Search results for "stereochemistry"

Molecular modeling of intercalation complexes of antitumor active 9-aminoacridine and a [d, e]-anellated isoquinoline derivative with base paired deo…

1996

Intercalators are molecules capable of sliding between DNA base pairs without breaking up the hydrogen bonds between the DNA bases. On the basis of molecular mechanics calculations structural, models of B-DNA tetranucleotide intercalation complexes of some cytostatic active 9-aminoacridines and of a [d, e]-anellated isoquinoline derivative are presented. The drug complexes are stabilized by energetically favouredvan der Waals interactions and by selective hydrogen bonds between the side chains of the drugs and the DNA bases. Semiempirical quantum chemistry calculations revealed that the chromophoric system of the intercalators is able to form π,π-charge-transfer interactions with the purine…

Stereocontrolled approach to quinuclidine derivatives

1998

Abstract Asymmetric Michael-type cyclization of chiral enamino ester (S)-7 furnished the quinuclidinone derivative (3R, 4S)-5, with a high degree of stereoselectivity.

Photoinduced switching of electrical properties in thin films of polar indandione type organic molecules

2006

The optically induced switching of organic materials with large dipole moments consisting of acceptor and donor groups bridged by a delocalized π-electron system is important for investigations of optoelectronic effects. To the contrary of azobenzene molecule, photoinduced change of dipole moment of indandione molecule does not need free volume in thin films. To modify the dipole moment and also to optimise properties of film formation, a number of novel indandione derivatives is investigated. Reversible switching of the surface potential of polymer films with incorporated or chemically attached indandione molecules is observed at irradiation in photoinduced intramolecular electron transfer…

ChemInform Abstract: Photochemical Electrocyclization of 3-Vinylindoles (VIII) to Pyrido[2,3-a]- (IX), Pyrido[4,3-a]- (X) and Thieno[2,3-a]-carbazole…

2009

Synthesis and NMR configurational study of imidazo[2,1-b]thiazoles from 1H-1,4-diazepine-7(6H)-thiones

1993

Abstract A thermal intramolecular cyclization of 1-vinyl2,3-dihydro-3 H -imidazole-2-thiones to imidazo[2,1-b]thiazoles is reported. A heteronuclear correlation study of these systems was made in order to establish the configuration of the products.

A dft study of the regioselectivity in intramolecular diels-alder reactions with formation of a tricyclodecane skeleton

2011

Three different intramolecular Diels-Alder (IMDA) reactions associated with the formation of fused and bridged tricyclodecane skeletons have been studied at the B3LYP/6-31G(d) computational level. While substitution on the diene and dienophile fragments modulates the polar character of the reaction, the strain effect produced by the methylene tether affects the activation energy, and its torsion controls the different regioisomeric channels of the IMDA process. Analysis of the reactivity indices recently proposed (J. Soto-Delgado et al., Org. Biomol. Chem., 2010, 8, 3678) within the conceptual density functional theory allows for the characterization of the mechanism including the charge tr…

Structure of an [alpha],[beta]-unsaturated dipeptide, racemic N-[(phenylmethoxy)carbonyl]phenylalanyl-[Delta]2-phenylalanine

1987

Synthesis of Peptides with α,β-Dehydroamino Acids, II. Synthesis oftert-Butyloxycarbonyldipeptides of Dehydroalanine and Dehydrophenylalanine

1985

Condensation of amides of Boc-amino acids3) with pyruvic acid leads to Boc-dipeptides 1 – 3 of dehydroalanine and 1-Boc-5-alkyl-2-methyl-4-oxo-2-imidazolidinecarboxylic acids 8 – 10. The amides, however, do not condense with phenylpyruvic acid. Boc-dipeptides of dehydroalanine (1 – 3) and dehydrophenylalanine (4 – 7) are synthesized using (Boc)2O and dehydrodipeptides with a free unmasked N-terminal amino group. Synthese von Peptiden mit α,β-Dehydroaminosauren, II1). – Synthese von tert-Butyloxycarbonyldipeptiden von Dehydroalanin und Dehydrophenylalanin2) Die Kondensation von Boc-Aminosaureamiden3) mit Brenztraubensaure fuhrt zu Boc-Dipeptiden 1 – 3 des Dehydroalanins und 1-Boc-5-alkyl-2-m…

Der 2-(4-pyridyl)Ethoxycarbonyl-(4-Pyoc)-rest - eine hydrophile, säure- und basenstabile aminoschutzgruppe für die peptidsynthese

1984

Abstract The title amino blocking function is stable under basic and acidic conditions frequently used in the peptide synthesis. Its hydrophilicity permits an effective peptide synthesis in water. After the easy conversion to the pyridinium form the 4-Pyoc group can be removed by morpholine.

ChemInform Abstract: A Theoretical Determination of the Dissociation Energy of the Nitric Oxide Dimer.

2010

Multi-reference CI methods have been applied to determine the dissociation energy and structure of thecis-N2O2 molecule. The convergence of the theoretical result has been checked with respect to a systematic expansion of the one-electron basis set and the multi-reference CI wave function. The best calculated value, 13.8 kJ/mol, is in agreement with the experimental value, 12.2 kJ/mol. It has been obtained with an extended ANO-type basis set [6s5p3d2f], including the effect of the basis set superposition error (BSSE) in the geometry optimization, and additional effects, such as the electron correlation of core electrons and relativistic corrections, using the average coupled pair functional…