Synthesis of new benzimidazole linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates with efficient DNA-binding affinity and potent cytotoxicity

Article abstract of DOI:10.1016/j.bmcl.2008.03.039

The synthesis of new benzimidazole linked pyrrolobenzodiazepine conjugates is described. Some of these conjugates show significant DNA-binding affinity and, a representative compound 4c shows promising in vitro cytotoxicity against a number of human cance

Full text of DOI:10.1016/j.bmcl.2008.03.039

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 18 (2008) 2594–2598
Synthesis of new benzimidazole linked
pyrrolo[2,1-c][1,4]benzodiazepine conjugates with efficient
DNA-binding affinity and potent cytotoxicity
Ahmed Kamal,* P. Praveen Kumar, K. Sreekanth, B. N. Seshadri and P. Ramulu
Biotransformation Laboratory, Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 25 August 2007; revised 16 February 2008; accepted 14 March 2008
Available online 16 March 2008
Abstract—The synthesis of new benzimidazole linked pyrrolobenzodiazepine conjugates is described. Some of these conjugates show
significant DNA-binding affinity and, a representative compound 4c shows promising in vitro cytotoxicity against a number of
human cancer cell lines.
Ó 2008 Elsevier Ltd. All rights reserved.
Benzimidazole moiety is structurally related to purine
bases and is found in a variety of naturally occurring
compounds such as vitamin B12. The benzimidazoles
are potent antitumour,1 antifungal2 and antiparasitic
agents,3 whose mode of action is thought to result from
their inhibition of microtubule formations.4 Substituted
benzimidazoles have proven as drug leads, which have
exhibited pharmacological interest.5 A series of 2-substi-
tuted benzimidazole-4-carboxamides (1) have been syn-
thesized and evaluated for in vitro and in vivo
antitumour activity and DNA-binding affinity.1 More-
over, the architecture of benzimidazole moiety as a
new platform for the DNA-minor groove recognition
elements6 for, selective base pair recognition can be
achieved by introduction of heteroatoms and substitu-
ents in this ring system.7 This ring system can also be
considered as a new tool for the target specific transcrip-
tion factor at the binding sites relevant to biological sys-
tems. Recently, Dervan and co-workers reported the
down-regulation of the angiogenetic vascular endothe-
lial growth factor (VEGF) by a DNA-binding fluores-
cein–polyamide conjugate in cell culture.8
pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a group
of potent DNA interactive antitumour antibiotics de-
rived from Streptomyces species,9 well-known members
include DC-81 (2), anthramycin, chicamycin and tomay-
mycin. Their interaction with DNA has been extensively
investigated and it is considered unique since they bind
within the minor groove of duplex DNA forming a
covalent aminal bond with N2-amino group of guanine
base,10 giving rise to preference for Pu–G–Pu se-
quences.11 PBDs containing an N10–C11 lactam moiety
instead of an electrophilic N10–C11 imine or carbinol-
amine, and thus unable to interact covalently with
DNA, are also known. For example, Kaneko and co-
workers first reported12 that the PBD dilactam 3a has sig-
nificant in vivo antitumour activity in a P388 lymphocytic
leukaemia mouse model but did not propose a mecha-
nism of action. Jones and co-workers followed up this
observation by demonstrating, through DNA thermal
denaturation studies, that dilactam 3a and a number of
related analogues such as 3b can still bind to DNA but
through a non-covalent mechanism which was suggested
to account for the biological activity13,14 (Fig. 1).
On the other side, there is considerable interest in the
development of low molecular weight DNA-binding
agents towards their application on various biological
responses particularly anticancer activity. In this context
In the literature, some PBD conjugates have been syn-
thesized and evaluated for their biological activity, par-
ticularly for their antitumour potential.15–17 Wang and
co-workers have synthesized indole linked PBD conju-
gates as potential antitumour agents.18 We have also
been engaged for the last few years towards the struc-
tural modifications19–21 and the development of new
synthetic strategies22–24 for this ring system. Recently,
we have designed and synthesized a number of PBD hy-
Keywords: Pyrrolobenzodiazepine; Benzimidazoles; In vitro cytotoxic-
ity; DNA-binding affinity.
