Effect of N -Amide Substitution on Antioxidative Activities of Melatonin Derivatives

Five <i>N</i>-amide substituted melatonin (MLT) derivatives were synthesized and evaluated for antioxidative activities, and compounds <b>9</b>&#8722;<b>12</b> showed higher electron spin resonance (ESR) response than MLT. 4-Bromobenzoyl and naphthoyl derivatives (<b>10</b> and <b>11</b>) presented stronger hydroxyl radical inhibitory effect than MLT in Fenton reaction. The substitution at the <i>N1</i>-position on the MLT core structure with acetyl (<b>8</b>), benzoyl (<b>9</b>), 4-bromobenzoyl (<b>10</b>), and naphthoyl (<b>11</b>) and <i>N2</i>-substitution with 4-bromobenzoyl (<b>12</b>) decreased the reducing power of the derivatives in ferric reducing antioxidant power (FRAP) assay. Compounds <b>8</b>&#8722;<b>11</b> also presented lower antioxidant capacity than their parent compound in 2,2&#8242;-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) disodium salt (ABTS) assay; whereas, compound <b>12</b> presented radical scavenging activity similarly to MLT. All aryl derivatives (<b>9</b>&#8722;<b>12</b>) showed higher ability to quench peroxyl radicals than MLT about three times, especially the benzoylated derivatives (<b>9</b> and <b>10</b>) that presented the highest ability in oxygen radical absorbance capacity (ORAC) assay.

Abstract licence: CC BY

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