Search results for "selective synthesis"
showing 10 items of 430 documents
ChemInform Abstract: Enantioselective Synthesis of Herbertane Sesquiterpenes: Synthesis of (-)-α-Formylherbertenol.
2010
Abstract The synthesis of 4-hydroxy-3-[(1 S )-1,2,2-trimethylcyclopentyl]benzaldehyde [(−)-α-formylherbertenol 1 ], a herbertane-type sesquiterpene isolated from the leafy liverwort Herberta adunca , from β-cyclogeraniol is described. The synthesis is based on the previously described preparation of an enantiopure 1,2,2-trimethylcyclopentane synthon from which the characteristic aromatic moiety of 1 is elaborated, using a Robinson annulation and a palladium-catalysed methoxycarbonylation of an aryl triflate as key synthetic steps. The synthesis of the natural sesquiterpene (−)-α-herbertenol, also a natural sequiterpene, using the same methodology is also described.
Auxiliary-controlled stereoselective enolate protonation: Enantioselective synthesis of cis and trans annulated decahydroquinoline alkaloids
1998
Abstract The diastereoselective synthesis of the octahydroquinoline enone precursor of pumiliotoxin C is achieved via tandem Mannich-Michael reaction on N-galactosyl imines. Conjugate cuprate addition to the bicyclic enone stereoselectively forms the trans annulated 4a- epi -pumiliotoxin C skeleton in the presence of the carbohydrate auxiliary, and the cis annulated pumiliotoxin C skeleton in its absence.
Two-carbon bridge substituted cocaines: enantioselective synthesis, attribution of the absolute configuration and biological activity of novel 6- and…
1999
In an effort to learn more about the general structure-activity relationships of cocaine with the aim to elucidate those structural features that might confer antagonistic properties to such analogues, we describe herein our synthetic efforts to prepare two-carbon bridge functionalized (methoxylated and hydroxylated) analogues. Our approach makes use of a modification of the classical Willstatter synthesis of cocaine: Mannich type cyclization of acetonedicarboxylic acid monomethyl ester with methylamine hydrochloride and 2-methoxysuccindialdehyde in a citrate buffer solution afforded the 6- and 7-substituted 2-carbomethoxy-3-tropinones 3a,b and 4a,b in approximate yields of 64%. Reduction o…
Microbiological transformations. 30. Enantioselective hydrolysis of racemic epoxides: the synthesis of enantiopure insect juvenile hormone analogs (b…
1993
Abstract The enantioselective epoxide biohydrolysis of the racemic benzodioxole 6,7-epoxygeraniol derivative 1 has been achieved using the fungus A. niger . This new type of preparative scale bioconversion allows the synthesis of both enantiomers of Bower's compound, an analogue of insect juvenile hormone. Biological tests showed that the 6(R) enantiomer was about ten times more active than the 6(S) enantiomer against the yellow meal worm Tenebrio molitor .
Investigation of Diketopiperazines Containing a Guanidino-Functionalized Sidechain as Potential Catalysts of Enantioselective Strecker Reactions
2005
Diketopiperazine 1 consisting of L-(γ-guanidino-α-amino)butyric acid and L-phenylalanine was synthesized as the hydroacetate and as the hydronitrate. Its structure was confirmed by X-ray analysis. In contrast to reports in the literature (Lipton et al.), compound 1 does not induce enantioselevtive catalysis of Strecker reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Fast evaluation of enantioselective drug metabolism by electrophoretically mediated microanalysis: application to fluoxetine metabolism by CYP2D6.
2013
In this work, a capillary electrophoretic methodology for the enantioselective in vitro evaluation of drugs metabolism is applied to the evaluation of fluoxetine (FLX) metabolism by cytochrome 2D6 (CYP2D6). This methodology comprises the in-capillary enzymatic reaction and the chiral separation of FLX and its major metabolite, norfluoxetine enantiomers employing highly sulfated β-CD and the partial filling technique. The methodology employed in this work is a fast way to obtain a first approach of the enantioselective in vitro metabolism of racemic drugs, with the additional advantage of an extremely low consumption of enzymes, CDs and all the reagents involved in the process. Michaelis-Men…
Application of molecularly imprinted polymers in analytical chiral separations and analysis
2018
Over the last two decades the process of development and application of a new types of molecular imprinted polymer (MIP) sorbents in the field of analytical chemistry have been widely described in the literature. One of the new trends in analytical chemistry practice is the use of new types of MIP sorbents as specific sorption materials constituting the stationary phase in advanced separation techniques. The following review paper contains comprehensive information about the application of a specific and well defined MIP sorbents (with the data base in the paper about the reagents used in MIP preparation process) as stationary phases in separation techniques including high performance liqui…
Squaramide-Catalyzed Enantioselective Michael Addition of Pyrazol-3- ones to ortho-Quinone Methides
2020
A bifunctional squaramide catalyzed the enantioselective Michael addition of pyrazol-3- ones to ortho-quinone methides, generated in situ from 2-(1-tosylalkyl)phenols is presented. The corresponding chiral pyrazolones are obtained with good to excellent yields (27-98%) and enantiomeric excess (14-99% ee).
Organocatalytic Enantioselective Aminoalkylation of 5‐Aminopyrazole Derivatives with Cyclic Imines
2020
The first enantioselective alkylation of 5‐aminopyrazoles is described with good results. The organocatalytic alkylation of 5‐aminopyrazoles have been accomplished using benzoxathiazine 2,2‐dioxides as electrophiles and a bifunctional squaramide organocatalyst.
Asymmetric Oxidative Mannich Reactions
2020
The asymmetric Mannich reaction is one of the most straightforward methodologies for the enantioselective synthesis of chiral amines. In general, asymmetric Mannich reactions involve the use of imines as electrophiles. However, in recent years, several asymmetric oxidative Mannich reactions have been reported using amines as electrophiles. This review provides an overview of these recent publications, including the different oxidants used and the scope and limitations of the different catalytic systems.