Designed Synthesis, Cancer Chemopreventive Activities And Mechanisms Of Stilbene-chroman And Stilbene-benzopyrone Hybrids

Hybrid molecules are defined as chemical entities with two or more domains having different biological functions and dual activity. The hybrid approach has recently attracted much attention in medicinal chemistry and design of hybrid molecules encompassing two pharmacophores in one molecular scaffold is a niche area in a large field of drug discovery.We first synthesized three hydroxylated stilbene-chroman hybrids with resveratrol and vitamin E as the lead compounds by Wittig-Horner reaction and by the key step using EtSNa as the demethylating agent. We also synthesized a series of hydroxylated stilbene-benzopyrone hybrids (3-phenylcoumarins) including six novel o-hydroxy-methoxy substituted derivatives by Perkin reaction. We evaluated systematically the antioxidant, prooxidant and antiproliferative activities of the compounds, structure-activity relationship as well as the related mechanisms. The thesis includes the following details.1. Antioxidant activities and mechanisms of the hydroxylated stilbene-chroman hybrids(1) The DPPH·-and HNTTM·-scavenging activities and detailed mechanisms of the hydroxylated stilbene-chroman hybrids in different solvent systems were elucidated by kinetic and oxidative product analyses and redox potential determination. All of the hybrids exhibited remarkably higher radical-scavenging activity than the parent molecules (resveratrol and PMC). The formal abstraction of hydrogen atoms of the hybrids can follow four different chemical pathways depending on the character of the attacking radical, nature of the solvent, structure of the hybrids, and redox potentials of the species involved:direct hydrogen atom transfer (HAT), sequential proton loss electron transfer (SPLET), electron transfer then proton transfer (ETPT) and proton-coupled electron transfer (PCET) mechanism. Specifically, in methanol, that supports ionisation, the DPPH·-scavenging reaction of the hybrids occurs primarily by SPLET mechanism. In ethyl acetate, the reaction mechanism is only HAT for lla and the parent molecules (resveratrol and PMC), while, the other compounds (11b and 11c) could scavenge DPPH·by ETPT or PCET mechanism. Additionally, a SPLET mechanism does operate in the HNTTM·-scavenging reaction of the hybrids and PMC in chloroform/methanol.(2) All of the hybrids almost completely inhibited the AAPH-induced peroxidation of linoleic acid in tert-butyl alcohol/water (3/1, v/v) solution until the antioxidant was exhausted, and were more effective chain-breaking antioxidants than the parent molecules.(3) All of the hybrids displayed remarkably increased antihemolysis activity compared with the parent molecules.(4) All of the hybrids were more effective inhibitors against the production of NO induced by LPS in macrophage cells than the parent molecules, and 11c bearing o-dihydroxy groups ranked top with IC50 value of 4.9μM among the compounds investigated.2. Activity, mechanisms and biological implications of the hydroxylated stilbene-chroman hybrids as prooxidants in the presence of Cu(Ⅱ) ions.Prooxidant systems constructed by the hybrids and Cu(Ⅱ) ions could significantly induce pBR322 plasmid DNA damage by promoting production of reactive oxygen species, and their activity were remarkably more effective than the parent molecules (resveratrol and PMC). Compound 11c bearing o-dihydroxy groups was the most active among the hybrids examined. The interaction between 11c and Cu(Ⅱ) ions and the influence of ethylenediaminetetraacetic acid (EDTA), nitrogen gas, and pH value on the interaction were also studied to help elucidate the detailed prooxidant mechanism by using UV/Vis spectroscopic analysis. Interestingly, both acid and basic factors increased the reaction rate of 11c and Cu(Ⅱ) ions. Additionally, the intermediacy of phenoxyl radical was supported by isolation of benzofuran derivatives 12c from the Cu(Ⅱ)-mediated oxidation products. The formation of o-quinone with Michael reaction acceptor was also elucidated by the effect of phenylmethanethiol on UV/Vis spectroscopy of oxidation products due to the nucleophilic attack of the latter toα,β-unsaturated carbonyl moiety of o-quinone. On the basis of these observations, the mechanisms for 11c and Cu(Ⅱ) mediated DNA damage are proposed under acidic, neutral and basic conditions. More importantly, 11c and Cu(Ⅱ) could induce synergistically apoptosis of HepG2 cells by promoting production of reactive oxygen species.3. Hydroxylated 3-phenylcoumarins as antioxidants and antiproliferative agentsWe characterized hydroxylated 3-phenylcoumarins concerning their antioxidant activity against AAPH-induced pBR322 DNA strand breakage, and their antiproliferative effects on human promyelocytic leukemia HL60 and human lung adenocarcinoma epithelial A549 cells. Structure-activity relationship information suggests that introduction of o-hydroxy-methoxy groups and o-dihydroxy groups on the aromatic A ring could efficiently improve antiproliferative activity. Intriguingly, a new derivative,6-methoxy-7-hydroxy-3-(4’-hydroxyphenyl)coumarin, B1, behaved as a poor antioxidant but appeared to be the most potent antiproliferative agent among the compounds examined, and this activity was mediated by deregulation in cell cycle and induction of apoptosis.