 H, CH2CO), 3.48 (dt, J ϭ 9.5, J ϭ 6.5 Hz, 1 H, OCH2-octyl),
2
3
3
3.67 (s, 3 H, OMe), 3.67 (m, J5,5Ј ϭ 12.0, J5,OH ϭ 8.5, J5,4
ϭ
4.0 Hz, 1 H, 5-H), 3.75 (dt, 2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-
2
3
3
octyl), 3.88 (m, J5Ј,5 ϭ 12.0, J5Ј,OH ϭ 4.5, J5Ј,4 ϭ 3.0 Hz, 1 H,
5-H), 4.06 (m, J3,4 ϭ 5.5 Hz, 1 H, 3-H), 4.24 (m, 1 H, 4-H), 4.60
3
3-O-Benzyl-β-D-arabinofuranose 1,2,5-Orthoacetate (8): Compound
2
and 4.83 (2 d, J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.14 (br. s, 1
6
(200 mg, 0.60 mmol) and tributyltin hydride (0.81 mL,
H, 1-H), 5.37 (d, J2,1 ϭ 1.5 Hz, 1 H, 2-H) ppm. 13C NMR
3
3.00 mmol) were dissolved in toluene (6 mL). The mixture was
brought to reflux and AIBN (1.75 mL of a 0.24  solution in tolu-
ene, 0.42 mmol) was added over 7 h by syringe pump. Evaporation
of solvent and chromatography (petroleum ether/ethyl acetate, 8:1
to 6:1) gave 8 as a white solid (134 mg, 84%). [α]2D5 ϭ Ϫ38 (c ϭ
1.10 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.64
(62.89 MHz, CDCl3, 25 °C): δ ϭ 24.9, 26.0, 29.0, 29.1, 29.3, 34.1
(CH2-octyl), 51.5 (CH3), 62.0 (OCH2-octyl), 67.6 (C-5), 72.4 (CH2-
benzyl), 82.1, 82.9 (2) (C-2, C-3, C-4), 106.1 (C-1), 127.8, 128.4,
128.5, 128.5, 129.4, 129.7, 133.4, 137.6, 165.4 (CO-benzoyl), 174.4
(CO-methyl ester) ppm. C29H38O8 (514.6): calcd. C 67.68, H 7.44;
found C 67.37, H 7.55.
2
3
(s, 3 H, CH3), 3.77 (dd, J5,5Ј ϭ 13.0, J5,4 ϭ 3.0 Hz, 5-H), 3.91
(dd, 2J5Ј,5 ϭ 13.0, 3J5Ј,4 ϭ 1.0 Hz, 1 H, 5-H), 4.08 (br. s, 1 H, 3-H),
Octyl 2-O-Benzoyl-3-O-benzyl-α-D-arabinofuranoside (11): This
3
3
3
compound was prepared from 2 (29 mg, 0.09 mmol), petroleum
ether/ethyl acetate (3:1), 38 mg, 90%. [α]2D5 ϭ ϩ88 (c ϭ 1.05 in chlo-
roform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 0.88 (m, 3 H,
CH3-octyl), 1.22Ϫ1.41 and 1.53Ϫ1.69 (2 m, 4 H and 8 H, CH2-
4.41 (ddd, J4,5 ϭ 3.0, J4,5Ј ϭ 1.0, J4,3 ϭ 1.0 Hz, 1 H, 4-H), 4.63
(dd, 3J2,1 ϭ 4.0, 3J2,3 ϭ 1.5 Hz, 1 H, 2-H), 4.58 and 4.64 (2 d, 2J ϭ
12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.95 (d, 3J1,2 ϭ 4.0 Hz, 1 H, 1-H),
7.30Ϫ7.40 (m, 5 H, Ar-H) ppm. 13C NMR (62.89 MHz, CDCl3,
25 °C, TMS): δ ϭ 22.5 (CH3), 68.2 (C-5), 71.6 (CH2-benzyl), 81.2
(2), 83.4 (C-2, C-3, C-4), 103.9 (C-1), 122.1 (C-orthoester), 127.8,
128.6, 128.9, 137.0 (Ar) ppm. C14H16O5 (264.3): calcd. C 63.63, H
6.10; found C 63.40, H 5.82.
2
3
octyl), 1.90 (m, 1 H, 5-OH), 3.48 (dt, J ϭ 9.5, J ϭ 6.5 Hz, 1 H,
2
3
3
OCH2-octyl), 3.66 (m, J5,5Ј ϭ 12.0, J5,OH ϭ 8.5, J5,4 ϭ 4.0 Hz,
1 H, 5-H), 3.73 (dt, J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.88
2
(m, 2J5Ј,5 ϭ 12.0, 3J5Ј,OH ϭ 4.5, 3J5Ј,4 ϭ 3.0 Hz, 1 H, 5-H), 4.06 (m,
3J3,4 ϭ 5.5 Hz, 1 H, 3-H), 4.24 (m, J4,3 ϭ 5.5, J4,5 ϭ 4.0, J4,5
ϭ
3
3
3
3.0 Hz, 1 H, 4-H), 4.60 and 4.83 (2 d, 2J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-
General Procedure for the Opening of Orthoesters 1 and 2 with Alco-
3
hols: The orthoester was stirred in CH2Cl2 (0.2  solution) with
benzyl), 5.14 (br. s, 1 H, 1-H), 5.38 (d, J2,1 ϭ 1.5 Hz, 1 H, 2-H)
˚
ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ14.1, 22.7, 29.2,
29.36, 29.40, 31.8 (CH2-octyl), 62.0 (OCH2-octyl), 67.7 (C-5), 72.4
(CH2-benzyl), 82.1, 82.9 (2) (C-2, C-3, C-4), 106.1 (C-1), 127.8,
127.8, 128.4, 128.5, 129.4, 129.8, 133.4, 137.6 (Ar), 165.4 (CO-
benzoyl) ppm. C27H36O6 (456.6): calcd. C 71.03, H 7.95; found C
71.00, H 7.94.
the alcohol (5 equiv.) and 4 A molecular sieves for 15 min. The
mixture was cooled to 0 °C before addition of the Lewis acid (0.1
equiv. as a 1  solution in toluene). After completion of the reac-
tion, the mixture was hydrolyzed with 5% NaHCO3 and extracted
with CH2Cl2. Chromatographic purification gave the glycoside.
