稳定的五配位碳原子

介绍了稳定的五配位化合物存在的可能性并例证说明了存在的化合物     

蛋白激酶的五配位磷化学结构分析

基于实验合成的五配位磷氨基酸晶体的平方锥和三角锥的结构, 以及氨基酸侧链参与形成五配位磷化学结构实验的基础上, 设计了软件来搜索国际蛋白数据库中可能形成五配位磷结构的含磷蛋白. 利用自主编写的软件研究发现, 国际蛋白质数据库(PDB库)收录的398个含磷的蛋白激酶中, 有382个蛋白激酶(96%)在活化过程中可能经历了五配位磷化学过渡态或中间体. 例如1H8E蛋白的Lys16的N_Z原子与GNP2的P原子形成了可能的五配位化学结构, 将该结构与实验得到的氨基酸小分子晶体的实际五配位磷结构进行叠加, 结构符合很好, 相关结构的偏差RMSD值为0.71 Å. 文中的软件下载地址为: ftp://166.111.28.228, 软件版权登记号2002SR2943.     

氢膦烷的合成及其反应

氢膦烷能参与多种化学反应,可以衍生出许多类型的五配位磷化合物,而且在有机合成中也有重要的应用价值.本文结合作者的研究工作,对近年来氢膦烷研究的重要进展进行了评述.     

分子马达五配位磷化学结构分析

分子马达运动的“动因”是研究分子马达的关键问题．目前无论是线性分子马达还是旋转分子马达的研究,由分子马达构象变化引起整个分子马达运动的理论得到普遍认可．分子马达与高能物质(特别是含磷物质)发生构象变化,例如ATP与分子马达部件上氨基酸的弱结合(Weak binding)、强结合(Binding)及释放(Release)等引起的构象变化,往往被用来解释分子马达运动的原因．其化学机理国际     

五配位磷化合物与生物化学

综述了五配位磷化合物与生物化学的关系, 发现当a-氨基酸的氨基接上磷酰基团以后, 化学性质发生了许多奇特的现象, 在室温下可发生自身活化现象而成肽、成酯、磷上酯交换及N→O磷酰基转位; 丝氨酸和苏氨酸与核苷缀合以后, 在弱碱性条件下能够对不同的碱基进行识别; 磷酰化组氨酸和丝组二肽可以在中性条件下切割核酸、蛋白、酯. 发现上述现象的发生都经历了一个五配位磷中间体, 认为五配位磷中间体是决定它们活性的结构因素.     

硫代四配位磷化物与邻苯二酚反应

前文报^[1]道的硫代磷酰二氯在三乙胺存在下与邻苯二酚反应,不仅具有理论意义,而且是合成该类磷化物的新方法。本文将继续报道硫代磷酰一氯以及其它硫代四配位磷化物与邻苯二酚反应的结果,以期进一步揭示这类反应的本质及其影响因素。     

氨基酸和核苷的五配位磷化合物

五配位磷化合物在生物化学中起着重要作用。磷所参与的绝大多数生命化学过程,包括酶活性调节过程中蛋白质的磷酰化与去磷酰化,信息传导过程中蛋白质的磷酰化与去磷酰化,ATP的能量转移,RNA的自体切割等,其化学本质都是磷酰基转移反应。生物化学家们的研究表明,这些磷酰基转移反应都是通过五配位中间体来完成的。因此,对生物化学中五配位磷化合物的研究具有重要意义。     

五配位锗化合物研究进展

按两种不同的结构类型（中性分子型和离子型）着重对五配位锗化合物的结构特点、研究进展等方面的内容进行了综述。     

包含平面四配位和五配位碳原子的特殊硼碳化合物

采用密度泛函理论(DFT), 在B3LYP/6-311+G**水平上, 研究了三类包含平面四配位碳原子(ptC)和平面五配位碳原子(ppC)的硼碳化合物. 这三类新型化合物是由C3B2H4(包含ptC)、CB4H2(包含ptC)和CB5H2(包含ppC)三种稳定结构和—CHCH—单元连接起来而得到的. 在理论上探讨了这些新型的硼碳化合物的成键特征, 光谱性质以及芳香性. 研究结果表明: 包含ptC和ppC原子的能量最低的结构, 在不受对称面限制的条件下, 具有C2v对称性的顺式立体构型比具有反式平面构型的化合物稳定. 计算的核独立化学位移(NICS)显示, 这些新型化合物的三元环中心有强的芳香性. 计算最稳定硼碳化合物的ptC和ppC原子的Wiberg键指数(WBIs)表明ptC和ppC的成键遵循八隅规则.     

螺环五配位磷化物合成新方法

螺环五配位磷化物合成方法虽有不少报道,但有的路线较长;有的原料不易得到;有的条件苛刻且收率不高.本文提供一种新的简便合成路线,即在二甲二硫或二乙二硫存在下,含磷五元或六元环亚磷(膦)酸酯与含有两个活泼氢的双官能团化合物反应,一步制得相应的螺环五配位磷化物.反应式如下:     

NMR determination of the absolute configuration of chiral 1,2- and 1,3-diols

Each of the chiral 1,2- and 1,3-diols examined was derivatized exclusively to a single diastereomeric acetal by the use of a new axially chiral reagent, 2′-methoxy-1,1′-binaphthalene-8-carbaldehyde (MBC). The absolute configuration of the original 1,2- and 1,3-diols was determined by the NOE correlation between the proton signals of the reagent moiety and those of the diol moiety in the acetals.     

