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991.
S. Aravinda N. Shamala Rituparna S. Roy P Balaram 《Journal of Chemical Sciences》2003,115(5-6):373-400
An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from
the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments andDPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
992.
Dmitri V Sevenard Vyacheslav Ya SosnovskikhAlexander A Kolomeitsev Martin H KönigsmannGerd-Volker Röschenthaler 《Tetrahedron letters》2003,44(41):7623-7627
In a convenient and efficient procedure, the nucleophilic 1,4-trifluoromethylation of several α,β-enones using (trifluoromethyl)trimethylsilane was achieved. The high regioselectivity of the reaction has been reached by blocking the carbonyl moiety of the electrophile with a bulky aluminum-centered Lewis acid. 相似文献
993.
Several 2- and 4-alkylcyclohexadienones were prepared and shown to accept electrons to produce ketyl radical anions that dissociated rapidly at room temperature to release carbon-centered radicals and an aromatic phenoxide type anion. In the PET process with benzyl-substituted cyclohexadienones, initiated with triethylamine, the benzyl radicals dimerised or abstracted an H-atom from solvent. In electrochemical reductions, and in reductions with alkali metals in liquid ammonia, the benzyl radicals were further reduced to anions. 相似文献
994.
Aldehydes undergo smooth conjugate addition to α,β-unsaturated ketones in the presence of 5-(2-hydroxyethyl)-1,3-thiazolium halides and DBU adsorbed onto the surface of basic alumina under microwave irradiation and solvent-free conditions to afford 1,4-diketones in enhanced yields and reduced reaction times compared to conventional methods. 相似文献
995.
Matveeva E. D. Podrugina T. A. Grishin Yu. K. Tkachev V. V. Zhdankin V. V. Aldoshin S. M. Zefirov N. S. 《Russian Journal of Organic Chemistry》2003,39(4):536-541
A mixed phosphonium-iodonium ylide, phenyliodoniumethoxycarbonylmethylenetriphenylphosphorane borofluoride, was synthesized. Its structure was established by means of X-ray diffraction analysis. Temperature dependence of 1H, 13C, and 31P spectra of the ylide synthesized was investigated. A dynamic equilibrium between Z and E-isomers was observed. 相似文献
996.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
997.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
998.
A. Henderson 《Mathematische Zeitschrift》2003,243(1):127-143
We prove that the local intersection cohomology of nilpotent orbit closures of cyclic quivers is trivial when the two orbits
involved correspond to partitions with at most two rows. This gives a geometric proof of a result of Graham and Lehrer, which
states that standard modules of the affine Hecke algebra of GLd corresponding to nilpotents with at most two Jordan blocks are multiplicity-free.
Received: 7 February 2002 / Published online: 8 November 2002 相似文献
999.
It is proved that every finite group for which the degrees of its nonmonomial characters are primes is solvable. The proof uses the classification of the finite simple groups. 相似文献
1000.
M. S. Nikol'skii 《Differential Equations》2003,39(11):1603-1608