INFRARED AND H-1-NMR STUDIES OF HYDROGEN-BONDING IN DEOXY-BETA-D-GLUCOPYRANOSIDE)-N'-CARBAMOYL-L-AMINO ACID-ESTERS

Ureido 2-deoxy-beta-D-glucopyranosides with seven different amino acid ester residues were studied by means of LR and H-1 NMR spectroscopy, The H-D exchange rates increase in the order L-Val<L-Leu<L-Ala<Gly for both NH protons; however, the exchange rate st N-1-H (linked to the g lucopyranoside) is significantly faster than that at N-3-H (at the ami no acid residue). The analysis of IR spectra in the region of the NH s tretching vibrations shows, in agreement with other investigations, th at the signals at 3454, 3423 and 3355 cm(-1) are due to the free and t he intramolecular associated NH groups forming a five-and seven-member ed ring, respectively, It was found that the C-7 associated ring is fo rmed by hydrogen bonding between the N-1-H function and the C=0 of the acetyl group at the C-3 position in the glucopyranoside. The N-3-H gr oup is involved in a hydrogen bond with the C=0 function of the ester group protecting the amino acid residue. Furthermore, it was found tha t the ureido sugar with L-Val exhibits a stronger C-7 hydrogen bond th an the other amino acid residues. This result conforms with the lowest H-D exchange rate at the N-1 position of this compound, Steric effect s resulting In the shielding of this hydrogen bond against OD attack a re considered as a reason for this peculiarity. (C) 1997 John Wiley & Sons, Ltd.