Catalytic reduction of enteromycin methyl ester afforded demethoxyenteromycin methyl ester. Since demethoxyenteromycin amide was presumed to be 3-amino-N-(hydroxyiminoacetyl)-β-alanine, while enteromycin amide was considered to be N-(hydroxyamidinocarbonyl)-3-aminoacrylic acid, the two presumptive formulas, I–i and I–ii, were proposed for enteromycin. As the amido compound prepared by amidation of synthetic ethyl O-methyl-aci-nitroacetate was assumed to have the structure of hydroxyamido carbonyl amide (oxamide monoxime) and as enteromycin was deme-thoxylated by heating under evolution of formaldehyde, the formula I–i was found to be preferential, considering together other properties of the compound, and therefore the plane structure of enteromycin was established to be N-(O-methyl-aci-nitroacetyl)-3-aminoacrylic acid. The steric configuration of the 3-amino acrylic acid seems to be trans and that of the O-methyl cis-nitroacetyl group (the configuration of the hydrogen attached to the α-carbon atom and of the coordinating oxygen) to be syn.
催化还原肠霉素甲酯可得到去甲氧基肠霉素甲酯。由于去甲氧基肠霉素酰胺被推定为 3-
氨基-N-(羟基亚
氨基乙酰基)-
β-丙氨酸,而肠霉素酰胺被认为是 N-(羟基
氨基羰基)-3-
氨基
丙烯酸,因此提出了肠霉素的两个推定式 I-i 和 I-ii。由于通过合成 O-甲基-aci-
硝基乙酸乙酯的酰胺化反应制备的
氨基化合物被认为具有羟酰胺基羰基酰胺(氧酰胺一
肟)的结构,而且肠霉素是在
甲醛挥发的情况下通过加热进行去甲氧基化的,因此综合考虑化合物的其他性质,发现式 I-i 更优,因此确定肠霉素的平面结构为 N-(O-甲基-aci-硝基乙酰基)-3-
氨基
丙烯酸。3-
氨基
丙烯酸的立体构型似乎是反式,而 O-甲基顺式硝基乙酰基的立体构型(连接到 α 碳原子上的氢的构型和配位氧的构型)似乎是合式。