Stereoselective synthesis of alpinoid-C and its analogues and study of their cytotoxic activity against cancer cell lines

Article abstract of DOI:10.1016/j.bmcl.2012.04.021

A simple, highly efficient and stereoselective synthetic route has been developed for synthesis of alpinoid-C (1) and its analogues (2, 3 and 4) from commercially available starting materials by using Wittig olefination, Sharpless asymmetric epoxidation,

Full text of DOI:10.1016/j.bmcl.2012.04.021

Bioorganic & Medicinal Chemistry Letters 22 (2012) 4182–4184
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Stereoselective synthesis of alpinoid-C and its analogues and study of their
cytotoxic activity against cancer cell lines
S. Purushotham Reddy a,b, B. Chinnababu a,b, V. Shekhar a,b, D. Kumar Reddy a,b, G.V.S. Bhanuprakash a,b
,
a,b,
L.R. Velatoor a,b, J. Venkateswara Rao a,b, , Y. Venkateswarlu
⇑
⇑
a Division of Natural Products Chemistry, IICT, Hyderabad 500 007, India
b Toxicology Laboratory, IICT, Hyderabad 500 007, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A simple, highly efficient and stereoselective synthetic route has been developed for synthesis of
alpinoid-C (1) and its analogues (2, 3 and 4) from commercially available starting materials by using
Wittig olefination, Sharpless asymmetric epoxidation, Grubbs cross metathesis as key steps. All the
compounds showed moderate anti-proliferative activity against human leukemia/carcinoma (U-937,
THP-1, COLO-205 and HepG2) and mouse melanoma (B16-F10) cancer cell lines. Compounds 3 and 4
Received 20 February 2012
Revised 21 March 2012
Accepted 4 April 2012
Available online 21 April 2012
are found to be most potent with an IC50 of 7.53
on COLO-205 cell lines, respectively.
lM and 32.26 lM on THP-1, 11.12 lM and 7.21 lM
Keywords:
Alpinoid-C
Alpinia officinarum
Ó 2012 Elsevier Ltd. All rights reserved.
Anti cancer drugs
PAF receptor binding inhibitory activity
Wittig olefination
Sharpless asymmetric epoxidation
Grubbs cross metathesis
Diarylheptanoids constitute an important class of natural
products due to their interesting biological and pharmacological
properties such as antiplatelet, anti-inflammatory, antioxidant,
anti-proliferative, antiemetic, antihepatotoxic.1 The structure of
diarylheptanoids is either cyclic or linear and more than 70 open
chain diarylheptanoids have been found since curcumin was iden-
tified in 1815.2 Characteristic feature of diarylheptanoids is the
presence of two aromatic rings together by a linear seven-carbon
chain.3 The linear diarylheptanoids consist of 1,3-diol system or
O
O
1 R = H
3 R = OMe
2 R = H
4 R = OMe
OH
OH
R
R
R
R
Figure 1. Diarylheptanoids.
potent PAF (platelet activating factor) receptor binding antagonis-
tic activity with IC50 1.3
M.6 Later in 2008 compound 1 was iso-
a
,b-unsaturated carbonyls and chiral alcohols. Recently we
synthesized and evaluated cytotoxic properties of diarylheptanoids
having 1,3-diol system.4 The diarylheptanoids containing
,b-
l
lated from the same plant Alpinia officinarum and established the
absolute configuration of the hydroxyl group with Mosher’s ester
analysis.7 In continuation of our work total synthesis, evaluation
of biological activity of natural products and their analogues,4,8,9
we wish to establish simple, efficient, stereoselective synthesis of
compound 1 and its analogues (2, 3, 4) by employing Wittig olefin-
ation, Sharpless asymmetric epoxidation, Grubb’s cross metathesis
as key steps and evaluate their cytotoxic properties against human
a
unsaturated carbonyl system possess a variety of pharmacological
activities such as inhibition of melanogenesis, antiinfluenza,
antiinflammatory, antibacterial, anti-proliferative activities.5
Alpinoid C (1, Fig. 1), a diarylheptanoid containing a,b-unsatu-
rated carbonyl system, was first isolated in 2007 from the plant
Alpinia officinarum (This plant has been traditionally used as a folk
medicine for the treatment of epigastric pains, nausea, indigestion,
and Tinea versicolor fungal infection.) along with other two diaryl-
heptanoids,6 its structure was established based on NMR, IR, EI-MS
data. The configuration of hydroxyl group in compound 1 has been
not determined and the bio-assays found that compound 1 showed
leukemia/carcinoma (THP-1, U-937, COLO205
mouse melanoma (B16-F10) cancer cell lines.
