Strained silacycle-catalyzed asymmetric Diels-Alder cycloadditions: the first highly enantioselective silicon Lewis acid catalyst

The first highly enantioselective silicon Lewis acid catalyst for an asymmetric organic transformation has been developed. The catalyst derives its activity from the strain induced in the silicon center by virtue of being constrained in a five-membered ring. A simple tridentate ligand has been developed and the derived chlorosilane complex catalyzes the Diels-Alder cycloaddition of methacrolein and cyclopentadiene with 94% ee.     

Cinnamic acid amides and lignanamides from Aptenia cordifolia

Examination of the hydroalcoholic extract of the leaves of Aptenia cordifolia has afforded three cinnamic acid amides and two lignanamides. Structures were established on the basis of spectroscopic data, including 2D-NMR analyses.     

脑细胞激活素药物的化学成分分析

采用日本岛津LC-60A型高压液相色谱仪和美国P-E3030型原子吸收分光光度计，对该药进行了氨基酸、维生素和化学元素的含量测定。结果表明，该药含有18种氨基酸，不少于3种维生素和20几种化学元素，为进一步改进该药物的合理配制方法和临床应用提供了参考数据。     

Interpretation of inorganic arsenic metabolism in humans in the light of observations made in vitro and in vivo in the rat

The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (As_i). In order to document the methylation process in humans, the kinetics of As_i, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of As_i. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As₂O₃) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of As_i metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of As_i uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems.     

Organometallic complexes with biological molecues,part 3. in vivo cytotoxicity of diorganotin (IV) chloro and triorganotin (IV) chloro derivatives of penicillin g on chromosomes of aphanius fasciatus (pisces,cyprinodontiformes)

In order to obtain a continuous source of mitotic metaphases, gill tissue of Aphaius fasciatus (Pisces, Cyprinodontiformes) has been successfully employed. Results gathered after exposure of fish to R₂SnClpenG, R₃SnClpenGNa, to the parents R₂SnCl₂, R₃SnCl and to penGNa (penGNa = penicillinGNa; R = methyl, butyl and phenyl) suggest that both the parent organotin (IV) chloride and organotin (IV) chloropenG derivatives are toxic while penGNa exerts no significant toxic activity. Essentially, all of the chromosome abnormalities are classifiable as irregularly staining of chromosomes, breakages, side-arm bridges or pseudochiasmata.     

Reaction of pentafluorobenzoylpyruvic acid with amines

Reactions of pentafluorobenzoylpyruvic acid with amines afford the respective enamines. The intramolecular cyclization of the latter results inN-substituted 4-quinolone-2-carboxylic acids. Ammonia and triethylamine favor the cyclization of pentafluorobenzoylpyruvic acid to 2-carboxychromone.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 299–302, February, 1994.     

Cubane derivatives 1. Synthesis and molecular structures of the esters of 1,4-cubanedicarboxylic acid

An effective method of esterification of 1,4-cubanedicarboxylic acid with alkylsulfuric acids is proposed. The derivatives of alkanols with substantially different pK_a Valus are obtained in high yields. Molecular structures of the esters obtained are confirmed by various methods. The X-ray study showed a remarkable effect of the nature of an alkyl radical on the geometry of the cubane core.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp.668–672, April, 1994.The authors thank Dr. G. V. Lagodzinskaya for analyzing the NMR spectra and for useful discussions.     

Synthesis and crystal structure of 1,3,5-tris [4-(phenylethynyl)phenyl]benzene

The crystal structure of 1,3,5-tris[4-(phenylethynyl)phenyl]benzene (1) has been investigated. Compound1 represents a model of the repeating unit of the most typical polyphenylene, which contains 1,3,5-trisubstituted benzene rings (chain centers) and acetylenic groups (complex-forming and cross-linking centers) in the main chain. The acetylene groups of neighboring molecules have a tendency to close mutual arrangement, which is favorable for their topochemical interaction. However, the relative conformational rigidity of molecules1 restricts not only the possibility of the optimal adjustment of the reactive sites of neighboring molecules to one another, but also hampers the close packing of molecules in the crystal, which contains channels filled by the solvent molecules (chloroform).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1986–1992, November, 1994.The work was carried out with the financial support of the International Science Foundation and the American Crystallographic Association.     

Electrochemical co-oxidation of C-H acids and methanol as a new route to functionalized cyclopropanes

Electrolysis of dimethyl malonate or methyl cyanoacetate in methanol in the presence of LiCl in an undivided cell leads to formation of 1,1,2,2-cyclopropanetetracarboxylic derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1835–1836, October, 1994.This work was supported by the International Science Foundation (Grant No MHY 000).