共查询到20条相似文献,搜索用时 218 毫秒
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用叠氮钠和D-苯基甘氨酸为原料合成了2-[4-取代苯基-2-氧-3-酰氨基-1-吖啶基]-2-苯基乙酸类化合物. 在叠氮乙酰氯和亚胺化合物在三乙胺存在下在-78℃时进行环缩合反应, 可导致立体专一性合成顺-甲基-2-(4-取代苯基-2-酮-3-叠氮-1-吖啶基)-2-苯基乙酸, 催化氢化或硫化氢可减少叠氮基和得到氨基β-内酰胺后者被酰化生成α-酰氨基-β-内酰胺, 在温和碱性条件下选择性地氢化酯基既不会影响β-内酰胺环, 又不全影响酰胺侧链. 合成了二十个标题化合物, 其中九个被表明对β-内酰胺酶有抑制活性. 相似文献
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维生素B12环B酰亚胺前体及琥珀胺类药物不对称合成的研究 总被引:1,自引:1,他引:0
从γ-丁内酯合成了维生素B12环B酰亚胺前体及琥珀酰胺类药物的3个衍生物,进行了其中不对称季碳的构筑,改进了TiCl3还原硝基乙烯类化合物的反应,同时发现了一个简便合成乙琥酰胺环的新方法. 相似文献
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5-溴戊酰氯与手性助剂(S)-4-苄基-2-噁唑烷酮经酰胺化反应制得手性酰胺(3);3与叠氮钠反应得烷基化前体(4);以苄溴为烷基化试剂,碱辅助在酰胺羰基邻位引入苄基高立体选择性地制得手性酰胺[(R)-5],dr>99/1。用H2O2脱除(R)-5中的助剂结构单元得多米诺反应的前体手性叠氮羧酸[(R)-6];用草酰氯预处理(R)-6,原位制得叠氮酰氯,随即以四氯化锡来实现分子内Schmidt反应,苯环原位捕获重排中间体合成内酰胺[(R)-7],92%ee;用红铝还原(R)-7合成了(R)-苯并吲哚里西啶,收率85%,总收率40.6%,其结构经1H NMR,13C NMR和IR确证。 相似文献
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以邻硝基苯甲酸或对氯邻硝基苯甲酸为原料,经酰氯化、胺化、还原、胺解4步反应,合成了6个新的邻甲酰胺基苯甲酰胺类化合物,总收率66%~73%,其结构经1 H NMR, MS和元素分析表征. 相似文献
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Paul S Kalaga RS Gololobov G Brenneman D 《Applied biochemistry and biotechnology》2000,83(1-3):71-82; discussion 82-4, 145-53
The autoimmune repertoire is well known from previous studies to be capable of producing catalytic antibodies directed to self-antigens. In the present study, we explored the ability of 26 monoclonal light chains (L chains) from multiple myeloma patients to cleave radiolabeled gp120, a foreign protein. One L chain with this activity was identified. 125I-gp120 and unlabeled gp120 were cleaved at several sites by the L chain, as shown by SDS-polyacrylamide gel electrophoresis, autoradiography, and immunoblotting, respectively. The apparent dissociation constant of the L chain was 130-145 nM, indicating high-affinity gp120 recognition. 125I-albumin was not cleaved by the L chain, and various proteins and peptides did not inhibit gp120 cleavage by the L chain, suggesting that the activity is not a nonspecific phenomenon. The substrate recognition determinants may be conserved in different HIV-1 strains, because gp120 isolated from strains SF2, MN, and IIIB was found to be cleaved by the L chain. Micromolar concentrations of a synthetic peptide corresponding to residues 23-30 of gp120 inhibited the cleavage of 125I-gp120, suggesting that these residues are components of the epitope recognized by the L chain. The toxic effect of gp120 in neuronal cultures was reduced by about 100-fold by pretreatment of the protein with the L chain. These observations open the possibility of utilizing gp120-cleaving antibodies in the treatment of AIDS. 相似文献
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Cristina I. De Matteis David A. Simpson Stephen W. Doughty Melvin R. Euerby P. Nicholas Shaw David A. Barrett 《Journal of chromatography. A》2010,1217(44):6987-6993
The retention behaviour of a series of 15 n-alkylbenzenes and pentylbenzene structural isomers and benzene were investigated using porous graphitic carbon (PGC) and octadecyl-bonded silica (ODS) stationary phases. Shorter chain n-alkylbenzenes and benzene (n = 0–6), and all the pentylbenzene isomers were more strongly retained on ODS, although the selectivity was greater with PGC. For the pentylbenzene analytes the degree of branching in the alkyl chain at the position adjacent to the aromatic ring affects retention on PGC, with higher retention in less branched molecules. Molecular modelling studies have provided new insights into the geometry of aromatic π–π stacking interactions in retention on PGC. For alkylbenzenes with high branching at the position adjacent to the ring, the preferred geometry of association with the surface is with the branched chain directed away from the surface, a geometry not seen in the other alkylbenzenes. The most energetically favoured orientation for interaction between analytes and the PGC surface was found to be cofacial for toluene and ethylbenzene, whereas for other analytes this interaction was in a face-edge orientation. The alternative geometry of association observed with both toluene and ethylbenzene may explain the enhanced retention of these two analytes on PGC compared with their longer chain analogues. Quantitative structure–retention relationships revealed the importance of compactness in analyte structure during retention on PGC, with decreased compactness (associated with longer chain length and reduced chain branching) improving retention. 相似文献
