查看更多>>摘要：? 2022 Elsevier LtdThe triterpenes represent one of the most reported subclasses of specialized metabolites from the plant kingdom. They play a key role in the protection of plants and their metabolism in addition to displaying a high structural diversity and large scale of biological activities. The scaffold can undergo several reactions like oxidation or substitution at different positions of the skeleton leading to the formation of several types of compounds. More specifically, triterpene dimer is a small group of compounds found in nature (from plants precisely). Until 2021, the chemical and pharmacological works reported in the literature indicated the identification of 90 natural dimeric triterpenes and 11 synthetic derivatives from 19 plants species and very few of them have been biologically evaluated for their antibacterial, antioxidant, antiproliferative or molluscicide activities. This review aims to compile the literature on the occurrence, chemistry and biological activities of the triterpenoid dimers. To attend this goal, a literature survey has been done in a number of online libraries including Scifinder, PubMed, Web of Science and Google Scholar using keywords terpene, triterpene, dimer, celastroloid without language restriction. This paper provides the easiest access to the information on triterpene dimers for readers and researchers in view to enhancing the continuity of research works on this topic.
查看更多>>摘要：? 2022 Elsevier LtdPhenolic acids represent naturally occurring antioxidants and play important role in free radicals scavenging. In this work, we have studied thermodynamics of the first step of primary antioxidant action for phenolic OH groups of benzoic and cinnamic acid derivatives, and their carboxylate anions. M06–2X/6–311++G(d,p) reaction enthalpies related to Hydrogen Atom Transfer (HAT), Single Electron Transfer – Proton Transfer (SET-PT), and Sequential Proton-Loss Electron-Transfer (SPLET) mechanisms were computed for model non-polar environment (benzene) and aqueous solution. The effect of acid structure on found reaction enthalpies was investigated, as well. For HAT, representing relevant reaction path in both environments, the lowest O–H bond dissociation enthalpies, BDE, were found for sinapic acid (347 kJ mol?1 in benzene and 337 kJ mol?1 in water). With two exceptions, carboxylate anions show lower BDEs than parent acids. In aqueous solution, enthalpies of the first step of SPLET from phenolic OH groups are low (135–199 kJ mol?1). It indicates thermodynamic feasibility of the mechanism for acids, as well as their carboxylate anions. Although enthalpies of electron transfer from dianions formed after successive deprotonations of carboxyl and phenolic groups in water are usually higher than BDEs, differences are within 25 kJ mol?1. Demethylation of OCH3 groups may affect radical scavenging activity of studied substances due to O–CH3 BDE considerably lower (230–269 kJ mol?1) in comparison to O–H ones.
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