1,721,019 research outputs found
Organometallic Chemistry on Solid-phase. An overview
No full textSolid-phase organic synthesis (SPOS) is the most important method for the production of combinatorial libraries and with the development of high-throughput screening, libraries are widespread in pharmaceutical and agricultural chemistry. Amongst all the synthetic transformations successfully applied to solid phase, the use of organometallic reagents for the formation of a new carbon-carbon bond has been scarcely pursued. In this overview we collected the most recent examples of the use of organometallic reagents of Li, Mg, Cu, Zn, Si and B for C-C bond formation. The use of organometallic reagents in Pd-catalysed cross-coupling reactions was not reviewed. Highly basic organometallics as organo-lithium and -magnesium reagents have been more largely employed than cuprates and zincates, suggesting that several kinds of resins can withstand relatively strong reaction conditions. © 2002 Published by Éditions scientifiques et médicales Elsevier SAS
Synthesis of N-boc-alpha-amino Acids With Nucleobase Residues As Building-blocks For the Preparation of Chiral Pna (peptidic Nucleic-acids)
No full textN-Boc-Glutamic acid alpha-benzyl ester was transformed into 4-bromo-2-(tert-butoxycarbonylamino)-butyric acid benzyl ester using the Barton-Crich protocol. This bromo derivative undergoes nucleophilic substitution with nucleobases to give optically active N-Boc-4-adeninbutyrine (Boc-Aby), N-Boc-4-thyminbutyrine (Boc-Tby), N-Boc-4-guaninbutyrine (Boc-Gby) or N-Boc-4-cytosinbutyrine (Boc-Cby), useful building blocks for the synthesis of chiral peptidic nucleic acids (PNA)
Copper(II) complex formation properties of a basic polymer containing SO2 groups in the main chain
No full textConformational investigation of two isomeric chiral porphyrins: a convergent approach with different techniques
No full textThe conformation in solution of two atropisomeric meso-tetrabinaphthyl porphyrins, used as catalytic precursors in asymmetric synthesis, was studied by means of experimental (H-1-NMR ROESY, UV-Vis, and circular dichroism) and computational (semiempirical structure optimization, DeVoe's coupled oscillators calculations) methods. UV-Vis and CID spectra are calculated for several molecular models, with a systematic sampling of the conformational space, and compared to the experimental ones, leading to a structural hypothesis which is confirmed by NMR and PM3
Colorimetric tools for solid-phase organic synthesis
No full textOne of the unresolved problems of solid-phase organic synthesis (SPOS) is the availability of general and rapid methods to monitor the transformation of functional groups present in molecules supported on insoluble supports. Color tests, far from providing the ultimate solution, may help in detection (and sometimes in quantification) of different functional groups. In this short review, we have collected most of the methods available and applied in SPOS with an Experimental Section that describes the procedure we have successfully applied to bead analyses in our laboratories
A general synthesis of oligopeptides containing an oxirane ring in the place of a peptidic bond
No full textMolecules structurally analogous to dipeptides, containing an oxirane ring in the place of the peptidic bond, can be prepared by oxidative conversion of beta-hydroxyselenides obtained by Mukaiyama aldol type reaction of N-protected beta-amino alpha-selenyl aldehydes derived from naturally occurring amino acids. Copyright (C) 1996 Elsevier Science Lt
Polyampholytes: thermodynamic and spectroscopic studies on the protonation and coordinating properties
No full textChiral atropisomeric metalloporphyrins in the enantioselective styrene epoxidation
No full textN-Phosphorylimines undergo Lewis acid-catalyzed Diels-Alder reactions with Danishefsky's diene. Application of the chiral catalyst zinc (II)- (S)-BINOL results in good-to-low asymmetric induction but poor chemical conversion. However, the absolute stereochemistry of novel aza-Diels-Alder cycloadducts, such as diethyl 4-oxo-2-phenyl-3,4-dihydropyridin-1(2H)-ylphosphonate, can be determined using circular dichroism (CD). Comparison between experimental and TDDFT-calculated CD spectrum shows that use of the (S)-catalyst results in predominant formation of the (6R) cycloadducts
Microwave-assisted transformation of esters into hydroxamic acids
No full textA general, mild and efficient procedure with which to access hydroxamic acids, in good yields and purity, is reported. Esters are used as substrates and reacted with hydroxylamine, in the presence of a base, under microwave activation. The method has been successfully applied to enantiomerically pure esters without loss of stereochemical integrity
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