Tetrahydroberberine (THB), otherwise known as canadine, is a natural alkaloid showing significant pharmacological properties and antioxidant protection against oxidative damage. Herein, we synthetized structurally complex THB analogues, namely pyrrolino-tetrahydroberberines (PTHBs) 4a–g, containing the pyrrolino[2,3-b]pyridine system, by means of the reactions of 1,2-diaza-1,3-dienes and 7,8-dihydroberberine. Aim of the study was to explore the in vitro antioxidant properties of PTHBs in comparison to THB thus to identify the most effective against free radical-induced oxidative injury, by using three different antioxidant tests: the ORAC method, the DNA nicking assay, and the DCFH-DA cellular assay. As a result, PTHB 4d emerged among the other THB analogues by exhibiting the best antioxidant properties. First, it was the only compound having an ORAC value completely comparable to that of THB, indicating the same ability to neutralize peroxyl radicals. Secondly, 4d showed an even better antioxidant capacity than THB in protecting DNA against ferrous ion-induced strand breaks. These observations were also confirmed in NCTC-2544 human keratinocytes exposed to hydrogen peroxide. Indeed, 4d protected cells against oxidation more efficiently than THB both in the short (1 and 3 h) and long (24 h) period of incubation, possibly suggesting increased cell membrane permeability and/or intracellular stability of 4d as compared to THB.

四氢小ber碱（THB），也称为卡达丁（canadine），是一种天然生物碱，显示出显着的药理特性和抗氧化损伤的抗氧化保护作用。本文中，我们通过1,2-二氮杂-1,3-二烯的反应合成了结构复杂的THB类似物，即吡咯烷-四氢小ine碱（PTHBs）4a-g，其中含有吡咯并[2,3- b ]吡啶体系。和7,8-二氢小ber碱。该研究的目的是探索与THB相比PTHBs的体外抗氧化特性，从而通过使用三种不同的抗氧化剂测试来鉴定最有效的抗自由基诱导的氧化损伤的方法：ORAC方法，DNA缺口分析和DCFH-DA细胞分析。结果，PTHB 4d通过表现出最佳的抗氧化性能，在其他THB类似物中脱颖而出。首先，它是唯一具有与THB完全可比的ORAC值的化合物，表明具有相同的中和过氧自由基的能力。其次，在保护DNA免受亚铁离子诱导的链断裂方面，4d表现出比THB更好的抗氧化能力。这些观察结果在暴露于过氧化氢的NCTC-2544人角质形成细胞中也得到了证实。实际上，在孵育的短时间（1小时和3小时）和长时间（24小时）中，4d都比THB更有效地保护细胞免受氧化，这可能表明与THB相比，4d的细胞膜通透性和/或细胞内稳定性增加。