Nucleosides LXXVII. Rotational isomerism of certain 3-β--glucopyranosyl-6-methyluracils

Photochemical transformations of 5-halogeno-4-thiouridines

“…A similar downfield shift (≈1 ppm) of the sugar anomeric proton signal in uracil 3-β--ribofuranoside as compared with the 1-β--ribofuranoside, 10 as well as the existence of two rotational isomers of 3-β--glucopyranosyl-6-methyluracils, was demonstrated previously by 1 H NMR spectroscopy. 11 We must stress that although the chemical shifts, multiplicity and integration of all signals present in the 1 H NMR spectra of 4 and 7 in D 2 O are fully compatible with their proposed structures, in neither case could an expected exchangeable-proton signal in the NMR spectra recorded in DMSO-d 6 be observed. In the structural formula of photoproduct 7 (Scheme 1), which represents one of its several possible tautomeric forms, this H atom is connected to N( 3).…”