Selection of enantioselective acyl transfer catalysts from a pooled peptide library through a fluorescence-based activity assay: An approach to kinetic resolution of secondary alcohols of broad structural scope

An assay employing a fluorescently labeled split and pool peptide library h as been applied to the discovery of a new class of octapeptide catalysts fo r the kinetic resolution of secondary alcohols. A highly diverse library of peptide-based catalysts was synthesized on solid-phase synthesis beads suc h that each individual bead was co-functionalized with (i) a uniform loadin g of a pH-sensitive fluorophore and () a unique peptide-based catalyst. The library was then screened for activity in acylation reactions employing (/-)-sec-phenylethanol as the substrate and acetic anhydride as the acylatio n agent. From the most active catalysts, a lead peptide (4) was identified that provides a selectivity-factor (k(rel)) of 8.2 upon resynthesis and eva luation under homogeneous conditions. A "directed" second-generation split and pool peptide library was synthesized such that the new peptide sequence s in the library were biased toward the lead structure. Random samples of t he second generation library were screened in single bead assays that revea led several new peptide-based catalysts that afford improved selectivities in kinetic resolutions. Peptide catalyst 13 proves effective for the kineti c resolution of sec-phenylethanol (k(rel) = 20), as well as eight other sec ondary alcohols of a broad substrate scope (k(rel) = 4 to > 50).