Phytochemical studies of the bark and leaves of Croton palanostigma Klotzsch (Euphorbiaceae) led to the isolation of a new clerodane diterpene, 8-epicordatin (2), in addition to 12-oxohardwickiic acid methyl ester (3), aparisthman, cordatin (1), ent-trachyloban-18-oic acid, ent-13-epimanoyl oxide, ent-3-oxo-13-epimanoyl oxide, ent-3β-hydroxy-13-epimanoyl oxide, sitosterol, stigmasterol, stigmastan-3-one, 6β-hydroxystigmast-4-en-3-one, 6β-hydroxystigmasta-4,22-dien-3-one, stigmast-4-en-3-one, stigmasta-4,22-dien-3-one, 3-O-acetylaleuritolic acid, 11α-hydroxyurs-12-en-3-one, α-amyrenone, 24-methylenecycloartenone and lupenone. These compounds were isolated using typical phytochemical procedures and the structures were deduced from spectroscopic studies, including 2D NMR experiments. In addition, the crystalline structure of 8-epicordatin (2) was determined by X-ray diffraction. NMR theoretical calculations at the B3PW91/DGDZVP level were used to confirm the assignment of the chemical shifts of the H-7α and H-7β hydrogens of 8-epicordatin.
|
