Discovery, X-ray Crystallography and Antiviral Activity of Allosteric Inhibitors of Flavivirus NS2B-NS3 Protease.

Flaviviruses, including dengue, West Nile and recently emerged Zika virus, are important human pathogens, but there are no drugs to prevent or treat these viral infections. The highly conserved Flavivirus NS2B-NS3 protease is essential for viral replication and therefore a drug target. Compound screening followed by medicinal chemistry yielded a series of drug-like, broadly active inhibitors of Flavivirus proteases with IC50 as low as 120 nM. The inhibitor exhibited significant antiviral activities in cells (EC68: 300-600 nM) and in a mouse model of Zika virus infection. X-ray studies reveal that the inhibitors bind to an allosteric, mostly hydrophobic pocket of dengue NS3 and hold the protease in an open, catalytically inactive conformation. The inhibitors and their binding structures would be useful for rational drug development targeting Zika, dengue and other Flaviviruses.

Enantioselective Synthesis of Thailanstatin A Methyl Ester and Evaluation of in Vitro Splicing Inhibition.

Thailanstatin A has been isolated recently from the fermentation broth of B. thailandensis MSMB43. We describe here an enantioselective convergent synthesis of thailanstatin A methyl ester and evaluation of its splicing activity. Synthesis of both highly functionalized tetrahydropyran rings were carried out from commercially available tri- O-acetyl-d-glucal as the key starting material. Our convergent synthesis involved the synthesis of both tetrahydropyran fragments in a highly stereoselective manner. The fragments were then coupled using cross-metathesis as the key step. The synthesis of the diene subunit included a highly stereoselective Claisen rearrangement, a Cu(I)-mediated conjugate addition of MeLi to set the C-14 methyl stereochemistry, a reductive amination reaction to install the C16-amine functionality, and a Wittig olefination reaction to incorporate the diene unit. The epoxy alcohol subunit was synthesized by a highly selective anomeric allylation, a Peterson olefination, and a vanadium catalyzed epoxidation that installed the epoxide stereoselectively. Cross-metathesis of the olefins provided the methyl ester derivative of thailanstatin A. We have carried out in vitro splicing studies of the methyl ester derivative, which proved to be a potent inhibitor of the spliceosome.

Total synthesis of nucleoside antibiotic A201A.

A201A, a unique nucleoside antibiotic with potent antibacterial activities, has been synthesized for the first time in a total of 47 steps in a highly modular and linear manner, highlighting the elaboration/incorporation of an unprecedented hexofuranoside unit bearing an exocyclic enol ether moiety.

Deacylative arylation and alkynylation of unstrained ketones.

Ketones are ubiquitous in bioactive natural products, pharmaceuticals, chemical feedstocks, and synthetic intermediates. Hence, deacylative coupling reactions enable the versatile elaboration of a plethora of chemicals to access complex drug candidates and natural products. Here, we present deacylative arylation and alkynylation strategies for the synthesis of a wide range of alkyl-tethered arenes and alkynes from cyclic ketones and methyl ketones under dual nickel/photoredox catalysis. This reaction begins by generating a pre-aromatic intermediate (PAI) through the condensation of the ketone and N'-methylpicolino-hydrazonamide (MPHA), followed by the oxidative cleavage of the PAI α-C─C bond to form an alkyl radical, which is subsequently intercepted by a Ni complex, facilitating the formation of diverse C(sp3)-C(sp2)/C(sp) bonds with remarkable generality. This protocol features a one-pot reaction capability, high regioselectivity and ring-opening efficiency, mild reaction conditions, and a broad substrate scope with excellent functional group compatibility.

Green synthesis for diverse bioactive benzo-fused spiroindolines through DBU-catalysed post-Ugi double cyclization.

A metal-free protocol utilizing DBU catalysis for post-Ugi amide-ester exchange and Conia-ene double cyclization has been successfully developed, allowing the synthesis of diverse highly functionalized benzo-fused spiroindolines with anti-cancer activities under mild conditions. Remarkably, this methodology demonstrates promising prospects for green chemistry, as it allows for the preparation of the spiroindolines in water. Control experiments indicate that a crucial role of the cyclic imide, specifically ring rigidification, facilitates the subsequent Conia-ene cyclization.

[4 + 2] Cyclization or Lossen Rearrangement: Rhodium-Catalyzed Divergent Synthesis of Carboline Derivatives with Anticancer Activity.

An unusual rhodium-catalyzed C-H activation/Lossen rearrangement/oxa-Michael addition tandem cyclization has been achieved along with a tunable well-known C-H activation/[4 + 2] annulation, leading to regio-, chemo-, and diastereoselective access to diverse pentacyclic α-carbolines and ß-carboline-1-one derivatives in moderate to good yields with significant anticancer activity.

Discovery, Structure-Activity Relationship and In Vitro Anticancer Activity of Small-Molecule Inhibitors of the Protein-Protein Interactions between AF9/ENL and AF4 or DOT1L.

