Concise synthesis of the unnatural sphingosine and psychosine enantiomer

Article abstract of DOI:10.1002/ejoc.201000024

The accumulation of psychosine (galactosyl sphingosine) has been associated with the pathogenesis of Krabbe disease; however, the exact mechanism, of its cytotoxicity remains unclear. Herein, we describe the synthesis of the unnatural enantiomer of erythr

Full text of DOI:10.1002/ejoc.201000024

FULL PAPER
DOI: 10.1002/ejoc.201000024
Concise Synthesis of the Unnatural Sphingosine and Psychosine Enantiomer
Archana R. Parameswar,[a] Jacqueline A. Hawkins,[b] Laurel K. Mydock,[a] Mark S. Sands,[b]
and Alexei V. Demchenko*[a]
Keywords: Carbohydrates / Enantioselectivity / Glycosylation / Sphingolipids
The accumulation of psychosine (galactosyl sphingosine) has
been associated with the pathogenesis of Krabbe disease;
however, the exact mechanism of its cytotoxicity remains un-
clear. Herein, we describe the synthesis of the unnatural en-
antiomer of erythro-sphingosine, psychosine, and related de-
rivatives thereof that would allow for the mechanistic eluci-
dation of the toxicity of psychosine.
In order to resolve this fundamental question, we needed
to discriminate between the two plausible mechanisms of
toxicity. As such, an investigation of the enantiomer of nat-
ural psychosine (ent-psychosine, 1) was seen as a reliable
approach whereby the two differing pathways could be dis-
tinguished. Because of the high stereochemical specificity
of protein interactions, it can be assumed that the ent-psy-
chosine would no longer be able to bind to any partner
proteins. If psychosine toxicity is due to protein interac-
tions, ent-psychosine would not exhibit any cytotoxic effect.
However, if the toxicity of psychosine is mediated through
LRs within the cell membrane, the hydrophobic interac-
tions between ent-psychosine and the achiral lipid mem-
brane will be preserved, along with toxicity. Previously,
Covey and others have made considerable progress elucidat-
ing the mechanisms of various signaling pathways by syn-
thesizing and applying unnatural ent-steroids.[9] Hence, the
synthesis of unnatural ent-psychosine (1) and the investiga-
tion of its mode of action appealed to us as an important
first step toward the elucidation of the psychosine toxicity
pathways in GLD.
Introduction
Psychosine (galactosyl sphingosine) is a natural glyco-
sphingolipid found in a variety of mammalian cells. While
it typically exists in very low concentrations, elevated levels
of psychosine are linked to the pathogenesis of Globoid
Cell Leukodystrophy (GLD) or Krabbe disease.[1,2] In
GLD, the abnormal accumulation of psychosine is due to
a genetic deficiency in galactosylceramide-β-galactosidase
(also referred to as galactosyl ceramidase) activity, a de-
gradative lysosomal enzyme.[3] Additionally, psychosine is
highly cytotoxic[4] and is known to lead to the death of olig-
odendrocytes, the myelin-producing cells in the nervous sys-
tem.[5] As a consequence, patients with GLD suffer from a
number of neurological deficits and typically die before the
age of five.[2] Despite its obvious relevance to the pathogen-
esis of GLD,[6] very little is understood about the mecha-
nisms underlying the toxicity of psychosine. Initially, it was
presumed that the interactions between psychosine and spe-
cific protein partners were solely responsible for the result-
ant toxicity.[7] However, more recently it has been demon-
strated that the accumulation of psychosine in the central
nervous system (CNS) may also interfere with membrane
lipid raft (LR) function, significantly disrupting cellular sig-
naling processes.[8] As such, it remains unclear which of
these general mechanisms is responsible for the toxicity of
psychosine, or whether both pathways are involved during
different stages of the disease.
In spite of the considerable progress that has been made
toward the synthesis of various glycosphingolipids and ana-
logues thereof,[10] there still remains a challenge in ob-
[a] Department of Chemistry and Biochemistry, University of
Missouri – St. Louis,
One University Boulevard, St. Louis, Missouri 63121, USA
Fax: +1-314-516-5342
E-mail: demchenkoa@umsl.edu
[b] Department of Internal Medicine and Department of Genetics,
Washington University School of Medicine,
St. Louis, Missouri 63110, USA
Figure 1. Sphingosine, Psychosine, and enantiomers thereof.
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3269
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A. V. Demchenko et al.
FULL PAPER
taining such targets in high yields, with minimal synthetic
steps and with complete stereochemical purity. These char-
acteristics are essential, as the interpretation of biological
toxicity studies often hinges on the differential action of
enantiomers. Herein, we report the synthesis of unnatural
ent-psychosine (1) from the chirally pure starting material
(Figure 1). Unlike a number of previously reported ap-
proaches to the synthesis of enantio- and diastereomeric
sphingosine analogues,[11] our synthetic target is derived
from a readily available carbohydrate precursor of the -
series containing predetermined stereocenters.
