Synthesis of C-8 methanesulphonate substituted pyrrolobenzodiazepines as potential antitumour agents

Article abstract of DOI:10.1016/S0960-894X(03)00738-8

The facile synthesis of C-8 methanesulphonate substituted pyrrolobenzodiazepines is described. These have been prepared by linking the methanesulphonate at C-8 position with alkanol spacer and their in vitro cytotoxicity have been described.

Full text of DOI:10.1016/S0960-894X(03)00738-8

Bioorganic & Medicinal Chemistry Letters 13 (2003) 3517–3519
Synthesis of C-8 Methanesulphonate Substituted
Pyrrolobenzodiazepines as Potential Antitumour Agents
Ahmed Kamal,* P. Ramulu, O. Srinivas and G. Ramesh
Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500007, India
Received 25 April 2003; accepted 10 July 2003
Abstract—The facile synthesis of C-8 methanesulphonate substituted pyrrolobenzodiazepines is described. These have been pre-
pared by linking the methanesulphonate at C-8 position with alkanol spacer and their in vitro cytotoxicity have been described.
# 2003 Elsevier Ltd. All rights reserved.
Pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are of con-
siderable current interest due to their ability to recog-
nize and subsequently form covalent bonds to specific
base sequences of double stranded DNA. Such agents
have potential therapeutic targets, in the therapy of genetic
based diseases (e.g., cancer) and validation of DNA
sequences.1À3 The pyrrolo[2,1-c][1,4]benzodiazepines
(PBDs) are a family of DNA interactive antitumour anti-
biotics derived from Streptomyces species that include
anthramycin, tomaymycin, sibiromycin and DC-81.4
A large number of PBD conjugates have been prepared
and evaluated for their biological activity, particularly
their antitumour potential.6 Thurston and co-workers
have synthesized novel PBD dimers as cross-linking
agents.7 Recently, we have designed and synthesized
non-cross-linking mixed imine-amide PBD dimers that
have significant DNA-binding ability and potent anti-
tumour activity.8 Alkanediol dimethanesulphonates of
general formula CH3SO2O(CH2)nOSO2CH3 constitute a
very interesting class of bifunctional chemotherapeutic
agents. Busulphan is one of these homologous series,
which is in the treatment of chronic myeloid leukemia
for last 30 years.9 Recently, two long-chain busulphan
analogues have been prepared to improve the drug
effectiveness.10
Furthermore, Indisulam and related sulphonamides
have shown interesting anticancer avtivity.11 Therefore,
it has been considered of interest to design and synthe-
size C8 linked alkanol methylsulphonate (alkylating
part of busulphan) PBD hybrids as cross-linking
bifunctional chemotherapeutic agents. We have been
engaged in the last few years in the structural modifi-
cations12 and the development of new synthetic strate-
gies13 for the PBD based ring systems. In continuation
of these efforts, we herein report the synthesis and anti-
cancer activity of PBD ring system linked to methane-
sulphonate with different alkanol spacers at C8
position.
The cytotoxicity and antitumour activity of these com-
pounds are attributed to their property by forming a
covalent bond between the C11 position of DNA and
the N2 amino group of a guanine base, and they usually
span approximately three base pairs with a preference of
Pu-G-Pu.5
The compounds (1a–b) were prepared from the (2S)-N-
(4-benzyloxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-
carboxaldehyde diethylthioacetal 2. This compound 2
has been prepared by literature method,14 which upon
*Corresponding author. Tel.: +91-40-2719-3157; fax: +91-40-2719-
3189; e-mail: ahmedkamal@iict.ap.nic.in
0960-894X/$ - see front matter # 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00738-8

