Stereoselective total synthesis of Jaspine B (Pachastrissamine) utilizing iodocyclization and an investigation of its cytotoxic activity

Article abstract of DOI:10.1016/j.tetasy.2013.07.003

The stereoselective synthesis of Jaspine B has been achieved from easily available (S)-Garner's aldehyde. The trisubstituted tetrahydrofuran core of Jaspine B was constructed by utilizing a diastereoselective iodocyclization as the key step. Deiodination

Full text of DOI:10.1016/j.tetasy.2013.07.003

Tetrahedron: Asymmetry 24 (2013) 903–908
Contents lists available at SciVerse ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
Stereoselective total synthesis of Jaspine B (Pachastrissamine)
utilizing iodocyclization and an investigation of its cytotoxic activity
Partha Ghosal a, , Sama Ajay a, , Sanjeev Meena b, Sudhir Sinha b, Arun K. Shaw a,
⇑
a Division of Medicinal and Process Chemistry, CSIR-Central Drug Research Institute, Lucknow 226 031, India
b Drug Target Discovery and Development, CSIR-Central Drug Research Institute, Lucknow 226 031, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 April 2013
Accepted 4 July 2013
The stereoselective synthesis of Jaspine B has been achieved from easily available (S)-Garner’s aldehyde.
The trisubstituted tetrahydrofuran core of Jaspine B was constructed by utilizing a diastereoselective iod-
ocyclization as the key step. Deiodination and debenzylation were performed in a single step by using n-
Bu3SnH and ABCN as a conjugate catalyst system. The in vitro cytotoxicity of compounds 1 and 1a against
3 human cancer cell lines-A549 (lung), MCF7 (breast), and KB (oral); and a non-cancer cell line (NIH3T3)
was determined by sulphorhodamine B based assay.
Dedicated to Dr Soundar Divakar on the
occasion of his 60th birthday
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
O
C14H29
O
C14H29
2
5
Jaspine B is a natural cyclic anhydrophytosphingosine deriva-
tive with three contiguous stereogenic centers within a tetrahydro-
furan core. It was initially isolated from an Okinawa marine sponge
Pachastrissa sp. (family Calthropellidae) by Higa et al. who named it
‘Pachastrissamine’.1 It showed marked cytotoxicity, at submicrom-
olar levels, against the human lung carcinoma A549 and some
other cancer cell lines-HT29, MEL28, and P388. Shortly thereafter,
Debitus et al. independently reported on the isolation of two cyto-
toxic compounds, Jaspine A and Jaspine B, from the Vanuatuan
marine sponge Jaspis sp (Fig. 1).2 Based on high resolution NMR,
mass spectra analysis, and chemical derivatization studies, the
structures of Jaspine B and Pachastrissamine were proven to be
identical, having an all-syn trisubstituted structural framework
with a (2S,3S,4S)-absolute configuration.
4
3
O
HN
OH
H2N
OH
H
Jaspine B
(2S,3S,4S)
Jaspine A
Figure 1. Structures of Jaspine A and Jaspine B.
a one-pot intramolecular asymmetric ring opening reaction under
Sharpless asymmetric epoxidation conditions followed by subse-
quent isopropylidene protection of the diol in a consecutive fash-
ion to afford THF domain with three contiguous stereocenters
was the key step.8
In continuation of our efforts toward the synthesis of highly
functionalized chiral building blocks and their utilization for the
synthesis of natural products or biologically important mole-
cules8,14 we were motivated to synthesize natural Jaspine B
through a high efficiency synthetic strategy. Herein, we report a
short route for the synthesis of Pachastrissamine from (S)-Garner’s
aldehyde15,16 in which the long hydrocarbon chain was installed by
involving olefin cross metathesis while construction of the THF
part was achieved by a diastereoselective iodocyclization reaction.
Delgado et al. reported that the cytotoxic potency is dependent
on the stereochemistry of the tetrahydrofuran moiety, although lit-
tle is known about the influence of the aliphatic chain of the mol-
ecule on its activity.3
The impressive bioactivity profile and novel structural features
of Jaspine B encouraged chemists to synthesize it from a large vari-
ety of chiral pool materials such as
xylose,6 -glucose,7 tri-O-benzyl-
sine,9 (R)-glycidol,10 and
L D-
-serine,4 Garner’s aldehyde,5
D
D D-ribo-phytosphingo-
-galactal,8
D
-(ꢀ)tartaric acid.11 Several total synthe-
ses of Jaspine B and its stereoisomers have been reported since
its isolation.4–13 In 2007, we reported on the practical synthesis
of Jaspine B starting from 3,4,6-tri-O-benzyl-D-galactal, in which
2. Results and discussion
As per the retrosynthetic analysis of the title molecule Jaspine B
1 shown in Scheme 1, we envisaged that it could be derived from 9
by N-Boc deprotection which could be obtained by deiodination of
⇑
Corresponding author. Tel.: +91 9415403775; fax: +91 (522) 2623405.
E-mail address: akshaw55@yahoo.com (A.K. Shaw).
These authors contributed equally to this work.
0957-4166/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetasy.2013.07.003

904
P. Ghosal et al. / Tetrahedron: Asymmetry 24 (2013) 903–908
I
O
(S)
(S)
(S)
C13H27
O
O
(R)
(S)
NHBoc
C14H29
C14H29
C13H27
(S)
(S)
(S)
(
)
S
(R)
(S)
H2N
OH
OH
OBn
BocHN
BocHN
OBn
6
OH
1
7a
9
Jaspine B
C13H27
NBoc
NBoc
NBoc
(R)
(R)
O
O
O
CHO
(S)
(S)
(S)
OBn
OBn
2
4
5
(S)-Garner's aldehyde
Scheme 1. Retrosynthetic analysis of Jaspine B 1.
iodide 7a. Iodide 7a could be derived by the iodocyclization of 6,
whose synthesis was possible from acetonide 5 by chemoselective
deprotection. Acetonide 5 could be synthesized by cross metathe-
sis of 1-pentadecene and 4, which could be easily prepared from
(S)-Garner’s aldehyde 2.
