A convergent total synthesis of a new antiepileptic ceramide and its triacetyl derivative using olefin cross metathesis

Article abstract of DOI:10.1016/j.tet.2010.07.049

A convergent total synthesis of a new antiepileptic ceramide 1b and its triacetyl derivative 1b′ was completed by using two important C-C bond forming reactions, Wittig methylenation and olefin cross metathesis as the key steps. The easily available 3,4,6

Full text of DOI:10.1016/j.tet.2010.07.049

Tetrahedron 66 (2010) 7504e7509
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
A convergent total synthesis of a new antiepileptic ceramide and its triacetyl
derivative using olefin cross metathesis
*
Partha Ghosal, Vikas Kumar, Arun K. Shaw
Division of Medicinal and Process Chemistry, Central Drug Research Institute (CDRI), CSIR, Lucknow 226 001, India
a r t i c l e i n f o
a b s t r a c t
A convergent total synthesis of a new antiepileptic ceramide 1b and its triacetyl derivative 1b0 was
completed by using two important CeC bond forming reactions, Wittig methylenation and olefin cross
metathesis as the key steps. The easily available 3,4,6-tri-O-benzyl-D-galactal was used as a chiral pool for
the synthesis of highly functionalized amide 3 and the commercially available 1,12-dodecanediol for the
long chain olefin counterpart 4. The long hydrocarbon chain of the new ceramide 1b was installed by
Article history:
Received 23 June 2010
Received in revised form 20 July 2010
Accepted 20 July 2010
Available online 23 July 2010
using olefin cross metathesis between amide
hydrogenation.
3
and long chain terminal olefin
4 followed by
Dedicated in memory of Professor Sailendra
Jha Jadavpur University
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Natural product
Ceramide
Epilepsy
D
-Galactal
Olefin cross metathesis
1. Introduction
epilepsy. In 2008, Ahmed et al.4 reported isolation of ceramide
mixture 1 having two ceramides 1a and 1b from Negombata corti-
cata, a red sea sponge (Fig. 1). This mixture was found to exhibit in
vivo anticonvulsant5a activity comparable to diazepam.5b The anti-
epileptic activity of this mixture of natural products 1a and 1b and,
also as a result of our interest toward the total synthesis of natural
products and their analogues starting from commercially available
sugars6 motivated us to take attempt toward the total synthesis of
ceramide 1a or 1b. Hereinwewish to report a chiron approach to the
total synthesis of ceramide 1b via olefin cross metathesis reaction
between two terminal olefin building blocks.5c
Epilepsy is a seizure disorder, which affects the nervous system.
The disease is characterized by 40 different types of recurrent un-
provoked seizures.1 According to WHO around 50 million pop-
ulation of world is affected by epilepsy out of which 90% found in
developing countries.2 Although the current marketed drugs pro-
vide ample seizure control in many patients, they have to compro-
mise with notable adverse side effects and about 28e30% patients
are not seizure free with the available antiepileptic drugs.3 As the
epilepsy cannot be totally controlled by available medicines, there is
always need of safe andmoreeffectiveantiepilepticagents to control
O
O
O
C17H35
HO
NH
C17H35
PO
NH OP
OH
13
13
HN
n2
OH
OH
1b
OP
2
HO
n1
OH
O
O
OH OP
1a n1 = 3, n2 = 1
1b n1 = 1, n2 = 3
PO
PO
NH OP
C17H35
PO
12
4
OP OP
6
OP
Figure 1. Structure of stereo isomeric ceramide 1a and 1b.
8
OP
3
P = Protecting group
Scheme 1. Retrosynthesis analysis of ceramide 1b.
* Corresponding author. Tel.: þ919415403775; fax: þ91 522 2623405; e-mail
address: akshaw55@yahoo.com (A.K. Shaw).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.07.049

P. Ghosal et al. / Tetrahedron 66 (2010) 7504e7509
7505
i. Tf2O, Py, Dry DCM
-20 oC
2. Results and discussion
N3
OBn
BnO
x
The retrosynthetic strategy for target ceramide 1b is depicted in
Scheme 1. We envisaged that 1b could be elaborated from pro-
tected amide 2 by hydrogenation of the double bond and removal
of protecting groups. The amide 2 could in turn be prepared by
utilizing the olefin cross metathesis between the amide 3 and the
long chain olefin counterpart 4. The amide part 3 could be obtained
ii. NaN3, Dry DMF
-20 oC to rt
OBn
N3
i. CH3SO2Cl, Dry DCM
Py, 0 oC to rt
x
OBn
OH OBn
BnO
BnO
ii. NaN3, Dry DMF
OBn
OBn OBn
60-120 o
C
from -galactal derived alcohol 6 by SN2 displacement of free OH
D
6
with a nitrogen nucleophile to generate amino functionality and
subsequent N-acylation of the free amine.
