Nucleophilic reactions of some anhydro-sugars

Abstract

The vast majority of the work done so far on the synthesis and reactions of monosaccharide epoxides has been on the aldoses. Some ketoses have therefore been studied.The work falls into 3 partsThe known compound 1,2-0-isopropylidene-3,4-anhydro-beta-D-psicopyranose has been made from fructose. Synthesis of methyl 1,3-0-benzylidene-4,5-anhydro-a-L-psicoside and methyl 1,3-0-benzylid-ene-4, 5-anhydro-beta-D-fructoside from L-sorbose was attempted. Conformational factors prevented the formation of either of these 4,5-anhydro-compounds. b) In the absence of any entirely satisfactorymethod of cyanating sugars, an attempt has been made to develop one. Two methods were used: i) Potassium cyanide in acetonitrile, with 18-crown-6 as phase transfer catalyst. ii) Tetra-n-butylammonium cyanide in a variety of dipolar aprotic solvents. Methyl 2,3-anhydro-4,6-0-benzylidene-a-D-mannoside and 1,2-0-isopropylidene-3,4-anhydro-B-D-psicose were the starting materials. The crown ether was found to be ineffective as a phase transfer catalyst. No cyano-sugars were obtained using the second method, but some reactions produced lactones. Tetra-n-butylammonium cyanide was unstable even at temperatures as low as 100°C. Ring-opening of 1,2-0-isopropylidene-3,4-anhydro-5"0-benzoyl-(3-D-psicose was carried out with sodium azide to give the 4-azido-sorboside. Reduction of the mesyl derivative of this with Raney nickel gave the amine. Treatment with sodium methoxide gave a benzamido- compound. Some oxazoline may also have been formed. Reduction of the 3-mesyl-4-azido-sorboside with lithium aluminium hydride gave a mixture of the amine and an unknown substance which gave, after acetylation, 1,2-0-isopropylidene-3-dideoxy-4-deoxy-4-acetamido-5-0-acetyl-beta-D-sorbopyranose. Thin layer chromatography suggested the presence of a little of the 3-acetamido- compound. In both cases there are conformational reasons for failure to produce an epimine. In previous reports of synthesis of epimines from azides, the intermediate amine has not been isolated. Apart from the epoxide used as starting material, none of the other compounds has been reported in the literature before.