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.