Characterization of the Rv3377c Gene Product,a Type‐B Diterpene Cyclase,from the Mycobacterium tuberculosis H37 Genome

The Rv3377c gene from the Mycobacterium tuberculosis H37 genome is specifically limited to those Mycobacterium species that cause tuberculosis. We have demonstrated that the gene product of Rv3377c is a diterpene cyclase that catalyzes the formation of tuberculosinol from geranylgeranyl diphosphate (GGPP). However, the characteristics of this enzyme had not previously been studied in detail with homogeneously purified enzyme. The purified enzyme catalyzed the synthesis of tuberculosinyl diphosphate from GGPP, but it did not bring about the synthesis of tuberculosinol. Optimal conditions for the highest activity were found to be as follows: pH 7.5, 30 °C, Mg^II (0.1 mM ), and Triton X‐100 (0.1 %). Under these conditions, the kinetic values of K_M and k_cat were determined to be 11.7±1.9 μM for GGPP and 12.7±0.7 min^?1, respectively, whereas the specific activity was 186 nmol min^?1 mg^?1. The enzyme activity was inhibited at substrate concentrations higher than 50 μM . The catalytic activity was strongly inhibited by 15‐aza‐dihydrogeranylgeraniol and 5‐isopropyl‐N,N,N,2‐tetramethyl‐4‐(piperidine‐1‐carbonyloxy)benzenaminium chloride (Amo‐1618). The DXDTT_293–297 motif, corresponding to the DXDDTA motif conserved among terpene cyclases, was mutated in order to investigate its function. The middle D295 was found to be the most crucial entity for the catalysis. D293 and two threonine residues function synergistically to enhance the acidity of D295, possibly through hydrogen‐bonding networks. The Rv3377c enzyme could also react with (14R/S)‐14,15‐oxidoGGPP to generate 3α‐ and 3β‐hydroxytuberculosinyl diphosphate. Conformational analyses were carried out with deuterium‐labeled GGPP and oxidoGGPP. We found that GGPP and (14R)‐oxidoGGPP adopted a chair/chair conformation, but (14S)‐oxidoGGPP adopted a boat/chair conformation. Interestingly, the conformations of oxidoGGPP for the A‐ring formation are the opposite of those of oxidosqualene when it is used as a substrate by squalene cyclases for the biosynthesis of hopene and tetrahymanol. (3R)‐Oxidosqualene is folded in a boat conformation, whereas (3S)‐2,3‐oxidosqualene folds into a chair conformation, for the formation of the A‐rings of the hopene and tetrahymanol skeletons, respectively.     

Development of a New Spiro‐BOX Ligand and Its Application in Highly Enantioselective Palladium‐Catalyzed Cyclization of 2‐Iodoanilines with Allenes

In this communication, we report the synthesis of a new chiral spiro‐bisoxazoline ligand, i.e., β‐naphthylmethyl‐substituted spiro‐BOX [(R_a,S,S)‐ L7 ] and have successfully applied it to the palladium‐catalyzed enantioselective cyclization reaction of simple allenes with o‐aminoiodobenzenes, affording highly optically active 3‐alkylideneindolines in good yields with excellent enantiomeric excesses.     

聚丙烯腈基预氧化纤维环化程度及力学性能的表征

以聚丙烯腈(PAN)基碳纤维原丝为原料制成预氧化纤维(PANOF),采用芳构化指数(AI)和差热分析法测定了PANOF的环化指数,研究了预氧化温度和时间对其环化程度和力学性能的影响。结果表明,AI实际上反映了吡啶环与氰基间交联程度。在吡啶基与氰基间的交联点数未达到极大值前,AI才能表征PANOF的环化程度。随预氧化温度升高和预氧化时间的延长,PANOF的环化程度提高,断裂强度和断裂伸长率降低。     

Stability Is Not Everything: The Case of the Cyclisation of a Thrombin-Binding Aptamer

With the aim of developing a new approach to obtain improved aptamers, a cyclic thrombin-binding aptamer (TBA) analogue (cycTBA) has been prepared by exploiting a copper(I)-assisted azide–alkyne cycloaddition. The markedly increased serum resistance and exceptional thermal stability of the G-quadruplex versus TBA were associated with halved thrombin inhibition, which suggested that some flexibility in the TBA structure was necessary for protein recognition.     

N-苯基马来酰亚胺合成新工艺研究

以苯胺和顺丁烯二酸酐为原料,采用两步法制得了 N-苯基马来酰亚胺,并确定了较佳的反应条件,产品收率达90%.     

三（正）丁基锡氢化物存在下的自由基环化反应

三(正)丁基锡氢化物在 AIBN 存在下可使某些分子中含有重键的卤化物或羰基化合物发生分子内环化反应,形成各种环状化合物,而且反应条件温和,收率高。     

6，11-二氢二苯骈[6，e]氧杂[艹卓]革-11-酮-2二乙酸的合成

采用对羟基苯乙酸（Ⅱ）和苯酞为原料，在甲醇钠的催化下，以n（Ⅱ）：n（苯酞）：n（甲醇钠）=1．0：1．1：2．2，于130℃反应7h制备4-（2碳基苄氧基）苯乙酸（Ⅲ）。Ⅲ与乙酰氯经氯化、环合得6，11-二氢二苯骈[b，e]氧杂[艹卓]-11-酮-2-乙酸（Ⅰ），该步优化的反应条件为：n（Ⅲ）：n（乙酰氯）=1：125，反应温度为100％，反应时间为6h。以Ⅱ计，总收率达48．16％。Ⅰ的结构经IR、^1H NMR和MS确证。     

3,7-二氟-10,11-二氢-二苯并[b,f]-氮杂▌的合成

以4-氟-2-硝基甲苯为原料,经聚合、还原、缩合得到标题化合物,总收率20.3%。该方法步骤少、操作简便、收率较高,具有工业应用价值。     

Palladium‐Carbene Catalysts for Aerobic,Intramolecular Wacker‐Type Cyclisation Reactions

A catalyst derived from in situ complexation of N‐heterocyclic carbenes to palladium bistrifluoroacetate promotes efficient intramolecular Wacker‐type cyclisation reactions under aerobic conditions. A variety of 2‐allylphenols undergo oxidative conversion to dihydrobenzofurans.     

用大孔树脂催化合成甲基紫罗兰酮的研究

以国产Ｄｏｏ／ＣＣ树脂为催化剂,将假性甲基紫罗兰酮环化为甲基紫罗兰酮。考察了溶剂、Ｄｏｏ／ＣＣ用量、反应温度、反应时间等因素对环化产率的影响,得出优化的反应条件为：溶剂为二氯甲烷,Ｄｏｏ／ＣＣ用量为假性甲基紫罗兰酮质量的１５倍,反应温度为体系的回流温度（４５℃）,反应时间为４ｈ。按此条件进行平行实验,平均产率７９９％,沸点９０～１００℃／２６７～４００Ｐａ,ｎ２０Ｄ＝１５０００～１５０２０,甲基紫罗兰酮含量９１８％。考察了催化剂的活性,Ｄｏｏ／ＣＣ树脂连续使用７次,环化平均产率为８０６％。