A rapid synthesis of sphingosine from phytosphingosine

Article abstract of DOI:10.1016/j.carres.2018.04.006

A simple and efficient protocol for the synthesis of a sphingosine starting from cost-effective phytosphingosine has been described. Two alternative synthetic pathway have been disclosed based on the use of two different kinds of protective groups for the protection of the amino group in the phytosphingosine. The protected phytosphingosine was subsequently transformed into sphingosine in 5 steps i.e. protection of the amine group, protection of 1,3-diol, leaving group insertion, elimination, and one-pot deprotection.

Full text of DOI:10.1016/j.carres.2018.04.006

Accepted Manuscript
A rapid synthesis of sphingosine from phytosphingosine
Arumugam Sankar, I-Cheng Chen, Shun-Yuan Luo
PII:
S0008-6215(18)30179-4
10.1016/j.carres.2018.04.006
CAR 7551
DOI:
Reference:
To appear in: Carbohydrate Research
Received Date: 22 March 2018
Revised Date: 12 April 2018
Accepted Date: 12 April 2018
Please cite this article as: A. Sankar, I.-C. Chen, S.-Y. Luo, A rapid synthesis of sphingosine from
phytosphingosine, Carbohydrate Research (2018), doi: 10.1016/j.carres.2018.04.006.
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Graphical Abstract
A Rapid Synthesis of Sphingosine from
Phytosphingosine
Leave this area blank for abstract info.
Arumugam Sankar, I-Cheng Chen and Shun-Yuan Luo*
Department of Chemistry, National Chung Hsing University, 250 Kuo-Kuang Rd., Taichung 402, Taiwan

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A Rapid Synthesis of Sphingosine from Phytosphingosine
Arumugam Sankar, I-Cheng Chen and Shun-Yuan Luo*
Department of Chemistry, National Chung Hsing University, Taichung 402, Taiwan.
E-mail: syluo@dragon.nchu.edu.tw
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1. Abstract
A simple and efficient protocol for the synthesis of a sphingosine starting from cost-effective
phytosphingosine has been described. Two alternative synthetic pathway have been disclosed based on
the use of two different kinds of protective groups for the protection of the amino group in the
phytosphingosine. The protected phytosphingosine was subsequently transformed into sphingosine in 5
steps i.e. protection of the amine group, protection of 1,3-diol, leaving group insertion, elimination, and
one-pot deprotection.
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Key words: Phytosphingosine, Sphingosine, Regioselective, Protection, Elimination, Deprotection
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2. Introduction
Sphingosine and its derivatives are collectively called sphingolipids and these are key signaling
molecules and also play an important role in biological activities. As these molecules are the potentially
specific inhibitor of protein kinase C which shows an important role for transduction.1-4 Metabolites of
their family like ceramide, sphingosine and sphingosine-1-phosphate are the important component in
the cell process.5-8 Has its hydrophobic moieties are inside the membrane layer while its hydrophilic
moieties are along the cell surface.9 It plays important role in regulating fundamental and diverse cell
processes that include survival, adhesion, cell growth, differentiation, migration, apoptosis10 etc...
Sphingolipids are associated with common diseases such as cancer,11 heart disease,12 Alzheimer’s
disease13 etc., and are unique markers that indicate the existence of metabolic disorders arising from
deletion, duplication and point mutations in the gene encoding to the enzymes.14 Sphingosine is an
important building block for several biologically important molecules like ceramides, which has a long
chain 2-amino-1,3-diol, C-4 and C-5 trans double bond and a polar head group at a C-1 position
through ester linkage.15
Hence their need for large-scale to understand its biological properties in depth has been prompted the
development of various synthetic procedures including from phytosphingosine to sphingosine.16-17
Among them, carbohydrates like D-mannose18-19 and D-glucose19-20 were efficient precursors to
sphingosine. However, these methods needed more than 10 steps. In another method, sphingosine was
derived from serine by the reduction of N-PMP and Boc-N-PMP by the diastereoselective method.
Even though in that last step PMP de-protection had some problems and the lengthy procedure was
employed.21 Among them, Recently Panza et al reported the synthesis of sphingosine in excellent yield
by the way of approaching proper protecting groups and it led less number of protection and
deprotection steps.22 On the other hand, Chung et al reported the synthesis of four diastereomers of
sphingosine by using of N-trityl protecting group.23 In 2006 Kim’s group also reported synthesis of
sphingosine from phytosphingosine with less number of steps.24 It was a convenient way to access to
all four diastereomers. We envisioned that Panza et al approach is a convenient protocol which will
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offer a facile access to the sphingosine. Herein, we report a facile protocol for the synthesis of
sphingosine from phytosphingosine with a major thrust on developing an efficient route with fewer
reaction steps and improved yields. We have selected phytosphingosine as starting materials because of
both sphingosine and phytosphingosine are structurally related to each other and the removal of C4-OH
of phytosphingosine and arising of C4 and C5 double bond will lead to sphingosine (Figure 1).
