Practical and efficient approach to the synthesis of guineensine

Article abstract of DOI:10.1080/10286020.2010.546356

A total synthesis of guineensine, a secondary metabolite of the Piperaceae family, has been executed in 12 steps with an overall yield of 27%. Key steps in the synthesis featured novel application of a Julia-Kocienski olefination reaction which effectively constructed alkenamide skeleton. This contributes a unique approach to the synthesis of the piperamide alkaloids.

Full text of DOI:10.1080/10286020.2010.546356

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Practical and efficient approach to the
synthesis of guineensine
Shailesh D. Shingala a , G. Venkateswar Reddy a , R. Sateesh
Chandra Kumar a , P. Ashok Yadav a & K. Suresh Babu a
a Organic Chemistry Division I, Natural Products Laboratory, Indian
Institute of Chemical Technology, Hyderabad, 500 607, India
Published online: 28 Jan 2011.
To cite this article: Shailesh D. Shingala , G. Venkateswar Reddy , R. Sateesh Chandra Kumar ,
P. Ashok Yadav & K. Suresh Babu (2011): Practical and efficient approach to the synthesis of
guineensine, Journal of Asian Natural Products Research, 13:02, 128-135
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Journal of Asian Natural Products Research
Vol. 13, No. 2, February 2011, 128–135
Practical and efficient approach to the synthesis of guineensine
Shailesh D. Shingala, G. Venkateswar Reddy, R. Sateesh Chandra Kumar, P. Ashok
Yadav and K. Suresh Babu*
Organic Chemistry Division I, Natural Products Laboratory, Indian Institute of Chemical
Technology, Hyderabad 500 607, India
(Received 28 September 2010; final version received 6 December 2010)
A total synthesis of guineensine, a secondary metabolite of the Piperaceae family, has
been executed in 12 steps with an overall yield of 27%. Key steps in the synthesis
featured novel application of a Julia–Kocienski olefination reaction which effectively
constructed alkenamide skeleton. This contributes a unique approach to the synthesis of
the piperamide alkaloids.
Keywords: piper amide alkaloids; guineensine; Piperaceae family; Julia–Kocienski
olefination; Corey–Fuchs reaction
1. Introduction
three decades [3]. Structurally, guineen-
sine possesses a highly conjugated iso-
butyl amide group and an aromatic ring
which are linked through a six carbon
chain (Figure 1) [4].
Plants of the Piperaceae family are widely
distributed throughout tropical and sub-
tropical regions. Piper species have been
used in traditional medicinal systems for
thousands of years, including the Chinese
and the Indian systems of medicine [1].
For years, the chemistry of the Piper
species has been widely investigated, and
phytochemical studies from all over the
world have resulted in the isolation of
numerous structurally diverse amides with
the wide range of bioactivities such as
cytotoxic, stomach aches, insect repel-
lents, anti-inflammatory, insecticidal, and
anti-feedant activities [1]. Recently, Mat-
suda et al. [2] have isolated three new
amide alkaloids from the roots of Piper
chaba and assessed their hepatoprotective
activity. Piperamides (alkenamides) share
a common skeleton with conjugated linear
chain attached both sides with various
amides and aromatic ring, which has made
them attractive synthetic targets for the last
The array of conjugated double bonds
in a linear structure of 1 has provided us
with a strong motive to investigate a novel
strategy for an effective construction of the
alkenamide core that will enable the
synthesis of the diverse class of pipera-
mides for the pharmacological screening.
Syntheses of these compounds have gener-
ally involved in the construction of linear
chain followed by amide formation via the
condensation with the cyclic amines or
acyclic amines. Recently, Rao et al. [5]
have accomplished the first stereoselective
synthesis of piperamides in which key
reactions are the Wittig reaction, Sharpless
asymmetric dihydroxylation, epoxidation,
and a trans-regioselective opening of 2,3-
epoxy alcohol. To date, only two syntheses
of the guineensine have been reported,
*Corresponding author. Email: suresh@iict.res.in
ISSN 1028-6020 print/ISSN 1477-2213 online
q 2011 Taylor & Francis
DOI: 10.1080/10286020.2010.546356
http://www.informaworld.com

Journal of Asian Natural Products Research
129
O
O
O
O
O
N
N
n = 5
H
H
O
Guineensine
Retrofractamide D
2
1
O
O
O
O
O
N
N
H
n = 3
H
O
Retrofractamide A
3
Pipericide
4
Figure 1. Representative alkenamides of Piperaceae family.
which also utilized the modified Wittig
reaction as a key step [3,6]. Given the
importance of these types of scaffolds, we
were intrigued by the prospect of an
alternative route to their synthesis.
protected decanediol (12) and pipernal
(11) via the Julia olefination reaction.