Scheme 2. Synthesis of perbenzoylated SBox -galactosyl donor 3.
Among a plethora of available approaches[14] for the syn-
thesis of ent-sphingosine precursor 4, we adapted a very
effective strategy developed by Schmidt et al. for the synthe-
sis of natural sphingosine from -arabitol.[15] Accordingly,
-arabitol was first converted into 1,3-O-benzylidene arabi-
tol 7 in 60% yield by using benzaldehyde in the presence of
HCl gas (Scheme 3).[16] Compound 7 was then subjected
to oxidative cleavage by using sodium periodate. Resulting
aldehyde 5, which was found to exist in the dimeric form
(as reported for similar analogous compounds),[17] was ob-
tained in 99% yield. Next, Wittig olefination of aldehyde 5
was accomplished by using (1-tetradecyl)triphenylphosphon-
ium bromide (TPPBr) in the presence of 2  PhLi/Bu2O
and 4  LiBr/THF to yield predominantly (E)-8. It was
found that the addition of LiBr can benefit the preferential
formation of E isomers[18] and proved essential in obtaining
a good isolated yield of 50% for compound 8. Nevertheless,
this reaction also yielded (Z)-8 in 11% yield; however, the
stereoisomers were easily separable by column chromatog-
raphy. The free hydroxy group in compound 8 was then
converted into an azide by sequential trifluoromethanesul-
fonation with triflic anhydride in pyridine, followed by
treatment with sodium azide in DMF. Resulting compound
9 was isolated in 62% yield over two steps. Acetal cleavage
of 9 was carried out by using p-toluenesulfonic acid in
methanol, and resulting diol intermediate 10 was obtained
in 80% yield. Lastly, compound 4 was obtained in 43%
yield through a three-step protocol involving sequential tri-
tylation with trityl chloride, benzoylation with benzoyl bro-
mide, and detritylation with BF3·Et2O. Intermediate 10 was
also deprotected by using PMe3 in THF to afford ent-sphin-
gosine (11) in 71% yield.
Results and Discussion
ent-Psychosine (1) is a complex glycosphingolipid that is
comprised of the sphingosine enantiomer (ent-sphingosine)
and -galactose moieties (Figure 1). Synthetically, we envis-
aged that fully protected precursor 2 could be assembled
from a suitable -galactose donor, such as S-benzoxazolyl
(SBox) -galactoside 3 (Scheme 1), whereas partially pro-
tected enantiomeric sphingosine derivative 4 could serve as
a suitable glycosyl acceptor. Although glycosyl donor 3
could be obtained in three steps from -galactose, as de-
scribed previously for the synthesis of its counterpart of the
-galacto series,[12,13] the synthesis of acceptor 4 required
careful retrosynthetic analysis. As depicted in Scheme 1, we
decided that the most suitable option would be to base the
synthesis on the inexpensive -arabitol, which contains a
predetermined stereochemistry at the C-2 and C-3 carbon
atoms that would be appropriate for our synthesis of ent-
sphingosine. Subsequent regioselective 1,3-O-benzylidene
protection, followed by oxidative cleavage with sodium per-
iodate, could then provide desired precursor 5.
Having obtained protected ent-sphingosine precursor 4,
we investigated its capability as a glycosyl acceptor. For this
purpose, it was subjected to glycosylation with SBox - and
-galactosyl donors 3 and 12 (Scheme 4). These glycosyl-
ations were promoted with silver(I) triflate to afford the cor-
responding glycosides 2 and 13 in 70 and 87% yield, respec-
tively. Complete deprotection of psychosine precursors 2
and 13 was accomplished by deacylation in the presence of
1  NaOMe in MeOH, followed by azide reduction by
Scheme 1. Retrosynthetic analysis of ent-psychosine (1).
To initiate this route, we first synthesized -galactosyl using PMe3 in THF. This sequence yielded target ent-psy-
donor 3 as shown in Scheme 2. Benzoylation of -galactose chosine (1) in 65% yield and its -galactose diastereomer
resulted in the formation of perbenzoate 6, which was sub- 14 in 63% yield. It should be noted that the use of PMe3
jected to sequential anomeric bromination and the intro- for the azide reduction step was found to be the most ad-
duction of the SBox leaving group by the protocol devel- vantageous,[19] as other methods that used H2S, HS(CH2)3-
oped in our laboratory for -sugars (Scheme 2).[12] Re- SH, PPh3, or NaBH4 either failed or yielded the unprotec-
sulting glycosyl donor 3 was obtained in 88% overall yield. ted derivatives in lower yields.