*
Corresponding author. Tel.: +91 40 27193157; fax: +91 40
27193189; e-mail: ahmedkamal@iict.res.in
0960-894X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2008.03.039

A. Kamal et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2594–2598
2595
H
O
N
HO
N
N
HO
H
H
N
H
X
N
MeO
N
MeO
N
OR
O
O
N
O
H
3a R = Ac
3b R = H
2 (DC 81)
1 X = O, S, NH
H
N
O
N
O
O
N
N
X
n
N
N
X
n
H
H
N
MeO
N
MeO
O
O
5a X = O, n = 1
5b X = S, n = 3
4a-c X = O, n = 1-3
4d-f X = S, n = 1-3
Figure 1. Chemical structures of 2-substituted benzimidazole-4-carboxamide (1), DC-81 (2), PBD dilactoms (3), new benzimidazole–PBD conjugates
(4a–f) and benzimidazole–PBD dilactom conjugates (5a–b).
brids and amongst them C8-linked PBD–benzimidazole
(i)
N
conjugates exhibited remarkable DNA-binding affin-
ity.25 In continuation of these efforts, we herein report
the synthesis of new benzimidazoles linked to pyrrolo-
[2,1-c][1,4]benzodiazepine conjugates as a significant
and important aspect in the development of novel
PBD conjugates with potential anticancer activity and
DNA-binding ability.26
CHO
X
X
N
H
7a X = O
7b X = S
6a X = O
6b X = S
Scheme 1. Reagents and condition: (i) O-phenelenediamine, Na2S2O5,
EtOH, reflux, 4 h, 75%.
NO2
NO2
CH(SEt)2
BnO
MeO
HO
CH(SEt)2
(i)
N
N
MeO
O
O
9
8
(ii)
X
NO2
O
CH(SEt)2
NO2
O
Br
CH(SEt)2
N
N
n
n
(iii)
N
MeO
N
MeO
O
O
10a-c
11a-c X = O, n = 1-3
11d-f X = S, n = 1-3
(iv)
X
N
X
N
NH2
O
N
O
CH(SEt)2
O
N
N
(v)
n
n
H
N
MeO
N
MeO
O
12a-c X = O, n = 1-3
12d-f X = S, n = 1-3
4a-c X = O, n = 1-3
4d-f X = S, n = 1-3
Scheme 2. Reagents and conditions: (i) EtSH–BF3OEt2, CH2Cl2, 12 h, rt, 75%; (ii) dibromoalkanes, K2CO3, DMF, rt, 28 h, 70%; (iii) 7a–b, K2CO3,
acetone, reflux, 24 h, 70%; (iv) SnCl22H2O, MeOH, reflux, 60 min, 70%; (v) HgCl2–CaCO3, CH3CN/H2O (4:1), 8–12 h, 52%.

2596
A. Kamal et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2594–2598
H
NO2
O
BnO
MeO
COOMe
N
HO
(i)
H
N
N
MeO
O
O
13
14
(ii)
X
N
H
O
H
O
N
O
N
O
Br
N
n
H
(iii)
n
H
N
MeO
N
MeO
O
O
15a-b
5a X = O, n = 1
5b X = S, n = 3
Scheme 3. Reagents and conditions: (i) 10% Pd/C, H2, EtOH, 8 h, rt, 65%; (ii) dibromoalkanes, K2CO3, DMF, rt, 28 h, 75%; (iii) 7a–b, K2CO3,
acetone, reflux, 24 h, 70%.
Synthesis of benzimidazole–PBD conjugates 4a–f has
been carried out by employing the benzyloxy nitro-
thioacetal compound 8 as the starting material, which
has been prepared by the literature method.27 This upon
debenzylation gives hydroxy nitrothioacetal compound
9 and further etherification by dibromoalkanes provide
monoalkylated compounds 10a–c. The oxidative
cyclization of O-phenylenediamine and aldehyde
compounds 6a–b with Na2S2O5 in ethanol provides
the benzimidazole compounds 7a–b (Scheme 1).28
Further, N-alkylation of these benzimidazole com-
pounds with monoalkylated compounds 10a–c give the
benzimidazole linked nitrothioacetal precursors 11a–c,
which upon reduction followed by deprotection of thi-
oacetal group afford the target imine compounds 4a–f
(Scheme 2).29
pounds having odd number of carbon chain spacer there
is a substantial increase in the DNA-binding affinity.
