Synthesis of unsymmetrical biphenyls as potent cytotoxic agents

Article abstract of DOI:10.1016/j.bmcl.2008.08.050

Twenty-six unsymmetrical biphenyls were synthesized and evaluated for cytotoxic activity against DU145, A549, KB and KB-Vin tumor cell lines. Three compounds 27, 35 and 40 showed very potent activity against the HTCL panel with an IC₅₀ value range of 0.04-3.23 μM. In addition, fourteen active compounds were all more potent against the drug-resistant KB-Vin cell line than the parental KB cell line. Preliminary SAR analysis indicated that two bulky substituents on the 2,2′-positions of unsymmetrical biphenyl skeleton are necessary and crucial for in vitro anticancer activity, thus providing a good starting point to develop unsymmetrical biphenyls as novel anticancer agents.

Full text of DOI:10.1016/j.bmcl.2008.08.050

Bioorganic & Medicinal Chemistry Letters 18 (2008) 5272–5276
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of unsymmetrical biphenyls as potent cytotoxic agents
Gang Wu a,d, Huan-Fang Guo a, Kun Gao d, Yi-Nan Liu b, Kenneth F. Bastow c,
Susan L. Morris-Natschke b, Kuo-Hsiung Lee b, Lan Xie a,
a Beijing Institute of Pharmacology and Toxicology, Beijing 100850, China
*
b Natural Products Research Laboratories, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC 25799, USA
c Division of Medicinal Chemistry & Natural Products, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, NC 25799, USA
d State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Twenty-six unsymmetrical biphenyls were synthesized and evaluated for cytotoxic activity against
Received 16 May 2008
Revised 14 August 2008
Accepted 18 August 2008
Available online 22 August 2008
DU145, A549, KB and KB-Vin tumor cell lines. Three compounds 27, 35 and 40 showed very potent activ-
ity against the HTCL panel with an IC50 value range of 0.04–3.23 lM. In addition, fourteen active com-
pounds were all more potent against the drug-resistant KB-Vin cell line than the parental KB cell line.
Preliminary SAR analysis indicated that two bulky substituents on the 2,20-positions of unsymmetrical
biphenyl skeleton are necessary and crucial for in vitro anticancer activity, thus providing a good starting
point to develop unsymmetrical biphenyls as novel anticancer agents.
Keywords:
Unsymmetrical biphenyls
Suzuki coupling reaction
Anticancer agents
Ó 2008 Elsevier Ltd. All rights reserved.
Natural products continue to play a highly significant role today
in the discovery and development of new drugs, new leads and
new chemical entities. This fact is particularly evident in the areas
of cancer and infectious diseases, where over 60% and 75% of drugs,
respectively, are of natural origin.1,2 Dibenzocyclooctandiene lign-
ans have been identified as major bioactive constituents from the
traditional Chinese medicinal plant Schizandra chinese and show
a wide variety of interesting biological activities,3,4 including anti-
viral,5 anticancer,6,7 hepatoprotective,8 and anti-inflammatory.9
Recently, it was also reported that several dibenzocyclooctadiene
lignans, such as gomisin A, schisandrins A and B, and schisantherin
A, have activity against cancer multidrug resistance mediated by P-
glycoprotein (P-gp) and effectively restore the action of anticancer
drugs,10–12 such as vinblastine, daunorubicin, doxorubicin, and VP-
16.
However, because natural lignans with multiple chiral centers
are not always ideal as drug candidates, even though many total
synthesis studies have been reported,13 we were prompted to
use lignans as leads for new compounds with simpler, more acces-
sible structures. The biphenyl moiety in natural dibenzocyclooct-
adiene lignans is substituted with methoxy and methylenedioxy
groups at different positions, resulting in either symmetrical
(wuweizi C) or unsymmetrical (wuweizi B) biphenyls, as shown
in Fig. 1, and this feature is crucial for biological activity. Structural
simplification of the symmetrical wuweizi C to simpler biphenyl
O
O
O
O
O
H
H
H
H
H3CO
H3CO
H3CO
H3CO
H3CO
O
H3CO
Wuweizi B
Wuweizi C
OCH3
OCH3
O
O
O
O
O
O
COOCH3
COOCH3
COOCH3
CH2OH
O
O
OCH3
-DDB
OCH3
Bicyclol
α
Figure 1. Structures of natural dibenzocyclooctadiene lignans and biphenyl
derivatives.
