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121.
Laurie A. Christianson Melissa J. Lucero Daniel H. Appella Daniel A. Klein Samuel H. Gellman 《Journal of computational chemistry》2000,21(9):763-773
We added parameters to the AMBER* force field to model cyclic β‐amino acid derivatives more accurately within the commonly used MacroModel program. In an effort to generate an improved treatment of cyclohexane and cyclopentane conformational preferences, carbon–carbon torsional parameters were modified and incorporated into a force field we call AMBER*C. Simulation of trans‐2‐aminocyclohexanecarboxylic acid (trans‐ACHC) and trans‐2‐aminocyclopentanecarboxylic acid (trans‐ACPC) derivatives using AMBER*C produces more realistic energy differences between (pseudo)diaxial and (pseudo)diequatorial conformations than does simulation using AMBER*. AMBER*C molecular dynamics simulations more accurately reproduce the experimental hydrogen‐bonding tendencies of simple diamide derivatives of trans‐ACHC and trans‐ACPC than do simulations using the AMBER* force field. More importantly, this modified force field allows accurate qualitative prediction of the helical secondary structures adopted by β‐amino acid homo‐oligomers. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 763–773, 2000 相似文献
122.
Lee J. Silverberg Tapas K. Mal Carlos N. Pacheco Megan L. Povelones Madeline F. Malfara Anthony F. Lagalante Mark A. Olsen Hemant P. Yennawar Hany F. Sobhi Kayla R. Baney Robin L. Bozeman Craig S. Eroh Michael J. Fleming Tracy L. Garcia Casey L. Gregory Julia E. Hahn Alyssa M. Hatter Lexi L. Johns Tianna L. Klinger Jennie J. Li Andrew J. Menig Grace C. Muench Melissa E. Ramirez Jordyn Reilly Nicole Sacco Alexandra M. Sheidy Marla M. Stoner Eric N. Thompson Soroush F. Yazdani 《Molecules (Basel, Switzerland)》2021,26(20)
A series of fourteen 2-aryl-3-phenyl-2,3-dihydro-4H-pyrido[3,2-e][1,3]thiazin-4-ones was prepared at room temperature by T3P-mediated cyclization of N-phenyl-C-aryl imines with thionicotinic acid, two difficult substrates. The reactions were operationally simple, did not require specialized equipment or anhydrous solvents, could be performed as either two or three component reactions, and gave moderate–good yields as high as 63%. This provides ready access to N-phenyl compounds in this family, which have been generally difficult to prepare. As part of the study, the first crystal structure of neutral thionicotinic acid is also reported, and showed the molecule to be in the form of the thione tautomer. Additionally, the synthesized compounds were tested against T. brucei, the causative agent of Human African Sleeping Sickness. Screening at 50 µM concentration showed that five of the compounds strongly inhibited growth and killed parasites. 相似文献
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Novel polyisobutylene/poly(dimethylsiloxane) bicomponent networks. I. Synthesis and characterization
Melissa A. Sherman Joseph P. Kennedy 《Journal of polymer science. Part A, Polymer chemistry》1998,36(11):1891-1899
The synthesis of novel polyisobutylene (PIB)/poly(dimethylsiloxane) (PDMS) bicomponent networks is described. The synthesis strategy (see Figure 1) was to prepare well-defined and -characterized allyl-tritelechelic polyisobutylenes [ϕ(PIB—C—C=C)3] and SiH-ditelechelic poly(dimethylsiloxanes) (HSi–PDMS–SiH) and then crosslink these moieties by hydrosilation. The ϕ(PIB—C—C=C)3 was prepared by living isobutylene polymerization followed by end-quenching with allyltrimethylsilane, whereas the HSi–PDMS–SiH was obtained by equilibrium polymerization of octamethylcyclotetrasiloxane and tetramethyldisiloxane. The detailed structures of the starting polymers were characterized by GPC and 1H-NMR spectroscopy. A series of PIB/PDMS bicomponent networks of varying compositions and average molecular weights between crosslinks (M c) of ∼ 20,000 g/mol were assembled. Optimum crosslinking conditions were defined in terms of H2PtCl6 catalyst concentration, nature of solvent, time, temperature, and stoichiometry of ∼ CH2CH=CH2/∼SiH groups, allowing for the convenient synthesis of well-defined model bicomponent networks. Swelling studies and elemental analysis confirm the correctness of the synthetic strategy. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1891–1899, 1998 相似文献
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Beverly S Colley Melissa A Cavallin KC Biju David R Marks Debra A Fadool 《BMC neuroscience》2009,10(1):8
Background
Neurotrophins are important regulators of growth and regeneration, and acutely, they can modulate the activity of voltage-gated ion channels. Previously we have shown that acute brain-derived neurotrophic factor (BDNF) activation of neurotrophin receptor tyrosine kinase B (TrkB) suppresses the Shaker voltage-gated potassium channel (Kv1.3) via phosphorylation of multiple tyrosine residues in the N and C terminal aspects of the channel protein. It is not known how adaptor proteins, which lack catalytic activity, but interact with members of the neurotrophic signaling pathway, might scaffold with ion channels or modulate channel activity. 相似文献128.
