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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]

B3LYP/6-31+G** level computations were performed for the formation of four trimethylammonium salts in the reaction of methyl chloride ( 1a), ( S)-1,4-andydro-5-chloro-2,3,5-trideoxypentitol ( 2a), (2 S,5 S)-2,5-andydro-6-chloro-1,3,4,6-tetradeoxyhexitol ( 3a) and methyl 5-chloro-2,3,5-trideoxy-β-D-pentofuranoside ( 4a) with trimethylamine. All the structures were fully optimized in the gas phase, in chloroform and water. In addition, B3LYP/6-311++G** and MPW1K/6-31+G** level calculations were carried out to estimate activation barrier heights in the gas phase. A detailed description of all stationary points is presented, and the conformational behavior of the THF ring is discussed. B3LYP and MPW1K activation barriers indicate the reaction between methyl chloride and trimethylamine to be the fastest, whereas reaction 4 is the slowest one, both in the gas phase and in solvents. THF ring conformation changes were observed for reactions 2 and 3 along the reaction pathway, whereas it was almost unchanged for reaction 4, in the gas phase. In the case of reactions 2 and 3, different shapes of the THF ring were found for the transition state geometry in the gas phase and in water. The E→ E and E→ E conformational changes were observed for reactions 2 and 3, respectively. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The formation of pyridinium salts in the transformation of three O-isopropylidene-protected mesylates of furanoid sugar derivatives under pyridine action is considered at the B3LYP/6-31+G** computation level. All the structures were optimized in the gas phase, in chloroform and water. Activation barrier heights in the gas phase were also estimated at the B3LYP/6-311++G**, MPW1K/6-31+G** and MPW1K/6-311++G** levels. The conducted calculations, both in the gas phase (regardless of the computation level) and in solvents, revealed the barrier height increasing order as follows: 1>2>3 for the three reactions studied. The conformational behavior of the five-membered ring is discussed in the gas phase and in solvents. The fused dioxolane ring makes the furanoid ring less likely to undergo conformational changes. In the case of reaction 3, the furanoid ring shape does not change either in the gas phase or in solvents. All conformers are close to E0 or 0E. [ABSTRACT FROM AUTHOR]