beta,gamma-Alkynyl alpha-amino acids: A synthetic challenge

Ethynyl glycine is a naturally occurring unusual alpha-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 other beta,gamma-alkynyl alpha-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 of beta,gamma-alkynyl alpha-amino acids derivatives, and details the only satisfactory strategy that has led to optically active beta,gamma-alkynyl alpha-amino acids derivatives up to now.