Several attempts were made to prepare key
fragment from pipernal (11) and to employ
it as a potential intermediate, but, unfortu-
nately, resulted the products in diminished
yields (5–10%).
During our continuing efforts in the
synthesis of alkaloids of natural origin [7],
we developed a new and efficient synthetic
route to alkenamide skeleton using com-
mercially available starting material, and
then by taking advantage of the Julia–
Kocienski olefination reaction as a key
step, we realized the construction of
alkenamide skeleton that represents the
core structures of amide type alkaloids of
Piperaceae family. In this paper, we report
the approach for the construction of the
alkenamide core followed by the total
synthesis of guineensine (1).
However, switching solvents and con-
ducting the reaction with more equivalents
of sulfone as well as pipernal in the
presence of various bases (lithium bis
(trimethylsilyl)azide (LHMDS), sodium
bis(trimethylsilyl)amide (NaHMDS),
lithium diisopropyl amide (LDA), and
BuLi) also did not improve the reaction
yields. Then, we turned our retrosynthetic
strategy to realize that the key fragment
was envisaged with the Julia–Kocienski
olefination between sulfone derivative of
the pipernal 11 and aldehyde 9. Thus, our
present total synthesis will be highlighted
by the utilization of Julia olefination which
directs the construction of the alkenamide
core. More importantly, we have success-
fully implemented a strategy that mini-
mizes protecting group manipulation in a
unique fashion, a common and unavoid-
able practice in the synthesis of piper-
amide alkaloids that are reported earlier.
The brevity of this analysis along with the
structural simplicity of the precursors
makes this route attractive for the
implementation of the library synthesis of
diverse Piperaceae family alkaloids for the
2. Results and discussion
As outlined retrosynthetically in Scheme
1, initial disconnection of 1 revealed
fragment 5, which could be subjected to
condensation with amine to realize the
target molecule. The acid fragment 5, in
turn, was obtained from the key fragment 7
through sequential steps of the Swern
oxidation, Corey–Fuchs reaction, and
ester hydrolysis. To access the key
fragment 7, initially it was thought that
basic alkenamide skeleton would arise
from sulfone derivative of mono-THP-

130
S.D. Shingala et al.
O
O
O
O
O
O
N
H
OH
5
5
1
5
O
O
O
O
OTHP
7
7
O
O
Julia-Kocinski
olefination
6
7
Julia-Kocinski
olefination
N
N
O
S
O
N
O
O
X
N
THPO
H
+
Ph
O
9
8
O
Ph
O
S
O
O
N
N
OTHP
H
O
+
N
N
5
HO
HO
O
H
11
12
10
Scheme 1. Retrosynthetic analysis of guineensine.
biological screening and further structure–
activity relationship studies.
in dry tetrahydrofuran (THF) at 2788C to
room temperature to give the key fragment 7
with the desired E-olefin predominately
in modest yield (70% yield). The presence
of two olefinic proton signals at d 5.56–5.45
(dd, J ¼ 15.6, 10.0 Hz) and 6.17 (d,
J ¼ 15.8 Hz) with the coupling constant
of 15.6 Hz in 300MHz, 1H NMR spectrum
also confirmed the trans-geometry of the
newly generated double bond (Scheme 2).
Having achieved a reliable synthesis of
key fragment 7 of alkenamide skeleton, we
proceeded for the preparation of target com-
pound guineensine (1). Accordingly, the
THP group was removed under acidic
conditions [11] using PTSA in MeOH to
deliver alcohol 15 in 95%, which upon
subjected to IBX [12] oxidation gave the
corresponding aldehyde 16. The modified
Corey–Fuchs [13] homologation of alde-
hyde 16 followed by dibromomethylenation
with CBr4 and PPh3 furnished the dibromo
olefin 17 in essentially quantitative yield.
