Synthesis of Chiral Methyl Cucurbate and Its Analogs

Abstract

Natural (+)-(1R, 2S, 3S)-methyl cucurbate (1b) and the (-)-δ-lactone of 3-epi-cucurbic acid (16) were synthesized from (+)-(1R, 6S, 7R)-bicyclo[4.3.0]non-3-en-7-ol (5). Asymmetric hydrolysis of the acetate (8) of (±)-5 with pancreatin gave optically pure the (+)-(7R)-alcohol (5) and (-)-(7S)-acetate (8). An ozonolysis product of (+)-5 was transformed to (-)-16 and (+)-(3S)-lb with inversion of the (7R)-hydroxyl group. Similarly, unnatural (-)-lb and (+)-16 were prepared from optically pure (-)-5. The growth inhibitory activities of these synthesized chiral compounds toward lettuce seedlings were examined.