Molecular models and chemical equation showing the Strecker synthesis of the amino acid alanine. This is a two-step procedure that enables a wide variety of amino acids to be synthesised from aldehydes or ketones. Here acetaldehyde reacts with ammonia to form an imine that has hydrogen cyanide added to form the aminonitrile aminopropionitrile. This is then hydrolysed by aqueous acid to form alanine. Amino acids are the building blocks of proteins.