SYNTHESIS OF 'C-GLYCOSIDES' AND THEIR POTENTIAL APPLICATION TO AFFINITY LABELING OF O-GLYCOSIDASES (PHOTOAFFINITY LABELING, GLYCOSYL CYANIDES)

Aldohexopyranosyl diazomethyl ketones (3,7-anhydro-1-deoxy-1-diazo-2-octuloses) are C-glycosyl compounds in which the anomeric hydroxyl group has been replaced by the diazoacetyl functional group (-COCHN(,2)). Since diazoketones can be converted into highly reactive alkylating agents by protonation, photolysis, or addition of certain transition metal ions, it was proposed that diazomethyl glycosyl ketones would be useful as photoaffinity- and classical affinity-labeling reagents for the corresponding, specific carbohydrate-binding proteins. In view of the importance of acid catalysis in the mechanism of action of O-glycosidases, it was also envisioned that such compounds would be of particular value as suicide inactivators of these enzymes.;Aldohexopyranosyl cyanides (2,6-anhydroheptononitriles) are C-glycosyl compounds in which the anomeric hydroxyl group has been replaced by the synthetically versatile cyano functional group. Their O-protected derivatives possess considerable potential as intermediates in the synthesis of C-glycosyl analogs of naturally occurring aldohexoses, as well as of other chiral molecules of biochemical interest. Realization of this potential requires the availability of facile, stereoselective, high yield, and large scale preparations of these compounds.;Herein, I describe such syntheses for the per-O-acetylated 1,2-trans-aldohexopyranosyl cyanides of D-galactose, L-fucose, D-mannose, and 2-deoxy-2-phthalimido-D-glucose; the derivative of D-glucose is similarly available in moderate yield. In addition, much lower yields of the per-O-acetylated 1,2-cis-aldohexopyranosyl cyanides of D-galactose, L-fucose, D-mannose, and D-glucose were obtained from these syntheses. Characterization of these synthons by, inter alia, laser-Raman spectroscopy and ('1)H- and ('13)C-nuclear magnetic resonance spectroscopy, demonstrated correlations between their physical properties and anomeric configurations.;To test these hypotheses, the first examples of this class of compounds have been synthesized, viz., diazomethyl (beta)-D-galactopyranosyl and (beta)-D-glucopyranosyl ketone. These compounds were prepared in good overall yield from D-galactose and D-glucose, respectively, via a six step reaction sequence in which per-O-acetyl-(beta)-D-galactopyranosyl and -glucopyranosyl cyanide, respectively, are the key intermediates. These syntheses can be readily executed on a relatively large scale, to provide ample quantities of the target molecules for future biochemical studies and for further synthetic manipulations leading to other C-glycosyl compounds of interest. The reaction sequence was designed to be sufficiently versatile to allow the preparation of an extended series of C-glycosyl-based potential affinity labeling reagents from presently available glycosyl cyanides (vide infra). Diazomethyl glycosyl ketones exhibit good stability under physiological conditions.