General Procedure for the Opening of Orthoester 6 with Alcohols:
Compound 6 (0.3  solution) was stirred in CH2Cl2 with the alco-
hol (5 equiv.) and 4 A molecular sieves for 15 min. The mixture
Methyl 2-O-Benzoyl-α-D-arabinofuranoside (12): This compound
was prepared from 1 (50 mg, 0.21 mmol), petroleum ether/ethyl
˚
Eur. J. Org. Chem. 2002, 3864Ϫ3873
3869

S. Sanchez, T. Bamhaoud, J. Prandi
FULL PAPER
acetate (1:1), 40 mg, 72%. [α]2D5 ϭ ϩ88 (c ϭ 0.97 in chloroform).
form). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.25Ϫ1.40 and
1.50Ϫ1.65 (2 m, octyl), 2.06 (dd, JOH,5 ϭ 6.5, JOH,5 ϭ 4.5 Hz, 1
3
3
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 3.40 (m, 1 H, 3-H), 3.46
3
(s, 3 H, OMe), 3.79 (br. d, J5,5Ј ϭ 12.0 Hz, 1 H, 5-H), 3.95 (br. d, H, 5-OH), 2.30 [t, 3J ϭ 7.5 Hz, 2 H, C(O)CH2-octyl], 2.77 (d,
3J5,5Ј ϭ 12.0 Hz, 1 H, 5-H), 4.20 (m, 1 H, 4-H), 5.08 (br. d, 3J2,3
1.5 Hz, 1 H, 2-H), 5.16 (s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz,
CDCl3, 25 °C): δ ϭ 55.0 (OMe), 61.8 (C-5), 76.3, 84.0, 85.9 (C-2, 1 H, 5-H), 3.66 (s, 3 H, OMe), 3.70 (dt, J ϭ 9.5, J ϭ 6.5 Hz, 1
ϭ
3JOH,2 ϭ 8.0 Hz, 1 H, 2-OH), 3.42 (dt, 2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H,
2
3
OCH2-octyl), 3.63 (ddd, J5,5 ϭ 12.0, 3J5,OH ϭ 6.5, J5,4 ϭ 2.5 Hz,
2
3
3
3
C-3, C-4), 106.4 (C-1), 128.5, 128.9, 129.7, 133.6, 166.6 (CO-
benzoyl) ppm. C13H16O6 (268.3): calcd. C 58.20, H 6.01; found C 3.87 (ddd, J5,5 ϭ 12.0, J5,OH ϭ 4.0, J5,4 ϭ 2.5 Hz, 1 H, 5-H),
58.49, H 6.14.
H, OCH2-octyl), 3.86 (dd, J3,4 ϭ 4.5, J3,2 ϭ 2.0 Hz, 1 H, 3-H),
2
3
3
2
4.19 (m, 2 H, 2-H, 4-H), 4.58 and 4.71 (2 d, J ϭ 12.0 Hz, 2 ϫ 1
H, CH2-benzyl), 4.97 (s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz,
CDCl3, 25 °C, TMS): δ ϭ 24.8, 25.9, 28.9, 29.0, 29.3, 33.9 (CH2-
octyl), 51.4 (OMe), 61.8 (C-5), 67.4 (OCH2-octyl), 71.9 (CH2-
benzyl), 78.8, 83.4, 84.9 (C-2, C-3, C-4), 108.6 (C-1), 127.6, 127.6,
128.3, 137.8, 174.4 (CO-ester) ppm. C22H34O7 (410.5): calcd. C
64.37, H 8.35; found C 64.03, H 8.40.
4-Methoxybenzyl 2-O-Benzoyl-α-D-arabinofuranoside (13): This
compound was prepared from 1 (30 mg, 0.13 mmol), petroleum
ether/ethyl acetate (3:2), 36 mg, 76%. [α]2D5 ϭ ϩ121 (c ϭ 0.95 in
1
chloroform). H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 2.10 (br, 1
H, 5-OH), 3.39 (d, 3JOH,3 ϭ 5.5 Hz, 1 H, 3-OH), 3.80 (ddd, 2J5,5Ј
12.0, J5,OH ϭ 7.5, J5,4 ϭ 4.5 Hz, 1 H, 5-H), 3.80 (s, 3 H, OMe),
ϭ
3
3
2
3
3
3.95 (ddd, J5Ј,5 ϭ 12.0, J5Ј,4 ϭ 4.5, J5Ј,OH ϭ 3.0 Hz, 1 H, 5-H),
Ethyl 2-O-Benzoyl-3-O-benzyl-1-thio-α-D-arabinofuranoside (17):
3
3
3
4.18 (m, J3,4 ϭ 6.0, J3,OH ϭ 5.5, J3,2 ϭ 2.5 Hz, 1 H, 3-H), 4.24
Orthoester
2
(4.04 g, 12.38 mmol) was dissolved in CH2Cl2
3
3
3
˚
(ddd, J4,3 ϭ 6.0, J4,5 ϭ 4.5, J4,5 ϭ 3.0 Hz, 1 H, 4-H), 4.53 and
(100 mL), powdered 3 A molecular sieves were added, and the mix-
ture was stirred for 1.5 h at room temperature. The temperature
was brought to Ϫ15 °C, and EtSH (1.12 mL, 15.12 mmol) and
SnCl4 (62 µL of a 1  solution in toluene, 0.06 mmol) were added.
After 1 h at Ϫ15 °C, another portion of SnCl4 (37 µL of a 1 
solution in toluene, 0.04 mmol) was added and the reaction mixture
was left for 30 min before quenching with a few drops of satd.
NaHCO3 and filtration through Celite. Workup of the filtrate
(H2O/CH2Cl2) and chromatography (petroleum ether/ethyl acetate,
4:1 then 3:1) gave 17 as a colorless oil (3.72 g 77%). [α]2D5 ϭ ϩ178
(c ϭ 1.10 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ
2
3
4.77 (2 d, J ϭ 11.5 Hz, 2 ϫ 1 H, CH2-benzyl), 5.14 (dd, J2,3
ϭ
2.5, J2,1 ϭ 1.0 Hz, 1 H, 2-H), 5.31 (br. s, 1 H, 1-H) ppm. 13C
NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 55.2 (OMe), 61.9 (C-5),
68.7, 76.4 (CH2-benzyl), 84.1, 86.0, 104.0 (C-1), 113.9, 128.5, 128.9,
129.7, 133.6, 159.3, 166.6 (CO-benzoyl) ppm. C20H22O7 (374.4):
calcd. C 64.16, H 5.92; found C 64.33, H 6.04.
3
9-Decenyl 2-O-Benzoyl-α-D-arabinofuranoside (14): This compound
was prepared from 1 (200 mg, 0.85 mmol), petroleum ether/ethyl
acetate (2:1), 270 mg, 81%. [α]2D5 ϭ ϩ84 (c ϭ 1.10 in chloroform).
