Synthesis of enantiomerically pure amino acids containing 2,5-disubstituted THF rings in the molecular backbone

N- and C-protected derivatives of 2,5-disubstituted trans-and cis-THF amino acids 6 and 7 were prepared in enantiomerically pure form from L-alanine. Felkin-Anh-controlled reduction of the ketone 9 was achieved with a 85:15 d iastereoselectivity. Epoxidation of 10 and subsequent intramolecular epoxid e opening gave the trans- and cis-THF alcohols 11 and 12, which were furthe r transformed into the corresponding N- and C-protected 2,5-disubstituted t rans- and cis-THF amino acids. Conformational studies show that the cis-THF diamide 34 is a beta-turn mimetic in the solid state and in CDCl3 solution .