Studies on the Constituents of Asclepiadaceae Plants. II. On the Struture of Cynanchogenin from Cynanchum caudatum Max.

Hydrogenation of cynanchogenin (I), m.p. 167°, C_<28>H_<42>O_6,gave a dihydro compound (II). Alkaline hydrolysis of (I) gave an unsaturated acid (VIII) and deacylcynanchogenin (VII), C_<21>H_<32>O_5. The same treatment of (II) gave (VII) and a saturated acid (IX). The satruated acid was proved to be 3,4-dimethylpentanoic acid by synthesis . By the permanganate oxidation, the unsaturated acid was shown to be 3,4-dimethyl-2-pentenoic acid. Deacylcynanchogenin has one ketone group, one double bond, and four hydroxyl groups, two of which easily undergo acetylation. Reduction of cynanchogenin with lithium aluminum hydride gave a polyol compound (XIV), which was also obtained by the reduction of deacylcynanchogenin with sodium borohydride.