截短侧耳素C-14侧链的修饰及其抗菌活性研究进展#br#

抗生素的广泛使用和滥用导致耐药性细菌日益增加。为了应对这种局面,研究人员加大了对抗耐药性细菌抗生素的研发力度。基于此,20世纪50年代,从高等真菌中分离的具有良好抗菌活性的先导化合物截短侧耳素得到了越来越多的关注和研究。构效关系研究表明,截短侧耳素的三环母核结构的改造对抗菌活性的提高作用不大,而对C-14侧链的修饰则可以增加截短侧耳素的抗菌活性和改善其药动学性质。本文就近10年来国内外对截短侧耳素C-14侧链的修饰、抗菌活性和构效关系研究进行综述,并总结了目前研究中存在的问题。     

人用截短侧耳素类抗生素的研究现状与发展趋势

为了应对日益严重的细菌耐药性问题,人们不断研发具有新型作用机制的抗菌药物,其中截短侧耳素及其衍生物作为重要的一类兽用抗生素,具有独特的作用机制,其特点不易产生交叉耐药性.已经上市的泰妙菌素、沃尼妙林均具有抗菌谱广及较强的抗菌活性,而2007年4月批准的瑞他莫林是近二十年来首个新的局部应用的抗菌药物,被认为是第一个人用截短侧耳素衍生物,标志着截短侧耳素类从兽用跨越到人用领域.本文就截短侧耳素的作用机制、耐药机制、人用截短侧耳素的临床研究现状以及新型截短侧耳素衍生物研发等方面的最新进展做简要概述.     

截短侧耳素类抗生素及其耐药研究进展

截短侧耳素(Pleuromutilins)是从担子菌纲侧耳属Pleurotus mutilus和Pleurotus passeckerianus中分离得到的二萜类抗生素，对革兰阳性菌和支原体具有良好的抗菌活性。截短侧耳素类药物用途广泛，泰妙菌素(Tiamulin)和沃尼妙林(Valnemulin)作为兽用药用于防治由病原微生物引起的猪痢疾、支原体肺炎等疾病；人用批准的瑞他莫林(Retapamulin)和来法莫林(Lefamulin)主要用于治疗球菌感染和获得性细菌性肺炎。近年来，截短侧耳素类药物耐药监测表明，在病原微生物的rplC、rplD、23sRNA、Cfr和vga基因中报道了多种新的突变位点，导致侧耳素类药物敏感性降低。本文对已上市的截短侧耳素类药物进行回顾，并对近十年该类药物的耐药机制研究进行综述，以期为新型截短侧耳素类药物的创制提供参考。     

截短侧耳素制备方法的研究概况

截短侧耳素作为中间体用于半合成抗生素的制备,其市场需求不断扩大,截短侧耳素的制备方法备受关注,通过文献资料检索和市场调研,从生物合成途径、生物发酵方法、分离纯化技术3个方面归纳总结截短侧耳素的制备方法研究进展。     

截短侧耳素及其衍生物的研究进展

截短侧耳素是重要的二萜类兽用抗生素.发现至今,针对其衍生物进行了深入研究,发现了抗菌活性更强、应用范围更广的泰妙菌素、沃尼妙林、retapamulin和一系列水溶性衍生物等.其中retapamulin是2007年4月FDA批准的近二十年来第一个新的局部应用的抗菌药物,同时作为第一个人用截短侧耳素衍生物,标志着此类抗生素实现了从兽用到人用的飞跃.本文就截短侧耳素的作用机制、生物合成及其衍生物应用等方面的最新进展做简要概述.     

