Synthesis and properties of isoviagra. A 2-methyl-2H-pyrazolo[4,3-d]pyrirnidin-7-one isomer of viagra®

✍ Scribed by Mustafa M. El-Abadelah; Salim S. Sabri; Monther A. Khanfar; Hani A. Yasin; Wolfgang Voelter

• Publisher: Journal of Heterocyclic Chemistry
• Year: 2002
• Tongue: English
• Weight: 52 KB
• Volume: 39
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570390532

✦ Synopsis

Abstract

The synthesis and spectral properties (ir, ms, nmr) of a substituted 2‐methyl‐2__H__‐pyrazolo[4,3‐d]‐pyrimidin‐7‐one (3), an isomer of Viagra^®^, are described. The key synthon, 4‐amino‐1‐methyl‐5‐propyl‐3‐pyrazolecarboxamide (7), is prepared via the reaction of ethyl 2,4‐dioxoheptanoate with methylhydrazine, followed by cyclization, nitration, amidation, and nitro group reduction. Interaction of 7 with 2‐ethoxyben‐zoyl chloride yielded the respective bis‐amide (8) which was cyclized in polyphosphoric acid to the corresponding pyrazolo[4,3‐d]pyrimidin‐7‐one derivative 9. Chlorosulfonylation of 9, and subsequent treatment with 1‐methylpiperazine furnished iso Viagra (3).