BIOLOGICALLY-ACTIVE CYCLOPROPANES AND CYCLOPROPENES

The variety of biological systems which are modulated by naturally occurring cyclopropanes has only been realized recently. They range from antibiotic, antiviral, antifungal and insecticidal activities, control of plant growth and fruit ripening, antimycotic, thyromimetic, hormonal, carcinogenic or antitumoral activities, enzyme and gluconeogenesis inhibitions, to neurochemical activity. Cyclopropanes are also major components of membranes, for instance in tuberculosis cells, and key intermediates in many biosynthetic processes. Many synthetic drugs include cyclopropanes in their structure and they are also widely used to probe the mechanisms of biological processes. Naturally occurring cyclopropenes are known to be potent enzyme inhibitors controlling key processes on the fatty acid desaturation cycle and, in one case, to be an antibacterial agent. Synthetic analogues similarly inhibit pheromone production in insects, and the production of bacterial membranes, and interfere with the behaviour of insects by blocking pheromone receptors. When they have been demonstrated, the mechanisms responsible for the specific bioactivity of these systems are also reviewed.