从Clitopilus pinsitus制备原生质体的一种方法

本文报导一种快速、可靠地分离和再生担子菌C.Pinsitus原生质体的方法。担子菌C.Pinsitus产生一种叫做截短侧耳素(Pleuromutilin)的双萜类抗生素。自从它于1951年被发现以来,已报道了它的发酵、结构和生物合成。截短侧耳素具有有限的抑菌谱,主要是抑制支原体属革蓝氏阳性细菌的生长。截短侧耳素是一种用于硫粘菌素酸式富马酸盐(tiamulin hydrogen fumarate)化学合成的发酵产品,硫粘菌素酸式富马酸盐有效地用于治疗猪的痢疾和肺炎。     

国外植物内生真菌活性物质的研究进展

植物内生真菌的研究已成为热点。由于内生真菌与宿主植物之间存在明显的互惠共生关系,并能产生与宿主相同或相似的具有生理活性的代谢产物,近年来,国外对内生真菌代谢产物研究有新进展,本文对内生真菌代谢活性产物进行归纳、总结,为进一步开发利用植物内生真菌提供参考研究。     

截短侧耳素在醇-水复合溶剂体系溶解度的测定与关联

截短侧耳素是一种三环二萜类抗生素，因其抗菌机制独特，与一般抗菌药物不发生交叉耐药，而日益受到重视。本 研究测定了截短侧耳素在不同甲醇 ( 或乙醇 )- 水复合溶剂 ( 醇含量 0~50%) 中在 273.15~333.15K 溶解度，并采用多项式经验方程 和 Apelblat 方程进行关联。结果表明，随着温度的提高，随溶剂中甲醇或乙醇含量的增加，截短侧耳素的溶解度显著同步增加。 多项式经验方程和 Apelblat 方程都能很好拟合截短侧耳素溶解度数据，回归系数都在 0.993 以上。热力学分析表明，截短侧耳 素在甲醇 ( 或乙醇 )- 水复合溶剂中的溶解过程焓变都是正值，且随着溶剂中醇含量的增加而增加，是一吸热过程。溶解过程的 熵变在纯水中是负值，随着溶剂中醇含量的增加，熵变也随之增加并且成为溶解度大幅提升的主要驱动力。本论文的研究结果 可为截短侧耳素的提取工艺优化及制剂工艺开发提供重要的科学依据。     

截短侧耳素与Tiamulin

一、引言截短侧耳素(Pleuromutilin)是由高等真菌担子菌纲侧耳属 Pleurotus mutilus 和 Pl-eurotas passeckerianus 菌种经深层培养产生的一种主要对革兰氏阳性菌和枝原体有活性的抗菌物质,它在化学上属于双萜类化合物。1951年,Kavanagh 等人首次报道了这种结晶状抗菌物质的分离及定性,把它命名为Pleuromutilin,并提出它的实验式为 C_(22)     

瓶花木内生真菌C22发酵液中生物活性成分的分离、纯化与鉴定

目的 分离、鉴定红树林植物瓶花木内生真菌C22的活性次生代谢产物.方法 利用硅胶柱层析等方法进行分离纯化:利用光谱分析进行结构解析.结果 内生真菌C22的活性次生代谢产物为一大环内酯类抗生素布雷菲尔德菌素A和一倍半菇类抗生素木霉菌醇.结论 以上两种抗生素对肺癌细胞SMMC-7721、胃癌细胞SGC-7901具有较强的肿瘤细胞毒活性,并且在内生真菌C22中含量较大,因此,红树林植物瓶花木内生真菌菌株 C22具有广阔的应用价值和开发前景.     

Mitochondrial tRNAThr G15927A mutation may modulate the phenotypic manifestation of ototoxic 12S rRNA A1555G mutation in four Chinese families

OBJECTIVE: To investigate the role of mitochondrial modifiers in the development of deafness associated with 12S rRNA A1555G mutation. METHODS: Four Chinese families with nonsyndromic and aminoglycoside-induced deafness were studied by clinical and genetic evaluation, molecular and biochemical analyses of mitochondrial DNA (mtDNA). RESULTS: These families exhibited high penetrance and expressivity of hearing impairment. Penetrances of hearing loss in WZD31, WZD32, WZD33, and WZD34 pedigrees ranged from 50 to 67% and from 39 to 50%, respectively, when aminoglycoside-induced hearing loss was included or excluded. Matrilineal relatives in these families developed hearing loss at the average of 14, 13, 16, and 15 years of age, respectively, when aminoglycoside-induced deafness was excluded. Mutational analysis of entire mtDNA in these families showed the homoplasmic A1555G mutation and distinct sets of variants belonging to haplogroup B5b1. Of these, the tRNA G15927A mutation locates at the fourth base in the anticodon stem (conventional position 42) of tRNA. A guanine (G42) at this position of tRNA is highly conserved from bacteria to human mitochondria. The lower levels and altered electrophoretic mobility of tRNA were observed in cells carrying A1555G and G15927A mutations or only G15927A mutation but not cells carrying only A1555G mutation. The abolished base pairing (28C-42G) of this tRNA by the G15927A mutation caused a failure in tRNA metabolism, worsening the mitochondrial dysfunctions altered by the A1555G mutation. CONCLUSION: The G15927A mutation has a potential modifier role in increasing the penetrance and expressivity of the deafness-associated 12S rRNA A1555G mutation in those Chinese pedigrees.     

