<unk>  is a non-proteinogenic amino acid structurally related to<unk> , with an<unk> yl group in place of the methyl group.<unk>  is an antimetabolite and<unk>  antagonist. It prevents amino acid incorporation into proteins and interferes with cellular use of adenosine triphosphate (ATP).  Because of these pharmacological effects,<unk>  is highly toxic and is a potent carcinogen.
Ethionine
Acetylleucine
Cysteamine 
Sardine
Arginine
Phenylalanine
Bromisoval
Fructosamine