| Popis: |
(3,4-13C2)-L-proline and (15N)-L-proline were prepared from the correspondingly labeled L-glumatic acids via a single scheme in high yield and on a gram scale. The synthetic route is based on the ring closure of L-glutamic acid to L-5-oxoproline and the selective reduction of the 5-amide function, without interference with the 2-carboxylate function and the asymmetric center. The selective reduction is effected by first converting the amide into the corresponding thioamide and subsequently reducing the thioamide to the amine using tributyltin hydride, in combination with protection and deprotection steps. In earlier work we described the preparation of L-glutamic acid isotopically labeled at any position or combination of positions starting from simple highly enriched synthons. The synthetic scheme in this publication makes L-proline, 13C- or 15N-labeled at any position or combination of positions, easily available. The labeled L-prolines are characterized by 1H-, 13C- and 15N-NMR and mass spectrometry. |
