STEREOSELECTIVE THIOGLYCOSIDE SYNTHESES .6. ARYL 4-THIOMALTOOLIGOSACCHARIDES AS CHROMOGENIC SUBSTRATES FOR KINETIC-STUDIES WITH ALPHA-AMYLASE

Nucleophilic bimolecular substitution, of either o- or p-nitrophenyl 2,3,6-tri-O-benzoyl-4-O-trifluoromethylsulfonyl-.alpha.-D-galactopyranoside (1) or (2) with the sodium salt of 1-thio-.alpha.-D-glucopyranose in hexamethylphosphoramide afforded, after the usual deprotection sequencies, o- and p-nitrophenyl 4-thio-.alpha.-maltosides (7) and (8). A similar synthetic scheme with (1) and the 1-.alpha.-thiolate of 4-thiomaltose led to o-nitrophenyl 4,4''-dithio-.alpha.-maltotrioside. These 4-thio-oligosaccharides and their corresponding oxygen analogs were used, in comparative assays, as chromogenic substrates with porcine and human pancreatic .alpha.-amylases. In both series, enzymic velocity was higher for the maltotrioside derivatives than for the maltodisaccharides. o-Nitrophenyl glycosides behave as better substrates than the corresponding para isomers. Replacement of intersaccharide O2 atoms by S increased slightly the Km but had a negative effect on the hydrolysis rate. As a consequence, 4-thiomaltosyloligosaccharides were less sensitive substrates for pig pancreatic .alpha.-amylase as compared with their O-glycosyl counterparts. However, as the former class of compounds is split exclusively at the chromogenic site, they appear to be substrates of interest for direct kinetic studies with .alpha.-amylases.