In the present approach, the hydroxy group at C3 of the natural
product was introduced via diastereoselective nucleophilic addi-
tion of vinylmagnesium bromide to Garner’s aldehyde15 at
ꢀ78 °C. The required anti allylic alcohol 3a was separated from a
mixture of anti and syn allylic alcohols 3a and 3b (6:1) by column
chromatography in 74% yield. Its formation as the major isomer
can be explained by considering the Felkin-Ahn model involving
a non-chelated transition state.17a In the next step, the olefin cross
metathesis between anti allylic alcohol 3a and 1-pentadecene in
the presence of Grubbs’ second generation catalyst (5–10 mol %)
was attempted14a,b but the reaction did not work efficiently result-
ing in the formation of several inseparable products. Here, it was
presumed that the free hydroxyl group interfered with the metath-
esis reaction and therefore, we decided to protect the alcohol
functionality. Thus, the free OH in the major isomer 3a was pro-
tected as the O-benzyl ether to obtain olefin 4.17b–d Its olefin cross
metathesis reaction with 1-pentadecene was then attempted and
the desired cross coupled olefin 5 was obtained in 92% yield (E:Z,
94:6) when 3 equiv of 1-pentadecene in the presence of Grubbs’
second generation catalyst (3.5 mol %) were used in this reaction
(Scheme 2).
In the next step, a chemoselective isopropylidene opening was
carried out with p-TSA in MeOH at 0 °C to obtain N-Boc protected
1,2-amino alcohol 6 in 91% yield. Its iodocyclization reaction to
give the required trisubstituted THF 7 (diastereomeric mixture of
HO
BnO
MgBr
CHO
Dry THF,-78 oC
BnBr,NaH, DMF,
0 oC - rt, 2 h
2-4 h,
NBoc
NBoc
O
NBoc
O
O
74% for 3a
91%
6:1
2
Major
4
(S)-Garner'saldehyde
3a
C13H27
C13H27
BnO
O
BnO
C13H27
Grubbs Catalyst
II Gen.
(R)
PTSA,Dry THF
NIS (1eq) + I2 (1eq)
Dry THF, 0 oC - rt
(S)
0 oC, 1 h, 91%
NHBoc
NBoc
OBn
Dry DCM, Reflux
6 h, 92%
OH
1.5 h, 90%
5
6
OBn
BocHN
OH
BocHN
BocHN
OBn
BocHN
C13H27
(S)
(S)
S
(
)
(S)
n-Bu3SnH,ABCN
C
13H27
(R)
7a
C14H29
)
S
(
C14H29
(R)
O
O
90 oC, reflux,1 h
O
O
9
I
I
7b
Minor
7a
Major
H2
Pd/C,MeOH
6 h, 95%
TFA·H2N
OH
H2N
OH
)
S
(
2.5M methanolic
(S)
NaOH, rt, 15 min.
97%
DCM:TFA (4:1)
0 oC, 1 h, 90%
9
C14H29
C14H29
(S)
O
O
1a
Scheme 2. Stereoselective synthesis of Jaspine B 1.

P. Ghosal et al. / Tetrahedron: Asymmetry 24 (2013) 903–908
905
Table 1
steric crowding near the si-re (upper) face of the double bond in
6 favored the iodine electrophile to attack the double bond from
Various conditions of iodocyclization
its re-si (bottom) face to form the p
-complex 6’ and then the inter-
Entry
Reagents
Conversion (%)
Isolated yield (%)
Time (h)
nal nucleophile OH approached from the si-re face resulting in the
formation of 7a as the major isomer. The formation of the minor
isomer 7b was attributed to the involvement of another conforma-
tion of 6 in which the allylic –OBn was ‘outside’ to the double bond.
1
2
3
4
I2
50
100
70
42
63
64
90
4
2
4
1.5
I2, NaHCO3
NIS
NIS+I2 (1:1)
100
Here iodine formed the disfavored p-complex 6’’ at the si-re face of
the double bond and therefore OH approached from the re-si face
to furnish the minor isomer 7b. It is worth mentioning that Cham-
berlin’s model rationalizes the selectivity on the basis of a mecha-
7a and 7b) was screened under different conditions (Table 1). First
it was tried with molecular I2 (1.5 equiv) in THF solvent; only 50%
of the starting material was converted into product, yielding the
THF 7 in 42% yield. In an attempt to improve the yield of 7, we per-
formed the same iodocyclization reaction in the presence of I2
(1.5 equiv) and NaHCO3 in THF.18 The THF 7 was obtained in 63%
yield, with 100% conversion. When we tried this reaction with
NIS (1.5 equiv), which is more electrophilic in nature compared
to molecular I2, a slight improvement in conversion (70%) of 6 into
7 was observed. However, the 100% conversion of 6 into iodocyc-
lized product 7 was made possible with a combination of two io-
dine sources (NIS+I2). Thus, performing this transformation by
using equimolar (1.0 equiv) I2 and NIS led to complete conversion
of 6 into 7 in 90% yield, with 10:1 diastereoselectivity (HPLC). The
major isomer 7a was then separated by silica gel column chroma-
tography in 81% yield. It is worth mentioning that the thermody-
nism with an early, reactant like transition state (formation of a p-
complex) as the RDS (and hence stereodefining step), rather than a
fast and reversible formation and subsequent slow attack on an
iodonium ion intermediate (Scheme 4).
