Iron-stabilized carbocations as intermediates for organic synthesis

Attachment of a transition metal moiety to an olefinic ligand presents the organic chemist with unequaled opportunities to control the regio- and stereospecificities of bond formation. Applications of cationic dienyliron-carbonyl complexes to a range of natural product syntheses have been developed. These applications show how the iron-carbonyl unit directs the regio- and stereochemistry of nucleophile addition. They also show that the iron-carbonyl unit can be used to stabilize otherwise inaccessible carbocations, thereby making them readily available as synthetic intermediates.     

Bulk isolation in nonaqueous media of nuclei from lyophilized cells

Intact lyophilized nuclei are obtainable from a variety of tissues, either in situ or in culture, by freezing at -156 degrees C, drying at -25 degrees C, and mechanical disassociation in glycerol at 2 degrees C. Centrifugal separation of nuclei is accomplished in an 85 : 15 by volume mixture of glycerol and 3-chloro-1,2 propanediol at 2 degrees C. The method gives homogeneous nuclear preparations in high yield with preservation of labile and water-soluble constituents.     

培养基中添加相关外源物对茶氨酸生物合成的影响

以龙井43的嫩叶等为材料,考察在培养基中添加茶氨酸合成前体物、代谢中间物及NO供体硝普钠对愈伤组织中茶氨酸含量的影响,并研究水培苗中添加一定浓度的硫酸铵对茶氨酸含量的影响.结果表明:培养基中添加25 mmol/L的盐酸乙胺可促进茶氨酸的合成,特别是在培养的第6～12天,愈伤组织中茶氨酸的含量增加明显,培养至第12天时,...     

A stable high-index surface of silicon: si(5 5 12)

A stable high-index surface of silicon, Si(5 5 12), is described. This surface forms a 2 x 1 reconstruction with one of the largest unit cells ever observed, 7.7 angstroms by 53.5 angstroms. Scanning tunneling microscopy (STM) reveals that the 68 surface atoms per 2 x 1 unit cell are reconstructed only on a local scale. A complete structural model for the surface is proposed, incorporating a variety of features known to exist on other stable silicon surfaces. Simulated STM images based on this model have been computed by first-principles electronic-structure methods and show excellent agreement with experiment.     

Porphyrin-heme pathway: regulation by intermediates in bile acid synthesis

Dihydroxycoprostane and trihydroxycoprostane, intermediates in normal bile acid synthesis in the liver, enhanced the rate of porphyrin synthesis in cultured liver cells by induction of delta-aminolevulinate synthetase, the rate-limiting enzyme for this pathway. Other 5beta-cholestane derivatives and cholest-5-ene derivatives were ineffective. The selectivity of the induction may indicate that the above-mentioned coprostanes have a physiological role in porphyrin synthesis.     

First occurrence of the garnet-ilmenite transition in silicates

Pyrope garnet (Mg(3)Al(2)Si(3)O(12)) has been found to transform to an ilmenite-type phase at a loading pressure between 240 and 250 kilobars and at about 1000 degrees to 1400 degrees C in a diamond-anvil press coupled with laser heating. The lattice parameters for the ilmenite-type phase of (Mg(.75) Al(.25))(Si(.75) Al(.25))O(3) are a(0) = 4.755 +/- 0.002 and c(0) = 13.360 +/- 0.005 angstroms. The zero-pressure volume change associated with the garnet-ilmenite transition is calculated to be -7.1 percent. This result verifies the prediction that pyrope garnet would transform to the ilmenite structure at high pressure first suggested in 1962 by Clark et al. and Ringwood.     

2-chain immunoglobulin A molecules: abnormal or normal intermediates in synthesis

Immunoglobulin A (gammaA) myeloma proteins secreted by plasma-cell tumors of mice are of two types, a common four-chain molecule and a rare two-chain (3.9S) molecule. The close similarity between two-chain gammaA molecules and four-chain gammaA molecules and their polymers is demonstrated in tryptic peptide maps of isolated polypeptide chains and by precipitin reactions with rabbit antiserums to gammaA immzunoglobulins. However, a difference between these two types is distinguishable with homologous antiserums. Homologous antiserums to two-chain gammaA immunoglobulins are specific and do not cross-react with four-chain gammaA immutnoglobulins.     

一种喹啉类化合物的合成新方法

以无水醋酸铜为氧化剂,醋酸钯为催化剂,实现了烯丙基苯胺的氧化环化反应,有效得到喹啉类化合物,为喹啉类化合物的合成提供一种新方法。该方法具有环境友好、原子经济性高、反应条件温和等特点。通过对反应溶剂、催化剂、氧化剂、时间、反应温度和添加剂的筛选,得到了最优的反应条件。结果表明,当催化剂醋酸钯为10 mol%,氧化剂无水醋酸铜为0.8 equiv,添加剂4?分子筛为30.0 mg,溶剂为醋酸和1,4-二氧六环的混合且体积比为9/1,反应温度为100 ^oC,反应时间为4 h时,该氧化环化反应效率最高,目标产物收率为68%。     

Primordial carbonylated iron-sulfur compounds and the synthesis of pyruvate

Experiments exploring the potential catalytic role of iron sulfide at 250 degrees C and elevated pressures (50, 100, and 200 megapascals) revealed a facile, pressure-enhanced synthesis of organometallic phases formed through the reaction of alkyl thiols and carbon monoxide with iron sulfide. A suite of organometallic compounds were characterized with ultraviolet-visible and Raman spectroscopy. The natural synthesis of such compounds is anticipated in present-day and ancient environments wherever reduced hydrothermal fluids pass through iron sulfide-containing crust. Here, pyruvic acid was synthesized in the presence of such organometallic phases. These compounds could have provided the prebiotic Earth with critical biochemical functionality.     

