1	PGG	Para-nitrophenylphosphonobutanoyl-glycine	1.000
2	PDE	Para-nitrophenyl phosphonobutanoyl D-alanine	0.958
3	PNE	Para-nitrophenyl phosphonobutanoyl L-alanine	0.958
4	PNF	6-{4-[hydroxy-(4-nitro-phenoxy)-phosphoryl]-butyrylamino}-hexanoic acid	0.724