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.25Ϫ1.42 and 1.56Ϫ1.67
(2 m, 2H and 12 H, CH2-decenyl), 1.88 [m, 1 H, 5-OH), 2.09Ϫ1.99
(m, 2 H, CH2ϪCHϭCH2), 3.26 (m, 1 H, 3-OH), 3.49 (dt, 2J ϭ 9.5,
1.33 (t, 3J ϭ 7.5 Hz, 3 H, S CH2CH3), 1.79 (dd, JOH,5 ϭ 8.0,
3
3JOH,5Ј ϭ 4.0 Hz, 1 H, 5-OH), 2.60Ϫ2.83 (m, 3J ϭ 7.5 Hz, 2 H,
2
3
3
SCH2CH3), 3.70 (ddd, J5,5Ј ϭ 12.0, J5,OH ϭ 8.0, J5,4 ϭ 4.0 Hz,
1 H, 5-H), 3.90 (ddd, J5Ј,5 ϭ 12.0, J5Ј,OH ϭ 4.0, J5Ј,4 ϭ 3.0 Hz,
1 H, 5-H), 4.12 (m, J3,4 ϭ 5.5 Hz, 1 H, 3-H), 4.39 (m, 1 H, 4-H),
2
3
3J ϭ 6.5 Hz, 1 H, OCH2-decenyl), 3.78 (dt, J ϭ 9.5, J ϭ 6.5 Hz,
2
3
3
2
3
3
1 H, OCH2-decenyl), 3.80 (m, J5,5Ј ϭ 12.5, J5,OH ϭ 7.5, J5,4
ϭ
3
2
3
3
4.0 Hz, 1 H, 5-H), 3.95 (ddd, J5Ј,5 ϭ 12.5, J5Ј,OH ϭ 5.0, J5Ј,4
ϭ
2
4.61 and 4.82 (2 d, J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.40 (dd,
3.0 Hz, 1 H, 5-H), 4.14Ϫ4.24 (m, 2 H, 3-H, 4-H), 4.90Ϫ5.04 (m, 2
3J2,3 ϭ 1.5, J2,1 ϭ 1.5 Hz, 1 H, 2-H), 5.48 (br. s, 1 H, 1-H) ppm.
3
3
3
H, CH2ϭCH-decenyl), 5.08 (dd, J2,3 ϭ 2.5, J2,1 ϭ 1.0 Hz, 1 H,
13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 14.7 (SCH2CH3), 25.2
(SCH2CH3), 61.6 (C-5), 72.4 (CH2-benzyl), 82.6, 82.7 (2) (C-2, C-
3, C-4), 88.1 (C-1), 127.9, 128.4, 128.5, 129.2, 129.7, 133.5, 137.4,
165.4 (CO-benzoyl) ppm. C21H24O5S (388.5): calcd. C 64.92, H
6.23; found C 64.99, H 6.47.
2-H), 5.25 (br. s, 1 H, 1-H), 5.81 (m, 3J9Ј,10Ј ϭ 16.5, 3J9Ј,10Ј ϭ 10.0,
3J9Ј,8Ј ϭ 6.5, J9Ј,8Ј ϭ 6.5 Hz, 1 H, CH2ϭCH-decenyl) ppm. 13C
3
NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 26.0, 28.8, 29.0, 29.3, 29.4,
29.4, 33.7 (CH2-decenyl), 61.9 (C-5) 67.9 (OCH2-decenyl), 76.4 (C-
3), 84.0, 86.0 (C-2, C-4), 105.2 (C-1), 114.1, 128.5, 129.0, 129.7,
133.6, 139.2, 166.7 (CO-benzoyl) ppm. C22H32O6 (392.5): calcd. C
67.32, H 8.22; found C 67.10, H 7.86.
Ethyl 3-O-Benzyl-1-thio-α-D-arabinofuranoside (18): Compound 6
(1.38 g, 4.14 mmol) was dissolved in CH2Cl2 (20 mL) and treated
at 0 °C with SnCl4 (0.41 mL of a 1  solution in toluene,
0.41 mmol) and ethanethiol (0.37 mL, 4.97 mmol). After 15 min, a
further portion of SnCl4 (0.41 mL of a 1  solution in toluene,
0.41 mmol) was added and the mixture was stirred for 2 h at 0 °C.
The reaction was quenched with cold satd. NaHCO3 and the mix-
ture filtered through Celite. The filtrate was washed with water and
dried, and the solvent was evaporated. The residue was treated for
1 h at room temp with NaOMe (0.01  solution in MeOH). Neut-
ralization with IR 120 Hϩ resin, filtration, concentration, and chro-
matographic purification with toluene/ethyl acetate (2:1) gave thi-
oglycoside 18 (748 mg, 64%). [α]2D5 ϭ ϩ115 (c ϭ 1.10 in chloro-
form). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.31 (t, 3J ϭ
7.5 Hz, 3 H, SCH2CH3), 2.65 and 2.72 (2 dq, 2J ϭ 13.0, 3J ϭ
Octyl 2-O-Benzoyl-α-D-arabinofuranoside (15): This compound was
prepared from 1 (142 mg, 0.60 mmol), petroleum ether/ethyl acetate
(2:1 then 3:2), 211 mg (95%). [α]2D5 ϭ ϩ89 (c ϭ 1.10 in chloroform).
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 0.88 (m, 3 H, CH3-octyl),
1.20Ϫ1.40 and 1.55Ϫ1.70 (2 m, 4 H and 8 H, CH2-octyl), 1.82 (dd,
3
3
3JOH,5 ϭ 7.5, JOH,5 ϭ 5.0 Hz, 1 H, 5-OH), 3.24 (d, JOH,3
ϭ
2
3
5.5 Hz, 3-OH), 3.49 (dt, J ϭ 9.5, J ϭ 6.5 Hz, 1 H, OCH2-octyl),
3.78 (dt, 2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.80 (ddd,
2J5,5 ϭ 12.0, J5,OH ϭ 7.5, J5,4 ϭ 4.5 Hz, 1 H, 5-H), 3.94 (ddd,
3
3
2J5Ј,5 ϭ 12.0, J5Ј,OH ϭ 5.0, J5Ј,4 ϭ 3.0 Hz, 1 H, 5-H), 4.14Ϫ4.24
3
3
3
3
(m, 2 H, 3-H, 4-H), 5.08 (dd, J2,3 ϭ 2.5, J2,1 ϭ 1.0 Hz, 1 H, 2-
H), 5.26 (br. s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25
°C): δ ϭ 14.0, 22.6, 25.9, 29.1, 29.3, 29.4, 31.7 (CH2-octyl), 61.8
(C-5), 67.8 (OCH2-octyl), 76.2 (C-3), 83.9, 85.9 (C-2, C-4), 105.2
(C-1), 128.4, 128.9, 129.7, 133.5, 166.6 (CO-benzoyl) ppm.
C20H30O6 (366.4): calcd. C 65.55, H 8.25; found C 65.46, H 7.99.