Cytochrome P450 dependent metabolism of the new designer drug 1-(3-trifluoromethylphenyl)piperazine (TFMPP). In vivo studies in Wistar and Dark Agouti rats as well as in vitro studies in human liver microsomes

1-(3-Trifluoromethylphenyl)piperazine (TFMPP) is a designer drug with serotonergic properties. Previous studies with male Wistar rats (WI) had shown, that TFMPP was metabolized mainly by aromatic hydroxylation. In the current study, it was examined whether this reaction may be catalyzed by cytochrome P450 (CYP)2D6 by comparing TFMPP vs. hydroxy TFMPP ratios in urine from female Dark Agouti rats, a model of the human CYP2D6 poor metabolizer phenotype (PM), male Dark Agouti rats, an intermediate model, and WI, a model of the human CYP2D6 extensive metabolizer phenotype. Furthermore, the human hepatic CYPs involved in TFMPP hydroxylation were identified using cDNA-expressed CYPs and human liver microsomes. Finally, TFMPP plasma levels in the above mentioned rats were compared. The urine studies suggested that TFMPP hydroxylation might be catalyzed by CYP2D6 in humans. Studies using human CYPs showed that CYP1A2, CYP2D6 and CYP3A4 catalyzed TFMPP hydroxylation, with CYP2D6 being the most important enzyme accounting for about 81% of the net intrinsic clearance, calculated using the relative activity factor approach. The hydroxylation was significantly inhibited by quinidine (77%) and metabolite formation in poor metabolizer genotype human liver microsomes was significantly lower (63%) compared to pooled human liver microsomes. Analysis of the plasma samples showed that female Dark Agouti rats exhibited significantly higher TFMPP plasma levels compared to those of male Dark Agouti rats and WI. Furthermore, pretreatment of WI with the CYP2D inhibitor quinine resulted in significantly higher TFMPP plasma levels. In conclusion, the presented data give hints for possible differences in pharmacokinetics in human PM and human CYP2D6 extensive metabolizer phenotype subjects relevant for risk assessment.     

Pleuromutilin and its derivatives-the lead compounds for novel antibiotics

Due to the rapid onset of resistance to most antibacterial drugs, research efforts are focusing on new classes of antibacterials with different mechanisms of action from clinically used antibacterials. Pleuromutilin derivatives have received more and more scientific attention for their unique mechanism of action. Two pleuromutilin derivatives, tiamulin and valnemulin have been successfully developed as antibiotics for veterinary use. Retapamulin, another pleuromutilin derivative has been approved for use in humans in April 2007 by Food and Drug Administration (FDA). It has been shown that there is rarely cross-resistance between pleuromutilin derivatives and other antimicrobial agents, and the development of resistance bacterial is still low. This review will demonstrate mechanism of action of pleuromutilin derivatives and reveal the structure-activity relationship (SAR) of pleuromutilin derivatives. Additionally, the pleuromutilin antibacterial derivative agents in the market, such as tiamulin, valnemulin and retapamulin, will be discussed. It is proposed that new antibacterial agents might be developed from pleuromutilin derivatives in the future.     

盐酸沃尼妙林的合成

截短侧耳素经苯磺酰化后经1-氨基-2-甲基丙-2-硫醇盐酸盐取代,得到[(2.氨基-1,1-二甲基乙基)硫基]乙酸(3aS,4R,5S,6S,8R,9R,9aR,10R)-6-乙烯基十氢-5-羟基-4,6,9,10-四甲基-1-氧代-3a,9-丙醇-3aH-环戊二烯并环辛烯-8-基酯(5).另用D-缬氨酸和乙酰乙酸甲酯反应后,与氯甲酸异丁酯成酸酐,与5成酰胺后用盐酸脱保护,制得抗生素盐酸沃尼妙林,总收率约为64%(以截短侧耳素计).     

