Extensive Studies on the AlEt3/THF-Promoted Diastereoselec-tive Tandem Rearrangement/Reduction of a-Hydroxy (Amino) Heterocyclopropane: An Efficient Approach to 2-Quaternary 1,3-Diheteroatom Units

Introduction Diastereoselective construction of 1,3-diheteroatom units, especially 1,3-amino alcohols and 1,3-diols, has always been in high demands in synthetic organic chemistry, as they are widely present in many natural products and potent drugs, such as nucleoside antibiot-ics and the HIV protease inhibitors.1,2 They have also been used as chiral ligands for asymmetric catalysts and as synthetic intermediates.3 Although several methods for the construction of 1,3-amino alcohols have been…     

新型手性氨基醇的合成及其用于不对称催化醛类烷基化反应

制备了一种由糖类化合物衍生的新型手性氨基醇（Ⅰ），并将其作为手性源用于醛类的不对称烷基化反应．考察了在手性氨基醇的存在下，各种醛和二乙基锌作用生成相应的手性仲醇的光学收率及化学收率．结果表明，该催化剂对于芳香醛的烷基化更为有效．并考察了几种反应条件对于苯甲醛的不对称催化烷基化反应的影响，其中最佳结果为１－苯基－１－丙醇的光学收率达８２．７％，而化学收率达５８．８％．     

Studies on separation mechanisms of biological molecules on a polyvinyl alcohol column

Summary The chromatographic separation mechanism on a polyvinyl alcohol (PVA) column in aqueous systems was explored utilizing several different types of compound such as polyethylene glycols, carbohydrates, pyrimidine and purine bases, fatty acids, monophosphate nucleotides and glycyl-peptides. Two types of separation mechanisms were found to occur for these substrates. The polyethylene glycols and the carbohydrates were eluted by size-exclusion chromatography. The retention behavior of the other substrates could be explained by the solvophobic theory, suggesting that the predominant separation mode was reversed-phase chromatography. The occurrence of reversed-phase chromatography was also indicated by the remarkable effect of the addition of ion-association reagents to the chromatographic system on the retention of the monophosphate nucleotides.     

Ag+ ion transport studies in a polyvinyl alcohol-based polymer electrolyte system

Thick films of pure polyvinyl alcohol and polyvinyl alcohol doped with silver nitrate with different compositions have been prepared by solution cast technique. The FT-IR spectrum confirms the complexation process. The conductivity of the pure polyvinyl alcohol is of the order of 10⁻⁷ Sm⁻¹ at 90 °C, and its value increases by two orders of magnitude when doped with 20 wt% of AgNO₃. The activation energy, calculated from the Arrhenius plot for all compositions of the poly vinyl alcohol doped with silver nitrate, is between 0.24 and 0.35 eV. The migration energy for the ion in polymer electrolyte has been calculated from the modulus spectrum, and is in good agreement with the activation energy calculated from the Arrhenius plot. The modulus spectra indicate the non-Debye nature of the material.     

Preparation and partial characterization of a soluble site-to-site directed enzyme complex composed of alcohol dehydrogenase and lactate dehydrogenase

A soluble, bifunctional enzyme complex has been prepared by crosslinking lactate dehydrogenase and alcohol dehydrogenase with glutaraldehyde. The crosslinking was performed on a solid phase while the active sites of alcohol dehydrogenase and lactate dehydrogenase were held adjacent to one another with the aid of a bis-NAD analog. Subsequently, the enzyme complex was released from the solid phase. The soluble enzyme complex was then purified by using NAD-Sepharose as an affinity adsorbent. Based on gel filtration experiments, the complex was estimated to consist of one of each dehydrogenase. By using a third enzyme, lipoamide dehydrogenase, which competes with lactate dehydrogenase for NADH produced by alcohol dehydrogenase, the effect of site-to-site orientation was studied. It was found that about 83% of the NADH produced by alcohol dehydrogenase was oxidized by site-to-site oriented lactate dehydrogenase compared to a figure of only about 61% obtained in an identical system of separate enzymes. This indicates that given two alternative routes, the preference for the one to lactate dehydrogenase over the one to lipoamide dehydrogenase is enhanced when lactate dehydrogenase and alcohol dehydrogenase are site-to-site oriented.     