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Concise Synthesis of the Unnatural Sphingosine and Psychosine Enantiomer
Experimental Section
General: Column chromatography was performed on silica gel 60
(70–230 mesh); reactions were monitored by TLC on Kieselgel 60
F254. The compounds were detected by examination under UV
light and by charring with 10% sulfuric acid in methanol. Solvents
were removed under reduced pressure at Ͻ40 °C. ClCH2CH2Cl was
distilled from CaH2 directly prior to application. Methanol was
dried by heating at reflux with magnesium methoxide, distilled, and
stored under an argon atmosphere. Toluene was distilled from
CaH2 under an argon atmosphere and was heated at reflux for 2 h
before application. THF was distilled from metallic sodium by
using benzophenone as indicator under an argon atmosphere and
was heated at reflux for 2 h before use. Anhydrous pyridine, anhy-
drous DMF, and redistilled benzaldehyde were obtained from
Sigma–Aldrich and used as is. (1-Tetradecyl)triphenylphospho-
nium bromide and -galactose were purchased from TCI chemicals.
Molecular sieves (3 Å) were crushed and activated in vacuo at
390 °C during 8 h in the first instance and then for 2–3 h at 390 °C
directly prior to application. AgOTf was coevaporated with toluene
(3ϫ10 mL) and dried in vacuo for 2–3 h directly prior to applica-
tion. Optical rotations were measured with a Jasco P-1020 polari-
meter. Melting points were measured with a Thomas Hoover capil-
lary melting point apparatus. Unless noted otherwise, 1H NMR
spectra were recorded in CDCl3 at 300 MHz (Bruker Avance); 13C
NMR spectra and 2D experiments were recorded in CDCl3 at
75 MHz (Bruker Avance) or at 125 MHz (Bruker ARX-500).
HRMS determinations were made with a JEOL MStation (JMS-
700) Mass Spectrometer.
Scheme 3. Synthesis of ent-sphingosine acceptor 4.
Benzoxazolyl 2,3,4,6-Tetra-O-benzoyl-1-thio-β-L-galactopyranoside
(3): Benzoyl chloride (1.14 mL, 9.9 mmol) was added dropwise to a
stirring mixture of -galactose (0.255 g, 1.41 mmol) in dry pyridine
(3.0 mL) under an argon atmosphere at room temperature. Upon
completion (≈16 h), the reaction mixture was quenched by the ad-
dition of methanol (≈5 mL), evaporated, and coevaporated with
toluene (3ϫ25 mL). The residue was diluted with CH2Cl2 (50 mL),
washed with water (20 mL), 1  HCl (20 mL), water (20 mL),
NaHCO3 (2ϫ20 mL), and water (2ϫ20 mL). The organic layer
was separated, dried, and concentrated under reduced pressure.
The residue was purified by column chromatography on silica gel
(ethyl acetate/hexanes gradient elution) to afford 1,2,3,4,6-penta-
O-benzoyl--galactopyranoside (6; 0.98 g, 99%) as a white foam.
HBr (30% v/v) in glacial AcOH (1.0 mL) was added to a stirred
solution of pentabenzoate 6 (0.98 g, 1.4 mmol) in CH2Cl2 (5 mL)
at room temperature. Upon completion (≈2 h), the reaction mixture
was diluted with CH2Cl2 (50 mL), washed successively with ice-
cold water (20 mL), saturated aqueous NaHCO3 (2ϫ20 mL), and
cold water (3ϫ20 mL). The organic layer was separated, dried, and
concentrated in vacuo. The crude residue was purified by crystalli-
zation from anhydrous diethyl ether and hexanes to afford 2,3,4,6-
tetra-O-benzoyl-α--galactopyranosyl bromide (0.83 g, 89%) as
Scheme 4. Synthesis of ent-psychosine (1) and its -galactose ana-
logue 14.
Conclusions
In conclusion, we developed an efficient protocol for the
synthesis of enantiomeric sphingosine and psychosine de-
rivatives. The approach is based on sugar precursors, which
eliminates the need for a stereocontrolled synthesis and en- white crystals. Potassium benzoxazole-2-thiolate[12] (0.36 g,
1.9 mmol) was added to the stirring solution of the freshly prepared
2,3,4,6-tetra-O-benzoyl-α--galactopyranosyl bromide (0.83 g,
1.25 mmol) in dry acetone (8.0 mL) under an argon atmosphere at
room temperature. Upon completion (≈3 h), the mixture was di-
luted with CH2Cl2 (30 mL) and washed successively with 1% aque-
ous NaOH (2ϫ15 mL), saturated aqueous NaHCO3 (15 mL), and
water (3ϫ15 mL). The organic layer was separated, dried, and con-
centrated in vacuo. The residue was purified by column chromatog-
raphy on silica gel (hexane/EtOAc gradient elution) to afford title
compound 3 (0.92 g, 99%). Rf = 0.49 (ethyl acetate/hexanes, 3:7).
sures complete enantiomeric purity of the end product. It
is expected that the developed route would be suitable for
the synthesis and application of other classes of natural and
unnatural glycosphingolipids.[20] With the successful syn-
thesis of ent-psychosine (1) and its -galactose analogue 14,
the next step will be the biological evaluation of these com-
pounds, wherin the elucidation of the toxicity pathways of
psychosine in GLD afflicted mammalian nervous systems
will be determined. This research is currently under way in
our laboratories and will be reported in due course.