As per retrosynthesis shown in Scheme 1, synthesis of assembly
3 was commenced from readily available 3,4,6-tri-O-benzyl-
PPh3
DIAD
Phthalimide
THF, 12h
75%
N3
OBn
DPPA, DIAD, PPh3, THF
-20 oC to rt
-20 o
to rt,
C
OBn
D
-gal-
-ga-
Decomposed
actal. Its exposure to 4 M H2SO4 in THF furnished 2-deoxy-
D
Stearoyl
Chloride
Aq. K2CO3
lactose 7 quantitatively (Scheme 2).7 In the next step Wittig
methylenation of hemiacetal 7 was essentially required to obtain
alcohol 6. Therefore, several trial experiments were carried out to
optimize the condition for Wittig methylenation8 of the hemiacetal
7 with methyltriphenylphosphonium bromide in the presence of n-
BuLi (1.6 M solution in THF) at various temperatures (0 ꢀC to
ꢁ30 ꢀC). Here, performing the reaction at ꢁ20e0 ꢀC was not very
clean. The column chromatographic purification of the reaction
mixture led to the isolation of the desired olefin 6 in less than 30%
yield along with an inseparable mixture containing 6 and by
products. However, the reaction was found trouble free when it was
strictly carried out below ꢁ20 ꢀC and the best result was obtained
when the reaction was performed at ꢁ25 ꢀC using an ethanol bath
cooled by an immersion cooler furnishing 6 in 82% yield (Table 1).
O
O
O
OBn
NH2
MeNH2
N
OBn
NH OBn
C17H35
BnO
EtOH-H2O
Dry DCM
0
oC to rt, 2h,
(1:1), 48 h OBn OBn
OBn OBn
OBn
77% from 5
5
5a
3
Scheme 3. Synthesis of amide 3.
complex 5 to the corresponding amine and this was done smoothly
by treating 5 with MeNH2 in EtOH/H2O (1:1) for 48 h at room
temperature.11 The crude amine was passed through a short filter
column of silica gel and then the required N-acylation12 was ac-
complished by treating the column filtered amine with stearoyl
chloride in presence of aqueous K2CO3 to obtain 3 with the natural
ceramide backbone in 77% yield over two steps (Scheme 3).
With the assembly 3 in hand, our next attempt was focused
toward the synthesis of long chain olefin counterpart 4. To
accomplish its synthesis, the commercially available 1,12-dodeca-
nediol was protected with TBSCl to give the monoprotected
12-(tert-butyldimethylsilyloxy)dodecan-1-ol 8 in 55% yield.13 Oxi-
dation of the long chain primary alcohol 8 with IBX in acetonitrile
and Wittig olefination6c of the resulting aldehyde 9 furnished olefin
10 in 81% yield over two steps. The cleavage of silyl ether in 10 with
TBAF in THF yielded alcohol 11 in excellent yield (92%). The internal
double bond of alcohol 11 was then hydrogenated with H2 in
presence of Pd/C to obtain the saturated alcohol 12, which on ox-
idation with IBX in acetonitrile followed by Wittig olefination of the
resulting aldehyde 13 furnished the desired long chain olefin 4 in
89% yield over three steps (Scheme 4).
OBn
OBn
4 M H2SO4
O
OH
O
OBn
Ph3PCH3Br
OH
THF, 0 oC to rt
12 h, quantitative
BnO
BnO
nBuLi, THF
- 25 oC, 3 h,
82%
OBn OBn
OBn
OBn
Benzylated-D-galactal
7
6
Scheme 2. Synthesis of alcohol 6.
Table 1
Wittig reaction of hemiacetal
conditions
7 with CH3PPh3Br and n-BuLi under different
Entry
Temperature (in ꢀC)
Time (h)
Isolated yield (%) of 6
1
2
3
4
5
6
7
0 to rt
ꢁ5
2
2
2.5
2.5
3
<10
12
17
20
27
82
80
ꢁ10
ꢁ15
ꢁ20
ꢁ25
ꢁ30
TBDMSCl,NaH
THF, 55%
OH
IBX, CH3CN
Reflux, 1h
1,12 dodecanediol
TBSO
9
8
3
6
iPrCH2CH2PPh3Br
t-BuOK, Dry THF
TBAF, THF
TBSO
TBSO
HO
CHO
10
10
9
0 oC to rt,
2h, 92%
-20 oC to rt, 3h
81% for 2 steps
To complete the synthesis of compound 3, the free hydroxyl
group at C-2 in compound 6 had to be converted into amino
functionality with inversion of configuration. This requires SN2
displacement of OH with a nitrogen nucleophile. Unfortunately, the
stereochemical inversion at C-2 was unsuccessful when 6 was
subjected to Mitsunobu inversion in presence of triphenylphos-
phine (TPP), diphenylphosphoryl azide (DPPA), and diisopropyl
azidocarboxylate (DIAD) in THF at ꢁ20 ꢀC to 0 ꢀC.8a To overcome
this problem, the free OH in 6 was derivatized to 2-O-mesylate but
its SN2 displacement with sodium azide in DMF was disappointing
and yielded a complex mixture of products. Similarly, SN2 dis-
placement of its 2-O-triflate derivative with sodium azide at 0 ꢀC to
room temperature was also futile (Scheme 3).
9
H2/ Pd-C
IBX, CH3CN
HO
EtOH, rt
OHC
12
12
11
11
Reflux
1h
12h
12
13
Ph3P=CH2
Dry THF
- 20oC to rt
2h, 89 % for
3 steps
12
4
Scheme 4. Synthesis of alkene 4.
