In a screening programme directed towards the discovery of drugs that could enhance sexual activity, we found that a decoction of the root bark of Neobeguea mahafalensis displayed an extraordinarily high potency and remarkably long duration in augmenting sexual activity in male rodents. Bioassay-guided fractionation led to the isolation of two pharmacoactive constituents, which turned out to be novel 1,8,9-orthoacetate phragmalin limonoids that we named libiguins A and B, each with a C-16/30 δ-lactone ring. Chemical structures were established by the interpretation of their 1D and 2D NMR data. In vivo pharmacological tests showed that starting with a treatment from 0.004-0.4 mg/kg/day for three consecutive days, over a 3-h sampling period, these limonoids induced a long-lasting augmentation of frequency and sustainment of mounting behaviour in male rodents, with an effect lasting for up to 11 days post-treatment. Libiguin A proved to be markedly more potent than libiguin B. This report is the first of limonoids having such an effect, and the findings could lead to novel therapies for the treatment of sexual dysfunction. Moreover, the results can serve as an opening to elucidate the central physiological control of mating behaviour, which is still not well mapped out.
Georg Thieme Verlag KG Stuttgart · New York.