Surprisingly, for compounds 4b and 4e having even
number of carbon chain spacer possessing the DTm val-
ues are almost negligible and particularly, compound 4b
has not exhibited any DNA-binding affinity. A similar
phenomenon has been recently observed by us with
other related PBD conjugates.33 On the other hand,
the dilactam PBD conjugates (5a–b) also show lower
DTm values due to the absence of imine functionality,
that is, absence of covalent binding in these molecules.
Moreover the naturally occurring compound DC-81
(1) exhibits a DTm of 0.7 °C, under similar experimental
conditions as illustrated in Table 1.
The restriction endonuclease inhibition studies carried
out on these molecules also confirm the relative binding
affinity of these PBD hybrids. The experimental proto-
Synthesis of dilactam compounds 5a–b has been carried
out by employing the benzylated ester compound 13 as
the starting material, which was prepared by the litera-
ture method30 and further debenzylation followed by
reductive cyclization with 10% Pd/C–H2 provides
hydroxydilactom compound 14. This on monoalkyla-
tion by dibromoalkanes provides monoalkylated dilac-
tom compounds 15a–b. The benzimidazole compounds
7a–b coupled with monoalkylated dilactom compounds
15a–b afford the desired final dilactom compounds 5a–b
(Scheme 3).31
Table 1. Thermal denaturation data for new benzimidazole–PBD
conjugates with calf thymus DNA
b
PBD
conjugates
[PBD]:[DNA]
molar ratioa
DTm (°C) after
incubation at
37 °C for
0 h
18 h
4a
4b
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
5.1
0.0
5.1
3.9
0.1
6.1
0.3
0.4
0.3
6.1
0.0
7.0
5.1
1.0
6.1
0.7
0.8
0.7
4c
4d
The DNA-binding ability of the novel PBD conjugates
(4a–f and 5a–b) has been investigated by thermal dena-
turation studies using calf thymus (CT) DNA at pH 7.0,
incubated at 37 °C, where PBD/DNA molar ratio is
1:5.32 In this assay, it is interesting to observe that com-
pounds 4a, 4c, 4d and 4f elevates the helix melting tem-
perature of CT-DNA by 6.1, 7.0, 5.1 and 6.1 °C,
respectively, after incubation for 18 h at 37 °C. The
enhancement of DNA-binding ability of these conju-
gates can be correlated to other interactions produced
by the benzimidazole component in addition to covalent
linkage of the imine component. Moreover, for the com-
4e
4f
5a
5b
DC-81 (2)
a For a 1:5 molar ratio of [PBD]/[DNA], where CT-DNA concentra-
tion = 100 lM and ligand concentration = 20 lM in aqueous sodium
phosphate buffer [10 mM sodium phosphate + 1 mM EDTA,
pH = 7.00 0.01].
b For CT-DNA alone at pH 7.00 0.01, Tm = 69.2 °C 0.01 (mean
value from 10 separate determinations), all DTm values are 0.1–
0.2 °C.

A. Kamal et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2594–2598
2597
Figure 2. RED100-restriction endonuclease digestion assay for benzimidazole–PBD conjugates with CT-DNA inhibitory activity of 4b and 4c on the
cleavage of plasmid pBR322 by restriction endonuclease BamH1 (20 U in 2 lL) for 1 h at 37 °C. The cut (C) and uncut (UC) products were separated
by agarose gel electrophoresis and visualized by ethidium bromide staining under UV illumination. Lane 1, control pBR322; lane 2, complete digest
of pBR322 by BamH1.
col described in the previous study has been em-
ployed.32,34 The result of this experiment for a represen-
tative compound 4c suggested that there is inhibition of
BamH1 by this PBD hybrid. However, there is no inhi-
bition by compound 4b as shown in Figure 2. Similarly,
compounds 5a and 5b have not shown noticeable inhibi-
tion of BamH1.