Chromosomal translocations involving the mixed lineage leukemia (MLL) gene cause 5-10% acute leukemias with poor clinical outcomes. Protein-protein interactions (PPI) between the most frequent MLL fusion partner proteins AF9/ENL and AF4 or histone methyltransferase DOT1L are drug targets for MLL-rearranged (MLL-r) leukemia. Several benzothiophene-carboxamide compounds were identified as novel inhibitors of these PPIs with IC50 values as low as 1.6 µM. Structure-activity relationship studies of 77 benzothiophene and related indole and benzofuran compounds show that a 4-piperidin-1-ylphenyl or 4-pyrrolidin-1-ylphenyl substituent is essential for the activity. The inhibitors suppressed expression of MLL target genes HoxA9, Meis1 and Myc, and selectively inhibited proliferation of MLL-r and other acute myeloid leukemia cells with EC50 values as low as 4.7 µM. These inhibitors are useful chemical probes for biological studies of AF9/ENL, as well as pharmacological leads for further drug development against MLL-r and other leukemias.

Rapid access to C2-quaternary 3-methyleneindolines via base-mediated post-Ugi Conia-ene cyclization.

Highly efficient synthesis of diverse 2,2-disubstituted 3-methyleneindoline derivatives through a one-pot base-promoted post-Ugi 5-exo-dig "Conia-ene"-type cyclization has been disclosed. The mechanism study indicates that an intramolecular hydrogen bond may play a vital role in this process. The antiproliferative evaluation of cancer cell lines reveals that this protocol provides practical use in the green synthesis of bioactive compound libraries.

Structure-activity relationship and antitumor activity of 1,4-pyrazine-containing inhibitors of histone acetyltransferases P300/CBP.

Acetylation of histone lysine residues by histone acetyltransferase (HAT) p300 and its paralog CBP play important roles in gene regulation in health and diseases. The HAT domain of p300/CBP has been found to be a potential drug target for cancer. Compound screening followed by structure-activity relationship studies yielded a novel series of 1,4-pyrazine-containing inhibitors of p300/CBP HAT with their IC50s as low as 1.4 µM. Enzyme kinetics and other studies support the most potent compound 29 is a competitive inhibitor of p300 HAT against the substrate histone. It exhibited a high selectivity for p300 and CBP, with negligible activity on other classes of HATs in human. Compound 29 inhibited cellular acetylation of several histone lysine residues and showed strong activity against proliferation of a panel of solid and blood cancer cells. These results indicate it is a novel pharmacological lead for drug development targeting these cancers as well as a useful chemical probe for biological studies of p300/CBP.

Signaling Pathway and Small-Molecule Drug Discovery of FGFR: A Comprehensive Review.

Targeted therapy is a groundbreaking innovation for cancer treatment. Among the receptor tyrosine kinases, the fibroblast growth factor receptors (FGFRs) garnered substantial attention as promising therapeutic targets due to their fundamental biological functions and frequently observed abnormality in tumors. In the past 2 decades, several generations of FGFR kinase inhibitors have been developed. This review starts by introducing the biological basis of FGF/FGFR signaling. It then gives a detailed description of different types of small-molecule FGFR inhibitors according to modes of action, followed by a systematic overview of small-molecule-based therapies of different modalities. It ends with our perspectives for the development of novel FGFR inhibitors.

A Class of Disulfide Compounds Suppresses Ferroptosis by Stabilizing GPX4.

Ferroptosis is a nonapoptotic form of cell death characterized by iron-dependent lipid peroxidation and has been implicated in multiple pathological conditions. Glutathione peroxidase 4 (GPX4) plays an essential role in inhibiting ferroptosis by eliminating lipid peroxide using glutathione (GSH) as a reductant. In this study, we found Ellman's reagent DTNB and a series of disulfide compounds, including disulfiram (DSF), an FDA-approved drug, which protect cells from erastin-induced ferroptosis. Mechanistically, DTNB or DSF is conjugated to multiple cysteine residues in GPX4 and disrupts GPX4 interaction with HSC70, an adaptor protein for chaperone mediated autophagy, thus preventing GPX4 degradation induced by erastin. In addition, DSF ameliorates concanavalin A induced acute liver injury by suppressing ferroptosis in a mouse model. Our work reveals a novel regulatory mechanism for GPX4 protein stability control. We also discover disulfide compounds as a new class of ferroptosis inhibitors and suggest therapeutic repurposing of DSF in treating ferroptosis-related diseases.

Small-molecule inhibitor of AF9/ENL-DOT1L/AF4/AFF4 interactions suppresses malignant gene expression and tumor growth.

