Synthesis of PI-88 analogue using novel O-glycosidation of exo-methylenesugars

Acid-promoted α-stereoselective O-glycosidation of 1-exo-methylenesugars was successfully applied to the synthesis of a PI-88 analogue. By using methanesulfonic acid as a promoter, 1′-C-methyl-α-disaccharides with p-methoxybenzyl protection were obtained in high yield. The sequence of selective deprotection and glycosidation provided 1-C-methyl-pentasaccharide efficiently.     

Adsorptive passivation of iron by organic acid anions

Studies on the iron passivation by organic acid anions in aqueous solutions are briefly reviewed. It is shown that the passivation can be caused only by their adsorption, retarding both the iron dissolution and the formation of oxide films. Earlier, it had been believed that oxide films play a dominant role in the iron passivation in neutral solutions. The recent viewpoint is that such nonoxide iron passivation can occur in solutions of salts of not only aromatic amino acids (sodium phenylantranilate and its substitutes), but other carboxylic acids as well. An important role of chemisorption and hydrophobic properties of anions for the formation of adsorption passive films is emphasized. New possibilities for inhibitor protection of iron against corrosion, which is based on adsorptive passivation, are pointed out.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1503–1507.Original Russian Text Copyright © 2004 by Kuznetsov.     

High temperature corrosion behaviour of M(Co,Ni)CrAIY-coatings on high temperature materials-microanalytical investigations

In our former investigations, the phenomenon high temperature corrosion (HTC) was described exemplarily on selected materialcoating combinations for blades of stationary gas turbines, mainly in the temperature region of up to 750° C. To answer the question, in which manner higher gas inlet and/or higher material surface temperature would influence the HTC behaviour, a special analytical technique—the integral layer profile analysis—was introduced to ameliorate concentration profile methods. By examining IN 738 LC specimens with CoCrAlY plasma spray coating, stressed by hot gas at 900° C, the limits of this system are shown by explaining the corrosion mechanism; the method is also used for other systems, e.g. U 520 with NiCrAlY coating at 750° C.     

Efficient routes to optically active azido-, amino-, di-azido- and di-amino-cyclitols with chiro- and allo-configuration from myo-inositol

Efficient routes to hitherto unknown 1d-2,5-di-azido-di-deoxy-allo-inositol, 1d-2,5-di-amino-di-deoxy-allo-inositol, 1l-1-azido-1-deoxy-chiro-inositol and 1l-1-amino-1-deoxy-chiro-inositol were developed by using cheaply available myo-inositol as the starting material. Preliminary investigations on the enzyme inhibitory properties were done. The methodology reported is amenable to gram scale synthesis and thus can find application in natural product synthesis.     

Copper corrosion in buffered and non-buffered synthetic seawater: a comparative study

The electrochemical behaviour of copper in neutral buffered and non-buffered synthetic seawater and in pure chloride solutions has been studied by cyclic voltammetry, weight loss measurements, open circuit potential and scanning electron microscopy (SEM). Values of the repassivation potentials of Cu in non-buffered and buffered synthetic seawater, at 50 mV s^–1, were 0.12 and 0.46 V vs. SCE, respectively. The sharpness, heights and location of the different peaks as well as their charges were shown to be influenced by the composition of the solution, buffering conditions, deoxygenation, polarization potential and time. High chloride concentrations lead to higher oxidation charges. The anodic and the cathodic charges were shown to increase as the chloride concentration increases. The open circuit potential transients of copper in non-deoxygenated, non-buffered synthetic seawater indicate pitting from the beginning of the exposure, while in buffered solutions the pitting appeared only after a quite long exposure period, i.e. after 40 days. Corrosion rates of Cu samples after 3 months of immersion were higher in solutions of pure chloride (0.5 M) than in synthetic seawater. After six months the differences were even more noticeable. SEM images have showed a somewhat higher density of pits on copper samples immersed in the chloride solution (0.5 M), in comparison with those in synthetic seawater.     

The isolation, structural determination, and total synthesis of terfestatin A, a novel auxin signaling inhibitor from Streptomyces sp.

Indole 3-acetic acid, a plant hormone auxin, regulates every aspects of plant growth and development. In the screening for specific inhibitors on auxin signaling using the transgenic Arabidopsis plant harboring the auxin-responsive reporter gene, terfestain A was found to be a novel inhibitor of auxin signaling from the culture of Streptomyces sp. F40. The structure of terfestatin A was determined to be p-terphenyl β-glucoside on the basis of spectroscopic analyses, chemical degradation, and total synthesis.     

Cu-P系稀土耐候钢中最佳稀土含量的研究

利用光学显微镜、图像分析仪和电子探针对低氧低硫的10PCuRE耐候钢板坯进行了观察和检测,采用干-湿周浸室内加速试验方法测得了试验钢的腐蚀率.用电化学方法测得了带锈样的阳极极化曲线.研究得出对于S:～0.004%,O:～0.002%的10PCuRE耐候钢,最佳稀土含量为0.0065%～0.012%,此稀土含量对非金属夹杂物的变质作用和耐蚀性能的提高最为有利.     

植入用Co—Cr—Mo合金与Ti—6Al—4V合金的电偶腐蚀研究

组件式设计常被用地人工髋关节，钴络钼合金（Ｃｏ－Ｃｒ－Ｍｏ）与钛合金（Ｔｉ－６Ａｌ－４Ｖ）的压配最常用，本文应用电化学方法研究了静态条件下两种合金的电偶腐蚀行为，浸泡实验表明，钴络钼合金为阳极，但电偶电流与其维钝电流相近，并无明显加速度腐蚀效应，钛合金为阴极，受到保护，失重及金相观察结果显示，在４５天的浸泡实验周期内，未发现腐蚀痕迹，混合电位理论和电位处于两种合金的钝化电位区，电偶电流为合金的维钝     

Absolute stereochemistries and total synthesis of (+)-arisugacins A and B, potent, orally bioactive and selective inhibitors of acetylcholinesterase

In the current studies, we used the Kakisawa-Kashman modification of the Mosher NMR method to determine the complete absolute stereochemistry of arisugacins. We also report the convergent total synthesis of (+)-arisugacins A and B by a sequence including (i) ruthenium complex-catalyzed asymmetric reduction of the cyclohexenone derivative; (ii) stereoselective construction of the arisugacin skeleton by a Knoevenagel-type reaction of an α,β-unsaturated aldehyde derivative with production of a 4-hydroxy-2-pyrone derivative as a key reaction; and (iii) stereoselective dihydroxylation to give the diol derivative, followed by deoxygenation. Accordingly, we defined the absolute structures of arisugacins A and B as 4a-(R),6a-(R),12a-(R), and 12b-(S). Finally, we characterized the bioactivities of the synthetic intermediates to understand the structure-activity relationships of the arisugacins.     

Synthesis of novel rigid triazine-based calix[6]arenes

In this report, the stepwise synthesis of a novel rigid and functionalised macrocycle 2 based on triazine and phenylenediamine linkers, is presented. Poor recognition of the macrocycle 2 for its substrates is observed, which shows experimentally that for the meltriazine based-calix[6]arene system, the binding ability of the melamine moiety gets more benefit from the ring flexibility derived from a xylenediamine linker 1 than from a phenylenediamine linker 2.