Synthesis of a Novel Pyrazolo[1, 5-C]Pyrimidine C-Nucleoside and Conformational Analysis By NMR Spectroscopy

Abstract

Isopropylidenation of [4-methoxycarbonyl-5-(β-D-ribofuranosyl)-1H-pyrazol-3-yl]acetamide (1a) followed by the acidic cleavage of the sugar acetonide afforded 3-methoxycarbonyl-7, 7-dimethyl-2-(β-D-ribofuranosyl)-4H, 7H-pyrazolo[1,5-c] pyrimidine-5(6H)-one (2b), the structure of which was established unequivocally by X-ray structure analysis of the monocrystals. Compounds 1a and 2b have 75% and 70% preference for the N-type puckering between C3′-endo and C3′-endo-C4′-exo forms, and a great preference of 69% and 74% for γ+ rotamers in solution, respectively.