1,4-双(9-O-奎宁)-2,3-二氮杂萘-OsO4催化烯烃的不对称氨羟化反应

在氧化-供氮试剂N-氯代氨基甲酸苄酯存在下,1,4-双(9-O-奎宁)-2,3-二氮杂萘-OsO4催化剂在5种烯烃的不对称氨羟化反应中表现出极高的对映选择性(85%～99%e.e.)和区域选择性,产率48%～68%.     

Novel Stereoselective Synthesis of (E)- α，β-Unsaturated Esters by the Tandem Reaction of Deprotonation-Oxidation-Wittig Reaction from Phosphonium and Arsonium Salt

Phosphonium or arsonium salt 1 can undergo the tandem reaction of deprotonation -oxidation-Wittig reaction with alcohol 2 in the presence of sodium hydroxide and manganese dioxide,which affords a general simplified method for the stereoselective synthesis of (E)- α-β-unsaturated esters 3.     

三价锰离子引发烯类单体在聚乙烯醇上接枝聚合的研究

<正> 无论是淀粉;纤维素,还是聚乙烯醇(PVA)的接枝反应,Ce(Ⅳ)被认为是一个十分有效的引发剂,已有较详尽的研究。与Ce(Ⅳ)相类似,Mn(Ⅲ)也可以和一些高聚物组成氧化还原引发体系,由此产生自由基,引发烯类单体在高分子主干上进行接枝聚合。Ranby等人,以焦磷酸络合的三价锰离子引发烯类单体在纤维素和淀粉的接枝反应中,获得了高效的接枝产物。有用这种引发体系在淀粉上接枝丙烯腈获得吸水276     

Ester synthesis catalyzed by Mucor miehei lipase immobilized on magnetic polysiloxane-polyvinyl alcohol particles

Mucor miehei lipase was immobilized on magnetic polysiloxane-polyvinyl alcohol particles by covalent binding with high activity recovered. The performance of the resulting immobilized biocatalyst was evaluated in the synthesis of flavor esters using heptane as solvent. The impact on reaction rate was determined for enzyme concentration, molar ratio of the reactants, carbon chain length of the reactants, and alcohol structure. Ester synthesis was maximized for substrates containing excess acyl donor and lipase loading of 25 mg/mL. The biocatalyst selectivity for the carbon chain length was found to be different concerning the organic acids and alcohols. High reaction rates were achieved for organic acids with 8 or 10 carbons, whereas increasing the alcohol carbon chain length from 4 to 8 carbons gave much lower esterification yields. Optimal reaction rate was determined for the synthesis of butyl caprylate (12 carbons). Esterification performance was also dependent on the alcohol structure, with maximum activity occurring for primary alcohol. Secondary and tertiary alcohols decreased the reaction rates by more than 40%.     

Bifunctional pyridyl alcohols with the bicyclo[3.3.0]octane scaffold in the asymmetric addition of diethylzinc to aldehydes

Some new pyridyl alcohols with the cis-bicyclo[3.3.0]octane scaffold were synthesized and used as chiral ligands for the enantioselective addition of diethylzinc to aldehydes. Ligands 4 were found to be far superior to the C₂-symmetric ligands 2 in terms of enantioselectivities. Quantitative yields and enantiomeric excesses of up to 92% were obtained when the ligand 4 was used. The carbonyl function in 4 proved to be beneficial for the high enantioselectivities in the addition of diethylzinc to aldehydes. Conversion of the carbonyl group into oxime or oxime ether group led to a sort of more active ligands, which catalyzed the same reaction with rate acceleration.