2′-溴代-2′-脱氧-3′,5′-O-二丙酰基-β-D-核糖胸苷合成工艺的研究

目的改进2′-溴代-2′-脱氧-3′,5′-O-二丙酰基-β-D-核糖胸苷的合成工艺.方法以胸腺嘧啶和四乙酰核糖为原料,经过硅烷化保护、缩合、皂化、卤化反应合成.结果与其他文献方法比较,该法具有操作简单、收率高、成本低等特点.结论 适用于工业化生产.     

2’-溴代-2’-脱氧-3’，5＇-0-二丙酰基-β-D-核糖胸苷合成工艺的研究

目的改进2‘-溴代-2’-脱氧-3’，5‘-0-二丙酰基-β-D-核糖胸苷的合成工艺。方法以胸腺嘧啶和四乙酰核糖为原料，经过硅烷化保护、缩合、皂化、卤化反应合成。结果与其他文献方法比较，该法具有操作简单、收率高、成本低等特点。结论适用于工业化生产。     

HPLC法测定齐多夫定中有关物质

目的 建立HPLC法测定齐多夫定中有关物质B和有关物质C的含量.方法 采用HPLC法,Cosmosil ODS C18（4.6mm×250 mm,5μm）色谱柱,流动相：甲醇-水（20∶80）,检测波长：265nm,流速：1 mL·min-1,进样量：10 μL.结果 有关物质B（3＇-氯-3＇-脱氧胸腺嘧啶）、有关物质C（胸腺嘧啶）分别在0.792 ～9.9 mg·L-1（r =0.999 9）,0.979 ～12.24 mg· L-1（r=1）的浓度范围内线性关系良好;平均回收率分别为92.36％,88.41％;RSD为6.57％,2.03％.结论 该方法简便、准确、可靠,可用于测定齐多夫定中有关物质B（3＇-氯-3＇-脱氧胸腺嘧啶）和有关物质C（胸腺嘧啶）的含量.     

帕博西尼的合成工艺研究

目的优化抗癌药帕博西尼的合成工艺。方法以4-氯-2-甲硫基嘧啶-5-羧酸乙酯为原料,依次经过亲核取代、水解、缩合、甲基化、Wittig-Horner反应、NBS溴化和氧化、亲核取代、Heck偶联以及水解制备得到帕博西尼。结果与结论目标物的结构经~1H-NMR和~(13)C-NMR谱确证,总收率为26.3%(以4-氯-2-甲硫基嘧啶-5-羧酸乙酯计),HPLC检测纯度为99.36%。改进后的工艺原料价格低廉、反应条件温和、操作简便,适合工业化生产。     

黄海葵的化学成分研究（Ⅰ）

从青岛产黄海葵的乙酸乙酯部位，首次分离到６个化合物，分别为尿嘧啶（１）、２’－脱氧核糖尿嘧啶（２）、胸腺嘧啶（３）、脱氧核糖胸腺嘧啶（４）     

吡贝地尔的合成工艺研究

目的 改进吡贝地尔的合成工艺。方法 以邻苯二酚和二氯甲烷为原料经环和反应合成胡椒环,胡椒环与多聚甲醛经Blanc氯甲基化反应合成重要中间体胡椒基氯(3);以哌嗪和二氯嘧啶为原料经氮烷基化反应合成重要中间体1-(2-嘧啶基)哌嗪(4);(3)和(4)经氮烷基化反应得到目标化合物。结果与讨论 目标化合物的结构经1H-NMR、GC-MS谱确证,总收率为44.2%,改进后的工艺操作简便,成本低廉,有利于工业化生产。     

2-(取代苯氧基)-5-羟基嘧啶类化合物的制备方法研究

目的探索2-取代苯氧基-5-苯甲氧基嘧啶、2-取代苯氧基．5-羟基嘧啶类化合物的制备方法。方法以2．氯-5-羟基嘧啶为起始原料,经溴苄羟基保护、威廉森醚合成法、脱苄基保护等多步反应制得目标化合物。结果采用该合成路线制得13个未见文献报道的取代苯氧基嘧啶类化合物。结论本研究提出了一条操作简便、条件温和的全新苯氧基嘧啶类化合物合成方法。     

