Two minor diterpene glycosides and an eudesman sesquiterpene from Coleus forskohlii

Two new labdane diterpene glycosides, forskoditerpenosides A, B (1, 2) and a new eudesmane sesquiterpene, 4beta,7beta,11-enantioeudesmantriol (3), were isolated from the ethanol extract of the whole plant of Coleus forskohlii. Their structures and stereochemistry were elucidated by extensive spectroscopic analysis and chemical methods. The structure of compound 3 was confirmed by X-ray diffraction. This is the first report about the occurrence of glycosides derived from the kind of labdane diterpene, 8,13-epoxy-labd-14-en-11-one, in the nature. Compounds 1 and 2 showed relaxative effects on isolated guinea pig tracheal spirals in vitro.