Journal: ACS combinatorial science
A novel solid-phase methodology has been developed for the synthesis of N-alkyl, N-acyl, and N-sulfonyl-2-aminobenzo[d]thiazole derivatives. The key step in this procedure involves the preparation of polymer-bound 2-aminobenzo[d]thiazole resins 5 by cyclization reaction of 2-iodophenyl thiourea resin 3. The resin-bound 2-iodophenyl thiourea 3 is produced by addition of 2-iodophenyl isothiocyanate 2 to the amine-terminated linker amide resin 1. These core skeleton 2-aminobenzo[d]thiazole resins 5 undergo functionalization reaction with various electrophiles, such as alkyl halides, acid chlorides, and sulfonyl chlorides to generate N-alkyl, N-acyl, and N-sulfonyl-2-aminobenzo[d]thiazole resins 6, 7, and 8, respectively. Finally, N-alkyl, N-acyl, and N-sulfonyl-2-aminobenzo[d]thiazole derivatives 9, 10, and 11 are then generated in good yields and purities by cleavage of the respective resins 6, 7, and 8 under trifluoroacetic acid (TFA) in dichloromethane (DCM).
Marine cone snail venoms consist of large, naturally occurring combinatorial libraries of disulfide-constrained peptide neurotoxins known as conotoxins, which have profound potential in the development of analgesics. In this study, we report a synthetic combinatorial strategy that probes the hypervariable regions of conotoxin frameworks to discover novel analgesic agents by utilizing high diversity mixture-based positional-scanning synthetic combinatorial libraries (PS-SCLs). We hypothesized that the direct in vivo testing of these mixture-based combinatorial library samples during the discovery phase would facilitate the identification of novel individual compounds with desirable antinociceptive profiles while simultaneously eliminating many compounds with poor activity or liabilities of locomotion and respiration. A PS-SCL was designed based on the α-conotoxin RgIA-R n-loop region and consisted of 10,648 compounds systematically arranged into 66 mixture samples. Mixtures were directly screened in vivo using the mouse 55°C warm-water tail-withdrawal assay, which allowed deconvolution of amino acid residues at each position that confer antinociceptive activity. A second generation library of 36 individual α-conotoxin analogs was synthesized using systematic combinations of amino acids identified from PS-SCL deconvolution and further screened for antinociceptive activity. Six individual analogs exhibited comparable antinociceptive activity to the recognized analgesic α-conotoxin RgIA-R, and were selected for further examination of antinociceptive, respiratory and locomotor effects. Three lead compounds were identified that produced dose-dependent antinociception without significant respiratory depression or decreased locomotor activity. Our results represent a unique approach for rapidly developing novel lead α-conotoxin analogs as low-liability analgesics with promising therapeutic potential.
Perovskite CaCu3Ti4O12 has drawn a great attention for various electronic applications due to the giant dielectric property as well as a strong stability at a wide range of temperature. In this paper, we use an off-axis continuous composition-spread (CCS) sputtering method to investigate the full range dielectric characteristics of calcium copper titanate thin films. The film compositions are continuously distributed by deposition from two targets of CaTiO3 and CuTiO3. A slightly Ca-deficient, Cu- and Ti-rich film, which has a 0.9:3.2:4.3 ratio for Ca:Cu:Ti, demonstrated the best performance by showing a dielectric constant of 781 at 100 kHz. On the other hand, all other films far away from the CaCu3Ti4O12 composition showed suppressed dielectric properties. Analyses by X-ray photon spectroscopy, micro-Raman microscopy, transmission electron microscopy and Rutherford backscattering spectroscopy reveal that there are three possible origins for such superior performance at off stoichiometric thin films: (1) bulk doping by excessive Cu and Ti ions, (2) chemically modified grain boundary, and (3) the lowered electrode-sample interface resistance. Our result will provide a new insight to engineer the dielectric properties using off-stoichiometric synthesis.
An efficient three-component strategy for the improved synthesis of multi-functionalized 6,7-dihydrobenzofuran-4(5H)-ones under microwave irradiation for short periods has been established. The synthesized benzofuran-4(5H)-ones have been readily converted into polyfunctionalized cinnoline-4-carboxamides by treating with hydrazine hydrate through a regioselective ring-opening of furan. Tedious work-up procedures can be avoided due to the direct precipitation of products from the reaction solution.
Cyclic peptides have great potential as therapeutic agents and research tools. However, their applications against intracellular targets have been limited, because cyclic peptides are generally impermeable to the cell membrane. It was previously shown that fusion of cyclic peptides with a cyclic cell-penetrating peptide resulted in cell-permeable bicyclic peptides that are proteolytically stable and biologically active in cellular assays. In this work, we tested the generality of the bicyclic approach by synthesizing a combinatorial library of 5.7 x 106 bicyclic peptides featuring a degenerate sequence in the first ring and an invariant cell-penetrating peptide in the second ring. Screening of the library against oncoprotein K-Ras G12V followed by hit optimization produced a moderately potent and cell-permeable K-Ras inhibitor, which physically blocks the Ras-effector interactions in vitro, inhibits the signaling events downstream of Ras in cancer cells, and induces apoptosis of the cancer cells. Our approach should be generally applicable to developing cell-permeable bicyclic peptide inhibitors against other intracellular proteins.
