(D-Ala2,D-Leu5)enkephalin 2-Alanyl-leucine enkephalin 5-Leucine-2-alanine enkephalin 63631-40-3 D-Leucine, N-(N-(N-(N-L-tyrosyl-D-alanyl)glycyl)-L-phenylalanyl)- ENKEPHALIN, LEUCINE-2-ALANINE Enkephalin-leu,ala(2) Leucine enkephalin-2-alanine