Synthesis of yashabushidiol and its analogues and their cytotoxic activity against cancer cell lines

Article abstract of DOI:10.1016/j.bmcl.2009.03.061

A total synthesis of yashabushidiol (1a), a linear diarylheptanoid having 1,3- diol system and its analogues has been achieved by alkynylation of 3-hydroxy-5-phenyl pentanal with substituted phenyl acetylenes. All the compounds have shown significant anti

Full text of DOI:10.1016/j.bmcl.2009.03.061

Bioorganic & Medicinal Chemistry Letters 19 (2009) 3125–3127
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of yashabushidiol and its analogues and their cytotoxic activity
against cancer cell lines
M. Narasimhulu a, T. Srikanth Reddy a, K. Chinni Mahesh a, A. Sai Krishna b, J. Venkateswara Rao b,
Y. Venkateswarlu a,
*
a Organic Division-I, Natural Products Laboratory, Indian Institute of Chemical Technology, Hyderabad 500 007, India
b Toxicology Laboratory, Indian Institute of Chemical Technology, 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 total synthesis of yashabushidiol (1a), a linear diarylheptanoid having 1,3- diol system and its ana-
logues has been achieved by alkynylation of 3-hydroxy-5-phenyl pentanal with substituted phenyl acet-
ylenes. All the compounds have shown significant anti-proliferative activity on human leukemia (THP-1,
U-937) and melanoma (A-375) cell lines. Compounds 2a and 2b were found to be most potent with an
Received 1 January 2009
Revised 24 February 2009
Accepted 17 March 2009
Available online 20 March 2009
IC50 of 12.82
l
g/mL and 12.62
l
g/mL, respectively, on THP-1 leukemia cell line.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Diarylheptanoids
Yashabushidiol
Cytotoxic activity
Alkynylation
OH R3
Diarylheptanoids are a family of natural plant metabolites
whose characteristic feature is the presences of two aromatic rings
tethered by a linear seven-carbon chain which are derived biosyn-
thetically from phenylalanine (C9 precursors).1 These linear diaryl-
heptanoids are found in various monocotyledon and dicotyledon
plant species and more than 70 open chain diaraylheptanoids have
been isolated from nature.2 The Zingiberaceae family is an espe-
cially rich source of diarylheptanoids and the most well known
diarylheptanoid is curcumin3 a pigment principle of Curcuma longa
(Zingiberaceae) was first isolated in 1815 by Vogel and Pelletier3
and exhibits strong antioxidant and chemopreventive activities.4,5
Yoshikawa and co-workers isolated hepatoprotective and antioxi-
dant diarylheptanoid glycosides from Betula platyphylla var. japon-
ica.6 The linear diarylheptanoids having 1,3-diol system exhibit
various biological activities such as antioxidative, hepatoprotec-
tive, antiproliferative, anti-inflammatory and antiemitic activities.7
Recent findings on the potent cytotoxic activity of diarylheptanoids
having 3,5-dihydroxy system7a spurred us to do synthesis and ex-
tend the evaluation of the cytotoxic activity of the following
diarylheptanoids.
R2
R1
1a. R1 = R2 = H, R3 = β - OH
1b. R1 = R2 = H, R3 = α - OH
2a. R1 = OH, R2 = H, R3 = β - OH
2b. R1 = OH, R2 = H, R3 = α - OH
3a. R1 = OH, R2 = OMe, R3 = β - OH
3b. R1 = OH, R2 = OMe, R3 = α - OH
Hashimoto et al. isolated a diarylheptanoid 3,5-dihydroxy-1,7-di-
phenyl-heptane named yashabushidiol (1a)8 from the male flowers
of Alnus sieboldiana and other related 3,5-dihydroxy-1,7-diphenyl-
heptanes (2 and 3) were isolated from Alpinia officinarum by Takah-
ashi and co-workers7c The retrosynthetic analysis for
diarylheptanoids 1, 2 and 3 may be represented as shown in
Scheme 1. We envisaged the reaction between b-hydroxy aldehyde
(4) and substituted phenyl acetylenes (5, 6 and 7) to yield 3,5-dihy-
droxy diarylheptanoids after hydrogenation of triple bond. The
substituted phenyl acetylenes (6 and 7) were prepared by using
Corey–Fuchs reaction.9
The synthesis of the b-hydroxy-aldehyde (4) was started from
the readily available D-mannitol diacetonide, which was oxidized
to give (R)-2,3-O-isopropylidine aldehyde 10. The aldehyde 10
was subjected to Wittig reaction with benzyl phosphonium bro-
mide using n-BuLi in THF at 0 °C to produce compound 11 in 90%
yield followed by the hydrogenation of the Wittig product using
* Corresponding author. Tel.: +91 40 27193167; fax: +91 40 27165012.
E-mail address: luchem@iict.res.in (Y. Venkateswarlu).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.03.061