spectrum of cell lines in nine panels, with GI50 values
less than 10 nM. Compound 4e also possess cytotoxic
potency against many cell lines with GI50 values ranging
from 0.24 to 15.50 lM (Table 2). The GI50 values of
compound 4e against leukaemia cancer CCRF-CEM
and RPMI-8226 cell lines are 0.24 and 0.31 lM, respec-
tively. The in vitro cytotoxicity (IC50) for the naturally
occurring DC-81 is 0.38 and 0.33 lM in L1210 and
PC6 cell lines, respectively.35
Compounds 4c and 4e have been evaluated in the 60 cell
line cancer screen of NCI. Especially compound 4c
shows significant in vitro cytotoxic potency in a wide
In conclusion, new benzimidazole linked–PBD conju-
gates have been synthesized that exhibit significant
DNA-binding ability. More importantly, compound 4c
exhibits potential in vitro cytotoxicity in a number of
cancer cell lines. This investigation further reveals the
significance of combining a non-covalent DNA-binding
component (benzimidazole core) to the covalent binding
PBD moiety. The detailed anticancer activity and molec-
ular modelling studies will be published in due course.
Table 2. In vitro cytotoxicity data for benzimidazole–PBD conjugates
(4c and 4e)
Panel/cell line
GI50 (lM)
4c 4e
Panel/cell line
GI50 (lM)
4c
4e
Leukemia
CCRF-CEM
HL-60(TB)
K-562
Melanoma
LOX IMVI
MALME-3M
M14
<0.01
<0.01
0.24
5.18
<0.01 0.78
0.01 1.74
<0.01 15.50
<0.01 1.35
0.02 1.47
Acknowledgments
MOLT-4
RPMI-8226
SR
<0.01
<0.01
<0.01
3.79
0.31
0.45
SK-MEL-2
SK-MEL-28
SK-MEL-5
UACC-257
UACC-62
<0.01 1.53
<0.01 1.09
<0.01 2.54
<0.01 1.57
We thank the National Cancer Institute (NCI), Mary-
land, for the primary anticancer assay in human cancer
cell lines. We are also grateful to CSIR, New Delhi, for
the award of research fellowships to P.P.K., K.S.,
B.N.S. and P.R.
Lung cancer
A549/ATCC
EKVX
<0.01
<0.01
<0.01
0.01
3.22
3.36 Ovarian Cancer
HOP-62
HOP-92
—
OVCAR-1
OVCAR-3
OVCAR-4
OVCAR-5
OVCAR-8
SK-OV-3
0.01 0.75
<0.01 1.72
<0.01 1.61
<0.01 3.27
<0.01 2.58
<0.01 3.32
1.33
2.13
2.05
2.70
1.55
NCI-H226
NCI-H23
NCI-H322M
NCI-H460
NCI-H522
Colon cancer
COLO 205
HCC-2998
HCT-116
HCT-15
<0.01
<0.01
0.03
References and notes
<0.01
<0.01
1. Denny, W. A.; Rewcastle, G. W.; Baguly, B. C. J. Med.
Chem. 1990, 33, 814.
2. Goker, H.; Kus, C.; Boykin, D. W.; Yildiz, S.; Altanlar,
N. Bioorg. Med. Chem. 2002, 10, 2589.
3. Seth, P. P.; Jefferson, E. A.; Risen, L. M.; Osgood, S. A.
Bioorg. Med. Chem. Lett. 2003, 13, 1669.
4. Nare, B.; Liu, Z.; Prichard, R. K.; George, E. Biochem.
Pharmacol. 1994, 48, 2215.
5. Mahaimeed, H. A. Int. Med. Res. 1997, 25, 175.
6. Marques, M. A.; Doss, R. M.; Foister, S.; Dervan, P. B.
J. Am. Chem. Soc. 2004, 126, 10339.
7. Viger, A.; Dervan, P. B. Bioorg. Med. Chem. 2006, 14,
8539.
