MOLECULAR DOCKING OF 5-PHENYL-5,6-DIHYDROTETRAZOLO-[1,5-c]QUINAZOLINES TO RIBOSOMAL 50S PROTEIN L2P (2QEX)

Summary. Given the presence of antimicrobial activity for various tetrazole derivatives and its condensed analogues, it was proposed to analyze 13 novel 5-phenyl-5,6-dihydrotetrazolo[1,5-c]quinazolines for molecular docking to ribosomal 50S protein L2P (2QEX) in comparison with Tedizolid, tetrazole-oxazolidinone antibiotic. Hence, 4-(5-methyl-5,6-dihydrotetrazolo[1,5-c]-quinazolin-5-yl)benzoic acid 12 proved to be the most probable in terms of antimicrobial activity in vitro as a result of in silico molecular


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of derivatives is to find a molecule with a proven mechanism of antimicrobial action to select a biological target for molecular docking.
The review by Gao F. at al. [5] covers the recent advances of tetrazole hybrids including tetrazole-azole, tetrazole-chalcone/coumarin/flavonoid, tetrazolefuran/pyrrole/thiophene, tetrazole-pyridine/pyrimidine, tetrazolequinoline/quinolone, tetrazole-β-lactam and tetrazole-sugar hybrids as potential antibacterial agents. And Tedizolid 25 [5,6] (formally known as torezolid and TR-700, trade name Sivextro, Fig. 1) and Tedizolid phosphate -tetrazole-oxazolidinone antibiotics, have already been marketed in 2014 year for the treatment of acute bacterial skin and skin structure infections caused by certain susceptible bacteria, including S. aureus (also methicillin-susceptible S. aureus/MSSA, methicillin-resistant S. aureus/MRSA, linezolid-resistant staphylococci), various Streptococcus species (S. pyogenes, S. agalactiae, S. anginosus, S. intermedius and S. constellatus), and E. faecalis. It was shown that Teridozolid can exert bacteriostatic activity via inhibition of protein synthesis by binding to the 50S ribosomal subunit of the bacteria [7]. Protein synthesis involves the action of ribosomes, multi-subunit complexes composed of both protein and ribosomal RNA (rRNA) substituents. The bacterial 70S ribosome comprises a small (30S) and a large (50S) subunit. Translocation along the length of a messenger RNA and concomitant protein synthesis involves the action of the A, P, and E sites of the peptidyltransferase center, which accepts charged aminoacyl-tRNAs and catalyzes the formation of peptide bonds between them.
Nevertheless, sequence analysis of 23S rRNA, rrlC gene and ribosomal protein genes rplA and rspQ, performed on the recovered WIS 423 tedizolid-mutant strain, revealed that this strain possessed the G2576T mutation in one of the six copies of 23S rRNA. These results support the evidence that spontaneous mutation leading to reduced Tedizolid susceptibility is present at low frequency events, including for CF-S. aureus strains [8].
Aim. Thus, based on the abovementioned data, new 5-phenyl-5,6dihydrotetrazolo [1,5-c]quinazolines could be promising antimicrobials, and to predict their activity by in silico molecular docking, 50S ribosomal protein was selected as the antimicrobial target.
Results and discussion. The studied 5-phenyl-5,6-dihydrotetrazolo[1,5-c]quinazolines differ in hydrogen-methyl-propyl substituent in the 5 th position, or/and have thrifluoromethyl, halogen, hydroxyl, cyano or carboxylic group in the phenyl substituent ( Fig. 1). The choice of substituent was conditioned by the fact, that incorporation of fluorine to phenyl ring can improve the therapeutic efficacy due to hydrogen bonding interactions at the active sites of enzyme [11], as well as carboxylic and hydroxyl groups enhance antibacterial properties [12].
In the result of molecular docking, the following affinities were found (Table 1). Table 1 Affinity to binding sites of 2QEX, with decreasing of score # 12 Tedizolid 11 As it can be seen from Table 1, the best affinity was shown by substance 12, scoring even higher (-8.7 kcal/mol), than the reference Tedizolid (-8.4 kcal/mol).
All other tetrazole derivatives had affinity lower than the reference compound. Still substance 11, 6, 10, 2 and 9 had affinity score more than 8 kcal/mol.
Analyzing the structure-affinity correlation, a score of 6 was of lower value than that of 12, and the same for: 5 / 9, and 13 / 7. So, introduction of carboxylic group to the 4 th position of 5-phenyl substituent along with addition of 5-methyl substituent into 5-phenyl-5,6-dihydrotetrazolo [1,5-c]quinazoline were the most favorable suggestions for substance to be promising ligand for the studied target, than prolongation of alkyl substituent to propyl into 5 th position. Also, 4-cyano or 4hydroxy group into the 5-phenyl ring were preferable groups too.
In the results of data comparisons of 5 to 4, 5 to 3, it was found that position and type of halogen atoms were practically not important. However, bromide substituent in the 4th position compared to its 2nd position in the 5-phenyl ring increased the affinity score to 0.1. Also, as it was expected, the introduction of 3trifluorophenyl substituent of 2, than of 4-methylphenyl of 1 or 4-chlorophenyl of 3 was more suitable for the studied target.
According to the number of the formed bonds (Table 2), substance 2 made the highest number of them -10 bonds due to CF 3 group. Among them were Carbon and Pi-Donor Hydrogen Bonds, electrostatic Pi-Anion bonds and Halogen (Fluorine) ones. And Tedizolid had formed only 5 bonds of the same type, except Halogen one.

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Conclusions. The 4-(5-methyl-5,6-dihydrotetrazolo(1,5-c]quinazolin-5-yl)benzoic acid 2.12 proved to be the most probable in terms of antimicrobial activity in vitro as a result of in silico molecular docking to the antimicrobial target 2QEX. Prediction of these series' ADME properties is ongoing too.