Gratifyingly, when the alcohol 6 was subjected to Mitsunobu
inversion in presence of PPh3, phthalimide, and DIAD in THF at
ꢁ20 ꢀC to room temperature, the desired inverted phthalimido
compound 5 was obtained in 75% yield as a sole stereoisomer
(Scheme 3).8b,9,10 The next step was conversion of phthalimido
Having synthesized two building blocks 3 and 4, our next target
was to couple them together to obtain 2, a synthetic precursor of
ceramide 1b. Removal of double bond and benzyl ether protection
by hydrogenation of 2 should then furnish the target molecule 1b.
Thus, the cross metathesis between 3 and 4 in presence of Grubbs’

7506
P. Ghosal et al. / Tetrahedron 66 (2010) 7504e7509
second generation catalyst (5 mol %) generated compound
2
10% Pd/C and the resulting worked up crude product mixture was
treated with Ac2O and pyridine in the presence of catalytic amount
of DMAP to obtain its corresponding triacetyl derivative 1b0 in 52%
yield over two steps from 2 (Scheme 5 and Table 3, entry 6). The
identification of the triacetyl derivative 1b0 was completed by an-
alyzing its detailed spectral data, which further led to confirm the
formation of the target trihydroxy natural ceramide 1b (see
Supplementary data).
(Scheme 5).14 It was observed that by increasing the equivalents of
long chain alkene 4 the yield of cross metathesis product was
enhanced6a,6b and therefore, when 3 equiv of alkene 4 were used
the cross metathesis product 2 was obtained in 79% yield (Table 2,
entry 3).
O
O
Grubbs IInd gen.
C17H35
BnO
OBn
C17H35
BnO
NH
NH OBn
+
3. Conclusion
12 catalyst, Dry DCM
Reflux, 6 h, 79%
4
12
16
OBn
2
OBn
3
In summary, herein we achieved the first total synthesis of
ceramide 1b and its triacetyl derivative 1b0 by utilizing olefin cross
metathesis reaction between long chain alkene 4 and amide 3. The
highly functionalized amide 3 with a terminal double bond could
also serve as a versatile building block for synthesis of various kinds
of ceramides. Since the reported natural ceramide mixture 1 (1a
and 1b) was found to exhibit in vivo anticonvulsant activity com-
parable to diazepam,4 this class of compounds and their analogues
thus may deserve interest for their development as more potent
and safe antiepileptic agents. Therefore, by using carbohydrate
based amide building block 3 one can install different cross olefin
counterparts and this flexibility will facilitate the synthesis of var-
ious analogues of this ceramide for more improved anticonvulsant
activity.
O
O
Ac2O, Pyridine
H2/Pd-C
C17H35
HO
NH OH
C17H35
AcO
NH OAc
MeOH:CHCl3:AcOH
(5:3:2), rt, 10 h.
DMAP, 0 oC to rt,12 h,
52% over two steps
16
OH
1b
OAc
1b'
Scheme 5. Synthesis of ceramide 1b and 1b0.
Table 2
Optimization of cross metathesis reaction of 3 with long chain alkene 4 in DCM in
presence of Grubbs’ second generation catalyst (5 mol %)
Entry
Equivalent of alkene 4
Time (h)
Isolated yield (%) of 2
1
2
3
4
1
2
3
5
6
6
6
6
62
70
79
81
4. Experimental section
4.1. General
Unfortunately our efforts to cleave three benzyl groups and re-
duction of the internal double bond in 2 under an atmosphere of H2
in presence of catalytic amount of 10% Pd/C or Pd(OH)2 by dis-
solving it in different solvent systems ended with very low yield of
the desired product 1b and it was presumably due to the problem
associated with poor solubility of the corresponding intermediates
and the target ceramide formed during hydrogenation. However,
the hydrogenation of 2 in MeOH/CHCl3/AcOH (5:3:2) by H2 in the
presence of 10% Pd/C by adopting the method reported by Lee et al.
was proceeded smoothly to provide the target natural product 1b
(Table 3).15 The chromatographic purification of the reaction mix-
ture furnished 1b in 28% yield. Here, it is presumed that most of the
hydrogenated product got stuck in the column during its column
chromatography (silica gel) owing to the highly polar nature of the
ceramide 1b and thus reduces its isolated yield.
All the organic solvents were dried by standard methods. NMR
spectra of the synthesized compounds were recorded on Bruker
Avance DPX 200FT, Bruker Robotics, and Bruker DRX 300 Spec-
trometers at 200, 300 MHz (1H) and 50, 75 MHz (13C), respectively.
Experiments were recorded in CDCl3 and CD3OD at 25 ꢀC. Chemical
shifts are given on the
d scale and are referenced to the TMS at
0.00 ppm for proton and 0.00 ppm for carbon. For 13C NMR refer-
ence CDCl3 appeared at 77.4 ppm. Mass spectra were recorded on
a JEOLJMS-600H high resolution spectrometer using EI and DART
mode at 70 eV and IR spectra on PerkineElmer 881 and FTIR-8210
PC Shimadzu Spectrophotometers. Analytical TLC was performed
using 2.5ꢂ5 cm plates coated with a 0.25 mm thickness of silica gel
(60 F-254), and visualization was accomplished with CeSO4 (1% in
2 N H2SO4) followed by charring over hot plate. Silica gel (100e200
and 230e400 mesh) was used for column chromatography. All the
products were characterized by 1H, 13C, IR, ESI-MS spectroscopy.