2
3
7.5 Hz, 2 H, SCH2CH3), 3.67 (dd, J5,5 ϭ 12, J5,4 ϭ 3.0 Hz, 1 H,
2
3
5-H), 3.86 (dd, J5Ј,5 ϭ 12, J5Ј,4 ϭ 2.5 Hz, 1 H, 5-H), 3.92 (dd,
3
3
3J3,4 ϭ 4.5 Hz J3,2 ϭ 2.0 Hz, 1 H, 3-H), 4.23 (dd, J2,3 ϭ 2.0,
3J2,1 ϭ 1.5 Hz, 1 H, 2-H), 4.28 (ddd, 3J4,3 ϭ 4.5, 3J4,5 ϭ 3.0, 3J4,5 ϭ
3
8-Methoxycarbonyloctyl 3-O-Benzyl-α-D-arabinofuranoside (16):
2.5 Hz, 1 H, 4-H), 4.57 and 4.72 (2 d, J ϭ 12.0 Hz, 2 ϫ H, CH2-
3
This compound was prepared from 6 (107 mg, 0.32 mmol), toluene/
benzyl), 5.26 (d, J1,2 ϭ 1.5 Hz, 1 H, 1-H) ppm. 13C NMR
ethyl acetate (2:1), 79 mg, 60%. [α]2D5 ϭ ϩ97 (c ϭ 1.21 in chloro-
(62.89 MHz, CDCl3, 25 °C):
δ ϭ 15.0 (SCH2CH3), 25.7
3870
Eur. J. Org. Chem. 2002, 3864Ϫ3873

Elaboration of Monoarabinofuranosidic Building Blocks
FULL PAPER
(SCH2CH3), 62.1 (C-5), 72.3 (CH2-benzyl), 80.0, 82.9, 84.7 (C-2,
133.2, 133.3, 135.6, 137.5, 165.4 (CO-benzoyl) ppm. C37H42O5SSi
C-3, C-4), 91.1 (C-1), 127.8, 127.9, 128.5, 137.6 ppm. C14H20O4S (626.9): calcd. C 70.89, H 6.75; found C 70.55, H 6.38.
(284.4): calcd. C 59.13, H 7.59; found C 58.79, H 7.17.
Ethyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-1-thio-α-D-arabinofur-
anoside (22). From 18: Compound 18 (118 mg, 0.41 mmol) was sily-
lated with imidazole (42 mg, 0.62 mmol) and tert-butyldiphenylsilyl
chloride (160 µL, 0.62 mmol) for 3 h at room temperature as de-
scribed for the preparation of 21. Chromatography (petroleum
ether/ethyl acetate, 6:1) gave 22 as a colorless oil (174 mg, 80%).
From 21: Compound 21 (145 mg, 0.24 mmol) was dissolved in
methanol (1.5 mL) and treated overnight at room temperature with
sodium methoxide (2.42 mL of a 0.01  solution in methanol, 24
µmol). Neutralization (IR 120, Hϩ resin) filtration and chromato-
graphy gave 22 (96 mg, 80%). [α]2D5 ϭ ϩ54 (c ϭ 1.05 in chloroform).
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.03 (s, 9 H, tBuSi), 1.33
2-O-Benzoyl-3-O-benzyl-D-arabinose Diethyl Dithioacetal (19):
Orthoester 2 (63 mg, 0.10 mmol) was dissolved in CH2Cl2 (2 mL)
˚
and treated at Ϫ18 °C with 4 A molecular sieves, EtSH (43 µL,
0.58 mmol), and SnCl4 (0.21 mL of a 1  solution in toluene,
0.21 mmol). The reaction was quenched after 20 min with a few
drops of NEt3, the mixture was filtered, and the solvent was evap-
orated. Chromatography (petroleum ether/ethyl acetate, 2:1) gave
19 as a colorless oil (54 mg, 62%). [α]2D5 ϭ ϩ105 (c ϭ 0.69 in chloro-
1
form). H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.20 and 1.26 (2
t, 3J ϭ 7.5 Hz, 2 ϫ 3 H, SCH2CH3), 2.04 (br, 1 H, 5-OH),
2.58Ϫ2.79 (2 dq, 2J ϭ 13.0, 3J ϭ 7.5 Hz, 2 ϫ 2 H, SCH2CH3), 3.33
3
3
(t, J ϭ 7.5 Hz, 3 H, SCH2CH3), 2.79Ϫ2.64 (m, J ϭ 7.5 Hz, 2 H,
3
2
3
(d, JOH,4 ϭ 7.5 Hz, 1 H, 4-OH), 3.63 (m, J5,5 ϭ 11.5, J5,OH
ϭ
SCH2CH3), 3.50 (d, 3JOH,2 ϭ 9.5 Hz, 1 H, 2-OH), 3.64 (dd, 2J5,5 ϭ
5, 3J5,4 ϭ 3.5 Hz, 1 H, 5-H), 3.73 (m, 1 H, 4-H), 3.83 (ddd, 2J5,5
ϭ
3
2
3
11.5, J5,4 ϭ 2.5 Hz, 1 H, 5-H), 3.85 (dd, J5,5 ϭ 11.5, J5,4
ϭ
3
3
3
11.5, J5,OH ϭ 6, J5,4 ϭ 3.5 Hz, 1 H, 5-H), 4.27 (dd, J3,4 ϭ 8.0,
2.5 Hz, 1 H, 5-H), 4.05 (m, 1 H, 3-H), 4.23Ϫ4.30 (m, 2 H, 2-H, 4-
3J3,2 ϭ 3.5 Hz, 1 H, 3-H), 4.32 (d, J1,2 ϭ 8.5 Hz, 1 H, 1-H), 4.73
3
2
H), 4.54 and 4.73 (2 d, J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.32
2
3
and 4.83 (2 d, J ϭ 11.5 Hz, 2 ϫ 1 H, CH2Ph), 5.54 (dd, J2,1
ϭ
3
(d, J1,2 ϭ 2.0 Hz, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3,
8.5, 3J2,3 ϭ 3.5 Hz, 1 H, 2-H) ppm. 13C NMR (62.89 MHz, CDCl3,
25 °C): δ ϭ 14.3 (SCH2CH3), 24.3, 24.6 (SCH2CH3), 52.0 (C-1),
63.3 (C-5), 74.7 (CH2-benzyl), 75.1, 78.1, 127.6, 127.8, 128.5, 130.2,
133.5 ppm. C23H30O5S2 (450.6): calcd. C 61.30, H 6.31; found C
61.43, H 6.59.
25 °C): δ ϭ18.1 (SCH2CH3), 19.1 [SiC(CH3)3], 26.0 (SCH2CH3),
26.7 [SiC(CH3)3], 63.9 (C-5), 72.0 (CH2-benzyl), 79.2, 83.7, 84.5
(C-2, C-3, C-4), 91.5 (C-1), 127.8, 127.8, 127.9, 128.5, 129.9, 130.0,
132.2, 132.3, 135.5, 135.6, 137.6 ppm. C30H38O4SSi (522.8): calcd.
C 68.92, H 7.32; found C 68.62, H 7.47.
