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Racemic Form (racemic + form)
Selected AbstractsStereospecific and Stereoselective Polymerization of 4-Methyl-1-hexene by Enantiomeric Binaphthyl-Bridged Salen Dichlorozirconium (IV) ComplexesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18-19 2007Maria Strianese Abstract Two enantiomers of a chiral binaphthyl-bridged salen dichlorozirconium (IV) complex (namely R-,- 1 and S-,- 1) were synthesized and tested as pre-catalysts for 4-methyl-1-hexene (4MH) polymerization. Their behavior was compared with that of the same complex in its racemic form. Isotactic poly(4-methyl-1-hexene) was produced in both cases, but the polymerization of racemic 4MH promoted by the optically active catalysts preferentially consumed one antipode, showing some stereoselectivity for the process. [source] Enantiorecognition on solid chiral selectors using microbatch technology: an example of limitation in case of strong association in the racemateBIOMEDICAL CHROMATOGRAPHY, Issue 6 2005Christian Roussel Abstract When they were independently tested, the enantiomers of N,N,-bis(salicylidene)- trans -1,2-cyclohexanediamine showed a large difference in adsorption on new chiral selectors using microbatch technology. Surprisingly, when these enantiomers were applied on the same supports as a racemic mixture, no discrimination was observed even though suitable adsorption existed. When a mixture enriched in one enantiomer (scalemic mixture) was applied, the resulting supernatant contained the racemic form and the enantiomer in excess was adsorbed on the support together with a part of racemate. This behavior, which militates in favor of a strong heterochiral dimer formation in the racemate, was revealed using microbatch technology but remained hidden on classical column chromatography on chiral support. Molecular dynamics calculations corroborate this hypothesis, showing a favorite binding mode of the heterochiral dimer, which is stabilized by various inter- and intramolecular interactions. Our findings may be considered as a new limitation of microbatch technology, but they may have some inference in case of chiral amplification using the N,N,-bis(salicylidene)- trans -1,2-cyclohexanediamine enantiomers as chiral ligands. Copyright © 2005 John Wiley & Sons, Ltd. [source] ChemInform Abstract: A Concise Total Synthesis of (+)-Tetrabenazine and (+)-,-Dihydrotetrabenazine.CHEMINFORM, Issue 32 2010Seung-Mann Paek Abstract Tetrabenazine (I) is applied in racemic form as drug for the treatment of chorea associated with Huntington,s disease. [source] Chiral separation and CD characterisation of enantiomeric cyclotriphosphazene derivativesCHIRALITY, Issue 8 2005Tam T.T. Bui Abstract The gem-disubstituted cyclotriphosphazene 1 reacted with piperazine (pip) to give the piperazine-bridged derivative 2, which is expected to exist in meso and racemic forms because the two PCl (pip) groups are stereogenic. The proton-decoupled 31P NMR spectrum of 2 gave rise to two similar sets of ABX signals in a 1:1 ratio, consistent with formation of diastereoisomers. The meso and racemic forms of compound 2 were separated by column chromatography on silica gel and characterised by elemental analysis, mass spectrometry, 31P NMR spectroscopy, and X-ray crystallography. Using HPLC with a chiral stationary phase, the racemic form of compound 2 was further separated into enantiomers, which were characterised by circular dichroism (CD) spectroscopy. This is the first report of the separation of enantiomers in the field of cyclophosphazene chemistry and hence the first CD spectra of derivatives in which the cyclophosphazene ring is at the chiral centre. © 2005 Wiley-Liss, Inc. Chirality 17:438,443, 2005. [source] | ||||||||||