Reaction of this material with n-BuLi
The total synthesis based on the above-
mentioned plan was initiated from
commercially available 3,4-dihydroxy ben-
zaldehyde 10 as a synthon. Thus, protection
of the 3,4-hydroxyl groups with methylene
iodide in the presence of K2CO3 in DMF
gave its methylenedioxy-protected aldehyde
as a pale yellow colored liquid 11 in 80%
yield [8], which upon reduction with NaBH4
inmethanolledthecorrespondingalcohol13
in 98% yield. Conversion of the alcohol 13
into corresponding thioether by Kocienski
[9] procedure followed by the Mitsunobu-
type reaction with diisopropyl azodicarbox-
ylate, triphenylphosphine, and1-phenyl-1H-
tetrazol-5-thiol yielded 14 in 95% yield.
Oxidation of 14 with ammonium heptamo-
lybdate and H2O2 afforded sulfone deriva-
tive 8 with 80% yield. The sulfone 8 was
further subjected to Kocienski-modified
Julia olefination [10] reaction with the
aldehyde 91 in the presence of LiHDMS

Journal of Asian Natural Products Research
131
O
O
O
O
O
HO
HO
a
H
OH
b
H
O
13
10
11
N
N
N
N
N
O
S
N
N
d
O
O
c
O
N
S
Ph
O
Ph
O
8
14
O
OTHP
O
Scheme 2. Synthesis of key fragment 7. Reagents and conditions: (a) CH2I2, K2CO3, DMF, reflux,
5 h, 80%; (b) NaBH4, MeOH, 08C, 15 min, 98%; (c) PPh3, 1-phenyl-1H-tetrazol-5-thiol, di
isopropylazodicarboxylate (DIAD), dry THF, rt, 0.5 h, 95%; (d) ammonium heptamolybdate
tetrahydrate, EtOH, 08C to rt, 7 h, 80%; (e) aldehyde 9, LHMDS, THF, 2788C to rt, 12 h, 70%.
and quenching with chloroethylformate
furnished alkynoate 6. Exposure of alkyno-
ate 6 to the Rychnovsky variant of the Trost
isomerization [14], (Ph3P/PhOH) yielded
dienoate 18 in excellent yield (95%) with
perfect double bond stereoselectivity.
Finally, treatment of dienoate 18 to a
mixture of aqueous LiOH and THF
saponified the ethyl ester group to the
corresponding carboxylic acid, followed by
condensation[15] with isobutylamine in the
presenceofEDC/HOBtsystem;guineensine
1 was successfully yielded. All the inter-
mediate compounds including guineensine
were well characterized by IR, NMR, and
MS spectral data. The spectral data of
synthetic guineensine were also comparable
to the reported data for natural product [16].
Comparison of our physical and spectro-
scopic data with the published data con-
firmed our successful synthesis of
guineensine.
therefore, offer certain advantages over
the previous synthesis of the guineensine
and related alkenamides of Piperaceae
family natural products. The synthesis
appears to be general, and it should allow
access to the preparation of a variety of
structural analogs for investigation of
pharmacological
structure–activity
relationships. In addition, it demonstrates
that the formation of core can be
accomplished via Julia–Kocienski olefi-
nation with reasonable yield, which will
allow for facile modification of aliphatic
chain. Studies directed toward the prep-
aration of guineensine analogs and their
evaluation as cytotoxic and aldose
reductase inhibitors are currently under-
way and will be reported in due course.
3. Experimental
3.1 General experimental procedures
1H and 13C NMR spectra were recorded
either in CDCl3 or in MeOH-d 4 solvent on
300, 500, or 75 MHz spectrometer at
ambient temperature. Chemical shifts d are
given in parts per million and coupling
In summary, the guineensine synthesis
outlined in Schemes 2 and 3 proceeds in 12
simple steps from a commercially avail-
able starting material, with an overall yield
of 27%. The general approach does,

132
S.D. Shingala et al.
O
7
O
O
O
OH
O
O
H
f
g
OTHP
7
7
O
7
15
16
O
k
Br
h
O
O
O
O
i, j
O
7
7
5
Br
6
17
O
O
O
O
m
OH
l
O
O
O
5
5
18
O
O
O
N
H
5
1
Scheme 3. Synthesis of guineensine (1). Reagents and conditions: (f) PTSA, MeOH, 08C, 45 min,
95%; (g) IBX, DMSO, THF, rt, 98%; (h) CBr4, TPP, dry DCM, 08C, 2 h, 95%; (i) n-BuLi, dry THF,
2788C; (j) chloroethyl formate, dry THF, 2788C, 2 h, 90%; (k) TPP, phenol, benzene, reflux, 95%;
(l) LiOH, THF/H2O, rt, 12 h, 96%; (m) EDC, HOBt, isobutyl amine, DCM, 08C to rt, 8 h, 90%.
