Abstract
The method of solid phase synthesis was applied to the preparation of isariin (Ia), a β-hydroxydodecanoic acid-containing cyclodepsipeptide metabolite of Isaria cretacea, and its isomer (Ib). The open-chain depsipeptide, H-Val-D-Leu-Ala-Val-DL-Hyd-Gly-OH, was synthesized by coupling successively BOC-Val-DL-Hyd-OH, alanine, and Z-Val-D-Leu-OH to resin-bound glycine using dicyclohexylcarbodiimide (DCC) or DCC+hydroxysuccinimide (HOSu) as coupling agent. After cleavage from the resin the depsipeptide was cyclized by means of DCC+HOSu. The cyclization product was successfully resolved, after chromatographic purification on Dowex 50×4 and Sephadex LH-20 column, by preparative thin-layer chromatography on silica gel to afford Ia and Ib in moderate yields.