3518
A. Kamal et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3517–3519
Scheme 1. (i) EtSH–BF3OEt2, CH2Cl2, 12 h, rt, 75%; (ii) bromoalkanol, K2CO3, DMF, 24 h, rt, 94–96%; (iii) CH3SO2Cl, Et3N, CH2Cl2, 8 h, 0 ꢀC,
.
90–91%; (iv) SnCl2 2H2O, MeOH, reflux, 4 h, 85–87%; (vi) HgCl2–CaCO3, CH3CN–H2O, 12 h, rt, 68–71%.
Table 1. In vitro cytotoxicity of compound 1a in selected cancer cell
lines
Cancer panel/cell line
GI50 (mM)
Cancer panel/cell line
GI50 (mM)
Leukemia
CCRF-CEM
SR
Renal
786-0
A498
ACHN
CAKI-1
TK-10
UO-31
14.5
11.1
12.2
17.0
17.1
16.0
17.7
18.1
15.2
RPMI-8226
Non-small cell lung
NCI-H226
NCI-H23
15.4
12.2
10.9
Breast
NCI/ADR-RES
MDA-MB-231/ATCC
NCI-H522
13.5
16.5
Colon
HCT-116
HCT-15
SW-620
18.5
16.5
14.6
debenzylation gives 3. Etherification of (2S)-N-(4-
hydroxy-5-methoxy-2-nitrobenzoyl)pyrrolidine-2-car-
boxaldehyde diethylthioacetal 3 by bromoalkanols pro-
vides 4a–b. Mesylation of these alcohols 4a–b gives the
desired precursors 5a–b. Further, these upon reduction
followed by deprotection of thioacetal group affords the
target compounds 1a–b15 (Scheme 1).
CNS
SF-539
U251
18.6
17.1
Melanoma
LOX EMVI
MALME-3M
M14
SK-MEL-5
UACC-257
UACC-62
15.7
13.6
18.7
16.9
18.2
19.4
Compounds 1a–b have been evaluated for cytotoxicity
activities against nine panels containing 60 human cell
lines. A 48 h continuous drug exposure protocol was
used and a sulfurhodamine B protein assay was used to
estimate cell viability or growth.
Ovarian
OVCAR-3
16.3

