Search results for " molecule"
showing 10 items of 1523 documents
Synthese und Reaktionen der 3-O-Phosphoniogluco-und -allofuranosen
1982
Aus den bicyclischen Gluco- (3, 5, 7 und 9) und Allofuranosen 11 werden mit Triphenylphosphan (1), Azodicarbonsaure-diethylester (2) und Alkylierungs- oder Acylierungsmitteln isolierbare 3-O-Phosphoniokohlenhydrate (4, 6, 8, 10 und 12) hergestellt. Durch Erwarmen der allo-konfigurierten Salze 12 konnen an C-3 epimere gluco-konfigurierte Substitutionsprodukte in groser Vielfalt gewonnen werden. Die Reaktionen der gluco-konfigurierten Salze werden stark vom Charakter des einzufuhrenden Nucleophils und von Nachbargruppen im Kohlenhydratgerust beeinflust. Wahrend das Iodid 4a und das Azid 4g unter Substitution zum allo-Derivat 15 reagieren, tritt in den Fallen mit Bromid, Chlorid oder Sulfonat …
Stannacycloalkyl and stannepinyl derivatives of dipeptides
1994
Stannacyclohexyl and stannacycloheptyl derivatives of dipeptides (CH2)nSnAA · xH2O (H2AA = H2GlyGly, with n = 5, x = 2 or n = 6, x = 1; H2AA = H2GlyAla, H2GlyVal, H2GlyMet, with n = 5, 6, x = 1) and stannepinyl glycylglycinate monohydrate have been obtained by the reaction of (CH2)nSnCl2 or stannepinyl dichloride with Na2AA. According to infrared and 119Sn Mossbauer data of the solid compounds, AA acts as a tridentate ONN ligand and tin has a trigonalbipyramidal environment. An analogous structure has been inferred from 1H, 13C, and 119Sn NMR data for the undissociated molecules in methanol solution.
Synthesis of fluorinated piperidine and azepane β-amino acid derivatives
2016
Abstract A convenient and robust stereocontrolled procedure has been developed for the synthesis of novel trifluoromethyl-containing piperidine and azepane β-amino ester stereoisomers. The synthesis started from readily available unsaturated bicyclic β-lactams and was based on oxidative cleavage of the ring C C double bond followed by ring closure of the diformyl intermediates in the presence of 2,2,2-trifluoroethylamine hydrochloride through reductive amination. The synthetic procedure has efficiently been extended towards the synthesis of mono- and difluorinated analogs.
Synthesis of densely functionalized cispentacin derivatives through selective aziridination and aziridine opening reactions: Orthogonally protected d…
2014
A novel substrate-directed synthetic route to a series of highly functionalized, orthogonally protected di- or triaminocyclopentanecarboxylate derivatives with multiple chiral centres from an unsaturated bicyclic β-lactam has been accomplished by applying stereoselective ring C–C double bond aziridination with chloramine-T and phenyltrimethylammonium tribromide, followed by regioselective aziridine opening with different N,O nucleophiles and hydrides. The functionalization strategy was successfully extended for access to enantiomerically pure orthogonally protected triaminocarboxylates.
Dissociation energies within selected configuration interaction and perturbation theory
1993
Abstract Selected configuration interaction (CI) calculations and second-order perturbational theory are used to truncate systematically multireference single and double excitation CI (MRCI) expansions in the calculation of the bond dissociation energies of several systems like the single-bonded LiF molecule or the multiple-bonded N2, NO and O2 diatomic systems. The method is extended to compute the CH bond dissociation energy ofethene C2H4. It is shown how the proposed scheme (perturbation-selected MRCI (MRCI-PS)) is able to reproduce the accuracy of complete MRCI expansions with only a small number of configurations variationally evaluated.
Enzymatic and Metabolic Studies on Isolated Nuclei
1957
Publisher Summary In protein synthesis it is important to distinguish between the net synthesis of protein, as measured by an increased amount of protein nitrogen or by the formation of proteins with specific biological properties, such as enzymatically and immunologically active proteins, and exchange reactions, which may be observed in isotope experiments and, which reflect the replacement of an amino acid in a protein molecule with one from its environment. Incorporation of an amino acid into a protein can occur only during net synthesis; both types of reaction occur in similar systems. In true synthesis of protein it is usually difficult to obtain synthesis of a specific entity, especia…
Two phosphonodehydrotripeptides: Boc0–Gly1–Δ(Z)Phe2–α‐Abu3PO3Me2 and Boc0–Gly1–Δ(Z)Phe2–α‐Nva3PO3Et2
2012
The present paper reports the crystal structures of two short phosphonotripeptides (one in two crystal forms) containing one ΔPhe (dehydrophenylalanine) residue, namely dimethyl (3-{[tert-butoxycarbonylglycyl-α,β-(Z)-dehydrophenylalanyl]amino}propyl)phosphonate, Boc0–Gly1–Δ(Z)Phe2–α-Abu3PO3Me2, C21H32N3O7P, (I), and diethyl (4-{[tert-butoxycarbonylglycyl-α,β-(Z)-dehydrophenylalanyl]amino}butyl)phosphonate, Boc0–Gly1–Δ(Z)Phe2–α-Nva3PO3Et2, as the propan-2-ol monosolvate 0.122-hydrate, C24H38N3O7P·C3H8O·0.122H2O, (II), and the ethanol monosolvate 0.076-hydrate, C24H38N3O7P·C2H6O·0.076H2O, (III). The crystals of (II) and (III) are isomorphous but differ in the type of solvent. The phosphono gr…
Restricted and complete-active-space multiconfiguration linear response calculations of the polarizability of formamide and urea
1991
Abstract Using the polarized basis sets of Sadlej, we have carried out multiconfiguration linear response (MCLR) calculations of static and dynamic polarizabilities of water, carbon dioxide, formamide and urea. It is found that the polarized basis sets give a good description of the polarizabilities. The uncorrelates (self-consistent field) polarizabilities are in general 10% or more lower than the experimental values. The correlation as introduced in the complete-active-space (CAS) and restricted-active-space (RAS) MCLR calculations recovers the major part of this deviation.
Sesquiterpene lactones from Artemisia lucentica
1997
Abstract The aerial parts of Artemisia lucentica yielded, in addition to several known compounds, a bicyclic monoterpene ketone, two germacranolides, an eudesmanolide, a 10- epi neudesmanolide, a 2-norelemanolide and three bisabolene derivatives. The stereochemistry of a germacranolide, described as 2α-hydroxyartemorin in a previous investigation of the species, has now been corrected and the compound has been renamed lucentolide.
Dunham coefficients of 14N2 from CARS measurements of high vibrational states in a low-pressure discharge
1988
Spectroscopic constants of the X1Σg+ ground state of 14N2 are deduced from CARS spectra recorded in a 4 Torr d.c. N2 glow discharge. Vibrational states up to ν = 14 have been observed but only the 11 lower levels which have a good signal-to-noise ratio have been processed. The Dunham constants that were deduced yield vibrational band centre positions in good agreement with those of Lofthus and Krupenie.