β,γ-Alkynylα-amino acids: a synthetic challenge.

Ethynyl glycine is a naturally occurring unusualα-amino acid. Its known chemical and biological properties are summarized in the first part of this review. The second part is an overview on racemic syntheses of ethynyl glycine and otherβ,γ-alkynylα-amino acid derivatives, including patent data. These small polyfunctional compounds revealed as being very labile and the synthesis of mainly fully or partially protected forms seemed to have been actually performed. The last part deals with the approaches to the enantioselective synthesis ofβ,γ-alkynylα-amino acids derivatives, and details the only satisfactory strategy that has led to optically activeβ,γ-alkynylα-amino acids derivatives up to now.