The 1D and 2D NMR experiments on 7a showed the formation
of a trisubstituted THF skeleton. However, we were unable to ana-
lyze its stereochemistry due to the appearance of overlapping sig-
nals belonging to the THF skeleton in 1H NMR spectra. Therefore, to
establish the absolute stereochemistry of the newly formed THF
core, iodide 7a was subjected to reductive deiodination using an
n-Bu3SnH/AIBN system.20 This led to the formation of two com-
pounds which were separated by silica gel column chromatogra-
phy. The major product was isolated in 32% yield where both the
iodine and benzyl functionalities were removed and was charac-
terized as 9. The minor product isolated in 27% yield was identified
as deiodinated THF derivative 8. In order to improve the yield of 9,
ABCN (azobis (cyclohexanecarbonitrile)),21 which is a more reac-
tive radical initiator than AIBN was used in this transformation.
However, only a slight improvement in the yield of 9 (42%) was ob-
served. Replacing n-Bu3SnH/AIBN with tris(trimethylsilyl)-silicon
hydride (TMS)3SiH)/AIBN or ABCN22 did not give better results
(Scheme 5). We then performed this reaction at different temper-
atures (50–120 °C) and continued each set of reactions for a longer
period, but the yield of 9 did not increase beyond 42% (Table 2).
namically more stable major E-isomer of olefin
6 upon
iodocyclization furnished THF compounds 7a (major) and 7b (min-
or, not isolated). The other diastereomers of 7 were not isolated
from this reaction, which could be obtained from the less stable
minor Z-isomer of 6 (Scheme 3).
The predominant formation of diastereomer 7a over 7b could
be explained by considering the model for iodocyclization pro-
posed by Chamberlin et al..19 The more favored iodine pi (
p) com-
plex 60 in which allylic—OBn was ‘inside’ to the double bond
participated in iodocyclization to form the major isomer 7a. The
C13H27
I
I
O
O
BnO
NIS or I2 or NIS+I2
C13H27
C13H27
dry THF, 0 °C - rt
BocHN
OBn
BocHN
OBn
NHBoc
HO
7a
7b
Major
Minor
6
Scheme 3. Iodocyclization of compound 6.
OH
OH
H
R
I
OBn
(S)
H
si
re
C13H27
H
(S)
O
(R)
C13H27
C13H27
BocHN
BocHN
(R)
(R)
(R)
C
13H27
si
H
re
H
(S)
(S)
I2
H
I2
OBn
6
BocHN
OBn
OBn
I2
favoured π-complex 6'
desired diastereomer 7a
R = -CH(NHBoc)CH2OH
I2
I
I2
OBn
I2
H
H
O
si re C13H27
C13H27
H
OH
C13H27
H
H
(R)
H
(R)
C13H27
H
OH
re si
OBn
(S)
(S)
OBn
R
H
BocHN
OBn
(S)
BocHN
(S)
BocHN
6
6
"
disfavoured π-complex
Scheme 4. Mechanism of iodocyclization.
7b
undesired diastereomer

906
P. Ghosal et al. / Tetrahedron: Asymmetry 24 (2013) 903–908
I
O
O
O
C14H29
C14H29
n-Bu3SnH, ABCN,
90 °C, reflux, 1 h
C13H27
BocHN
BocHN
BocHN
OBn
OH
OBn
7a
9
8
Scheme 5. Reductive deiodination and debenzylation of compound 7a.
ble 3). However, a higher IC50 value for the non-cancer cells sug-
gested some ‘selectivity’ in action. In terms of the Selectivity
Index (SI), compound 1a was more selective (SI range 3.35–5.57)
than 1 (SI range 2.18–3.14). This raises the hope that the structure
of Jaspine B, which apparently acts as a sphingosine kinase inhib-
itor,26 could be suitably optimized with a view to enhance its selec-
tivity as well as cytotoxic potency. Eventually, this may pave the
way for its use in the chemotherapy of cancers.
Table 2
Conditions for the deiodination and debenzylation
Entry
1
Reductant
Catalyst
Yield% of 9:8
Time (h)
n-Bu3SnH
AIBN
ABCN
AIBN
ABCN
32:27
42:32
27:21
32:25
2
1
4
4
2
(TMS)3SiH
3. Conclusion
Since our aim at this stage was to complete the synthesis of the
title molecule 1, we required its precursor 9 exclusively from 7a.
Thus, debenzylation of 8 was performed by H2 (balloon) in the
presence of Pd/C in MeOH to obtain 9 in 95% yield (overall yield
of 9 from 7a was approximately 68%). Here, the 1D, 2D NMR, and
specific rotation of 9 fully matched the reported data.3 The stereo-
chemistry of 9 was further confirmed on the basis of its NOE spec-
trum. The H-1 showed an NOE correlation with both H-2 and H-3,
confirming the presence of all three protons in the same plane. The
N–H showed an NOE correlation with Ha-4, which indicated the
syn-relationship between them. Thus, all of these correlations sup-
ported the syn-relationship between H-1, H-2, H-3, and Hb-4
(Fig. 2).
The deprotection of N-Boc THF 9 under standard acidic condi-
tions (TFA/DCM 1:4, 0 °C, 1 h) led to the formation of the TFA salt
of Pachastrissamine 1a. Finally, salt free Pachastrissamine 1 (Jas-
pine B) was obtained in 97% yield by neutralization of 1a with
2.5 M methanolic NaOH in DCM.23 The spectroscopic and analytical
data of our synthesized compounds 1 and 1a were found to be
identical with the reported values.24
In summary, we have completed an efficient and stereoselective
synthesis of Jaspine B. Here, construction of the THF part was
achieved by utilizing a diastereoselective iodocyclization of unsat-
urated 1,2-aminoalcohol 6. The usage of equimolar amount of I2
and NIS in this transformation was found to be the most successful
combination. The radical deiodination and debenzylation of iodo-
cyclized product 7a was also optimized by n-Bu3SnH and ABCN
as a conjugate catalyst system in a single step. The biological activ-
ity of Jaspine B and its salt was carried out against A549 (lung),
MCF7 (breast), and KB (oral); and a non-cancer cell line (NIH3T3)
by sulphorhodamine B based assay. Cytotoxicity of Jaspine B to-
ward non-cancer cells may pave the way for its use in chemother-
apy of cancers.
