Antimicrobial activities of the bromophenols from the red alga Odonthalia corymbifera and some synthetic derivatives

A series of bromophenols was obtained by isolation from red alga Odonthalia corymbifera and by reactions of bis(hydroxyphenyl)methanes with bromine. New bromophenols including 3,3′,5,5′-tetrabromo-2,2′,4,4′-tetrahydroxydiphenylmethane (10), a regioisomer of the potent antimicrobial natural product, together with known derivatives were synthesized in high yield. All of the isolated and synthesized compounds were tested for antimicrobial activity against Gram-negative, Gram-positive bacteria and fungi. The preliminary structure–activity relationship, to elucidate the essential structure requirements for antimicrobial activity, has been described. Among the isolated natural products 2,2′,3,3′-tetrabromo-4,4′,5,5′-tetrahydroxydiphenylmethane (4) was found to be the most active derivative against Candida albicans, Aspergillus fumigatus, Trichophyton rubrum, and Trichophyton mentagrophytes. The synthetic bromophenols 3,3′-dibromo-6,6′-dihydroxydiphenylmethane (13) and 3,3′,5,5′-tetrabromo-6,6′-dihydroxydiphenylmethane (14) showed potent antibacterial effect against Staphylococcus aureus, Bacillus subtilis, Micrococcus luteus, Proteus vulgaris, and Salmonella typhimurium.