[α]2D3 = –130.77 (c = 1, CHCl3). H NMR: δ = 4.46 (dd, 1 H, 6a-
1
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H), 4.54–4.61 (m, 2 H, 5-H, 6b-H), 5.79 (dd, J2,3 = 8.8 Hz, J3,4
=
aromatic), 7.47–7.50 (m, 2 H, aromatic) ppm. 13C NMR: δ = 14.3,
3.4 Hz, 1 H, 3-H), 5.97–6.07 (m, 3 H, 1-H, 2, 4), 7.20–7.51 (m, 16 22.8, 29.1, 29.4, 29.5, 29.6, 29.7, 29.8 (4 C), 32.1, 32.6, 66.5, 72.5,
H, aromatic), 7.77 (dd, 2 H, aromatic), 7.90 (m, 4 H, aromatic), 80.8, 101.5, 126.1 (2 C), 126.2 (2 C), 128.4, 129.1, 135.2, 138.1 ppm.
8.08 (dd, 2 H, aromatic) ppm. 13C NMR: δ = 68.4, 68.6, 72.8, 84.4, HRMS (FAB): calcd. for C25H40O3Na [M + Na]+ 411.2875; found
110.2, 119.0, 124.7 (2 C), 128.6 (4 C), 128.7 (2 C), 128.8 (2 C),
128.9, 129.0, 129.4, 129.9 (3 C), 130.0 (2 C), 130.1 (2 C), 130.2 (2
C), 133.2, 133.5, 133.7, 133.8, 141.5, 152.0, 161.1, 165.4 (2 C),
165.6, 166.1 ppm. HRMS (FAB): calcd. for C41H32NO10S [M +
H]+ 730.1747; found 730.1740.
411.2852.
(2R,3S,4E)-2-Azido-1,3-O-benzylidene-4-octadecen-1,3-diol (9): To
a stirred solution of compound 8 (1.5 g, 3.86 mmol) in CH2Cl2
(10.5 mL) was added pyridine (0.75 mL) followed by triflic anhy-
dride (0.8 mL, 4.6 mmol) at –20 °C under an argon atmosphere.
When TLC showed complete disappearance of the starting material
(≈5 min), DMF (35 mL) was added followed by NaN3 (0.75 g,
0.011 mmol). The external cooling was removed, and the reaction
mixture was stirred for 3 h at room temperature. After that, the
reaction mixture was extracted with ethyl acetate (3ϫ150 mL), and
the combined organic extract was dried with MgSO4, filtered, and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (ethyl acetate/hexanes gradient elu-
tion) to afford title compound 9 (0.98 g, 62%) as a colorless oil. Rf
= 0.55 (ethyl acetate/hexanes, 1:9). [α]2D4 = +8.45 (c = 1, CHCl3).
1H NMR: δ = 0.86 (t, 3 H, CH3), 1.20–1.42 [m, 22 H, (CH2)11CH3],
2.10 (m, 2 H, CH=CHCH2), 3.45–3.50 (m, 1 H, CHN3), 3.60 (dd,
J = 11.8 Hz, 1 H, 0.5 OCH2), 4.05 (m, 1 H, CHCH=CH), 4.30–
4.35 (m, 1 H, 0.5 OCH2), 5.48–5.62 (m, 2 H, PhCH, CHCH=CH),
5.94–6.01 (m, 1 H, CHCH=CH), 7.34–7.38 (m, 3 H, aromatic),
7.47–7.49 (m, 2 H, aromatic) ppm. 13C NMR: δ = 14.3, 22.9, 28.9,
29.4, 29.6, 29.7, 29.8, 29.9 (4 C), 32.2, 32.7, 57.7, 69.3, 81.9, 101.3,
126.1, 126.6 (2 C), 128.5 (2 C), 129.2, 137.6, 137.9 ppm. HRMS
(FAB): calcd. for C25H39N3O2Na [M + Na]+ 436.2940; found
436.2929.
1,3-O-Benzylidene-L-arabitol (7): Hydrogen chloride gas (generated
by the dropwise addition of H2SO4 to NaCl) was bubbled through
a mixture of -arabitol (5.0 g, 32.0 mmol) and freshly distilled benz-
aldehyde (4.0 mL, 39 mmol) for 1 h until -arabitol was completely
dissolved. The reaction mixture was kept for an additional 16 h;
after that, the resulting solidified mass was broken up and placed
in a desiccator containing KOH and H2SO4 and dried for 24 h in
vacuo. The resulting solid was then triturated with diethyl ether
(≈10 mL) and mixed with 20% aqueous NaHCO3 (≈20 mL). The
solid containing compound 7 was filtered off and rinsed with water
(10 mL) and diethyl ether (10 mL). The resulting solid was recrys-
tallized from 2-propanol to afford title compound 7 (4.5 g, 60%)
as white crystals. Analytical data for 7 was essentially the same as
reported previously.[21] 1H NMR (CD3OD): δ = 3.56 (m, 1 H), 3.69
(br. s, 1 H), 3.71 (br. s, 1 H), 3.80 (br. s, 2 H), 4.00–4.13 (m, 2 H),
5.50 (s, 1 H, PhCH), 7.21–7.26 (m, 3 H, aromatic), 7.41–7.44 (m,
2 H, aromatic) ppm. 13C NMR (CD3OD): δ = 64.1, 64.2, 71.1,
73.9, 80.2, 102.7, 127.6 (2 C), 129.1, 129.9, 140.1 ppm.
