Binding of cationic and neutral phenanthridine intercalators to a DNA oligomer is controlled by dispersion energy: quantum chemical calculations and molecular mechanics simulations

Correlated ab initio as well as semiempirical quantum chemical calculations and molecular dynamics simulations were used to study the intercalation of cationic ethidium, cationic 5-ethyl-6-phenylphenanthridinium and uncharged 3,8-diamino-6-phenylphenanthridine to DNA. The stabilization energy of the cationic intercalators is considerably larger than that of the uncharged one. The dominant energy contribution with all intercalators is represented by dispersion energy. In the case of the cationic intercalators, the electrostatic and charge-transfer terms are also important. The DeltaG of ethidium intercalation to DNA was estimated at -4.5 kcal mol(-1) and this value agrees well with the experimental result. Of six contributions to the final free energy, the interaction energy value is crucial. The intercalation process is governed by the non-covalent stacking (including charge-transfer) interaction while the hydrogen bonding between the ethidium amino groups and the DNA backbone is less important. This is confirmed by the evaluation of the interaction energy as well as by the calculation of the free energy change. The intercalation affects the macroscopic properties of DNA in terms of its flexibility. This explains the easier entry of another intercalator molecule in the vicinity of an existing intercalation site.     

Novel Total Synthesis of Mansouramycin B

A novel total synthesis of Mansouramycin B ( 1 ) was performed via 10 steps in 28% overall yield starting from the readily available and cheap salicylaldehyde. Two key steps of this total synthesis are noteworthy. The first one is base‐promoted one‐pot aerobic aromatization of N‐tosyltetrahydroisoquinoline 6 , the second one is oxidation of 5‐hydroxy‐3‐methyl‐isoquinoline 8 with iodobenzene diacetate [PhI(OAc)₂].     

Solvent‐Free Photooxidation of Alkanes by Dioxygen with 2,3‐Dichloro‐5,6‐dicyano‐p‐benzoquinone via Photoinduced Electron Transfer

Photooxidation of alkanes by dioxygen occurred under visible light irradiation of 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) which acts as a super photooxidant. Solvent‐free hydroxylation of cyclohexane and alkanes is initiated by electron transfer from alkanes to the singlet and triplet excited states of DDQ to afford the corresponding radical cations and DDQ^??, as revealed by femtosecond laser‐induced transient absorption measurements. Alkane radical cations readily deprotonate to produce alkyl radicals, which react with dioxygen to afford alkylperoxyl radicals. Alkylperoxyl radicals abstract hydrogen atoms from alkanes to yield alkyl hydroperoxides, accompanied by regeneration of alkyl radicals to constitute the radical chain reactions, so called autoxidation. The radical chain is terminated in the bimolecular reactions of alkylperoxyl radicals to yield the corresponding alcohols and ketones. DDQ^??, produced by the photoinduced electron transfer from alkanes to the excited state of DDQ, disproportionates with protons to yield DDQH₂.     

Microwave-assisted synthesis of 5-aryl-3-hydroxy-2-oxindole derivatives and evaluation of their antiglaucomic activity

A set of new 5-aryl-3-hydroxy-2-oxindoles was synthesized by decarboxylative condensation of the corresponding 5-aryl-substituted isatins with malonic or cyanoacetic acids under microwave irradiation. The antiglaucomic activity of the obtained compounds was evaluated. The most water soluble compounds can reduce the intraocular pressure (IOP) up to 2 Torr.     

新型羟基和醌碳自由基产生的分子机理

羟基自由基（·OH）被公认是生物系统中最具活性的活性氧物种,能导致生物体内DNA等生物大分子氧化损伤. 目前,最被广泛接受的·OH的产生机理是过渡金属离子催化的Fenton反应. 五氯酚(PCP)是一种重要的生物杀灭剂,主要用作木材保护. 采用电子自旋共振二级自旋捕获等分析手段,发现H₂O₂和五氯酚的代谢产物之一四氯苯醌（TCBQ）能通过不依赖于金属离子的途径产生·OH;进一步的研究发现是TCBQ,而非其相应的半醌自由基对·OH的产生极其重要. 基于这些数据和分析,提出以下新型·OH产生分子机理：H₂O₂对TCBQ进行亲核攻击形成不稳定的三氯氢过氧基苯醌中间产物,其可均裂产生·OH. 综合采用电子自旋共振自旋捕获和其他分析方法,第1次检测到一种新型的以碳为中心的醌自由基.     