Phenyl
2-O-Benzoyl-3-O-benzyl-1-seleno-α-D-arabinofuranoside
Ethyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-2-O-(4-methoxyben-
zyl)-1-thio-α-D-arabinofuranoside (23): Compound 22 (326 mg,
(20): A solution of compound 2 (100 mg, 0.30 mmol) in acetonitrile
containing 4 A MS was stirred for 15 min at room temp. After this
˚
0.62 mmol), dissolved in acetonitrile (3 mL), was treated at 0 °C
with BEMP (452 µL, 1.56 mmol) and 4-methoxybenzyl bromide
(313 mg, 1.56 mmol). The mixture was allowed to warm to room
temperature and stirred for 1 h before quenching with saturated
NaHCO3 solution (3 mL) and further stirring for 3 h until com-
plete hydrolysis of the excess of 4-methoxybenzyl bromide. CH2Cl2/
water extraction and chromatography (petroleum ether/ethyl acet-
ate, 12:1) gave 23 (280 mg, 70%). [α]2D5 ϭ ϩ76 (c ϭ 0.74 in chloro-
form). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.04 (s, 9 H,
mixture had been cooled to 0 °C, selenophenol (2.5 mL of a 0.12 
solution in CH2Cl2, 0.30 mmol) and mercuric bromide were added.
After 30 min and warming to room temp, the reaction mixture was
filtered through Celite. Concentration and chromatography (petro-
leum ether/ethyl acetate, 4:1) gave 20 (116 mg, 78%). [α]2D5 ϭ ϩ146
(c ϭ 0.99 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ
3
3
1.77 (dd, JOH,5 ϭ 8.5, JOH,5 ϭ 4.5 Hz, 1 H, 5-OH), 3.73 (ddd,
2J5,5 ϭ 12.0, J5,OH ϭ 8.5, J5,4 ϭ 4.0 Hz, 1 H, 5-H), 3.92 (ddd,
3
3
2J5,5 ϭ 12.0, J5,OH ϭ 4.5, J5,4 ϭ 3.0 Hz, 1 H, 5-H), 4.16 (br. d,
3J3,4 ϭ 5.0 Hz, 1 H, 3-H), 4.53 (m, 1 H, 4-H), 4.65 and 4.88 (2 d,
2J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.68 (br. s, 1 H, 2-H), 5.97
(br. s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ
61.6 (C-5), 72.4 (CH2-benzyl), 82.6 (2), 84.1 (C-2, C-3, C-4), 87.7
(C-1), 127.8, 128.5, 129.1, 129.7, 133.5, 134.1, 137.3, 165.3 (CO-
benzoyl) ppm. C25H24O5Se (483.4): calcd. C 62.11, H 5.00; found
C 62.30, H 5.12.
3
3
3
3
tBuSi), 1.31 (t, J ϭ 7.5 Hz, 3 H, SCH2CH3), 2.56Ϫ2.81 (m, J ϭ
2
3
7.5 Hz, 2 H, SCH2CH3), 3.78 (dd, J5,5 ϭ 11.0, J5,4 ϭ 6.5 Hz, 1
H, 5-H), 3.80 (s, 3 H, OCH3), 3.84 (dd, 2J5,5 ϭ 11.0, 3J5,4 ϭ 4.5 Hz,
3
3
1 H, 5-H), 3.98 (dd, J2,1 ϭ 3.0, J2,3 ϭ 3.0 Hz, 1 H, 2-H), 4.05
(dd, 3J3,4 ϭ 6.5, 3J3,2 ϭ 3.0 Hz, 1 H, 3-H), 4.23 (m, 1 H, 4-H), 4.47
2
and 4.53 (2 d, J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-methoxybenzyl), 4.42
and 4.55 (2 d, 2J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 5.32 (d, 3J1,2 ϭ
3.0 Hz, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C):
δ ϭ 15.0 (SCH2CH3), 19.3 [SiC(CH3)3], 25.3 (SCH2CH3), 26.7
[SiC(CH3)3], 55.3 (OMe), 63.5 (C-5), 71.6, 72.0 (CH2-benzyl), 81.7,
83.4, 87.2 (C-2, C-3, C-4), 88.3 (C-1), 113.8, 127.6, 127.6, 128.3,
129.6, 129.6, 133.4, 135.6, 135.7, 137.8, 159.3 ppm. C38H46O5SSi
(642.9): calcd. C 70.99, H 7.21; found C 70.96, H 7.20.
Ethyl 2-O-Benzoyl-3-O-benzyl-5-O-tert-butyldiphenylsilyl-1-thio-α-
D-arabinofuranoside (21): Compound 17 (332 mg, 0.85 mmol) in
DMF (1.5 mL) was treated at 0 °C with imidazole (87 mg,
1.28 mmol) and tert-butyldiphenylchlorosilane (328 µL,
1.28 mmol) and then allowed to warm to room temperature. After
1 h, the reaction mixture was quenched with methanol (a few
Ethyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-2-O-(9-fluorenylme-
drops) and the DMF was evaporated under vacuum. CH2Cl2/water thoxycarbonyl)-1-thio-α-D-arabinofuranoside (24): Compound 22
extraction and chromatography (petroleum ether/ethyl acetate, 8:1)
gave 21 as a colorless oil (496 mg, 93%). [α]2D5 ϭ ϩ69 (c ϭ 0.8 in
chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.32 (t, 3J ϭ
(563 mg, 1.08 mmol), dissolved in CH2Cl2 (2 mL), was treated at
room temperature with pyridine (175 µL) and 9-fluorenylmethyl
chloroformate (418 mg, 1.61 mmol) for 1 h. Water/CH2Cl2 workup
7.5 Hz, 3 H, SCH2CH3), 2.59Ϫ2.83 (m, 3J ϭ 7.5 Hz, 2 H, and chromatography (toluene/petroleum ether, 4:1) gave 24 as a
SCH2CH3), 3.86 (m, 2 H, 5-H), 4.21 (m, 3J3,4 ϭ 5.5 Hz, 1 H, 3-H), colorless oil (658 mg, 82%). [α]2D5 ϭ ϩ84.7 (c ϭ 0.90 in chloroform).