3126
M. Narasimhulu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3125–3127
TPSO
O
R2
R1
+
H
+
+
3
1
2
5. R1 = R2 = H
4
6. R1 = OH, R2 = H
7. R1 = OH, R2 = OMe
OH
OH
D-mannitol
9
8
Scheme 1.
OH
O
O
O
a
OH
d
O
c
b
O
H
O
O
11
10
12
8
OH
OH
OTPS
g
OTs
CN
CN
f
e
4
13
14
15
Scheme 2. Reagents and conditions: (a) [PhCH2Ph3]Br, n-BuLi, THF, 0 °C, 0.5 h, 90%, E/Z = 80:20; (b) H2, 10% Pd/C, MeOH, rt, 6 h, 96%; (c) 2 M HCl, MeOH, rt, 1 h, 95%; (d) TsCl,
(C2H5)3N, (n-Bu)2SnO, 0 °C–rt, 4 h, 76%; (e) KCN, Ethanol/H2O (3:2), rt, 10 h, 90%; (f) TBDPS-Cl, imidazole, anhydrous CH2Cl2, rt, 3 h, 96%; (g) DIBAL-H, anhydrous CH2Cl2,
À78 °C, 0.5 h, 72%.
10% Pd/C in methanol under hydrogen atmosphere at room
temperature afforded compound 12 in 96% yield. The acetonide
group in 12 was removed by using 2 M HCl in methanol at room
temperature to afford the (S)-diol 8 in 95% yield. The saturated diol
was short of one carbon as required in b-hydroxy aldehyde (4) and
the one carbon homologation was carried out in two steps; (i) the
primary hydroxyl group in diol 8 was tosylated by using tosylchlo-
ride and triethylamine in dichloromethane at room temperature to
provide the mono tosylate 13 in 76% yield, (ii) which was reacted
with KCN in ethanol/H2O (3:2) at room temperature to afford the
corresponding nitrile 14 in 90% yield. The secondary hydroxyl
group in compound 14 was protected as tertiary-butyldiphenylsi-
lyl (TBDPS) ether 15 by using TBDPS-Cl and imidazole in dichloro-
methane at 0 °C to afford compound 15 in 96% yield. Finally, the
nitrile functional group in compound 15 was reduced by using
DIBAL-H in anhydrous CH2Cl2 at À78 °C to afford b-hydroxy alde-
hyde 4 in 72% yield (Scheme 2).
to Wittig reaction using triphenylphosphine (TPP) and CBr4 in
CH2Cl2 at 0 °C leads to dibromoalkenes 20 and 21 in 90% yield
which were converted into alkynes 6 and 7 using Grignard reaction
conditions by treating 20 and 21 with ethyl magnesium bromide in
THF at 0 °C in 95% yield (Scheme 3). The formation of products was
confirmed by 1H NMR spectra, which displayed the alkyne proton
signals at d 2.82 (1H, s) and 2.99 (1H, s), respectively.
With the required aldehyde 4 and the phenyl acetylenes 5, 6
and 7 in our hand, we carried out alkenylation of compound 4 with
substituted phenyl acetylenes 5, 6 and 7 by using n-BuLi in THF at
À78 °C to room temperature to produce each alkyne two diastereo-
mers 22, 23 and 24 in the ratio of 40:60 (syn:anti) in 90% yield.
These diastereomeric alcohols were separated by silica gel column
chromatography. After separation of alcohols, the reduction of ace-
tylinic functionality as well as the deprotection of benzyl group in
the alcohols 22, 23 and 24 was occurred in a single step by using
10% Pd/C in methanol under hydrogen atmosphere at room tem-
perature to afford the saturated isomeric pair of alcohols of 25,
26 and 27 in 95% yield, respectively. Finally the tertiarybutyldiphe-
nylsilyl group in compounds 25, 26 and 27 was removed by using
p-toluene sulfonic acid (PTSA) in methanol at room temperature to
afford the diarylheptanoids 1, 2 and 3 of both isomers in 94% yield
(Scheme 4). The optical rotation of compound 1a is identical with
The substituted phenyl acetylenes 6 and 7 were prepared from
4-hydroxy benzaldehyde 16 and vanillin 17, respectively, by using
Corey–Fuchs reaction.9 The phenolic hydroxyl groups in 16 and 17
were protected with benzyl bromide in presence of K2CO3 in ace-
tone to yield benzyl ethers 18 and 19 in 95% yield, respectively.
The benzyl group protected aldehydes 18 and 19 were subjected
Br
Br
O
O
R2
R1
R2
R1
R2
R1
R2
R1
a
c
b
H
H
18. R1 = OBn, R2 = H
6. R1 = OBn, R2 = H
20. R1 = OBn, R2 = H
16. R1 = OH, R2 = H
19. R1 = OBn, R2 = OMe
7. R1 = OBn, R2 = OMe
21. R1 = OBn, R2 = OMe
17. R1 = OH, R2 = OMe
Scheme 3. Reagents and conditions: (a) BnBr, K2CO3, Acetone, 0 °C–rt, 95%; (b) PPh3, CBr4, CH2Cl2, 0 °C, 0.5 h, 90%; (c) EtMgBr, THF, 0 °C–rt, 0.5 h, 95%.