4. Experimental
4.1. General
In vitro cytotoxicity of compounds 1 and 1a against three hu-
man cancer cell lines-A549 (lung), MCF7 (breast), and KB (oral);
and a non-cancer cell line (NIH3T3) was determined by sulpho-
rhodamine B based assay.25 To the best of our knowledge, this is
the first report incorporating the cytotoxicity of Jaspine B toward
non-cancer cells. Both compounds were similarly active against
Organic solvents were dried by standard methods. Analytical
TLC was performed using 2.5 ꢁ 5 cm plates coated with
a
0.25 mm thickness of silica gel (60F-254), visualization was accom-
plished with CeSO4 and subsequent charring over hot plate. Col-
umn chromatography was performed using silica gel (60–
120 mesh) and silica gel (230–400 mesh). All the products were
characterized by 1H, 13C, heteronuclear single quantum coherence
(HSQC), IR, and ESI-HRMS. NMR spectra were recorded on Bruker
Avance 300 MHz spectrometer at 300 MHz (1H) and 75 MHz
all three cancer types (IC50 values between 1.4 and 2.66 lM) (Ta-
H
Hb
(
13C), 400 MHz spectrometer at 400 MHz (1H) and 100 MHz (13C).
O
Experiments were recorded in CDCl3and 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 77.40 ppm and CD3OD appeared at
48.70 ppm. For IR spectra were recorded on Perkin–Elmer 881
and FTIR-8210 PC Shimadzu Spectrophotometers. Optical rotations
were determined on an Autopol III polarimeter using a 1 dm cell at
17–32 °C in chloroform and methanol as the solvents; concentra-
tions mentioned are in g/100 mL. Mass spectra were recorded on
a JEOL JMS-600H high resolution spectrometer using EI mode at
70 eV. ESI-HRMS were recorded on a JEOL-Accu TOF, JMS-T100LC
spectrometer.
Ha
C14H29
4
1
3
2
H
BocHN
OH
H
Figure 2. NOE correlations of N-Boc protected Jaspine-B 9.
Table 3
Cytotoxicity study of compounds 1 and 1a
Compound
A549
MCF7
KB
NIH3T3
5.81
TFA salt of Jaspine B (1a)
2.66a
(2.18)b
1.87
2.64
(2.20)
2.33
1.85
(3.14)
1.40
4.1.1. Synthesis of (S)-tert-butyl 4-((R)-1-hydroxyallyl)-2,2-di-
methyloxazolidine-3-carboxylate (compound 3a)
Jaspine B (1)
7.80
(4.17)
(3.35)
(5.57)
To a solution of (s)-Garner’s aldehyde 2 (1.2 g, 5.237 mmol) in
dry THF under N2 at ꢀ78 °C was added vinylmagnesium bromide
a
IC50 values in
l
M.
b
Selectivity index (=IC50 against NIH3T3 cells/IC50 against cancer cells).

P. Ghosal et al. / Tetrahedron: Asymmetry 24 (2013) 903–908
907
(1 M solution in THF, 10.5 mL, 10.474 mmol) drop wise over a per-
iod of 30 min. The reaction mixture was stirred for 2 h at the same
temperature and then allowed to warm to room temperature. After
completion of the reaction, reaction mixture was quenched with
aqueous NH4Cl solution and extracted with ethyl acetate
(2 ꢁ 50 mL). The combined organic layers were dried over anhy-
drous Na2SO4. The solvent was removed on a rotary evaporator
and the residue was purified by silica gel chromatography using
ethyl acetate/hexane as eluent to give a mixture of 3a and 3b
(6:1) as a colorless oil(1.22 g, 91%). Pure 3a was further obtained
by flash chromatography of the product mixture on silica gel
(992 mg, 74%). Eluent for column chromatography: EtOAc/hexane
152.7; IR (neat, cmꢀ1) 3437, 3017, 2927, 2142, 1687, 1459, 1251,
1172, 971, 849, 765 and 699. ESI-HRMS: m/z [M+Na]+ calcd for
C
33H55NNaOþ 552.4029, measured 552.4023.
4
4.1.4. Synthesis of tert-butyl (2S,3R)-3-(benzyloxy)-1-
hydroxyoctadec-4-en-2-ylcarbamate (compound 6)
To a solution of acetonide 5 (1.4 g, 2.64 mmol) in methanol at
0 °C, p-TSA (603 mg, 3.168 m mol) was added in portion wise.
The reaction mixture was stirred at same temperature for 1 h. After
completion of reaction, methanol was removed under reduced
pressure at low temperatures to give an oily residue, which was di-
luted with ethyl acetate (150 mL). The organic layer was washed
with water (2 ꢁ 50 mL), dried over Na2SO4, and concentrated un-
der reduced pressure. The residue was purified by silica gel column
chromatography, giving compound 6(1.178 gr, 91%) as a colorless
oil. Eluent for column chromatography: EtOAc/hexane (8/92, v/
(7/93, v/v); ½a 2D9
¼ ꢀ34:2 (c 1.21 CH3OH); Rf = 0.4 (1:4, EtOAc/Hex-
ꢂ
ane); 1H NMR (300 MHz, CDCl3)d 1.48–1.58 (m, 15H), 3.89–4.01
(m, 2H), 4.15–4.29 (m, 2H), 5.19–5.23 (m, 1H), 5.34–5.39 (m,
1H), 5.83–5.90 (m, 1H).; 13C NMR (75 MHz, CDCl3) d 24.8, 26.6,
28.7, 62.3, 65.0, 74.5, 81.5, 94.8, 116.5, 137.2, 154.5; IR (neat,
cmꢀ1) 3450, 2979, 2342, 1693, 1379 and 1272. ESIMS m/z 258
[M+1]+.
