The conformation of <i>N</i>-acetyl-α-<scp>D</scp>-muramic acid and its relationship to penicillin

Abstract

N-Acetyl-~-D-muramic acid monohydrate, ClIH19NOa.H20, crystallizes in space group P212121 with a= 7.833 + 0005, b= 8084_+ 0.005, c= 23495_+ 0018/~ and Z=4. The structure was solved by direct methods and refined by least-squares calculations to R= 0.079 for 1060 observed reflections. The molecule has the 4C1 conformation with internal torsion angles ranging from 49 to 62 °. The C(1)-O(1)H bond (1.38_+ 0.01 A) is significantly shorter than the mean of four other single bonds. Ring C-O distances are 1-42 and 145 _+ 0-01 A for C(1)-O(5) and C(5)-O(5), respectively. An intramolecular hydrogen bond of 2.96/~ exists between the N-acetyl amide and the lactyl carbonyl. The resulting molecular conformation is unlike that proposed in earlier model studies which pointed to a similarity between penicillin and Nacetyl muramic acid as the basis for the activity of the antiboitic.