二氢叶酸还原酶抑制剂的高效毛细管电泳法筛选模型的建立与应用

建立了一种采用毛细管电泳法(CE)测定二氢叶酸还原酶(DHFR)反应动力学参数的新方法。以含0.002%Brij-35的50 mmol/L 的硼砂缓冲溶液（pH 9.18）作为电泳介质,检测波长280 nm,于19 min内实现了体系中各组分的基线分离。根据酶反应过程中反应物和反应产物的浓度变化计算有关反应动力学参数。将已知的氨甲喋呤、甲氧苄胺嘧啶和叶酸3种抑制剂作用于所建立的二氢叶酸还原酶体系,测得抑制剂的半数抑制浓度与文献值相接近,证明本体系可用于二氢叶酸还原酶抑制剂(DHFRI)的筛选。     

毛细管电泳法研究中草药有效成分对二氢叶酸还原酶的抑制作用

利用已建立的二氢叶酸还原酶抑制剂的毛细管电泳法筛选模型,研究了10种中草药有效成分对二氢叶酸还原酶的抑制作用.经实验测定发现木樨草素、表儿荼素、紫杉醇和槲皮素对二氢叶酸还原酶(DHFR)有抑制作用,且抑制效果为木樨草素>紫杉醇>表儿荼素>槲皮素.通过对产物NADP(氧化型辅酶Ⅱ)峰面积的定量测定,计算了4种抑制剂的抑制率.     

毛细管电泳测定鸡肝二氢叶酸还原酶活力及其抑制剂的抑制率

本文采用毛细管电泳法对亲和层析提取的鸡肝二氢叶酸还原酶（DHFR）的反应体系进行了研究,根据体系中反应物还原辅酶Ⅱ（NADPH）和反应产物氧化型辅酶Ⅱ（NADP）的浓度变化,测得鸡肝二氢叶酸还原酶的米氏常数Km=1.35×10^-5mol／L。将该体系用于鸡肝二氢叶酸还原酶抑制剂（DHFRIs）抑制率的测定,测得氨甲喋呤的半数抑制浓度（Ic50）为7.46×10^-8mol／L。     

N~8-去氮-N~5-取代四氢叶酸类似物的设计合成及生物活性研究

以2,4-二氨基-6-羟甲基吡啶并[3,2-d]嘧啶为原料,在4-位氨基转换为羟基后与对氨基苯甲酰谷氨酸二乙酯连接生成叶酸类似物分子骨架,采用Adams催化方法还原吡啶环,在N5-位连接不同类型的取代基得到3个新的N8-去氮四氢叶酸类似物.经1H NMR,MS对化合物的结构进行了表征.初步生物活性结果表明,此类化合物对人重组二氢叶酸还原酶的抑制活性与N5-位的取代基有关联.     

应用毛细管电泳法分离测定6种取代苯化合物

采用毛细管电泳法对六种取代苯化合物进行了分离研究，考察了3种电泳模式对分离的影响。环糊精的胶束毛细管电泳法可使各组分达到基线分离，正交设计法得到了最佳实验条件，在质量浓度为30－300mg/L的范围内，可进行定量分析，该方法已应用于废液中苯类化合物的测定。     

在线富集二维毛细管电泳分析新体系检测尿样中药物及对映体

将在线富集技术同二维(2D)毛细管电泳(CE)分离相结合同时提高复杂样品中痕量组分的分离度和检测灵敏度.毛细管区带电泳(CZE)作为第一维,分析物根据淌度不同进行分离,第一维流出组分进入第二维毛细管,根据分配系数不同进行胶束电动毛细管色谱(MEKC)分离.采用阳离子选择性耗尽进样(CSEI)在柱预富集,延长进样时间,增大进样量;同时在二维毛细管接口处采用动态pH联接/胶束扫集在线富集技术不仅避免第一维分离组分在接口处扩散,还可进一步压缩样品区带.同常规电动进样CE分离相比,该在线富集二维分离技术的分离能力远远高于一维CZE或MEKC分离,富集倍数达到(0.5～1.2)×104.该法成功应用于人体尿样中四种药物及对映体的分析测定,浓度检出限为0.1～0.3μg/L.进一步研究了人体尿样中四种药物24h内的药代动力学规律.     

