Antiradical and photoprotective activity of oxibiol, a novel water-soluble heteroaromatic antioxidant

5-Hydroxybenzo [d]thiazol-2-ylammonium N-acetyl-L-cysteinate (oxibiol) was synthesized and studied. This novel water-soluble azaheterocyclic antioxidant is a white crystalline solid (m.p. 148-150 degrees C) soluble in ethanol and water. The UV spectrum of oxibiol shows two absorption bands at 220 +/- 1 and 265 +/- 1 nm. Its antiradical activity was examined using a homogeneous hydrophilic chemiluminescent system. The emission quenching constant of oxibiol is (2.4 +/- 0.4) . 105 L mol(-1), which is nearly seven times that of the antioxidant mexidol widely used in current medical practice. Oxibiol efficiently inhibits the free radical oxidation of photoreceptor cells that is induced by iron(II) ions and UV and visible light in the presence of photosensitizers. Oxibiol is especially effective in suppressing the photoinduced lipid peroxidation sensitized by lipofuscin granules from human retinal pigment epithelial cells. Oxibiol is highly resistant when exposed to UV light. Being a novel, more efficient and photoresistant antioxidant, oxibiol can also find other medical applications and replace the widely used agent mexidol.