Chemistry of the genus Dorstenia

The genus Dorstenia contains many plants that are used as anti-snakebite, a nti-infection and anti-rheumatic remedies in the medicinal plant therapy of many countries in Africa, Central and South America. The genus is now reco gnized as a rich source of prenyl and geranyl-substituted coumarins, chalco nes, flavones and flavanones. The first examples of naturally occurring sty renes (2 and 3) were reported from D. barnimiana. The geranyl substituted f urocoumarin (5) has been found in many species. D. poinsettifolia furnished the unusual 4-phenyl substituted dihydrocoumarin, and the rare geranyl and prenyl substituted chalcone (17). Prenylated flavonoids have so far been r eported from African Dorstenia only. Compound 18 from D. proropens is the o nly example of a bis-geranylated chalcone in the literature. D. manni furni shed the novel chalcone (13), 6-prenylchrysoeriol (22 R = OMe), the geranyl derivative (43), eight diprenylated flavanones (28, 30-36) and one flavono l (29). These dorsmannins appear to be derived from 6,8-diprenyleriodictyol and a possible biosynthetic scheme for them is presented (Fig. 5). Compoun d 21 was reported from D. zenkeri and is believed to arise from 20. The lat ter is probably formed via an enzymatic Diels-Alder reaction of isobavachal cone (10) and its dehydroderivative (19). D. psilurus provided all the trip renylated compounds (37-42) found in Dorstenia and, of these, 42 is unique in having ring B of the flavonoid structure modified to a dienone. The phar macological data on this genus are scanty. Extracts of D. multiradiata show antileishmanial activity. Extracts and/or compounds from other species sho w anti-inflammatory, analgesic, anti-oxidant and cytotoxic activities.