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Figure 1. Structures of sphingosine 1 and phytosphingosine 2.
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Based on our experience on this kind of chemistry, we envisaged that commercially available
phytosphingosine 2 would serve as appropriate starting material for the synthesis of sphingosine 1. As
shown in the retrosynthetic strategy (Scheme 1) the sphingosine 1 would be obtained from fully
protected olefin intermediate 3 via N-deprotection and benzylidene deprotection. The intermediate 3
would be obtained via deiodination at C4 of intermediate 4 which would be derived from 5 by Appel’s
reaction (SN2). The mono-ol 5 would be generated from the triol 6 by stereo and regio-selective
protection of 1,3-diol by using 1-(dimethoxymethyl)benzene. The triol 6 would be synthesized from
phytosphingosine 2 by the protection of different protecting groups.
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P2P1N
NH2
n-C13H27
HO
n-C13H27
O
O
Ph
OH
1
3
P2P1N
OH
P2P1N
O
I
n-C13H27
n-C13H27
O
O
O
H
Ph
Ph
5
4
P2P1N
HO
OH
NH2 OH
HO
n-C13H27
n-C13H27
OH
OH
6
2
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Scheme 1. Retrosynthetic strategy for the synthesis of sphingosine 1.
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3. Results and Discussion
Accordingly, initially, the protection of amine group of phytosphingosine 2 was carried out by using
phthalic anhydride (1.8 equiv.) at reflux condition for 16 hours, provided 6a in 76% yield.22 The 6a was
treated with benzaldehyde dimethyl acetal (2.0 equiv.) and camphorsulfonic acid (CSA, 1.0 equiv.) in
acetonitrile at room temperature for the regioselective synthesis of benzylidene 5a in 77% yield.22 The
regioselective ring formation between C1 and C3-OH is the key step which led to a stable
thermodynamic six-member ring of 5a and left the C4-OH free for further smooth reactions. The ring
formation between C3 and C4 not only would lead us to extra steps but also the formed ring is kinetic
five-member.
Since alcohol is a poor leaving group to form the double bond, we have introduced a known leaving
group at C4 position in order to get olefin. At first, we treated 5a with methanesulfonyl chloride which
would provide C4 methanesulfonate derivative in 92% yield. We expected that the -OMs
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(methanesulfonate) group would serve as a good leaving group to obtain olefin 3a. However, while we
tried to eliminate -OMs from C4-position, we only obtained desired olefin product 3a in 18% yield. In
order to enhance the yield of olefin 3a, our task was to introduce a good leaving group at C4 position.
Accordingly, we have tried to introduce the iodine to replace C4-OH by Appel’s reaction which was a
good leaving group at C4 position. Though iodine is a bulky moiety compare to that of Br and Cl to fit
in the C4 secondary alcohol position but it has good leaving property than any other halogen. For
Appel’s reaction, we have treated 5a with PPh3 (2.0 equiv.), imidazole (5.0 equiv.), I2 (2.0 equiv.) in
toluene at 80 oC for overnight and 4a was obtained in 99% yield.22 Then 4a was the treated with DBU
(4.0 equiv.) in toluene to afford trans-olefin 3a in 93% yield.22 The trans selectivity might be attributed
to the steric hindrances of the bulky group on double bond at C4 and C5 carbons which in principle try
to be far apart from each other and therefore presumably this reaction occurs via anti-coplanar. Also,
DBU is a bulky base; hence it takes the proton from a less hindered side and produced the selectively
trans olefin 3a desired product in good yield.
Next, in order to achieve our target, we have tried different approaches to remove the -Phth and
benzylidene groups from 3a. The first approach was involved that selective deprotection of the
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benzylidene group from 3a by using 85% TFA and water at 50 C provided the precursor for
sphingosine and treatment of this precursor with hydrazine (1.5 equiv.) in methanol at reflux condition
resulted into our desired product sphingosine 1 in 61% yield22 in two steps. In another approach, we
have tried this deprotection process in one-pot operation. For that, firstly 3a was treated with hydrazine
(1.5 equiv.) in methanol at reflux condition to deprotect the Phth-group and after the completion of the
reaction, the crude product was then treated with 85% AcOH in water at 50 oC to afford the
sphingosine 1 in 47% yield in two steps (Path A, Scheme 2).