Escherichia coli Modulator of Drug Activity B (MdaB) Has Different Enzymological Properties to Eukaryote Quinone Oxidoreductases

Some quinone oxidoreductases exhibit negative cooperativity towards inhibitors. In human NQO1, this is mediated by flexibility around glycine‐150. Here we investigated the eubacterial orthologue, Modulator of Drug Activity B (MdaB) to determine if it shows cooperativity towards substrates or inhibitors and to investigate molecular recognition of the inhibitor, dicoumarol. Like human NQO1, MdaB did not show cooperativity towards substrates. However, unlike NQO1, it was only weakly inhibited by dicoumarol. Alanine‐127 in MdaB is the structurally equivalent residue to Gly‐150 in human NQO1. With the intention of increasing protein flexibility in MdaB, this alanine was altered to glycine. This change did not increase cooperativity towards inhibitors or NADPH. Based on structural alignment to NQO1 in complex with dicoumarol, an asparagine in the active site was changed to alanine to reduce steric hindrance. This change resulted in enhanced inhibition by dicoumarol, but the inhibition was not cooperative. Both changes were then introduced simultaneously. However, the additional increase in flexibility afforded by the change to glycine did not enable negative cooperativity towards dicoumarol. These results have implications for the evolution of quinone oxidoreductases and their potential use as biocatalysts.     

The Antileukemic Effect of Xestoquinone,A Marine-Derived Polycyclic Quinone-Type Metabolite,Is Mediated through ROS-Induced Inhibition of HSP-90

Xestoquinone is a polycyclic quinone-type metabolite with a reported antitumor effect. We tested the cytotoxic activity of xestoquinone on a series of hematological cancer cell lines. The antileukemic effect of xestoquinone was evaluated in vitro and in vivo. This marine metabolite suppressed the proliferation of Molt-4, K562, and Sup-T1 cells with IC₅₀ values of 2.95 ± 0.21, 6.22 ± 0.21, and 8.58 ± 0.60 µM, respectively, as demonstrated by MTT assay. In the cell-free system, it inhibited the activity of topoisomerase I (Topo I) and II (Topo II) by 50% after treatment with 0.235 and 0.094 μM, respectively. The flow cytometric analysis indicated that the cytotoxic effect of xestoquinone was mediated through the induction of multiple apoptotic pathways in Molt-4 cells. The pretreatment of Molt-4 cells with N-acetyl cysteine (NAC) diminished the disruption of the mitochondrial membrane potential (MMP) and apoptosis, as well as retaining the expression of both Topo I and II. In the nude mice xenograft model, the administration of xestoquinone (1 μg/g) significantly attenuated tumor growth by 31.2% compared with the solvent control. Molecular docking, Western blotting, and thermal shift assay verified the catalytic inhibitory activity of xestoquinone by high binding affinity to HSP-90 and Topo I/II. Our findings indicated that xestoquinone targeted leukemia cancer cells through multiple pathways, suggesting its potential application as an antileukemic drug lead.     

依赖新辅基PQQ甲醇脱氢酶的研究

生长在以甲醇作唯一碳源的甲基营养菌（Ｍｅｔｈｙｌｏｔｒｏｐｈｉｃｂａｃｔｅｒｉａ）Ｎｏ．２细胞,经超声波破碎,缓冲液抽提,ＤＥＡＥ－和ＣＭ－纤维素柱层析等纯化步骤,可得到纯化的甲醇脱氢酶（ＭＤＨ）,其比活力为５．７ｕ／ｍｇ．该酶进行不连续聚丙烯酰胺凝胶电泳后,用相应的试剂分别染色,其蛋白质,酶活性和醌蛋白谱带均呈现一条迁移距离相同的主带．该酶由两个β亚基（６０ｋｂ）和两个α亚基（１０ｋｂ）构成,每个α亚基束缚一个新辅基ＰＱＱ（吡咯喹啉醌）．光谱分析显示,２９０ｎｍ有一肩峰,３４５ｎｍ有一特征峰,４００ｎｍ有一平台．这些数据表明,ＭＤＨ是一种依赖ＰＱＱ的醌酶     

竹红菌甲素衍生物13-SO3Na-DDHA电化学及光诱导还原的研究

本工作研究了化合物13-SO₃Na-DDHA在不同pH的缓冲溶液中的电化学氧化还原行为。实验证明:化合物中羰基的还原电位与pH之间存在线性关系,其直线的斜率为60mV/pH.并证明了此过程为一步两电子、两质子还原过程:Q+2H⁺+2e=QH₂.DMF作为非质子溶剂,具有很好的稳定自由基的作用。向缓冲溶液中加入DMF后,化合物13-SO₃Na-DDHA为两步单电子还原过程,相应溶液中的光诱导电子转移吸收光谱证实了以上电化学的结果。     

Selective synthesis of 2-(5-oxo-1-arylhex-1-yn-3-yl)phenyl benzoates via FeCl3-mediated cascade reactions of propargylamines with β-enamino ketones

A mild and efficient FeCl₃-mediated cascade reaction of ortho-hydroxyl propargylamines with β-enamino ketones has been developed. This protocol provided a practical and selective method to synthesize 2-(5-oxo-1-arylhex-1-yn-3-yl)phenyl benzoates via in situ generated alkynyl o-quinone methides following a cascade intermolecular 1,4-conjugate addition/intramolecular nucleophilic addition/reverse Claisen condensation/hydrolysis pathway. Furthermore, a series of 2-(3-oxo-1-arylbutyl)phenyl benzoates with good functional group tolerance were prepared in good to high yields under these reaction conditions.