放射致敏剂和防护剂的新进展

需氧细胞放射致敏剂(Oxic Cell Radiosensitizers)放射生物学研究表明,放射敏感部位主要在细胞核中,即在 DNA 或与核膜有关联的 DNA的靶分子上,而 DNA 结构的某些改变与细胞放射敏感性的增强有关。卤化嘧啶类如5-氯代、5-溴代或5-碘代脱氧嘧啶是胸腺嘧啶的结构类似物,它们很容易参入到复制 DNA 中,增强对放射损伤的敏感性,但胸腺嘧啶类似物引起放射致敏的确切机制尚未明了,可能是由于带负电荷的卤素原子     

胸苷(Thymidine)的立体选择性合成

胸苷(Thymidine,Ⅰ)是组成生物体DNA的4种脱氧核苷之一,也是抗艾滋病药物齐多夫定(Zidovudine,AZT)和司他夫定(Stavudine,d4T)合成的重要原料.经典的化学合成方法是将保护的胸腺嘧啶与保护的2-脱氧-D-核糖在Lewis酸催化缩合[1,2].Baud[3]等来报道嘧啶等碱基可以不经保护与脱氧核糖在PTC条件下进行缩合,且有较为满意的收率,不过,由直接缩合方法所得产物均为α、β端基异构体的混合物,较难分离纯化,且2-脱氧-D-核糖来源稀少.     

嘧啶与吡啶衍生物硝化方法的改进

目的：改进6-氯-3-甲基脲嘧啶和2．羟基吡啶的硝化方法,分别制备6-氯-3-甲基-5-硝基脲嘧啶和2-羟基-3-硝基吡啶。方法：采用KNO3代替浓硝酸与浓硫酸组成的复合硝化剂分别对两原料进行硝化,同时考察原料与KNO3的摩尔比、加料温度以及反应时间和温度对硝化收率的影响,以确定最佳工艺条件。结果：适宜于6-氯-3-甲基脲嘧啶硝化和制备相应目标产物的反应条件是：原料与硝酸钾的摩尔比为1：1．25—1：1．3,加料温度为5℃,反应时间为2h,反应温度为25℃。而适宜于2．羟基吡啶硝化和制备相应目标产物的反应条件基本上与之相同,只是反应温度为45℃-50℃。两个目标产物的收率分别达53％和54％。结论：本方法操作简便,其反应温和、安全、易控,且收率较高。     

Establishment of inherent stability of stavudine and development of a validated stability-indicating HPLC assay method

The present study describes degradation of stavudine under different stress conditions (hydrolysis, oxidation, photolysis and thermal stress), and establishment of a stability-indicating reversed-phase HPLC assay method. The drug was found to hydrolyse in acidic, neutral and alkaline conditions and also under oxidative stress. The major degradation product formed under various conditions was thymine, as evidenced through comparison with the standard and spectral studies (NMR, IR and MS) on the isolated product. Separation of drug, thymine and another minor degradation product was successfully achieved on a C-18 column utilising water–methanol in the ratio of 90:10. The detection wavelength was 265 nm. The method was validated with respect to linearity, precision (including intermediate precision), accuracy and specificity. The response was linear in the drug concentration range of 25–500 μg ml⁻¹. The mean values (±R.S.D.) of slope and correlation coefficient were 24256 (±0.679) and 0.9994 (±0.0265), respectively. The R.S.D. values for intra- and inter-day precision studies were <0.210 and <1%, respectively. The recovery of the drug ranged between 99.7 and 101.5% from a mixture of degraded samples. The method even proved to be affective on application to a stressed marketed capsule formulation.     

HPLC isolation and mass spectrometric characterization of two isomers of thymine glycols in oligodeoxynucleotides

Thymine glycol, or 5,6-dihydroxy-5,6-dihydrothymine, is the major oxidation product of thymine. Herein we report the isolation of both the (5S, 6R) and (5R, 6S) isomers of cis thymine glycols from several synthetic oligodeoxynucleotides (ODNs) upon oxidation with osmium tetraoxide. Our results show that tandem mass spectrometry can determine the sites of thymine glycol in ODNs by producing characteristic fragment ions, [a - 143] and its complementary w ions at the modification site. We further demonstrate that the [M + H]+ and [M + Na]+ ions of the two cis stereoisomers of thymine glycol in the dinucleotides, which are extricated from the ODNs by nuclease P1, gave distinctive product-ion spectra.     