(methyl 4,40-dimethoxy-5,6,50,60-dimethylenedioxy biphenyl-2,2-
dicarboxylate) and bicyclol (Fig. 1), which are widely used medic-
inally in China and Asia. In our current study, we decided to focus
on unsymmetrical biphenyls, as such compounds have not been
previously well explored for cytotoxic activity. Our goal was to
analogs led to the anti-hepatotoxic (liver injury) drugs
a-DDB
* Corresponding author. Tel./fax: +86 10 6931690.
E-mail address: lanxieshi@yahoo.com (L. Xie).
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.08.050

G. Wu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5272–5276
5273
identify novel biphenyl leads with potent anticancer effects, hope-
fully with activity against multidrug resistance.
which are desired moieties for building different biphenyl deriva-
tives. The benzaldehyde analogs of benzoates 2, 10, and 13 were
prepared by the following sequence. The carboxylic esters in 1
and 14 were converted to aldehydes in 4 and 15 by reduction of
an intermediate hydrazone. Bromination of 4 and 15 with Br2 in
CH2Cl2 then afforded 2-bromo-3,4,5-trimethoxybenzaldehyde 5
and a mixture of 2-bromo- and 6-bromo-3-methoxy-4,5-methyl-
enedioxybenzaldehyde (16 and 17), respectively.
Herein, we report the synthesis of twenty-six unsymmetrical
biphenyl compounds (18-43) and their cytotoxic activity against
DU154, A549, KB and drug-resistant KB-Vin cell lines. Among
them, three compounds (27, 35 and 40) showed very promising
inhibitory activity against all tested tumor cells with an IC50 range
of 0.04–3.23 lM.
Unsymmetrical biphenyls are frequently prepared by using
Stille, Suzuki, Ullmann, and Grignard cross-coupling reactions. A
Suzuki cross-coupling reaction14,15 of an aryl halide with an aryl
boronic acid offers convenient access to unsymmetrical biaryls
with a wide range of structural diversity. Accordingly, this ap-
proach was used to obtain our target compounds because of phen-
ylboronic acid commercial availability, mild reaction conditions,
and a little or no homocoupling by-products. The different aryl bro-
mide precursors were synthesized as shown in Scheme 1 following
literature methods.16,17 Using methyl sulfate in strongly basic con-
ditions, gallic acid was methylated completely to provide methyl
3,4,5-trimethoxybenzoate (1), followed by bromination to give
the aryl bromide 2. In methanol under acidic conditions, gallic acid
was methylated only at the carboxylic acid to yield methyl gallate
6. The three hydroxyls of 6 were then selectively modified by using
different reactions to produce methylenedioxy 8 or monomethoxy
11. Using 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) as a bro-
minating reagent,17 bromination of both 8 and 11 occurred regio-
selectively at the ortho-position to the free hydroxyl to afford 9
and 12, respectively. Next, the remaining free hydroxyls in 9 and
12 were converted to methoxy and methylenedioxy groups,
respectively, to give isomeric aryl bromide precursors 10
(methyl 2-bromo-3-methoxy-4,5-methylenedioxybenzoate) and
13 (methyl 6-bromo-3-methoxy-4,5-methylenedioxybenzoate),
Next, Suzuki cross-coupling reactions were performed using
palladium acetate [Pd(AcO)2] as catalyst in the presence of anhy-
drous Cs2CO3 to synthesize unsymmetrical biphenyls I–IV as
shown in Scheme 2 and Table 1. Coupling between commercially
available phenylboronic acid (B1) or 2-formylphenyl boronic acid
(B2) and the synthetic aryl bromides described above (2 or 5, 13
or 17, 10 or 16) gave biphenyls of types I (18–20), III (38–40),
and IV (41–43), respectively. Type II biphenyls (28, 29) were pre-
pared by reaction between 2 or 5 with 2-formyl-4,5-methylenedi-
oxyphenyl boronic acid (B3), which was prepared according to
literature methods.16 After coupling, the aldehyde or methyl ester
(substituents R1 and R2) on the biphenyls was easily converted to
various functional groups, including hydroxymethyl, oxime, car-
boxylic acid, and various esters, by common synthetic methods,
to produce additional unsymmetrical biphenyls (21–27, 30–37).