毛细管电泳法同时测定炎可宁片中五种有效成分

建立了区带毛细管电泳法同时测定炎可宁片中小檗碱、巴马汀、药根碱、大黄素、大黄酸5种药效成分含量的方法.在60 cm×75 μm(有效长度50 cm)未涂层弹性石英毛细管中,以90 mmol/L Tris-10 mmol/L柠檬酸(含30％乙腈,pH=8.0)为电泳缓冲溶液,分离电压为25 kV时,5种被测组分在10 m...     

毛细管电泳法进行化妆品中砷的形态分析

从样品前处理、毛细管电泳修饰、进样方式、分离模式和检测条件等方面对毛细管电泳法研究化妆品中砷的形态进行讨论。在不同pH值的缓冲溶液中，用毛细管电泳法进行化妆品中砷的形态分析，测定波长为197nm。采用磷酸盐缓冲溶液，化妆品中As(Ⅲ)、二甲基胂(DMA)、对氨苯基胂酸(ANA)、一甲基胂(MMA)和As(V)等5种形态的砷可通过毛细管电泳法得到有效分离。     

毛细管电泳法对南方水牛奶乳清蛋白的分离和定量分析

利用毛细管区带电泳对广东省水牛乳乳清蛋白成分进行了分离和定量分析研究.采用1.2%的十四水合硼酸钠电泳缓冲液,对水牛奶乳清蛋白的四种主要组分α-乳白蛋白(α-La)、β-乳球蛋白(β-Lg)、牛血清白蛋白(BSA)、免疫球蛋白(IgG)进行了很好的分离,其迁移时间和峰面积的RSD分别小于1.5%和0.5%,加标回收率范围91%～102%.建立了基于毛细管区带电泳的分析方法,对牛乳及其乳制品中的乳清蛋白进行了快速分离和定量分析.     

糖蛋白微观不均一组分的毛细管电泳分离

为分离糖蛋白的微观不均一组分 ,建立了以醇胺为电泳缓冲液主要成分、以聚丙烯酰胺涂层毛细管为分离通道的电泳方法 .利用本法可使琼脂糖电泳纯的鸡卵白蛋白分裂出 2 5个以上的峰 ,使转铁蛋白分裂出 1 0个左右的峰 .控制分离能力的关键因素包括缓冲液的组成、浓度、pH和毛细管内壁的性质等 ,其选择与样品有关 .     

Radioenzymatic determination of subpicomole quantities of folic acid and dihydrofolate based on differential reduction by dihydrofolate reductase

A sensitive method for the determination of folic acid in the presence of dihydrofolate has been described. The analysis is based on the difference in reactivity of dihydrofolate reductase toward folic acid and dihydrofolate. The tetrahydrofolate formed was measured by stoichiometric entrapment into a covalent, ternary complex with thymidylate synthase and [³H]fluorodeoxyuridylate. Differentiation between folic acid and dihydrofolate was accomplished by the use of two levels of dihydrofolate reductase. Recovery of both folic acid and dihydrofolate was quantitative in the range of 0.1 to 2.0 pmol.     

The synthesis of new 2,4‐diaminofuro[2,3‐d]pyrimidines with 5‐biphenyl,phenoxyphenyl and tricyclic substitutions as dihydrofolate reductase inhibitors

Nonclassical 2,4‐diamino‐5‐substituted furo[2,3‐d]pyrimidines 4a‐i, 5a‐b and 7a‐f were synthesized as extended aromatic ring appended analogs of previously reported antifolates 1a‐b. The extended aromatic system was designed to better interact with a phenylalanine residue (Phe69) of dihydrofolate reductase from the opportunistic pathogen Pneumocystis carinii to afford potent and selective inhibitors of Pneumocystis carinii dihydrofolate reductase. The target compounds were synthesized by nucleophilic displacement of 2,4‐diamino‐5‐(chloromethyl)furo[2,3‐d]pyrimidine 3 with the appropriate aromatic amine or thiol. The compounds were evaluated as inhibitors of dihydrofolate reductase from Pneumocystis carinii and Toxoplasma gondii, and their selectivity was determined using rat liver dihydrofolate reductase as the mammalian reference. In the C8‐N9 bridged series, compound 4e , with a 3‐(2‐methoxydibenzofuran)‐ side chain, exhibited greatest potency and was more than 3 times as selective for Pneumocystis carinii dihydrofolate reductase compared to rat liver dihydrofolate reductase. Compounds 4b and 4c also exhibited selectivity. Compounds in the C8‐S9 bridged series showed comparable potencies, and each showed higher selectivity for Pneumocystis carinii dihydrofolate reductase compared to rat liver dihydrofolate reductase.     