Optical rotations were determined on an Autopol III polarimeter
using a 1 dm cell at 28 ꢀC in chloroform as the solvents; concen-
trations mentioned are in g/100 mL. Low-temperature reactions
were performed by using immersion cooler with ethanol as the
cooling agent. Grubbs’ second generation catalyst was purchased
from SigmaeAldrich Co.
Table 3
Optimization of solvent system and catalyst for hydrogenation reaction of com-
pound 2
Entry
Solvent system
Catalyst
Isolated yielda (%)
1
2
3
4
5
6
MeOHþCHCl3 (1:1)
MeOHþCHCl3 (2:1)
EtOAcþCHCl3 (1:1)
MeOHþCHCl3 (1:1)
MeOHþCHCl3 (2:1)
MeOH/CHCl3/AcOH (5:3:2)
Pd(OH)2
Pd(OH)2
Pd/C
Pd/C
Pd/C
16
19
12
10
17
52
4.2. Compound 6
Pd/C
a
Isolated yield of the acetylated ceramide 1b0 from 2 (over two steps, hydroge-
Methyltriphenylphosphonium bromide (2.9 g, 8.1 mmol) was
taken in dry THF (25 mL) and the mixture was cooled to ꢁ78 ꢀC.
n-BuLi (3.62 mL, 5.8 mmol, 1.6 M in THF) was added to the mixture
dropwise under N2 atmosphere and the resulting mixture was
stirred for 1 h at ꢁ30 ꢀC. Hemiacetal 7 (0.504 g, 1.16 mmol) in THF
(3 mL) was added to the reaction mixture in dropwise manner. The
reaction mixture was then stirred at ꢁ25 ꢀC for 3 h. After comple-
tion of the reaction it was quenched with saturated aqueous NH4Cl,
and the mixture was extracted with EtOAc (3ꢂ20 mL). The com-
bined organic layers were washed twice with brine, dried over
Na2SO4, and evaporated under reduced pressure to give a residue.
nation and acetylation).
Ahmed et al. reported 1H and 13C NMR spectra of ceramide
mixture 1 (1a and 1b) in CHCl3 as well as in C5D5N.4 Our synthe-
sized chromatographic pure ceramide 1b was insoluble in CHCl3
and also in MeOH but was sparingly soluble in CHCl3/MeOH mix-
ture (2:1). Here, the 1H NMR of 1b was recorded in CDCl3 and
CD3OD mixture but due to the solubility problem, we were not able
to record its 13C NMR spectrum. In order to further confirm its
structure, the precursor 2 was hydrogenated with H2 in presence of

P. Ghosal et al. / Tetrahedron 66 (2010) 7504e7509
7507
Column chromatography purification of the residue yielded com-
pound 6 as an oil (0.411 g, 0.95 mmol, 82%).
d
0.88 (t, J¼6.1 Hz, 3H), 1.25 (br m, 28H), 1.51 (t, J¼5.9 Hz, 2H),
1.97e2.02 (m, 2H), 2.49e2.51(m, 2H), 3.50 (dd, J¼4.0, 9.5 Hz, 1H),
3.55e3.60 (m, 1H), 3.76e3.80 (m, 2H), 4.23e4.31 (m, 1H),
4.39e4.84 (m, 6H), 5.04e5.16 (m, 2H), 5.75 (d, J¼9.0 Hz, 1H),
5.85e5.98 (m, 1H), 7.26e7.35 (m, 15H, AreH); 13C NMR (75 MHz,
Eluent for column chromatography: EtOAc/hexane (1/15, v/v);
Rf¼0.34 (1/6, EtOAc/hexane); [
a]
28 ꢁ60.82 (c 1.43, CHCl3); IR (neat,
D
cmꢁ1): 3459, 3021, 2926, 2360, 1549, 1216; 1H NMR (200 MHz,
CDCl3)
d
2.41e2.46 (m, 2H), 2.84 (br s, 1H, OH), 3.49 (m, 2H), 3.61 (q,
CDCl3) d 14.5 (CH3), 23.1 (CH2), 26.1 (CH2), 29.7e30.1 (12 CH2), 32.3
J¼2.8 Hz, 1H), 3.68e3.77 (m, 1H), 4.00 (m, 1H), 4.40e4.69 (m, 6H),
(CH2), 34.7 (CH2), 37.2 (CH2), 49.8 (CH), 69.4 (CH2), 72.2 (CH2), 73.5
(CH2), 74.0 (CH2), 79.4 (CH), 80.4 (CH), 117.3 (]CH2), 128.0e128.8
(15ꢂAreC), 136.0 (]CH), 138.4 (AreqC), 138.9 (AreqC), 139.0
(AreqC), 173.0 (C]O); DARTeHRMS: m/z [MþH]þ calcd for
C46H68NO4: 698.5148, found 698.5127.
5.04e5.13 (m, 2H), 5.75e5.90 (m, 1H), 7.22e7.33 (m, 15H, ArH); 13C
NMR (50 MHz, CDCl3þCCl4)
d 35.8 (CH2), 70.0 (CH), 71.6 (CH2), 72.9
(CH2), 73.8 (CH2), 74.1 (CH2), 79.3 (CH), 79.7 (CH), 117.9 (]CH2),
128.1e128.8 (15ꢂArC), 135.3 (]CH), 138.5e138.6 (3ꢂAreqC);
DARTeHRMS: m/z [MþH]þ, calcd for C28H33O4 433.2379, found
433.2364.