We have also established an alternative synthetic pathway for the synthesis of sphingosine 1 by using
the same phytosphingosine 2 as our starting material. It was shown in Path B (Scheme 2). The azido
compound 6b was obtained via the reaction of phytosphingosine 2 with in situ prepared
trifluoromethane sulfonyl azide (TfN3, 2.0 equiv.), under the influence of copper sulphate (0.016 equiv.)
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and potassium carbonate (5.0 equiv.) by using the mixture of dichloromethane, water and methanol as
the solvent system.25 Without further purification 6b was then treated with benzaldehyde dimethyl
acetal (2.0 equiv.) and CSA (1.0 equiv.) in acetonitrile at room temperature provided benzylidene 5b in
75% yield for two steps.22 By Appel’s reaction the mono-ol 5b could not convert to the iodinated
desired product and instead of that amine derivative was obtained. A little modification was made
where 5b was treated with TsCl (3.6 equiv.) in pyridine which provided tosylation at C4 position (4b)
in 99% yield. The 4b was then treated with DBU (4 equiv.) in toluene to afford trans-olefin 3b in 51%
yield. It was then deprotected by using Staudinger’s reaction (PPh3, THF and water) followed by
de-benzylidene reaction with 85% AcOH resulted in sphingosine 1 in 46% yield.
4. Conclusions
In conclusion, we have successfully developed two alternative synthetic methodologies for the
synthesis of biologically important sphingosine 1 from commercially available phytosphingosine 2.
Both azido and phthalic group were used as potent protecting groups for amine in phytosphingosine 2.
In two alternative strategies were lead to facile transformation to sphingosine over 5 steps which
include protection, leaving group insertion, elimination and finally one pot deprotection. The developed
protocol is superior as it effectively reduces the number of steps providing the sphingosine 1 in overall
25% and 17% yield.
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phytosphingosine 2
TfN3, K2CO3,
CuSO4, DCM,
H2O, MeOH
PA, Pyr.,
reflux, 76%
Path B
Path A
PhthN
HO
OH
N3 OH
C13H27
HO
C13H27
6a
6b
OH
OH
PhCH(OMe)2,
PhCH(OMe)2,
CSA, ACN
75% in 2 steps
CSA, ACN, 77%
PhthN
OH
N3 OH
C13H27
C13H27
O
O
O
O
Ph
Ph
5a
5b
PPh3, Im, I2,
toluene, 99%
TsCl, Pyr.
99%
PhthN
I
N3 OTs
C13H27
C13H27
O
O
O
O
4a
93%
4b
51%
Ph
Ph
DBU,
DBU,
toluene
toluene
PhthN
N3
C13H27
C13H27
O
O
O
O
3a
3b
Ph
Ph
NH2NH2, MeOH, reflux;
85% AcOH, 50 oC, 47%
PPh3, THF, H2O;
85% AcOH, 46%
sphingosine 1
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Scheme 2. Synthesis of sphingosine from phytosphingosine.
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4. Experimental Section
4.1. General Information.
Some reactions were conducted in flame-dried glassware, under the nitrogen atmosphere. Acetonitrile
and toluene were purified and dried from a safe purification system containing activated Al2O3
(PubChem CID: 9989226); All reagents obtained from commercial sources were used without
purification unless otherwise mentioned. Phytosphingosine (PubChem CID: 122121); was purchased
from Tokyo Chemical Industry Co. Ltd, Japan. Flash column chromatography was carried out on Silica
Gel 60 (230-400 mesh, E. Merck). TLC was performed on pre-coated glass plates of Silica Gel 60 F254
(0.25mm, E. Merck); detection was executed by spraying with a solution of Ce(NH4)2(NO3)6 (0.5 g),
(NH4)6Mo7O24 (24.0 g) and H2SO4 (28.0 mL) in water (500.0 mL) and subsequent heating on a hot
plate. Optical rotations were measured at 589 nm (Na), H, 13C NMR, DEPT, H-1H COSY, H-13C
COSY, and NOESY spectra were recorded with 400 and 600 MHz instruments. Chemical shifts are in
ppm from Me4Si generated from the CDCl3 lock signal at δ7.26. IR spectra were taken with a FT-IR
spectrometer using KBr plates. Mass spectra were analyzed on Orbitrap instrument with an ESI source.
