Part one. Conformational analysis of the equlibria and rates for the anomerization of acetylated aldopyranoses. Part two. The characterization of 1,2:5,6-diisopropylidene-3-deoxy-3-amino-alpha-D-allofuranose.

Abstract

A quantitative conformational analysis was made of the anomerization equilibria of the acetylated aldopyranoses. The following non-bonded interaction energies were obtained, based on the assumption that the difference in free energy between the anomeric pairs can be taken as equal to the difference in non bonded interactions. (1) The anomeric effect, 1290 Gals./mole. (2) An acetoxymethyl group on carbon 5 enhances the anomeric effect by 220 call,/mole. (3) The skew interaction between two acetoxy groups, O/O-H/H, is 540 cals,/mole. (4) The diaxial interaction between an acetoxy group and a hydrogen atom, H:O-H:H, is 180 cals./mole. (5) The diaxial interaction between two acetoxy groups, O:O-H:H, is 2020 cals/mole. These interaction energies are all related to the interaction term H/O-H/H, that is the skew interaction between an acetoxy group and a hydrogen atom relative to the same inter action between two hydrogen atoms. The above values for the interaction energies are based on the assumption that the value of H/O-H/H is negligibly small. This type of assumption has been made by all previous workers in the field of conformational analysis and is required for a comparison of the values presently obtained with those values of similar interactions reported in the literature. The acetylated amono-sugars with an acetamido group on carbon. 2 or 3 were found to undergo anomalous anomerization reactions, These results could be due to the formation of stable oxazolinium or oxazinium ions in the anomerization media. The relative stabilities of the transition states in the anomerization of the acetylated aldopyranoses were examined in a number of different ways. It was concluded that the results would best be rationalized on the basis of a bimolecular mechanism. Conformational analyses of the transition states indicated that the activated complexes of the aldopentopyranose tetraacetates may assume a half-chair form. However, a deformed chair seemed more plausible for the transition states of the al dohexopyranose pentaacetates. The reason for this difference between the pentoses and hexoses is discussed. The reaction of the base-catalyzed anomerization of the D-glucopyranose pentaacetates was investigated. T he amino-sugar moieties from the hydrolysis of the new antibiotic kanamycin were identified as 3-D-glucosamine and 6-D-glucosamine. The configuration of 1,2;5,6-diisopropylidene-3-deoxy-3-amino-alpha-D-allofuranose was established. This proves that inversion occurs in the replacement of a tosyloxy group on secondary carbon atoms with ammonia or hydrazine and provided unequivocal identification of 3-D-glucosamine.