Total Synthesis of ent-lepadin F and G by a tandem ene-yne-ene ring closing metathesis

The first total synthesis of the decahydroquinoline-alkaloids lepadin F and G is described. As key steps, the decahydroquinoline skeleton has been synthesized by utilizing a tandem ene-yne-ene ring closing metathesis of an acyclic precursor followed by a stereoselective hydrogenation of the resulting diene moiety. The selectivity of these two steps was achieved by a well-directed hydroxyl protection strategy. The synthesized compounds were found to be enantiomers of natural lepadin F and G, consequently the absolute configuration of the natural compounds could be assigned.     

Synthesis of 3-(3-Hydroxypropyl)-phthalide and Pedicellosine

3-(3-Hydroxypropyl)-phthalide1andpedicellosine2aretwoofthephthalidesisolatedfromtheflowersandleavesofGentianapedice/lateWall,respectively'.'SincetheextractofGentianapedicellateWallisusedintreatmentofmanydiseases',andnaturallyoccurringphthalidealwayshasbioactivities',itisdeemedworthwhiletosearchforsVnthesisofthetwophthalides,whichhasnotbeensynthesizedbefore.WeinitiallyattempttoobtainIbycondensationof2-carboxybcnzaldehyde3with2.5eqoftheGrignardreagent5inTHFandseveraleffortsweremade.Unfortuna…     

Biomimetic type approach to the tricyclic core of xyloketals. Application to a short, stereocontrolled synthesis of alboatrin and first synthesis of xyloketal G

A convenient approach to the linear tetrahydrofurano benzopyran ring system of xyloketals is described. An orthoester Claisen rearrangement of a chromenol and an intra-molecular cationic cyclization are the key steps in the synthesis. A short, stereocontrolled and high yield synthesis of the phytotoxic metabolite alboatrin was achieved employing this strategy. A unique case of Lewis acid catalyzed isomerization of epi-alboatrin to alboatrin was observed. Subsequently this methodology was extended for the first total synthesis of xyloketal G, where a one pot reaction of three steps viz., acetylation, isomerization and demethylation occurred during acetylation of a mixture of nor-o-methyl xyloketal G and nor-o-methyl epi xyloketal G in presence of AlCl₃ to furnish xyloketal G in very good overall yield.     

Asymmetric Total Synthesis of Propindilactone G,Part 3: The Final Phase and Completion of the Synthesis

Two independent synthetic approaches were evaluated for the final phase of the asymmetric total synthesis of propindilactone G ( 1 ). The key steps that led to the completion of the asymmetric total synthesis included: 1) an intermolecular oxidative heterocoupling reaction of enolsilanes to link the core structure to the side chain; 2) an intermolecular Wittig reaction for the formation of the α,β,γ,δ‐unsaturated ester; and 3) a regio‐ and stereoselective OsO₄‐catalyzed dihydroxylation of an α,β,γ,δ‐unsaturated enone, followed by an intramolecular lactonization reaction to afford the final product. These reactions enabled the synthesis of (+)‐propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)‐propindilactone G has been revised. Furthermore, the direct oxidative coupling strategy for ligation of the core of propindilactone G with its side chain may find application in the syntheses of other natural products and complex molecules.     

The Total Synthesis of Spirotryprostatin A

Eight concise steps suffice for the first total synthesis of the title compound 1 , which inhibits the transitions from the G2 and M phases into the next phases of the cell cycle. Key steps in the synthesis are a stereocontrolled oxidative rearrangement of an indole to form the chiral spiroindolinone nucleus and a regioselecitve sulfoxide elimination.     

基于表面占位效应和合理动力学模型的电催化火山关系

电催化在水电解、燃料电池等能源和环境领域起着至关重要的作用.电催化火山关系是预测和理解催化剂活性趋势的通用和标准工具.N?rskov等提出的基于最大反应自由能(ΔG0max)的现代电催化火山关系理论,由于未充分考虑电极电位、中间体及毒物的表面占位以及溶液pH等对电催化动力学的影响,在高活性催化剂的准确预测方面存在局限....     