8. Olenyuk, B. Z.; Zhang, G.; Klco, J. M.; Nickols, N. G.;
Kaelin, W. G., Jr.; Dervan, P. B. Proc. Natl. Acad. Sci.
U.S.A. 2004, 101, 16768.
9. Thurston, D. E. In Molecular Aspects of Anticancer Drug–
DNA Interactions; Neidle, S., Waring, M. J., Eds.; The
Macmillan Ltd.: London, 1993; Vol. 1, p 54.
1.04 Renal cancer
786-0
<0.01 1.71
<0.01 1.68
<0.01 2.81
<0.01 0.94
<0.01 1.34
<0.01 2.50
0.01 2.09
<0.01
—
1.07
2.08
1.75
3.19
1.97
1.92
1.84
A498
ACHN
<0.01
0.02
CAKI-1
RXF 393
SN 12C
TK-10
HT29
KM12
<0.01
<0.01
<0.01
SW-620
Breast cancer
MCF7
UO-31
0.10 1.23
Prostate cancer
DU-145
3.24 CNS cancer
<0.01
0.23
0.01
0.66
0.02 1.32
NCI/ADR-RES
MDA-MB-231
HS 578T
1.39
1.70
1.39
0.41
0.50
0.33
SF-268
SF-539
SNB-19
SNB-75
U251
<0.01 1.80
<0.01 1.72
<0.01 1.53
<0.01 1.22
<0.01 1.77
<0.01
<0.01
<0.01
<0.01
<0.01
MDA-MB-435
BT-549
T-47D
MDA-MB-468

2598
A. Kamal et al. / Bioorg. Med. Chem. Lett. 18 (2008) 2594–2598
10. Petrusek, R. L.; Uhlenhopp, E. L.; Duteau, N.; Hurley, L.
H. J. Biol. Chem. 1982, 257, 6207.
11. Hurley, L. H.; Reck, T.; Thurston, D. E.; Langley, D. R.;
Holden, K. G.; Hertzberg, R. P.; Hoover, J. R. E.;
Gallagher, G., Jr.; Faucette, L. F.; Mong, S. M.; Johnson,
R. K. Chem. Res. Toxicol. 1988, 1, 258.
Compound (4b): 1H NMR (CDCl3): d 7.77 (d, J = 7.5 Hz,
1H), 7.62–7.69 (d, J = 3.7 Hz, 1H), 7.57 (s, 1H), 7.44–7.55
(m, 2H), 7.10–7.33 (m, 4H), 6.50 (s, 1H), 5.00–5.52 (m, 1H),
4.76 (t, J = 5.0 Hz, 1H), 4.65 (t, J = 6.7 Hz, 1H), 4.10–4.19
(m, 2H), 3.92 (s, 3H), 3.45–3.87 (m, 2H), 2.30–2.39 (m, 2H),
1.85–2.20 (m, 6H); ESIMS: m/z 485 (M+).
12. Kaneko, T.; Wong, H.; Doyle, T. W.; Rose, W. C.;
Bradner, W. T. J. Med. Chem. 1985, 28, 388.
13. Jones, G. B.; Davey, C. L.; Jenkins, T. C.; Kamal, A.;
Kneale, G. G.; Neidle, S.; Webster, G. D.; Thurston, D. E.
Anti-Cancer Drug Des. 1990, 5, 249.
14. Antonow, D.; Jenkins, T. C.; Howard, P. W.; Thurston,
D. E. Bioorg. Med. Chem. 2007, 15, 3041.
15. Thurston, D. E.; Morris, S. J.; Hartley, J. A. Chem.
Commun. 1996, 563.
16. Wilson, S. C.; Howard, P. W.; Forrow, S. M.; Hartley, J.
A.; Adams, L. J.; Jenkins, T. C.; Kelland, L. R.; Thurston,
D. E. J. Med. Chem. 1999, 42, 4028.
17. Reddy, B. S. P.; Damayanthi, Y.; Reddy, B. S. N.; Lown,
W. J. Anti-Cancer Drug Des. 2000, 15, 225.
18. Wang, J. J.; Shen, Y. K.; Hu, W. P.; Hsieh, M. C.; Lin, F.
L.; Hsu, M. K.; Hsu, M. H. J. Med. Chem. 2006, 49, 1442.
