Pyrrolizines: natural and synthetic derivatives with diverse biological activities

Abstract

The pyrrolizine nucleus is a bicyclic ring system that consists of a pyrrole ring fused to another pyrrolidin ring. It constitutes the basic skeleton in many natural and synthetic compounds with diverse biological activities such as the anti-inflammatory, nootropic, antiemetic, antibacterial, antiviral, anticonvulsant, antiarrhythmic, and anticancer activities. At least two of these derivatives, ketorolac and mitomycin C, have been approved for the treatment of inflammation and cancer, respectively. Licofelone, a dual inhibitor of COX and 5-LOX, was also evaluated in clinical trials for the treatment of osteoarthritis. On the other hand, a large number of the pyrrolizine-based derivatives have displayed anticancer activity against different types of cancer cells. In this review, the pyrrolizine-based derivatives with anticancer activity were classified based on their chemical structure into substituted, fused, and spiro-pyrrolizine. The mechanisms of action of these compounds included alkylation of the DNA, inhibition of COX, or alteration of the permeability of the cytoplasmic membrane in cancer cells. In addition, other pyrrolizines were found to act by inhibiting DNA replication, rRNA, Rac1 kinase, thioredoxin reductase, or oncogenic kinases. The last section of this review also focuses on the reported X-ray crystal structures of these compounds with different proteins. The binding modes and interactions of ketorolac and licofelone were illustrated in this review. To sum up, we anticipate that the data compiled in this review will be useful to researchers in the design of pyrrolizines with potent biological activities.