4.5. Compound 10
4.3. Compound 5
The mono TBS protected alcohol 8 (500 mg, 1.58 mmol) and IBX
(1.7 g, 6.32 mmol) was taken in a 100 mL round bottom flask in
acetonitrile (15 mL) and the resulting reaction mixture was
refluxed for 1 h. The reaction mixture was then cooled to room
temperature and diluted with ether and cooled to 0 ꢀC. After 1 h the
reaction mixture was filtered through a Celite bed and the filtrate
was concentrated under reduced pressure to obtain an oil 9
(490 mg), which was immediately used for the next step without
further purification.
3-Methyl-1-butane triphenylphosphonium bromide (1.96 g,
4.74 mmol) and t-BuOK (354 mg, 3.16 mmol) were taken in a flame
dried two neck round bottom flask and cooled to ꢁ20 ꢀC using an
ethanol bath cooled by an immersion cooler. Dry THF (25 mL) was
added to the reaction mixture under nitrogen atmosphere and it
was stirred for 1 h without further cooling. After 1 h, the reaction
mixture was again cooled to ꢁ20 ꢀC. The solution of above obtained
aldehyde 9 in THF (3 mL) was added to the mixture dropwise at
ꢁ20 ꢀC. The reaction mixture was allowed to warm to room tem-
perature and stirred for 3 h. After completion of the reaction, sat-
urated aqueous NH4Cl was added to the reaction mixture. The
reaction mixture was extracted with EtOAc (3ꢂ20 mL). The com-
bined organic layers were washed twice with brine, dried over
Na2SO4, and concentrated under reduced pressure to give a residue.
Column Chromatography of the residue yielded compound 10 as oil
(472 mg, 1.28 mmol, 81% for two steps).
A solution of phthalimide (342 mg, 2.32 mmol), triphenyl-
phosphine (609 mg, 2.32 mmol), and the alcohol 6 (500 mg,
1.16 mmol) in dry THF (10 mL) was cooled to ꢁ20 ꢀC under argon
atmosphere. An ice cooled solution of DIAD (0.46 mL, 2.32 mmol) in
dry THF (2 mL) was added dropwise to the solution and then the
reaction mixture was stirred at the same temperature for 2 h and
then at room temperature. After overnight stirring, the reaction
mixture was evaporated under reduced pressure to give a residue,
which on column chromatographic purification provided com-
pound 5 (490 mg, 0.87 mmol, 75%).
Eluent for column chromatography: EtOAc/hexane (1/15, v/v);
Rf¼0.44 (1/6, EtOAc/hexane); [
a
]
28 ꢁ103.3 (c 1.27, CHCl3); IR (neat,
D
cmꢁ1): 3855, 3750, 3679, 3455, 3022, 2364, 1708, 1650, 1519, 1216;
1H NMR (300 MHz, CDCl3)
d 2.35e2.41 (m, 1H), 2.47e2.52 (m, 1H),
3.40e3.43 (m, 1H), 3.89 (dd, J¼4.1, 10.2 Hz, 1H), 4.13 (t, J¼10.3 Hz,
1H), 4.35e4.50 (m, 4H), 4.59e4.67 (m, 3H), 4.90 (d, J¼11.2 Hz, 1H),
4.96 (d, J¼10.2 Hz, 1H), 5.04 (dd, J¼1.3, 17.2 Hz, 1H), 5.77e5.84 (m,
1H), 7.13e7.32 (m, 15H, ArH), 7.69 (m, 2H, ArH), 7.79 (m, 2H, ArH);
13C NMR (75 MHz, CDCl3)
d 34.2 (CH2), 52.1 (CH), 67.6 (CH2), 71.9
(CH2), 73.0 (CH2), 74.5 (CH2), 76.8 (CH), 80.4 (CH), 117.2 (]CH2),
123.7 (2ꢂAreC), 127.8e128.7 (15ꢂAreC), 132.2 (2ꢂAreqC), 134.3
(2ꢂAreC), 135.9 (]CH), 138.4 (AreqC), 138.5 (AreqC), 138.6
(AreqC), 168.7 (2ꢂC]O); DARTeHRMS: m/z [MþH]þ calcd for
C36H36NO5 562.2594, found 562.2594.
Eluent for column chromatography: EtOAc/hexane (1/30, v/v);
Rf¼0.59 (1/49, EtOAc/hexane); IR (neat, cmꢁ1): 2928, 2857, 2363,
4.4. Compound 3
2106, 1218, 1096; 1H NMR (300 MHz, CDCl3)
d 0.05 (m, 6H),
0.88e0.91 (m, 15H), 1.27 (m, 16H), 1.47e1.67 (m, 3H), 1.89e2.04 (m,
A solution of compound 5 (170 mg, 0.30 mmol) in EtOH/H2O
(1:1, 10 mL) was treated with a 40% aqueous solution of methyl
amine (20 equiv) and stirred at room temperature for 48 h. The
reaction mixture was then concentrated under reduced pressure,
dissolved in water (15 mL), and extracted with ethyl acetate
(3ꢂ10 mL). The combined organic extracts were washed twice with
brine, dried over Na2SO4, and evaporated under reduced pressure.