Total synthesis of (-)-senepodine G and (-)-cermizine C

An efficient, stereospecific synthesis of the alkaloids senepodine G (2) and cermizine C (1) has been completed using the BF3.Et2O-promoted stereospecific addition of Me2CuLi to alpha,beta-unsaturated lactam 6 to provide lactam 3, the addition of MeMgBr followed by HCl to convert 3 to senepodine G (2) (six steps, 40% overall yield), and the stereospecific NaBH4 reduction of 2 to give cermizine C (1) (seven steps, 40% overall yield).     

The complete gene cluster of the antitumor agent gilvocarcin V and its implication for the biosynthesis of the gilvocarcins

Gilvocarcin V, an antitumor agent produced by the bacterium Streptomyces griseoflavus G? 3592, is the most studied representative of the distinct family of benzo[d]naphtho[1,2-b]pyran-6-one aryl C-glycoside antibiotics, which show excellent antitumor activity and a remarkably low toxicity. Its biosynthesis contains many intriguing steps, including an oxidative rearrangement, the C-glycosylation, and the generation of a vinyl side chain. These steps all contribute to structural elements of the drug, which are essential for its biological activity, but only poorly understood. Herein we report the cloning and characterization of the gilvocarcin (gil) gene cluster from S. griseoflavus G? 3592, and its heterologous expression in a foreign host (S. lividans). This is the first reported gene cluster encoding the biosynthesis of a benzo[d]naphtho[1,2-b]pyran-6-one aryl C-glycoside antibiotic, which not only provides insights regarding the biosynthesis of gilvocarcin V but also lays the foundation for the detailed studies of its intriguing biosynthetic steps and possibly for the generation of gilvocarcin analogues with improved biological activities through combinatorial biosynthesis.     

Thermochemical investigation of guest-host interactions in Werner clathrates of type [Ni(4-Etpy)4(NCS)2]·nG (G=naphthalene derivatives)

The stoichiometry of thermal decomposition and the thermochemistry were studied for [NiL₄(NCS)₂] (I) as a host complex, and for its clathrates of type [NiL₄(NCS)₂]·2G, where L=4-ethylpyridine and guest molecule G=1-methylnaphthalene in clathrate (II), 1-chloronaphthalene in (III) or 1-bromonaphthalene in (IV). For I, the loss of volatile components proceeds in three steps (–2L, –L, –L); the first steps for II–IV also involve the release of G (–2G, –2L). DSC and X-ray powder measurements indicated a phase transition in the host lattice, and allowed differentiation of the escape of G and L molecules. The enthalpy changes give the following sequence of thermodynamic stability for the studied chlathrates: I>II>III.     

Labeling of immunoglobulin G with multitracer

Labeling of antibodies, immunoglobulin G (IgG), with a multitracer was investigated with the aim of its utilization in the preparation of radiopharmaceuticals. The labeling procedure consists of two steps: conjugation of diethylenetriaminepentaacetic acid (DTPA) cyclic dianhydride with IgG and subsequent labeling with the multitracer.     

Acidity effects on the fluorescence properties and adsorptive behavior of rhodamine 6G molecules at the air-water interface studied with confocal fluorescence microscopy

The effects of acidity on fluorescence originated from rhodamine 6G (R6G) molecules adsorbed at the air-water interface of extremely low-concentration aqueous solutions have been studied with confocal fluorescence microscopy. Similarities and differences in the observed acidity effects between R6G molecules at the interface and those in the bulk solution have been discussed. With increasing the subphase-pH from 1 to 6, height and frequency of photon bursts as well as intensity of the interface-originated fluorescence change in two steps, while bulk fluorescence changes in one step and a little change in the number of adsorbed R6G molecules is verified with surface tension measurements. The results suggest that there is an interface-specific equilibrium among the chemical forms of R6G molecules. Chemical forms contributing to the interface-originated fluorescence above pH 5 are discussed.     

Asymmetric synthesis and absolute configuration of streptophenazine G

The asymmetric synthesis of the antibacterial natural product, streptophenazine G, has been achieved by employing asymmetric alkylation and asymmetric aldol reactions using chiral oxazolidinones as the key steps. The originally proposed structure for streptophenazine G has been revised, and its absolute configuration has been determined to be 1'S,2'R,6'S. The asymmetric total synthesis of 6'-epi-streptophenazine G is also described.     

