Preparation and structural characterization of N-glycated amino acid and linear or cyclic dipeptides containing the 6-amino-6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose moiety

N-Glycated derivatives of glycine, glycylglycine, and 2,5-piperazinedione, containing the 6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactos-6-yl moiety, were synthesized and studied by X-ray crystallography and NMR spectroscopy. The crystal structures of N-(6-deoxy-1,2:3,4-di-O-isopropylidene-alpha-D-galactos-6-yl)glycine (2), its glycylglycine analogue (3), and 2,5-piperazinedione congener (4) were determined. The crystals of 2 are monoclinic; space group P2(1) with a = 10.5098(5), b = 5.7632(5), c = 13.0938(7) Angstrom, beta = 90.245(5)degrees, Z = 2. The compounds 3 and 4 crystallized in the orthorhombic space group P2(1)2(1)2(1) with a = 5.3429(9), b = 15.1484(4), c = 22.853(2) Angstrom, Z = 4 (3) and a = 28.69(6), b = 15.478(3), c = 15.504(2) Angstrom, Z = 4 (4). In the solid state the alpha-D-galactopyranose moiety of 2 and 3 existed in the twisted T-0(2) conformation, whereas in 4 a transition state between T-0(2) and S-0(2) was recorded. H-1 NMR spectroscopy revealed that the conformation in solution for the galactopyranose moiety of compounds 2-4 closely resembled that found in the crystals. (C) 1996 Elsevier Science Ltd.