A new methodology for the synthesis of β-amino acids

A differentially functionalized succinic acid unit 6 undergoes alkylation with excellent regio- and high stereocontrol at the carbon α to the imide to furnish the alkylated product 7 in 60-83% yield. Selective removal of the imide provides 8 in 80-90% yields. Curtius rearrangement of 8 with retention of stereochemistry provides N-protected β-amino acids (9) in 70-83% yields. Alternatively, selective deprotection of the ester group followed by Curtius rearrangement provides isomeric β-amino acids 14a, 14b, and 14e in good yields. The methodology has been successfully applied to the synthesis of N-Boc-iturinic acid and 2-methyl-3-aminopropanoic acid, components of the antifungal peptide iturin and the cytotoxic depsipeptide cryptophycin respectively.