Isolation and Structures of Three Seco-limonoids, Insect Antifeedants from Trichilia roka (Meliaceae)

Abstract

The stem bark of African medicinal plant TrichiZia roka has been found to contain a number of limonoids.Three of these has been isolated as insect antifeedant; They are all of the ring B-cleaved meliacan group and are closely related to known prieurianin.TrichiZio roka is a large tree found in drier part of East Africa.It has been 1used medicinally and a decoction of the bark is used as a purgative .We have already described the isolation of limonoids.trichilin A-F and 7-acetyltrichilin A 2, as insect antifeedant from the root bark .We now describe the isolation and structures of three prieurianin type limonoids from the stem bark.The group of 3 limonoid related to prieurianin , mainly found from T ~i c h i Z i a species, is rapidly growing and more than 20 are now known, in which hispidins from PrichiZio hispida 4 have been reported to have cytotoxic properties .The compounds from the stem bark of T. ~o k o also exhibited insect antifeedant activity against the larvae of the Japanese pest insect, "nekiri-mushi", Ajrotis sejetum Denis (200 ppm) with the leaf disk choice test.The stem bark (1.3 ~g]' was deffated with petroleum ether and extracted with ether to yield 5.2 g of an extract.An insoluble resin (1.1 g) of the extract in ether contained various congeners of limonoids.The isolation was a tedius process required very careful use of HPLC and pure compounds also showed 5-7 peaks on the CI8 reversed-phase column.Because of these chromatographic properties, it was expected that these compounds would belong to the ring B-cleaved meliacan group of limonoids.As is common with this type of extract, separation was a major problem