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Synthesis and biological evaluation of a new class of 1-aryl-4-amino-1H-pyrazolo[3,4-d]pyrimidine derivatives are reported. A preliminary cellular assay system using the tumor cell line A431 responding to epidermal growth factor (EGF) for its growth, shows that the new compounds are potent inhibitors of cell growth. The inhibition of tumor cell proliferation is not associated with blockage of EGF receptor (EGFR), but substantially due to the interference with the signalling pathway at the level of Src tyrosine kinase and at the level of the downstream effector signal mitogen activated protein kinases (MAPKs), ERK1-2.

Single-crystal X-ray work has been carried out on the 2-benzyl-5-cyano-1,6-dihydro-6-oxo-3-methoxycarbonyl pyridine compound 1f. It crystallizes in the triclinic system space group P 1 . Minimum energy conformations of 2-(alkyl or arylalkyl) 5-cyano-1,6-dihydro-6-oxo-3-pyridine carboxylates showing different biological activity have been calculated by the semiempirical MNDO and AM1 methods. A most critical factor for the different inotropic activities (positive or negative) of compounds 1a–1f seems to be related to the location and the steric requirements of a ‘pocket’ in the receptor boundary that limit the size of the substituent at position 2.

The synthesis of ethyl or methyl esters of 2-substituted 5-acetyl-1,6-dihydro-6-oxo-3-pyridinecarboxylic acids 2a-d, f and 5 by reaction of sodium acetoacetamide with ethyl or methyl 2-dimethylaminomethylene-3-oxoalkanoates and ethyl 2-ethoxymethylene-4,4,4-trifluoro-3-oxobutanoate, respectively, has been described. These esters routinely gave the corresponding carboxylic acids by alkaline hydrolysis followed by acidification. As milrinone analogues, the above compounds were tested on contractile activity and frequency rate of spontaneously beating atria and on contractile activity of electrically-driven left atrium from reserpinetreated guinea pigs. Among the tested compounds, ethyl 5-acetyl-1,6-dihydro-6-oxo-2-phenyl-3-pyridinecarboxylate was found to be more potent and more effective than milrinone as a positive inotropic agent, while only marginally affecting the frequency rate.

The X-ray structural characterization of ethyl 5-cyano-1,6-dihydro-2-isopropyl-6-oxo-3-pyridine carboxylate is reported. Its solid state conformation has been compared with that of ethyl 2-methyl- and 2- tert -butyl-5-cyano-1,6-dihydro-6-oxo-3-pyridine carboxylate and with the results of a quantum chemical analysis at MNDO level in order to study the structure-activity relationship. Theoretical data indicate that the 2-substituent appears to be primarily responsible for the potencies and the different inotropic activities (positive or negative) of compounds 1–3 .

Among cannabinoid type-1 (CB1) receptor antagonists, those developed around the 1,5-diarylpyrazole scaffold of rimonabant (Acomplia™) are the most extensively investigated. In recent years, many SAR and QSAR reports on this topic have been published, focusing on the substitution and orientation of the N1 and C5 aryl functionalities and on the substituents at the 3-carboxamide position. In this context, the purpose of our study was to design and synthesize a set of 1-(2,4-dichlorophenyl)-5-arylpyrazoles strictly related to rimonabant, but with the hydrazide/amide group shifted from position 3 to position 4 of the pyrazole scaffold. The synthesized compounds were evaluated in vitro for their affinity on human CB1 and CB2 (cannabinoid type-2) receptors. Computational studies, performed both in the design step and after biological assays, contributed to rationalize the obtained results in terms of specific molecular interactions between antagonists and the human CB1 receptor.

The synthesis of ethyl and methyl esters of 2-substituted 5-cyano-1,6-dihydro-6-oxo-3-pyridinecar☐ylic acids by reaction of ethyl or methyl 2-dimethylaminomethylene-3-oxoalkanoates with sodium cyanoacetamide is described. These esters gave by alkaline hydrolysis the corresponding car☐ylic acids, which were decar☐ylated to 6-substituted 1,2-dihydro-2-oxo-3-pyridinecarbonitriles. As milrinone analogues, nearly all the above compounds were tested on contractile activity and frequency rate of spontaneously beating atria and electrically driven left atria from guinea pigs. Among the esters, ethyl 5-cyano-1,6-dihydro-2-methyl-6-oxo-3-pyridinecar☐ylate induced positive inotropic and chronotropic effects superior to those caused by milrinone. By increasing or branching the 2-substitutent, the activity decreased until faded or even reversed. Car☐ylic acids and nitriles were less active than milrinone. Some aspects of the structure-activity relationship of these compounds are discussed on the basis of X-ray structural analyses of 2-methyl, 2- t -butyl and 2-phenyl esters.