PMID:
16503940 [PubMed - indexed for MEDLINE
Betulinic
acid derivatives as anticancer agents: structure activity relationship.
Medicinal Chemistry, Dabur Research
Foundation, 22 Site IV, Sahibabad, Ghaziabad 201010, UP, India .
Betulinic acid, a pentacyclic triterpene, is
widely distributed throughout the tropics. It possesses several biological
properties such as anticancer, anti-inflammatory, antiviral, antiseptic,
antimalarial, spermicidal, antimicrobial, antileshmanial, antihelmentic and
antifeedent activities. However, betulinic acid was highly regarded for its
anticancer and anti-HIV activities. Anticancer role of betulinic acid appeared
by inducing apoptosis in cells irrespective of their p53 status. Due to high
order safety in betulinic acid, a number of structural modifications carried
out to improve its potency and efficacy. The C-1, C-2, C-3, C-4, C-20 and C-28
positions are the diversity centers in betulinic acid, and the derivatives
resulted on various structural modifications at these positions screened for
their anticancer activity. This review presents the structure activity
relationship carried out on C-1, C-2, C-3, C-4, C-20, C-28, A-ring, D-ring and
E-ring modified betulinic acid derivatives. We have compiled the most active
betulinic acid derivatives along with their activity profile in each series.
Structure activity relationship studies revealed that C-28 carboxylic acid was
essential for the cytotoxicity. The halo substituent at C-2 position in betulinic
acid enhanced the cytotoxicity. Though the relation of the cytotoxicity with
the nature of substituents at C-3 position could not be generalized but the
ester functionality appeared to be a better substituent for enhancing the
cytotoxicity. An interesting observation is that the three rings skeleton (A, B
and C rings) had played an important role in eliciting anticancer activity,
which could be a new molecular skeleton to design new anticancer drugs.
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