(2S,3S,4E)-1,3-O-Benzylidene-4-octadecen-1,2,3-triol (8): Com-
pound 7 (2.7 g, 11 mmol) was dissolved in methanol (80 mL), and
the solution was cooled to 0 °C. An aqueous solution of NaIO4
(2.4 g, 11.0 mol) in water (30 mL) was added dropwise, and the
resulting mixture was stirred for 45 min. The reaction mixture was
then concentrated in vacuo, and the residue was coevaporated with
ethanol (3ϫ20 mL). The residue was extracted with warm (≈40 °C)
ethyl acetate (3ϫ150 mL), and the combined organic extract was
washed with water (100 mL). The organic layer was separated,
dried with MgSO4, and concentrated in vacuo to yield 2,4-O-
benzylidene--threose (5; 2.3 g, 99%), which was used for the sub-
sequent step without further purification. To a stirred suspension
of 1-tetradecyl triphenylphosphonium bromide (12.2 g, 22.6 mmol)
in dry toluene (100 mL) was added a solution of PhLi (2  in di-
butyl ether, 27 mL) followed by a solution of LiBr (4  in THF,
14 mL) at –10 °C under an argon atmosphere. The resulting
orange-red solution was stirred for 30 min at room temperature;
after that it was cooled to –35 °C, and a solution of compound 5
(3.8 g, 18.0 mmol) in dry THF (27 mL) was added. The stirring
reaction mixture was allowed to gradually warm to 0 °C over a
period of 3 h. After that, methanol (≈10 mL) was added, the re-
sulting mixture was poured in water (50 mL), and the resulting
emulsion was vigorously stirred for 20 min, transferred into a sepa-
ratory funnel, and extracted with CH2Cl2 (2ϫ250 mL). The com-
bined organic extract was washed with water (100 mL), separated,
dried, and concentrated in vacuo. The crude residue was purified
by column chromatography on silica gel (ethyl acetate/CH2Cl2 gra-
dient elution). Title compound 8 was obtained as a white solid
(3.5 g, 50%). Z-isomer of 8 was also isolated in 11% yield. Analyti-
cal data for 8: Rf = 0.56 (ethyl acetate/hexanes, 3:7). [α]2D3 = +3.21
(c = 1, CHCl3). 1H NMR: δ = 0.85 (t, 3 H, CH3), 1.20–1.36 [m, 22
(2R,3S,4E)-2-Azido-4-octadecen-1,3-diol (10): p-TsOH monohy-
drate (31 mg) was added to a stirred solution of compound 9
(0.98 g, 2.37 mmol) in a mixture of methanol (25 mL) and DCM
(10 mL) at room temperature. Upon completion (≈24 h), solid
NaHCO3 was added until neutral pH (≈7); the solid was filtered
off and the filtrate was concentrated in vacuo. The crude residue
was purified by column chromatography on silica gel (ethyl acetate/
hexanes gradient elution) to afford title compound 10 (0.6 g, 80%
yield). Rf = 0.41 (ethyl acetate/hexanes, 3:7). [α]2D4 = +39.34 (c = 1,
CHCl3). 1H NMR: δ = 0.85 (t, 3 H, CH3), 1.20–1.36 [m, 22 H,
(CH2)11CH3], 2.02–2.14 (m, 2 H, CH=CHCH2), 2.29 (br. s, 2 H, 2
OH), 3.44–3.50 (m, 1 H, CHN3), 3.76 (br. s, 2 H, OCH2), 4.23 (m,
1 H, CHCH=CH), 5.46–5.54 (m, 1 H, CHCH=CH), 5.75–5.84 (m,
1 H, CHCH=CH) ppm. 13C NMR: δ = 14.3, 22.9, 29.1, 29.4, 29.5,
29.7, 29.8, 29.9 (4 C), 32.1, 32.5, 62.7, 66.9, 73.8, 128.2, 136.2 ppm.
HRMS (FAB): calcd. for C18H35N3O2Na [M + Na]+ 348.2627;
found 348.2626.