constants J are given in Hertz. The chemical
shifts are reported in parts per million on
scale downfield from TMS as internal
standard and signal patterns are indicated
as follows: s, singlet; d, doublet; dd, doublet
of doublet; t, triplet; m, multiplet; br s, broad
singlet. FT-IR spectra were recorded as thin
films on KBr or neat. For MS and HR-MS,
m/z ratios are reported as values in atomic
mass units. All the reagents and solvents
were reagent grade and were used without
further purification unless specified other-
wise. Technical grade ethyl acetate and
hexane used for column chromatography
weredistilledpriortouse.THFwhenusedas
solvent for the reactions wasfreshly distilled
from sodium benzophenone ketyl. Column
chromatography was carried out using silica
gel (60–120 and 100–200 mesh) packed in
glass columns. All the reactions were
performed under an atmosphere of nitrogen
in flame or oven-dried glassware with
magnetic stirring.
3.2 Spectral data
3.2.1 Compound 7
1H NMR (300 MHz, CDCl3): d 6.75–6.65
(3H, m), 6.17 (1H, d, J ¼ 15.8 Hz), 5.93
(2H, s), 5.56–5.45 (1H, dd, J ¼ 15.8,
10 Hz), 4.54 (1H, t, J ¼ 3.02 Hz), 3.86–
3.76 (1H, m), 3.73–3.62 (1H, m), 3.50–
3.41 (1H, m), 3.36–3.27 (1H, m), 2.33–
2.23 (2H, m), 1.72–1.39 (8H, m), 1.33–
1.24 (12H, m); 13C NMR (75 MHz,
CDCl3): d 147.4, 146.1, 131.8, 129.7,
128.7, 122.3, 120.2, 109.0, 108.0, 100.6,
67.2, 61.2, 30.7, 30.0, 29.8, 29.6, 29.6,
29.4, 26.4, 25.7, 19.4; ESI-MS: m/z 397.2
[M þ Na]þ. HR-ESI-MS: m/z 397.2316
[M þ Na]þ (calcd for C23H34O4Na,
397.2355).

Journal of Asian Natural Products Research
133
3.2.2 Compound 6
NMR (75 MHz, CDCl3): d 148.2, 147.6,
130.1, 128.7 (3C), 128.5, 126.8 (2C),
126.0, 124.6, 112.6, 112.0, 100.8, 62.4.
ESI-MS: m/z 345.1 [M þ H]þ. HR-ESI-
MS: m/z 345.0650 [M þ H] (calcd for
C15H13N4O4S, 345.0658).
1H NMR (300 MHz, CDCl3): d 6.87–6.65
(3H, m), 6.23 (1H, d, J ¼ 16.3 Hz), 6.01–
5.92 (1H, m), 5.90 (2H, s), 4.18 (2H, q,
J ¼ 6.7, 14.4 Hz), 2.34–2.25 (2H, m),
2.19–2.12 (2H, m), 1.47–1.27 (12H, m),
0.92 (3H, t, J ¼ 6.7 Hz); 13C NMR
(75 MHz, CDCl3): d 153.1, 148.0, 146.2,
131.7, 129.9, 128.8, 122.4, 120.3, 109.1,
108.2, 108.1, 100.6, 88.2, 73.8, 61.2, 33.1,
30.1, 29.6, 29.3, 27.7, 18.8, 14.3; ESI-MS:
m/z 357.2042 [M þ H]þ. HR-ESI-MS: m/z
357.2042 [M þ H]þ (calcd for C22H29O4,
357.2066).
3.2.6 Compound 15
1H NMR (300 MHz, CDCl3): d 7.13 (1H,
s), 6.83 (1H, d, J ¼ 4.0 Hz), 6.72 (1H, d,
J ¼ 4.0 Hz), 6.68 (1H, d, J ¼ 8 Hz), 5.98
(1H, d, J ¼ 8.0 Hz), 5.91 (2H, s), 3.60 (2H,
t, J ¼ 6.8, 12.8 Hz), 2.28 (1H, m), 2.15–
2.10 (2H, m), 1.54–1.56 (2H, m), 1.43–
1.42 (2H, m), 1.30–1.32 (10H, m). 13C
NMR (75 MHz, CDCl3): d 147.8, 147.6,
133.0, 126.8, 126.6, 120.8, 110.1, 109.2,
101.0, 62.0, 34.8, 32.0, 29.7, 29.3 (2C),
22.0 (2C), 25.4. ESI-MS: m/z 291.0
[M þ H]þ. HR-ESI-MS: m/z 291.1942
[M þ H]þ (calcd for C18H27O3,
291.1960).
