Methyl 2-acetamido-2-deoxy-β-D-glucopyranoside dihydrate and methyl 2-formamido-2-deoxy-β-D-glucopyranoside

Abstract

Methyl 2-acetamido-2-deoxy-β-D-glucopyranoside (β-GlcNAcOCH(3)), (I), crystallizes from water as a dihydrate, C(9)H(17)NO(6)·H(2)O, containing two independent molecules [denoted (IA) and (IB)] in the asymmetric unit, whereas the crystal structure of methyl 2-formamido-2-deoxy-β-D-glucopyranoside (β-GlcNFmOCH(3)), (II), C(8)H(15)NO(6), also obtained from water, is devoid of solvent water molecules. The two molecules of (I) assume distorted (4)C(1) chair conformations. Values of φ for (IA) and (IB) indicate ring distortions towards B(C2,C5) and (C3,O5)B, respectively. By comparison, (II) shows considerably more ring distortion than molecules (IA) and (IB), despite the less bulky N-acyl side chain. Distortion towards B(C2,C5) was observed for (II), similar to the findings for (IA). The amide bond conformation in each of (IA), (IB) and (II) is trans, and the conformation about the C-N bond is anti (C-H is approximately anti to N-H), although the conformation about the latter bond within this group varies by ~16°. The conformation of the exocyclic hydroxymethyl group was found to be gt in each of (IA), (IB) and (II). Comparison of the X-ray structures of (I) and (II) with those of other GlcNAc mono- and disaccharides shows that GlcNAc aldohexopyranosyl rings can be distorted over a wide range of geometries in the solid state.