The spectroscopic data of all target biphenyl compounds are shown
at endnote.20
The synthesized biphenyl compounds were tested for in vitro
cytotoxic activity against a human tumor cell line (HTCL) panel,
including A549 (lung), DU145 (prostate), KB (nasopharyngeal),
and drug-resistant KB-Vin, according to a reported SRB method.18
Homoharringtonine and etoposide served as reference antitumor
compounds. The structures and bioassay data of all unsymmetrical
biphenyls 18–43 are summarized in Table 1. Among them,
COOH
COOCH3
R
CONHNH2
CHO
CHO
i
iii
iv
ii
Br
81%
79%
90%
82-92%
HO
OH H3CO
OCH3 H3CO
OCH3
OCH3
H3CO
OCH3
OCH3
H3CO
OCH3
OH
OCH3
OCH3
1
2
R = H
R = Br
3
4
5
v
80%
ii
COOCH3
COOCH3
COOCH3
COOCH3
Br
COOCH3
Br
vi
vii
77%
viii
i
95%
95%
79%
HO
OH
O
OH
O
OH
O
OH
O
OCH3
OH
O
O
O
O
6
7
8
9
10
EtO
ix
80%
COOCH3
COOCH3
CHO
CHO
CHO
Br
Br
ii
x
iii, iv
+
97%
HO
OCH3
O
OCH3
O
OCH3
O
OCH3
O
OCH3
OH
ii
COOCH3
O
O
O
O
11
14
15
16
17
COOCH3
Br
Br
x
HO
OCH3
O
OCH3
OH
O
12
13
Scheme 1. Synthesis of aryl bromide precursors. Reagents and conditions: (i) Me2SO4/NaOH aq, rt, 1.5 h; (ii) Br2/CH2Cl2, 0 °C, 1–3 h; (iii) NH2NH2ꢀH2O, 95 °C, 3 h; (iv)
K3Fe(CN)6/NH3ꢀH2O, toluene/H2O, rt, 0.5–1.5 h; (v) MeOH/H2SO4, reflux, 5 days; (vi) (EtO)3CH/H+, benzene, reflux, 16 h; (vii) (a) BnBr, K2CO3, DMF, 70 °C, 1.5 h, 90%; (b) HCl aq.
(2%), MeOH, rt, 2 h, 99%; (c) CH2Cl2/K2CO3, DMF, 105 °C, 6 h, 96%; (d) TiCl4/CHCl3, rt, 12 h, 90%; (viii) DBDMH/CHCl3, rt, 10 h; (ix) Me2SO4/NaOH aq, Na2B4O7, rt, 5 h; (x) CH2Cl2/
K2CO3, DMF, 105 °C, 6 h.

5274
G. Wu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5272–5276
0.11–0.51 lM and 0.31–3.23 lM, respectively, against the HTCL
Br
A
B(OH)2
R2
R'
A
R1
panel. Compounds 19, 20, 28, 39, and 43 showed greater activity
against DU145 and KB-Vin cell lines than against the other two cell
lines.
R1
R2
i
+
60-85%
R'
R"
B
R"
B
From a structure-activity relationship (SAR) viewpoint, various
patterns of methoxy and methylenedioxy substitution on the A
and B ring had less impact on inhibitory potency than changes in
the functional groups at the 2,20-positions of biphenyls. With the
2,20-substituents held constant (R1 = CHO or COOMe, R2 = CHO),
Type III (39 and 40; 4-methoxy-5,6-methylenedioxy substitution)
biphenyls were somewhat more potent than Type I (19 and 20;
4,5,6-trimethoxy substitution), II (28 and 29; 4,5,6-trimethoxy-
40,50-methylenedioxy substitution), or IV (42 and 43; 4,5-methyl-
endioxy-6-methoxy substitution) compounds. However, more sig-
nificant changes in potency were found by changing the
substituents at the 2,20-positions as described below.
