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

• Published in: Carbohydrate research 2017-06, Vol.446-447, p.85-92
• Main Authors: Walczak, Dominik, Nowacki, Andrzej, Trzybiński, Damian, Samaszko-Fiertek, Justyna, Myszka, Henryk, Sikorski, Artur, Liberek, Beata
• Format: Article
• Language: English
• Subjects: Aniline Compounds - chemistry; Anomeric effect; Carbohydrate Conformation; Delocalization; Glucuronides - chemistry; Lactones - chemistry; Models, Molecular; N-Furanoside; N-Glucuronide; Quantum Theory; Ring conformation; Rotamer
• ISSN: 0008-6215; 1873-426X
• DOI: 10.1016/j.carres.2017.05.011

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 3T2/3E-like conformation in the crystal lattice, solution and gas phase. Thus, the structure of recorded for N-furanoside 1H NMR spectrum is indicative of the 3T2/3E 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 1T2/E2/3T2/3E 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 4C1 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 sp2 hybridisation. [Display omitted] •N-(α-d-Glucofuranurono-6,3-lactone)-p-nitroaniline adopts a 3T2/3E-like conformation.•The characteristic 1H NMR spectrum for a 3T2/3E-like conformation is presented.•The 1T2/E2/3T2/3E region is characterised by the lack of coupling between trans oriented H2 and H3 protons.•N-(Methyl β-d-glucopyranuronate)-p-nitroaniline adopts the 4C1 conformation, both in the crystal lattice and solution.•The amine group of p-nitroaniline in N-glycosides is planar.