An improved, scalable synthesis of bis-amino acids

trans-4-Hydroxy-L-proline derived bis-amino acids are chiral, cyclic building blocks that display two alpha-amino acids that are differentiated from each other with protecting groups. They are assembled into spiroligomers—rigid, shape-programmable spirocyclic oligomers that are both stereochemically and functionally diverse. The synthesis presented here focuses on recent improvements that allow for a convenient, large-scale synthesis of twelve stereochemically pure bis-amino acids from inexpensive trans-4-hydroxy-L-proline. The bis-amino acids differ in stereochemistry as well as the amine protecting group, one of which (para-nitrobenzyl carbamate) has not been previously incorporated into bis-amino acids.