Synthesis of new Ca-tetrasubstituted a-amino acids

Abstract

Cα-Tetrasubstituted α-amino acids are important building blocks for the synthesis of peptidemimetics with stabilized secondary
structure, because of their ability to rigidify the peptide backbone. Recently our group reported a new class of cyclic Cα-tetrasubstituted
tetrahydrofuran α-amino acids prepared from methionine and aromatic aldehydes. We now report the extension of this methodology
to aliphatic aldehydes. Although such aldehydes are prone to give aldol products under the reaction conditions used, we
were able to obtain the target cyclic amino acids in low to moderate yields and in some cases with good diastereoselectivity.