4.2. (2S,3S,4R)-2-(Phthalimido)-octadecane-1,3,4-triol (6a).
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To a solution was added phytosphingosine 2 (1.00 g, 3.15 mmol) and phthalic anhydride (840 mg, 5.67
mmol) in pyridine (50 mL). The resulting mixture was immersed in a preheated oil bath to reflux and
stirred for 16 hours at the same temperature until TLC indicated the complete disappearance of starting
material. Then the solvent was removed under reduced pressure and the residue was chromatographed
on silica gel to afford triol 6a (2.11 g, 76%) as a white solid. Rf 0.62 (EtOAc/Hex = 2/1); mp 85-86 oC;
[α]25D -33.46 (c 1.00, Pyridine). IR (KBr): 3513, 3317, 2918, 2853, 1770, 1704, 1613, 1465, 1391 cm-1.
1H NMR (CDCl3, 400 MHz): δ = 7.87 (dd, J = 5.4, 3.1 Hz, 2H, ArH), 7.76 (dd, J = 5.4, 3.1 Hz, 2H,
ArH), 4.66 (dd, J = 9.6, 4.9 Hz, 1H, H-2) 4.18 (dd, J = 12.1, 4.9 Hz, 1H, H-1a), 4.09-3.95 (dd, J = 8.8,
3.2 Hz, 2H, H-1b, H-3), 3.76 (dd, J = 8.7, 3.5 Hz, 1H, H-4), 1.62-1.18 (m, 26H, CH2), 0.88 (t, J = 6.8
Hz, 3H, CH3). 13C NMR (CDCl3, 100 MHz): δ = 169.4 (C × 2), 134.4 (CH × 2), 131.6 (C × 2), 123.6
(CH × 2), 101.0 (CH2), 75.0 (CH), 72.9 (CH), 60.9 (CH2), 53.8 (CH), 32.6 (CH2), 31.9 (CH2), 29.7
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(CH2 × 2), 29.65 (CH2), 29.63 (CH2), 29.6 (CH2), 29.5 (CH2 × 2), 29.3 (CH2), 25.7 (CH2), 22.7 (CH2),
14.1 (CH3).
HRMS (ESI): m/z [M+Na]+ calcd for C26H41O5NNa 470.2882; found 470.2892.
4.3. (2S,3S,4R)-2-(Phthalimido)-1,3-benzylidene-octadecan-1,3,4-triol (5a).
To a solution of the triol 6a (2.11 g, 4.7 mmol) and benzaldehyde dimethyl acetal (1.4 mL, 9.4 mmol)
in anhydrous acetonitrile (21.0 mL) was treated with camphorsulfonic acid (1.09 g, 4.7 mmol) at room
temperature under nitrogen atmosphere. After completion of the reaction, the reaction mixture was
quenched by trimethylamine and extracted by water (10 mL) and dichloromethane (20 mL × 3). The
combined organic layers were washed with brine, dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure. The crude was purified by column chromatography on silica gel
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to afford 5a (2.84 g, 77%) as a white solid. Rf 0.47 (EtOAc/Hex = 1/4); mp 68-72 C; [α]25D +15.97 (c
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0.86, CH2Cl2). IR (KBr): 3467, 2922, 2851, 1708, 1646, 1502, 1467, 1387, 1120, 1012 cm-1. H NMR
(CDCl3, 400 MHz): δ = 7.88-7.80 (m, 2H, ArH), 7.78-7.68 (m, 2H, ArH), 7.57-7.46 (m, 2H, ArH),
7.45-7.30 (m, 3H, ArH), 5.70 (s, 1H, CHPh), 4.72 (dd, J = 9.9, 4.4 Hz, 1H, H-2), 4.68-4.60 (m, 1H,
H-3), 4.56 (t, J = 10.5 Hz, 1H, H-4), 4.10 (dd, J = 10.1, 4.6 Hz, 2H, H-1a, H-1b), 1.85-1.11 (m, 26H,
CH2), 0.86 (t, J = 6.9 Hz, 3H, CH3).
13C NMR (CDCl3, 100 MHz): δ = 168.0 (C), 137.55 (C × 2), 134.2 (CH × 2), 131.6 (C × 2), 129.1
(CH), 128.3 (CH × 2), 126.2 (CH × 2), 123.5 (CH × 2), 101.2 (CH), 78.0 (CH), 78.9 (CH), 66.2 (CH2),
45.7 (CH), 32.03 (CH2), 31.9 (CH2), 29.7 (CH2), 29.65 (CH2), 29.63 (CH2 × 2), 29.6 (CH2), 29.5 (CH2),
29.45 (CH2), 29.4 (CH2), 29.3 (CH2), 25.4 (CH2), 22.7 (CH2), 14.1 (CH3). HRMS (ESI): m/z [M+H]+
calcd for C33H46NO5 536.3370; found 536.3366.
