ANODIC OXIDATION OF N-ACYL AND N-ALKOXYCARBONYL DIPEPTIDE ESTERS AS A KEY STEP FOR THE FORMATION OF CHIRAL HETEROCYCLIC SYNTHETIC BUILDING BLOCKS

Article abstract of DOI:10.1016/S0040-4020(01)87046-0

The anodic oxidation of N-protected dipeptide esters using chloride as a redox catalyst can be performed regioselectively at the C-terminal amino acid.With methanol as solvent, glycine as the C-terminal, and L-valine or L-proline as N-terminal amino acid methoxylation at the glycine residue takes place.Deprotection of this product leads to the (3S,6RS)-6-methoxy-2,5-piperazinedione (3) which can be applied as a chiral cationic glycine equivalent.The exchange of the methoxy group by C-nucleophiles takes place with high trans-diastereoselectivity under steric control by the substituent in 3-position.With branched amino acids at the C-terminus of the dipeptide ester the anodic oxidation in acetonitrile/methanol (95:5) as solvent with tetraethylammonium chloride as supporting electrolyte and redox catalyst leads to methyl imidazolidin-4-one-2-carboxylates.The cyclization takes place via the intermediate formation of the N-acylimino ester of the C-terminal amino acid.