CONFORMATIONS OF 2-C-1-N-CARBONYL-2-DEOXY-D-GLYCOPYRANOSYLAMINES

Geometry and molecular conformation of the N-toluenesulfonyl 1 and N-a cetyl- 2 derivatives of peracetylated C:1-N-carbonyl-2-deoxy-alpha-D-g lucopyranosylamine were investigated with the use of X-ray diffraction methods. Compound 1 (C20H23NSO10) crystallizes in the monoclinic P2(1 ) space group, with Z = 2 and a = 8.238(1), b = 7.988(1), c = 16.928(2 ) Angstrom, beta = 99.12(1)degrees. Compound 2 (C15H19NO9) crystallize s in orthorhombic P2(1)2(1)2(1) space group with Z = 4 and a = 8.385(1 ), b = 8.550(1), c = 24.000(2) Angstrom. Analysis of differences in bo nd lengths and angles between compounds 1 and 2 and other compounds of this class showed that the electron-withdrawing effect by the residue located at the nitrogen atom can be manifested by lengthening of the beta-lactam C-N bonds, with simultaneous shortening of the distance be tween two carbon atoms at the ring fusion. Semi-empirical calculations suggested that the title compounds displayed two positively charged c enters, susceptible for attack of nucleophiles, one at the carbonyl gr oup of beta-lactam and the second at the anomeric carbon atom. Atomic charges, however, calculated for compounds 1 and 2 did not explain the ir different reaction directions during alcoholysis.