v); ½a 3D0
ꢂ
¼ ꢀ24:8 (c 0.73 CHCl3); Rf = 0.41 (1:4, EtOAc/Hexane); 1H
NMR (300 MHz, CDCl3)d 0.86–0.88(m, 3H), 1.26 (s, 22H), 1.42 (s,
9H), 2.05–2.10 (m, 2H), 2.81 (br s, 1H), 3.63–3.68 (m, 2H), 3.94–
3.97 (m, 2H), 4.31 (d, 1H, J = 11.82 Hz), 4.57–4.63 (m, 1H), 5.25
(br s, 1H), 5.42 (dd, 1H, J1 = 7.71 Hz, J2 = 7.47 Hz), 5.71–5.81 (m,
1H), 7.29–7.33 (m, 5H, ArH); 13C NMR (75 MHz, CDCl3) d 14.5,
23.0, 28.7, 29.4, 29.5, 29.7, 29.8, 30.0, 32.3, 32.7, 55.3, 56.1, 62.7,
70.3, 70.9, 79.8, 79.9, 82.3, 126.7, 126.9, 128.1, 128.2, 128.8,
137.1, 137.3, 138.3, 138.4, 156.2, 156.8; IR (neat, cmꢀ1) 3441,
2924, 2854, 1696, 1502, 1367, 1169, 768. ESI-HRMS: m/z
4.1.2. Synthesis of (S)-tert-butyl 4-((R)-1-(benzyloxy)allyl)-2,2-
dimethyloxazolidine-3-carboxylate (compound 4)
To a solution of alcohol 3a (2.1 g, 8.166 mmol) in DMF at 0 °C
was added NaH (392 mg, 16.332 mmol), followed by benzyl bro-
mide (1.45 mL, 12.249 mmol). The reaction mixture was allowed
to warm to room temperature and then stirred for 2 h. Upon com-
pletion of the reaction, the excess NaH was quenched with metha-
nol and solvent was evaporated. The residue was extracted with di
ethyl ether (2 ꢁ 50 mL). The combined organic layer was dried over
Na2SO4 and concentrated in vacuo. The residue was purified by sil-
ica gel chromatography to furnish the product 4 (1.47 g, 91%). Elu-
ent for column chromatography: EtOAc/hexane (3/97, v/v);
[M+Na]+ calcd for C30H51NNaOþ 512.3710, measured 512.3710.
4
4.1.5. Synthesis of tert-butyl (3S,4S and 5R)-4-(benzyloxy)-5-
((R)-1-iodotetradecyl) tetrahydrofuran-3-ylcarbamate
(compound 7a)
To a solution of compound 6 (121 mg, 0.247 mmol) in dry THF
(20 mL) at 0 °C was added NIS (56 mg, 0.247 mmol) and I2
(63 mg, 0.247 mmol) in four portions during 30 min. After stirring
for an additional 1 h at room temperature, 10% aqueous Na2S2O3
(10 mL) was added to the reaction mixture and extracted with
EtOAc (3 ꢁ 20 mL). The combined organic layer was dried over Na2-
SO4 and concentrated under reduced pressure to obtain a residue
that was subjected to column chromatography to afford compound
7a (122 mg, 81%) as a white semi solid. Eluent for column chroma-
½
a 2D9
ꢂ
¼ ꢀ47:9 (c 0.42 CHCl3); Rf = 0.5 (1:9, EtOAc/Hexane); 1H
NMR (400 MHz, CDCl3)d 1.43–1.59 (m, 15H), 3.86–3.90 (m, 2H),
4.02–4.14 (m, 2H), 4.36 (d, 1H, J = 11.64 Hz), 4.61 (d, 1H,
J = 11.64 Hz), 5.24–5.32 (m, 2H), 5.78–5.86 (m, 1H), 7.26–7.32
(m, 5H); 13C NMR (100 MHz, CDCl3) d 27.3, 28.8, 32.0, 60.4, 64.7,
65.6, 71.2, 80.6, 81.7, 94.6, 118.8, 119.7, 128.2, 128.3, 128.7,
128.8, 136.7, 138.4, 152.3; IR (neat, cmꢀ1) 3959,3872, 3721,
3542, 2979, 1840, 1701, 1342, 1172 and 1082. ESIMS m/z 348
[M+1]+.