B1 R" = R2 = H
I - IV
2, 5, 10,
B2 R" = H, R2 = CHO
B3
13, 16, 17
R" = OCH2O, R2 = CHO
R1 / R2 = CHO
ii
iii
R
R
1 / R2 = CH2OH
v
1 / R2 = CH=N-OH
iv
R3 = Me, CH2CH2COOH, Ph
R1 / R2 = CH2OCOR3
R1 / R2 = CH=C(Me)NO2
R1 / R2 = COOMe
vi
R1 / R2 = COOH
Scheme 2. Synthesis of unsymmetrical biphenyls. Reagents and conditions: (i)
Pd(OAc)2, PPh3, Cs2CO3, DME, 70 °C, 2–10 h; (ii) NaBH4/MeOH, rt, 1–2 h, 99%; (iii)
NH2OHꢀHCl, NaOH aq /C2H5OH, rt, 2 h, 81–98%; (iv) CH3CH2NO2, n-BuNH2/HOAc,
toluene, reflux, 3 days, 63%; (v) R3COCl, Py, rt, 12 h, 90–96%; (vi) NaOH/H2O, 100 °C,
4 h, 70%.
Generally, methyl carboxylate (R1) was preferred to an alde-
hyde on ring A, and an aldehyde (R2) was better than hydrogen
on ring B. This trend was most apparent against DU154 and KB-
Vin cell lines (compare 19/20, 39/40, 42/43). Data for compounds
18–27 and 28–35 (Types I and II in Table 1) supported our hypoth-
esis that variation of substituents at the biphenyl 2,20-positions
could greatly affect in vitro anticancer potency. Compounds with
hydroxymethyl (21, 22, 30, 31), dicarbaldehyde oxime (23, 32),
methyl acetate (24, 33), and methyl 4-oxobutanoic acid (25, 34)
at these positions showed either no inhibitory activity or were
much less potent than corresponding active compounds 19 and
40,50-methylenedioxy-(4,5,6-trimethoxy-biphenyl-2,20-diyl)bis-
(methylene)dibenzoate (35) showed the most potent inhibitory
effects with an IC50 value of 0.04 lM against the above four tumor
cell lines. 2,3,4-Trimethoxy-20,6-bis(2-nitroprop-1-enyl)biphenyl
(27) and methyl 20-formyl-4,5,6-trimethoxybiphenyl-2-carboxyl-
ate (40) were also significantly active with IC50 value ranges of
Table 1
In vitro growth inhibition of DU145, A549, KB and KB-vin tumor cell lines
OCH3
OCH3
OCH3
A
O
H3CO
O
H3CO
O
O
A
A
A
R1
R2
R1
R2
H3CO
O
R1
H3CO
H3CO
R1
R2
R2
B
B
B
B
I
II
III
IV
O
a
a
R1
R2
I/#
IC50
A549
(
l
V)
II/#
IC50 (lV)
DU145
KB
KBvin
DU145
A549
KB
KBvin
CHO
CHO
H
CHO
CHO
CHOH
CH2OH
CH@NOH
CH2OCOMe
18
19
20
21
22
23
24
NTc
4.29
5.25
NAd
NA
9.52
9.10
7.76
NA
NA
NA
11.9
16.1
12.0
NA
NA
NA
10.4
9.83
4.97
NA
NA
NA
28
29
30
31
32
33
3.66
NA
NA
NA
NA
NA
20.2
NA
NA
NA
19.2
NA
15.7
NA
NA
NA
11.2
NA
4.10
NA
NA
NA
15.8
NA
COOMe
CHOH
COOMe
CH@NOH
CH2OCOMe
NA
NA
NA
32.5
NA
O
O
O
O
25
NA
NA
NA
NA
34
35
NA
NA
NA
NA
CO2H
CO2H
CH2OCOPh
CH@C(Me)NO2
CH2OCOPh
CH@C(Me)NO2
26
27
NT
NA
0.11
14.4
0.41
12.0
0.51
0.04
0.04
0.04
0.04
0.29e
A-COO-B; See Figure 2
A-COOCH2-B, See Figure 2
36
37
NA
15.6
NA
21.2
NA
18.4
NA
15.3
III/#
IV/#
CHO
CHO
COOMe
H
CHO
CHO
38
39
40
NA
3.87
0.31
NA
7.15
1.70
NA
6.13
3.23
NA
2.46
0.86
41
42
43
NT
9.61
2.23
21.8
9.08
19.6
NA
9.15
12.8
18.7
6.58
1.88
Homoharringtonineb
Etoposideb
0.03
9.98
0.004
14.2
0.51
NA
a
IC50: concentration that causes a 50% reduction of cell growth.
