Chemistry of the genus Dorstenia

The genus Dorstenia contains many plants that are used as anti-snakebite, anti-infection and anti-rheumatic remedies in the medicinal plant therapy of many countries in Africa, Central and South America. The genus is now recognized as a rich source of prenyl and geranyl-substituted coumarins, chalcones, flavones and flavanones. The first examples of naturally occurring styrenes (2 and 3) were reported from D. barnimiana. The geranyl substituted furocoumarin (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 reported from African Dorstenia only. Compound 18 from D. proropens is the only example of a bis-geranylated chalcone in the literature. D. manni furnished the novel chalcone (13), 6-prenylchrysoeriol (22 R = OMe), the geranyl derivative (43), eight diprenylated flavanones (28, 30-36) and one flavonol (29). These dorsmannins appear to be derived from 6,8-diprenyleriodictyol and a possible biosynthetic scheme for them is presented (Fig. 5). Compound 21 was reported from D. zenkeri and is believed to arise from 20. The latter is probably formed via an enzymatic Diels-Alder reaction of isobavachalcone (10) and its dehydroderivative (19). D. psilurus provided all the triprenylated 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 pharmacological data on this genus are scanty. Extracts of D. multiradiata show antileishmanial activity. Extracts and/or compounds from other species show anti-inflammatory, analgesic, anti-oxidant and cytotoxic activities.