SYNTHESIS OF 3-BETA-D-RIBOFURANOSYLPYRAZOLE-1-CARBOXAMIDE

The synthesis of 3-beta-D-ribofuranosylpyrazole-1-carboxamide (12) is described. Treatment of glycosyl enaminone 4 with semicarbazide hydroc hloride in dioxane afforded three cyclocondensation products, enzoyl-b eta-D-ribofuranosyl)pyrazole-1-carboxamide (5), 2,3,5-tri-O-benzoyl-be ta-D-ribofuranosyl)pyrazole- 1-carboxamide (6), and (2,3,5-tri-O-benzo yl-beta-D-ribofuranosyl)pyrazole (7), in 51, 5, and 16% yields, respec tively. Compound 5 was gradually converted to 7 at room temperature as a result of the elimination of the carbamoyl group. Treatment of the 4 with hydrochloric acid in methanol at room temperature afforded 3,3- dimethoxy-1 (2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)propane- 1-one ( 9) in 90% yield. Treatment of 9 with semicarbazide afforded the corres ponding semicarbazone 10, which was cyclized in trifluoroacetic acid t o afford 6. Deblocking of 6 with 10% aq ammonia gave 12. (C) 1998 Else vier Science Ltd. All rights reserved.