New natural products and other constituents of sphaerocoryne gracilis.

This thesis reports on phytochemical investigations of the root and stem barks of Sphaerocoryrce gracilis ssp. gracilis Scheff. ex Ridley (formerly called Melodorum gracile Lour). Three hitherto unreported polyhydroxybenzyl flavanones which were named gracinol, isogracinol and hydroxygracinol, were isolated from the stem bark, together with the heptanolides [S-(Z]-5-(2,3-dihydroxypropylidene)-2(5H)-furanone which was previously obtained as an intermediate in the synthesis of (S)-(+)-acetylmelodorinol, and (S)-(+)-acetylmelodorinol which was previously isolated from Sphaerocoryne fruticosum, the catechinoids cinchonain la and cinchonain lb, dichamanetin and polycarpol. Both gracinol and isogracinol have the molecular skeleton of dichamanetin; however, unlike in dichamanetin, C-3" in gracinol is substituted by a 2,3dihydroxybenzyl group while in isogracinol the latter group is at C-5". In hydroxygracinol both C-3" and C-5" have 2,3-dihydroxybenzyl substituents. The catechinoids obtained in the investigations reported in this thesis are not commonly encountered natural products. So far these diastereomeric compounds have been isolated only from the bark of Cinchona succiruba (Rubiaceae) and dried twigs of Phyllocladus trichomanoides (Podacarpaceae). The root bark of S. gracilis ssp. gracilis yielded the new benzopyranyl sesquiterpenoic acid which has been named gracilenic acid. Unlike benzopyranyl sesquiterpenoids which so far have been isolated from plants of the genus Uvaria, gracilenic acid consists of a bisabolane skeleton, which is joined to the benzopyranyl unit through a spiro linkage and one of the side chain methyl groups having been oxidised to the carboxylic acid function. The root bark also yielded (S-(+)-acetylmelodorinol. Other compounds which were isolated from the root bark included dichamanetin, uvarinol, isouvarinol and polycarpol, all of which were previously isolated from some other plants of the family Annonaceae.