tography: EtOAc/hexane (2/98, v/v); ½a D28
¼ ꢀ1:9 (c 0.34 CHCl3);
ꢂ
Rf = 0.6 (1/9, EtOAc/hexane); 1H NMR (300 MHz, CDCl3)d 0.86–
0.90 (m, 3H), 1.26 (s, 22H), 1.45 (s, 9H), 1.69–1.77 (m, 1H), 1.92–
2.04 (m, 1H), 3.58–3.68 (m, 1H), 4.02–4.10 (m, 1H), 4.14–4.18
(m, 1H), 4.30–4.42 (m, 2H), 4.55–4.69 (m, 1H), 4.81–4.93 (m,
2H), 7.33–7.40 (m, 5H); 13C NMR (75 MHz, CDCl3) d 14.5, 23.1,
28.7, 29.3, 29.5, 29.7, 29.9, 30.0, 32.3, 34.3, 36.1, 53.5, 71.7, 76.2,
80.4, 86.4, 128.5, 128.6, 129.0, 138.1, 155.7; IR (neat, cmꢀ1) 3436,
2921, 2853, 2143, 1639, 1461, 1368, 1219, 1168 and 771. ESI-
4.1.3. Synthesis of (S)-tert-butyl 4-((R)-1-(benzyloxy) hexadec-2-
enyl)-2, 2-dimethyloxazolidine-3-carboxylate (compound 5)
To a 50 mL two necked oven-dried round-bottomed flask fitted
with a reflux condenser and septum was added Grubbs IInd gener-
ation catalyst (44 mg, 0.055 mmol) under N2 atmosphere. Dry de-
gassed CH2Cl2 (5 mL) was added through a syringe and the
solution was kept for stirring. Compound 4 (543 mg, 1.562 mmol)
and 1-pentadecene (988 mg, 4.695 mmol) in DCM (3 mL each)
were added simultaneously through a syringe to the stirring solu-
tion. The septum was replaced with a glass stopper while the stir-
ring was continued. The solution was refluxed for 6 h. The
temperature of the mixture was cooled slowly to room tempera-
ture. The organic solvent was evaporated under reduced pressure
to give a black residue which was purified by column chromatog-
raphy to give Compound 5 as colorless oil (588 mg, 92.3%). Eluent
for column chromatography: EtOAc/hexane (3/97, v/v);
HRMS: m/z [M+Na]+ calcd for C30H50INNaOþ 638.2677, measured
4
638.2675.
4.1.6. Synthesis of tert-butyl (3S,4S and 5S)-4-hydroxy-5-
tetradecyltetrahydrofuran-3-ylcarbamate (compound 9)
4.1.6.1. From 7a.
To a stirred solution of 7a (250 mg,
0.406 mmol) in dry toluene (20 mL) were added n-Bu3SnH
(0.33 mL, 1.218 mmol) and ABCN (catalytic) at room temperature
under N2 atmosphere. The reaction mixture was gently refluxed
with stirring for 2 h. After completion of the reaction, solvent
was removed under vacuum and the residue was purified by silica
gel column chromatography to give compound 9 (68 mg, 42%) as a
white solid and compound 8 (64 mg, 32%) as a pale yellow liquid.
½
a 2D9
ꢂ
¼ ꢀ40:2 (c 0.35 CHCl3); Rf = 0.6 (1:9, EtOAc/Hexane);1H
NMR (300 MHz, CDCl3)d 0.86–0.88 (m, 3H), 1.26 (s, 22H), 1.43–
1.51 (m, 15H), 2.06–2.10 (m, 2H), 3.87–4.20 (m, 4H), 4.31–4.38
(m, 1H), 4.59 (d, 1H, J = 11.73 Hz), 5.43–5.66 (m, 2H), 7.30 (s, 5H,
ArH); 13C NMR (50 MHz, CDCl3) d 14.5, 23.0, 23.7, 25.3, 27.0,
27.4, 28.8, 29.4, 29.6, 29.7, 29.8, 30.0, 32.3, 32.6, 32.7, 33.0, 60.7,
65.0, 65.7, 70.6, 79.8, 80.1, 80.5, 81.2, 94.0, 94.5, 127.7, 127.9,
128.1, 128.2, 128.6, 128.7, 136.3, 136.9, 138.7, 139.0, 152.3,
4.1.6.2. From 8.
A suspension of Pd/C (10% on carbon, 5 mg)
in a methanolic solution of compound 8 (64 mg, 0.13 mmol,
5 mL) was stirred under a positive pressure of H2 at room temper-

908
P. Ghosal et al. / Tetrahedron: Asymmetry 24 (2013) 903–908
ature for 6 h. After completion of the reaction, Pd/C was filtered
through a celite pad and the filtrate was concentrated under vac-
uum to a residue. It was purified by column chromatography to af-
ford compound 9 (49.6 mg, 95%) as a white solid.
(m, 24H), 1.61–1.72 (m, 2H), 3.49–3.53 (m, 1H), 3.66–3.75 (m,
2H), 3.87–3.94 (m, 2H); 13C NMR (100 MHz, CDCl3) d 14.5, 23.1,
26.7, 29.8, 29.8, 30.0, 30.1, 30.2, 32.3, 54.7, 72.1, 72.7, 83.6; IR
(neat, cmꢀ1) 3436, 2921, 2853, 1639, 1219 and 771. ESI-HRMS:
m/z [M+H]+ calcd for C18H38NOþ 300.2897, measured 300.2924.
2
4.1.6.3. Compound 8.
Eluent for column chromatography:
EtOAc/hexane (4/96, v/v); ½a D25
ꢂ
¼ ꢀ8:0 (c 0.16 CHCl3); Rf = 0.63
Acknowledgments
(1/4, EtOAc/hexane); 1H NMR (300 MHz, CDCl3)d 0.86–0.90 (m,
3H), 1.25 (s, 24H), 1.44 (s, 9H), 1.62 (br m, 2H), 3.59–3.64 (m,
1H), 3.79–3.80 (m, 1H), 3.88–3.94 (m, 2H), 4.34–4.36 (m, 1H),
4.58 (s, 2H), 5.00 (d, 1H, J = 8.49 Hz), 7.31-7.35 (m, 5H).;13C NMR
(100 MHz, CDCl3) d 14.5, 23.1, 26.8, 28.8, 29.8, 29.9, 30.0, 30.0,
30.1, 30.1, 30.2, 30.7, 32.3, 53.5, 70.9, 74.6, 79.4, 80.0, 82.3, 128.4,
128.4, 128.9, 138.1, 156.0; IR (neat, cmꢀ1) 3436, 3019, 2927,
2855, 2400, 1626, 1453, 1368, 1216, 1166, 929, 757 and 669. ESI-
We are thankful to Mr. A.K. Pandey for technical assistance and
Mr. R.K. Purshottam for providing HPLC data, DST (project SR/SI/
OC-17/2010) for financial support and SAIF, CDRI, for providing
spectral data. P.G. thanks CSIR for awarding Senior Research
Fellowship and S.A. thanks CSIR for awarding Junior Research
Fellowship. CDRI Communication No. 8485. The constructive and
valuable input provided by one of the referees is gratefully
acknowledged.