Positive control.
NT, not tested.
NA, not active.
Data obtained from PC-3 (prostate) cell line.
b
c
d
e

G. Wu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5272–5276
5275
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OCH3
A
OCH3
A
5. Chen, D. F.; Zhang, S. X.; Xie, L.; Xie, J. X.; Chen, K.; Kashiwada, Y.; Zhou, B. N.;
Wang, P.; Cosentino, L. M.; Lee, K. H. Bioorg. Med. Chem. 1997, 5, 1715.
6. Kuo, Y. H.; Kuo, L. M.; Chen, C. F. J. Org. Chem. 1997, 62, 3242.
7. Yasukawa, K.; Ikeya, Y.; Mitsuhashi, H.; Iwasaki, M.; Aburada, M.; Nakagawa, S.;
Takeuchi, M.; Takido, M. Oncology 1992, 49, 68.
8. Zhu, M.; Lin, K. F.; Yeung, R. Y.; Li, R. C. J. Ethnopharmacol. 1999, 67, 61.
9. Wang, J. P.; Raung, S. L.; Hsu, M. F.; Chen, C. C. Br. J. Pharmacol. 1994, 113, 945.
10. Wan, C. K.; Zhu, G. Y.; Shen, X. L.; Chattopadhyay, A.; Dey, S.; Fong, W. F.
Biochem. Pharmacol. 2006, 72, 824.
11. Pan, Q.; Lu, Q.; Zhang, K.; Hu, X. Cancer Chemother. Pharmacol. 2006, 58, 99.
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14. Collier, P. N.; Campbell, A. D.; Patel, I.; Raynham, T. M.; Taylor, R. J. J. Org. Chem.
2002, 67, 1802.
H3CO
H3CO
H3CO
H3CO
O
O
O
O
B
B
O
O
O
O
36
37
Figure 2. Structures of lactone-linked biphenyl derivatives.
15. Urawa, Y.; Ogura, K. Tetrahedron Lett. 2003, 44, 271.
16. Monovich, L. G.; Le Huerou, Y.; Roenn, M.; Molander, G. A. J. Am. Chem. Soc.
2000, 122, 52.
28 (R1 = R2 = aldehyde), respectively. In contrast, biphenyls 27 and
35 with two bulky groups, 2-nitroprop-1-enyl and methylbenzo-
ate, respectively, showed significant potency against all tested tu-
mor cell lines.
17. Alam, A.; Takaguchi, Y.; Ito, H.; Yoshida, T.; Tsuboi, S. Tetrahedron 2005, 61, 1909.
18. Rubinstein, L. V.; Shoemaker, R. H.; Paull, K. D.; Simon, R. M.; Tosini, S.; Skehan,
P.; Scudiero, D. A.; Monks, A.; Boyd, M. R. J. Natl. Cancer Inst. 1990, 82, 1113.
19. Min, H. Y.; Park, E. J.; Hong, J. Y.; Kang, Y. J.; Kim, S. J.; Chung, H. J.; Woo, E. R.;
Hung, T. M.; Youn, U. J.; Kim, Y. S.; Kang, S. S.; Bae, K.; Lee, S. K. Bioorg. Med.
Chem. Lett. 2008, 18, 523.
These results prompted us to consider whether steric compres-
sion between adjacent 2,20-substituents could alter the biphenyl
torsional angle, resulting in a stereo-configuration that would di-
rectly affect the molecular affinity with a target receptor/enzyme
and result in different inhibitory activity against tumor cell lines.
Biphenyl configuration (S- or R-) in natural dibenzocyclooctandi-
ene lignans can play an important role in antiproliferative effects.
For example, wuweizisu B with R-biphenyl configuration is less po-
tent than gomisin N with S-biphenyl configuration.19 To obtain re-
lated information in our study, lactone-linked biphenyls 36 and 37
(Fig. 2) were evaluated in the same assays. Although neither com-
pound showed significant potency, the latter compound with a se-
ven-membered lactone ring was more active than the former with
a six-membered lactone ring. These data suggest that both bigger
torsional angles caused by two bulky substituents on the 2,20-posi-
tions and the configuration of the biphenyls might play important
roles in inhibition of tumor cell growth.
