Unstabilized diazo derivatives from carbohydrates. Application to the synthesis of 2-deamino-tunicamine and products related to C-disaccharides

Abstract

We applied a new synthetic method to C-disaccharides to obtain 2-deamino-tunicamine, the 2-hydroxy analogue of tunicamine, which is the main nucleus of tunicamycin antibiotics. 6-Deoxy-6-diazo-1:2,3:4-di-O-isopropylidene-D-galactopyranose was synthesized and reacted with methyl 2,3-O-isopropylidene-β-D-ribopentonodialdo-1,4-furanoside, to obtain a mixture of ketone and an epoxide with C-disaccharide structures. The epoxide was obtained in a reasonably good yield and full stereoselectivity, and was reduced to protected 2-deamino-tunicamine. Reduction of the ketone isomer, yielded the 7-epimer of 2-deamino-tunicamine. This is the first reported instance of an epoxy-C-disaccharide, the primary interest of which lies in its potential inhibition of glycosidase enzymes.