4H), 3.60 (t, J¼6.6 Hz, 2H), 5.32e5.45 (m, 2H); 13C NMR (75 MHz,
CDCl3)
d
ꢁ4.9 (2ꢂCH3), 18.8 (qC), 22.8 (2ꢂCH3), 26.2 (CH2), 26.4
(3ꢂCH3), 27.7 (CH2), 29.1 (CH(CH3)2), 29.8e30.2 (7ꢂCH2), 33.3
(CH2), 36.8 (CH2), 63.7 (CH2), 128.9 (]CH), 131.0 (]CH);
DARTeHRMS: m/z [MþH]þ calcd for C23H49OSi 369.3553, found
369.3531.
The crude amine was passed through
a
filter column for
4.6. Compound 11
purification.
To a solution of amine 5a in DCM (7 mL) was added an aqueous
potassium carbonate solution (3 mL, 50%) at 0 ꢀC and at the same
temperature after 10 min under vigorous stirring to this reaction
mixture was added portion wise stearoyl chloride (0.11 mL,
0.33 mmol). The mixture was further vigorously stirred for 2 h at
room temperature. After completion of the reaction, the reaction
mixture was poured into brine and extracted with DCM (3ꢂ10 mL).
The combined organic extracts were dried over Na2SO4 and evap-
orated under reduced pressure to give a residue. Flash chroma-
tography of this residue yielded compound 3 as an oil (162 mg,
0.23 mmol, 77% for two steps).
To a stirred solution of 10 (450 mg, 1.22 mmol) in THF (10 mL)
was added TBAF (1.35 mL, 1.0 M solution in THF) at 0 ꢀC and left for
stirring at room temperature. After 2 h, saturated aqueous solution
of NH4Cl (20 mL) was added to the reaction mixture and it was
extracted with EtOAc (3ꢂ15 mL). The combined organic layers were
dried over Na2SO4 and concentrated under reduced pressure to give
a residue, which on column chromatographic purification provided
compound 11 (285 mg, 1.12 mmol, 92%) as a colorless oil.
Eluent for column chromatography: EtOAc/hexane (1/15, v/v);
Rf¼0.44 (1/4, EtOAc/hexane); IR (neat, cmꢁ1): 3414, 2364, 1637,
1440, 1219; 1H NMR (300 MHz, CDCl3)
d 0.87e0.89 (m, 6H), 1.27 (m,
Eluent for column chromatography: EtOAc/hexane (1/20, v/v);
16H), 1.51e1.63 (m, 4H), 1.89e2.03 (m, 4H), 3.62 (t, J¼6.6 Hz, 2H),
5.31e5.43 (m, 2H); 13C NMR (75 MHz, CDCl3)
22.7 (2ꢂCH3), 26.1
(CH2), 27.7 (CH2), 29.1 (CH), 29.7e30.1 (7ꢂCH2), 33.2 (CH2), 36.7
Rf¼0.50 (1/4, EtOAc/hexane); [
a]
28 ꢁ27.92 (c 2.43, CHCl3); IR (neat,
d
D
cmꢁ1): 3439, 2927, 2363, 1637, 1219; 1H NMR (300 MHz, CDCl3)

7508
P. Ghosal et al. / Tetrahedron 66 (2010) 7504e7509
(CH2), 63.4 (CH2), 128.9 (]CH), 131.0 (]CH); DARTeHRMS: m/z
[MþH]þ calcd for C17H35O 255.2688, found 255.2714.
through a syringe to the stirring reaction mixture. The septum was
replaced with a glass stopper while the stirring was continued. The
solution was refluxed for 6 h. The temperature of the reaction
mixture was brought slowly to room temperature. The organic
solvent was evaporated under reduced pressure to give a black
residue, which was purified by column chromatography to give
compound 2 as a semi-solid compound (210 mg, 0.228 mmol, 79%).
Eluent for column chromatography: EtOAc/hexane (1/20, v/v);
4.7. Compound 12
Catalytic amount of 10% Pd/C (20 mg) was added to a solution of
11 (250 mg, 0.982 mmol) in ethanol (10 mL). A vacuum was created
in a round bottom flask containing the above reaction mixture with
the help of pump and left for stirring under a positive pressure of H2
in a balloon. After the completion of the reaction (TLC control, 12 h)
catalyst was removed by filtration, washed with methanol twice
and the combined filtrate was concentrated to afford compound 12
(260 mg) as a semi-solid residue, which was immediately used for
the next step without further purification.
