Preparation of D-galactofuranosyl nitromethanes: a revision and a new approach.

Sodium methoxide-promoted methanolysis of 7-deoxy-7-nitro-L-glycero-L-galacto-heptitol peracetate rapidly and nearly quantitatively accumulates 7-deoxy-6-O-methyl-7-nitro-L-glycero-L-galacto-heptitol. The prolonged treatment then provides 76% of D-galactofuranosyl nitromethanes and finally results in the equilibrium of 77% of ß-D-galactopyranosyl nitromethane and 7-9% of three other tautomeric D-galactosyl nitromethanes. Thermal treatment of 7-deoxy-7-nitro-L-glycero-L-galacto-heptitol in boiling water peaks at a 58% content of D-galactofuranosyl nitromethanes and ends in a similar equilibrium mixture of four D-galactosyl tautomers. The relevant kinetic parameters of the latter transformation are determined by a curve fitting using the nonlinear least-squares Marquardt-Levenberg algorithm.

One-pot synthesis of 2-C-glycosylated benzimidazoles from the corresponding methanal dimethyl acetals.

A series of 2-glycosyl-benzimidazoles with alpha-d-arabinopyranosyl, beta-d-galactopyranosyl, beta-d-glucopyranosyl, beta-d-mannopyranosyl, and beta-l-rhamnopyranosyl configurations were obtained in 52-73% yields from the corresponding C-glycosylmethanal dimethyl acetals and o-phenylenediamine under catalysis with hydrogen chloride or a strongly acidic cation-exchange resin. Intermediate benzimidazolines were spontaneously oxidized by air to produce the final products in the one-pot procedure. The prepared compounds did not show any inhibitory effect on the growth of 12 strains of five different species of pathogenic yeasts.

Extension of the Nef reaction to C-glycosylnitromethanes.

Acid-catalysed methanolysis of 3,4,5,6-tetra-O-acetyl-1,2-dideoxy-l-arabino-hex-1-enitol proceeds via a cascade set of consecutive reactions resulting in its regiospecific conversion to a mixture of alpha- and beta-C-L-arabinofuranosylmethanal dimethyl acetals and a mixed internal methyl acetal. Structures of the final products of the overall process provide unique evidence that a kinetically controlled, five-membered-ring closure precedes a six-membered-ring closure in reversible systems capable of giving both five-membered and six-membered all-sp3-atom rings. Determination of the reaction intermediate enabled extension of the Nef reaction to C-glycosylnitromethanes. Protonated aci-nitro forms of C-glycosylnitromethanes that are resistant to the Nef reaction in aqueous acidic media undergo a modified Nef reaction in acidified methanol, and the corresponding C-glycosylmethanal dimethyl acetals with alpha-L-arabinopyranosyl, beta-D-glucopyranosyl, beta-D-galactopyranosyl, beta-D-mannopyranosyl and beta-L-rhamnopyranosyl configurations were obtained in moderate yields.