Total syntheses of (+)-1893B and its three diastereomers and evaluation of their biological activities.

The total syntheses of natural (+)-1893B (2) and three other diastereomers 14, 18, and 21 were accomplished. Starting from the sequential metathesis product 5 prepared in turn from a 7-oxanorbornene derivative (+)-4, 2 was synthesized by means of an epoxy-ring opening of 9a with trimethylsilylacetylide followed by Wacker-type oxidation of the resulting alkyne 10 for the construction of the gamma-lactone moiety. By applying the same synthetic sequence, three additional diastereomers of 2, 14, 18, and 21 were also synthesized. The biological activities of previously synthesized 1893A (1), 1893B (2), and the diastereomers of 1893B 14, 18, and 21 were investigated.