All the synthesized compounds were shown to possess remarkable activities against the tested microbes, by showing a significant zone of inhibitions relative to that of the standard drugs used as shown in Table 2. Compound 1b showed prominent zone of inhibition of 30 mm against Aspergillus niger, while compounds 1a, 2d, 1c, 2b and 2c showed zone of inhibitions of 25 mm, 23 mm, 22 mm and 21 mm also, against Aspergillus niger. Compounds 1c, 1d, 2a, 2b and 2c each showed zone of inhibition of 20 mm against Bacillus subtilis, Pseudomonas aeruginosa, Candida albicans and Aspergillus niger. While, compounds 1a, 1b and 2a showed the lowest zone of inhibition of 13 mm each against Candida albicans, Staphylococus aureus and Escherichia coli. Thus, compounds 1a, 1b, 1c and 1d showed zone of inhibitions (25 mm, 30 mm and 23 mm) greater than the standard drugs (Fluconozole and ciprofloxacin) against Aspergillus nigger Singh et al. (2019).
Table 3 presents the results of the MIC and showed that compounds 1a, 1b, 1c, 1d and 2d possess the least MIC and inhibit the growth of Aspergillus niger at 12.5 µg/ml. While compounds 1b, 1c, 1d, 2a, 2b, 2c and 2d inhibit the growth of Candida albicans, Bacillus subtilis, MRSA, Escherichia coli, Pseudomonas aeruginosa and Aspergillus niger at 25 µg/ml. At 50 µg/ml, the growth of Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans, MRSA, Salmonella typhi, Staphylococus aureus and Escherichia coli were inhibited by compounds 1a, 1b, 1c, 1d, 2a, 2b, 2c and 2d. Compounds 1a, 1b, 1c, 1d, 2a, 2b, 2c and 2d inhibit the growth of Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, Staphylococus aureus, Bacillus subtilis and MRSA at 100 µg/ml.
The results of MBC/MFC showed that compounds 1a, 1b, 1c, 1d, 2a, 2b, 2c and 2d completely killed Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, Candida albicans and Aspergillus niger at 50 µg/ml, while a concentration of 100 µg/ml was required by compounds 1a, 1b, 1c, 1d, 2a, 2b, 2c and 2d to completely kill Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi, MRSA, Staphylococus aureus, Bacillus subtilis and Candida albicans as shown in Table 4.
Molecular docking studies
Each ligand/chalcones was successively docked to the binding site of the receptor (PDB: 5VBU), in order understand the mode of interaction of the triphenylamine chalcones with the target receptor. The analysis of the docking investigations provided us with an insight into the interactional relation of the novel triphenylamine chalcone analogues and human cytochrome P450 21A2 Hydroxyprogestrerone complex.
Table 5 shows the results of the binding affinity of the synthesized triphenylamine chalcones/ligands, which ranges between − 11.2 and − 9.4 kcal/mol. Compound 2a showed the highest docking score of − 11.2 kcal/mol, followed by compounds/ligands 1b and 2b which showed the binding energy of − 10.7 kcal/mol. While compounds 1c, 2c, 2d and 1a showed the docking scores of − 10.4, − 10.3, − 10.3 and − 10.1 respectively. Compound/ligand 1d showed the least binding score of − 9.4. The eight (8) ligands (novel triphenylamine chalcones analogues) showed highest binding score compared to that of the standard ligand/compounds (fluconazole and ciproflaxacin), which showed the docking scores of − 7.9 and − 7.3 kcal/mol, respectively.
Ligand/triphenylamine chalcone (2a) showed the highest binding affinity (− 11.2 kcal/mol) compared to other compounds. The interaction of the ligand/ triphenylamine chalcone (2a) with the target receptor (PDB: 5BVU) is shown in Figs. 3, 4 and 5. The interaction was observed with one hydrogen, one electrostatic attraction and six hydrophobic interactions (2.5449, 4.0569, 3.73562, 4.34337. 5.2863, 5.48907, 5.44454 and 5.35682 Å) with (ARG427, LYS121, VAL470, TRP202, VAL360, LEU364, LEU108, LEU430) as shown in Figs. 6 and 7. The two-dimensional structural form of the ligand-receptor complex is shown in Fig. 8. One hydrogen bond interaction with ARG427 was formed, due to the presence of OH group in the triphenylamine chalcone/chalcone (2a). The electrostatic interaction of the ligand/triphenylamine chalcone was detected with LYS121. Also, the hydrophobic interactions were noticed with VAL470, TRP202, VAL360, LEU364, LEU108 and LEU430 of the target receptor. The areas which represent the both hydrogen bond and hydrophobic interactions between the target receptor and the ligand/triphenylamine chalcone are shown in Figs. 6 and 7. Therefore, ligand/triphenylamine chalcone (2a) fits perfectly into the binding site of the receptor (PDB: 5VBU). All type of interactions, amino acids and bond length are shown in Table 6.
Correlation of molecular docking studies and antimicrobial studies
The docking studies of the synthesized chalcones with the binding site of the Human cytochrome P450 21A2 Hydroxyprogesterone (PDB: 5VBU) reveal that the binding affinity of the synthesized chalcones was in the range of − 11.2 to − 9.4 kcal/mol and showed highest binding score compared to that of the standard drugs (fluconazole and ciproflaxacin), with docking scores of − 7.9 and − 7.3 kcal/mol, respectively. Compound 2a displayed best docking score of -11.2 kcal/mol. The binding affinity, hydrogen bond and hydrophobic interactions of the synthesized chalcones and the standard controls (fluconazole and ciproflaxacin) are summarized in Tables 5 and 6. Compared to fluconazole, compound (1b) showed similar residual interactions (hydrophobic) profiles with amino acid residues TRP 202, LEU 110 and VAL 470, (1a) TRP 202 and LEU 110, (2a) VAL 470 and (1c) TRP 202. Similarly, compounds 1b, 1d and 2d showed Hydrophobic interactions LEU 40, as shown by the standard drug ciproflaxacin. Therefore, the synthesized compounds showed similarities in the residual amino acid interactions with clinical drugs against the Human cytochrome P450 21A2 Hydroxyprogesterone enzyme. The docking investigations are in agreement with the in vitro antimicrobial assay results. Hence, compound 1b indicated higher antifungal potential by showing similarities in residual interactions with amino acids residue as shown by standard antifungal drug (fluconozole), while the antimicrobial investigation reveals that compound 1b showed the highest ZOI of 30 mm, least MIC and MBC/MFC of 12.5 and 50 µg/ml against Aspergillus niger, respectively.