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Michael Buback Mark Egorov Vladimir Kaminsky 《Macromolecular theory and simulations》1999,8(5):520-528
An approach for modeling chain‐length dependent termination rate coefficients is presented. The method is based on the assumption that free‐radical chain length may be considered as a continuous variable. As compared to discrete numerical methods, in continuous modeling the number of independent dimensionless parameters can be significantly reduced. As a consequence, for a wide variety of monomers the conversion dependence of kt can be predicted without extensive numerical calculations. The method may also be used to determine polymerization conditions under which simpler models of kt (which neglect effects arising from the dependence of kt on chain length) may be applied. Calculations for methyl methacrylate, styrene, and butyl acrylate bulk polymerizations up to high degrees of monomer conversion show that the impact of chain length on termination varies with conversion and strongly depends on the type of monomer. 相似文献
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Directed metalation route to ferroelectric liquid crystals with a chiral fluorenol core: the effect of restricted rotation on polar order 总被引:1,自引:0,他引:1
McCubbin JA Tong X Wang R Zhao Y Snieckus V Lemieux RP 《Journal of the American Chemical Society》2004,126(4):1161-1167
A new series of smectic C* (SmC*) mesogens containing a chiral (R)-2-octyloxy side chain and either a fluorenone (2a-e) or chiral fluorenol (3a-e) core were synthesized using a combined directed ortho metalation-directed remote metalation strategy. The SmC phase formed by the fluorenol mesogens is more stable and has a wider temperature range than that formed by the fluorenone mesogens, which may be ascribed to intermolecular hydrogen bonding according to variable-temperature FT-IR measurements. The C11 fluorenol mesogens (R,R)-3d and (S,R)-3d were obtained in diastereomerically pure form and gave reduced polarization (Po) values of +106 and +183 nC/cm2, respectively, at 10 K below the SmA*-SmC* phase transition temperature. The difference in Po values suggests that the chiral fluorenol core contributes to the spontaneous polarization of the SmC* phase. This is ascribed to the bent shape of the fluorenol core, which should restrict its rotation with respect to the side chains in the SmC* phase and favor one orientation of its transverse dipole moment along the polar axis, and to steric coupling of the core to the chiral 2-octyloxy side chain. 相似文献
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Sudhir Paul Ravi S. Kalaga G. Gololobov Douglas Brenneman 《Applied biochemistry and biotechnology》2000,83(1-3):71-84
The autoimmune repertoire is well known from previous studies to be capable of producing catalytic antibodies directed to
self-antigens. In the present study, we explored the ability of 26 monoclonal light chains (Lchains) from multiple myeloma
patients to cleave radiolabeled gp 120, a foreign protein. One L chain with this activity was identified. 125I-gp120 and unlabeled gp 120 were cleaved at several sites by the L chain, as shown by SDS-polyacrylamide gel electrophoresis,
autoradiography, and immunoblotting, respectively. The apparent dissociation constant of the L chain was 130–145 nM, indicating high-affinity gp 120 recognition. 125I-albumin was not cleaved by the L chain, and various proteins and peptides did not inhibit gp 120 cleavage by the L chain,
suggesting that the activity is not a nonspecific phenomenon. The substrate recognition determinants may be conserved in different
HIV-1 strains, because gp 120 isolated from strains SF2, MN, and IIIB was found to be cleaved by the L chain. Micromolar concentrations
of a synthetic peptide corresponding to residues 23–30 of gp 120 inhibited the cleavage of 125I-gp 120, suggesting that these residues are components of the epitope recognized by the L chain. The toxic effect of gp120
in neuronal cultures was reduced by about 100-fold by pretreatment of the protein with the L chain. These observations open
the possibility of utilizing gp120-cleaving antibodies in the treatment of AIDS. 相似文献
