SYNTHESIS OF 3,4-DI-O-ACETYL-2,5-ANHYDRO-1,6-DIDEOXY-1,6-DIIODO-D-MANNITOL - COMPARISON OF NMR SPECTRAL RESULTS FOR THE SOLID STATE AND SOLUTION WITH THOSE OF THE X-RAY STRUCTURAL DETERMINATION

摘要

3,4-Di-O-acetyl-2,5-anhydro-1,6-dideoxy-1,6-diiodo-D-mannitol (3) is prepared from 2,5-anhydro-D-mannitol (1) in three steps. The solution and solid-state NMR spectra of 3 indicate considerable variation in conformation. In solution, it adopts, on average, a symmetric T-4(3) conformation, whereas in the solid state it adopts an asymmetric conformation as revealed by C-13 NMR cross polarization and magic angle spinning techniques. A single-crystal X-ray structure analysis confirmed the asymmetric conformation of 3 in a monoclinic crystal, space group P2(1) with a = 8.9608(4), b = 8.6348(5), c = 9.6468(4)Angstrom, beta = 96.139(4)degrees, V = 742.1(1) Angstrom(3), D-c = 2.085 g cm(-3), mu (MoKalpha) = 4.2 mm(-1) and Z = 2. The structure was refined to R = 0.039 and R(w) = 0.047 for 5181 observed reflections. The furanoid ring of 3 adopts an envelope E(5) conformation slightly distorted towards 4 T-4(5), with puckering parameters phi = 313.49 degrees and q = 0.37 Angstrom. The asymmetric conformation is rationalized in terms of the weak packing forces in the crystal. [References: 27]