(2R,3S,4E)-2-Azido-3-benzoyloxy-4-octadecen-1-ol (4): Trityl chlo-
ride (0.34 g, 1.22 mmol) was added to a stirring solution of com-
pound 9 (0.305 g, 0.937 mmol) in pyridine (3.0 mL). The reaction
mixture was stirred at room temperature for 16 h. Additional trityl
chloride (0.3 g, 1.2 mmol), pyridine (1.0 mL), and DMAP (50 mg)
were added, and the reaction was stirred for 24 h. The resulting
mixture was concentrated under reduced pressure, and the residue
was diluted with CH2Cl2 (125 mL), washed with water (50 mL),
NaHCO3 (2ϫ50 mL), and water (3ϫ50 mL). The organic layer
was separated, dried, and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (ethyl acetate/hex-
anes gradient elution) to afford (2R,3S,4E)-2-azido-1-trityloxy-4-
octadecen-3-ol (0.60 g) as a white solid. The latter compound
H, (CH2)11CH3], 2.04 (m, 2 H, CH=CHCH2), 2.71 (d, JCH,OH
=
10.0 Hz, 1 H, OH), 3.47 (br. d, 1 H, CHOH), 4.00 (dd, J = 11.8,
1.2 Hz, 1 H, 0.5 OCH2), 4.18 (d, J = 11.8, 1.8 Hz, 1 H, 0.5 OCH2), (0.54 g, 0.95 mmol) was dissolved in pyridine (4 mL) and benzoyl
4.34 (d, J = 6.0 Hz, 1 H, CHCH=CH), 5.56–5.65 (m, 2 H, PhCH, chloride (0.22 mL, 1.9 mmol) was added dropwise; the resulting re-
CHCH=CH), 5.78–5.85 (m, 1 H, CHCH=CH), 7.25–7.33 (m, 3 H, action mixture was stirred under an argon atmosphere for 18 h at
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Concise Synthesis of the Unnatural Sphingosine and Psychosine Enantiomer
room temperature. After that, methanol (≈10 mL) was added, the
mixture was concentrated in vacuo, and the residue was coevapo-
H, 0.5 OCH2), 3.92–4.05 (m, 2 H, 0.5 OCH2, CHN3), 4.29–4.40
(m, 2 H, 6a, 6b-H), 4.45–4.65 (m, 1 H, 5-H), 4.85 (d, J1,2 = 7.9 Hz,
rated with toluene (2ϫ25 mL). The residue was then diluted with 1 H, 1-H), 5.39–5.50 (m, 1 H, CHCH=CH), 5.55–5.65 (m, 2 H, 3-
CH2Cl2 (100 mL), washed with water (40 mL), 1  HCl (40 mL),
water (40 mL), NaHCO3 (2ϫ40 mL), and water (2ϫ40 mL). The
organic layer was separated, dried, and evaporated under reduced
pressure. The residue was purified by column chromatography on
silica gel (ethyl acetate/hexanes gradient elution) to afford
(2R,3S,4E)-2-azido-3-benzoyloxy-1-trityloxy-4-octadecene (0.38 g,
60%) as a colorless syrup. The latter compound (0.32 g, 4.76 mmol)
was dissolved in methanol (4.0 mL) and BF3·OEt2 (62 µL) was
added dropwise; the resulting mixture was stirred for 15 h at room
temperature. After that, the reaction mixture was diluted with
CH2Cl2 (25 mL), washed with water (10 mL), NaHCO3 (10 mL),
and water (2ϫ10 mL). The organic layer was separated, dried, and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (ethyl acetate/hexanes gradient elu-
tion) to afford title compound 4 (0.15 g, 72%) as a colorless syrup.
Rf = 0.56 (ethyl acetate/hexanes, 3:7). [α]2D3 = +51.04 (c = 1, CHCl3).
1H NMR: δ = 0.85 (t, 3 H, CH3), 1.20–1.36 [m, 22 H, (CH2)11CH3],
2.02–2.10 (m, 2 H, CH=CHCH2), 3.58–3.64 (m, 1 H, 0.5 OCH2),
3.71–3.80 (m, 2 H, 0.5 OCH2, CHN3), 5.54–5.61 (m, 2 H,
CHCH=CH, CHCH=CH), 5.89–5.94 (m, 1 H, CHCH=CH), 7.40–
7.54 (m, 3 H, aromatic), 8.02–8.05 (m, 2 H, aromatic) ppm. 13C
NMR: δ = 14.3, 22.9, 28.9, 29.3, 29.5, 29.6, 29.7, 29.8 (4 C), 32.1,
32.6, 62.2, 66.4, 74.8, 123.4, 128.7 (2 C), 129.9 (3 C), 133.5, 139.0,
165.7 ppm. HRMS (FAB): calcd. for C25H39N3O3Na [M + Na]+
452.2889; found 452.2939.
H, CHCH=CH), 5.66–5.74 (m, 1 H, CHCH=CH), 5.75–5.87 (dd,
J1,2 = 7.9 Hz, J2,3 = 10.3 Hz, 1 H, 2-H), 5.97 (br. d, J3,4 = 3.1 Hz,
1 H, 4-H), 7.12–8.11 (m, 25 H, aromatic) ppm. 13C NMR: δ = 14.3
(2 C), 22.9 (2 C), 28.8, 29.3, 29.4 (2 C), 29.5, 29.7, 29.8 (4 C), 32.0
(2 C), 32.5, 62.0, 63.6, 68.1 (2 C), 69.8, 71.5, 71.7, 74.8, 101.4,
122.8, 128.3 (2 C), 128.4 (2 C), 128.6 (3 C), 128.8, 128.9, 129.0,
129.1, 129.3, 129.5, 129.8 (2 C), 129.9 (5 C), 130.1, 130.2, 133.2,
133.3, 133.4, 133.7, 139.1, 165.1 (2 C), 165.7 (2 C), 166.1 ppm.
