Search results for "stereochemistry"
showing 10 items of 4831 documents
Preparative and spectroscopic features of ferricenium tetrachloroferrate(III). Interconversion to diferricenium ?-oxo-bis[trichloroferrate(III)]
1985
Ferricenium tetrachloroferrate(III)(1), one of the more frequently cited ferricenium salts, has recently attracted biomedical interest because of its pronounced antineoplastic activity against Ehrlich ascites murine tumor. In this paper, synthetic methods are reinvestigated in an effort to prepare pure(1) free from a common contaminant, diferriceniumμ-oxo-bis(trichloroferrate)(3). The oxodiferrate, or mixtures of this salt with(1), can readily be converted into pure(1) under acidic conditions. Conversely, dimerization of(1) with participation of water to give the oxodiferrate(3) is brought about by recrystallization of the former from moist acetonitrile/methanol in the presence of base; thi…
Diphenoxido‐Bridged Co II and Zn II Complexes of Tripodal N 2 O 2 Ligands: Stabilisation of M II ‐Coordinated Phenoxyl Radical Species
2010
Three new tripodal ligands with an N 2 O 2 donor set, namely 2-tert-butyl-6-({(2-hydroxybenzyl)[2-(2-pyridyl)ethyl]amino}-methyl)-4-methylphenol (H 2 L 1 ), 2-tert-butyl-6-({(2-hydroxybenzyl)[2-(2-pyridyl)ethyl]amino}methyl)-4-methoxy-phenol (H 2 L 2 ) and 2-tert-butyl-6-({[2-(dimethylamino)ethyl]-(2-hydroxybenzyl)amino}methyl)-4-methoxyphenol (H 2 L 3 ) have been synthesised. Treatment of the ligands with Co-(CH 3 CO 2 ) 2 ·4H 2 O or [Zn(H 2 O) 6 ][ClO 4 ] 2 in the presence of Et 3 N provides the corresponding Co II and Zn" complexes of composition [M II 2 (L 1 ) 2 ] [M = Co (1) (single-crystals are a solvate with the composition [Co II 2 (L 1 ) 2 ]·2CHCl 3 , i.e. 1·2CHCl 3 ); M = Zn (2)],…
Substituent effects on the reaction mode between 2-hydroxybenzyl alcohol derivatives and MEM chloride:synthesis and mechanistic aspects of seven-and …
2004
Abstract The synthesis of (RS)-2- or (RS)-3-methoxy-2,3-dihydro-5H-1,4-benzodioxepins and (RS)-5- or (RS)-3-methoxy-2,3,5,6-tetrahydro-8H-benzo-[1,4,7]-trioxecins has been developed. The mechanism of such a reaction via the boron trifluoride etherate-promoted transformation of 2-(methoxyethoxymethoxy)benzyloxyacetaldehyde dimethyl acetals or 2-(methoxyethoxymethoxymethyl)phenyloxyacetaldehyde dimethyl acetals has been proposed. Transannular versions of the reaction results in the facile ring contraction of 12-membered intermediates to the 10- and to 7-membered benzene-fused O,O-acetals. The characterization of the by-products strongly supports the mechanisms proposed.
ChemInform Abstract: The Reaction of 2,4,5,6-Tetraaminopyrimidine with Chalcones.
2010
The reaction of the tetraaminopyrimidine 1 with the chalcones 2a-f yields, in the presence of catalytic amounts of acetic acid, the 1H-pyrimido[4,5-b][1,4]diazepine derivatives 3a-f. The cyclization process consists of a condensation reaction and a Michael type addition.
ChemInform Abstract: The Mechanism of Formation of 3H,9H-Pyrano(3,4-b)indol-3-ones from 3- Indolalkanoic Acids.
2010
The mechanism of the formation of 1-methyl-3H,9H-pyrano[3,4-b]indol-3-one (4) from the corresponding 3-indolacetic acid 1 is discussed. The suggested mechanism is substantiated by the isolation of a stable intermediate 2 and its transformations in the presence of acetic anhydride and/or Lewis acids.
Acetogenins from Annonaceae: Recent Progress in Isolation, Synthesis and Mechanisms of Action
2005
Covering: the literature from 1998 to 2004 The aim of the present review is to summarise the knowledge about newly isolated acetogenins (ACGs) in the last six years. It will also report the total syntheses that have allowed either the confirmation or the revision of some structures, together with the biological activities and mechanism of action of such interesting natural products. In fact, of the 417 isolated compounds reviewed, over 176 have been added during the period from 1998 to 2004.
Inhibitory effects on mitochondrial complex I of semisynthetic mono-Tetrahydrofuran acetogenin derivatives
2003
Modifications in the terminal alpha,beta-unsaturated gamma-methyl-gamma-lactone moiety or in the alkyl chain that links this terminal gamma-lactone with the alpha,alpha'-dihydroxylated THF system of the natural mono-tetrahydrofuranic acetogenins, annonacin and annonacinone, led to the preparation of eight semisynthetic derivatives. Their inhibitory effects on mitochondrial complex I is discussed and compared with that of the classical complex I inhibitor, rotenone.
A molecular dynamics study on the role of the protonation state in the biosynthesis of R-PAC by AHAS
2019
Abstract The effect of the protonation state of the hydroxyl-ethylthiamin diphosphate intermediate, HEThDP, on the enzyme-substrate interactions and their consequences on the biosynthesis of R-phenylacetylcarbinol, R-PAC, by the acetohydroxy acid synthase, AHAS, is addressed by molecular dynamics simulations. It is found that the form of HEThDP, which favors the formation of R-PAC, is that having the 4-aminopyrimidine ring with the N1′ atom protonated and the N4′ atom as aminopyrimidinium ion. Under this form both active sites of AHAS have the ability to perform the catalysis, unlike that observed for the other possible protonation states of N1′ and N4′ atoms.
Synthesis of 3-Oxa-guaianolides from Santonin
2000
Abstract This article reports on the transformation of santonin into two C10-epimeric 3-oxa-guaianolides which are 8-deoxyderivatives of several natural 3-oxaguaianolides isolated from Achillea species. The synthesis involved the photochemical rearrangement of the eudesmane skeleton into a guaiane skeleton and the transformation of the cyclopentane ring into a furan moiety with the concomitant loss of C3. Comparison of the NMR data of the synthetic products with those of the natural products confirms the β orientation of the hydroxyl group at C10 in the products isolated from Achillea.
Zur protonenkatalysierten Aralkylierung von 1,2,3-Trimethylindol und 1,2,3,4-Tetrahydrocarbazol mit Arylaldehyden
1987
1,2,3-Trimethylindol (2) liefert mit Benzaldehyden die Kondensationsprodukte 5 und 6, wahrend aus den NH-Indolen 1 und 3 die Verbindungen 7 und 8 entstehen. Proton-catalyzed Aralkylation of 1,2,3-Trimethylindole and 1,2,3,4-Tetrahydrocarbazole with Arylaldehydes Reaction of 1,2,3-trimethylindole (2) with benzaldehydes leads to the condensation compounds 5 and 6, the NH-indoles 1 and 3, however, give 7 and 8.