Synthesis of ketosyl and ulosonyl phosphonates by Arbuzov-type glycosidation of thiazolylketol acetates

Some members of two novel classes of glycosyl phosphonates (galacto, 2- azido-2-deoxy-galacto, gluco, manno) carrying a diethyl phosphonate and a hydroxymethyl (ketosyl derivatives) or carboxymethyl group (ulosonyl derivatives) at the anomeric carbon have been prepared. The synthetic route involves the trimethylsilyl triflate promoted Arbuzov-type coupling between thiazolylketol acetates and triethylphosphite to give thiazolylglycosyl phosphonates in good yields (78-93%). This glycosidation reaction was highly stereoselective giving rise to the α-D-glycosyl phosphonate as single product with the exception of the reaction with the gluco derivative which afforded the α- and β-D-anomer in almost equal amount. The phosphono glycosides were converted by the thiazole-to-formyl deblocking protocol (N- alkylation, reduction, hydrolysis) into aldehydes that in turn served as common intermediates to ketosyl and ulosonyl diethylphosphonates via reduction or oxidation of the formyl group, respectively. The configuration at the anomeric carbon of all new compounds was assigned by NMR analysis through the hydrogen-phosphorus coupling constant values and HETNOE experiments. The feasibility of access to the free ketosyl and ulosonyl phosphonic acids is demonstrated taking as an example the galactopyranosyl derivatives.