CONSPECTUS: The advent of high-throughput screening (HTS) for chiral catalysts has encouraged the development of fast methods for determining enantiomeric excess (ee). Traditionally, chromatographic methods such as chiral HPLC have been used for ee determination in HTS. These methods, however, are not optimal because of high duty cycle. Their long analysis time results in a bottleneck in the HTS process. A more ideal method for HTS that requires less analysis time such as chiroptical methods are thus of interest. In this Account, we summarize our efforts to develop host-guest systems for ee determination. The first part includes our enantioselective indicator displacement assays (eIDAs), and the second part focuses on our circular dichroism based host-guest systems. Our first eIDA utilizes chiral boronic acid receptors, along with prescreened indicators, to determine ee for chiral α-hydroxyacids and vicinal diols with ±7% average error (AE). To further the practicality for this system, a HTS protocol was developed. Our second eIDA uses diamino chiral ligands and Cu(II) as the receptor for the ee determination of α-amino acids. The system reported ±12% AE, and a HTS protocol was developed for this system. Our first CD based host-guest system uses metal complexes composed of Cu(I) or Pd(II) with enantiopure 2,2'-diphenylphosphino-1,1'-binaphthyl (BINAP) as host to determine the ee of chiral vicinal diamines (±4% AE), primary amines (±17% AE), and cyclohexanones (±7% AE). Primary amines and cyclohexanones were derivatized to form chiral imines or chiral hydrazones to allow coordination with the metal complex. Upon coordination of chiral analytes, the metal-to-ligand (BINAP) charge transfer band was modulated, thus allowing the discrimination of chiral analytes. As an effort to improve the accuracy for chiral primary amine ee determination, a system with a host composed of o-formylphenyl boronic acid (FPBA) and enantiopure 1,1'-bi-2-naphthol (BINOL) was used to reduce the AE to ±5.8%. In the presence of amines, the FPBA-BINOL host forms an imine-coordinated boronic ester, thus affecting the CD signal of the boron complex. Another chiral primary amine ee determination system was developed with Fe(II) and 3-hydroxy-2-pyridinecarbaldehyde. The chiral imines, formed by the pyridinecarbaldehyde and chiral amines, would coordinate to the Fe(II) ion yielding exciton-coupled circular dichroism (ECCD) active metal complexes. This system was able to determine the ee of chiral amines with ±5% AE. Furthermore, this imine-Fe(II) complex system also successfully determined the ee of α-chiral aldehydes with ±5% AE. Other ECCD based hosts were subsequently developed; one with bisquinolylpyridylamine and Cu(II) for chiral carboxylates and amino acids and another multicomponent system with pyridine chromophores for chiral secondary alcohol ee determination. Both of the systems were able to determine ee of the chiral analytes with ±3% AE. Overall, our group has developed ee determining host-guest systems that target various functionali...

In Ig light-chain (LC) amyloidosis (AL), the unique antibody LC protein that is secreted by monoclonal plasma cells in each patient misfolds and/or aggregates, a process leading to organ degeneration. As a step toward developing treatments for AL patients with substantial cardiac involvement who have difficulty tolerating existing chemotherapy regimens, we introduce small-molecule kinetic stabilizers of the native dimeric structure of full-length LCs, which can slow or stop the amyloidogenicity cascade at its origin. A protease-coupled fluorescence polarization-based high-throughput screen was employed to identify small molecules that kinetically stabilize LCs. NMR and X-ray crystallographic data demonstrate that at least one structural family of hits bind at the LC-LC dimerization interface within full-length LCs, utilizing variable-domain residues that are highly conserved in most AL patients. Stopping the amyloidogenesis cascade at the beginning is a proven strategy to ameliorate postmitotic tissue degeneration.kinetic stabilizer | high-throughput screen | dimerization | structural biology | proteotoxicity S ecretion of an Ig light chain (LC) by a clonally expanded plasma cell population can lead to the disease LC amyloidosis (AL)-both a cancer and a proteinopathy (1, 2). "Free" LCs secreted without an associated antibody heavy chain (HC) initially adopt a well-defined homodimeric structure, wherein the monomers may be covalently linked by an interchain disulfide bond ( Fig. 1A) (3). LC monomers comprise an N-terminal variable (V) domain attached to a C-terminal constant (C) domain (SI Appendix, Fig. S1). Each patient's clonal plasma cells secrete a single, unique LC sequence. Most LCs are rapidly removed by the kidney.However, since amyloidogenic full-length (FL) LCs are generally less stable than nonamyloidogenic FL LCs, they can misfold, or misfold and misassemble, into nonnative species including cross-β-sheet amyloid fibrils, which are a hallmark of AL (4-8). Sequence also seems to play a role, as not all destabilized FL LCs aggregate in patients (4-8). How aggregation occurs in patients is not known, but several processes have been described in vitro, including destabilization-dependent endoproteolysis that releases amyloidogenic LC fragments (4,9,10). LC fragments including V domains are observed in patient deposits alongside FL LCs (11-13).Since we do not understand the structure-proteotoxicity relationships driving AL, a conservative strategy is to block FL LC misfolding at its origin by stabilizing the FL LC native state. Such a strategy has been effective at ameliorating the transthyretin amyloidoses (14-19). A small molecule that stabilizes FL LC dimers should prevent any misfolding and/or endoproteolysis that lead to LC aggregation and organ toxicity. We refer to such molecules as kinetic stabilizers, since they reduce the rate at which LCs transiently visit nonnative, aggregation-prone, and protease-sensitive conformations (20). The interfaces between the domains of the LC dimer are an important...

Porphyrins have been used frequently to construct supramolecular assemblies. In contrast, noncovalent ensembles derived from expanded porphyrins, larger congeners of naturally occurring tetrapyrrole macrocycles, are all but unknown. Here we report a series of expanded porphyrin-anion supramolecular assemblies. These systems display unique environmentally responsive behavior. Addition of polar organic solvents or common anions to the ensembles leads to either a visible color change, a change in the fluorescence emission features, or differences in solubility. The actual response, which could be followed easily by the naked eye, was found to depend on the specifics of the assembly, as well as the choice of analyte. Using the ensembles of this study, it proved possible to differentiate between common solvents, such as diethyl ether, THF, ethyl acetate, acetone, alcohol, acetonitrile, DMF, and DMSO, identify complex solvent systems, as well as distinguish between the fluoride, chloride, bromide, nitrate, and sulfate anions.

We report an approach to the asymmetric Baeyer–Villiger oxidation utilizing bioinformatics-inspired combinatorial screening for catalyst discovery. Scaled-up validation of our on-bead efforts with a circular dichroism-based assay of alcohols derived from the products of solution-phase reactions established the absolute configuration of lactone products; this assay proved equivalent to HPLC in its ability to evaluate catalyst performance, but was far superior in its speed of analysis. Further solution-phase screening of a focused library suggested a mode of asymmetric induction that draws distinct parallels with the mechanism of Baeyer–Villiger monooxygenases.

No abstract