4.4. (2S,3S,4S)-2-(Phthalimido)-1,3-benzylidene-4-iodooctadecane-1,3-diol (4a).
To a solution of compound 5a (2.84 g, 5.3 mmol) in dry toluene (28.4 mL) under nitrogen condition
triphenylphosphine (2.78 g, 10.6 mmol), imidazole (1.80 g, 26.5 mmol) and iodine (2.69 g, 10.6 mmol)
were added sequentially and the reaction mixture was stirred at 80 °C for 4 h. The resulting solution
was washed with saturated aq. Na2S2O3 and extracted by water (30 mL) and dichloromethane (30 mL ×
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3). The combined organic layers were washed with brine, dried over anhydrous MgSO4, filtered and
concentrated under reduced pressure. The residue was purified by column chromatography on silica gel
to afford iodine 4a (3.38 g, 99%) as colorless viscous liquid. Rf 0.52 (EtOAc/Hex = 1/4); [α]25 +9.75
D
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(c 0.93, CH2Cl2); IR (KBr) v 3747, 2923, 2853, 2107, 1460 cm-1; H NMR (400 MHz, CDCl3) δ
7.89-7.87 (m, 2H, ArH), 7.78-7.76 (m, 2H, ArH), 7.58-7.55 (m, 2H, ArH), 7.42-7.38 (m, 3H, ArH),
5.83 (s, 1H, CHPh), 4.82 (ddd, J = 10.9, 9.9, 5.1 Hz, 1H, H-3), 4.49 (t, J = 10.8 Hz, 1H, H-1a), 4.32 (dd,
J = 9.8, 1.7 Hz, 1H, H-2), 4.14 (dd, J = 10.5, 5.1 Hz, 1H, H-1b), 4.02 (ddd, J = 9.2, 5.4, 1.7 Hz, 1H,
H-4), 1.39-1.15 (m, 26H, CH2), 0.88 (t, J = 6.9 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3) δ 167.6 (C),
137.5 (C × 2), 134.4 (CH × 2), 131.5 (C × 2), 129.1 (CH), 128.3 (CH × 2), 126.3 (CH × 2), 123.6 (CH
× 2), 101.1 (CH), 77.0 (CH) 65.9 (CH2), 49.3 (CH), 37.0 (CH2), 34.5 (CH), 31.9 (CH2), 29.74 (CH2),
29.7 (CH2), 29.64 (CH2), 29.62 (CH2 × 2), 29.6 (CH2), 29.5 (CH2), 29.4 (CH2), 29.3 (CH2), 28.7 (CH2),
22.7 (CH2), 14.1 (CH3); HRMS (ESI, M+Na+) calcd for C33H44IO4NNa 668.2207, found 668.2188.
4.5. (2S,3R,4E)-2-(Phthalimido)-1,3-benzylidene-octadec-4-ene-1,3-diol (3a).
To a solution of the iodo compound 4a (3.38 g, 5.23 mmol) in anhydrous toluene (34 mL) was added
1,8-diazabicyclo[5.4.0]undec-7-ene (DBU, 3.1 mL, 3.19 mmol) under nitrogen atmosphere. The
resulting mixture was kept at 110 °C for 2 hours, after the disappearance of the starting material in TLC.
