Cassane- and Norcassane-Type Diterpenes from Caesalpinia crista of Indonesia and Their Antimalarial Activity against the Growth of Plasmodium falciparum

Abstract

The CH₂Cl₂ extract of the seed kernels of Caesalpinia crista, which exhibited promising antimalarial activity against Plasmodium berghei-infected mice in vivo, was examined and resulted in the isolation of seven new furanocassane-type diterpenes [caesalpinins C−G (1−5) and norcaesalpinins D and E (6, 7)] together with norcaesalpinins A−C (8−10) and 11 known compounds (norcaesalpinins A−C, 2-acetoxy-3-deacetoxycaesaldekarin e, caesalmin B, caesaldekarin e, caesalpin F, 14(17)-dehydrocaesalpin F, 2-acetoxycaesaldekarin e, 7-acetoxybonducellpin C, and caesalmin G). Their structures were determined on the basis of spectroscopic analysis. The isolated diterpenes showed significant dose-dependent inhibitory effects on Plasmodium falciparum FCR-3/A2 growth in vitro. Their IC₅₀ values ranged from 90 nM to 6.5 μM, and norcaesalpinin E (7) showed the most potent inhibitory activity (IC₅₀, 90 nM).