Catalytic roles of CYP2D6.10 and CYP2D6.36 enzymes in mexiletine metabolism: in vitro functional analysis of recombinant proteins expressed in Saccharomyces cerevisiae

Cytochrome P450 2D6 (CYP2D6) metabolizes approximately one-third of the medicines in current clinical use and exhibits genetic polymorphism with interindividual differences in metabolic activity. To precisely investigate the effect of CYP2D6*10B and CYP2D6*36 frequently found in Oriental populations on mexiletine metabolism in vitro, CYP2D6 proteins of wild-type (CYP2D6.1) and variants (CYP2D6.10 and CYP2D6.36) were heterologously expressed in yeast cells and their mexiletine p- and 2-methyl hydroxylation activities were determined. Both variant CYP2D6 enzymes showed a drastic reduction of CYP2D6 holo- and apoproteins compared with those of CYP2D6.1. Mexiletine p- and 2-methyl hydroxylation activities on the basis of the microsomal protein level at the single substrate concentration (100 microM) of variant CYP2D6s were less than 6% for CYP2D6.10 and 1% for CYP2D6.36 of those of CYP2D6.1. Kinetic analysis for mexiletine hydroxylation revealed that the affinity toward mexiletine of CYP2D6.10 and CYP2D6.36 was reduced by amino acid substitutions. The Vmax and Vmax/Km values of CYP2D6.10 on the basis of the microsomal protein level were reduced to less than 10% of those of CYP2D6.1, whereas the values on the basis of functional CYP2D6 level were comparable to those of CYP2D6.1. Although it was impossible to estimate the kinetic parameters for the mexiletine hydroxylation of CYP2D6.36, the metabolic ability toward mexiletine was considered to be poorer not only than that of CYP2D6.1 but also than that of CYP2D6.10. The same tendency was also observed in kinetic analysis for bufuralol 1'-hydroxylation as a representative CYP2D6 probe. These findings suggest that CYP2D6*36 has a more drastic impact on mexiletine metabolism than CYP2D6*10.     

A click chemistry approach to pleuromutilin conjugates with nucleosides or acyclic nucleoside derivatives and their binding to the bacterial ribosome

Pleuromutilin and its derivatives are antibacterial drugs that inhibit protein synthesis in bacteria by binding to ribosomes. To promote rational design of pleuromutilin based drugs, 19 pleuromutilin conjugates with different nucleoside fragments as side chain extensions were synthesized by a click chemistry protocol. Binding was assessed by chemical footprinting of nucleotide U2506 in 23S rRNA, and all conjugates bind to varying degree reflecting their binding affinity to the peptidyl transferase center. The side chain extensions also show various protections at position U2585. Docking studies of the conjugates with the highest affinities support the conclusion that despite the various conjugations, the pleuomutilin skeleton binds in the same binding pocket. The conjugated triazole moiety is well accommodated, and the nucleobases are placed in different pockets in the 50S ribosomal subunit. The derivative showing the highest affinity and a significantly better binding than pleuromutilin itself contains an adenine-9-ylpropylene triazole conjugate to pleuromutilin C-22.     

A click chemistry approach to pleuromutilin derivatives, part 2: conjugates with acyclic nucleosides and their ribosomal binding and antibacterial activity

Pleuromutilin is an antibiotic that binds to bacterial ribosomes and thereby inhibit protein synthesis. A new series of semisynthetic pleuromutilin derivatives were synthesized by a click chemistry strategy. Pleuromutilin was conjugated by different linkers to a nucleobase, nucleoside, or phenyl group, as a side-chain extension at the C22 position of pleuromutilin. The linkers were designed on the basis of the best linker from our first series of pleuromutilin derivatives following either conformational restriction or an isosteric methylene to oxygen exchange. The binding of the new compounds to the Escherichia coli ribosome was investigated by molecular modeling and chemical footprinting of nucleotide U2506, and it was found that all the derivatives bind to the specific site and most of them better than pleuromutilin itself. The effect of the side-chain extension was also explored by chemical footprinting of nucleotide U2585, and the results showed that all the compounds interact with this position to varying degrees. Derivatives with a conformational restriction of the linker generally had a higher affinity than derivatives with an isosteric exchange of one of the carbons in the linker with a hydrophilic oxygen. A growth inhibition assay with three different bacterial strains showed significant activity of several of the new compounds.     

