2-Methyl-4H-pyrido(1,2-a)pyrimidin-4-one

2-Methyl-4H-pyrido[1,2-a]pyrimidin-4-one is a heterocyclic compound belonging to the [[pyrido(1,2-a)pyrimidine|pyrido[1,2-a]pyrimidine]] ring system. It consists of a pyridine ring fused to a pyrimidine ring through a shared nitrogen atom, with a methyl substituent at the 2-position and a ketone oxygen at the 4-position.

Synthesis

The correct structure of 2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one was established by Antaki and Petrow in 1951. Earlier workers, including Palazzo and Tamburini (1911), Seide (1925), Crippa and Scevola (1937), and Khitrik (1939), had assigned the incorrect 2-keto isomeric structure to the product obtained from 2-aminopyridine and ethyl acetoacetate. Antaki and Petrow demonstrated by an independent synthesis — the reaction of 2-bromopyridine with ethyl β-aminocrotonate — that the correct product was the 4-keto isomer. This assignment was confirmed independently by Adams and Pachter in 1952.

The synthesis was extended in 1958 to 3-substituted derivatives, including 3-acetyl and 3-cyano analogues, via condensation of ethyl ethoxymethyleneacetoacetate and cyanoacetate with 2-aminopyridine and its methyl derivatives. The 1958 study provided the first systematic spectroscopic characterisation of the pyrido[1,2-a]pyrimidine series, enabling structural distinction between bicyclic isomers by UV absorption.

Reference reagent

The 1958 synthesis is cited as the primary reference (Reference 1a) for the reagent ethyl ethoxymethyleneacetoacetate in the Encyclopedia of Reagents for Organic Synthesis (e-EROS), published by Wiley.

Pharmaceutical research

The pyrido[1,2-a]pyrimidin-4-one ring system has been cited as prior art in pharmaceutical patent research. Pfizer cited the 1951 and 1958 papers directly in patent specifications related to cardiovascular and antiasthmatic research.

Derivatives of the pyrido[1,2-a]pyrimidine scaffold have been reported to exhibit tranquiliser, antiallergic, antiulcerative, antiasthmatic, and bronchodilator activity, as well as analgesic activity and human platelet aggregation inhibitory properties.