Conformational studies of N-(α-d-glucofuranurono-6,3-lactone)- and N-(methyl β-d-glucopyranuronate)-p-nitroanilines.

N -(α- d -Glucofuranurono-6,3-lactone)- p -nitroaniline and N -(methyl β- d -glucopyranuronate)- p -nitroaniline were obtained as crystalline solids. The single-crystal X-ray diffraction, NMR data and DFT calculations for N -(α- d -glucofuranurono-6,3-lactone)- p -nitroaniline indicate that this N -furanoside adopts a 3 T 2 / 3 E -like conformation in the crystal lattice, solution and gas phase. Thus, the structure of recorded for N -furanoside 1 H NMR spectrum is indicative of the 3 T 2 / 3 E region of the pseudorotational itinerary for furanose derivatives with α- d -gluco, β-L-ido and α- d -xylo configurations. Moreover, it is concluded that the 1 T 2 / E 2 / 3 T 2 / 3 E region of the pseudorotational itinerary for furanose derivatives with d -gluco, L-ido and d -xylo configurations should be characterised by the lack of coupling between H2 and H3 protons, irrespective of the anomeric configuration. Such a lack of vicinal coupling is characteristic for some of the trans- oriented furanose ring protons. The single-crystal X-ray diffraction and NMR data for N -(methyl β- d -glucopyranuronate)- p -nitroaniline indicate that this N -glucuronide adopts the 4 C 1 conformation, both in the crystal lattice and solution. The occurrence of anomeric effects in the presented N -glycosides is discussed. The crystal structure analysis of both N -glycosides gives evidence that the amine group in p -nitroaniline is planar due to the nitrogen sp 2 hybridisation. [ABSTRACT FROM AUTHOR]