Hydroxyl radical scavenging of the compatible solute ectoine generates two N-acetimides

Living cells employ various defence mechanisms against reactive oxygen species and free radicals. Besides protecting enzymes such as superoxide dismutase, catalase and peroxidase, non-enzymatic antioxidant molecules also play an important role as radical scavengers. Within bacteria the amino acid derivative ectoine (2-methyl-3,4,5,6-tetrahydropyrimidine-4-carboxylate) is the most abundant compatible solute and stress protectant. Although this compound is already produced commercially for applications as moisturizer and skin-care product, it has been a matter of debate whether ectoine also has radical-scavenging activity. Here we report on its hydroxyl radical scavenging activity in comparison to other compatible solutes and describe the reaction products obtained when ectoine is exposed to hydroxyl radicals generated by the Fenton reaction. In a sodium salicylate scavenging test system this compatible solute performed as well as mannitol. As a consequence of its reaction with hydroxyl radicals, ectoine was converted into two major products: N-acetimide aspartate and N-acetimide-β-alanine. We propose a reaction mechanism in which the heterocycle of the compatible solute ectoine is cleaved and further oxidized at the C-terminus. The proven radical scavenging ability of ectoine will help to explain observed effects as anti-inflammatory compound in skin, lung and bowel disease.