CONFORMATIONS AND STRUCTURE STUDIES OF SUGAR LACTONES .3. THE COMPOSITION AND CONFORMATION OF D-MANNURONO-GAMMA-LACTONE IN SOLUTION, AND THE STRUCTURAL-ANALYSIS OF ITS BETA-ANOMER IN THE SOLID-STATE

Complete analyses of the proton and carbon chemical-shift assignments of D-mannurono-gamma-lactone (1) have been achieved by 1D and 2D NMR s pectral measurements. At equilibrium, the anomeric alpha and beta form s were present in the ratio of 34:66 in D2O and 72:28 in Me(2)SO-d(6). The solution data indicated that the dienvelope conformation (2)E:E(4 ), to be the favored conformation of 1 in solution. The crystal struct ure of 1 was determined, and it showed that the crystalline form is th e beta anomer, a bicyclic structure, consisting of fused five-membered furanose and lactone rings, in agreement with an earlier deduction fr om chemical evidence. In contrast to the solution conformation, the fu ranose ring adopts a twist conformation lying between the T-1(2) and ( 1)E conformations with phase angle (P) and pseudorotation amplitude (t au(m)) of -44.23 degrees and 37.9 degrees, respectively, whereas the l actone ring adopts an envelope E(5) conformation slightly distorted to wards T-6(5), With a phase angle (P) of -22.3 degrees and a pseudorota tion amplitude (tau(m)) of 18.4 degrees. The molecules are linked in t he crystal through a hydrogen-bonding network that involves all hydrox yl groups as well as the ring oxygen atoms.