4.40 (m, 1 H, 4-H), 4.78 and 4.58 (2 d, 2J ϭ 12.0 Hz, 2 ϫ 1 H,
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.04 (s, 9 H, tBuSi), 1.31
3 2
3
3
CH2-benzyl), 5.43 (dd, J2,3 ϭ 1.5, J2,1 ϭ 1.5 Hz, 1 H, 2-H), 5.48
(t, J ϭ 7.5 Hz, 3 H, SCH2CH3), 2.65 and 2.74 (2 dq, J ϭ 13.0,
(br. s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 3J ϭ 7.5 Hz, 2 H, SCH2CH3), 3.79 (dd, 2J5,5 ϭ 11.0, 3J5,4 ϭ 4.0 Hz,
2
3
14.8 (SCH2CH3), 19.2 [SiC(CH3)3], 25.2 (SCH2CH3), 26.7 1 H, 5-H), 3.86 (dd, J5,5 ϭ 11.0, J5,4 ϭ 3.5 Hz, 1 H, 5-H), 4.14
3
3
3
[SiC(CH3)3], 62.9 (C-5), 72.2 (CH2-benzyl), 82.9 (2), 83.0 (C-2, C-
(dd, J3,4 ϭ 5.0, J3,2 ϭ 2.0 Hz, 1 H, 3-H), 4.32 (ddd, J4,3 ϭ 5.0,
3, C-4), 87.9 (C-1), 127.6, 127.7, 127.9, 128.4, 129.3, 129.7, 129.8, 3J4,5 ഠ 3J4,5 ϭ 4.0 Hz, 1 H, 4-H), 4.45 (d, 3J ϭ 1.5 Hz, 2 H, OCH2-
Eur. J. Org. Chem. 2002, 3864Ϫ3873
3871

S. Sanchez, T. Bamhaoud, J. Prandi
FULL PAPER
fmoc), 4.52 and 4.69 (2 d, 2J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), (dt, J3,4 ϭ 4.5, J3,2 ϭ 1.0, J3,1 ϭ 1.0 Hz, 1 H, 3-H), 4.53 (m, 1
3
3
4
3
3
3
2
5.07 (dd, J2,3 ϭ 2.0, J2,1 ϭ 1.5 Hz, 1 H, 2-H), 5.42 (d, J1,2
ϭ
H, 4-H), 4.64 and 4.82 (2 d, J ϭ 12.0 Hz, 2 ϫ 1 H, CH2-benzyl),
3
3
1.5 Hz, 1 H, 1-H), 7.17Ϫ7.47, 7.57Ϫ7.77 and 7.74Ϫ7.80 (3 m, 23 5.70 (t, J2,3 ϭ 1.0, J2,1 ϭ 1.0 Hz, 1 H, 2-H), 5.96 (m, 1 H, 1-H)
H, Ar-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 14.8 ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 19.2 [C(CH3)3],
(SCH2CH3), 19.2 [SiC(CH3)3], 25.1 (SCH2CH3), 26.7 [C(CH3)3],
46.6 (CH-FMOC), 62.8 (C-5), 70.0 (CH2-FMOC), 72.0 (CH2- 2, C-3, C-4), 87.6 (C-1), 127.6, 127.7, 127.8, 128.4, 129.0, 129.7,
benzyl), 82.5, 82.8 (C-3, C-4), 85.9 (C-2), 87.3 (C-1), 120.0, 125.1, 133.1, 134.0, 135.5, 135.6 ppm. C41H42O5SeSi (721.8): calcd. C
26.7 [C(CH3)3], 62.8 (C-5), 72.2 (CH2-benzyl), 82.8, 82.8, 84.2 (C-
127.1, 127.6, 127.6, 127.7, 127.8, 127.9, 128.3, 129.6, 133.2, 133.2, 68.22, H 5.86; found C 68.24, H 5.97.
135.5, 137.3, 141.2, 143.1, 154.3 (CO-FMOC) ppm. C45H48O6SSi
Phenyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-1-seleno-α-D-arabin-
(745.0): calcd. C 72.55, H 6.49; found C 72.85, H 6.26.
ofuranoside (28): Compound 27 (271 mg, 0.37 mmol) was de-
benzoylated by the procedure described for the preparation of 22.
Chromatography (petroleum ether/ethyl acetate, 8:1) gave 28 as a
Ethyl 3-O-Benzyl-5-O-pivaloyl-1-thio-α- -arabinofuranoside (25):
D
Thioglycoside 18 (748 mg, 2.63 mmol) was dissolved in pyridine
(5 mL) at 0 °C. DMAP (32 mg, 0.26 mmol) and pivaloyl chloride colorless oil (194 mg, 84%). [α]2D5 ϭ ϩ188 (c ϭ 1.27 in chloroform).
(0.42 mL, 3.42 mmol) were then added, and the mixture was left at
0 °C for 1.5 h. Workup and chromatography with petroleum ether/
ethyl acetate (4:1) gave the 2,5-dipivaloylated compound (206 mg,
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.02 (s, 9 H, tBu), 3.67
2 3 2
(dd, J5,5 ϭ 11.5, J5,4 ϭ 2.0 Hz, 1 H, 5-H), 3.88 (dd, J5,5 ϭ 11.5,
3
3J5,4 ϭ 2.5 Hz, 1 H, 5-H), 4.04 (d, JOH,2 ϭ 11.0 Hz, 1 H, 2-OH),
17%), together with 25 (635 mg, 65%) as a colorless oil. [α]2D5
ϭ
4.06 (m, 1 H, 3-H), 4.41 (m, 1 H, 4-H), 4.56 and 4.74 (2 d, 2J ϭ
3
ϩ158 (c ϭ 1.23 in chloroform). 1H NMR (250 MHz, CDCl3, 25 12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 4.60 (d, J2,OH ϭ 11.0 Hz, 1 H, 1
°C): δ ϭ 1.31 (t, 3J ϭ 7.5 Hz, 3 H, SCH2CH3), 2.63 and 2.71 (2 H, 2-H), 5.87 (br. s, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3,
2
3
2
dq, J ϭ 13.0, J ϭ 7.5 Hz, 2 H, SCH2CH3), 3.83 (dd, J3,4 ϭ 6.0, 25 °C): δ ϭ 19.0 [C(CH3)3], 26.7 [C(CH3)3], 63.7 (C-5), 72.0 (CH2-
3
3
3J3,2 ϭ 3.5 Hz, 1 H, 3-H), 4.18 (ddd, J2,OH ϭ 6.0, J2,3 ϭ 3.5,
benzyl), 79.1, 84.5, 84.9 (C-2, C-3, C-4), 92.2 (C-1), 127.2, 127.8,
3J2,1 ϭ 3.5 Hz, 1 H, 2-H), 4.19 (dd, J5,5 ϭ 12.0, J5,4 ϭ 5.0 Hz, 1 127.9, 128.5, 129.1, 130.0, 133.6, 135.5, 135.6, 137.3 ppm.
2
3
2
3
H, 5-H), 4.28 (dd, J5,5 ϭ 12.0, J5,4 ϭ 3.0 Hz, 1 H, 5-H), 4.34 C34H38O4SeSi (617.7): calcd. C 66.11, H 6.20; found C 66.15, H
3
3
3
(ddd, J4,3 ϭ 6.0, J4,5 ϭ 5.0, J4,5 ϭ 3.0 Hz, 1 H, 4-H), 4.61 and
6.15.
4.71 (2 d, 3J ϭ 12.0 Hz, 2 ϫ H, CH2-benzyl), 5.14 (d, J1,2
ϭ
3
Phenyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-2-O-(4-methoxyben-
zyl)-1-seleno-α-D-arabinofuranoside (29): Treatment of 28 (250 mg,
3.5 Hz, 1 H, 1-H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C):
δ ϭ 15.1 (SCH2CH3), 25.4 (SCH2CH3), 27.1 [C(CH3)3], 39.0
[C(CH3)3], 63.4 (C-5), 72.4 (CH2-benzyl), 79.3, 81.0, 84.5 (C-2, C-3,
C-4), 89.8 (C-1), 127.8, 128.0, 128.5, 137.4, 178.1 (CO-ester) ppm.
