Maximizing the stereochemical diversity of spiro-ladder oligomers

[reaction: see text] We introduce all stereoisomers of a bis-amino acid building block derived from trans-4-hydroxy-L-proline. This small library of monomers allows arbitrary stereochemical configuration at any chiral center within our spiro-ladder oligomers. Three tetramer oligomers containing several combinations of the monomers 1-4 were synthesized; we explored the effect of monomer sequence on scaffold conformation by NMR.