19. Kamal, A.; Ramulu, P.; Srinivas, O.; Ramesh, G. Bioorg.
Med. Chem. Lett. 2003, 13, 3517.
20. Kamal, A.; Srinivas, O.; Ramulu, P.; Ramesh, G.; Kumar,
P. P. Bioorg. Med. Chem. Lett. 2004, 14, 4107.
21. Kamal, A.; Srinivas, O.; Ramulu, P.; Ramesh, G.; Kumar,
P. P. Bioorg. Med. Chem. Lett. 2003, 13, 3577.
22. Kamal, A.; Rao, M. V.; Laxman, N.; Ramesh, G.; Reddy,
G. S. K. Curr. Med. Chem. Anti-Cancer Agents 2002, 2,
215.
Compound (4c): 1H NMR (CDCl3): d 7.79 (d, J = 7.5 Hz,
1H), 7.63–7.68 (d, J = 3.7 Hz, 1H), 7.57 (s, 1H), 7.45–7.55
(m, 2H), 7.10–7.35 (m, 4H), 6.5 (s, 1H), 5.00–5.52 (m, 1H),
4.78 (t, J = 5.0 Hz), 4.67 (t, J = 6.7 Hz, 2H), 4.10–4.20 (m,
2H), 3.90 (s, 3H), 3.50–3.70 (m, 2H), 2.40–2.55 (m, 2H),
2.20–2.35 (m, 2H), 1.56–2.40 (m, 6H); ESIMS: m/z 499
(M+).
1
Compound (4d): H NMR (CDCl3): d 7.77–7.84 (m, 1H),
7.67 (d, J = 4.5 Hz, 1H), 7.56 (s, 1H), 7.48 (d, J = 4.53 Hz,
1H), 7.45 (d, J = 2.26 Hz,1H), 7.23–7.36 (m, 1H), 7.11–7.16
(m, 2H), 6.71 (s, 1H), 5.08–5.12 (m, 1H), 4.69 (t,
J = 7.45 Hz, 2H), 4.04–4.18 (m, 1H), 3.99 (s, 3H), 3.78–
3.92 (m, 1H), 3.50–3.75 (m, 2H), 2.25–2.50 (m, 4H), 2.00–
2.15 (m, 2H); ESIMS: m/z 487 (M++1).
1
Compound (4e): H NMR (CDCl3): d 7.75–7.85 (m, 1H),
7.69 (d, J = 4.5 Hz, 1H), 7.54 (s, 1H), 7.50 (d, J = 4.5 Hz,
1H), 7.40–7.47 (m, 1H), 7.26–7.34 (m, 3H), 7.07–7.16 (dd,
J = 3.7, J = 5.2 Hz, 1H), 6.80 (s, 1H), 4.94–5.04 (m, 1H),
4.53 (t, J = 7.5 Hz, 2H), 4.00–4.25 (m, 2H), 3.92 (s, 3H),
3.45–3.89 (m, 2H), 2.30–2.40 (m, 2H), 1.85–2.19 (m, 6H);
ESIMS: m/z 501 (M+).
Compound (4f): 1H NMR (CDCl3): d 7.72–7.80 (dd,
J = 1.7, J = 6.0 Hz, 1H), 7.62–7.65 (m, 1H), 7.52 (s, 1H),
7.45 (d, J = 4.3 Hz, 1H), 7.32–7.41 (m, 1H), 7.20–7.30 (m,
2H), 7.08–7.18 (m, 1H), 6.6 (s, 1H), 4.84 (d, J = 4.3 Hz, 1H),
4.64–4.76 (m, 3H), 4.05–4.15 (t, J = 4.3 Hz, 2H), 4.00 (s,
3H), 3.50–3.70 (m, 2H), 2.40–2.55 (m, 2H), 2.20–2.35 (m,
2H), 1.56–2.40 (m, 6H); ESIMS: m/z 516 (M++1).
