Antioxidant and tyrosinase docking studies of heterocyclic sulfide derivatives containing a thymol moiety

Abstract

Fourteen heterocyclic sulfide derivatives (4–17) containing a thymol moiety and oxadiazole, thiadiazole, triazole, oxazole, thiazole, imidazole, pyridine or purine heterocycles were synthesized in three steps. The cupric, Cu(II), ion reducing antioxidant capacity of the compounds was examined, and molecular docking studies were performed to determine whether the sulfur, thymol or heterocyclic moieties interact with the Cu ions in tyrosinase, a type-3 copper enzyme. Using the CUPRAC assay, eight compounds (5–8, 10, 15–17) showed equal or better Cu (II) reducing capacity than trolox at neutral pH, with trolox equivalent antioxidant capacity (TEAC) coefficients ranging between 1.00 and 1.48. The compounds containing a thiadiazole moiety were most effective, with the methyl thiadiazole derivative (8) having the highest Cu(II) reducing capacity. Molecular docking studies of the sulfide derivatives with tyrosinase revealed that there were no direct interactions between the sulfur atom and the active site copper ions. However, the compounds displayed two different binding interactions with the histidine-Cu catalytic center. For compounds 4–13, the thymol portion was embedded in the active site cavity, while for compounds 14–17 the heterocyclic portion of the molecule approached the cavity.