Heterogeneous catalysis of the asymmetric aldol reaction by solid-supported proline-terminated peptides

Peptides with prolyl N-termini, attached to a PEG-polystyrene (TG) synthesis resin, have been tested as heterogeneous catalysts for the aldol reaction between acetone and p-nitrobenzaldehyde. Proline directly attached to TG showed good activity but poor enantioselectivity. However. in combination with serine or threonine, the selectivity improved considerably. At -25 degrees C, the dipeptide H-Pro-Ser-NH-TG achieved 82% ee. The H-Pro-Ser/Thr dipeptides may be seen as self-contained 'catalytic head-groups' for the development of more sophisticated aldol organocatalysts. (C) 2005 Elsevier Ltd. All rights reserved.