methyl 5-amino-4-oxopentanoate methyl 5-amino-4-oxo-pentanoate 5-Amino-4-oxopentanoic acid methyl ester 5-amino-4-keto-valeric acid methyl ester 33320-16-0 Pentanoic acid, 5-amino-4-oxo-, methyl ester Aminolevulinic acid methyl ester Levulinic acid, 5-amino-, methyl ester Metvix