Rf¼0.61 (1/4, EtOAc/hexane); [
a]
28 ꢁ20.98 (c 0.33, CHCl3); IR (neat,
D
cmꢁ1) 3421, 2927, 2855, 2364, 1641, 1217; 1H NMR (300 MHz,
CDCl3)
d 0.85e0.87 (m, 9H), 1.16e1.18 (m, 2H), 1.25 (m, 50H),
1.49e1.56 (m, 3H), 1.95e1.98 (m, 4H), 2.34e2.43 (m, 2H), 3.50e3.54
(m, 2H), 3.73e3.78 (m, 2H), 4.32 (br s, 1H), 4.43e4.81 (m, 6H),
5.48e5.52 (m, 2H), 5.71 (d, J¼9.1 Hz, NH), 7.29e7.30 (br m, 15H,
Eluent for column chromatography: EtOAc/hexane (1/15, v/v);
ArH); 13C NMR (75 MHz, CDCl3)
d
14.46 (CH3), 23.0 (2ꢂCH3), 23.1
Rf¼0.44 (1/4, EtOAc/hexane); IR (neat, cmꢁ1): 3423, 3022, 2929,
(CH2), 26.1 (CH2), 27.8 (CH2), 28.4 (CH), 29.7e29.8 (4ꢂCH2), 29.9
(2ꢂCH2), 30.0 (CH2), 30.1 (15ꢂCH2), 32.3 (CH2), 33.1 (CH2), 33.5
(CH2), 37.2 (CH2), 39.5 (CH2), 49.8 (CH), 69.5 (CH2), 72.2 (CH2), 73.4
(CH2), 73.9 (CH2), 79.6 (CH), 80.7 (CH), 126.9 (]CH), 127.9e128.8
(15ꢂArC), 133.6 (]CH), 138.5 (AreqC), 139.0 (AreqC), 139.1
(AreqC), 172.9 (HNC]O); DARTeHRMS: m/z [MþH]þ calcd for
C62H100N1O4 922.7652, found 922.7644.
2368, 1217; 1H NMR (200 MHz, CDCl3)
d 0.84e0.87 (m, 6H), 1.25 (m,
24H), 1.45e1.54 (m, 3H), 3.61 (m, 2H); 13C NMR (75 MHz, CDCl3)
d
23.0 (2ꢂCH3), 26.1 (CH2), 27.8 (CH2), 28.4 (CH), 29.8e30.3
(9ꢂCH2), 33.2 (CH2), 39.5 (CH2), 63.5 (CH2); DARTeHRMS: m/z
[MꢁH]þ calcd for C17H35O 255.2688, found 255.2689.
4.8. Compound 4
4.10. Compound 1b
To a solution of compound 12 (260 mg) in acetonitrile (6 mL)
was added IBX (825 mg, 2.95 mmol) and the reaction mixture was
allowed to stir under reflux for 1 h. The resulting mixture was then
cooled to room temperature, diluted with anhydrous ether and
cooled to 0 ꢀC. After 1 h the resulting reaction mixture was filtered
through a Celite bed and the filtrate obtained was concentrated
under reduced pressure to give the corresponding aldehyde 13
(241 mg), which was immediately used for Wittig olefination
without further purification.
Catalytic amount of 10% Pd/C (20 mg) was added to a solution of
2 (40 mg, 0.043 mmol) in MeOH/CHCl3/AcOH (5:3:2, 5 mL). A vac-
uum was created in a round bottom flask containing the above
reaction mixture with the help of pump and left for stirring under
H2 in a balloon with a positive pressure. After the completion of the
reaction (TLC control, 10 h), the catalyst was removed by filtration,
washed with MeOH/CHCl3 (1:2, 2ꢂ10 mL) and the combined fil-
trate was concentrated under reduced pressure to afford a solid
residue, which was purified by column chromatography to give 1b
(8 mg, 0.012 mmol, 28%) as a white powder.
To a precooled (ꢁ20 ꢀC, using an ethanol bath cooled by im-
mersion cooler) mixture of methyltriphenylphosphonium bromide
(1.753 g, 4.91 mmol) and t-BuOK (330 mg, 2.95 mmol), dry THF
(20 ml) was added and the reaction mixture was stirred without
further cooling. After 1 h, the reaction mixture was again cooled to
ꢁ20 ꢀC and the solution of crude aldehyde 13 in dry THF (3 mL) was
added dropwise to the reaction mixture. The resulting mixture was
stirred at room temperature for 2 h. After completion of the re-
action, it was quenched with saturated aqueous NH4Cl, and the
resulting mixture was extracted with EtOAc (3ꢂ15 mL). The com-
bined organic layers were washed twice with brine, dried over
Na2SO4, and evaporated under reduced pressure. Flash chroma-
tography of the resulting residue yielded compound 4 as an oil
(220 mg, 0.87 mmol, 89% for three steps).
Eluent for column chromatography: MeOH/CHCl3 (1/5, v/v);
28
Rf¼0.55 (1/9, MeOH/CHCl3); [
a
]
D
þ41.23 (c 0.11, CHCl3); IR (neat,
cmꢁ1) 3424, 2921, 2853, 2359, 1644, 1219; 1H NMR (300 MHz,
0.85e0.87 (m, 9H), 1.16 (m, 2H), 1.26 (br m, 56H),
1.47e1.68 (m, 5H), 2.21 (t, J¼7.1 Hz, 2H), 3.38 (m, 2H), 3.54 (m, 1H),
3.78e3.82 (m, 1H), 4.08 (m,1H), 6.93 (d, 1H, J¼8.9 Hz, NH);
DARTeHRMS: m/z [MþH]þ calcd for C41H84N1O4 654.6400, found
654.6404.
CDCl3þCD3OD)
d
4.11. Compound 1b0
The crude trihydroxy ceramide (35 mg) obtained after hydro-
genation of compound 2 (50 mg, 0.054 mmol) was taken in pyri-
dine (1 mL), cooled to 0 ꢀC and after five min Ac2O (0.5 mL) and
catalytic amount of DMAP was added to it. The reaction mixture
was allowed to stir for overnight. After completion of the reaction,
the reaction mixture was concentrated and purified by column
chromatography to furnish acetylated ceramide 1b0 (22 mg,
0.028 mmol, 52% over two steps).
