Tigliane-Type Diterpene Esters from the Fruits of Shirakiopsis indica and Their Anti-HIV Activity

Four new diterpene esters, shirakindicans A-D (1-4), along with eight related known diterpene esters (5-12), were isolated from the fruits of the Bangladeshi medicinal plant Shirakiopsis indica. The structures of 1-4 were elucidated by spectroscopic data analysis and electronic circular dichroism (ECD) calculations. Shirakindican A (1) was assigned as a tigliane-type diterpene ester possessing an unusual 6β-hydroxy-1,7-dien-3-one structure, while shirakindican B (2) exhibits a tiglia-1,5-dien-3,7-dione structure. The anti-HIV activities of the isolated diterpene esters were evaluated and showed significant activities for sapintoxins A (5) and D (11), with EC₅₀ values of 0.0074 and 0.044 μM, respectively, and TI values of 1 100 and 5 290. Sapatoxin A (12) also exhibited anti-HIV activity with an EC₅₀ value of 0.13 μM and a TI value of 161.