Synthesis and spectroscopic characterization of enantiopure protected trans-4-amino-1-oxyl-2,2,6,6-tetramethyl piperidine-3-carboxylic acid (trans β-TOAC) |
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Authors: | Karen Wright Augustin de Castries Fernando Formaggio Antonio Toffoletti Jean-Paul Mazaleyrat |
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Affiliation: | a SIRCOB, UMR CNRS 8086, Bât. Lavoisier, University of Versailles, F-78000 Versailles, France b Department of Chemistry, University of Padova, 35131 Padova, Italy |
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Abstract: | Enantiomerically pure (3R,4S) and (3S,4R) protected 4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylic acids were synthesized by reduction of the enamines resulting from the condensation of 3-carboxymethyl-1-oxyl-2,2,6,6-tetramethyl-4-piperidone with (R) or (S)-α-methylbenzylamine. While NaBH3CN/CH3COOH reduction gave predominantly a mixture of the two possible cis-diastereomers, the use of NaBH4/(CH3)2CHCOOH resulted in a mixture of only one trans- and one cis-diastereomer. Removal of the chiral auxiliary from the separated diastereoisomers by hydrogenolysis and regeneration of the nitroxide radical gave the desired β-amino esters. The ESR spectrum of the (3R,4S)-enantiomer is also reported. |
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Keywords: | Chiral nitroxides Modified β-amino acids Spin-labelled amino acids trans-β-TOAC |
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