Glycosylation conformation

Previously, carbocyclic nucleosides have been studied in some detail, but these analogues were often poor substrates for enzymes. This may be a reason for why there have been so few reports on carbocyclic derivatives in oligonucleotides. The carbocyclic L-nucleoside derivatives (61, 62) which are fixed in the anti-glycosyl conformation, have been prepared to examine factors determining the helicity of dsDNA. The anti-conformer was prepared to determine whether... 

Laszlo, E., Hollo, J., Hoschke, A. and Sarosi, G. (1978) The active center of amylolytic enzymes. I. A study by means of lactone inhibition of the role of "halfchair" glycosyl conformation at the active center of amylolytic enzymes, Carbohydr. Res., 61, 387-394. 

Glycosyl bond conformation anti anti anti at C, syn at G... 

FIGURE 12.14 Comparison of the deoxy-guanosine conformation in B- and Z-DNA. In B-DNA, the Cl -N-9 glycosyl bond is always in the anti position (lefi). In contrast, in the left-handed Z-DNA structure, this bond rotates (as shown) to adopt the syn conformation. 

Other inverting glucosidases which conform to the pattern of direct hydrolysis of glycosyl fluorides having the correct anomeric configuration, and transglycosylation with inversion if the anomeric configuration is opposite to that of the natural substrates are trehalase from rabbit renal cortex and from the yeast Candida tropicalis, and ) -D-xylosidase from Bacillus pu-milis. ... 

Z = 8 D, = 1.84 R = 0.059 for 2,587 intensities. In the asymmetrical unit, there are two molecules that have similar conformations. The glycosyl dispositions are anti (45.8°, 40.9°) in both molecules. The D-ribosyl conformation is 2Tj (157.6°, 32.1°) in one molecule, and 2T3 (165.1°, 31.9°) in the other. The exocyclic, C-4 -C-5 bond torsion-angles are gauche+ (51.9°, 53.9°) in both molecules, and the C-5 -0-5 bond torsion-angles are trans (172.5°, 176.6°). The two UDP molecules form a dimer coordinated by three K+ ions. There is no metal-ion or water bridge between the pyrophosphate chain and the uracil base of the same molecule. The three K+ ions are coordinated by oxygen atoms of... 

C11H16N305S+ Cl- 2,2 -Anhydro-(l-/ -D-arabinofuranosyl-5-dimethyl-mercapto-6-oxocytosine chloride) (AFMSCY)166 P212121 Z = 4 DX= 1.57 R = 0.042 for 1,117 intensities. The glycosyl disposition of the anhydronucleoside is constrained to the syn (—57.3°) orientation. The conformation of the D-arabinofuranosyl group is a flat-... 

C13HuC1N307 2,2 -Anhydro-[5-chloro-l-(3,5-di-0-acetyl-/ -D-arabino-furanosyl)-6-oxocytosine] (ACAFCC)166 I4t Z — 8 D = 1.56 R = 0.066 for 818 intensities. The glycosyl disposition of the anhydronucleoside is constrained to the syn (— 68.8°) orientation. The conformation of the D-arabinofuranosyl group is a flattened 4E (232.6°, 18.0°), and the exocyclic, C-4 -C-5 bond torsion-angle is g auche+ (50.2°). The adjacent bases are connected by N-H O hydrogen-bonds between the N-4 atom of one molecule and the carbonyl oxygen atom (0-4) of another. The twofold-symmetry-related bases are stacked, with an interbase separation of 329 pm. 

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