Cucurbitacins fromCucurbita texana: Evidence for the role of isocucurbitacins

In addition to cucurbitacins E andI, cucurbitacins D,1, 3-epi-isocucurbitacin D,2, and B,3, were isolated from the fruits ofCucurbita texana and structurally identified by UV, IR,¹H NMR,¹³C NMR, and MS, and 2-O--glucopyranosylcucurbitacin I was identified. These compounds have not been reported previously as constituents of this species. The isolation of 3-epi-isocucurbitacin D2 together with normal cucurbitacins suggests that isocucurbitacins occur naturally. Evidence is also discussed that isocucurbitacins are biosynthesized one step ahead of normal cucurbitacin.     

Cucurbitacins of Cucumis prophetarum and Cucumis prophetarum

Cucurbitacin B, isocucurbitacin B, dihydrocucurbitacin B, cucurbitacin E, dihydrocucurbitacin E, isocucurbitacin D, dihydroisocucurbitacin D, cucurbitacin I, dihydrocucurbitacin I, cucurbitacin Q1, and dihydrocucurbitacin Q1 were identified for the first time as constituents of Cucumis prophetarum L.. Cucurbitacin B, cucurbitacin O, cucurbitacin P, cucurbitacin Q1, dihydrocucurbitacin Q1, isocucurbitacin E, and dihydroisocucurbitacin E also were identified as constituents of C. prophetarum Jusl. ssp. Dissectus. Isocucurbitacin E and dihydroisocucurbitacin E were isolated for the first time in nature. The chemical structures were determined with extensive spectroscopic analysis including 2D NMR, ¹H NMR, ¹³C NMR, correlated spectroscopy (COSY), heteronuclear chemical shift correlation (HETCOR), attached proton test (APT), and distortionless enhancement by polarization transfer (DEPT).