Interestingly, several active compounds (19, 20, 28, 37, 39, 40,
42, and 43) were also 1.4–6.8 times more potent against the
drug-resistant KB-Vin cell line than the KB cell line. Thus, we
hypothesize that the unsymmetrical biphenyl scaffolds are rela-
tively poor substrates for the drug efflux pump (MDR) and could
be developed as novel leads with low potential for drug resistance
development.
20. Compound 18: Yield 71%; white solid, mp 88–90 °C; 1H NMR 9.65 (1H, s), 7.43
(3H, m), 7.34 (3H, m), 4.00 (3H, s), 3.97 (3H, s), 3.60 (3H, s); ESI-MS m/z: 295
(M+Na+).
Compound 19: Yield 65%; white solid, mp 71–72 °C; 1H NMR 9.88 (1H, s), 9.60
(1H, s), 8.09 (1H, dd, J = 1.6 and 7.6 Hz), 7.68 (1H, dd, J = 1.6 and 7.6 Hz), 7.60
(1H, dd, J = 1.6 & 7.6 Hz), 7.42 (1H, s), 7.32 (1H, dd, J = 1.6 and 7.6 Hz), 4.00 (6H,
s), 3.55 (3H, s); ESI-MS m/z: 323 (M+Na+).
Compound 20: Yield 65%; white solid, mp 78–79 °C; 1H NMR 9.82 (1H, s), 8.02
(1H, dd, J = 1.2 and 8.0 Hz), 7.59 (1H, dd, J = 1.2 and 8.0 Hz), 7.50 (1H, d,
J = 8.0 Hz), 7.38 (1H, s), 7.19 (1H, d, J = 8.0 Hz), 3.96 (6H, s), 3.52 (6H, s); ESI-MS
m/z: 353 (M+Na+).
Compound 21: Yield 96%; white solid, mp 106–108 °C; 1H NMR 7.48 (1H, d,
J = 7.2 Hz), 7.37 (2H, m), 7.13 (1H, d, J = 7.2 Hz), 6.88 (1H, s), 4.31 (2H, s), 4.22
(2H, s), 3.92 (3H, s), 3.90 (3H, s), 3.54 (3H, s); ESI-MS m/z: 327 (M+Na+).
Compound 22: Yield 97%, white solid, mp 68–69 °C; 1H NMR: 7.54 (1H, d,
J = 8.0 Hz), 7.40 (1H, s), 7.30 (2H, m), 7.03 (1H, d, J = 8.0 Hz), 4.38 (2H, m), 3.96
(6H, s), 3.58 (3H, s), 3.52 (3H, s); ESI-MS m/z 355 (M+Na+).
Compound 23: Yield 90%, pale yellow solid, mp 123–124 °; 1H NMR (DMSO)
11.33 (1H, s), 11.27 (1H, s), 7.89 (1H, m), 7.57 (1H, s), 7.47 (2H, m), 7.35 (1H, s),
7.26 (1H, s), 7.20 (1H, s), 3.90 (3H, s), 3.84 (3H, s), 3.49 (3H, s); ESI-MS m/z 353
(M+Na+).
Compound 24: Yield 80%, white solid, mp 68–70 °C, 1H NMR 7.46 (1H, dd,
J = 1.2 & 7.2 Hz), 7.39 (2H, m), 7.18 (1H, dd, J = 1.2 and 7.2 Hz), 6.80 (1H, s),
4.71–4.87 (4H, m), 3.91 (6H, s), 3.59 (3H, s), 2.01 (6H, s); ESI-MS m/z: 411
(M+Na+).
Compound 25: Yield 20%; yellow oil, 1H NMR 7.45 (1H, m), 7.37 (2H, m), 7.15
(1H, dd, J = 1.2 and 6.8 Hz), 6.78 (1H, s), 4.93 (2H, s), 4.78 (2H, s), 3.90 (6H, s),
3.56 (3H, s), 2.58 (8H, m); ESI-MS m/z 527 (M+Na+).
Compound 26: Yield 99%, yellow oil; 1H NMR 7.97 (4H, m), 7.57 (1H, d, J = 7.2
Hz), 7.35–7.52 (8H, m), 7.27 (1H, dd, J = 7.2 and 2.8 Hz), 6.86 (1H, s), 5.17 (2H,
d, J = 7.6), 5.00 (2H, s), 3.89 (6H, s), 3.61 (3H, s);ESI-MS m/z: 535 (M+Na+).
