C-H Functionalization of N-Methylated Amino Acids and Peptides as Tool in Natural Product Synthesis: Synthesis of Abyssenine A and Mucronine E.

N-Methylated amino acids and peptides with an 8-aminoquinoline (AQ) directing group can be subjected to stereoselective Pd-catalyzed β-functionalizations. The best results are obtained with aryl iodides, but alkyl and alkenyl side chains can also be introduced. The AQ protecting group can easily be removed, providing the free carboxylic acid, which can be used directly in peptide couplings. This protocol was used successfully as a key step in the synthesis of the cyclopeptide alkaloids abyssenine A and mucronine E.