Synthesis, biological evaluation and molecular docking analysis of novel benzopyrimidinone derivatives as potential anti-tyrosinase agents

Discovery of novel 1,2,4-triazole tethered β-hydroxy sulfides as bacterial tyrosinase inhibitors: synthesis and biophysical evaluation through in vitro and in silico approaches

In this study, a series of 1,2,4-triazole-tethered β-hydroxy sulfide scaffolds 11a-h was synthesized in good to remarkable yields (69-90%) through the thiolysis of oxiranes by the thiols in aqueous basic catalytic conditions. The synthesized 1,2,4-triazole-tethered β-hydroxy sulfides were screened against bacterial tyrosinase enzyme, and Gram-positive and Gram-negative bacterial cultures i.e., (S. aureus) Staphylococcus aureus & (E. coli) Escherichia coli. Among the synthesized derivatives, the molecules 11a (IC50 = 7.67 ± 1.00 μM), 11c (IC50 = 4.52 ± 0.09 μM), 11d (IC50 = 6.60 ± 1.25 μM), and 11f (IC50 = 5.93 ± 0.50 μM) displayed the better tyrosinase inhibitory activity in comparison to reference drugs ascorbic acid (IC50 = 11.5 ± 1.00 μM) and kojic acid (IC50 = 30.34 ± 0.75 μM). The molecule benzofuran-triazol-propan-2-ol 11c proved to be the most potent bacterial tyrosinase inhibitory agent with a minimum IC50 of 4.52 ± 0.09 μM, as compared to other synthesized counterparts and both standards (kojic acid and ascorbic acid). The compound diphenyl-triazol-propan-2-ol 11a and benzofuran-triazole-propan-2-ol 11c showed comparable anti-bacterial chemotherapeutic efficacy with minimum inhibitory concentrations (MIC = 2.0 ± 2.25 mg mL-1 and 2.5 ± 0.00 mg mL-1, respectively) against S. aureus bacterial strain in comparison with standard antibiotic penicillin (MIC = 2.2 ± 1.15 mg mL-1). Furthermore, among the synthesized derivatives, only compound 11c demonstrated better anti-bacterial activity (MIC = 10 ± 0.40 mg mL-1) against E. coli, which was slightly less than the standard antibiotic i.e., penicillin (MIC = 2.4 ± 1.00 mg mL-1). The compound 11c demonstrated a better binding score (-7.08 kcal mol-1) than ascorbic acid (-5.59 kcal mol-1) and kojic acid (-5.78 kcal mol-1). Molecular docking studies also validate the in vitro anti-tyrosinase assay results; therefore, the molecule 11c can be the lead bacterial tyrosinase inhibitor as well as the antibacterial agent against both types of bacterial strains after suitable structural modifications.

Lead Optimization of the 5-Phenylpyrazolopyrimidinone NPD-2975 toward Compounds with Improved Antitrypanosomal Efficacy

Human African trypanosomiasis (HAT) still faces few therapeutic options and emerging drug resistance, stressing an urgency for novel antitrypanosomal drug discovery. Here, we describe lead optimization efforts aiming at improving antitrypanosomal efficacy and better physicochemical properties based on our previously reported optimized hit NPD-2975 (pIC50 7.2). Systematic modification of the 5-phenylpyrazolopyrimidinone NPD-2975 led to the discovery of a R4-substituted analogue 31c (NPD-3519), showing higher in vitro potency (pIC50 7.8) against Trypanosoma brucei and significantly better metabolic stability. Further, in vivo pharmacokinetic evaluation of 31c and experiments in an acute T. brucei mouse model confirmed improved oral bioavailability and antitrypanosomal efficacy at 50 mg/kg with no apparent toxicity. With good physicochemical properties, low toxicity, improved pharmacokinetic features, and in vivo efficacy, 31c may serve as a promising candidate for future drug development for HAT.

Synthesis and In Silico Docking Study towards M-Pro of Novel Heterocyclic Compounds Derived from Pyrazolopyrimidinone as Putative SARS-CoV-2 Inhibitors

In addition to vaccines, antiviral drugs are essential in order to suppress COVID-19. Although some inhibitor candidates have been determined to target the SARS-CoV-2 protein, there is still an urgent need to continue researching novel inhibitors of the SARS-CoV-2 main protease 'Omicron P132H', a protein that has recently been discovered. In the present study, in the search for therapeutic alternatives to treat COVID-19 and its recent variants, we conducted a structure-based virtual screening using docking studies for a new series of pyrazolo[3,4-d]pyrimidin-4(5H)-one derivatives 5-13, which were synthesized from the condensation reaction of pyrazolopyrimidinone-hydrazide (4) with a series of electrophiles. Some significant ADMET predictions-in addition to the docking results-were obtained based on the types of interactions formed and the binding energy values were compared to the reference anti- SARS-CoV-2 redocked drug nirmatrelvir.

Tyrosinase inhibition by novel benzimidazole-thione Schiff base derivatives

Background:

Tyrosinase is the enzyme responsible for the conversion of tyrosine to dopaquinone, which is related to melanoma, neurodegenerative disorders, freckles, pigmented acne and age spots. Controlling the tyrosinase activity could be an important way for treating overproduction of melanin.

Objective:

The development of safe and specific tyrosinase inhibitors could be used to treat hypermelanosis.

Methods:

5-nitro-1H-benzo[d]imidazole-2(3H)-thione was synthesized from 4-nitro-o-phenylenediamine and carbon disulfide. The nitro group of 5-nitro-1H- S-1 ESI-HRMS benzo[d]imidazole-2(3H)-thione was reduced with iron powder. The 5-amino-1H-benzo[d]imidazole- 2(3H)-thione Schiff base derivatives were obtained by the reaction of 5-amino-1H-benzo[d]imidazole-2(3H)-thione with substituted benzaldehyde. The tyrosinase inhibitory activities were investigated. The studies of kinetic analysis, metal-chelating properties, docking and cytotoxicity were also performed.

Results:

All of the compounds showed strong tyrosinase inhibitory activities with 5-((4-nitrobenzylidene) amino)-1H-benzo [d]imidazole-2(3H)-thione (S-4) as the best tyrosinase inhibitor with an IC50 value of 4.8 ± 1.4 nM. Compound S-4 exhibited mixed type inhibition of mushroom tyrosinase, with Ki 15 nM and Kis 42 nM. Copper binding to S-4 was detected spectrophotometrically and 1-100 ìÌ S-4 displayed negligible cytotoxicity to murine B16 melanoma cells.

Conclusion:

Our results demonstrated that these benzimidazolethione Schiff base derivatives might be promising candidates as tyrosinase inhibitors.

Recent advances in the design and discovery of synthetic tyrosinase inhibitors

Tyrosinase is a copper-containing metalloenzyme that is responsible for the rate-limiting catalytic step in the melanin biosynthesis and enzymatic browning. As a promising target, tyrosinase inhibitors can be used as skin whitening agents and food preservatives, thus having broad potential in the fields of food, cosmetics, agriculture and medicine. From 2015 to 2020, numerous synthetic inhibitors of tyrosinase have been developed to overcome the challenges of low efficacy and side effects. This review summarizes the enzyme structure and biological functions of tyrosinase and demonstrates the recent advances of synthetic tyrosinase inhibitors from the perspective of medicinal chemistry, providing a better understanding of the catalytic mechanisms and more effective tyrosinase inhibitors.