It was allowed to room temperature and the mixture was neutralized with 2M HCl, then the reaction
mixture was extracted by water (30 mL) and dichloromethane (20 mL × 3). The combined organic
layers were washed with brine, dried over anhydrous MgSO4, filtered and concentrated under reduced
pressure. The residue was purified by column chromatography on silica gel to provide 3a (2.53 g, 93%)
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as a white solid. Rf 0.63 (EtOAc/Hex = 1/4); mp 66-70 C; [α]25 +4.80 (c 0.93, CH2Cl2); IR (KBr) v
D
2922, 2852, 1774, 1715, 1468, 1454, 1380 cm-1; 1H NMR (400 MHz, CDCl3) δ 7.86-7.83 (m, 2H, ArH),
7.76-7.69 (m, 2H, ArH), 7.56-7.52 (m, 2H, ArH), 7.40-7.35 (m, 3H, ArH), 5.79-5.63 (m, 2H, CHPh,
H-5), 5.46 (dd, J = 15.4, 8.3 Hz, 1H, H-4), 5.06 (dd, J = 9.6, 8.4 Hz, 1H, H-3), 4.62 (t, J = 10.8 Hz, 1H,
H-1a), 4.52-4.40 (m, 1H, H-2), 4.18 (dd, J = 10.4, 4.8 Hz, 1H, H-1b), 1.97-1.76 (m, 2H, CH2),
1.35-0.92 (m, 22H, CH2), 0.88 (t, J = 6.8 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3) δ 137.6 (CH),
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134.2 (CH), 133.3 (C), 132.4 (C × 2), 132.3 (CH), 132.2 (CH), 131.53 (CH), 131.5 (CH), 131.47 (C ×
2), 128.5 (CH), 128.4 (CH), 128.3 (CH), 126.3 (CH), 123.4 (CH), 101.1 (CH), 78.2 (CH), 66.4 (CH2),
48.8 (CH), 32.1 (CH2), 31.9 (CH2), 29.7 (CH2 × 2), 29.6 (CH2 × 2), 29.35 (CH2), 29.33 (CH2), 29.3
(CH2), 28.8 (CH2), 28.7 (CH2), 22.7 (CH2), 14.1 (CH3); HRMS (ESI, M+Na+) calcd for C33H43O4NNa
540.3084, found 540.3075.
4.6. (2S,3S,4R)-2-(Azido)-1,3-benzylidene-octadecan-1,3,4-triol (5b).
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A solution of NaN3 (2.04 g, 31.5 mmol), DCM/H2O (5.0 mL/5.0 mL) was cooled to 0 C and Tf2O
(1.10 mL, 6.30 mmol) was added dropwise to the reaction mixture for 20 min, under nitrogen
atmosphere. The reaction mixture was kept at the same temperature for 3 hours. The mixture was
extracted with water and dichloromethane (10 mL × 2). The combined organic layer was washed with
saturated NaHCO3 (16 mL) and the organic layer was used to produce azido group in phytosphingosine
2. To the suspension of phytosphingosine (1.00 g, 3.15 mmol), K2CO3 (2.14 g, 15.8 mmol) and
CuSO4•5H2O (16.0 mg, 0.01 mmol) in the mixture of methanol and water (4.0 mL/3.0 mL) was added
the combined organic layer which contained TfN3. After reaction completion, the resulting solution was
concentrated to remove the organic solvent under vacuo. The mixture was extracted by water (10 mL)
and EtOAc (10 mL × 3). The combined organic layers were washed with brine, dried over anhydrous
MgSO4, filtered and concentrated under reduced pressure. The residue was used in the next step
reaction without further purification.24 A suspension of triol (1.08 g, 3.15 mmol) and benzaldehyde
dimethyl acetal (1.0 mL, 6.3 mmol) in anhydrous acetonitrile (10.8 mL) was treated with
camphorsulfonic acid (0.73 g, 3.15 mmol) in nitrigen atmosphere. The reaction stirred at room
temperature for 1 hour. The residue was purified by column chromatography on silica gel to afford the
compound 5b (1.02 g, 75%) as a colorless liquid. Rf 0.67 (EtOAc/Hex = 1/3); [α]25 +34.34 (c = 1.0,
D
CH2Cl2); IR (KBr) v 3475, 3068, 3038, 2848, 2122, 1466, 1398 cm-1; 1H NMR (400 MHz, CDCl3) δ
7.46-7.44 (m, 2H, ArH), 7.39-7.36 (m, 3H, ArH), 5.46 (s, 1H, CHPh), 4.38 (dd, J = 8.4, 3.0 Hz, 1H,
H-2), 3.88 (s, 1H, H-4), 3.67 (m, 3H, H-1a, H-1b, H-3 ), 1.62 (dd, J = 13.8, 7.2 Hz, 2H, H-5a, H-5b),
1.56-1.26 (m, 24H, CH2), 0.88 (t, J = 7.2 Hz, 3H, CH3); 13C NMR (100 MHz, CDCl3) δ 137.1 (C),
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129.0 (CH), 128.1 (CH × 2), 125.9 (CH × 2), 100.8 (CH), 82.1 (CH), 72.1 (CH), 68.5 (CH2), 52.9
(CH), 31.8 (CH2), 31.6 (CH2), 29.6 (CH2 × 2), 29.5 (CH2 × 3) 29.4 (CH2 × 2), 29.2 (CH2 × 2), 25.9
(CH2), 22.5 (CH2), 13.9 (CH3); HRMS (ESI, M+Na+) calcd for C25H41N3O3Na 454.3046, found
454.3040.
