A. Kamal et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3955–3958
3957
Scheme 3. (i) TEA, MsCl, CH2Cl2, 5 h, 0 ꢀC, 78%; (ii) SnCl2–2H2O, MeOH, 2 h, reflux, 68%; (iii) NaN3, DMF, 16 h, 60 ꢀC, 76%; (iv) TPP, THF–
H2O, 8 h, rt, 72%; (v) HOBt, EDCl, compound 5, CH2Cl2–H2O, 8 h, rt, 63–65%; (vi) SnCl2–2H2O, MeOH, 2 h, reflux, 68–73%; (vii) HgCl2, CaCO3,
CH3CN–H2O, 12 h, 51–55%.
Compounds 1a–c and 2a–b have been evaluated for the
primary anticancer activity in the standard three-cell
line panel comprising of the MCF7 (breast), NCI-H460
(lung) and SF-268 (CNS), and none of these compounds
showed significant cytotoxicity. The DNA binding abil-
ity for these novel A-C8/C-C2 alkoxyamido-linked PBD
dimers has been examined by thermal denaturation
studies using calf thymus (CT) DNA. Melting studies
show (Table 1) that these compounds stabilize the ther-
mal helix ! coil or melting stabilization (ÁTm) for the
CT–DNA duplex at pH 7.0, incubated at 37 ꢀC, where
PBD/DNA molar ratio is 1:5. The compounds 1a–c
exhibited a large value of ÁTm particularly after 18 h
incubation in comparison to DC-81 and for compounds
2a–c these values are insignificant.
DNA binding ability. On the contrary, the imine-amide
dimers (2a–c) have not exhibited any significant DNA
binding ability. Unlike for the previously reported PBD-
dimers a correlation between the DNA-binding affinity
and cytotoxictiy could not be derived in this class of
head to tail PBD dimers. Therefore, preparation of
structurally modified analogues of such dimers particu-
larly by incorporating exo- and endo-unsaturation at C2
and variation of linker length could probably address
the factors responsible for the insignificant cytotoxicity
of such efficient DNA-binding PBD dimers. The
detailed cross-linking ability, anticancer activity and
molecular modelling studies for these compounds is in
progress and will be published in due course.
It is observed from this preliminary data that imine-
imine PBD dimers (1a–c) have interesting profile of
Acknowledgements
We thank the National Cancer Institute, Maryland 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.R., O.S. and G.R.
Table 1. Thermal denaturation data for A-C8/C-C2 alkoxyamido-
linked PBD dimers with CT–DNA
PBD
dimers
[PBD]/[DNA]
molar ratiob
ÁTm (ꢀC)a after
incubation at 37 ꢀC for
References and Notes
0 h
18 h
1a
1b
1c
DC-81
DSB-120
1:5
1:5
1:5
1:5
1:5
0.9
3.7
6.1
0.3
4.7
9.3
10.9
0.7
1. Rajski, S. R.; Williams, R. M. Chem. Rev. 1998, 98, 2723.
2. (a) Gregson, S. J.; Howard, P. W.; Hartley, J. A.; Brooks,
N. A.; Adams, L. J.; Jenkins, T. C.; Kelland, L. R.; Thurston,
D. E. J. Med. Chem. 2001, 44, 737. (b) Gregson, S. J.;
Howard, P. W.; Corcoran, K. E.; Jenkins, T. C.; Kelland,
L. R.; Thurston, D. E. Bioorg. Med. Chem. Lett. 2001, 11,
2859.
10.2
15.1
aFor CT–DNA alone at pH 7.00ꢁ0.01, Tm=69.2 ꢀCꢁ0.01 (mean
value from 10 separate determinations), all ÁTm values are ꢁ0.1–
0.2 ꢀC.
bFor a 1:5 molar ratio of [PBD]/[DNA], where CT–DNA con-
centration=100 mM and ligand concentration=20 mM in aqueous
sodium phosphate buffer [10 mM sodium phosphate+1 mM EDTA,
pH 7.00ꢁ0.01].
3. (a) Farmer, J. D.; Rudnicki, S. M.; Suggs, J. W. Tetra-
hedron Lett. 1988, 29, 5105. (b) Farmer, J. D.; Gustafson,
G. R.; Conti, A.; Zimmt, M. B.; Suggs, J. W. Nucleic Acids
Res. 1991, 19, 899. (c) Bose, D. S.; Thompson, A. S.; Ching,