A. Kamal et al. / Bioorg. Med. Chem. Lett. 13 (2003) 3517–3519
3519
Compounds 1a–b possess cytotoxic potency against
many cell lines. Compound 1a (Table 1) exhibits a wide
spectrum of activity against 26 cell lines in eight cell
panels, with GI50 value of <20 mM. The average GI50
value of compound 1a against leukemia cancer CCRF-
CEM, RFMI-8226 and SR are 14.5, 12.2 and 11.1 mM,
respectively. In non-small cell lung cancer panel, the
growth of NCI-H226, NCI-H23 and NCI-H522 cell
lines are affected by compound 1a with an GI50 value as
15.4, 12.2 and 10.9 mM, respectively. The GI50 value of
colon cancer HCT-116, HCT-15 and SW-620 cell lines is
18.5, 16.5 and 14.6 mM respectively. In CNS cancer SF-
539 and U251 cell lines are affected with GI50 values are
18.6 and 17.1 mM. Most of the cell lines in melanoma
cell panel were affected by 1a at 13.6–19.4 mM con-
centrations. In the ovarian cancer panel the growth of the
OVCAR-3 cell line was affected by compound 1a with
GI50 value as 16.3 mM. The six cell lines in the renal can-
cer were affected by compound 1a with GI50 value at 15.2
to 18.1 mM concentrations. Compound 1a exhibits cyto-
toxic potency in breast cancer panel in which NCI/ADR-
RES and MDA-MB-231/ATCC cell lines were affected
with GI50 values of 13.5 and 16.5 mM, respectively.
4. Thurston, D. E. In Molecular Aspects of Anticancer Drug-
DNA Interactions; Macmillan: London, UK, 1993; Vol. 1,
p 54.
5. Kopka, M. L.; Goodsell, D. S.; Baikalov, I.; Grzeskowiak,
K.; Cascio, D.; Dickerson, R. E. Biochemistry 1994, 33, 13593.
6. (a) Thurston, D. E.; Morris, S. J.; Hartley, J. A. Chem.
Commun. 1996, 563. (b) Wilson, S. C.; Howard, P. W.; For-
row, S. M.; Hartley, J. A.; Adams, L. J.; Jenkins, T. C.; Kel-
land, L. R.; Thurston, D. E. J. Med. Chem. 1999, 42, 4028. (c)
Reddy, B. S. P.; Damayanthi, Y.; Reddy, B. S. N.; Lown, W.
J. Anti-Cancer Drug Design 2000, 15, 225. (d) Baraldi, P. G.;
Balboni, G.; Cacciari, B.; Guiotto, A.; Manfredini, S.;
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Med. Chem. 1999, 42, 5131.
7. (a) Thurston, D. E.; Bose, D. S.; Thompson, A. S.;
Howard, P. W.; Leoni, A.; Crocker, S. J.; Jenkins, T. C.; Nei-
dle, S.; Hartley, J. A.; Hurley, L. H. J. Org. Chem. 1996, 61,
8141. (b) 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. (c) Gregson,
S. J.; Howard, P. W.; Corcoran, K. E.; Jenkins, T. C.; Kel-
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11, 2859.
8. 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.
9. (a) Galton, D. A. G. Lancet 1953, 246, 208. (b) Champlin,
R. E. In Leukemia Therapy; Gale, R. P., Ed.; Blackwell Sci-
entific: Boston, 1986; p 147.
Compound 1b exhibits cytotoxic potency against leuke-
mia cancer cell lines CCRF–CEM and SR with the GI50
value of 52.8 and 62.9 mM, respectively, and its also
exhibits cytotoxicity against SNB-75 (CNS cancer) and
OVCAR-4 (ovarian cancer) cell lines with the GI50
value of 94.7 and 70.3 mM, respectively.
10. Kokotos, G.; Kokotou, V. C.; Padron, J. M.; Peters, G. J.
Bioorg. Med. Chem. Lett. 2001, 11, 861.
11. (a) Scozzafava, A.; Owa, T.; Mastrolorenzo, A.; Supuran,
C. T. Curr. Med. Chem. 2003, 10, 925. (b) Supuran, C. T.
Expert. Opin. Investig. Drugs 2003, 12, 283. (c) Casini, A.;
Scozzafava, A.; Mastrolorenzo, A.; Supuran, C. T. Curr.
Cancer Drug Targets 2002, 2, 55. (d) Supuran, C. T.; Briganti,
F.; Tilli, S.; Chegwidden, W. R.; Scozzafava, A. Bioorg. Med.
Chem. 2001, 9, 703.
In conclusion, new methanesulphonate–PBD hybrids
have been synthesized that exhibit cytotoxic activity in
some cancer cell lines. The detailed mechanistic studies
of these PBD hybrids are in progress.
12. (a) Kamal, A.; Laxman, N.; Ramesh, G.; Srinivas, O.;
Ramulu, P. Bioorg. Med. Chem. Lett. 2002, 12, 1917. (b)
Kamal, A.; Reddy, B. S. N.; Reddy, G. S. K.; Ramesh, G.
Bioorg. Med. Chem. Lett. 2002, 12, 1933.
Acknowledgements
We thank the National Cancer Institute, Maryland for
the in vitro anticancer assay in human cell lines. We are
also grateful to CSIR, New Delhi for the award of
research fellowships to P.R., O.S and G.R.
13. (a) Kamal, A.; Rao, M. V.; Laxman, N.; Ramesh, G.;
Reddy, G. S. K. Curr. Med. Chem. Anti-Cancer Agents 2002,
2, 215. (b) Kamal, A.; Reddy, G. S. K.; Reddy, K. L.;
Raghavan, S. Tetrahedron Lett. 2002, 43, 2103. (c) Kamal, A.;
Reddy, P. S. M. M.; Reddy, R. Tetrahedron Lett. 2002, 43,
6629.
14. Thurston, D. E.; Murty, V. S.; Langley, D. R.; Jones,
G. B. Synthesis 1990, 81, 10.
References and Notes
15. Selected data for compound 1a 1H NMR (CDCl3) d 1.80–
2.40 (m, 4H), 3.00 (s, 3H), 3.40–3.85 (m, 2H), 3.95 (s, 3H),
4.05–4.40 (m, 3H), 4.40–4.55 (m, 2H), 6.82 (s, 1H), 7.5 (s, 1H),
7.65 (d, 1H, J=4.4 Hz); MS (EI) m/z 368.
1. Hurley, L. H. J. Med. Chem. 1989, 32, 2027.
2. Dervan, P. B. Science 1989, 232, 464.
3. Thurston, D. E.; Thompson, A. S. Chem. Br. 1990, 26, 767.