HRMS (FAB): calcd. for C59H65N3O12Na [M + Na]+ 1030.4466;
found 1030.4497.
(2R,3S,4E)-2-Azido-3-benzoyloxy-1-(2,3,4,6-tetra-O-benzoyl-β-D-
galactopyranosyl)oxy-4-octadecene (13): The title compound was
obtained as a white foam in 87% from building blocks 4 and 12[12]
as described for the synthesis of 2. Analytical data for 13: Rf = 0.55
(ethyl acetate/hexanes, 3:7). [α]2D4 = +80.06 (c = 1, CHCl3). 1H
NMR: δ = 0.84 (t, 3 H, CH3), 1.15–1.35 [m, 22 H, (CH2)11CH3],
1.95–2.04 (m, 2 H, CH=CHCH2), 3.50–3.62 (m, 1 H, 0.5 OCH2),
3.90–4.02 (m, 1 H, CHN3), 4.05–4.18 (m, 1 H, 0.5 OCH2), 4.32–
4.40 (m, 2 H, 6a, 6b-H), 4.60–4.75 (m, 1 H, 5-H), 4.91 (d, J1,2
=
7.9 Hz, 1 H, 1-H), 5.42–5.48 (m, 2 H, CHCH=CH, CHCH=CH),
5.58–5.62 (br. dd, 1 H, 3-H), 5.79–5.85 (m, 2 H, 2-H, CHCH=CH),
5.99 (br. d, 1 H, 4-H), 7.15–7.60–8.11 (m, 25 H, aromatic) ppm.
13C NMR: δ = 14.3 (2 C), 22.9 (2 C), 28.8, 29.4, 29.5 (2 C), 29.6,
29.8, 29.9 (4 C), 32.1 (2 C), 32.5, 62.1, 64.5, 68.2, 69.4, 69.8, 71.6,
71.8, 74.8, 102.1, 123.1, 128.5 (2 C), 128.6 (2 C), 128.7 (3 C), 128.8,
128.9, 129.2, 129.4, 129.6, 129.9 (3 C), 130.0 (5 C), 130.2, 133.4 (2
C), 133.5, 133.8, 138.8, 165.3, 165.5, 165.7, 165.8, 166.2 ppm.
HRMS (FAB): calcd. for C59H65N3O12Na [M + Na]+ 1030.4466;
found 1030.4497.
(2R,3S,4E)-2-Amino-4-octadecen-1,3-diol (11): Compound 10
(48 mg, 0.15 mmol) was dissolved in THF (7.0 mL) and 0.1 
NaOH (1 mL) was added; the resulting mixture was stirred for
20 min. A solution of PMe3 (1  in THF, 0.15 mL) was then added
dropwise, and the reaction mixture was stirred for 16 h at room
temperature. After that, it was neutralized with 0.1  aqueous HCl
(≈0.5 mL) and concentrated under reduced pressure. The residue
was purified by column chromatography on silica gel [packed in
5% solution of methanol/ammonia (40/1 wt/wt) in DCM] to afford
title compound 11 (31 mg, 70%) as a white solid. [α]2D5 = –9.23 (c
(2R,3S,4E)-2-Amino-1-(β-L-galactopyranosyl)oxy-3-hydroxy-4-octa-
decene (1): To a stirred solution of 2 (173 mg, 0.171 mmol) in dry
methanol (3 mL) was added 1  NaOMe (≈0.4 mL, pH 10), and
the resulting mixture was stirred for 20 h at room temperature. Af-
ter that it was neutralized by the addition of Dowex (H+), and the
resin was filtered off and rinsed successively with methanol
(5ϫ5 mL). The filtrate was concentrated in vacuo, and the crude
residue (93 mg) was dissolved in THF (13.0 mL); 0.1  NaOH
(1.9 mL) was added, and the resulting mixture was stirred for
20 min. A solution of PMe3 (1  in THF, 0.19 mL) was then added
dropwise, and the reaction mixture was stirred for 16 h at room
temperature. After that, it was neutralized with 0.1  aqueous HCl
and concentrated under reduced pressure. The residue was purified
by column chromatography on silica gel [packed in 5% solution of
methanol/ammonia (40/1 wt/wt) in CH2Cl2] to afford title com-
pound 1 (58 mg, 65%) as a white solid. [α]2D6 = +1.46 (c = 1,
CH3OH). 1H NMR (CD3OD): δ = 0.82 (t, 3 H, CH3), 1.20–1.34
[m, 22 H, (CH2)11CH3], 1.97–2.02 (m, 2 H, CH=CHCH2), 2.80–
2.89 (m, 1 H, CHN3), 3.35–3.50 (m, 3 H, 2, 4, 5-H), 3.62–3.81 (m,
5 H, 3, 6a, 6b-H, OCH2), 3.90–3.95 (m, 1 H, CHCH=CH), 4.14
(d, J1,2 = 7.2 Hz, 1 H, 1-H), 5.38–5.48 (m, 1 H, CHCH=CH), 5.65–
5.76 (m, 1 H, CHCH=CH) ppm. 13C NMR (CD3OD): δ = 14.6,
23.9, 30.4, 30.5, 30.6, 30.7, 30.8 (2 C), 30.9 (3 C), 33.2, 33.5, 56.7,
62.7, 70.0, 70.5, 72.6, 73.2, 74.9, 76.9, 104.9, 129.9, 136.1 ppm.