& HepG2) and
The synthesis of 1, 2, 3 and 4 was started from the 2-phenyl-
acetaldehyde 5 which was subjected to C2-Wittig reaction using
[(ethoxycarbonyl)methylene]-triphenylphosphorane to afford
unsaturated ester 6 as mixture of geometrical isomers (E/Z 95:5),
which were separated over silica gel column to give E isomer in
⇑
Corresponding authors. Tel.: +91 40 27193167; fax: +91 40 27160512.
E-mail address: luchem@iict.res.in (Y. Venkateswarlu).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.04.021

S. Purushotham Reddy et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4182–4184
4183
OH
OEt
b
a
CHO
O
7
6
5
Cl
Cl
OH
OH
f
e
e
c
O
O
O
O
OH
9a
10a
8a
7
f
d
OH
8b
9b
10b
Scheme 1. Reagents and conditions: (a) Ph3P@CHCOOEt, dry benzene, reflux, 1 h, 85%; (b) DIBAL-H, CH2Cl2, 0 °C, 2 h, 87%; (c) (ꢀ)DIPT, Ti (OiPr)4, CHP, molecular sieves 4 Å,
dry DCM, ꢀ20 °C, 15 h, 81%; (d) (+)DIPT, Ti (OiPr)4, CHP, molecular sieves 4 Å, dry CH2Cl2, ꢀ20 °C, 15 h, 79%; (e) PPh3, CCl4, 80 °C, 2 h, 90%; (f) sodium metal, dry ether, 6 h, 80%;
85% yield. The ester 6 was reduced with DIBAL-H to allylic alcohol
O
OH
CHO
7 in 87% yield which was subjected to Sharpless epoxidation with
(ꢀ)DIPT, Ti(OiPr)4, and cumene hydroperoxide to afford 8a in 81%
yield. The epoxide 8a was converted into chloro epoxide 9a using
triphenylphosphine in CCl4, 9a followed by reaction with sodium
metal in dry ether gave (R)-allylic alcohol 10a in 80% (Scheme 1).9
Following same sequence of reactions on allylic alcohol 7 as in
Scheme 1 using (+)DIPT and chlorination and reaction with so-
dium metal afforded (S)-allylic alcohol 10b (Scheme 1). The other
fragments 5-phenylpent-1-en-3-one (13a) and 5-(3,4-dimethoxy
phenyl)pent-1-en-3-one (13b) were prepared from 3-phenylpro-
pionaldehyde (11a) and 3,4-dimethoxy 3-phenylpropropionald-
hyde (11b), respectively. In separate experiments compounds
11a and 11b were reacted with vinylmagnesium bromide to af-
ford allyl alcohols 12a and 12b. The allyl alcohols 12a and 12b
on oxidation with IBX afforded vinyl ketones 13a and 13b
(Scheme 2).10
a
b
R
R
R
13a =R=H
13b =R=OMe
R
11a =R=H
11b =R=OMe
12a =R=H
12b =R=OMe
R
R
Scheme 2. Reagents and conditions: (a) Vinylmagnesium bromide, dry THF, 0 °C to
rt, 1 h, 86%; (b) IBX, Dry DMSO, Dry CH2Cl2, 3 h, 90%.
