Jūratė Šiugždaitė

Continuing our work in the field of synthesis and research of amino acids, their derivatives, and cyclization products, in this work, we synthesized various 3-(6-bromo-2-oxo-1,3-benzoxazol-3(2H)-yl)propanoic acid derivatives and investigated their antimicrobial activity. A total of eighteen synthesized chemical compounds (No. 1–18), including several structural analogues (e.g., 3a, 3b, 4a–4e, 8a–8m, 9a–9d), were evaluated for their antibacterial properties. The antibacterial activity was assessed using the Kirby–Bauer disk diffusion method, and inhibition zone diameters (mm) were measured against five representative bacterial strains: S. aureus, MRSA, B. subtilis, E. coli, and P. aeruginosa. The minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of the most active synthesized compounds were determined against representative Gram-positive and Gram-negative bacterial strains, including S. aureus, MRSA, B. subtilis, and E. coli. Overall, these results indicate that the tested compounds display selective antibacterial activity, mainly against Gram-positive bacteria, with compound 12 emerging as the most promising derivative in the series. The antibacterial activities of several synthesized compounds were systematically evaluated against S. aureus and MRSA over a 24 h incubation period, with optical density measured at ten time points. Bacterial growth was monitored spectrophotometrically at 600 nm (OD₆₀₀) at 1, 2, 3, 4, 5, 6, 7, 8, 20, and 24 h, enabling a detailed assessment of growth kinetics and the temporal dynamics of inhibition. The effect of compound 11 on the growth kinetics of S. aureus was evaluated by quantifying viable bacterial counts (log₁₀ CFU/mL) over a 6 h incubation period, and the results are presented in the time–kill curve. Compound 11 was selected for this experiment because it exhibited the most pronounced antibacterial activity against S. aureus in the disk diffusion assay. The cytotoxicity of compounds 9a, 11, 12, and 13 was evaluated at concentrations ranging from 125 to 1.95 µg/mL. The results showed a clear, concentration-dependent decrease in cytotoxicity for all tested compounds. The molecular structure of compound 3a was confirmed by a single-crystal X-ray diffraction.

The anti-inflammatory scaffold 5-aminosalicylic acid, which is widely used in therapeutic applications, was chosen for the synthesis of N-[3-(hydrazinecarbonyl)-4-hydroxyphenyl]acetamide (1) to enhance its antibacterial properties. The condensation of hydrazide 1 with aromatic aldehydes provided hydrazone derivatives 2a–f, whereas cyclocondensation reactions and other related transformations afforded five-membered heterocycles, including pyrrole 3, pyrazole 4, pyrrolidinone 7, oxadiazoles 9, 10, thiadiazole 14, and triazole 15. Additional modifications yielded acetylhydrazine derivative 11, which was O-alkylated to analogue 12. Antibacterial evaluation showed stronger activity against Gram-positive bacteria such as S. aureus and MRSA than against Gram-negative strains of E. coli and S. Enteritidis, consistent with differences in cell membrane permeability. Notably, derivatives containing pyrrolidinone 7, thiosemicarbazide 13, and 1,3,4-thiadiazole 14 exhibited potent bactericidal activity against S. aureus and MRSA, while hydrazones 2b, 2c, 2f, pyrrole 3, and pyrrolidinone 7 exhibited activity against E. coli. These results provide a practical strategy for the discovery of heterocyclic compounds and emphasise the potential of functionalised 5-aminosalicylic acid derivatives as prime candidates for the development of broad-spectrum antibacterial agents.

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.

Bacteria are the primary microorganisms responsible for nosocomial infections. This study investigates the antibacterial, biofilm-disrupting, and cytotoxic properties of essential oils and their emulsions for the treatment of nosocomial pathogens. The antibacterial activity of selected essential oils and their emulsions was evaluated against clinically relevant strains, including Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Pseudomonas aeruginosa, and Salmonella Enteritidis. Among the tested compounds, cinnamaldehyde exhibited the most potent antibacterial activity, with minimum inhibitory concentrations ranging from 1.31 to 2.62 mg/mL against both Gram-positive and Gram-negative bacteria. Other essential oils, such as cinnamon, eucalyptus, and pine, also demonstrated antibacterial effects, although their efficacy against Pseudomonas aeruginosa was comparatively limited. In biofilm assays, cinnamaldehyde effectively disrupted biofilms formed by S. aureus, methicillin-resistant Staphylococcus aureus, and Pseudomonas aeruginosa, indicating its potential for treating biofilm-associated infections. Cytotoxicity testing revealed that while cinnamon essential oil and cinnamaldehyde exhibited cytotoxic effects at concentrations above 0.1%, other essential oils such as basil and eucalyptus were non-toxic at the tested concentrations. These findings suggest that cinnamaldehyde is a promising agent for managing nosocomial infections, combining effective antibacterial and biofilm-disrupting properties with acceptable safety for non-target cells at appropriate doses.

