Chemical optimization of artificial metalloenzymes based on the biotin-avidin technology : (S)-selective and solvent-tolerant hydrogenation catalysts via the introduction of chiral amino acid spacers

The selective artificial metalloenzymes were designed by incorporation of amino acid spacer (phenylalanine or proline) between biotin anchor and the rhodium-diphosphate moiety. The two pairs of epimeric ligands, biotin-phenylalanine and biotin-proline, were prepd. in three steps from com. available N-Boc-protected amino acids (Boc = tert-butoxycarbonyl). Incorporation of biotinylated [rhodium(diphosphine)]+ complexes with enantiopure amino acid spacers in streptavidin affords solvent-tolerant and selective artificial metalloenzymes. Catalytic hydrogenation of N-protected dehydroamino acids using prepd. artificial metalloenzymes gives up to 91% ee (S). [on SciFinder(R)]