THE MERRIFIELD RESIN SUPPORTED PROLINE-THREONINE DIPEPTIDE CATALYSTS FOR ASYMMETRIC ALDOL REACTION

The Merrifield resin supported proline-threonine dipeptide catalysts were prepared by solid-phase peptide synthesis (SPPS) and the amino acid incorporation was checked by means of the Kaiser or isatin test. The dipeptide catalyst grafted with the Merrifield resin by the hydroxyl group while keeping free the carboxyl group of L-threonine as the nature proline. Then the catalyst was tested in the Aldol reaction between ketones and aromatic aldehydes. In order to find the optimal reaction conditions for this kind of catalysts, the influence of different conditions was explored, such as solvents, surfactants and the amount of the catalyst. It was found that the surfactant can be used to significantly improve the performance of the catalyst (catalytic activity and stereo-selectivity), and this new peptide-based catalyst could efficiently catalyze the Aldol reaction to provide P-hydroxy ketones in good yields with good stereoselectivity. By employing Tween-20 water-soluble micelles as solvent, an medium stereoselectivity was observed at room temperature, up to 14: 86 syn. : anti. diastereomeric ratio and up to 78% enantiomeric excess. Besides, the immobilized catalyst can be recovered by simple filtration without the need for catalyst regeneration, and it retained catalytic activity and stereochemical reactivity even after being recycled for 4 times.