A 13C-N.M.R. investigation of glycosyl azides and other azido sugars: stereochemical influences on the one-bond 13C-1H coupling constants

Abstract Unambiguous 13 C assignments have been obtained, using 2D-n.m.r. techniques, for several glycosyl azides, 6-deoxyglycosyl azides, 2-acylamino-2-deoxyglycosyl azides, and some 2- and 3-azido monosaccharide derivatives. For non-anomeric CH bonds the 1 J C,H e values are 4–9 Hz larger than the 1 J C,H a values. A substituent (hydroxyl, acetoxyl, alkoxyl, azido, etc. ) in 1,3-diaxial relationship with H a significantly increases the value of 1 J C,H a . Bond-angle distortions in the fused-ring bicyclic systems of some isopropylidene derivatives result in 1 J C,H a values being larger than 1 J C,H e values. Electronic and steric effects of substituents at non-anomeric carbons may alter the 1 J C,H values for anomeric carbons to such an extent that they may no longer be useful for diagnosing anomeric configuration. Bond-angle deformations also influence the 13 C chemical shift differences in α- and β-anomers at C-5 and, to a lesser extent, at C-3.