CYP2B6 mediates the in vitro hydroxylation of bupropion: potential drug interactions with other antidepressants.

The in vitro biotransformation of bupropion to hydroxybupropion was studied in human liver microsomes and microsomes containing heterologously expressed human cytochromes P450 (CYP). The mean (+/-S.E.) K(m) in four human liver microsomes was 89 (+/-14) microM. In microsomes containing cDNA-expressed CYPs, hydroxybupropion formation was mediated only by CYP2B6 at 50 microM bupropion (K(m) 85 microM). A CYP2B6 inhibitory antibody produced more than 95% inhibition of bupropion hydroxylation in four human livers. Bupropion hydroxylation activity at 250 microM was highly correlated with S-mephenytoin N-demethylation activity (yielding nirvanol), another CYP2B6-mediated reaction, in a panel of 32 human livers (r = 0.94). The CYP2B6 content of 12 human livers highly correlated with bupropion hydroxylation activity (r = 0.96). Thus bupropion hydroxylation is mediated almost exclusively by CYP2B6 and can serve as an index reaction reflecting activity of this isoform. IC(50) values for inhibition of a CYP2D6 index reaction (dextromethorphan O-demethylation) by bupropion and hydroxybupropion were 58 and 74 microM, respectively. This suggests a low inhibitory potency versus CYP2D6, the clinical importance of which is not established. Since bupropion is frequently coadministered with other antidepressants, IC(50) values (microM) for inhibition of bupropion hydroxylation were determined as follows: paroxetine (1.6), fluvoxamine (6.1), sertraline (3.2), desmethylsertraline (19.9), fluoxetine (59.5), norfluoxetine (4.2), and nefazodone (25.4). Bupropion hydroxylation was only weakly inhibited by venlafaxine, O-desmethylvenlafaxine, citalopram, and desmethylcitalopram. The inhibition of bupropion hydroxylation in vitro by a number of newer antidepressants suggests the potential for clinical drug interactions.     

Regioselective hydroxylation of debrisoquine by cytochrome P4502D6: implications for active site modelling

1. Debrisoquine, a prototypic probe substrate for human cytochrome P4502D6 (CYP2D6), is hydroxylated at the alicyclic C4-position by this enzyme. Phenolic metabolites of debrisoquine (5-, 6-, 7- and 8-hydroxydebrisoquine) have also been reported as in vivo metabolites, but the role of CYP2D6 in their formation is unclear. 2. As part of studies to develop a predictive model of the active site of CYP2D6 using pharmacophore and homology modelling techniques, it became important to determine the precise regioselective hydroxylation of debrisoquine by CYP2D6. 3. Data from studies with human liver microsomes and yeast microsomes containing cDNA-derived CYP2D6 demonstrated unequivocally that debrisoquine was hydroxylated by CYP2D6 at each aromatic site in the molecule, as well as at the alicyclic 4-position. The four phenolic metabolites amounted to > 60% of the total identified products and the pattern of regioselective hydroxylation (4-HD > 7-HD > 6-HD > 8-HD > 5-HD) was similar in both in vitro systems. 4. A pharmacophore model for CYP2D6 indicated that while the hydroxylation of debrisoquine at alternative positions could arise from the substrate adopting multiple binding orientations, the energy constraints for the aromatic hydroxylations were unfavourable. An alternative proposal involving essentially a single binding orientation and a mechanism of hydroxylation based on benzylic radical spin delocalization could satisfactorily rationalize all the hydroxylations of debrisoquine. 5. This latter proposal demonstrates the need to consider the mechanism of oxidation as well as the spatial orientation of the substrate in the development of a predictive model of the active site of CYP2D6.