Improved Synthesis of Mitomycin G

Mitomycin G 2 was derived from mitomycin B 5 by 3 steps in an overall yield of 43 %.     

二氟硅烯与甲醛环加成反应机理的理论研究

The mechanism of the cycloadditohn reaction of singlet difluorosilylene with formaldehyde have been studied by RHF/6-311G* gradient method. The electron correlation energy corrections of energies for all the structures were computed using second-order Moller-Plesset perturbation theory(MP2). The results show that this reaction proceeds via two steps:1)Difluorosilylene and formaldehyde form an intermediate complex, it is an exothermal reaction with no barrier.2) The intermediate complex isomerizes to form the product, after being corrected by zero-point energies, the barrier is 127.28 kJ•mol-1 (MP2/6-311G* 6-311G*).     

Total synthesis of norleucosceptroids F and G

First total synthesis of norleucosceptroids F and G has been achieved through key steps of Michael–Aldol cascade, oxa-Michael cyclization–dehydration–deprotection cascade and cross metathesis(CM), this work developed a general and concise method to the synthesis of leucosceptroid and norleucosceptroid.     

Pinacol macrocyclization-based route to the polyfused medium-sized CDE ring system of lancifodilactone G

The polyfused medium-sized CDE ring system of lancifodilactone G is assembled via B-alkyl Suzuki-Miyaura cross-coupling and SmI 2-mediated pinacol macrocyclization as the key strategic steps.     

Spreading of block copolymer films and domain alignment at moving terrace steps

We investigate spreading of phase separated copolymer films, where domain walls and thickness steps influence polymer flow. We show that at early stages of spreading its rate is determined by slow activated flow at terrace steps (i.e., thickness steps). At late stages of spreading, on the other hand, the rate is determined by the flow along terraces, with diffusionlike time dependence t(-1/2). This dependence is similar to de Gennes and Cazabat's prediction for generic layered liquids [P. G. de Gennes and A. M. Cazabat, C.R. Acad. Sci. Paris II 310, 1601 (1990)], as opposed to the classical Tanner's law of drop spreading. We also argue that chain hopping at the spreading terrace steps should lead to the formation of aligned, defect-free domain patterns on the growing terraces.     

环丙基硅烯的理论研究: 环丙基硅烯C3H5SiH的重排反应及其机理

本文用限制的Hartree-Fock解析梯度方法在3-21G和6-31G^*水平上对环丙基硅烯的重排反应及其机理进行了从头算研究。以6-31G^*优化构型作了二级微扰计算, 并计算了各构型的频率。在此基础上得到了重排反应的热焓△H, 自由能△G和平衡常数K, 用Eyring过渡态理论计算了反应的速度常数k(T), 应用Woodward-Hoffmann规则讨论了环丙基硅烯重排反应过程中端基的旋转机理。结果表明, 环丙基硅烯经过113.4kJ/mol的势垒扩环重排为硅杂环丁烯为自发反应; 而其1,2-氢迁移重排反应热垒为190.0kJ/mol, 是非自发反应, 难于进行,不能与扩环重排相竞争。另外, 扩环重排反应可分为多步过程, 每步的端基旋转均可用Woodward-Hoffmann规则说明。     

Total syntheses of novel cytocidal beta-carboline alkaloids, oxopropalines D and G

A new type of beta-carboline nucleus, N-methoxymethyl-4-methyl-beta-carboline (4) was synthesized by thermal electrocyclic reaction of a 1-azahexatriene system, involving the indole 2,3-bond. The key compound N-methoxymethyl-1-methoxycarbonyl-4-methyl-beta-carboline (2) was then prepared in a four-step sequence. The total synthesis of oxopropaline G (1e) was achieved from this key compound in four steps. Furthermore, the enantioselective total syntheses of (+)-oxopropaline D (1c) and its enantiomer were also achieved by application of the Sharpless oxidation-procedure in nine steps from 2.     

Synthetic studies on oxindole spiro-lactones with thalliumd(III) trinitrate: A formal total synthesis of (±)-tryptoquivaline G

(±)-Tryptoquivaline G was formally synthesized through shortened steps from tryptophan, in which oxidation with thallium(III) trinitrate(TTN) was effected at the crucial stage. The present work also constitutes the first synthesis of oxindole lactones carrying 2-alkyl quinazolinones.