Chromosome translocations involving mixed lineage leukemia (MLL) gene cause acute leukemia with a poor prognosis. MLL is frequently fused with transcription cofactors AF4 (~35%), AF9 (25%) or its paralog ENL (10%). The AHD domain of AF9/ENL binds to AF4, its paralog AFF4, or histone-H3 lysine-79 (H3K79) methyltransferase DOT1L. Formation of AF9/ENL/AF4/AFF4-containing super elongation complexes (SEC) and the catalytic activity of DOT1L are essential for MLL-rearranged leukemia. Protein-protein interactions (PPI) between AF9/ENL and DOT1L/AF4/AFF4 are therefore a potential drug target. Methods: Compound screening followed by medicinal chemistry was used to find inhibitors of such PPIs, which were examined for their biological activities against MLL-rearranged leukemia and other cancer cells. Results: Compound-1 was identified to be a novel small-molecule inhibitor of the AF9/ENL-DOT1L/AF4/AFF4 interaction with IC50s of 0.9-3.5 µM. Pharmacological inhibition of the PPIs significantly reduced SEC and DOT1L-mediated H3K79 methylation in the leukemia cells. Gene profiling shows compound-1 significantly suppressed the gene signatures related to onco-MLL, DOT1L, HoxA9 and Myc. It selectively inhibited proliferation of onco-MLL- or Myc-driven cancer cells and induced cell differentiation and apoptosis. Compound-1 exhibited strong antitumor activity in a mouse model of MLL-rearranged leukemia. Conclusions: The AF9/ENL-DOT1L/AF4/AFF4 interactions are validated to be an anticancer target and compound-1 is a useful in vivo probe for biological studies as well as a pharmacological lead for further drug development.

Synthesis, structure-activity relationship and antiviral activity of indole-containing inhibitors of Flavivirus NS2B-NS3 protease.

Zika virus belongs to the Flavivirus family of RNA viruses, which include other important human pathogens such as dengue and West Nile virus. There are no approved antiviral drugs for these viruses. The highly conserved NS2B-NS3 protease of Flavivirus is essential for the replication of these viruses and it is therefore a drug target. Compound screen followed by medicinal chemistry optimization yielded a novel series of 2,6-disubstituted indole compounds that are potent inhibitors of Zika virus protease (ZVpro) with IC50 values as low as 320 nM. The structure-activity relationships of these and related compounds are discussed. Enzyme kinetics studies show the inhibitor 66 most likely exhibited a non-competitive mode of inhibition. In addition, this series of ZVpro inhibitors also inhibit the NS2B-NS3 protease of dengue and West Nile virus with reduced potencies. The most potent compounds 66 and 67 strongly inhibited Zika virus replication in cells with EC68 values of 1-3 µM. These compounds are novel pharmacological leads for further drug development targeting Zika virus.

Synthesis, Structure-Activity Relationships, and Antiviral Activity of Allosteric Inhibitors of Flavivirus NS2B-NS3 Protease.

Flaviviruses, including Zika, dengue, and West Nile viruses, are important human pathogens. The highly conserved NS2B-NS3 protease of Flavivirus is essential for viral replication and therefore a promising drug target. Through compound screening, followed by medicinal chemistry studies, a novel series of 2,5,6-trisubstituted pyrazine compounds are found to be potent, allosteric inhibitors of Zika virus protease (ZVpro) with IC50 values as low as 130 nM. Their structure-activity relationships are discussed. The ZVpro inhibitors also inhibit homologous proteases of dengue and West Nile viruses, and their inhibitory activities are correlated. The most potent compounds 47 and 103 potently inhibited Zika virus replication in cells with EC68 values of 300-600 nM and in a mouse model of Zika infection. These compounds represent novel pharmacological leads for drug development against Flavivirus infections.

Discovery, Structure-Activity Relationship, and Biological Activity of Histone-Competitive Inhibitors of Histone Acetyltransferases P300/CBP.

Histone acetyltransferase (HAT) p300 and its paralog CBP acetylate histone lysine side chains and play critical roles in regulating gene transcription. The HAT domain of p300/CBP is a potential drug target for cancer. Through compound screening and medicinal chemistry, novel inhibitors of p300/CBP HAT with their IC50 values as low as 620 nM were discovered. The most potent inhibitor is competitive against histone substrates and exhibits a high selectivity for p300/CBP. It inhibited cellular acetylation and had strong activity with EC50 of 1-3 µM against proliferation of several tumor cell lines. Gene expression profiling in estrogen receptor (ER)-positive breast cancer MCF-7 cells showed that inhibitor treatment recapitulated siRNA-mediated p300 knockdown, inhibited ER-mediated gene transcription, and suppressed expression of numerous cancer-related gene signatures. These results demonstrate that the inhibitor is not only a useful probe for biological studies of p300/CBP HAT but also a pharmacological lead for further drug development targeting cancer.

An unexpected rearrangement of pent-4-enofuranosides to cyclopentanones upon hydrogenolysis of the anomeric benzyl group.

During our synthesis toward the unique nucleoside antibiotic A201A, we were surprised to find that a benzyl arabino-pent-4-enofuranoside underwent a Ferrier II-like rearrangement readily to provide the corresponding cyclopentanone derivative in high yield and stereoselectivity upon hydrogenolysis of the anomeric benzyl group.