N. R. Reddy, G. M. Reddy, P. Reddy
Feb 1, 2004
Citations
0
Influential Citations
6
Citations
Journal
Organic Preparations and Procedures International
Abstract
Pyrazolo[4.3-d]pyrimidines have attracted interest in view of their immense pharmacological importance. As structural analogues of purines, they have shown adenosine receptor antagonist activty and some were found to act as vasodilators.2 As structural constituents of formycin A and B, they exhibited promising antibacterial a~tivity.’.~ They also have therapeutic value in the treatment of various cardiovascular disorder^.^.^ Earlier, Baraldi and co-workers reported the synthesis of ribofuranosyl pyrazolo[4,3-d]pyrimidine nucleosides containing 3methyl-6-substituted-7H-pyrazolo[4,3-d]pyrimidin-7-one as the aglycon m ~ i e t y . ~ These compounds are N-nucleoside analogues of formycin B and were found to have antiviral activity. A synthesis of the title compounds was envisaged from the condensation of methyl 4amino1 -methyl-3-n-propyl pyrazole-5-carboxylate (1) with triethyl orthoformate (TEOF) in the presence of aromatic amines. The required amino ester 1 was accessed from l-methyl-4-Ntro-3n-propyl pyrazole-5-carboxylic acid* through a two-step synthetic sequence. An equimolar mixture of 1 and p-toluidine in combination with slight excess of TEOF was refluxed in dry xylene for 6 h. Dilution of the reaction mixture with n-hexane yielded 1-methyl-6-(4methylphenyl)-3-n-propyl-6,7-dihydro1 H-pyrazolo[4,3-dJpyrimidin-7-one (2a), characterized based on its IR, Mass, IH and I3C NMR spectral data and elemental analysis. To test its generality, this method was extended to seven other aromatic amines and in all the cases corresponding pyrazolo[4,3-d]pyrimidines (2b-h) were isolated in good yields.