SPACER-MODIFIED, PHOTOLABILE TETRASACCHARIDES AS ANALOGS OF MALTOPENTAOSE ARE VERSATILE PROBES FOR PORCINE PANCREATIC ALPHA-AMYLASE

The syntheses are described of methyl 4'-O-[4-S-(3-azi-4-alpha-D-glucopyranosyloxybutyl)-6-deoxy-4-thio-alpha-D-xylo-hex-5-enopyranosyl]-alpha-maltoside (28), methyl 4-O-[4-S-(3-azi-4-alpha-maltosyloxybutyl)-6-deoxy-4-thio-alpha-D-xylo-hex-5-enopyranosyl]-alpha-D-glucopyranoside (29), and methyl 4-S-(3-azi-4-alpha-maltotriosyloxybutyl)-6-deoxy-4-thio-alpha-D-xylo-hex-5-enopyranoside (30), which are analogues of maltopentaose in which a central glucosyl unit is replaced by an acyclic, four-membered hydrocarbon spacer carrying a photolabile azi group. Only 30 was slowly cleaved by high concentrations of pancreatic alpha-amylase. The K(i) values (mM) were 0.15 (28), 2.1 (29), and 2.5 (30). Deactivation of the enzyme by irradiation in the presence severally of 28-30 was 96.4%, 98.1%, and 40%, respectively. There is an indication for regiospecific photoaffinity labelling of the binding subsites of the enzyme.