A short and practical route to 3-O-benzoyl azidosphingosine

Article abstract of DOI:10.1016/S0008-6215(00)00323-2

A short and practical route to 3-O-benzoyl azidosphingosine from D-xylose is described. The synthesis avoids the use of expensive and hazardous chemicals (i.e. mercury salts), and it is reproducible up to at least a 20 g scale. Furthermore, the synthesis proceeds to 3-O-benzoyl azidosphingosine with a minimum of protection group manipulation, by exploiting a regioselective protection of the primary HO-1 with thexyldimethylsilyl chloride.

Full text of DOI:10.1016/S0008-6215(00)00323-2

www.elsevier.nl/locate/carres
Carbohydrate Research 331 (2001) 91–94
Note
A short and practical route to 3-O-benzoyl
azidosphingosine
Jo¨rgen Ohlsson, * Go¨ran Magnusson 1
Organic Chemistry 2, Center for Chemistry and Chemical Engineering, Lund Uni6ersity, PO Box 124,
SE-221 00 Lund, Sweden
Received 20 September 2000; accepted 12 December 2000
Abstract
A short and practical route to 3-O-benzoyl azidosphingosine from
D
-xylose is described. The synthesis avoids the
use of expensive and hazardous chemicals (i.e. mercury salts), and it is reproducible up to at least a 20 g scale.
Furthermore, the synthesis proceeds to 3-O-benzoyl azidosphingosine with a minimum of protection group
manipulation, by exploiting a regioselective protection of the primary HO-1 with thexyldimethylsilyl chloride.
© 2001 Elsevier Science Ltd. All rights reserved.
Keywords: Glycolipid; Azidosphingosine; Synthesis
Glycosphingolipids are ubiquitous compo-
nents of cell membranes, where they function
as receptors for proteins, antibodies, and
other biomolecules, for example during the
initial phase of infection by pathogens.1 An
important component of the glycosphingo-
the carbon–carbon bond-formation8 has been
highly reproducible, and thus, suitable for
large scale preparation. However, the pub-
lished procedure uses mercury salts and in-
volves three protection and deprotection steps
for the transformation of azidosphingosine
into 1. We herein describe a modified synthe-
sis that avoids expensive chemicals, the use of
mercury salts and is reproducible on up to at
least a 20 g scale. Furthermore it proceeds
with a minimum protection groups manipula-
tions to 3-O-benzoyl azidosphingosine (1).
The synthesis of 1 starts with the conversion
lipids is
D-erythro-sphingosine. 3-O-Ben-
zoyl azidosphingosine (1) is the preferable gly-
cosyl acceptor in the preparation of these
glycolipids, since it minimizes the problem
with inferior yield of byproducts that gener-
ally accompanies glycosylations of suitably
protected ceramide or sphingosine deriva-
tives.2–4 A number of syntheses of azidosphin-
gosine have been published.3,5–9 In our study,
a synthesis involving a Grignard reagent for
of
-xylose to dithioethyl protected xylose,10,11
D
which without purification was converted to
212 with 2,2-dimethoxypropane and a catalytic
amount p-TsOH (Scheme 1). Compound 2
was purified by dry column chromatography13
giving 90 g in three 400 mL portions of sol-
vent. Deprotection of the dithioacetal 2 was
accomplished using I2 and NaHCO3 in ace-
* Corresponding author. Tel.: +46-46-2228211; fax: +46-
46-2228209.
E-mail address: jorgen.ohlsson@orgk2.lth.se (J. Ohlsson).
1 Deceased June 2000.
0008-6215/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0008-6215(00)00323-2

