Five N-amide substituted melatonin (MLT) derivatives were synthesized and evaluated for antioxidative activities, and compounds 9–12 showed higher electron spin resonance (ESR) response than MLT. 4-Bromobenzoyl and naphthoyl derivatives (10 and 11) presented stronger hydroxyl radical inhibitory effect than MLT in Fenton reaction. The substitution at the N1-position on the MLT core structure with acetyl (8), benzoyl (9), 4-bromobenzoyl (10), and naphthoyl (11) and N2-substitution with 4-bromobenzoyl (12) decreased the reducing power of the derivatives in ferric reducing antioxidant power (FRAP) assay. Compounds 8–11 also presented lower antioxidant capacity than their parent compound in 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) disodium salt (ABTS) assay; whereas, compound 12 presented radical scavenging activity similarly to MLT. All aryl derivatives (9–12) showed higher ability to quench peroxyl radicals than MLT about three times, especially the benzoylated derivatives (9 and 10) that presented the highest ability in oxygen radical absorbance capacity (ORAC) assay.
五种N-酰胺取代褪黑激素(MLT)衍生物被合成并评估其抗氧化活性,化合物9-12显示出比MLT更高的电子自旋共振(ESR)响应。4-溴苯甲酰和萘甲酰衍生物(10和11)在芬顿反应中表现出比MLT更强的羟自由基抑制作用。在MLT核心结构上N1位置的取代(乙酰基(8)、苯甲酰基(9)、4-溴苯甲酰基(10)和萘甲酰基(11))以及N2位置的4-溴苯甲酰基(12)减少了衍生物在铁还原抗氧化能力(FRAP)测定中的还原能力。化合物8-11在2,2'-叠氮基(3-乙基苯并噻唑啉-6-磺酸)二钠盐(ABTS)测定中也表现出比它们的母体化合物更低的抗氧化能力;而化合物12的自由基清除活性与MLT类似。所有芳基衍生物(9-12)对过氧自由基的熄灭能力比MLT高出约三倍,特别是苯甲酰化衍生物(9和10)在氧自由基吸收能力(ORAC)测定中表现出最高的能力。