cis-clerodane diterpene lactones from Amphiachyris dracunculoides

Four cis-ent-neoclerodane lactones, amphiacrolide A [2], amphiacrolide B [3], amphiacrolide C [4] and amphiacrolide D [5] were isolated from the aerial parts of Amphiachyris dracunculoides, and their structures established by physical and chemical methods. High field 1H- and 13C-nmr assignments were made for each compound and some of their derivatives by using one- and two-dimensional nmr techniques including nOe difference, COSY, and CH-correlation of one-bond and multiple bond (COLOC) relationships. A chemical correlation of the amphiacrolides to gutierolide [1], a compound with absolute stereochemistry determined by X-ray analysis, established the stereochemistry for the group. Consequently, a compound having reported properties identical with amphiacrolide D [5] must have its structure revised to contain the beta-faced epoxide. Amphiacrolide A [2] had not been reported previously.