C19H28O5S (368.5): calcd. C 61.93, H 7.66; found C 61.64, H 7.91.
0.40 mmol) with BEMP (293 µL, 1.01 mmol) and 4-methoxybenzyl
bromide (203 mg, 1.01 mmol) by the procedure described for the
preparation of 23 gave 29 as a colorless oil (224 mg, 75%) after
chromatography (petroleum ether/ethyl acetate, 14:1). [α]2D5 ϭ ϩ66
Ethyl 3-O-Benzyl-2-O-(4-methoxybenzyl)-5-O-pivaloyl-1-thio-α-
D-
(c ϭ 0.98 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ
3
arabinofuranoside (26): Compound 25 (475 mg, 1.29 mmol) in ace- 1.01 (s, 9 H, SitBu), 3.79 (s, 3 H, OCH3), 3.83 (d, J5,4 ϭ 5.0 Hz,
tonitrile (3.5 mL) was treated at 0 °C with BEMP (0.93 mL,
3.22 mmol) and a solution of 4-methoxybenzyl bromide (648 mg,
3.22 mmol) in acetonitrile (3 mL). After 2 h, the mixture was di-
2 H, 5-H), 4.05 (dd, 3J3,4 ϭ 5.5, 3J3,2 ϭ 2.5 Hz, 1 H, 3-H), 4.24 (m,
3
3J2,3 ϭ 2.5, J2,1 ϭ 2.0 Hz, 1 H, 2-H), 4.38 and 4.51 (2 d, 2J ϭ
11.5 Hz, 2 ϫ 1 H, CH2-benzyl), 4.40 (m, 1 H, 4-H), 4.52 (s, 2 H,
3
luted with CH2Cl2, hydrolyzed with satd. NaHCO3 solution CH2-methoxybenzyl), 5.87 (d, J1,2 ϭ 2.0 Hz, 1 H, 1-H) ppm. 13C
(6 mL), and vigorously stirred for 1.5 h. CH2Cl2 extraction and
chromatography (petroleum ether/ethyl acetate, 10:1) gave 26 as a
colorless oil (427 mg, 67%). [α]2D5 ϭ ϩ110 (c ϭ 1.07 in chloroform).
NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 19.2 [C(CH3)3], 26.7
[C(CH3)3], 55.2 (CH3O), 63.2 (C-5), 71.4 and 72.0 (CH2-benzyl),
83.0, 83.3, 87.2 (C-2, C-3, C-4), 88.2 (C-1), 113.8, 127.3, 127.6,
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.17 [s, 9 H, C(CH3)3], 128.4, 128.9, 129.4, 129.6, 130.7, 133.3, 133.6, 135.6, 137.7, 159.3
1.31 (t, 3J ϭ 7.5 Hz, 3 H, SCH2CH3), 2.62 and 2.72 (2 dq, 2J ϭ ppm.
3
13.0, J ϭ 7.5 Hz, 2 H, SCH2CH3), 3.81 (s, 3 H, OMe), 3.85 (dd,
8-Methoxycarbonyloctyl 3-O-Benzyl-5-O-tert-butyldiphenylsilyl-α-
3J3,4 ϭ 7.0, 3J3,2 ϭ 3.0 Hz, 1 H, 3-H), 3.94 (dd, 3J2,3 ϭ 3.0, 3J2,1
2.5 Hz, 1 H, 2-H), 4.18 (dd, J5,5 ϭ 12.0, J5,4 ϭ 6.0 Hz, 1 H, 5-
ϭ
D-arabinofuranoside (30): Silylation of 16 (103 mg, 0.25 mmol) was
2
3
accomplished by the procedure described for the preparation of 21.
Chromatography (petroleum ether/ethyl acetate, 6:1) gave 30 as a
colorless oil (113 mg, 69%). [α]2D5 ϭ ϩ60 (c ϭ 1.24 in chloroform).
1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.02 [s, 9 H, SiC(CH3)3],
2
3
H), 4.28 (dd, J5,5 ϭ 12.0, J5,4 ϭ 3.0 Hz, 1 H, 5-H), 4.32 (ddd,
3J4,3 ϭ 7.0, J4,5 ϭ 6.0, J4,5 ϭ 3.0 Hz, 1 H, 4-H), 4.46 and 4.54 (2
d, 3J ϭ 12.0 Hz, 2 ϫ H, OCH2C6H4OCH3), 4.41 and 4.56 (2 d,
3J ϭ 11.5 Hz, 2 ϫ H, CH2-benzyl), 5.34 (d, 3J1,2 ϭ 2.5 Hz, 1 H, 1-
H) ppm. 13C NMR (62.89 MHz, CDCl3, 25 °C): δ ϭ 14.9
(SCH2CH3), 25.2 (SCH2CH3), 27.0 [C(CH3)3], 38.7 [C(CH3)3], 55.1
(OMe), 63.0 (C-5), 71.6, 72.1 (CH2-benzyl), 78.5, 83.6, 87.2 (C-2,
C-3, C-4), 88.0 (C-1), 113.7, 127.7, 127.8, 128.3, 129.2, 129.6, 137.3,
159.3, 178.0 ppm. C27H36O6S (488.6): calcd. C 66.37, H 7.43; found
C 66.26, H 7.30.
3
3
3
1.24Ϫ1.40 and 1.52Ϫ1.66 (2 m, octyl), 2.29 (t, J ϭ 7.5 Hz, 2 H,
3
CH2CO-octyl), 3.26 (d, JOH,2 ϭ 10.5 Hz, 1 H, 2-OH), 3.46 (dt,
2
2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.57 (dd, J5,5 ϭ 11.0,
2
3J5,4 ϭ 3.0 Hz, 1 H, 5-H), 3.66 (s, 3 H, OMe), 3.71 (dt, J ϭ 9.5,
2
3
3J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.81 (dd, J5,5 ϭ 11.0, J5,4
ϭ
3
3
2.5 Hz, 1 H, 5-H), 3.98 (dd, J4,3 ϭ 3.0, J4,5 ϭ 2.5 Hz, 1 H, 4-H),
4.17 (dd, J3,4 ϭ 3.0, J3,2 ϭ 2.0 Hz, 1 H, 3-H), 4.18 (dd, J2,OH
3
3
3
ϭ
3
2
Phenyl
leno-α-
2-O-Benzoyl-3-O-benzyl-5-O-tert-butyldiphenylsilyl-1-se-
D-arabinofuranoside (27): Compound 20 (260 mg,
10.5, J2,3 ϭ 2.0 Hz, 1 H, 2-H), 4.52 and 4.70 (2 d, J ϭ 12.0 Hz,
2 ϫ 1 H, CH2-benzyl), 5.06 (s, 1 H, 1-H) ppm. 13C NMR
(62.89 MHz, CDCl3, 25 °C): δ ϭ 19.1, 24.9, 26.0, 26.7, 29.1, 29.2,
29.6, 34.1 (CH2-octyl), 51.5 (OMe), 64.4 (C-5), 67.6 (OCH2-octyl),
71.9 (CH2-benzyl), 77.9, 84.1, 84.7 (C-2, C-3, C-4), 108.7 (C-1),
0.54 mmol) was silylated by the procedure described for the pre-
paration of 22. After chromatography with toluene/ethyl acetate
(12:1), 27 was obtained as a colorless oil (334 mg, 86%). [α]2D5
ϭ
ϩ108 (c ϭ 0.92 in chloroform). 1H NMR (250 MHz, CDCl3, 25 127.7, 127.8, 127.8, 127.9, 128.4, 129.9, 130.0, 132.3, 132.4, 135.6,
°C): δ ϭ 0.98 (s, 9 H, tBuSi), 3.82 (dd, 2J5,5 ϭ 12.0, 3J5,4 ϭ 5.5 Hz, 135.7, 138.0, 174.4 (CO-ester) ppm. C38H52O7Si (648.9): calcd. C
