Synthesis and glycosidase inhibitory activity of 5-thioglucopyranosylamines. Molecular modeling of complexes with glucoamylase

Glucoamylase: structure/function relationships, and protein engineering

Glucoamylases are inverting exo-acting starch hydrolases releasing beta-glucose from the non-reducing ends of starch and related substrates. The majority of glucoamylases are multidomain enzymes consisting of a catalytic domain connected to a starch-binding domain by an O-glycosylated linker region. Three-dimensional structures have been determined of free and inhibitor complexed glucoamylases from Aspergillus awamori var. X100, Aspergillus niger, and Saccharomycopsis fibuligera. The catalytic domain folds as a twisted (alpha/alpha)(6)-barrel with a central funnel-shaped active site, while the starch-binding domain folds as an antiparallel beta-barrel and has two binding sites for starch or beta-cyclodextrin. Certain glucoamylases are widely applied industrially in the manufacture of glucose and fructose syrups. For more than a decade mutational investigations of glucoamylase have addressed fundamental structure/function relationships in the binding and catalytic mechanisms. In parallel, issues of relevance for application have been pursued using protein engineering to improve the industrial properties. The present review focuses on recent findings on the catalytic site, mechanism of action, substrate recognition, the linker region, the multidomain architecture, the engineering of specificity and stability, and roles of individual substrate binding subsites.

Novel 4-thiogalactofuranosyl-containing disaccharides with nitrogen in the interglycosidic linkage

The syntheses of three novel disaccharides containing a 4-thiogalactofuranosyl residue as the non-reducing unit and a nitrogen in the interglycosidic linkage are described. Acid-catalyzed condensation reactions of 4-thio-alpha/beta-D-galactofuranose with either methyl 3-amino-3-deoxy-alpha-D-mannopyranoside, methyl 2-amino-2-deoxy-alpha-D-mannopyranoside, or methyl 2-acetamido-6-amino-2,6-dideoxy-beta-D-glucopyranoside gave methyl 3-amino-3-deoxy-3-N-(4-thio-alpha/beta-D-galactofuranosyl)-alpha-D-manno pyranoside, methyl 2-amino-2-deoxy-2-N-(4-thio-alpha/beta-D-galactofuranosyl)-alpha-D-manno pyranoside, or methyl 2-acetamido-6-amino-2,6-dideoxy-6-N-(4-thio-alpha/beta-D-galactofuranosy l)-beta-D-glucopyranoside.

Is there a generalized reverse anomeric Effect? substituent and solvent effects on the configurational equilibria of neutral and protonated N-arylglucopyranosylamines and N-aryl-5-thioglucopyranosylamines

The effects of substitution and solvent on the configurational equilibria of neutral and protonated N-(4-Y-substituted-phenyl) peracetylated 5-thioglucopyranosylamines (Y = OMe, H, CF(3), NO(2)) 1-4 and N-(4-Y-substituted-phenyl) peracetylated glucopyranosylamines (Y = OMe, H, NO(2)) 9-11 are described. The configurational equilibria were determined by direct integration of the resonances of the individual isomers in the (1)H NMR spectra after equilibration of both alpha- and beta-isomers. The equilibrations of the neutral compounds 1-4 in CD(3)OD, CD(3)NO(2), and (CD(3))(2)CO were achieved by HgCl(2) catalysis and those of the neutral compounds 9-11 in CD(2)Cl(2) and CD(3)OD by triflic acid catalysis. The equilibrations of the protonated compounds in both the sulfur series (solvents, CD(3)OD, CD(3)NO(2), (CD(3))(2)CO, CDCl(3), and CD(2)Cl(2)) and oxygen series (solvents, CD(2)Cl(2) and CD(3)OD) were achieved with triflic acid. The substituent and solvent effects on the equilibria are discussed in terms of steric and electrostatic effects and orbital interactions associated with the endo-anomeric effect. A generalized reverse anomeric effect does not exist in neutral or protonated N-aryl-5-thioglucopyranosylamines and N-arylglucopyranosylamines. The anomeric effect ranges from 0.85 kcal mol(-)(1) in 2 to 1.54 kcal mol(-)(1) in 10. The compounds 1-4 and 9-11 show an enhanced endo-anomeric effect upon protonation, ranging from 1.73 kcal mol(-)(1) in 2 to 2.57 kcal mol(-)(1) in 10. We estimate the increase in the anomeric effect upon protonation of 10 to be approximately 1.0 kcal mol(-)(1). However, this effect is offset by steric effects due to the associated counterion which we estimate to be approximately 1.2 kcal mol(-)(1). The values of K(eq)(axial-equatorial) in protonated 1-4 increase in the order OMe < H < CF(3) < NO(2), in agreement with the dominance of steric effects (due to the counterion) over the endo-anomeric effect. The values of K(eq)(axial-equatorial) in protonated 9-11 show the trend OMe > H < NO(2) that is explained by the balance of the endo-anomeric effect and steric effects in the individual compounds. The trends in the values of the C(1)-H(1) coupling constants for 1-4 and the corresponding deacetylated compounds 5-8 as a function of substituent and alpha- or beta-configuration are discussed in terms of the Perlin effect and the interplay of the endo- and exo-anomeric effects.