Search results for "stereo"

A joint experimental and ab initio study on the reactivity of several hydroxy selenides. Stereoselective synthesis of cis-disubstituted tetrahydrofur…

2001

Abstract The reactivity of several hydroxy selenides bearing an ethereal chain with catalytic amounts of perchloric acid in dichloromethane was investigated. Results showed that the position of the oxygen atom with respect to the seleniranium ring was crucial in order to get a good yield of the cyclized product. The factors on which yields of the 5- endo cyclization of the seleniranium ions depend were analysed by ab initio (HF/3-21G ∗ ) studies. An explanation of the different coordinating ability, towards the positively charged selenium atom, of the allylic OMe and homoallylic OH-2 groups was given.

P-Chirogenic Phosphines Supported by Calix[4]arene: New Insight into Palladium-Catalyzed Asymmetric Allylic Substitution

2013

The first P-chirogenic mono- and diphosphine ligands supported on the upper rim of a calix[4]arene moiety were synthesized using the ephedrine methodology. The lithiated calix[4]arene mono- and dianions both react with the oxazaphospholidine–borane, prepared from ephedrine, to afford regio- and stereoselectively the corresponding calix[4]arenyl aminophosphine–boranes, by cleavage of the heterocyclic ring at the P–O bond position. Subsequent reactions with HCl and then organolithium reagent and finally decomplexation with DABCO lead to the corresponding calix[4]arenyl mono- or diphosphines. Both enantiomers of the calix[4]arenyl phosphines were obtained either by using (+)- or (−)-ephedrine …

Cyclopentadienylmolybdenum(II) and -(III) complexes containing diene and allyl ligands. Part 4. Reactivity studies of the bisallyl complex CpMo(supin…

1998

Abstract Compound CpMo( η 3 -C 3 H 5 ) 2 , 3, has been synthesized from CpMoCl 4 and four equivalents of allylmagnesium bromide. While the compound is stable in donor solvents at room temperature, warming in refluxing MeCN induces the formation of 1,5-hexadiene by a metal-mediated allyl-allyl coupling process. Treatment of 3 with Bu t NC at room temperature affords CpMo( η 3 -C 3 H 5 )(Bu t NC) 2 , 4. A similar reduction with presumed allyl radical loss occurs for [CpMo( η 3 -C 3 H 5 )( η 4 -C 4 H 6 )] + , [1c] + , to afford [CpMo( η 4 -C 4 H 6 )(Bu t NC) 2 ] + , 5. Treatment of [1c] + with methyllithium affords two products, the major one (1c) corresponding to the one-electron reduction pa…

Enantiodifferentiation of acyclic phosphonium salts in chiral liquid crystalline solutions

2006

Abstract The enantiodifferentiation of acyclic phosphonium salts bearing a stereogenic centre, whether on the phosphorus atom or on one of its substituents, was investigated by 2 H–{ 1 H}, 13 C–{ 1 H} and 31 P–{ 1 H} NMR in chiral liquid crystals composed of a polypeptide dissolved in an organic solvent. For the first time, the enantiomers of P-chirogenic phosphorus compounds were discriminated in these anisotropic media, affording good to excellent separation of the signals, allowing the determination of their proportion. While 31 P–{ 1 H} NMR spectra showed no chiral separation, 2 H–{ 1 H} NMR was efficient in the enantiodifferentiation of an isotopically labelled compound. Better still, …

Bioactive Alkaloids of Hallucinogenic Mushrooms

2015

Abstract The aim of our chapter is to review recent developments in a group of medicinally important natural products–alkaloids, with reference to the structure–activity studies in respect of certain diseases. Alkaloids covered by our review come from mushrooms called “hallucinogenic.” Hallucinogenic compounds have been chemically identified in mushrooms belonging to various genera, e.g., Agrocybe, Amanita, Conocybe, Galerina, Gymnopilus, Hypholoma, Inocybe, Panaeolus, Psilocybe, Pholiotina, Pluteus, and Weraroa [J.W. Allen, Ethnomycol. J. Sacred Mushroom Stud. 9 (2012) 130–175]. One of the largest classes of alkaloids is indole alkaloids. Indoles are probably the most widely distributed he…

Identification of a new series of amides as non-covalent proteasome inhibitors

2014

Proteasome inhibition has emerged as an important therapeutic strategy for the treatment of multiple myeloma (MM) and some forms of lymphoma, with potential application in other types of cancers. 20S proteasome consists of three different catalytic activities known as chymotrypsin-like (ChT-L), trypsin-like (T-L), and, post-glutamyl peptide hydrolyzing (PGPH) or caspase-like (C-L), which are located respectively on the β5, β2, and β1 subunits of each heptameric β rings. Currently a wide number of covalent proteasome inhibitors are reported in literature; however, the less widely investigated non-covalent inhibitors might be a promising alternative to employ in therapy, because of the lack o…

Cover Picture: A Versatile Approach to CF3-Containing 2-Pyrrolidones by Tandem Michael Addition-Cyclization: Exemplification in the Synthesis of Amid…

2015

Histaminanaloge, 28. Mitt. 2-Aryloxyalkyl- und 2-Aminoalkylhistamine

1987

Als Histaminderivate mit H1-affinitatsvermittelnden Strukturelementen in 2-Stellung des Imidazolrings wurden 2-Aryloxyalkyl- und 2-Aminoalkylhistamine sowie das racemische 2-(1-Phenylethyl)histamin dargestellt und auf Histamin-H1-agonistische Aktivitat untersucht. Histamine Analogues, XXVIII: 2-(Aryloxyalkyl)- and 2-(Aminoalkyl)histamines As histamine derivatives with structures at position 2 of the imidazole ring, which mediate H1-receptor affinity, 2-(aryloxyalkyl)- and 2-(aminoalkyl)histamines as well as racemic 2-(1-phenylethyl)histamine were prepared and tested for histamine H1-agonistic activity.

Pentafulvene durch Aminomethinylierung des Cyclopentadiens

1986

Aus der Dreikomponentenreaktion von Cyclopentadien (1) mit s-Triazin (2) und einem sekundaren Amin 4 gehen die cyclisch N,N-disubstituierten Pentafulven-6-amine 5 und die cyclisch N1,N1-disubstituierten N2-(6-Pentafulvenyl)formamidine 7 hervor. Unter den biologischen Eigenschaften der neuen Verbindungen ist besonders die anthelminthische Wirkung von 5d interessant. Pentafulvenes by Aminomethynylation of Cyclopentadiene The three component reaction comprising the interaction of cyclopentadiene (1) with s-triazine (2) and a secondary amine 4 leads to the cyclic N,N-disubstituted pentafulven-6-amines 5 and the cyclic N1,N1-disubstituted N2-(6-pentafulvenyl)formamidines 7. Among the biological …

ChemInform Abstract: A Versatile Approach to CF3-Containing 2-Pyrrolidones by Tandem Michael Addition-Cyclization: Exemplification in the Synthesis o…

2016

The synthesis of new fluorinated pyrrolidones starting from unprotected amino esters and amino nitriles through a Michael addition-lactamization sequence is described. The resulting CF3 -containing building blocks, bearing a quaternary stereogenic center adjacent to the fluorinated group, have been converted into amino pyrrolidines that display potent β-secretase 1 (BACE1) inhibitory activity. This work constitutes an example of selective fluorination as a valid strategy for the modulation of physicochemical and biological properties of lead compounds in drug discovery.