3.2.3 Compound 5
1H NMR (300 MHz, CDCl3): d 7.35–7.25
(1H, m), 6.83 (1H s), 6.74–6.66 (2H, m),
6.30–6.10 (3H, m), 6.04–5.90 (3H, m),
5.75 (1H, d, J ¼ 15.8 Hz), 2.23–2.10 (4H,
m), 1.50–1.27 (8H, m); 13C NMR
(75 MHz, CDCl3): d 170.7, 148.0, 147.7,
146.3, 142.7, 132.1, 129.2, 128.8, 128.2,
121.8, 120.1, 119.02, 108.0, 105.1, 100.7,
35.4, 32.7, 30.0, 29.5, 29.2, 28.9, 28.5,
27.4; ESI-MS: m/z 329.1701 [M þ H].
HR-ESI-MS: m/z 329.1701 [M þ H]
(calcd for C20H25O4, 329.1753).
3.2.7 Compound 16
1H NMR (300 MHz, CDCl3): d 9.72 (1H,
s), 7.20 (1H, s), 7.08 (1H, d, J ¼ 4.0 Hz),
6.96 (1H, d, J ¼ 4.0 Hz), 6.62 (1H, d,
J ¼ 8 Hz), 6.04 (1H, d, J ¼ 8 Hz), 5.91
(2H, s), 2.39–2.42 (2H, m), 2.21–2.24
(4H, m), 1.30–1.36 (10H, m). 13C NMR
(75 MHz, CDCl3): d 204.1, 147.8, 147.6,
143.5, 133.0, 126.8, 126.6, 120.8, 110.1,
109.2, 101.0, 34.8, 32.0, 29.7, 29.3 (2C),
28.1, 28.0. ESI-MS: m/z 289.0 [M þ H]þ.
HR-ESI-MS: m/z 289.1809 [M þ H]þ
(calcd for C18H25O3, 289.1804).
3.2.4 Compound 14
1H NMR (300 MHz, CDCl3): d 7.84 (1H,
d, J ¼ 8.0 Hz), 7.50 (2H, m), 7.35 (1H, d,
J ¼ 7.8 Hz), 7.40 (3H, m), 6.89 (1H, s),
5.89 (2H, s), 4.50 (2H, s). 13C NMR
(75 MHz, CDCl3): d 155.02, 148.2, 147.8,
136.8, 134.2, 128.5 (2C), 127.8, 124.6
(2C), 120.1, 112.6, 112.0, 100.8, 35.8.
ESI-MS: m/z 313.2 [M þ H]þ. HR-ESI-
MS: m/z 313.0712 [M þ H]þ (calcd for
C15H13N4O2S, 313.0759).
3.2.8 Compound 17
1H NMR (300 MHz, CDCl3): d 6.83 (1H,
s), 6.68–6.70 (2H, m), 6.23 (1H, d,
J ¼ 6.0 Hz), 6.40–6.35 (1H, m), 5.94–
6.00 (1H, m), 5.91 (2H, s), 2.16–2.20 (2H,
m), 2.09–2.10 (2H, m), 1.43–1.50 (4H,
m), 1.33–1.36 (8H, m). ESI-MS: m/z
444.7 [M þ H]þ. 13C NMR (75 MHz,
CDCl3): d 148.2, 148.0, 138.2, 133.0,
3.2.5 Compound 8
1H NMR (300 MHz, CDCl3): d 7.84 (1H,
d, J ¼ 8.0 Hz), 7.53–7.50 (2H, m), 7.30
(1H, d, J ¼ 7.8 Hz), 7.40–7.36 (3H, m),
6.70 (1H, s), 5.89 (2H, s), 5.29 (2H, s). 13
C

134
S.D. Shingala et al.
which one of the hydroxyl group was
selectively protected as a THP ether
(dihydropyran, PTSA, DCM, rt, 3 h) and
the resultant THP ether was subjected to
Swern oxidation condition.