Dihydrofolate reductase: structural aspects of mechanisms of enzyme catalysis and inhibition

The mechanism of catalytic reduction of folic and dihydrofolic acids to tetrahydrofolate, which proceeds under the action of dihydrofolate reductase and the coenzyme NADPH, is considered. The roles of the enzyme active site, the coenzyme, individual amino acid residues of the enzyme, and water molecules in the catalytic reaction are discussed. Interactions of the enzyme with competitive inhibitors many of which are widely used in medicine as antitumor and antibacterial drugs are examined. The factors controlling the selectivity of inhibitor binding to bacterial forms of the enzyme are analyzed. The results of X-ray diffraction and NMR spectroscopic studies of the structures of the enzyme and its complexes with the substrate and inhibitors are surveyed. The role of specific interactions and molecular motions of the protein and ligands in the mechanism of catalysis and in the binding of the ligands to the enzyme is discussed.     

荧光光度法二氢叶酸还原酶抑制剂筛选模型的建立和应用

本文应用二氢叶酸(DHFA)和辅酶Ⅱ(NADPH)的荧光性质,建立了二氢叶酸还原酶(DHFR)活力测定的反应体系,并对酸度等反应条件进行了优化。在该体系中,用双倒数作图法分别测定了二氢叶酸还原酶对二氢叶酸和辅酶Ⅱ的表观米氏常数。将所建立的体系应用于氨甲喋呤,甲氧苄氨嘧啶等已知抑制剂的抑制率的测定,结果满意。     

Design,synthesis and biological evaluation of 2,4‐diamino‐6‐methyl‐5‐substitutedpyrrolo[2,3‐d]pyrimidines as dihydrofolate reductase inhibitors

Nine novel nonclassical 2,4‐diamino‐6‐methyl‐5‐mioarylsubstituted‐ 7H ‐pyrrolo[2,3‐d]pyrimidines 2‐10 were synthesized as potential inhibitors of dihydrofolate reductase and as antitumor agents. The analogues contain various electron donating and electron withdrawing substituents on the phenylsulfanyl ring of the side chains and were synthesized from the key intermediate 2,6‐diamino‐6‐methyl‐7H‐pyrrolo[2,3‐d]‐pyrimidine, 14 . Compound 14 , was in turn obtained by chlorination of 4‐position of 2‐amino‐6‐methylpyrrolo[2,3‐d]pyrimidin‐4(3H)‐one, 16 followed by displacement with ammonia. Appropriately substituted phenyl thiols were appended to the 5‐position of 14 via an oxidative addition reaction using iodine, ethanol and water. The compounds were evaluated against rat liver, rat‐derived Pneumocystis, Mycobacterium avium and Toxoplasma gondii dihydrofolate reductase. The most potent and selective inhibitor, (2) has a 1‐naphthyl side chain. In this series of compounds electron‐withdrawing and bulky substituents in the side chain afford marginally active dihydrofolate reductase inhibitors. The single atom sulfur bridge in the side chain of these compounds is not conducive to potent dihydrofolate reductase inhibition.     

