Synthesis and antioxidant properties of diphenylmethane derivative bromophenols including a natural product

Bromination of bis(3,4-dimethoxyphenyl)methanone (5) gave four products (6–9) with mono, di, tri, and tetra Br under different conditions. Reduction and demethylation reactions of product 9 with tetra Br were performed, consecutively and a natural product, 5,5′-methylene bis(3,4-dibrombenzene-1,2-diol) (1), was obtained with a 53% yield. Five derivatives, (13–17) (bromophenols), of 1 were also synthesised. The antioxidant and radical scavenging activities of bromophenols 1 and 13–17 were determined by employing various in vitro assays such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH^?), 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid (ABTS^?+), N,N-dimethyl-p-phenylenediamine dihydrochloride radical cation (DMPD^?+), and superoxide anion radical (O₂^?-) scavenging, reducing ability determination by the Fe³⁺-Fe²⁺ and Cu²⁺-Cu⁺ cupric reducing antioxidant capacity (CUPRAC) transformation methods, hydrogen peroxide scavenging, and ferrous ion (Fe²⁺) chelating activities. Moreover, these activities were compared to those of synthetic standard antioxidant compounds such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol, and trolox. The results showed that the synthesised bromophenols had effective antioxidant power.