Application of chiral bidentate NMR solvents for assignment of the absolute configuration of alcohols: scope and limitation

The ¹³C NMR behaviors of several cyclic and biaryl secondary alcohols as well as acyclic tertiary alcohols have been studied in the chiral bidentate NMR solvent BMBA-p-Me (1). An empirical rule has been advanced to correlate the absolute configuration of each type of alcohols with the ¹³C chemical shift behaviors in (R,R)- and (S,S)-BMBA-p-Me.     

Monosaccharides as silicon chelators: pentacoordinate bis(diolato)(phenyl)silicates with the cis-furanose isomers of common pentoses and hexoses

Five-coordinate phenylsilicates are formed from the reaction of trimethoxy(phenyl)silane with monosaccharides in methanol in the presence of a stoichiometric amount of base. Five complexes have been isolated and characterized with two ketoses and three aldopentoses. The silicon central atom in [K([18]crown-6)][PhSi(beta-D-Fruf 2,3H-2)2].MeOH (1, Fru=fructose) is part of two chelate rings, with the ligands being beta-D-fructofuranose-O2,O3 dianions. The beta-furanose isomer is best suited for silicon ligation because it exhibits a torsion angle close to 0 degrees for the most acidic diol function, thus assuring a flat chelate ring. The same structural principles are also found in [K([18]crown-6)][PhSi(beta-D-Araf1,2H-2)2].2 MeOH (2, Ara=arabinose), [K([18]crown-6)][PhSi(alpha-D-Ribf1,2H-2)2] (3, Rib=ribose), [K([18]crown-6)][PhSi(alpha-D-Xylf1,2H-2)2]. acetone (4, Xyl=xylose), and [K([18]crown-6)][PhSi(alpha-D-Rulf2,3H-2)2] (5, Rul=ribulose).     

Phthalimide as a chromophoric tag in the circular dichroism determination of absolute configuration of α-aminoacid amides and dipeptides. A case of a dipeptide isostructurality

Both N-phthaloyl aminoacid amides and methyl amides as well as N-phthaloyl dipeptide methyl esters give Cotton effects of opposite signs at around 220 and 240 nm. The signs of these Cotton effects are directly correlated with the absolute configuration of the N-phthaloyl substituted stereogenic center: for -configuration the Cotton effect at 240 nm is positive and the Cotton effect at 220 is negative. The X-ray analysis shows that the diastereomeric , and , N-phthaloyl alanylvaline methyl esters form isostructural orthorombic crystals due to the conformational flexibility of the molecules and a similar space requirements of the methoxycarbonyl and isopropyl groups.     

蛋白质功能化新策略:嵌入非天然氨基酸

天然蛋白质由20种天然氨基酸组成,这些蛋白质的构筑基元包含功能基团:羧基、氨基、巯基、硫醚、羟基、碱性胺、烷基和芳基。然而,这些有限的功能基团却不足以完成生物体内所有的生物学功能。为了更好地让生命的体现者--蛋白质完成更加精确和多样的生物学功能,自然界会对蛋白质进行翻译后的修饰,包括:磷酸化,甲基化,乙酰化或者羟基化,甚至在某些情况下,进化出一种新型的翻译机制以便插入硒代半胱氨酸或者吡咯霉素。受此启发,生物化学家发展出各种生物或化学方法来改变或插入新的蛋白质构筑基元,使天然蛋白质完成其相应的生物学功能或者使其具有某些特殊的性质,甚至是创造一种新酶。该文将简单介绍这些蛋白质修饰策略以及该领域的最新进展。     

Crystallographic and chiroptical studies on tetraarylferrocenes for use as chiral rotary modules for molecular machines

A crystal structure of the racemic form of chiral molecular scissors 1 with a trans configuration at the azobenzene unit (rac-trans-1), in which the scissors adopt a closed geometry with two blade phenyl groups that overlap each other, was successfully determined. X-ray crystallographic determination of the structure of (1S,1'S)-10, which is a derivative of the key precursor of trans-1, was also successful. On the basis of the crystal structure of (1S,1'S)-10, the absolute configuration of 1 and related molecular machines, such as molecular pedal 2, and self-locking rotor 3, which all contain a chiral tetrasubstituted ferrocene module, were determined. A correlation between the absolute configuration and the circular dichroism properties of these molecular machines and their synthetic precursors was also determined.     

New sesquiterpenoid glycoside from the rhizomes of Atractylodes lancea

Abstract

Six sesquiterpenoids and four lignans (1–10) were isolated from the n-BuOH extract of the rhizomes of Atractylodes lancea. Among them, the new sesquiterpenoid glycoside named (4?R, 5S, 7R)-hinesolone-11-O-β-?-glucopyranoside (1), along with three known compounds (2–4) were first obtained from this genus. All the isolates were elucidated by spectroscopic analyses and chemical methods, and the absolute configurations were assigned by electronic circular dichroism spectroscopy technique. In addition, the cytotoxic bioassay of compound 1 was evaluated and results showed it had no significant antitumor activity against human cancer cell lines MCF-7, HepG-2 and Hela.     

Convenient synthesis of chiral tryptophan derivatives using Negishi cross-coupling

A facile synthetic procedure for chiral tryptophan derivatives using Negishi cross-coupling reaction of serine-derived iodoalanine with 3-haloindole is described. The best result was obtained when the reaction of N-tosyl-3-bromoindole with N-Cbz-iodoalanine methyl ester was carried out by the combination of Pd₂(dba)₃ and sterically hindered ferrocenyl ligand Q-PHOS. This reaction condition not only gave the desired tryptophan derivative as high as 76% yield, but also suppressed the formation of undesired products, the dehalogenated indole and the homodimer of indole, which were difficult to separate. This reaction was extended to the synthesis of various tryptophan derivatives having substituents on the benzene ring. The characteristic of this reaction is the practical biomimetic synthesis of chiral tryptophan derivatives in one-step.