Compound 27: Yield 63%, brown solid, mp 57–58 °C, 1H NMR 7.62 (1H, s), 7.49
(2H, m), 7.47 (2H, m), 7.26 (1H, m), 6.67 (1H, s), 3.95 (3H, s), 3.93 (3H, s), 3.61
(3H, s), 2.30 (3H, s), 2.28 (3H,s); ESI-MS 437 [M+Na+].
In conclusion, twenty-six unsymmetrical biphenyls were syn-
thesized and evaluated in DU145, A549, KB and KB-Vin tumor cell
lines. Three compounds 27, 35 and 40 showed very potent activity
Compound 28: Yield 69%, white solid, mp 129–130 °C; 1H NMR 9.64 (1H, s),
9.58 (1H, s), 7.51 (1H, s), 7.38 (1H, s), 6.74 (1H, s), 6.15 (2H, s), 4.00 (6H, s), 3.63
(3H, s); ESI-MS m/z: 367 (M+Na+).
against the HTCL panel with an IC50 value range of 0.04–3.23 lM.
In addition, fourteen active compounds were all more potent
against the drug-resistant KB-Vin cell line than the parental KB cell
line. Preliminary SAR analysis indicated that two bulky substitu-
ents on the 2,20-positions of unsymmetrical biphenyl skeleton are
necessary and crucial for in vitro anticancer activity. Current stud-
ies provide a good starting point to develop unsymmetrical biphe-
nyls as novel anticancer agents. Further lead optimization is
ongoing.
Compound 29: Yield 63%; pale yellow solid, mp 102–103 °C; 1H NMR 9.55 (1H,
s), 7.46 (1H, s), 7.36 (1H, s), 6.63 (1H, s), 6.10 (2H, s), 3.97 (6H, s), 3.63 (3H, s),
3.61 (3H, s); ESI-MS m/z: 397 (M+Na+).
Compound 30: Yield 90%; white solid, mp 109–110 °C; 1H NMR 7.00 (1H, s),
6.87 (1H, s), 6.62 (1H, s), 6.00 (2H, s), 4.31 (2H, d, J = 4 Hz), 4.21 (2H, d, J = 4 Hz),
3.90 (6H, s), 3.61 (3H, s); ESI-MS m/z: 371 (M+Na+).
Compound 31: Yield 93%; white solid, mp 81 °C; 1H NMR 7.25 (1H, s), 7.02 (1H,
s), 6.51 (1H, s), 6.01 (2H, s), 4.26 (2H, m), 3.96 (6H, s), 3.67 (3H, s), 3.58 (3H, s);
ESI-MS m/z: 399 (M+Na+).
Compound 32: Yield 81%, pale yellow solid, mp 82–84 °C, 1H NMR (DMSO-d6)
11.28 (1H, s), 11.15 (1H, s), 7.42 (1H, s), 7.40 (1H, s), 7.30 (1H, s), 7.23 (1H, s),
6.77 (1H, s), 6.14 (2H, ds), 3.87 (3H, s), 3.83 (3H, s), 3.53 (3H, s); ESI-MS m/z:
397 (M+Na+).
Acknowledgments
Compound 33: Yield 92%, white solid, mp 154–155 °C; 1H NMR 6.95 (1H, s),
6.78 (1H, s), 6.64 (1H, s), 6.02 (2H, s), 4.73–4.76 (4H, m), 3.92 (3H, s), 3.89 (3H,
s), 3.64 (3H, s), 2.04 (3H, s), 2.00 (3H, s); ESI-MS m/z: 455 (M+Na+).
Compound 34: Yield 91%, 1H NMR 7.00 (1H, s), 6.89 (1H, s), 6.71 (1H, s), 6.07
(2H, s), 4.63 (4H, m), 3.84 (3H, s), 3.76 (3H, s), 3.51 (3H, s), 2.40 (8H, m); ESI-MS
m/z: 571 (M+Na+).
This investigation was supported by a grant from the Ministry
of Science and Technology of P.R. China (2006DFA33560) awarded
to L. Xie and NIH Grant CA17625 from the National Cancer Institute
awarded to K.H. Lee.
