PubMed · 13221089
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J MORIN. Marsilid.. https://pubmed.ncbi.nlm.nih.gov/13221089/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The structures of the isomeric nucleosides 4-nitro-1-(beta-D-ribofuranosyl)-1H-indazole, C(12)H(13)N(3)O(6), (I), and 4-nitro-2-(beta-D-ribofuranosyl)-2H-indazole, C(12)H(13)N(3)O(6), (II), have been determined. For compound (I), the conformation of the glycosylic bond is anti [chi = -93.6 (6) degrees ] and the sugar puckering is C2'-exo-C3'-endo. Compound (II) shows two conformations in the crystalline state which differ mainly in the sugar pucker; type 1 adopts the C2'-endo-C3'-exo sugar puckering associated with a syn base orientation [chi = 43.7 (6) degrees ] and type 2 shows C2'-exo-C3'-endo sugar puckering accompanied by a somewhat different syn base orientation [chi = 13.8 (6) degrees ].
With a view to gaining evidence on the mechanism by which D-trehalose is able to stabilise biomolecules towards dehydration (anhydrobiosis) and heat, L-trehalose has been prepared in order to allow comparative studies to be made. Little change can be induced in the ratio of the alpha,alpha-, alpha,beta-, beta,beta-1,1'-stereoisomers of the disaccharide formed from 2,3,4,6-tetra-O-benzyl-L-glucose by using different reaction procedures and by varying the reaction conditions. Benzyl 2,3,4,6-tetra-O-benzyl alpha- and beta-L-glucopyranoside are by-products in the trimethylsilyl trifluoromethanesulphonate mediated formation of the 1,1'-linked disaccharides.
The tautomeric equilibria of a series of 3-hydroxypyridine derivatives including pyridoxal-5'-phosphate (PLP), the active form of vitamin B(6), have been studied using density functional calculations (B3LYP/6-311+G//B3LYP/6-31G) in the gas phase and in different solvents. Three different approaches, namely continuum, discrete, and hybrid (combined discrete/SCRF), were employed to investigate the effects of solvation on the tautomeric equilibria. In all cases, the neutral hydroxy form is significantly more stable than the zwitterionic oxo form (by 43-56 kJ mol(-)(1)) in the gas phase. The tautomeric energies reduce substantially in the presence of a polarizable dielectric medium. However, the neutral form is calculated to be the dominant form in nonpolar and aprotic polar solvents. On the other hand, a reversal of tautomeric equilibrium, in favor of the zwitterionic form, is predicted in an aqueous medium. This study highlights the role of both water molecules and bulk solvent effect in influencing the tautomeric equilibria of the PLP related compounds. A combination of explicit microsolvation and continuum reaction field is required to account fully for the energetic effect of aqueous solvation. The tautomeric free energy differences (deltaG(298)) of PLP in the gas phase and in aprotic polar (epsilon = 40) and aqueous media are predicted to be 47, 22, and -29 kJ mol(-)(1), respectively.