HRMS (FAB): calcd. for C24H48NO7 [M + H]+ 462.3431; found
462.3434.
1
= 1, CH3OH). H NMR (CD3OD): δ = 0.83 (t, 3 H, CH3), 1.15–
1.36 [m, 22 H, (CH2)11CH3], 1.98–2.05 (m, 2 H, CH=CHCH2),
2.68–2.80 (br. m, 1 H, CHN), 3.41–3.63 (br. m, 2 H, OCH2), 3.92–
3.96 (m, 1 H, CHCH=CH), 5.38–5.45 (m, 1 H, CHCH=CH), 5.63–
5.72 (dd, 1 H, CHCH=CH) ppm. 13C NMR (CD3OD): δ = 14.6,
23.9, 30.5 (2 C), 30.6, 30.7, 30.8 (2 C), 30.9 (3 C), 33.2, 33.6, 58.2,
63.8, 74.6, 130.6, 135.6 ppm. HRMS (FAB): calcd. for C18H38NO2
[M + Na]+ 300.2897; found 300.2899.
(2R,3S,4E)-2-Azido-3-benzoyloxy-1-(2,3,4,6-tetra-O-benzoyl-β-L-
galactopyranosyl)oxy-4-octadecene (2): A mixture of glycosyl donor
3 (0.22 g, 0.31 mmol), glycosyl acceptor 4 (0.12 g, 0.28 mmol), and
freshly activated molecular sieves (3 Å, 0.67 g) in ClCH2CH2Cl
(2.0 mL) was stirred under an argon atmosphere for 1.5 h. Freshly
conditioned AgOTf (0.24 g, 0.92 mmol) was added, and the reac-
tion mixture was stirred for 15 min at room temperature. After that,
it was diluted with CH2Cl2 (15 mL), the solid was filtered off, and
the residue was washed with CH2Cl2 (3ϫ5 mL). The combined
filtrate (35 mL) was washed with saturated aqueous NaHCO3
(15 mL) and water (2ϫ15 mL), and the organic phase was sepa-
rated, dried, and concentrated in vacuo. The residue was purified
by column chromatography on silica gel (ethyl acetate/hexane gra-
dient elution) to afford title compound 2 (0.2 g, 70%) as a white
foam. Rf = 0.55 (ethyl acetate/hexanes, 3:7). [α]2D7 = –44.49 (c = 1,
CHCl3). 1H NMR: δ = 0.83 (t, 3 H, CH3), 1.20–1.30 [m, 22 H,
(2R,3S,4E)-2-Amino-1-(β-D-galactopyranosyl)oxy-3-hydroxy-4-octa-
decene (14): The title compound was obtained as a white solid in
63% from 13 as described for the synthesis of 1. Analytical data
(CH2)11CH3], 1.85–1.90 (m, 2 H, CH=CHCH2), 3.62–3.72 (m, 1 for 14: [α]2D2 = –6.20 (c = 1, CH3OH). 1H NMR (CD3OD): δ = 0.82
Eur. J. Org. Chem. 2010, 3269–3274
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
3273

A. V. Demchenko et al.
FULL PAPER
Hart, P. Sinay), Wiley-VCH, Weinheim, New York, 2000, vol.
1, pp. 305–318.
(t, 3 H, CH3), 1.20–1.34 [m, 22 H, (CH2)11CH3], 1.97–2.04 (m, 2
H, CH=CHCH2), 2.80–2.90 (m, 1 H, CHNH2), 3.38–3.50 (m, 4 H,
2, 4, 5-H, 0.5 OCH2), 3.64–3.78 (m, 3 H, 3, 6a, 6b-H), 3.92–4.01
(m, 2 H, CHCH=CH, 0.5 OCH2), 4.14 (d, J1,2 = 7.2 Hz, 1 H, 1-
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Acknowledgments
This work was supported by awards from the National Science
Foundation (CHE-0547566 to A. V. D.), American Heart Associa-
tion (0855743G to A. V. D.), National Institutes of Health
(HD055461 to M. S. S.), and the Hunter’s Hope Foundations (to
M. S. S.).
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Received: January 10, 2010
Published Online: April 30, 2010
3274
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© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2010, 3269–3274