23. Kamal, A.; Reddy, G. S. K.; Reddy, K. L.; Raghavan, S.
Tetrahedron Lett. 2002, 43, 2103.
24. Kamal, A.; Reddy, P. S. M. M.; Reddy, R. Tetrahedron
Lett. 2002, 43, 6629.
1
Compound (5a): H NMR(CDCl3) d 8.9 (s, 1H), 7.74 (d,
25. Kamal, A.; Ramulu, P.; Srinivas, O.; Ramesh, G.; Kumar,
P. P. US Patent No: 6, 951,853 March 10, 05; Bioorg. Med.
Chem. Lett. 2004, 14, 4791.
26. PCT & US Patent Appl. Filed.
27. Thurston, D. E.; Murthy, V. S.; Langley, D. R.; Jones, G.
B. Synthesis 1990, 81.
28. Brthini, Y.; Lown, J. W. Synth. Commun. 1990, 20, 955.
29. Kamal, A.; Laxman, N.; Ramesh, G.; Neelima, K.;
Kondapi, A. K. Chem. Commun. 2001, 437.
30. Kamal, A.; Ramesh, G.; Laxman, N.; Ramulu, P.;
Srinivas, O.; Neelima, K.; Kondapi, A. K.; Srinu, V. B.;
Nagarajaram, H. M. J. Med. Chem. 2002, 45, 4679.
31. Spectral data for compound (4a): 1H NMR (CDCl3): d
7.82 (d, J = 7.8 Hz, 1H), 7.67 (s, 2H), 7.55 (s, 1H), 7.42–
7.52 (m, 3H), 7.07–7.19 (m, 2H), 6.72 (s, 1H), 5.06–5.18
(m, 1H), 4.58–4.76 (m, 2H), 4.05–4.15 (m, 1H), 4.00 (s,
3H), 3.78–3.90 (m, 1H), 3.65–3.75 (m, 1H), 3.45–3.65 (m,
1H), 2.38–2.49 (m, 1H), 2.25–2.36 (m, 1H), 1.95–2.15 (m,
4H); ESIMS: m/z 471 (M++1).
J = 6.79 Hz, 1H), 7.55–7.40 (m, 2H), 7.37 (s, 1H), 7.36–7.16
(m, 3H), 7.15–7.08 (q, 1H), 6.32 (s, 1H), 4.40 (t, J = 7.5 Hz,
2H), 4.00 (d, J = 5.2 Hz, 1H), 3.7 (s, 3H), 3.6–3.48 (m, 2H),
2.7–2.67 (m, 2H), 2.20–2.00 (m, 4H), 1.84–1.64 (m, 2H),
1.60–1.48 (m, 2H), 1.20–1.36 (m, 2H); MS (ESI) 487 [M]+.
Compound (5b): 1H NMR (CDCl3) d 8.25 (s, 1H), 7.77 (d,
J = 8.08 Hz, 1H), 7.40–7.56 (m, 3H), 7.17–7.30 (m, 3H),
6.57 (d, J = 2.20 Hz, 1H), 6.22 (s, 1H), 4.75 (t, J = 6.5 Hz,
2H), 3.81–4.11 (m, 6H), 3.52–3.83 (m, 2H), 2.42 (m, 2H),
1.96–2.12 (m, 4H); MS (ESI) 531 [M]+.
32. Puvvada, M. S.; Hartley, J. A.; Jenkins, T. C.; Thurston,
D. E. Nucleic Acids Res. 1993, 21, 3671.
33. Kamal, A.; Reddy, D. R.; Reddy, P. S. M. M.; Rajender
Bioorg. Med. Chem. Lett. 2004, 16, 1160.
34. Kamal, A.; Srinivas, O.; Ramulu, P.; Ramesh, G.; Kumar,
P. P.; Kumar, M. S. Bioorg. Med. Chem. 2004, 12, 4337.
35. Bose, D. S.; Thompson, A. S.; Smellie, M.; Berardini, M.
D.; Hartley, J. A.; Jenkins, T. C.; Neidle, S.; Thurston, D.
E. J. Chem. Soc., Chem. Commun. 1992, 1518.