Hetero Diels–Alder reaction: a novel strategy to regioselective synthesis of pyrimido[4,5-d]pyrimidine analogues from Biginelli derivative

Bicyclic 6 + 6 systems: the chemistry of pyrimido[4,5-d]pyrimidines and pyrimido[5,4-d]pyrimidines

The present study provides an overview of the chemistry and biological significance of pyrimido[4,5-d]pyrimidine and pyrimido[5,4-d]pyrimidine analogs as types of bicyclic [6 + 6] systems. The main sections include: (1) synthesis methods; (2) the reactivities of the substituents linked to the ring carbon and nitrogen atoms; and (3) biological applications. A discussion demonstrating the proposed mechanisms of unexpected synthetic routes is intended. The aim of this study is to discuss the synthetic significance of the titled compounds and to establish the biological characteristics of this class of compounds as studied to date, where the compounds have been applied on a large scale in the medical and pharmaceutical fields. This survey will help researchers in the fields of synthetic organic and medicinal chemistry to undertake and improve new approaches for the construction of new standard biological components.

A Five-Component Biginelli-Diels-Alder Cascade Reaction

A new multi-component condensation was discovered during the reaction of a urea, β-keto ester, and formaldehyde. In the presence of catalytic indium bromide, a Biginelli dihydropyrimidinone intermediate was further converted to a five-component condensation product through a formal hetero Diels-Alder reaction. The product structure was confirmed by NMR and NOE analysis, and the proposed stepwise mechanism was supported by the reaction of the Biginelli intermediate with ethyl 2-methylene-3-oxobutanoate.

A cascade reaction with iminium ion isomerization as the key step leading to tetrahydropyrimido[4,5-d]pyrimidines

A novel cascade reaction of aminopyrimidines 1 with N-alkyl amino acids or analogues was investigated. The keys to this cascade are the isomerization of an iminium ion formed between the aldehyde group in pyrimidine and the secondary amine of an amino acid, and subsequent cyclization to the neighboring amino group. This sequence could be useful in the synthesis of novel tetrahydropyrimido[4,5-d]pyrimidine libraries.

Synthesis and Evaluation of Antimicrobial Activity of Novel Hydrazino andN-Benzylidinehydrazino-Substituted 4,8-Dihydro-1H,3H-pyrimido[4,5-d]pyrimidin-2,7-dithiones

A number of novel pyrimido[4,5-d]pyrimidine-2,7-dithone derivatives bearing hydrazino and N-benzylidinehydrazino substitution were efficiently synthesized and screened for in vitro antibacterial activities against the representative panel of three Gram-positive and two Gram-negative bacteria. All the synthesized compounds showed the potent inhibitory action against Gram-positive bacteria. Particularly, N-benzylidinehydrazino-substituted compounds imparted profound effect. Furthermore, the Connolly-accessible surface area values were also calculated for the target compounds and correlated with the expressed biological activity.

Synthesis and QSAR studies on 5-[2-(2-methylprop1-enyl)-1H benzimidazol-1yl]-4,6-diphenyl-pyrimidin-2-(5H)-thione derivatives as antibacterial agents

A new series of 5-[2-(2-methylprop1-enyl)-1H benzimidazol-1yl]-4,6-diphenyl-pyrimidin-2-(5H)-thione derivatives [3a-q] has been synthesized and subjected to evaluate their antibacterial properties. All the synthesized compounds of the series displayed, remarkable activity in comparison to standard drug (ampicillin). A number of descriptors were tested to adjudge a quantitative correlation between activity and structural features. However, significant correlations have emerged between activity and physicochemical parameters viz. polarizability parameter (MR). Moreover, results are interpreted on the basis of multiple regression and cross-validation methodology.

Studies on synthesis and evaluation of quantitative structure–activity relationship of 10-methyl-6-oxo-5-arylazo-6,7-dihydro-5H-[1,3]azaphospholo[1,5-d][1,4]benzodiazepin-2-phospha-3-ethoxycarbonyl-1-phosphorus dichlorides

A new series of 10-methyl-6-oxo-5-arylazo-6,7-dihydro-5H-[1,3]azaphospholo[1,5-d][1,4]benzodiazepin-2-phospha-3-ethoxycarbonyl-1-phosphorus dichlorides 11a-p has been synthesized and evaluated as antimicrobial agents. Structures of all the synthesized compounds were established on the basis of elemental analysis and spectroscopic data. Quantitative structure-activity relationship (QSAR) investigations were applied to find out the correlation between the experimentally evaluated activity with various parameters of the compounds studied. QSAR equations showed that the molecular refractivity correlates significantly with the antimicrobial activity.