Pyrimidine Schiff Bases: Synthesis, Structural Characterization and Recent Studies on Biological Activities.

Recently, 5-[(4-ethoxyphenyl)imino]methyl-N-(4-fluorophenyl)-6-methyl-2-phenylpyrimidin-4-amine has been synthesized, characterized, and evaluated for its antibacterial activity against Enterococcus faecalis in combination with antineoplastic activity against gastric adenocarcinoma. In this study, new 5-iminomethylpyrimidine compounds were synthesized which differ in the substituent(s) of the aromatic ring attached to the imine group. The structures of newly obtained pyrimidine Schiff bases were established by spectroscopy techniques (ESI-MS, FTIR and 1H NMR). To extend the current knowledge about the features responsible for the biological activity of the new 5-iminomethylpyrimidine derivatives, low-temperature single-crystal X-ray analyses were carried out. For all studied crystals, intramolecular N-H∙∙∙N hydrogen bonds and intermolecular C-H∙∙∙F interactions were observed and seemed to play an essential role in the formation of the structures. Simultaneously, their biological properties based on their cytotoxic features were compared with the activities of the Schiff base (III) published previously. Moreover, computational investigations, such as ADME prediction analysis and molecular docking, were also performed on the most active new Schiff base (compound 4b). These results were compared with the highest active compound III.

Synthesis, Crystal Structure, and Biological Evaluation of Novel 5-Hydroxymethylpyrimidines.

Pyrimidine displays a wide array of bioactivities, and thence, it is still considered a potent unit of new drug research. Its derivative, 5-hydroxymethylpyrimidine, can be found as a scaffold of nontypical nitrogen bases in DNA and as a core of some natural bioactive compounds. In this study, we obtained a series of 5-hydroxymethylpyrimidines that vary in the 4-position by the reduction of proper esters. All compounds were characterized by spectroscopic analysis, and single-crystal X-ray diffraction was performed for some of them. Biological investigations estimated cytotoxic properties against normal (RPTEC) and cancer (HeLa, HepaRG, Caco-2, AGS, A172) cell lines. It was found that the derivatives with an aliphatic amino group at the 4-position are generally less toxic to normal cells than those with a benzylsulfanyl group. Moreover, compounds with bulky constituents exhibit better anticancer properties, though at a moderate level. The specific compounds were chosen due to their most promising IC50 concentration for in silico study. Furthermore, antimicrobial activity tests were performed against six strains of bacteria and one fungus. They demonstrated that only derivatives with at least three carbon chain amino groups at the 4-position have weak antibacterial properties, and only the derivative with 4-benzylsulfanyl constituent exhibits any antifungal action.

A New Pyrimidine Schiff Base with Selective Activities against Enterococcus faecalis and Gastric Adenocarcinoma.

Enterococcus faecalis is known as a significant nosocomial pathogen due to its natural resistance to many antibacterial drugs. Moreover, it was found that E. faecalis infection causes inflammation, production of reactive oxygen species, and DNA damage to human gastric cancer cells, which can induce cancer. In this study, we synthesized and tested the biological activity of a new Schiff base, 5-[(4-ethoxyphenyl)imino]methyl-N-(4-fluorophenyl)-6-methyl-2-phenylpyrimidin-4-amine (3), and compared its properties with an analogous amine (2). In the biological investigation, 3 was found to have antibacterial activity against E. faecalis 29212 and far better anticancer properties, especially against gastric adenocarcinoma (human Caucasian gastric adenocarcinoma), than 2. In addition, both derivatives were non-toxic to normal cells. It is worth mentioning that 3 could potentially inhibit cancer cell growth by inducing cell apoptosis. The results suggest that the presence of the -C=N- bond in the molecule of 3 increases its activity, indicating that 5-iminomethylpyrimidine could be a potent core for further drug discovery research.

Synthesis, crystal structure and cytotoxic activity of novel 5-methyl-4-thiopyrimidine derivatives.