4.7. (2S,3S,4S)-2-Azido-1,3-benzylidene-4-O-(toluenesulfonyl)-octadeca-ne-1,3-diol (4b).
To a solution of the compound 5b (2.51 g, 5.83 mmol) in pyridine (24.5 mL) was added
4-toluenesulfonyl chloride (3.97 g, 21.0 mmol) and stirred at room temperature for 24 hours. The
starting material was completely consumed as judged by TLC. Then the mixture was washed with
saturated aqueous Na2S2O3, extracted with dichloromethane (30 mL× 3) and water. The combined
organic layers were dried over anhydrous MgSO4, filtered and concentrated under reduced pressure.
The residue was purified by column chromatography on silica gel to afford iodine 4b (3.38 g, 99%) as
the colorless viscous liquid. Rf 0.43 (EtOAc/Hex = 1/8); [α]25D +28.18 (c 0.93, CH2Cl2); IR (KBr) v
3747, 2923, 2853, 2107, 1460, 1367, 1189, 1177 cm-1; 1H NMR (400 MHz, CDCl3) δ 7.81 (d, J = 12.6
Hz, 2H, ArH), 7.40-7.32 (m, 5H, ArH), 7.29-7.23 (m, 2H, ArH), 5.36 (s, 1H, CHPh), 4.78 (ddd, J = 9.6,
3.6, 1.8 Hz, 1H, H-2), 4.37 (dd, J = 10.9, 5.2 Hz, 1H, H-4), 3.80 (dd, J = 10.1, 1.8 Hz, 1H, H-3), 3.68 (t,
J = 10.7 Hz, 3H, H-1a), 3.49 (td, J = 10.3, 5.2 Hz, 1H, H-1b), 2.41 (s, 3H, CH3), 1.89 (m, 1H, H-5a),
1.63 (m, 1H, H-5b), 1.36-1.11 (m, 24H, CH2), 0.88 (t, J = 6.8 Hz, 3H, CH3); 13C NMR (100 MHz,
CDCl3) δ 137.1 (C), 129.0 (CH), 128.1 (CH × 2), 125.9 (CH × 2), 100.8 (CH), 82.1 (CH), 72.1 (CH),
68.5 (CH2), 52.9 (CH), 31.8 (CH2), 31.6 (CH2), 29.6 (CH2 × 2), 29.5 (CH2 × 3) 29.4 (CH2 × 2), 29.2
(CH2 × 2), 25.9 (CH2), 22.5 (CH2), 13.9 (CH3); HRMS (ESI, M+H+) calcd for C32H48N3O5S 586.3309,
found 586.3527.
4.8. (2S,3R,4E)-2-Azido-1,3-benzylidene-octadec-4-ene-1,3-diol (3b).
To a solution of compound 4b (606.1 mg, 1.03 mmol) were dissolved in toluene (6.0 mL) and DBU
(6.0 mL, 4.10 mmol) was added under nitrogen atmosphere. Then the reaction allowed to stir at 120 oC
for overnight. It was allowed to room temperature and the mixture was neutralized with 2M HCl, then
the reaction mixture was extracted by water (50 mL) and dichloromethane (50 mL). The combined
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organic layers were washed with brine, dried over anhydrous MgSO4, filtered and concentrated under
reduced pressure. The residue was purified by column chromatography on silica gel to afford 3b
(416.2 mg, 51%) as solid. Rf 0.82 (EtOAc/Hex = 1/8); [α]25 +13.38 (c = 1.0, CH2Cl2); IR (KBr) v
D
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2924, 2853, 2107, 1643, 1459, 1397 cm-1; H NMR (400 MHz, CDCl3) δ 7.73 (d, J = 12.6 Hz, 1H,
ArH), 7.41-7.27 (m, 3H, ArH), 7.20-7.17 (m, 1H, ArH), 5.91 (dt, J = 10.5, 10.2 Hz, 1H, H-5), 5.51 (dd,
J = 11.4, 10.8 Hz, 1H, H-4), 5.41 (s, 1H, CHPh), 4.33 (m, 1H, H-2), 4.25 (dd, J = 7.8, 7.2 Hz, 1H, H-4),
3.82 (d, J = 15.0 Hz, 1H, H-3), 3.97 (t, J = 12.3 Hz, 1H, H-1a), 3.44-3.35 (m, 1H, H-1b), 1.18 (m, 24H,
CH2), 0.8 (t, J = 6.8 Hz, CH3); 13C NMR (100 MHz, CDCl3) δ 137.7 (C), 129.1 (CH × 2), 128.6 (CH ×
2), 127.8 (CH × 2), 101.0 (CH), 81.8 (CH), 68.9 (CH), 57.3 (CH), 32.4 (CH2), 31.9 (CH2), 29.65 (CH2
× 2), 29.63 (CH2 × 2), 29.5 (CH2), 29.4 (CH2), 29.3 (CH2), 29.2 (CH2), 28.6 (24H, CH2), 22.7 (CH2),
13.9 (CH3); HRMS (ESI, M+H+) calcd for C25H40O2N3 414.3115, found 414.3348.