Endogenous phospholipid metabolite containing topical product inhibits ultraviolet light-induced inflammation and DNA damage in human skin

BACKGROUND: N-palmitoylethanolamine (PEA) and organic osmolytes are endogenous components of the human epidermis and are generated from phospholipids in the stratum granulosum. PEA has been shown to exert potent antioxidant and anti-inflammatory activities. The endogenous organic osmolytes such as betaine and sarcosine control skin humidity, but have also been shown to inhibit ultraviolet (UV) light-induced oxidative stress in keratinocytes. OBJECTIVES: To investigate the effect of a PEA- and organic osmolyte-containing topical product (Physiogel AI) on the development of UV light-induced erythema, thymine dimer formation and p53 tumor suppressor gene activation, as well as intercellular adhesion molecule 1 (ICAM-1) and Ki67 expression in normal human skin. METHODS: The UV-induced erythema was measured by a spectrofluorometric method. Thymine dimers, p53, ICAM-1 and Ki67 were detected in skin biopsies using immunohistochemistry. RESULTS: Physiogel AI cream significantly inhibited the development of UV light-induced erythema and thymine dimer formation in normal human skin, but did not alter the number of Ki67+ proliferating keratinocytes and the expression of p53 and ICAM-1. CONCLUSIONS: Our results suggest that PEA and organic osmolytes might represent a new generation of compounds which suppress UV-induced photodamage.     

A theoretical study on interactions between mitoxantrone as an anticancer drug and DNA: application in drug design

This research is an effort to further understand the physicochemical interaction between the novel drug, mitoxantrone (MTX) and its biologic receptor, DNA. The ultimate goal is to design drugs that interact more with DNA. Understanding the physicochemical properties of the drug as well as the mechanism by which it interacts with DNA, it should ultimately allow the rational design of novel anti-cancer or anti-viral drugs. Molecular modelling on the complex formed between MTX and DNA presented that this complex was indeed fully capable of participating in the formation of a stable intercalation site. Furthermore, the molecular geometries of MTX and the DNA bases (adenine, guanine, cytosine and thymine) were optimized with the aid of the B3LYP/6-31G* method. The properties of the isolated intercalator and its stacking interactions with the adenine...thymine (AT) and guanine...cytosine (GC) nucleic acid base pairs were studied with the DFTB method (density functional tight-binding), an approximate version of the DFT method, that was extended to cover the London dispersion energy. The B3LYP/6-31G* stabilization energies of the intercalator...base pair complexes were found 10.06 kcal/mol and 21.64 kcal/mol for AT...MTX and GC...MTX, respectively. It was concluded that the dispersion energy and the electrostatic interaction contributed to the stability of the intercalator.DNA base pair complexes. The results concluded from the comparison of the DFTB method and the Hartree-fock method point out that these methods show close results and support each other.     

A sensitive assay of 5-fluorouracil in plasma by gas chromatography-mass spectrometry.

1 A gas chromatographic-mass spectrometric method was developed for determining 5-fluorouracil in plasma, using methylated thymine as an internal standard. 2 5-fluorouracil was extracted from plasma by a novel procedure which removed plasma components interferring with the sensitivity of the assay. The method included heating the plasma, washing with ether and extracting the drug under optimum conditions. 3 The sensitivity of the assay was 10 ng/ml plasma, sufficient to determine the low concentrations of 5-fluorouracil found in plasma during continuous infusion of the drug in patients receiving chemotherapy for cancer.     

Photosensitization of thymine nucleobase by benzophenone derivatives as models for photoinduced DNA damage: Paterno-Büchi vs energy and electron transfer processes

Time-resolved and product studies have shown that there is a strong interaction between drugs containing the benzophenone chromophore and the free thymidine nucleoside. In quantitative terms, such an interaction is stronger for the lowest lying npi* triplet states (S-ketoprofen) than for mixed npi*-pipi* triplets (fenofibrate and fenofibric acid), as indicated by the quenching rate constants. This is consistent with a Paterno-Büchi photoreaction, where the initial step is the formation of a new bond between the excited carbonyl oxygen and one of the thymine olefinic carbons. Actually, oxetanes are obtained as photoproducts when benzophenone is irradiated in the presence of thymidine. Hence, triplet-triplet energy transfer resulting in formation of cyclobutane pyrimidine dimers, which would be thermodynamically disfavored, does not seem to play a major role. However, in DNA, the contribution of energy transfer could be higher, due to the lower energy of the thymine triplet in the biomacromolecule. These results are discussed in connection with the observed DNA damage upon photosensitization with ketoprofen, fenofibrate, and fenofibric acid.     