Eluent for column chromatography: hexane; Rf¼0.92 (hexane);
IR (neat, cmꢁ1) 3022, 2926, 2855, 2362, 1647, 1521, 1217; 1H NMR
(300 MHz, CDCl3)
d 0.87e0.89 (m, 6H), 1.16e1.18 (m, 2H), 1.27 (m,
20H), 1.37e1.41 (m, 2H), 1.47e1.60 (m, 1H), 2.05 (dd, J¼6.8, 12.5 Hz,
2H), 4.92e5.03 (m, 2H), 5.75e5.89 (m, 1H); 13C NMR (75 MHz,
CDCl3)
d
23.1 (2ꢂCH3), 27.9 (CH2), 28.4 (CH(CH3)), 29.4 (CH2), 29.6
(CH2), 30.0 (CH2), 30.1e30.2 (6ꢂCH2), 30.4 (CH2), 34.3 (CH2), 39.5
(CH2), 114.5 (]CH2), 139.6 (]CH); DARTeHRMS: m/z [MþH]þ calcd
for C18H37 253.2895, found 253.2877.
Eluent for column chromatography: EtOAc/hexane (1/7, v/v);
Rf¼0.55 (1/3, EtOAc/hexane); [
a]
28 þ30.74 (c 0.21, CHCl3); IR (neat,
D
cmꢁ1) 3427, 3022, 2924, 2362, 1713, 1654, 1218; 1H NMR (300 MHz,
4.9. Compound 2
CDCl3) d 0.85 (s, 3H), 0.87 (m, 6H), 1.16 (m, 2H), 1.26 (m, 56H),
1.41e1.58 (m, 5H), 2.04 (s, 6H), 2.07 (s, 3H), 2.18e2.23 (m, 2H), 3.99
(dd, J¼2.9, 11.7 Hz, 1H), 4.26e4.31 (m, 1H), 4.44e4.51 (br m, 1H),
4.91e4.95 (m,1H), 5.09e5.12 (m,1H), 5.94 (d, J¼9.4 Hz,1H, NH); 13C
To a 50 mL two necked oven dried round bottom flask fitted
with a reflux condenser and septum was added Grubbs’ second
generation catalyst (12 mg, 0.014 mmol) under argon atmosphere.
Dry degassed CH2Cl2 (2 mL) was then added to the above round
bottom flask through a syringe and the solution was kept for stir-
ring. Compounds 3 (200 mg, 0.287 mmol) and long chain alkene 4
(220 mg, 0.86 mmol) in DCM (2 mL each) were added in succession
NMR (75 MHz, CDCl3)
d 14.5 (CH3), 21.1 (CH3), 21.2 (CH3), 21.4
(COCH3), 23.0 (2ꢂCOCH3), 23.1 (CH2), 25.9 (CH2), 26.0 (CH2), 27.8
(CH2), 28.4 (CH), 28.5 (CH2), 29.6 (CH2), 29.7 (CH2), 29.8 (2ꢂCH2),
29.9 (2ꢂCH2), 30.1 (17ꢂCH2), 30.4 (CH2), 32.3 (CH2), 37.2 (CH2), 39.5
(CH2), 47.8 (CH), 63.3 (CH2), 72.4 (CH), 73.4 (CH), 170.5 (CH3C]O),

P. Ghosal et al. / Tetrahedron 66 (2010) 7504e7509
7509
sphingosine and sphingolipids see: (i) Howel, A. R.; So, R. C.; Richardson, S. K.
Tetrahedron 2004, 60, 11327e11347; (ii) Liao, J.; Tao, J.; Lin, G.; Liu, D. Tetrahe-
dron 2005, 61, 4715e4733; (iii) Risseeuw, M. D. P.; Berkers, C. R.; Ploegh, H. L.;
Ovaa, H. Tetrahedron Lett. 2006, 47, 3677e3679; (iv) Khaja, S. D.; Kumar, V.;
Ahmad, M.; Xue, J.; Matta, K. L. Tetrahedron Lett. 2010, 51, 4411e4414.
6. (a) Ghosal, P.; Shaw, A. K. Tetrahedron Lett. 2010, 51, 4140e4142; (b) Ghosal, P.;
Kumar, V.; Shaw, A. K. Carbohydr. Res. 2010, 345, 41e44; (c) Kumar, V.; Shaw, A.
K. J. Org. Chem. 2008, 73, 7526e7531; (d) Reddy, L. V. R.; Swamy, G. N.; Shaw, A.
K. Tetrahedron: Asymmetry 2008, 19, 1372e1375; (e) Reddy, L. V. R.; Reddy, P. V.;
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171.3 (CH3C]O), 171.5 (CH3C]O), 173.2 (NHC]O); DARTeHRMS:
m/z [MþH]þ calcd for C47H90N1O7 780.6717, found 780.6708.
Acknowledgements
We are thankful to Anup K. Pandey for technical assistance, and
SAIF, CDRI, for providing spectral data. P.G. and V.K. thank CSIR, New
Delhi, for financial support. CDRI communication number 7945.
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Supplementary data
Supplementary data associated with this article can be found in
online version at doi:10.1016/j.tet.2010.07.049. These data include
MOL files and InChIKeys of the most important compounds
described in this article.
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