132.6, 127.2, 119.7, 101.2, 95.8, 34.8, 29.7
(2C), 29.6 (2C), 29.0 (2C), 28.0, 27.3,
24.1. ESI-MS: m/z 444.7 [Mþ þ 2]. HR-
ESI-MS: m/z 444.0362 [M þ 2] (calcd for
C19H26Br2O2, 444.0300).
References
3.2.9 Compound 18
[1] V.S. Parmar, S.C. Jain, K.S. Bisht, R. Jain,
P. Taneja, A. Jha, O.D. Tyagi, A.K.
Prasad, J. Wengel, C.E. Olsen, and P.M.
Boll, Phytochemistry 46, 597 (1997).
[2] H. Matsuda, K. Ninomiya, T. Morikawa,
T. Yasuda, I. Yamaguchi, and M.
Yoshikawa, Bioorg. Med. Chem. 17,
7313 (2009).
[3] (a) D.W. Ma and X.Y. Lu, Tetrahedron
46, 6319 (1990). (b) A. Banerji, D.
Bandyopadhyay, and A.K. Siddhanta,
Phytochemistry 26, 3345 (1987). (c)
L.W. Rotherham and J.E. Semple, J. Org.
Chem. 63, 6667 (1998). (d) F. Kiuchi, N.
Nakamura, M. Saitoh, K. Komagome,
H. Hiramatsu, N. Takimoto, N. Akao, K.
Kondo, and Y. Tsuda, Chem. Pharm. Bull.
45, 685 (1997). (e) G.M. Strunz,
J. Heather, and H.J. Finlay, Can.
J. Chem. 74, 419 (1996).
1H NMR (300 MHz, CDCl3): d 7.19 (1H,
dd, J ¼ 4.0, 2.5 Hz), 6.83 (1H, s), 6.71
(1H, d, J ¼ 2.5 Hz), 6.68 (1H, d,
J ¼ 2.5 Hz), 5.98–6.0 (2H, m), 5.92 (2H,
s), 6.10–6.18 (2H, m), 5.72 (1H, d,
J ¼ 4.8 Hz), 4.18–4.20 (2H, m), 2.16–
2.19 (4H, m), 1.29–1.32 (8H, m), 0.90
(3H, t, J ¼ 4.6, 2.0 Hz). 13C NMR
(75 MHz, CDCl3): d 166.2, 148.2, 148.0,
145.0, 135.0, 133.1, 128.3, 127.0, 124.6,
119.2, 110.6, 108.2, 105.0, 101.2, 61.4,
30.0, 29.9, 29.7 (2C), 29.0 (2C), 14.7. ESI-
MS: m/z 357.0 [M þ H]þ. HR-ESI-MS:
m/z 357.2053 [M þ H]þ (calcd for
C22H29O4, 357.2066).
[4] S.K. Okwute, J.L. Okogun, and A. Okorie,
Tetrahedron 40, 2541 (1984).
3.2.10 Compound 1
mp 1198C. 1H NMR (300MHz, CDCl3): d
7.14 (1H, dd, J ¼ 14.7, 9.9 Hz), 6.84 (2H,
br s), 6.74–6.75 (2H, m), 6.27 (1H, d,
J ¼ 15.9Hz), 6.06–6.04 (2H, m), 5.93 (2H,
s), 5.73 (1H, d, J ¼ 15.9Hz), 3.15 (2H, dd,
J ¼ 6.6 Hz), 2.14–1.16 (4H, m), 1.76–1.79
(1H, m), 1.4–1.5 (2H, m), 1.25–1.4 (4H,
m), 0.92 (6H, d, J ¼ 6.6 Hz). 13C NMR
(75 MHz, CDCl3): d 166.3, 147.8, 146.4,
143.0, 141.2, 132.4, 129.2, 128.2, 121.7,
120.1, 120.0, 108.1, 105.3, 100.8, 46.8,
32.8, 32.7, 30.2, 29.2, 28.9, 28.6, 28.5, 20.2;
ESI-MS: m/z 384 [M þ H]þ.
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Acknowledgements
The authors gratefully acknowledge the keen
interest shown by Dr J.S. Yadav, Director, IICT,
Hyderabad. R.S.C.K and G.V.R. thank the CSIR
and UGC, New Delhi for financial support.
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Journal of Asian Natural Products Research
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