Reactivity and Selectivity of Iminium Organocatalysis Improved by a Protein Host

Abstract

There has been growing interest in performing organocatalysis within a supramolecular system as a means of controlling reaction reactivity and stereoselectivity. Here, a protein is used as a host for iminium catalysis. A pyrrolidine moiety is covalently linked to biotin and introduced to the protein host streptavidin for organocatalytic activity. Whereas in traditional systems stereoselectivity is largely controlled by the substituents added to the organocatalyst, enantiomeric enrichment by the reported supramolecular system is completely controlled by the host. Also, the yield of the model reaction increases over 10-fold when streptavidin is included. A 1.1 Å crystal structure of the protein-catalyst complex and molecular simulations of a key intermediate reveal the chiral scaffold surrounding the organocatalytic reaction site. This work illustrates that proteins can be an excellent supramolecular host for driving stereoselective secondary amine organocatalysis.

Directed Evolution of a Designer Enzyme Featuring an Unnatural Catalytic Amino Acid

“…Lastly,w es urmise that the impressive improvements observed for LmrR_pAF are not limited to an aniline side chain. Instead, we suggest that the introduction and fine-tuning of other organocatalysts, [38][39][40] which are versatile yet notoriously slow,t hrough geneticcode expansion will result in proficient designer enzymes for aw ide variety of new-to-nature reactions.U ltimately,s uch efforts could provide ap romising route for developing efficient protein catalysts for synthetically relevant transformations.…”

Directed Evolution of a Designer Enzyme Featuring an Unnatural Catalytic Amino Acid

“…Lastly, we surmise that the impressive improvements observed for LmrR_pAF are not limited to an aniline side chain. Instead, we suggest that the introduction and fine‐tuning of other organocatalysts, which are versatile yet notoriously slow, through genetic‐code expansion will result in proficient designer enzymes for a wide variety of new‐to‐nature reactions. Ultimately, such efforts could provide a promising route for developing efficient protein catalysts for synthetically relevant transformations.…”

Selection, Addiction and Catalysis: Emerging Trends for the Incorporation of Noncanonical Amino Acids into Peptides and Proteins in Vivo

“…For the incorporation of ncAAs that directly promote a target transformation, the creation and directed evolution of LmrR_V15pAF opens up questions that need to be answered. For example, is it a general phenomenon that the performance of organocatalysts, which are versatile yet notoriously slow, is boosted by placing them in protein scaffolds by ncAA incorporation? And, are the resulting designer enzymes generally privileged starting points for directed evolution efforts, as it was demonstrated for LmrR_pAF? Independent of the answers to these questions, designer enzymes will continue to make use of ncAAs to catalyze new‐to‐nature transformations.…”