The development of techniques to screen one-bead-one-compound (OBOC) libraries remains a critical step in identifying small molecules that bind target proteins. While great strides have been made, there remains a need to continue to develop OBOC screening techniques that not only reliably identify hit molecules but can also distinguish poor from excellent binders in a single screen. Similarly, relatively strong binding between a small molecule and protein target is required to be considered a hit from the initial pool of screened molecules. Here, we present the framework for a method to screen OBOC libraries using proteins and antibodies stained with a near infrared (NIR)-emitting fluorophore. These labeled proteins provide significant signal at very low concentrations because of their fluorescence quantum yield. This work revealed that we can detect proteins and antibodies interacting with a known binding partner at low nanomolar concentrations; binding is specific, and known binders to carbonic anhydrase can be detected and ranked.
Physicochemical property switching of chemical space is of great importance for optimization of compounds, for example for biological activity. Cyclization is a key method to control 3D and other properties. A two-step approach, which in-volves a multicomponent reaction followed by cyclization, is reported to achieve the transition from basic moieties to charge neutral cyclic derivatives. A series of multi-substituted oxazolidinones, oxazinanones, oxazepanones as well as their thio- and sulfur-derivatives are synthesized from readily available building blocks with mild conditions and high yields.
Current commercial fuel cells operate in acidic media where Pt-containing compositions have been shown to be the best oxygen reduction reaction (ORR) electrocatalysts, due to their facile reaction kinetics and long-term stability under operating conditions. However, with the development of alkaline membranes, alkaline fuel cells have become a potentially viable alternative that offers the possibility of using Pt-free (precious metal-free) electrocatalysts. However, the search for better electrocatalysts can be very effort-consuming, if we intend to test every potential bi- or tri-metallic combination. In this work, we have explored the application of physical vapor deposition using a custom-built getter co-sputtering chamber to prepare catalyst thin films on glassy carbon electrodes, enabling catalyst compositions to be screened in a combinatorial fashion. The activity of combinations containing Au, Cu, Ag, Rh, and Pd as binary metal catalysts, in alkaline media, was studied using rotating disk electrode (RDE) voltammetry with an exchangeable disk electrode holder. Subsequently, we investigated a composition gradient of Pd-Cu, the best performing bimetallic catalyst thin film identified in the initial screening tests. Our results show the viability of using metal getter co-sputtering as a rapid and effective tool for preliminary testing of ORR fuel cell electrocatalysts.
Peptide macrocyclization is typically associated with the development of higher affinity and more protease stable protein ligands, and, as such, is an important tool in peptide drug discovery. Yet, within the context of a diverse library, does cyclization give inherent advantages over linear peptides? Here, we used mRNA display to create a peptide library of diverse ring sizes and topologies (monocyclic, bicyclic, and linear). Several rounds of in vitro selection against streptavidin were performed and the winning peptide sequences were analyzed for their binding affinities and overall topologies. The effect of adding a protease challenge on the enrichment of various peptides was also investigated. Taken together, the selection output yields insights about the relative abundance of binders of various topologies within a structurally diverse library.
A new coronavirus (CoV) caused a pandemic COVID-19, which has become a global health care emergency in the present date. The virus has been termed as SARS-CoV-2 (Severe Acute Respiratory Syndrome-Cororavirus-2) and has a genome similar (~82%) to the SARS-CoV (SARS coronavirus). An attractive therapeutic target for CoVs is the Mpro (main protease) or 3CLpro (3-chymotrypsin-like cysteine protease) as the enzyme plays a key role in the polyprotein processing and is active in a dimeric form. Further, Mpro is highly conserved among various CoVs as the mutation in Mpro is often lethal to the virus. Thus, drugs targeting Mpro enzyme significantly reduce the risk of mutation-mediated drug resistance and display broad-spectrum antiviral activity. The combinatorial design of peptide-based inhibitors targeting the dimerization of SARS-CoV Mpro represent a potential therapeutic strategy. In this regard, we compiled the literature reports highlighting the effect of mutations and N-terminal deletion of residues of SARS-CoV Mpro on its dimerization and thus, catalytic activity. We believe that the present review will stimulate research in this less explored, yet quite significant area. The effect of the COVID-19 epidemic and the possibility of future CoV outbreaks strongly emphasize the urgent need for the design and development of potent antiviral agents against CoV infections.