Kinetic resolution of 1-oxyl-3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine derivatives by lipase-catalyzed enantiomer selective acylation

Three chiral stable free radicals containing a hydroxymethyl group have been resolved by biocatalysis. By recrystallization and/or re-esterification each molecule was produced in very high enantiomeric purity. The resolved 1-oxyl-3-hydroxymethyl-2,2,5,5-tetramethylpyrrolidine alcohols were converted to methanethiosulfonate spin labels, 1-oxyl-3-methanesulfonylthiomethyl-2,2,5,5-tetramethylpyrrolidines. Enantiomeric purities have been determined by the F-19 NMR method of the respective Mosher esters. Absolute configurations were assigned by comparing the chemical shifts of the Mosher esters and also by comparing the specific rotations obtained with the same enzyme preparations. (C) 2004 Elsevier Ltd. All rights reserved.