4.9. (2S,3R,4E)-2-Aminooctadec-4-ene-1,3-diol (1).
Method A: To a solution of compound 3a (241.0 mg, 0.54 mmol) in methanol (2.40 mL) was added
hydrazine (0.81 mL, 0.81 mmol) and the resulting mixture was stirred at preheated oil bath to reflux.
Upon completion of the reaction, as indicated by TLC (6 hours) cooled to room temperature and
concentrated. Then it dissolved in 85% TFA/EtOH (1.5 mL/0.2 mL) and the temperature was raised to
50 oC. After completion of the reaction, the residue was chromatographed on silica gel to provide 1
(104 mg, 61%) as a white solid. Method B: To a solution of compound 3b (210.mg, 0.051 mmol)
o
dissolved in THF/H2O (1.8/0.2 mL) and kept it in 0 C for 5 minutes. Then PPh3 (266.0 mg, 1.015
mmol) added and the reaction mixture was stirred for 15 minutes at same temperature after that, it was
allowed to stir at rt for 5-6 hours. After completion of the reaction judged by TLC, the solvent was
concentrated and the crude amine derivative was used to next step without further purification. The
amine derivative was dissolved in 85% AcOH/EtOH (1.3/0.2 mL) and it put into preheated oil bath at
o
50-60 C and stirred for 24 hours at same temperature. After completion of the reaction the solvent
removed under vacuum and extracted with water and EtOAc (3 × 10) the organic layer dried over
anhydrous MgSO4, concentrated under reduced pressure. The crude product purified by column
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chromatography to afford (70.0 mg, 46%) as a yield. Rf 0.37 (MeOH/DCM = 1/5); [α]25 -1.62 (c 0.9,
D
o
o
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CHCl3) (lit.9 [α]25 -1.6); mp 70-72 C (lit.9 72-75 C); IR (KBr) v 3747, 3351, 2918, 2850 cm-1; H
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NMR (400 MHz, CDCl3) δ 5.75 (dtd, J = 15.4, 6.8, 1.2 Hz, 1H), 5.45 (dd, J = 15.4, 6.9 Hz, 1H), 4.06 (t,
J = 5.9 Hz, 1H), 3.67 (dd, J = 10.6, 4.6 Hz, 2H), 2.88 (dd, J = 13.8, 3.9 Hz, 6H), 2.05 (dd, J = 14.1, 6.9
Hz, 2H), 1.36 (dd, J = 12.1, 5.4 Hz, 2H), 1.32-1.26 (m, 18H), 0.88 (t, J = 6.8 Hz, 3H); 13C NMR (100
MHz, CDCl3) δ 134.7 (CH), 129.2 (CH), 75.2 (CH), 75.0 (CH), 63.7 (CH2), 56.3 (CH2), 32.4 (CH2),
32.0 (CH2), 29.7 (CH2 × 2), 29.59 (CH2 × 3), 29.4 (CH2 × 2), 22.8 (CH2), 14.3 (CH3); HRMS (ESI,
M+H+) calcd for C18H38O2N 300.2903, found 300.2904.
Acknowledgements
The authors thank the Ministry of Science and Technology (MOST) in Taiwan (MOST
105-2113-M-005-007 and 106-2113-M-005 -007) and National Chung Hsing University for financial
support.
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Highlights
ò
ò
Sphingosine plays an important role in biological activities.
We used two kinds of protecting groups (Phthalic anhydride and azide) for
amino group in commercially available phytosphingosine.
This is the direct and simple synthetic strategy including C1 and C3-OH
protection, leaving group installing at C4, elimination and the global
de-protection.
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We have reported a facile protocol for the synthesis of sphingosine from
phytosphingosine with developing an efficient route with fewer reaction steps
and improved yields.