HRMS: m/z [M+Na]+ calcd for C30H51NNaOþ 512.3710, measured
4
512.3752.
References
4.1.6.4. Compound 9.
Eluent for column chromatography:
EtOAc/hexane (8/92, v/v); Mp 109-111 °C; ½a D26
¼ þ7:8 (c 0.24
ꢂ
1. Kuroda, I.; Musman, M.; Ohtani, I. I.; Ichiba, T.; Tanaka, J.; Gravalos, D. G.; Higa,
T. J. Nat. Prod. 2002, 65, 1505–1506.
2. Ledroit, V.; Debitus, C.; Lavaud, C.; Massiot, G. Tetrahedron Lett. 2003, 44, 225–
228.
3. Canals, D.; Mormeneo, D.; Fabrias, G.; Llebaria, A.; Casas, J.; Delgado, A. Bioorg.
Med. Chem. 2009, 17, 235–241.
4. Bhaket, P.; Morris, K.; Stauffer, C. S.; Datta, A. Org. Lett. 2005, 7, 875–876.
5. (a) Yoshimitsu, Y.; Inuki, S.; Oishi, S.; Fujii, N.; Ohno, H. J. Org. Chem. 2010, 75,
3843–3846; (b) Inuki, S.; Yoshimitsu, Y.; Oishi, S.; Fujii, N.; Ohno, H. Org. Lett.
2009, 11, 4478–4481; (c) Sudhakar, N.; Kumar, A. R.; Prabhakar, A.; Jagadeesh,
B.; Rao, B. V. Tetrahedron Lett. 2005, 46, 325–327; (d) Passiniemi, M.; Koskinen,
A. M. P. Tetrahedron Lett. 2008, 49, 980–983.
6. (a) Du, Y.; Liu, J.; Linhardt, R. J. J. Org. Chem. 2006, 71, 1251–1253; (b) Liu, J.; Du,
Y.; Dong, X.; Meng, S.; Xiao, J.; Cheng, L. Carbohydr. Res. 2006, 341, 2653–2657.
7. (a) Ramana, C. V.; Giri, A. G.; Suryawanshi, S. B.; Gonnade, R. G. Tetrahedron Lett.
2007, 48, 265–268; (b) Rao, G. S.; Chandrasekhar, B.; Rao, B. V. Tetrahedron:
Asymmetry 2012, 23, 564–569.
CHCl3); Rf = 0.34 (1/4, EtOAc/hexane); 1H NMR (300 MHz, CDCl3)d
0.86–0.90 (m, 3H), 1.25 (s, 24H), 1.45 (s, 9H), 1.56–1.66 (m, 2H),
2.04 (br s, 1H), 3.58 (t, 1H, J = 8.22 Hz), 3.78 (td, 1H, J = 2.73,
6.93 Hz), 4.02–4.07 (m, 2H), 4.31 (br m, 1H), 5.14(d, 1H,
J = 7.62 Hz); 13C NMR (75 MHz, CDCl3) d 14.5, 23.1, 26.5, 28.8,
29.4, 29.5, 29.7, 29.9, 30.0, 30.0, 30.1, 32.3, 54.7, 70.6, 72.3, 80.3,
82.6, 156.1; IR (neat, cmꢀ1) 3366, 2920, 2852, 1688, 1530, 1465,
1371, 1220, 1177 and1028. ESI-HRMS: m/z [M+Na]+ calcd for
C
23H45NNaOþ 422.3241, measured 422.3239.
4
4.1.7. Synthesis of (2S,3S and 4S)-4-amino-2-
tetradecyltetrahydrofuran-3-ol (TFA salt of Pachastrissamine
1a)
8. Reddy, L. V. R.; Reddy, P. V.; Shaw, A. K. Tetrahedron: Asymmetry 2007, 18, 542–
546.
A solution of 0.052 mmol of 9 in 5 mL of CH2Cl2/TFA (4:1) was
stirred for 1 h at 0 °C. After completion of the reaction, the solvent
was removed under vacuum and the resulting white solid was
purified by flash chromatography (CHCl3/CH3OH 96:4) to afford
the TFA salt of Pachastrissamine 1a (18.7 mg, 90%). Eluent for col-
umn chromatography: MeOH/CHCl3 (10/90, v/v); mp 121–123 °C;
9. (a) Van den Berg, R. J. B. H. N.; Boltje, T. J.; Verhagen, C. P.; Litjens, R. E. J. N.; Van
der Marel, G. A.; Overkleeft, H. S. J. Org. Chem. 2006, 71, 836–839; (b) Lee, T.;
Lee, S.; Kwak, Y. S.; Kim, D.; Kim, S. Org. Lett. 2007, 9, 429–432.
10. Ribes, C.; Falomir, E.; Carda, M.; Marco, J. A. Tetrahedron 2006, 62, 5421–5425.
11. Prasad, K. R.; Chandrakumar, A. J. Org. Chem. 2007, 72, 6312–6315.
12. Abraham, E.; Candela-Lena, J. I.; Davies, S. G.; Georgiou, M.; Nicholson, R. L.;
Roberts, P. M.; Russell, A. J.; Snchez-Fernandez, E. M.; Smith, A. D.; Thomson, J.