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The interactions between sodium dodecyl sulphate (SDS) and three autoassociative polymers (hydrophobically end-capped poly(ethylene oxide) urethanes) are studied by conductimetry, fluorescence, and viscometry. By the first two techniques the interactions are found to increase with the hydrophobicity of the polymer and to be stronger than those observed for a polyethylene oxide (PEO) of the same order of molecular weight. The results seem to be consistent with a model where SDS micelles are formed around hydrophobic chain ends in a first stage, and along the main chain in a second stage. For the more hydrophobic sample already self-aggregated in water and of relatively large reduced viscosity, the addition of SDS induces a loss in viscosity contrary to the less hydrophobic ones and PEO. Such effect may be attributed to the destruction of the chain end association by the formation of SDS micelles around one end in the first stage of the interaction. 相似文献
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Side chains of amino acid residues are the determining factor that distinguishes proteins from other unstable chain polymers. In simple models they are often represented implicitly (e.g., by spin states) or simplified as one atom. Here we study side chain effects using two-dimensional square lattice and three-dimensional tetrahedral lattice models, with explicitly constructed side chains formed by two atoms of different chirality and flexibility. We distinguish effects due to chirality and effects due to side chain flexibilities, since residues in proteins are L residues, and their side chains adopt different rotameric states. For short chains, we enumerate exhaustively all possible conformations. For long chains, we sample effectively rare events such as compact conformations and obtain complete pictures of ensemble properties of conformations of these models at all compactness region. This is made possible by using sequential Monte Carlo techniques based on chain growth method. Our results show that both chirality and reduced side chain flexibility lower the folding entropy significantly for globally compact conformations, suggesting that they are important properties of residues to ensure fast folding and stable native structure. This corresponds well with our finding that natural amino acid residues have reduced effective flexibility, as evidenced by statistical analysis of rotamer libraries and side chain rotatable bonds. We further develop a method calculating the exact side chain entropy for a given backbone structure. We show that simple rotamer counting underestimates side chain entropy significantly for both extended and near maximally compact conformations. We find that side chain entropy does not always correlate well with main chain packing. With explicit side chains, extended backbones do not have the largest side chain entropy. Among compact backbones with maximum side chain entropy, helical structures emerge as the dominating configurations. Our results suggest that side chain entropy may be an important factor contributing to the formation of alpha helices for compact conformations. 相似文献
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This paper reports a new model for rubber elasticity based on the geometric constraints imposed on a network chain and the chain segments by the crosslinks at each end. Through consideration of these constraints, the number of conformations available to a network chain can be calculated directly assuming the chain is on a lattice. By simplifying the model and by assuming affine deformation, the rigorous equations for the conformational entropy are reduced to an analytic expression for the strain-energy function. From this function, equations describing extension, compression and pure shear are derived. The model is tested against literature data for natural rubber and polybutadiene and is found to reproduce quantitatively all the salient features of the experimental stress-strain curves In the three modes of deformation. It is shown that the decrease in the Gaussian modulus with extension, often characterized by the C2 term in the Mooney-Rivlin theory, arises naturally from the conformational entropy of a network chain, and special effects such as structure, topology, etc., need not be invoked to explain this phenomenon. The theory also predicts the near-constant modulus of extended highly swollen gels, an effect often considered as verification of Gaussian theory. 相似文献