Carbon-deuterium bonds as probes of dihydrofolate reductase

Much effort has been directed toward understanding the contributions of electrostatics and dynamics to protein function and especially to enzyme catalysis. Unfortunately, these studies have been limited by the absence of direct experimental probes. We have been developing the use of carbon-deuterium bonds as probes of proteins and now report the application of the technique to the enzyme dihydrofolate reductase, which catalyzes a hydride transfer and has served as a paradigm for biological catalysis. We observe that the stretching absorption frequency of (methyl- d 3) methionine carbon-deuterium bonds shows an approximately linear dependence on solvent dielectric. Solvent and computational studies support the empirical interpretation of the stretching frequency in terms of local polarity. To begin to explore the use of this technique to study enzyme function and mechanism, we report a preliminary analysis of (methyl- d 3) methionine residues within dihydrofolate reductase. Specifically, we characterize the IR absorptions at Met16 and Met20, within the catalytically important Met20 loop, and Met42, which is located within the hydrophobic core of the enzyme. The results confirm the sensitivity of the carbon-deuterium bonds to their local protein environment, demonstrate that dihydrofolate reductase is electrostatically and dynamically heterogeneous, and lay the foundation for the direct characterization protein electrostatics and dynamics and, potentially, their contribution to catalysis.     

Dihydrofolate reductase: A potential drug target in trypanosomes and leishmania

Dihydrofolate reductase has successfully been used as a drug target in the area of anti-cancer, anti-bacterial and anti-malarial chemotherapy. Little has been done to evaluate it as a drug target for treatment of the trypanosomiases and leishmaniasis. A crystal structure of Leishmania major dihydrofolate reductase has been published. In this paper, we describe the modelling of Trypanosoma cruzi and Trypanosoma brucei dihydrofolate reductases based on this crystal structure. These structures and models have been used in the comparison of protozoan, bacterial and human enzymes in order to highlight the different features that can be used in the design of selective anti-protozoan agents. Comparison has been made between residues present in the active site, the accessibility of these residues, charge distribution in the active site, and the shape and size of the active sites. Whilst there is a high degree of similarity between protozoan, human and bacterial dihydrofolate reductase active sites, there are differences that provide potential for selective drug design. In particular, we have identified a set of residues which may be important for selective drug design and identified a larger binding pocket in the protozoan than the human and bacterial enzymes.     

Evidence for environmentally coupled hydrogen tunneling during dihydrofolate reductase catalysis

Hydride transfer during catalysis by dihydrofolate reductase from Thermotoga maritima has been studied by stopped flow spectroscopy. The reduction of dihydrofolate by NADPH showed a biphasic temperature dependence of the deuterium kinetic isotope effect. At temperatures above 25 degrees C the KIE was temperature independent, while the reaction rates were strongly temperature dependent. Below 25 degrees C the KIE becomes dependent on temperature, and the ratio of the preexponential factors is inverse, suggesting a greater role for active dynamics that modulate the tunneling distance.     

Conformationally restricted tricyclic analogues of lipophilic pyrido[2,3‐d]pyrimidine antifolates

The effect of conformational restriction of the C9‐N10 bridge on inhibitory potency and selectivity of trimetrexate against dihydrofolate reductase, was studied. Specifically three nonclassical tricyclic 1,3‐diamino‐8‐(3′,4′,5′‐trimethoxybenzyl)‐7,9‐dihydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidin‐6(5H,8H)‐one ( 4 ), 1,3‐diamino‐8‐(3′,4′,5′‐trimethoxybenzyl)‐9‐hydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidin‐6‐(8H)‐one ( 5 ) and 1,3‐diamino‐(8H)‐(3′,4′,5′‐trimethoxybenzyl)‐7,9‐dihydro‐pyrrolo[3,4‐c]pyrido[2,3‐d]pyrimidine ( 7 ) antifolates were synthesized. The tricyclic analogues 4 and 5 were obtained via the regiospecific cyclo‐condensation of the β‐keto ester 17 with 2,4,6‐triaminopyrimidine. The analogue 7 was obtained via reduction of the lactam 4 with borane in tetrahydrofuran. Compounds 4, 5 and 7 were evaluated as inhibitors of dihydrofolate reductase from Pneumocystis carinii, Toxoplasma gondii and rat liver. All three compounds were more selective than trimetrexate against Pneumocystis carinii dihydrofolate reductase and significantly more selective than trimetrexate against Toxoplasma gondii dihydrofolate reductase compared with rat liver dihydrofolate reductase.     

Identification of an anti-MRSA dihydrofolate reductase inhibitor from a diversity-oriented synthesis

The screening of a diversity-oriented synthesis library followed by structure-activity relationship investigations have led to the discovery of an anti-MRSA agent which operates as an inhibitor of Staphylococcus aureus dihydrofolate reductase.