E. Tetrahedron: Asymmetry 2007, 18, 2510–2513.
13. Eleuterio, A. S.; Quintero, L.; Piscil, F. S. J. Org. Chem. 2011, 76, 5466–5471.
14. (a) Ghosal, P.; Kumar, V.; Shaw, A. K. Tetrahedron 2010, 66, 7504–7509; (b)
Ghosal, P.; Kumar, V.; Shaw, A. K. Carbohydr. Res. 2010, 345, 41–44; (c) Reddy, L.
V. R.; Swamy, G. N.; Shaw, A. K. Tetrahedron: Asymmetry 2008, 19, 1372–1375;
(d) Pal, P.; Shaw, A. K. Tetrahedron 2011, 67, 4036–4047; (e) Kumar, V.; Das, P.;
Ghosal, P.; Shaw, A. K. Tetrahedron 2011, 67, 4539–4546; (f) Ghosal, P.; Sharma,
D.; Kumar, B.; Meena, S.; Sinha, S.; Shaw, A. K. Org. Biomol. Chem. 2011, 9, 7372–
7383; (g) Ghosal, P.; Shaw, A. K. J. Org. Chem. 2012, 77, 7627–7632.
15. Garner, P.; Park, J. M. J. Org. Chem. 1988, 53, 2979–2984.
16. Bera, S.; Mondal, D.; Singh, M.; Kale, R. K. Tetrahedron 2013, 69, 969–1011.
17. (a) Liang, X.; Andersch, J.; Bols, M. J. Chem. Soc., Perkin Trans. 1 2001, 2136–
2157; (b) Ghosal, P.; Shaw, A. K. Tetrahedron Lett. 2010, 55, 4140–4142; (c)
Srivastava, A. K.; Das, S. K.; Panda, G. Tetrahedron 2009, 65, 5322–5327; (d)
Srivastava, A. K.; Panda, G. Chem. Eur. J. 2008, 14, 4675–4688.
18. Kim, Y. G.; Cha, J. K. Tetrahedron Lett. 1988, 29, 2011–2013.
19. Chamberlin, A. R.; Mulholland, R. L., Jr.; Kahn, S. D.; Hehre, W. J. J. Am. Chem.
Soc. 1987, 109, 672–677.
20. Liu, J.; Jian, T.; Guo, L.; Atanasova, T.; Nargund, R. P. Tetrahedron Lett. 2009, 50,
5228–5230.
21. Pal, P.; Singh, P.; Kumar, B.; Gauniyal, H. M.; Shaw, A. K. Tetrahedron:
Asymmetry 2011, 22, 992–999.
22. Castro, M. D.; Marzabadi, C. H. Tetrahedron 2010, 66, 3395–3404.
23. Prasad, K. R.; Penchalaiah, K. Tetrahedron: Asymmetry 2011, 22, 1400–1403.
24. Abraham, E.; Davies, S. G.; Roberts, P. M.; Russell, A. J.; Thomson, J. E.
Tetrahedron: Asymmetry 2008, 19, 1027–1047.
25. Skehan, P.; Storeng, R.; Scudiero, D.; Monks, A.; McMahon, J.; Vistica, D.;
Warren, J. T.; Bodesch, H.; Kenney, S.; Boyd, M. R. J. Natl. Cancer Inst. 1990, 82,
1107–1112.
½
a 2D8
ꢂ
¼ þ12:9 (c 0.34 CH3OH); Rf = 0.45 (1/4, MeOH/CHCl3);1H
NMR (300 MHz, CD3OD)d 0.88–0.92 (m, 3H), 1.29 (s, 24H), 1.61–
1.66 (m, 2H), 3.71–3.72 (m, 1H), 3.80–3.81 (m, 1H), 3.84–3.94
(m, 2H), 4.25 (m, 1H).; 13C NMR (100 MHz, CD3OD) d 14.5, 23.7,
27.2, 29.7, 30.2, 30.5, 30.8, 31.2, 33.1, 54.7, 70.7, 71.1, 84.6; IR
(neat, cmꢀ1) 3435, 3020, 2925, 2850, 1637, 1522, 1423, 1215,
1046, 929 and 757. ESIMS m/z 300[(M+1-CF3COOH)+].
4.1.8. Pachastrissamine 1 (free base)
To a stirred solution of TFA salt of Pachastrissamine 1a (17 mg,
0.043 mmol) in DCM (10 mL) at 0 °C was added 2.5 M methanolic
NaOH (0.5 mL). The stirring of the reaction mixture was allowed
to continue at room temperature for 15 min. After completion of
hydrolysis, the solvents were removed on a rotary evaporator to
give a residue, which was purified by flash column chromatogra-
phy (CHCl3/CH3OH/aq NH4OH—89:10:1) to afford salt free Pachas-
trissamine 1 as a white amorphous solid (12.5 mg, 97%). Eluent for
column chromatography: CHCl3/CH3OH/aq. NH4OH (89/10/1, v/v);
mp 90–92 °C; ½a 1D7
ꢂ
¼ þ8:6 (c 0.32 CH3OH), {lit.8 [
a]D = +8.5 (c 0.047
CH3OH)}; Rf = 0.21 (1/4, MeOH/CHCl3); 1H NMR (300 MHz, CD3-
OD)d 0.86–0.90 (m, 3H), 1.28 (s, 24H), 1.60 (br m, 2H), 3.43–3.52
(m, 2H), 3.80–3.91 (m, 3H); 13C NMR (75 MHz, CD3OD) d 14.1,
23.4, 26.9, 30.2, 30.3, 30.4, 30.5, 30.6, 32.8, 55.8, 71.9, 73.0, 84.0;
1H NMR (400 MHz, CDCl3)d 0.86–0.90 (m, 3H), 1.25–1.30
26. Yoshimitsu, Y.; Oishi, S.; Miyagaki, J.; Inuki, S.; Ohno, H.; Fujii, N. Bioorg. Med.
Chem. 2011, 19, 5402–5408.