Compound 35: Yield 94%; white gum; 1H NMR 7.96 (4H, m), 7.50 (2H, m), 7.38
(4H, m), 7.05 (1H, s), 6.86 (1H, s), 6.73 (1H, s), 6.00 (2H, ds), 5.06–5.03 (4H, m),
3.89 (6H, s), 3.66 (3H, s); ESI-MS m/z: 579 (M+Na+).
References and notes
Compound 36: Yield 11%; pale yellow solid, mp 191–194 °C; 1H NMR 8.33 (1H,
s), 7.72 (1H, s), 6.87 (1H, s), 6.07 (2H, s), 4.04 (3H, s), 4.00 (3H, s), 3.96 (3H, s);
ESI-MS m/z: 353 (M+Na+).
1. Newman, D. J.; Cragg, G. M.; Snader, K. M. J. Nat. Prod. 2003, 66, 1022.
2. Saklani, A.; Kutty, S. K. Drug Discov. Today 2008, 13, 161.
3. Charlton, J. L. J. Nat. Prod. 1998, 61, 1447.

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G. Wu et al. / Bioorg. Med. Chem. Lett. 18 (2008) 5272–5276
Compound 37: Yield 98%; white solid, mp 163–164 °C; 1H NMR 7.26 (1H, s),
(3H, s); ESI-MS m/z: 337 (M+Na+).
7.21 (1H, s), 6.92 (1H, s), 6.03 (2H, ds), 4.93 (1H, d, J = 12 Hz), 4.81 (1H, s), 3.99
(3H, s), 3.95 (3H, s), 3.66 (3H, s); ESI-MS m/z 367 (M+Na+).
Compound 41: Yield 80%; white solid, mp 89–91 °C; 1H NMR 9.52 (1H, s), 7.43
(3H, m), 7.30 (2H, m), 7.24 (1H, s), 6.10 (2H, s), 3.82 (3H, s). ESI-MS m/z: 279
(M+Na+).
Compound 38: Yield 80%; white solid, mp 106–107 °C; 1H NMR 9.78 (1H, s),
7.48 (3H, m), 7.42 (2H, m), 7.36 (1H, s), 6.11 (2H, s), 4.00 (3H, s); ESI-MS m/z:
279 (M+Na+).
Compound 42: Yield 70%; white solid, mp 125–126 °C; 1H NMR 9.86 (1H, s),
9.47 (1H, s), 8.06 (1H, dd, J = 1.6 and 7.6 Hz), 7.67 (1H, dd, J = 1.6 and 7.6 Hz),
7.64 (1H, d, J = 7.6 Hz), 7.27 (1H, s), 7.25 (1H, d, J = 7.6 Hz), 6.13 (2H, s), 3.83
(3H, s); ESI-MS m/z: 295 (M+Na+).
Compound 39: Yield 70%; white solid, mp 112–114 °C; 1H NMR 9.95 (1H, s),
9.68 (1H, s), 8.07 (1H, dd, J = 1.6 and 7.6 Hz), 7.70 (1H, dd, J = 1.6 and 7.6 Hz),
7.61(1H, d, J = 7.6 Hz), 7.39 (1H, s), 7.37 (1H, dd, J = 1.6 and 7.6 Hz), 6.13 (2H, s),
3.83 (3H, s); ESI-MS m/z: 307 (M+Na+).
Compound 43: Yield 70%; white solid, mp 88–90 °C; 1H NMR 9.84 (1H, s), 8.02
(1H, dd, J = 1.2 and 7.6 Hz), 7.58 (1H, dd, J = 1.2 and 7.6 Hz), 7.50 (1H, d,
J = 7.6 Hz), 7.24 (1H, s), 7.15 (1H, d, J = 7.6 Hz), 6.10 (2H, s), 3.78 (3H, s), 3.52
(3H, s); ESI-MS m/z: 337 (M+Na+). All 1H NMR were measured in solvent CDCl3
unless indicated.
Compound 40: Yield 84%; white solid, mp 121–122 °C; 1H NMR 9.89 (1H, s),
8.02 (1H, dd, J = 1.2 and 7.6 Hz), 7.63 (1H, dd, J = 1.2 and 7.6 Hz), 7.52 (1H, d,
J = 7.6 Hz), 7.40 (1H, s), 7.27 (1H, d, J = 7.6 Hz), 6.01 (2H,s), 4.00 (3H, s), 3.58