Conformations and structure studies of sugar lactones. Part 111. The composition and conformation of d-mannurono-γ lactone in solution, and the structural analysis of its β anomer in the solid state

✍ Scribed by M.Ashraf Shalaby; Frank R. Fronczek; David Vargas; Ezzat S. Younathan

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 703 KB
• Volume: 265
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(94)00234-7

✦ Synopsis

Complete analyses of the proton and carbon chemical-shift assignments of D-mannurono-y-lactone (1) have been achieved by 1D and 2D NMR spectral measurements.

At equilibrium, the anomeric LY and p forms were present in the ratio of 34:66 in D,O and 72:28 in Me,SO-d,.

The solution data indicated that the dienvelope conformation 'E:E, to be the favored conformation of 1 in solution. The crystal structure of 1 was determined, and it showed that the crystalline form is the /3 anomer, a bicyclic structure, consisting of fused five-membered furanose and lactone rings, in agreement with an earlier deduction from chemical evidence. In contrast to the solution conformation, the furanose ring adopts a twist conformation lying between the $T and 'E conformations with phase angle (P) and pseudorotation amplitude (7,) of -44.23" and 37.9", respectively, whereas the lactone ring adopts an envelope E5 conformation slightly distorted towards 6T5 with a phase angle (P) of -22.3" and a pseudorotation amplitude (7,) of 18.4". The molecules are linked in the crystal through a hydrogen-bonding network that involves all hydroxyl groups as well as the ring oxygen atoms.