92
J. Ohlsson, G. Magnusson / Carbohydrate Research 331 (2001) 91–94
Scheme 1. (a) Aq HCl, EtSH.10,11 (b) 2,2-Dimethoxypropane, p-TsOH. (c) I2, NaHCO3, acetone, H2O. (d) ThexMe2SiCl, pyridine.
(e) MsCl, pyridine. (f) NaN3, 18-crown-6, DMF, 95 °C. (g) 1% aq HCl in EtOH.
tone–water14 giving a yield of 3 equivalent to
that reported using HgO–HgCl2.11 Compound
4 was prepared from 3 according to the re-
ported procedure8 and then selectively silyl-
ated in high yield with thexyldimethylsilyl-
chloride in pyridine at room temperature to
furnish 5. Other protection groups and condi-
tions (for example TIPS–ether, TBDMS–
ether and chloroacetate) were evaluated, but
they showed lower regioselectivity, gave ben-
zoyl migration, or lower yields in the follow-
0.070 mm) and TLC was performed on
Kieselgel 60 F254 plates (E. Merck).
Dichloromethane was distilled from CaH2.
,
Pyridine was stored over 4 A MS. DMF was
distilled under reduced pressure.
(2S,3R,4E)-2-Azido-3-benzoyloxy-octadec-
4-ene-1-ol (1).—To compound 7 (631 mg,
1.10 mmol) was added a 1% mixture of concd
aq HCl in EtOH (19 mL) and the solution was
stirred at rt overnight. A second aliquot of
concd aq HCl (0.2 mL) was added and the
resulting solution was stirred for 2 days.
Evaporation under reduced pressure gave a
crude that was purified as reported7 to give 1
ing steps. Treating compound
5
with
methanesulfonyl chloride in pyridine at room
temperature gave the mesylate 6. Attempts
were made to use trifluoromethanesulfonate as
a leaving group, but this turned out to be
unstable. Substitution of the mesylate with
NaN3 using 18-crown-6 as catalyst in DMF at
95°C for 4 days furnished the fully protected
azidosphingosine in 72% yield. Basic cleavage
(F−) of the silyl protection group gave ben-
zoyl migration as a major side reaction. For-
tunately, mild acidic hydrolysis15 furnished the
3-O-benzoylprotected azidosphingosine (1) in
good yield after purification on a chroma-
totron.
1
(347 mg, 73%). H NMR and [h]2D5 were in
agreement with reported data.2,7
2,3:4,5-Di-O-isopropylidene-1,1-dithioethyl-
D-xylose
(2).—Crude
1,1-dithioethyl- -
D
xylose11 was dissolved in 2,2-dimethoxy-
propane (400 mL), a catalytic amount of p-
toluenesulfonic acid was added, and the re-
sulting mixture was stirred overnight. Aq NH3
(25%) was added until the reaction mixture
was neutral (moist pH paper), and the mixture
was concentrated and flash chromatographed
(dry column SiO2 technique, 10:1“6:1 hep-
tane–EtOAc gradient) to give 2 (90 g, 80%).
1H NMR was in agreement with reported
data.16
1. Experimental
2,3:4,5-Di-O-isopropylidene- -xylose (3).—
D
General methods.—NMR spectra were
To a solution of 2 (5.00 g, 14.9 mmol) in
acetone (100 mL) and water (2.3 mL) at 0°C
was added NaHCO3 (5.5 g, 65.4 mmol) and I2
(8.3 g, 32.7 mmol). The mixture was slowly
warmed to rt and stirred overnight. A second
portion of NaHCO3 (0.62 g, 7.4 mmol) and I2
(1.89 g, 7.4 mmol) was added. After 5 h, a
satd aq solution of Na2S2O3 was added until
the reaction mixture was colorless. The mix-
1
recorded with a 400 MHz instrument. H
NMR spectral assignments were made by
COSY experiments. Concentrations were
made using rotary evaporation with a bath
temperature at or below 40°C. Optical rota-
tions were measured with a Perkin–Elmer 141
polarimeter. Flash chromatography was per-
formed on Grace Amicon Silica gel 60 (0.035–