Generation of thymine radicals from 6-alkoxy-5-bromo-5,6-dihydrothymine derivatives by radiolytic reduction and photolytic dehalogenation

The reduction of 6-alkoxy-5-bromo-5,6-dihydrothymine derivatives ( 1a, b) by hydrated electrons (e aq (-)) generated in the radiolysis of deoxygenated aqueous solution was investigated. As the major products, 1-(6'-alkoxy-5',6'-dihydrothymin-5'-yl)thymines ( 6a, b), 5-(hydroxymethyl)uracil ( 8), 6-alkoxy-5,6-dihydrothymines ( 9a, b), and thymine ( 10) were produced in sufficient yields. This product distribution is indicative of the generation of 6-alkoxy-5,6-dihydrothymin-5-yl radicals ( 2a, b) as primary intermediates that undergo elimination of alkoxide ions (RO (-)) into thymine radical cations ( 3) followed by deprotonation at the N1 to form N-centered thymine radicals ( 4). The transient absorption spectra of the 5-yl radicals 2a- c were observed by means of nanosecond laser flash photolysis of 1a, b and 5-bromo-6-ethoxy-5,6-dihydrothymidine ( 1c) in deoxygenated aqueous solution, in which homolytic C5-Br bond dissociation occurred. In contrast to the reaction characteristics in aqueous solutions, the dimeric products were not obtained in acetonitrile, probably because in-cage hydrogen abstraction from the C5 methyl group by bromine atom leads to formation of methide type intermediates 20.     

Computational studies on effects of MDMA as an anticancer drug on DNA

This research is designed to further understand the effects of the novel drug MDMA on biologic receptor of DNA. The ultimate goal is to design drugs that have higher affinity with DNA. Understanding the physicochemical properties of the drug as well as the mechanism by which it interacts with DNA should ultimately enable the rational design of novel anticancer or antiviral drugs. Molecular modeling on the complex formed between MDMA and DNA presented this complex to be fully capable of participating in the formation of a stable intercalation site. Furthermore, the molecular geometries of MDMA and DNA bases (Adenine, Guanine, Cytosine, and Thymine) were optimized with the aid of the B3LYP/6-31G* method. The properties of the isolated intercalator and its stacking interactions with adenine···thymine (AT) and guanine···cytosine (GC) nucleic acid base pairs were studied with the DFTB method. DFTB method is an approximate version of the DFT method that was extended to cover the London dispersion energy. The B3LYP/6-31G* stabilization energies of the intercalator···base pair complexes were found to be −9.40 and −12.57 kcal/mol for AT···MDMA and GC···MDMA, respectively. Results from comparison of the DFTB method and HF method conclude close results and support each other.     

Thiyl radical reaction with thymine: absolute rate constant for hydrogen abstraction and comparison to benzylic C-H bonds

Free radical damage of DNA is a well-known process affecting biological tissue under conditions of oxidative stress. Thiols can repair DNA-derived radicals. However, the product thiyl radicals may also cause biological damage. To obtain quantitative information on the potential reactivity with DNA components, we measured the rate constant for hydrogen abstraction by cysteamine thiyl radicals from thymine C5-CH(3), k = (1.2 +/- 0.8) x 10(4) M(-1) s(-1), and thymidine-5'-monophosphate, k = (0.9 +/- 0.6) x 10(4) M(-1) s(-1). Hence, the hydrogen abstraction from C5-CH(3) occurs with rate constants similar to the hydrogen abstraction from the carbohydrate moieties. Especially at low oxygen concentration such as that found in skeletal muscle, such hydrogen abstraction processes by thiyl radicals may well compete against other dioxygen-dependent reactions. The rate constants for hydrogen abstraction at thymine C5-CH(3) were compared to those with benzylic substrates, toluenesulfonic acid, and benzyl alcohol.     

UDP-N-methyl-D-glucosamine-phosphate--a possible intermediate of N-methyl-L-glucosamine moiety of streptomycin

The formation of N-methyl-L-glucosamine moiety of streptomycin from D-glucosamine by Streptomyces griseus was studied. The addition of thymine to the culture medium stimulated the formation of streptomycin and the incorporation of D-glucosamine into N-methyl-L-glucosamine moiety. During a study of sugar nucleotides in the mycelia, a novel UDP-amino sugar was isolated. The compound was formed before the maximum production of streptomycin. It was UDP-N-methyl-D-glucosamine-phosphate.