Imidazo purine 2,4-dione

Hydroxyethyl-l,3,6,7-tetrahydro-(8//)-imidazo[2,l-/]theophylline 256 was prepared by condensation of 7/3-bromoethyl-8-bromotheophylline 255 with 2-aminoethanol (Equation 112) <1999EJM1085>. Based on this strategy, a rapid access to 6,7-dihydro-l/f-thiazolo [2,3-/]purine-2,4-diones 258 was also described as in Equation (113) <1996PCJ194>. 

Imidazo[4,5-0]quinazoline-4,9-diones (406) were synthesized as purine mimics. They were obtained from the 4-amino precursor and Fremy s salt or from the 4,9-unsubstituted derivatives with nitrogen dioxide. In strong acid, a diprotonated quinone is present (86JOC4784). 

New pyrazolo[2,l purine 2,4-dione and imidazo[2,l- purine 2,4-dione derivatives have been identified as potent and selective human A3 adenosine receptor antagonists... 

The imino-amine (51.6) reacts at room temperature with aldehydes or ketones with the formation of purines. The products obtained from aldehydes are slowly oxidized (by loss of two hydrogen atoms from the pyrimidine ring) at room temperature, but the ketone-derived purines are stable and are accompanied by smaller amounts of an imidazo[l,S-c]imidazoIe. During cyclization, the nitrile group is converted into a carboxamide. Pentane-2,4-dione, 2-furfuraldehyde and but-2-enal give the fully aromatized purine as the main or only product isolated (in 38-49% yield). Stirring an imino-nitrile for several hours or heating it for a few minutes with an anhydride converts it into a fused pyrimidine. 

Fusion of imidazo[4,5-/]pyrido[2,l-6][l,3,5]oxadiazocine-5,12-dione (85) at 220-230°C results in ring contraction with elimination of carbon dioxide to produce the pyrido[2,l-/]purine (86), as shown in Equation (2) <82CPB3088>. 

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