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.

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-2phenylpyrimidine-5-carboxylate, C 21 H 19 ClN 2 O 2 S, (2), {4-[(4-chlorobenzyl)sulfanyl]-6-methyl-2-phenylpyrimidin-5-yl}methanol, C 19 H 17 ClN 2 OS, (3), and 4-[(4-chlorobenzyl)sulfanyl]-5,6-dimethyl-2-phenylpyrimidine, C 19 H 17 ClN 2 S, (4), which vary in the substituent at the 5-position of the pyrimidine ring. The compounds were characterized by 1 H NMR, 13 C 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 P1 with one molecule in the asymmetric unit, whereas compounds (3) and (4) crystallize in the space group P2 1 /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 hydrogenbond 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.

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.

The asymmetric unit of the title compound, C26H25FN4O, consists of two symmetry-independent mol­ecules, denoted A and B. The conformation of each mol­ecule is mainly determined by an intra­molecular 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 mol­ecule A, and 15.9 (2), 2.7 (2) and 61.8 (2)° in mol­ecule B. Inter­molecular N—H⋯N hydrogen bonds and π–π stacking inter­actions between pyrimidine rings [centroid–centroid distance = 3.692 (4) Å] connect mol­ecules A and B into dimers and C—H⋯O hydrogen bonds link the dimers into zigzag chains along [011]. The (4-eth­oxy­anilino)methyl group of the B mol­ecule is disordered over two sets of sites, the occupancy factor for the major component being 0.900 (2).

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