Cucurbitane-Type Triterpenoids from the Fruit of Momordica charantia

The structures of three new cucurbitane-type triterpenoids isolated from the methanol extract of the fruit of Japanese Momordica charantia were established as (19R,23E)-5β,19-epoxy-19-methoxycucurbita-6,23,25-trien-3β-ol (1), (23E)-3β-hydroxy-7β-methoxycucurbita-5,23,25-trien-19-al (2), and (23E)-3β-hydroxy-7β,25-dimethoxycucurbita-5,23-dien-19-al (3) on the basis of spectroscopic methods. These compounds were accompanied by the known (19R,23E)-5β,19-epoxy-19,25-dimethoxycucurbita-6,23-dien-3β-ol (4) and (19R,23E)-5β,19-epoxy-19-methoxycucurbita-6,23-diene-3β,25-diol (5). This is the first report of the isolation of tetracyclic triterpenoids possessing a Δ23,25-conjugated diene system, viz., 1 and 2, from a natural source.