Aline G. Cunha Gloria Fernández-Lorente Melissa L. E. Gutarra Juliana V. Bevilaqua Rodrigo V. Almeida Lúcia M. C. Paiva Roberto Fernández-Lafuente Jose M. Guisán Denise M. G. Freire 《Applied biochemistry and biotechnology》2009,156(1-3):133-145
Lipases are an enzyme class of a great importance as biocatalysts applied to organic chemistry. However, it is still necessary to search for new enzymes with special characteristics such as good stability towards high temperatures, organic solvents, and high stereoselectivity presence. The present work’s aim was to immobilize the lipases pool produced by Penicillium simplissicimum, a filamentous fungi strain isolated from Brazilian babassu cake residue. P. simplissicimum lipases were separated into three different fractions using selective adsorption method on different hydrophobic supports (butyl-, phenyl-, and octyl-agarose) at low ionic strength. After immobilization, it was observed that these fractions’ hyperactivation is in the range of 131% to 1133%. This phenomenon probably occurs due to enzyme open form stabilization when immobilized onto hydrophobic supports. Those fractions showed different thermal stability, specificity, and enantioselectivity towards some substrates. Enantiomeric ratio for the hydrolysis of (R,S) 2-O-butyryl-2-phenylacetic acid ranged from 1 to 7.9 for different immobilized P. simplissicimum lipase fractions. Asymmetry factor for diethyl 2-phenylmalonate hydrolysis ranged from 11.8 to 16.4 according to the immobilized P. simplissicimum lipase fractions. Those results showed that sequential adsorption methodology was an efficient strategy to obtain new biocatalysts with different enantioselectivity degrees, thermostability, and specificity prepared with a crude extract produced by a simple and low-cost technology. 相似文献
129.
Edwin B. Villhauer Zhengming Du Kevin Vargas Lech Ciszewski Yansong Lu Michael Girgis Melissa Lin Mahavir Prashad 《Tetrahedron》2009,65(45):9067-1868
A scalable synthetic strategy of a chiral, trisubstituted imidazolidinone (1), a novel cannabinoid-1 antagonist, starting from a commercially available mandelic acid (5) is described. The key step involves a regio- and stereoselective ring-opening of an aziridinium ion by an aniline nucleophile (3). A mechanistic study revealed the insight into rate amplification at a lower temperature for vicinal diamine 12 formation via a aziridinium ion 14. Although most intermediates are not isolable by crystallization due to their intrinsic physical properties (oil or foamy solid), the reported synthesis furnished pure 1 without any chromatography purification throughout the entire synthesis. Employing green chemistry principles, this novel synthesis appears to be highly efficient for the manufacturing of multi-kilogram quantities of an optically-pure active pharmaceutical ingredient. 相似文献
130.
Robert J. Hinkle Yajing Lian Lee C. Speight Heather E. Stevenson Melissa M. Sprachman Lauren A. Katkish M. Christa Mattern 《Tetrahedron》2009,65(34):6834-9277
The rapid synthesis of cis-2,6-disubstituted dihydropyrans is achieved in a three-component, one-pot cascade reaction. BiBr3-mediated addition of ketene silyl acetals or silyl enol ethers to β,γ-unsaturated cis-4-trimethylsilyl-3-butenal provides a Mukaiyama aldol adduct containing a vinylsilane moiety tethered to a silyl ether. Addition of a second aldehyde initiates a domino sequence involving intermolecular addition followed by an intramolecular silyl-modified Sakurai (ISMS) reaction. Isolated yields of this one-pot reaction vary from 44 to 80% and all compounds were isolated as the cis-diastereomers (10 examples). 相似文献