O
O
a
+
OH
OH
10a
1
13a
Scheme 3. Reagents and conditions: (a) Grub’s 2ndgeneration catalyst (5 mol %),
dry CH2Cl2, 50 °C, 5 h,75%.
Finally, the allylic alcohol 10a and vinyl ketone 13a were sub-
jected to olefin cross metathesis using second generation Grubbs
catalyst (5 mol %) in dry CH2Cl2 under reflux to afford natural prod-
uct alpinoid-C 1 in 75% yield.9 Its physical {½a 2D5
= ꢀ3.3 (c = 0.02
ꢁ
O
CHCl3)} and spectroscopic data were identical to those reported
for natural product {lit7, ½a D25
= ꢀ3.22 (c = 0.02 CHCl3)} (Scheme 3).
ꢁ
a
13a
+
10b
10a
Further, the allyl alcohol 10b and 13a was subjected to olefin
cross metathesis using second generation Grubbs catalyst
(5 mol %) in dry CH2Cl2 under reflux to afford 2 in 71% yield.9
Similarly olefin cross metathesis reaction of 10a and 10b with
13b afforded compounds 3 and 4 in 78% and 81%, respectively
(Scheme 4).
OH
2
O
a
+
13b
OH
3
MeO
MeO
The biological activities of alpinoid-C (1) and its derivatives (2,
3, 4) were evaluated to investigate their anti-proliferative activi-
ties in different types of human leukemia/carcinoma (U-937,
THP-1, COLO-205 and HepG2) and mouse melanoma (B16-F10)
cell lines. Test molecules were classified as low active or high ac-
tive based on their IC50 values. It is evident from the results that
all the test derivatives have shown moderate decrease in cell via-
bility against all the test cell lines dependent on concentration
OMe
OMe
O
a
+
10b
13b
4
OH
Scheme 4. Reagents and conditions: (a) Grub’s 2nd generation catalyst (5 mol %),
dry CH2Cl2, 50 °C, 5 h,71%, 78%, 81% for 2, 3, and 4, respectively.
Table 1
IC50 values for anti-proliferative activities of compounds 1–4 against cancer cell linesa
Compound
IC50
(lM)
U-937
THP-1
B16-F10
COLO-205
HepG2
1
2
3
4
139.27 9.56
168.21 2.62
22.26 0.80
120.46 5.58
195.36 3.09
7.53 0.58
32.26 2.3
2.16 0.1
130.29 1.12
337.18 2.74
38.15 1.91
96.94 6.9
194.93 2.01
497.57 2.63
11.12 0.5
7.21 0.39
0.43 0.08
184.86 1.41
354.68 1.93
32.56 1.51
53.53 8.97
4.76 0.16
31.94
3
Etoposideb
17.96 3.07
18.71 2.99
a
IC50 is defined as the concentration, which results in a 50% decrease in cell number as compared with that of the control cultures in the absence of an inhibitor and were
calculated using the respective regression analysis. The values represent the mean SE of three individual observations.
b
Etoposide was employed as positive control.

4184
S. Purushotham Reddy et al. / Bioorg. Med. Chem. Lett. 22 (2012) 4182–4184
(Table 1) and the cytotoxic activity of these test compounds
greatly differed in respect to the type of cell line. In this study,
compound 3 showed significant (IC50 less than 40 lM) cytotoxic
References and notes
1. Huang, C. P.; Bai, S. P.; Li, Y. Nat. Prod. Res. Dev. 1996, 9, 98.
2. Lee, K. K.; Bahler, B. D.; Hofmann, G. A.; Mattern, M. R.; Johnson, R. K.; Kingston,
D. G. I. J. Nat. Prod. 1998, 61, 1407.
3. Roughley, P. J.; Whiting, D. A. J. Chem. Soc., Perkin Trans. 1 1973, 2379.
4. (a) Narasimhulu, M.; Reddy, T. S.; Mahesh, K. C.; Krishna, A. S.; Rao, J. V.;
Venkateswarlu, Y. Bioorg. Med. Chem. Lett. 2009, 19, 3125; (b) Reddy, S. P.;
Ashalatha, K.; Reddy, D. K.; Chinnababu, B.; Venkateswarlu, Y. Synthesis 2011,
19, 3180.