Deformation of silicates from the sea of tranquillity

Plagioclase and olivine crystals in the crystalline rocks from the Sea of Tranquillity show little or no evidence of either static or dynamic deformation. The large disorientations in many of the pyroxene crystals are commonly consistent with slip on the system T -(100), t = [001], but these distortions are not due to plastic flow. They are ascribed to rapid growth and quenching phenomena as deduced from studies of chondrules and of quenched natural and experimentally produced melts. Some of the silicates in the breccias and regolith show evidence of shock deformation, from mild to intense, as indicated by pervasive featuring, shock lamallae, and partial transformatiion of pyroxene and plagioclase crystals to glass.     

微生物合成5-羟基色氨酸的研究进展

5?羟基色氨酸 (5-hydroxytryptophan,5-HTP)是血清素和褪黑素生物合成的中间代谢物,可有效治疗多种疾病,如抑郁症、头痛、肥胖和失眠等。传统生产5-HTP的方法是植物提取或化学合成,然而,这些方法效率低,难以大规模生产,无法满足不断增长的市场需求。随着代谢工程和合成生物学的发展,利用微生物合成目标产物成为必然趋势。笔者综述了微生物合成5-HTP的研究进展,通过定向进化羟化酶以及引入辅酶因子合成与再生途径,实现了微生物合成5-HTP,再经代谢工程调控,通过平衡宿主细胞内代谢流提高5-HTP生产效率,为工业微生物有效合成5-HTP提供了理论基础和技术支持。     

Fluorous mixture synthesis: a fluorous-tagging strategy for the synthesis and separation of mixtures of organic compounds

The solution-phase synthesis of organic compounds as mixtures rather than in individual pure form offers efficiency advantages that are negated by the difficulty in separating and identifying the components of the final mixture. Here, a strategy for mixture synthesis that addresses these separation and identification problems is presented. A series of organic substrates was tagged with a series of fluorous tags of increasing fluorine content. The compounds were then mixed, and multistep reactions were conducted to make enantiomers or analogs of the natural product mappicine. The resulting tagged products were then demixed by fluorous chromatography (eluting in order of increasing fluorine content) to provide the individual pure components of the mixture, which were detagged to release the final products.     

Condensation of nonequilibrium phases of refractory silicates from the vapor

Silicon monoxide solid was evaporated in a bell jar containing reducing, neutral, or oxidizing atmospheres at pressures of a few torr. The vapor invariably condensed as smoke-sized particles of silicon sesquioxide, Si(2)O(3). The condensation of a solid whose composition differs from that of the parent gas and is apparently the least stable of the three solid species illustrates the importance of specific nucleation effects in the condensation process. This result has significant implications for theories of formation of grains in space.     

Histone H5 in the control of DNA synthesis and cell proliferation

The linker histones (H1, H5, H1 degrees) are involved in the condensation of chromatin into the 30-nanometer fiber. This supranucleosome organization correlates with the resting state of chromatin, and it is therefore possible that the linker histones play an active role in the control of chromatin activity. The effect of H5 has been directly determined by expression of an inducible transfected H5 gene in rat sarcoma cells, which do not produce H5. Transfection resulted in the reversible inhibition of DNA replication and arrest of cells in G1, at which time H5 concentrations approached that of terminally differentiated avian erythrocytes. The arrest of proliferation was accompanied by specific changes in gene expression probably related to the cell cycle block. The selectivity of these effects suggest that H5 plays an active role in the control of DNA replication and cell proliferation.     

Low-temperature synthesis of zintl compounds with a single-source molecular precursor

Thermolysis of the heterobimetallic phosphinidene complex [Sb(PCy)3]2- Li6.6HNMe2 (Cy = C6H11) at 303 to 313 kelvin gives Zintl compounds containing (Sb7)3- anions. The complex thus constitutes a stable molecular single-source precursor to Zintl compounds and provides a potential low-temperature route to photoactive alkali metal antimonates. The new chemical reaction involved, which is driven thermodynamically by the formation of P-P bonds, has implications in the low-temperature synthesis of other technologically important materials (such as gallium arsenide).     

Induced synthesis of liver microsomal enzymes which metabolize foreign compounds

The administration of 3,4-benzpyrene to rats markedly increases the activities of certain liver microsomal enzymes which metabolize foreign compounds. Evidence based on studies of enzyme induction is presented which suggests the presence in liver microsomes of several enzymes which can catalyze the same type of reaction.     

Formation of organic compounds and their role in transformation of mineral root media in a controlled agroecosystem

The effect of organic matter forming during long-term growing of tomato and wheat plants on transformation of originally abiogenic media (broken granite) into a bioinert body with properties similar to young soils that formed under natural conditions during rehabilitation of mining dumps is shown.     

微波辐射下香豆素基缩氨基硫脲化合物的合成和抑菌活性研究

从含不同取代基的水杨醛与乙酰乙酸乙酯出发,利用微波法合成了一系列新的含有香豆素骨架的缩氨基硫脲类化合物.首先水杨醛与乙酰乙酸乙酯反应得到一系列乙酰基香豆素中间体,然后使之在微波加热条件下与氨基硫脲发生缩合反应得到含有香豆素骨架的缩氨基硫脲化合物,目标化合物的结构均经IR,1H NMR进行了表征.选择2种有害菌对其抑菌活性检测,结果表明,该合成物对测试菌种具有优良的抑制效果,抑菌活性从大到小的顺序是:3b＞3e＞3c＞3f＞3d＞3a.