H-1-NMR STUDY OF HYDROGEN-BONDING AND HYDROGEN TO DEUTERIUM-ISOTOPE EXCHANGE IN UREIDO SUGARS

The acidic properties of ureido NH protons in two new derivatives of m ethyl 3,4,6-triacetyl-3-deoxy-beta-D-glucopyranoside and i-butylamine (1) and L-leucine (2) were studied by H-1 NMR. Stronger influence of p olar aprotic solvents, more effective interaction with nitroxyl radica l and faster H/D exchange indicate that N1'-H proton which is proximat e to the glucopyranose ring is more acidic than N3'-H one in both urei do sugars; this conclusion was supported by semi-empirical AM1 calcula tion. Hydrogen to deuterium exchange rates are 1.2x10(-2) to 5.5x10(-3 ) M(-1) min(-1). Significantly slower exchange of N3'-H proton standin g by Leu residue in 2 can be explained by the existence of internal H- bonds.