This article presents the synthesis of three new 4-thiopyrimidine derivatives obtained from ethyl 4-methyl-2-phenyl-6-sulfanylpyrimidine-5-carboxylate as the starting material, namely, ethyl 4-[(4-chlorobenzyl)sulfanyl]-6-methyl-2-phenylpyrimidine-5-carboxylate, C21H19ClN2O2S, (2), {4-[(4-chlorobenzyl)sulfanyl]-6-methyl-2-phenylpyrimidin-5-yl}methanol, C19H17ClN2OS, (3), and 4-[(4-chlorobenzyl)sulfanyl]-5,6-dimethyl-2-phenylpyrimidine, C19H17ClN2S, (4), which vary in the substituent at the 5-position of the pyrimidine ring. The compounds were characterized by 1H NMR, 13C NMR, IR and mass spectroscopies, and also elemental analysis. The molecular structures were further studied by single-crystal X-ray diffraction. Compound (2) crystallizes in the space group P-1 with one molecule in the asymmetric unit, whereas compounds (3) and (4) crystallize in the space group P21/c with two and one molecule, respectively, in their asymmetric units. The conformation of each molecule is best defined by the dihedral angles formed between the pyrimidine ring and the planes of the two aryl substituents attached at the 2- and 4-positions. The only structural difference between the three compounds is the substituent at the 5-position of the pyrimidine ring, but they present significantly different features in the hydrogen-bond interactions. Compound (2) displays a one-dimensional chain formed by hydrogen bonds and the chains are further extended into a two-dimensional network. Molecules of (3) and (4) generate one-dimensional chains formed through intermolecular interactions. The study examines the cytotoxicity of compounds (3) and (4) against Human umbilical vein endothelial cells (HUVEC) and HeLa, K562 and CFPAC cancer cell lines. The presence of the hydroxymethyl and methyl groups in (3) and (4), respectively, offers an interesting new insight into the structures and behaviour of these derivatives. Compound (4) was found to be nontoxic against CFPAC and HUVEC; however, it shows weak activity against the HeLa and K563 cell lines. The presence of a hydroxy group in (3) significantly increases its cytotoxicity towards both, i.e. the cancer (HeLa, K562 and CFPAC) and normal (HUVEC) cell lines.

Synthesis and antibacterial properties of pyrimidine derivatives.

In this study, a series of syntheses was conducted on the pyrimidine system, obtaining bisulfite carboxyl derivatives 4 and hydroxy derivatives 5. In addition, a series of syntheses were carried out as a result of which both alkyl and aromatic amines were obtained. Then, the attempt was made to cyclize these amines in the Mannich reaction to pyrimido[4,5-d]pyrimidines 11, 12. After determination of chemical structure using physicochemical tests, also by means of crystallographic tests, all the newly obtained derivatives underwent microbiological tests on bacterial strains and fungi. The most interesting results of the microbiological tests are included later in the study.

5-[(4-Fluoro-anilino)meth-yl]-6-methyl-N-(4-methyl-phen-yl)-2-phenyl-pyrimidin-4-amine.

In the title compound, C(25)H(23)FN(4), the pyrimidine ring makes dihedral angles of 11.3 (2), 24.5 (2) and 70.1 (2)° with the phenyl and two benzene rings, and the mol-ecular conformation is stabilized by an intra-molecular N-H⋯N hydrogen bond with an S(6) ring motif. In the crystal, a pair of weak C-H⋯F hydrogen bonds link two mol-ecules into an inversion dimer with an R(2) (2)(16) motif. In the dimer, there is also an inter-molecular π-π stacking inter-action [centroid-centroid distance = 3.708 (4) Å] between the fluorinated benzene rings. The dimers are further linked by a C-H⋯π inter-action, so forming a column along the c axis.

5-[(4-Eth-oxy-anilino)meth-yl]-N-(2-fluoro-phen-yl)-6-methyl-2-phenyl-pyrimidin-4-amine.

The asymmetric unit of the title compound, C(26)H(25)FN(4)O, consists of two symmetry-independent mol-ecules, denoted A and B. The conformation of each mol-ecule is mainly determined by an intra-molecular N-H⋯N hydrogen bond, which closes a six-membered ring. The dihedral angles between the pyrimidine ring and the phenyl, fluorophenyl and ethoxyphenyl rings are 15.4 (2), 28.4 (2) and 77.5 (2)°, respectively, in mol-ecule A, and 15.9 (2), 2.7 (2) and 61.8 (2)° in mol-ecule B. Inter-molecular N-H⋯N hydrogen bonds and π-π stacking inter-actions between pyrimidine rings [centroid-centroid distance = 3.692 (4) Å] connect mol-ecules A and B into dimers and C-H⋯O hydrogen bonds link the dimers into zigzag chains along [011]. The (4-eth-oxy-anilino)methyl group of the B mol-ecule is disordered over two sets of sites, the occupancy factor for the major component being 0.900 (2).

Synthesis and antibacterial properties of pyrimidine derivatives.

The paper presents the synthesis of 1,2,3,7-tetraaryl-1,2,3,4-tetrahydropyrimido[4,5-d]pyrimidines. The structures of the obtained compounds were confirmed by crystallographic and spectroscopic analyses, and their antibacterial activity was tested on 9 selected strains, comparing chemical structure changes with increased microbiological activity. It was confirmed that aromatic residues in the hydrogenated pyrimidine ring constitute a significant element influencing antibacterial activity. Electronegative radicals increase microbiological activity, but decrease solubility of the compounds. Therefore, substituents should be selected in a manner ensuring a balanced effect. The presented crystal structure of 6f includes two stereoisomers, which we decided to isolate and compare the microbiological properties in further studies.