In the present study, new series of benzoxazolin-2-one linked to a variety of hydrazones and azoles were synthesized and assessed for their antibacterial properties against different bacterial microorganisms. All the synthesized target compounds were characterized by ¹H NMR, ¹³C NMR and IR spectroscopy, and elemental analysis as well. The antibacterial activity of the synthesized compounds was evaluated according to the bacteriostatic and bactericidal activity against the tested pathogen strains by determining the minimum inhibition (MIC) and minimum bactericidal (MBC) concentrations and MBC/MIC ratios. The MIC was evaluated by the broth dilution and the MBC was evaluated by plating methods. The in vitro analysis suggested that some compounds, namely, amide, 5-chlorobenzimidazole, hydrazones with a 3-chloro substitution on the additional phenyl ring, and hydrazones with 2-furyl and 5-nitro-2-furyl substituents, demonstrated wide antibacterial activity against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Salmonella Enteritidis. The most sensitive strains appeared to be Gram-negative E. coli and Gram-positive B. subtilis, while S. aureus showed some resistance. The most resistant pathogen was found to be S. enteritidis. The remaining compounds demonstrated moderate to low antibacterial potential. The research results have shown that benzoxazolinone-based derivatives are suitable for the development of a library of compounds and can be used in the future development of antibacterial drugs against various Gram-positive and Gram-negative pathogens, which is of great importance in therapy practice.

In this study, clove essential oil (CL), eugenol (EU), and cinnamaldehyde (CI) were immobilized in starch sodium octenyl succinate (SSO) using an emulsification method. The main characteristics, stability, and biological properties of the prepared emulsions were established. Particle size analyses using dynamic light scattering showed that the smaller droplets were characteristic of emulsions containing CI (205–218 nm) and EU (181–236 nm), while the largest droplets were determined for CL emulsions (293–348 nm). Moreover, the highest antioxidant activity was determined for CL (79–83%) and EU (80–88%) emulsions, while CI emulsions showed the greatest antibacterial activity. The obtained emulsions were applied to the paper sheets and the bioactive properties of coated paper were studied. Evaluation of antioxidant properties revealed that high antioxidant activity reaching 76–92% and 87–91% was characteristic of coatings containing CL and EU, respectively. Meanwhile, coatings containing CI showed quite low antioxidant activity (4–9%) but demonstrated the greatest antimicrobial effect on Gram-negative and Gram-positive bacteria as well as yeasts. Hence, CL and EU emulsions could be used as effective natural antioxidants, whereas CI emulsions could be applied as an antimicrobial agent on cellulose-based substrates for a wide range of human health protection applications.

Benign prostatic hyperplasia (BPH) is an androgen-related non-neoplastic enlargement of the prostate gland that commonly affects both reproductive capabilities and the general health of intact dogs. The subclinical form of BPH can be challenging to diagnose due to a lack of clinical signs, even if rectal palpation is performed. Left untreated, this condition poses risks to the dogs’ health and breeding status. This study, involving 65 male dogs, aimed to investigate subclinical BPH through rectal palpation, ultrasonography, and analysis of canine prostatic-specific esterase (CPSE). Of the participants, 35 had subclinical BPH, and 30 served as a healthy control group. Dogs suspected of subclinical BPH, as determined by examination results from ultrasonography and CPSE analysis, underwent fine needle aspiration (FNA) guided by ultrasound to enhance diagnostic precision. Findings revealed distinct differences in rectal palpation and ultrasonography between subclinical BPH and healthy dogs. This study established diagnostic thresholds based on prostatic volume and CPSE values and proposed new thresholds for subclinical BPH. Additionally, results showed that prostate gland volume depended on the weight and the age of the dog. In conclusion, early detection of this condition is possible through various examinations, such as changes in ultrasound features, CPSE levels, and rectal palpation. All together, these methods can aid practitioners in early detection of BPH and assist with scheduling screening programs for dogs, ultimately promoting their overall health and reproductive well-being. In conclusion, we advocate for routine, non-invasive prostate screenings in breeding males, underlining the effectiveness of a combination of various multiple techniques for early subclinical BPH detection.

