Synthesis of 1-(2-Hydroxy-5-methylphenyl)-5-oxopyrrolidine-3-carboxylic Acid Derivatives as a Promising Scaffold Against Disease-Causing Bacteria Relevant to Public Health

Abstract

The increasing number of antibiotic-resistant pathogens forces us to accelerate the search for new antimicrobial agents. Based on this, we chose to synthesize a library of 1-(2-hydroxy-5-methylphenyl)-5-oxopyrrolidine-3-carboxylic acid derivatives and evaluate their antibacterial activity against various pathogens. A series of (2-hydroxy-5-methylphenyl)-5-oxopyrrolidine-3-carboxylic acid and its hydrazide derivatives were prepared and identified by the methods of IR, ¹H, and ¹³C NMR spectroscopy and a microanalysis technique. The resulting compounds were evaluated in vitro for their efficacy against the Gram-positive Staphylococcus aureus (ATCC 9144), Listeria monocytogenes (ATCC 7644), and Bacillus cereus (ATCC 11778) bacterial strains as well as the Gram-negative Escherichia coli (ATCC 8739) bacteria. Oxacillin, ampicillin, and cefuroxime were used as control antibiotics. Among the obtained compounds, hydrazone with a 5-nitrothien-2-yl fragment surpassed the control cefuroxime (7.8 μg/mL) against almost all strains tested. Hydrazone with a 5-nitrofuran-2-yl moiety showed a slightly lower but also potent effect on all bacterial strains. Moreover, hydrazone with a benzylidene moiety demonstrated very strong inhibition of S. aureus (3.9 μg/mL) in comparison with the antibacterial drug cefuroxime (7.8 μg/mL). In addition, some of these compounds exhibited remarkable bactericidal properties. In a complete biofilm disruption study, 5-nitrothienylhydrazone showed excellent results in disrupting S. aureus and E. coli biofilms. The test results show the potential of the newly obtained derivatives as a source of antibacterial agents. Therefore, further studies on the molecular optimization of these compounds are necessary for the development of new antibacterial drugs.

Keywords: 5-oxopyrrolidine; antibacterial activity; biofilm formation; heterocycles; hydrazone.

Figure 1

Naturally occurring alkaloids featuring a 2-pyrrolidone core.

Scheme 1

Synthesis of aza-heterocycles. Reagents and conditions: (i) itaconic acid, water, Δ, 2 h; (ii) MeOH, H₂SO₄, Δ, 8 h; (iii) N₂H₄·H₂O, i-PrOH, Δ, 8 h; (iv) phenyl isothiocyanate (for 5) or phenyl isocyanate (for 6), MeOH, Δ, 4 (for 5) or 6 (for 6) h; (v) aqueous 4% NaOH, Δ, 3 (for 7) or 4 (for 8) h; (vi) unsubstituted (9a) or the corresponding substituted (9b–d) benzene-1,2-diamine, 4N HCl, Δ, 24 h; (vii) EtI, KOH, K₂CO₃, DMF, r.t. 6 h. 2–10. 5, 7 X = S; 6, 8 X = O; 9a R = H; 9b R = F; 9c R = Cl; 9d R = Me.

Scheme 2

Synthesis of compounds 12–16. Reagents and conditions: (i) the corresponding carbaldehyde, i-PrOH, Δ, 2 h; (ii) the corresponding aromatic aldehyde, i-PrOH, Δ, 2 (for 12a–i) or 3 (for 12j) h; (iii) for 13a, b, acetone or ethyl methyl ketone, Δ, 4 h; for 13c, 4-aminoacetophenone, glacial AcOH, i-PrOH, Δ, 20 h; (iv) isatin, MeOH, AcOH, Δ, 3 h; (v) pentane-2,4-dione, conc. hydrochloric acid, i-PrOH, Δ, 2 h; (vi) hexane-2,5-dione, glacial AcOH, i-PrOH, Δ, 4 h. 11a Het = thien-2-yl; 11b Het = 5-nitro-2-thienyl; 11c Het = furan-2-yl; 11d Het = 5-nitrofuran-2-yl; 12a Ar = Ph; 12b Ar = 2,4-F₂Ph; 12c Ar = 4-ClPh; 12d Ar = 4-BrPh; 12e Ar = 4-O₂NPh; 12f Ar = 4-MePh; 12g Ar = 4-Me₂NPh; 12h Ar = 2,3,4-(MeO)₃Ph; 12i Ar = 3,4,5-(MeO)₃Ph; 12j Ar = 1-naphthyl; 13a R = R¹ = Me; 13b R = Me, R¹ = Et; 13c R = Me, R¹ = 4-H₂N-Ph.

Figure 2

In vitro MIC and MBC of the tested compounds (2–16) against Staphylococcus aureus (ATCC 9144), expressed in µg/mL. The antibacterial activity of the compounds was compared with standard antibiotics: oxacillin, ampicillin, and cefuroxime.

Figure 3

In vitro MIC and MBC of the tested compounds (2–16) against expressed in L. monocytogenes (ATCC 7644) µg/mL. The antibacterial activity of the compounds was compared with standard antibiotics: oxacillin, ampicillin, and cefuroxime.

Figure 4

In vitro MIC and MBC of the tested compounds (2–16) against expressed in B. cereus (ATCC 11778) µg/mL. The antibacterial activity of the compounds was compared with standard antibiotics: oxacillin, ampicillin, and cefuroxime.

Figure 5

In vitro MIC and MBC of the tested compounds (2–16) against expressed in E. coli (ATCC 8739) µg/mL. The antibacterial activity of the compounds was compared with standard antibiotics: oxacillin, ampicillin, and cefuroxime.