In this study, twenty 3,5-diaryl-4,5-dihydro-1H-pyrazole derivatives with hydroxyl(s) (1a–1p, 2a–2d) were synthesized and their inhibitory activity on mushroom tyrosinase was examined. The results showed that among these compounds, 1-(5-(3,4-dihydroxyphenyl)-3-(4-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone 1d was found to be the most potent tyrosinase inhibitor with IC50 value of 0.301 μM. Kinetic study revealed that these compounds were competitive inhibitors of tyrosinase and their structure–activity relationships were investigated in this article.

A series of 2-arylbenzimidazole derivatives (3a–3p and 4a–4i) were synthesized and evaluated as potential antioxidant and antimicrobial agents. Their antioxidant properties were evaluated by various in vitro assays including hydroxyl radical (HO) scavenging, superoxide radical anion (O2−) scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging, and ferric reducing antioxidant power. Results demonstrated that compounds with hydroxyl group at the 5-position of benzimidazole ring had a comparable or better antioxidant activity in comparison to standard antioxidant tert-butylhydroquinone (TBHQ). Markedly, compound 4h that showed the highest HO scavenging activity (EC50 = 46 μM) in vitro had a significant reduction of 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH)-induced intracellular oxidative stress and H2O2-induced cell death. In addition, these compounds showed moderate to good inhibitory activity against Staphylococcus aureus selectively at noncytotoxic concentrations.Twenty-five 2-arylbezimidazole derivatives were synthesized and their potential antioxidant and antimicrobial activities were evaluated in our present study.

In our research, 14 benzyl benzoates with hydroxyl(s) (3–16) were synthesized and their inhibitory activity on mushroom tyrosinase was tested. Results indicated that among these compounds, 4-hydroxybenzyl 3,5-dihydroxybenzoate (3), 4-hydroxybenzyl 2,4-dihydroxybenzoate (5), 4-hydroxybenzyl 2,4,6-dihydroxybenzoate (7), 3-hydroxybenzyl 3,5-dihydroxybenzoate (8), 3-hydroxybenzyl 2,4-dihydroxybenzoate (10) exhibited inhibitory activity with their IC50 less than 10 μM. Further studies showed these five compounds were competitive inhibitors of tyrosinase and their structure–activity relationships were investigated in this article.Fourteen Benzyl benzoates with hydroxyl(s) (3–16) were synthesised and their inhibitory activity on mushroom tyrosinase were tested. Results indicated that five among these 14 compounds exhibited an IC50 value less than 10 μM, while 4-hydroxybenzyl 2,4-dihydroxybenzoate (5), got the best inhibitory activity. Further studies showed these five compounds were competitive inhibitors of tyrosinase.

A novel class of hydroxycoumarin derivatives were found to be potent α-glucosidase inhibitors. Their syntheses were reported and the structure−activity relationship was established. Kinetic enzymatic assays indicated that compound 10 was a slow-binding and noncompetitive inhibitor with a Ki value of 589 nM, while compound 11 was a competitive inhibitor with a Ki value of 4.810 μM. Among all hydroxycoumarin derivatives studied, compounds 10 and 11 exhibited the highest activities, were specific inhibitors of α-glucosidase, and could be exploited as the lead compounds for the development of potent α-glucosidase inhibitors. Compounds 10 and 11 were also selected for further discussion for the mechanism of enzymatic inhibition.

The inhibitory effects of vitamin C esters 1 and 2 on the diphenolase activity of mushroom tyrosinase have been studied. The results showed that compounds 1 and 2 inhibited tyrosinase with IC50 values of 0.58 and 0.16 mM, respectively. The dose–response curves demonstrated that compounds 1 and 2 not only lengthened the lag time, but also decreased the steady-state rate. The kinetic analyses showed that the inhibition by compound 2 was reversible and its mechanism was mixed type, which was different from compound 1 (irreversible inhibitor). Furthermore, the antioxidant activities of these compounds against hydroxyl radical scavenging, superoxide anion radical scavenging, and DPPH radical scavenging were also investigated. Compounds 1 and 2 exhibited potential antioxidant activities. In particular, compound 2 was found to be the most effective antioxidant, more potent than the well-known antioxidants vitamin C and TBHQ.