Increasing antimicrobial resistance among Gram-positive pathogens and pathogenic fungi remains one of the major public healthcare threats. Therefore, novel antimicrobial candidates and scaffolds are critically needed to overcome resistance in Gram-positive pathogens and drug-resistant fungal pathogens. In this study, we explored 1-(2-hydroxyphenyl)-5-oxopyrrolidine-3-carboxylic acid and its 3,5-dichloro-2-hydroxyphenyl analogue for their in vitro antimicrobial activity against multidrug-resistant pathogens. The compounds showed structure-dependent antimicrobial activity against Gram-positive pathogens (S. aureus, E. faecalis, C. difficile). Compounds 14 and 24b showed promising activity against vancomycin-intermediate S. aureus strains, and favorable cytotoxic profiles in HSAEC-1 cells, making them attractive scaffolds for further development. 5-Fluorobenzimidazole, having a 3,5-dichloro-2-hydroxyphenyl substituent, was found to be four-fold, and hydrazone, with a thien-2-yl fragment, was two-fold stronger than clindamycin against methicillin resistant S. aureus TCH 1516. Moreover, hydrazone, bearing a 5-nitrothien-2-yl moiety, showed promising activity against three tested multidrug-resistant C. auris isolates representing major genetic lineages (MIC 16 µg/mL) and azole-resistant A. fumigatus strains harboring TR34/L98H mutations in the CYP51A gene. The anticancer activity characterization demonstrated that the 5-fluorobenzimidazole derivative with a 3,5-dichloro-2-hydroxyphenyl substituent showed the highest anticancer activity in an A549 human pulmonary cancer cell culture model. Collectively these results demonstrate that 1-(2-hydroxyphenyl)-5-oxopyrrolidine-3-carboxylic acid derivatives could be further explored for the development of novel candidates targeting Gram-positive pathogens and drug-resistant fungi.

The p-aminobenzoic acid was applied for the synthesis of substituted 1-phenyl-5-oxopyrrolidine derivatives containing benzimidazole, azole, oxadiazole, triazole, dihydrazone, and dithiosemicarbazide moieties in the structure. All the obtained compounds were evaluated for their in vitro antimicrobial activity against Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes, Salmonella enteritidis, Escherichia coli, and Pseudomonas aeruginosa by using MIC and MBC assays. This study showed a good bactericidal activity of γ-amino acid and benzimidazoles derivatives. The antimicrobial activity of the most promising compounds was higher than ampicillin. Furthermore, two benzimidazoles demonstrated good antimicrobial activity against L. monocytogenes (MIC 15.62 µg/mL) that was four times more potent than ampicillin (MIC 65 µg/mL). Further studies are needed to better understand the mechanism of the antimicrobial activity as well as to generate antimicrobial compounds based on the 1-phenyl-5-oxopyrrolidine scaffold.

Thiazole derivatives attract the attention of scientists both in the field of organic synthesis and bioactivity research due to their high biological activity. In the present study, thiazole ring was obtained by the interaction of 1-(4-(bromoacetyl)phenyl)-5-oxopyrrolidine-3-carboxylic acid with thiocarbamide or benzenecarbothioamide, as well as tioureido acid. A series of substituted 1-(3-(1,3-thiazol-2-yl)phenyl)-5-oxopyrrolidines with pyrrolidinone, thiazole, pyrrole, 1,2,4-triazole, oxadiazole and benzimidazole heterocyclic fragments were synthesized and their antibacterial properties were evaluated against Gram-positive strains of Staphylococcus aureus, Bacillus cereus, Listeria monocytogenes and Gram-negative Pseudomonas aeruginosa, Escherichia coli and Salmonella enterica enteritidis. The vast majority of compounds exhibited between twofold and 16-fold increased antibacterial effect against the test-cultures when compared with Oxytetracycline.