2-(b-D-Ribofuranosyl)-4-(p-tolylazo)-5-trifluoromethyl-2,4-dihydropyrazol-3-one

The desired compound 2 was obtained by complete deprotection of the acetylated nucleoside 1 [1] using triethylamine [2]. To a solution of 1 (0.8g, 1.5 mmol) in methanol (25 ml) was added triethylamine (2 ml). The mixture was stirred at room temperature and the reaction was followed by tlc. After complete deprotection (24 hours), the reaction mixture was evaporated and coevaporated with methanol (3 x 30 ml), then chromatographed over silica gel using CH₂Cl₂/MeOH (95:5 v/v) to give 0.55 g (90%) of 2 as yellow powder.

R_f: 0.30 (CH₂Cl₂/MeOH, 95/5 v/v).

UV (lmax , 95% ethanol): 384nm

IR (KBr, cm^-1): 3414 (OH), 1662 (CO pyrazolone).

MS (m/z): 402.

¹H-NMR (250 MHz, DMSO-d₆): 2.38(s, 3H, CH₃); 2.40(s, 1H, CH); 3.73(dd, 1H, H-5` J5`,4`=2.4 Hz) 3.91-3.96(dd, 1H, H-5`` J5``,4`=2.4 Hz); 4.23-4.24(m, 1H, H-4`); 4.53(t, 1H, H-3` J3`,2`=3.66 Hz); 4.75(t, 1H, H-2` J2`,3`=5.13 Hz); 5.94(d, 1H, H-1`, J1`,2`=4.92 Hz); 7.21-7.37(m, 4H, aromatic CH).

¹³C-NMR (75 MHz, DMSO-d₆): 22.0(CH3); 48.9(CH); 63.08(C-5`), 71.71(C-3`); 73.90(C-2`); 85.63(C-4`); 88.08(C-1`); 116.9 (2 aromatic carbons), 121.0, 122.0 (2 aromatic carbons), 130.4, 144.0 (2 quaternary aromatic carbons); 137.7(q, CF₃); 148.5(C=N); 173.5(CO).