J. Ohlsson, G. Magnusson / Carbohydrate Research 331 (2001) 91–94
93
7.6, 15.6 Hz, ꢀCHꢁCHOBz), 4.85–4.81 (m, 1
H, CHOMs), 3.94 (dd, 1 H, J 3.4, 11.6 Hz,
SiOCH2), 3.86 (dd, 1 H, J 4.8, 11.4 Hz,
SiOCH2), 2.99 (s, 3 H, SAc), 2.10–2.04 (m, 2
H, ꢀCHꢁCH2), 1.64 (heptet, 1 H, J 6.9 Hz,
CHMe2), 1.40–1.23 (m, 22 H, CH2), 0.91–
0.87 (m, 15 H, (CH3)21C3 H, CH3, (CH3)2C),
0.12 (s, 6 H, (CH3)2Si). C NMR (CDCl3): l
165.6, 139.0, 133.6, 130.4, 130.2, 128.9, 123.4,
83.4, 73.6, 62.7, 39.2, 34.5, 32.8, 32.4, 32.3,
30.1, 30.1, 30.0, 29.9, 29.8, 29.6, 29.5, 29.1,
25.7, 23.1, 20.7, 20.6, 19.0, 18.9, 14.6, −3.1,
−3.2. HRMS Calcd for C34H60O6SSiNa
(M+Na): m/z 647.3778; Found: m/z
647.3771.
ture was partly concentrated and the aq phase
was saturated with NaCl and extracted with
EtOAc (6×100 mL). The combined extracts
were dried (Na2SO4), concentrated, and flash
chromatographed (4:1“1:2 heptane–EtOAc
1
gradient) to give 3 (3.12 g, 84%). H NMR
was in agreement with reported data.17
(2S,3R,4E)-3-Benzoyloxy-1-thexyldimethyl-
silyloxy-octadec-4-ene-2-ol (5).—To a solu-
tion of 4 (1.00 g, 2.47 mmol) in anhyd pyri-
dine (14 mL) at −40°C was added
thexyldimethylsilylchloride (0.580 mL, 2.97
mmol). The mixture was stirred overnight at
rt, then diluted with CH2Cl2 (20 mL), and
washed with satd aq NaHCO3 (15 mL). The
aqueous phase was extracted with CH2Cl2
(3×10 ml), and the organic phases were com-
bined, dried (Na2SO4), concentrated, and flash
chromatographed (10:1 heptane–EtOAc) to
give 5 (1.28 g, 95%). [h]2D3 +12 (c 0.9, CHCl3).
1H NMR (CDCl3): l 8.10–8.06 (m, 2 H, Ph),
7.59–7.54 (m, 1 H, Ph), 7.47–7.43 (m, 2 H,
Ph), 5.95–5.88 (m, 1 H, ꢀCHꢁCH2), 5.61–
5.52 (m, 2 H, ꢀCHꢁCHOBz), 3.85–3.80 (m, 1
H, CHOH), 3.70 (ddd, 2 H, J 4.0, 6.2, 11.2
Hz, SiOCH2), 2.51 (d, 1 H, J 6.3 Hz, OH),
2.10–2.04 (m, 2 H, ꢀCHꢁCH2), 1.64 (heptet, 1
H, J 6.9 Hz, CHMe2), 1.40–1.23 (m, 22 H,
CH2), 0.91–0.87 (m, 15 H, (CH3)2CH, CH3,
(CH3)2C)), 0.12 (s, 6 H, (CH3)2Si). 13C NMR
(CDCl3): l 166.3, 137.6, 133.3, 130.9, 130.1,
128.7, 124.9, 76.3, 73.7, 63.7, 34.6, 32.8, 32.4,
30.1, 30.1, 30.0, 29.9, 29.8, 29.6, 29.3, 29.3,
25.6, 23.1, 20.7, 20.7, 19.0, 19.0, 14.6, −3.1.
HRMS Calcd for C33H58O4SiNa (M+Na):
m/z 569.4002; Found: m/z 569.4002.
(2R,3R,4E) - 2 - Azido - 3 - benzoyloxy - 1-
thexyldimethylsilyloxy-octadec-4-ene (7).—To
a solution of 6 (3.70 g, 5.92 mmol) in freshly
distilled DMF (50 mL) was added NaN3 (3.9
g, 59 mmol) and a catalytic amount of 18-
crown-6, and the mixture was stirred at 95°C
for 4 days. The reaction mixture was poured
into 1:1 Et2O–water (400 mL) and the
aqueous phase was extracted with Et2O (3×
80 mL). The organic phases were combined,
washed with brine (1×80 mL), dried
(MgSO4), concentrated, and flash chro-
matographed (19:1“10:1 heptane–EtOAc
gradient) to give 7 (2.44 g, 72%) and recovered
starting material (0.61 g, 16%). [h]2D3 −17 (c
1
1.0, CHCl3). H NMR (CDCl3): l 8.09–8.06
(m, 2 H, Ph), 7.61–7.56 (m, 1 H, Ph), 7.49–
7.44 (m, 2 H, Ph), 5.97–5.90 (m, 1 H,
ꢀCHꢁCH2),
5.60–5.54
(m,
2
H,
ꢀCHꢁCHOBz), 3.80 (m, 1 H, CHN3), 3.73–
3.65 (m, 2 H, SiOCH2), 2.11–2.06 (m, 2 H,
ꢀCHꢁCH2), 1.64 (heptet, 1 H, J 6.9 Hz,
CHMe2), 1.40–1.23 (m, 22 H, CH2), 0.91–
0.87 (m, 15 H, (CH3)21C3 H, CH3, (CH3)2C),
0.12 (s, 6 H, (CH3)2Si). C NMR (CDCl3): l
165.7, 139.0, 133.5, 130.5, 130.2, 128.9, 123.6,
75.0, 66.3, 62.9, 34.5, 32.8, 32.4, 30.1, 30.1,
30.0, 29.9, 29.8, 29.6, 29.2, 25.5, 23.1, 20.6,
20.6, 18.9, 18.9, 14.6, −3.2, −3.2. HRMS
Calcd for C33H57N3O3SiNa (M+Na): m/z
594.4067; Found: m/z 594.4062.
(2S,3R,4E)-3-Benzoyloxy-2-methylsulfonyl-
oxy - 1 - thexyldimethylsilyloxy - octadec - 4 - ene
(6).—To a solution of 5 (1.23 g, 2.25 mmol)
in anhyd pyridine (20 mL) at 0°C was added
methanesulfonyl chloride (0.261 mL, 3.38
mmol) and the mixture was stirred at rt
overnight. The reaction was quenched by ad-
dition of MeOH (4 mL), and the mixture was
co-concentrated with toluene. The residue was
flash chromatographed (10:1 heptane–EtOAc)
to give 6 (1.35 g, 96%). [h]2D3 −0.6 (c 0.8,
1
CHCl3). H NMR (CDCl3): l 8.11–8.08 (m, 2
Acknowledgements
H, Ph), 7.61–7.56 (m, 1 H, Ph), 7.49–7.44 (m,
2 H, Ph), 6.04–5.95 (m, 1 H, ꢀCHꢁCH2), 5.76
(t, 1 H, J 7.4 Hz, CHOBz), 5.50 (dd, 1 H, J
This work was supported by the Swedish
Natural Science Research Council and by a

94
J. Ohlsson, G. Magnusson / Carbohydrate Research 331 (2001) 91–94
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grant from the programme ‘Glycoconjugates
in Biological Systems’ sponsored by the
Swedish Foundation for Strategic Research.
We are grateful to Dr Ulf J. Nilsson for
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