2
3
1 H, 5-H), 3.89 (dd, J5,5 ϭ 11.0, J5,4 ϭ 5.0 Hz, 1 H, 5-H), 4.21 70.33, H 8.08; found C 70.45, H 7.80.
3872 Eur. J. Org. Chem. 2002, 3864Ϫ3873

Elaboration of Monoarabinofuranosidic Building Blocks
8-Methoxycarbonyloctyl 3-O-Benzyl-5-O-pivaloyl-α- -arabinofur-
FULL PAPER
J. D. Ayers, T. L. Lowary, C. B. Morehouse, G. S. Besra, Bioorg.
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[11]
D
anoside (31): Compound 16 (251 mg, 0.61 mmol) was pivaloated
according to the procedure described for the preparation of 25 to
give 31 as a colorless oil (241 mg, 80%) after chromatography (pet-
roleum ether/ethyl acetate, 3:1). [α]2D5 ϭ ϩ74 (c ϭ 1.18 in chloro-
form). 1H NMR (250 MHz, CDCl3, 25 °C): δ ϭ 1.18 [s, 9 H,
C(CH3)3], 1.27Ϫ1.35 and 1.50Ϫ1.65 (2 m, octyl), 1.92 (d, 3JOH,2 ϭ
6.5 Hz, 1 H, 2-OH), 2.30 (t, 3J ϭ 7.5 Hz, 2 H, CH2CO-octyl), 3.42
[12]
[13]
´
´
[14]
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2
3
(dt, J ϭ 9.5, J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.66 (s, 3 H, OMe),
3.67 (dt, 2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.75 (dd, 3J3,4 ϭ
6.0, 3J3,2 ϭ 3.0 Hz, 1 H, 3-H), 4.14 (dd, 2J5,5 ϭ 11.0, 3J5,4 ϭ 4.0 Hz,
[18]
[19]
[20]
3
3
3
1 H, 5-H), 4.22 (ddd, J4,3 ϭ 6.0, J4,5 ϭ 4.0, J4,5 ϭ 2.5 Hz, 1 H,
3
3
4-H), 4.23 (dd, J2,OH ϭ 6.5, J2,3 ϭ 3.0 Hz, 1 H, 2-H), 4.29 (dd,
2J5,5 ϭ 11.0, J5,4 ϭ 2.5 Hz, 1 H, 5-H), 4.60 and 4.69 (2 d, 2J ϭ
3
F. Barresi, O. Hindsgaul, J. Am. Chem. Soc. 1991, 113,
12.0 Hz, 2 ϫ 1 H, CH2-benzyl), 4.92 (s, 1 H, 1-H) ppm. 13C NMR
(62.89 MHz, CDCl3, 25 °C): δ ϭ 24.8, 25.9, 27.1, 29.1, 29.4, 34.0,
38.8 (CH2-octyl), 51.5 (OMe), 63.6 (C-5), 67.7 (OCH2-octyl), 72.4
(CH2-benzyl), 79.7, 80.6, 85.0 (C-2, C-3, C-4), 108.0 (C-1), 127.8,
128.0, 128.5, 137.6, 174.4, 178.1 (CO-esters) ppm. C27H42O8
(494.6): calcd. C 65.56, H 8.56; found C 65.40, H 8.91.
9376Ϫ9377.
[21]
[22]
[23]
[24]
[25]
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[26]
[27]
Octyl 2-O-Benzoyl-5-O-tert-butyldiphenylsilyl-α-D-arabinofurano-
side (32): Compound 15 (140 mg, 0.38 mmol) was silylated as de-
scribed for the preparation of 21. Chromatography (toluene/acet-
one, 100:3) gave 32 as a colorless oil (211 mg, 77%). [α]2D5 ϭ ϩ33
(c ϭ 1.19 in chloroform). 1H NMR (250 MHz, CDCl3, 25 °C):
δ ϭ 0.88 (m, 3 H, CH3-octyl), 1.04 (s, 9 H, tBuSi), 1.24Ϫ1.40 and
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C. Krog-Jensen, S. Oscarson, J. Org. Chem. 1996, 61,
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3
1.56Ϫ1.68 (2 m, 2H and 10 H, CH2-octyl), 3.08 (m, J ϭ 6.0 Hz,
1 H, 3-OH), 3.48 (dt, 2J ϭ 9.5, 3J ϭ 6.5 Hz, 1 H, OCH2-octyl),
2007Ϫ2010.
2
3
N. K. Kochetkov, A. Y. Khorlin, A. F. Bochkov, I. G. Yazlovet-
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3.74 (dt, J ϭ 9.5, J ϭ 6.5 Hz, 1 H, OCH2-octyl), 3.83Ϫ3.90 (m,
3
2 H, 5-H), 4.18Ϫ4.23 (m, 2 H, 3-H, 4-H), 5.10 (br. d, J2,1
ϭ
1.5 Hz, 1 H, 2-H), 5.22 (br. s, 1 H, 1-H) ppm. 13C NMR
(62.89 MHz, CDCl3, 25 °C): δ ϭ 14.1, 19.3, 22.7, 26.1, 26.7, 26.7,
26.8, 29.2, 29.3, 29.5, 31.8 (CH2-octyl), 63.6 (C-5), 67.9 (OCH2-
octyl), 76.8, 84.7, 85.2 (C-2, C-3, C-4), 105.1 (C-1), 127.7, 128.5,
129.7, 129.8, 133.3, 133.5, 135.6, 166.5 (CO-benzoyl) ppm.
C36H48O6Si (604.9): calcd. C 71.49, H 8.00; found C 71.40, H 8.37.
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´
Support of this work by the Comite Mixte Inter Universitaire
Franco-Marocain (AI, 00/235/SVS) is gratefully acknowledged.
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Received June 5, 2002
[O02305]
Eur. J. Org. Chem. 2002, 3864Ϫ3873
3873