Monatsh Chem 139, 1091–1093 (2008)
DOI 10.1007/s00706-008-0903-7
Printed in The Netherlands
Synthesis of rimonabant regioisomer
Kotagiri Vijay Kumar1, Jambula mukunda Reddy1, Sashi Kanth Suthrapu1, Chitneni Prasad Rao2,
P. Pratap Reddy1, Apurba Bhattacharya1, Rakeshwar Bandichhor1
1
Innovation Plaza, IPD, R&D, Dr. Reddy’s Laboratories Ltd., Bachupally, Qutubullapur, A.P., India
2
Department of Chemistry, Osmania University, Hyderabad, A.P., India
Received 23 November 2007; Accepted 16 January 2008; Published online 21 April 2008
# Springer-Verlag 2008
Abstract A novel synthesis route for a rimonabant
regioisomer was developed.
impurities. Despite the synthesis of the desired one,
our affair also involves identifying and characterizing
impurities by means of spectroscopy and other tech-
niques. Since they are present only in traces, the
spectroscopic characterization and documentation are
practically impossible that enforces us to design
route(s) for their synthesis if they are of organic origin.
Keywords Rimonabant; Anti-obesity; Regioisomer.
Introduction
Impurities’ profiling of active pharmaceutical ingre-
dients (APIs) imposes a great challenge in pharma-
ceutical industries and a renaissance for the same is
now seen as an indispensable aspect of drugs and
their process development for the following reasons:
i) to assure that the elicited pharmacological or tox-
icological effects are only due to the API and not due
to impurities, ii) also to ensure that in the due course
of the product formulation and marketing the im-
purities should not be generated or elevated, and
iii) impurities can not be considered always to be
inferior, it may have better pharmacological and in-
ferior toxicological properties [1].
Results and discussion
Synthesis of 1 and their analogs are extensively ex-
plored [2–6]. The only synthesis of regioisomer 2
(Fig. 1) in trace amount (as an impurity) is given in
Ref. [7]. Herein, we report a novel synthesis of 2 in
moderate yield.
As presented in Scheme 1, we were able to
accomplish the synthesis of 2 in three steps. Pre-
paration of the ethyl 4-(4-chlorophenyl)-3-methyl-
2,4-dioxobutanoate (4) was achieved by reacting
When it comes to profiling of impurities generated
from chemistry involved in the synthesis it becomes
more stringent and demanding. In general, during the
synthesis of desired species, traces of certain unde-
sired byproducts used to be observed that we refer
Correspondence: Rakeshwar Bandichhor, Innovation Plaza,
IPD, R&D, Dr. Reddy’s Laboratories Ltd., Survey Nos. 42,
45, 46& 54, Bachupally, Qutubullapur, R. R. Dist. 500073, A.P.,
India. E-mail: rakeshwarb@drreddys.com; Chitneni Prasad
Rao, DepartmentofChemistry, OsmaniaUniversity, Hyderabad
5000007, A.P., India. E-mail: prasadraoch@yahoo.com
Fig. 1 Rimonabant (1) and its regioisomer 2