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61.
62.
Ming Li Rugang Xie Changwei Hu Xin Wang Anmin Tian 《International journal of quantum chemistry》2000,78(4):245-251
The ab initio molecular orbital method is employed to study the structures and properties of chiral cyclic sulfur‐containing oxazaborolidine, as a catalyst, and its borane adducts. All the structures are optimized completely by means of the Hartree–Fock method at 6‐31g* basis sets. The catalyst is a twisted chair structure and reacts with borane to form four plausible catalyst–borane adducts. Borane–sulfur adducts may be formed, but they barely react with aromatic ketone to form catalyst–borane–ketone adducts, because they are repulsed greatly by the atoms arising from the chair rear of the catalyst with a twisted chair structure. Borane–N adduct has the largest formation energy and is predicted to react easily with aromatic ketone to form catalyst–borane–ketone adducts. The formation of the catalyst–borane adducts causes the BBH3 HBH3 bond lengths of the BH3 moiety to be increased and thus enhances the activity of the enantioselective catalytic reduction. The borane–N adduct is of great advantage to hydride transfer. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 78: 245–251, 2000 相似文献
63.
Wolfgang Fraenk Thomas M. Klaptke Burkhard Krumm Peter Mayer Holger Piotrowski Martin Vogt 《无机化学与普通化学杂志》2002,628(4):745-750
The Lewis acid (C6F5)3B was reacted with ICN, NH2CN, C3N3X3 (X = H, Cl, F). The resulting Lewis acid base adducts ( 1—5 ) were fully characterized by analytic and spectroscopic methods. Additionally, the structures of the adducts 1—4 were determined by single crystal X‐ray analyses. It has been qualitatively shown, that a high field shift of the 11B as well as the 19F NMR resonances of the o‐F atoms of the C6F5‐substituents suggests a longer B—N distance. 相似文献
64.
Toralf Peymann Axel Herzog Carolyn B. Knobler M. Frederick Hawthorne 《Angewandte Chemie (International ed. in English)》1999,38(8):1061-1064
No explosion , but per-B-hydroxylation occurs if the icosahedral boron hydrides [closo-B12H12]2− (see picture), [closo-CB11H12]−, or closo-1,12-(CH2OH)2-1,12-C2B10H10 are refluxed in 30 % hydrogen peroxide. Thus, the three isoelectronic species [closo-B12(OH)12]2−, [closo-1-H-1-CB11(OH)11]−, and closo-1,12-H2-1,12-C2B10(OH)10 were obtained. ○=BH, ○=BOH. 相似文献
65.
The dialysis method has been traditionally used for the conversion of native human plasminogen (Glu-Hpg) to lys-plasminogen(Lys-Hpg). Here is described a solid-phase synthesis method for the preparation of an acyl-plasminogen-streptokinase activator complex(APSAC) from Lys-Hpg, streptokinase (SK) and chemical modification agent(4-amidinophenyl-4‘-aminobenzoate hydrochloride) with the L-lysine-Sepharose 4B Column as the carrier. The new method significantly increases the product yield and purity over the liquidphase methods. The APSAC prepared with the new method exhibits a significant thrombolytic effect with a long half-life of about 8.8 h in rabbits. 相似文献
66.
Urokinase-type plasminogen activator (uPA) is a trypsin-like serine protease and plays a key role in several biological processes, including tissue remodeling, cell migration, and matrix degradation. The inhibitors of uPA have been shown to prevent the spread of metastasis and tumor growth, and accordingly uPA is widely recognized as a target for the treatment of cancer. In this work, we report the crystal structures of the complexes of uPA with its inhibitors: 4- (aminomethyl)-benzoic acid (AMBA) and 4-(aminomethyl-phenyl)-methanol (AMPM), both at a resolution of 2.35 А. The inhibitory constants of these two inhibitors were measured by a chromogenic competitive assay, and it was found that AMBA is a better inhibitor for uPA (Ki = 2.68 mM) than AMPM (Ki = 13.99 mM). The structural study shows that the binding mode of inhibitor AMBA on uPA is similar to that of AMPM on uPA, both docked into the active site S1 pocket of uPA. Structural details of these complexes are provided to explain the difference of inhibitory constants. 相似文献
67.
Tris(pentafluorophenyl)borane [B(C6F5)3] has been used as an efficient catalyst for reductive alkylation of alkoxy benzenes using aldehydes as an alkylating agent in the presence of polymethylhydrosiloxane (PMHS). Various alkylated trimethoxybenzene derivatives have been prepared in good to high yields. In addition, B(C6F5)3 was also used as a catalyst for the reaction of electron-rich arenes with aldehydes to obtain triarylmethanes. The use of reductive alkylation protocol for the synthesis of an isochroman and tetrahydroisoquinoline derivatives has also been demonstrated. 相似文献
68.
A number of 2-azetidinones were synthesized in good to excellent yields by a novel reaction between Schiff bases, substituted acetic acids and alkoxymethylene-N,N-dimethyliminium salts, the adduct formed from DMF and O-alkylating agents. The advantages of this new method are mild reaction conditions, low cost, avoiding the use of chlorinating agents and easy purification of the products. The best results were obtained when DMF and dimethyl sulfate were used at room temperature. 相似文献
69.
Paul M. Zimmerman Ankan Paul Dr. Zhiyong Zhang Dr. Charles B. Musgrave Prof. 《Angewandte Chemie (International ed. in English)》2009,48(12):2201-2205
Enders' N‐heterocyclic carbene (NHC) dehydrogenates ammonia–borane with a relatively low barrier, producing NH2BH2 and NHC–(H)2. The nickel NHC catalyst present in the reaction media can activate the NHC–(H)2 produced to regenerate the free NHC and release H2. The release of free NHC enables further dehydrogenation of ammonia–borane.
70.
Holger Braunschweig Prof. Dr. Rian D. Dewhurst Dr. 《Angewandte Chemie (International ed. in English)》2009,48(11):1893-1895
A reaction with many facets : The facile dehydrogenative synthesis of a borylene complex (left in scheme) from a dihydroborane (right), proceeds reversibly at room‐temperature. The implications of this reaction for the fields of inorganic, main‐group, and hydrogen‐storage chemistry are covered in this Highlight.