5. (a) Matsuda, H.; Nakashima, S.; Oda, Y.; Nakamura, S.; Yoshikawa, M. Bioorg.
Med. Chem. Lett. 2009, 17, 6048; (b) Swamura, R.; Sun, Y.; Yasukawa, K.;
Shimizu, T.; Watanabe, W.; Kurokawa, M. J. Nat. Med. 2010, 64, 117; (c)
Yasukawa, K.; Sun, Y.; Kitanaka, S.; Tomizawa, N.; Miura, M.; Motohashi, S. J.
Nat. Med. 2008, 62, 374; (d) Zhang, B.; Dai, Y.; Liao, Z.; Ding, L. Fitoterapia 2010,
81, 948; (e) Ali, M. S.; Tezuka, Y.; Awale, S.; Banskota, A. H.; Kadota, S. J. Nat.
Prod. 2001, 64, 289; (f) Martin-Cordero, C.; Lopez-Lazaro, M.; Agudo, A. A.;
Navarro, E.; Trujillo, J.; Ayuso, M. J. Phytochemistry 2001, 58, 567; (g) Lee, K.; Li,
G.; Kim, S. H.; Lee, C.; Woo, M.; Lee, S.; Jhang, Y.; Son, J. J. Nat. Prod. 2002, 65,
1707; (h) Mshvildadze, V.; Legault, J.; Lavoie, S.; Gauthier, C.; Pichette, A.
Phytochemistry 2007, 68, 2531.
activity in all the test cell lines, followed by compounds 4, 1
and 2. The order of activity of these derivatives against different
cell lines is as follows: U-937: 3>4>1>2; THP-1: 3>4>1>2;
B16-F10: 3>4>1>2; COLO-205: 4>3>1>2 and HepG2: 3>4>1>2.
The IC50 values of these compounds were comparatively less than
that of the standard drug, etoposide.
In conclusion we have developed a simple, efficient and stereo-
selective synthetic route for synthesis of alpinoid-C (1) and its ana-
logues (2, 3 and 4) from commercially available starting materials
by using Wittig olefination, Sharpless asymmetric epoxidation,
Grubbs cross metathesis as key steps. All the compounds are
screened for cytotoxic activity. Compounds 3 and 4 are found to
be potent with an IC50 of 7.53
lM and 32.26 lM on THP-1,
11.12 M and 7.21 M on COLO-205 cell lines, respectively.
l
l
6. Fan, G. J.; Kang, Y. H.; Han, Y. N.; Han, B. H. Bioorg. Med. Chem. Lett. 2007, 17,
6720.
7. Sun, Y.; Matsubara, H.; Kitanaka, S.; Yesukawa, K. Helv. Chim. Acta. 2008, 91,
118.
Acknowledgement
8. Reddy, D. K.; Shekhar, V.; Prabhakar, P.; Babu, D. C.; Ramesh, D.; Siddhardha,
B.; Murthy, U. S. N.; Venkateswarlu, Y. Bioorg. Med. Chem. Lett. 2011, 21,
997.
The authors are thankful CSIR-UGC, New Delhi, India for the
financial support.
9. Reddy, D. K.; Shekhar, V.; Prabhakar, P.; Babu, B. C.; Siddhardha, B.; Murthy, U.
S. N.; Venkateswarlu, Y. Eur. J. Med. Chem. 2010, 45, 4657.
10. Reddy, D. K.; Shekhar, V.; Reddy, T. S.; Reddy, S. P.; Venkateswarlu, Y.
Tetrahedron: Asymmetry. 2009, 20, 2315.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2012.04.
021.