a series of analogues of pro-leu-gly-nh2 ( plg ) in which the leucine residue has been replaced with the aliphatic amino acids l-isoleucine , l-2-aminohexanoic acid ( ahx ) , l-2-aminopentanoic acid , and l-2-aminobutanoic acid and the aromatic amino acids l-phenylalanine , l-phenylglycine , l- and d-2-amino-4-phenylbutanoic acid , l-o-methyltyrosine , and l-4-nitrophenylalanine have been synthesized .
C0301713
aromatic
C0031453
phenylalanine