M. Narasimhulu et al. / Bioorg. Med. Chem. Lett. 19 (2009) 3125–3127
3127
TPSO
R3
TPSO
O
R2
R1
a
b
H
R2
R1
+
22a. R1 = R2 = H, R3 = β - OH
5. R1 = R2 = H
4
22b. R1 = R2 = H, R3 = α - OH
6. R1 = OBn, R2 = H
23a. R1 = OBn, R2 = H, R3 = β - OH
23b. R1 = OBn, R2 = H, R3 = α - OH
24a. R1 = OBn, R2 = OMe, R3 = β - OH
24b. R1 = OBn, R2 = OMe, R3 = α - OH
7. R1 = OBn, R2 = OMe
TPSO
R3
R2
c
1a,1b, 2a, 2b, 3a, 3b
R1
25a. R1 = R2 = H, R3 = β - OH
25b. R1 = R2 = H, R3 = α - OH
26a. R1 = OH, R2 = H, R3 = β - OH
26b. R1 = OH, R2 = H, R3 = α - OH
27a. R1 = OH, R2 = OMe, R3 = β - OH
27b. R1 = OH, R2 = OMe, R3 = α - OH
Scheme 4. Reagents and conditions: (a) n-BuLi, THF, 0 °C–rt, 2 h, 90%; (b) 10% Pd/C, MeOH, rt, 8 h, 95%; (c) PTSA, MeOH, rt, 1 h, 95%.
cancer cell lines such as THP-1 and U-937 (leukemia), and A-375
(melanoma). It is evident from the results that the test compounds
have shown significant cytotoxic activity on all tested cell lines in a
concentration-dependent manner (Table 1). Test molecules were
classified as low active or high active based on their IC50 values.
In this study, compounds 2a and 2b showed significant cytotoxic
activity in all the test cell lines, although they were still less active
than the more widely used anti-cancerous drug derived from nat-
ural products, etoposide. By comparing the cytotoxic activities of
these compounds, we found that compounds 3a and 3b were also
shown to have significant cytotoxic potency in the U-937 cell line
similar to 2a and 2b.
Table 1
§IC50 values for antiproliferative activities of compound 1a, 2a and 3a and their
isomers 1a, 2a and 3b against cancer cell linesa
Compound
THP-1 (lg/mL)
U-937 (
lg/mL)
A-375 (lg/mL)
1a
1b
2a
2b
3a
3b
99.75 0.4
40.50 0.21
12.82 0.89
12.62 0.69
42.66 1.59
72.22 4.49
1.27 0.09
128.25 0.3
187.74 10.6
31.09 8.07
32.99 5.03
27.66 5.92
32.67 4.88
10.56 0.70
147.75 0.7
164.25 0.2
56.30 3.88
57.78 5.02
69.11 8.63
75.24 3.4
2.31 0.08
Etoposideb
a
Exponentially growing cells were treated with different concentrations of test
compounds for 48 h and cell growth inhibition was analyzed through MTT assay.
§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.
Experimental section. General experimental procedures are
described in the Supplementary data.
Supplementary data
b
Etoposide was employed as positive control.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.bmcl.2009.03.061.
reported value in literature,8 which fixed the stereochemistry of
the newly generated hydroxy group at C-5 is in b orientation. Also,
the relative stereochemistry of 1,3-diol in 1a and 1b was estab-
lished by their conversion to the corresponding acetonide. The
syn and anti relative configuration of the hydroxy groups was con-
firmed by the analysis of 13C NMR spectrum,10 which showed sig-
nals at d 30.1 and 19.8 for the two methyl groups and d 98.4 for the
quaternary carbon of the acetonide in syn 1,3-diol, while in the anti
1,3-diol acetonide having signals at d 24.52 and 24.54 for the two
methyl groups and d 100.4 for the quaternary carbon. Similarly, the
relative stereochemistry of 1,3 diols in 2a, 2b, 3a, and 3b was
established by converting them to corresponding acetonides,
respectively, and studying their 13C NMR chemical shift values.
The biological activities of diarylheptanoids (1a, 2a and 3a) and
their isomers (1b, 2b and 3b) were evaluated to investigate their
anti-proliferative activities in three different types of human
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