Practical Thiol Surrogates and Protective Groups for Arylthiols for Suzuki−Miyaura Conditions

General cross-coupling reactions with adaptive dynamic homogeneous catalysis

Cross-coupling reactions are among the most important transformations in modern organic synthesis^1-3. Although the range of reported (het)aryl halides and nucleophile coupling partners is very large considering various protocols, the reaction conditions vary considerably between compound classes, necessitating renewed case-by-case optimization of the reaction conditions⁴. Here we introduce adaptive dynamic homogeneous catalysis (AD-HoC) with nickel under visible-light-driven redox reaction conditions for general C(sp²)-(hetero)atom coupling reactions. The self-adjustive nature of the catalytic system allowed the simple classification of dozens of various classes of nucleophiles in cross-coupling reactions. This is synthetically demonstrated in nine different bond-forming reactions (in this case, C(sp²)-S, Se, N, P, B, O, C(sp³, sp², sp), Si, Cl) with hundreds of synthetic examples under predictable reaction conditions. The catalytic reaction centre(s) and conditions differ from one another by the added nucleophile, or if required, a commercially available inexpensive amine base.

Discovery of a PDZ Domain Inhibitor Targeting the Syndecan/Syntenin Protein-Protein Interaction: A Semi-Automated "Hit Identification-to-Optimization" Approach

The rapid identification of early hits by fragment-based approaches and subsequent hit-to-lead optimization represents a challenge for drug discovery. To address this challenge, we created a strategy called "DOTS" that combines molecular dynamic simulations, computer-based library design (chemoDOTS) with encoded medicinal chemistry reactions, constrained docking, and automated compound evaluation. To validate its utility, we applied our DOTS strategy to the challenging target syntenin, a PDZ domain containing protein and oncology target. Herein, we describe the creation of a "best-in-class" sub-micromolar small molecule inhibitor for the second PDZ domain of syntenin validated in cancer cell assays. Key to the success of our DOTS approach was the integration of protein conformational sampling during hit identification stage and the synthetic feasibility ranking of the designed compounds throughout the optimization process. This approach can be broadly applied to other protein targets with known 3D structures to rapidly identify and optimize compounds as chemical probes and therapeutic candidates.

Controlled Selectivity through Reversible Inhibition of the Catalyst: Stereodivergent Semihydrogenation of Alkynes

Catalytic semihydrogenation of internal alkynes using H₂ is an attractive atom-economical route to various alkenes, and its stereocontrol has received widespread attention, both in homogeneous and heterogeneous catalyses. Herein, a novel strategy is introduced, whereby a poisoning catalytic thiol is employed as a reversible inhibitor of a ruthenium catalyst, resulting in a controllable H₂-based semihydrogenation of internal alkynes. Both (E)- and (Z)-alkenes were obtained efficiently and highly selectively, under very mild conditions, using a single homogeneous acridine-based ruthenium pincer catalyst. Mechanistic studies indicate that the (Z)-alkene is the reaction intermediate leading to the (E)-alkene and that the addition of a catalytic amount of bidentate thiol impedes the Z/E isomerization step by forming stable ruthenium thiol(ate) complexes, while still allowing the main hydrogenation reaction to proceed. Thus, the absence or presence of catalytic thiol controls the stereoselectivity of this alkyne semihydrogenation, affording either the (E)-isomer as the final product or halting the reaction at the (Z)-intermediate. The developed system, which is also applied to the controllable isomerization of a terminal alkene, demonstrates how metal catalysis with switchable selectivity can be achieved by reversible inhibition of the catalyst with a simple auxiliary additive.

ATRP of MIDA Boronate-Containing Monomers as a Tool for Synthesizing Linear Phenolic and Functionalized Polymers

Despite numerous novel polymeric materials that have been produced by incorporating boronic acid or ester groups into polymers, it remains a challenge to prepare well-defined boronate-containing polymers due to their inherent instability. Herein, we used N-methyliminodiacetic acid (MIDA) to stabilize the reactive organoboron structure. MIDA boronate-containing polymers were synthesized in a good control by initiators for continuous activator regeneration atom transfer radical polymerization (ICAR ATRP). Oxidation and Suzuki-Miyaura coupling were conducted to prepare linear phenol-containing polymers and aromatic functionalized polymers. Upon comparison of similar polymers prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization, of which the chain transfer agent (CTA) end groups cause multiple undesired side reactions, the halogen end groups of polymers prepared by ATRP are nontoxic to metal catalysts and stable during the postmodifications, thus providing a more facile tool for synthesizing various functionalized polymers with great potentials in advanced materials.

Mechanical switching of current-voltage characteristics in spiropyran single-molecule junctions

The electrical properties of a single-molecule junction of spiropyran are investigated through the break junction (BJ) method, and the current-voltage (I-V) characteristics are switched from rectified to symmetric through mechanical stimulus. This phenomenon indicates isomerization from spiropyran to merocyanine. In addition, an increase in the conductance associated with isomerization is observed.

2-Aminomethylene-5-sulfonylthiazole Inhibitors of Lysyl Oxidase (LOX) and LOXL2 Show Significant Efficacy in Delaying Tumor Growth

The lysyl oxidase (LOX) family of extracellular proteins plays a vital role in catalyzing the formation of cross-links in fibrillar elastin and collagens leading to extracellular matrix (ECM) stabilization. These enzymes have also been implicated in tumor progression and metastatic disease and have thus become an attractive therapeutic target for many types of invasive cancers. Following our recently published work on the discovery of aminomethylenethiophenes (AMTs) as potent, orally bioavailable LOX/LOXL2 inhibitors, we report herein the discovery of a series of dual LOX/LOXL2 inhibitors, as well as a subseries of LOXL2-selective inhibitors, bearing an aminomethylenethiazole (AMTz) scaffold. Incorporation of a thiazole core leads to improved potency toward LOXL2 inhibition via an irreversible binding mode of inhibition. SAR studies have enabled the discovery of a predictive 3DQSAR model. Lead AMTz inhibitors exhibit improved pharmacokinetic properties and excellent antitumor efficacy, with significantly reduced tumor growth in a spontaneous breast cancer genetically engineered mouse model.

Discovery and preclinical development of AR453588 as an anti-diabetic glucokinase activator

Glucose flux through glucokinase (GK) controls insulin release from the pancreas in response to high levels of glucose. Flux through GK is also responsible for reducing hepatic glucose output. Since many individuals with type 2 diabetes appear to have an inadequacy or defect in one or both of these processes, identifying compounds that can activate GK could provide a therapeutic benefit. Herein we report the further structure activity studies of a novel series of glucokinase activators (GKA). These studies led to the identification of pyridine 72 as a potent GKA that lowered post-prandial glucose in normal C57BL/6J mice, and after 14d dosing in ob/ob mice.

Synthesis of Air-stable, Odorless Thiophenol Surrogates via Ni-Catalyzed C-S Cross-Coupling

Thiophenols are versatile synthetic intermediates whose practical appeal is marred by their air sensitivity, toxicity and extreme malodor. Herein we report an efficient catalytic method for the preparation of S-aryl isothiouronium salts, and demonstrate that these air-stable, odorless solids serve as user-friendly sources of thiophenols in synthesis. Diverse isothiouronium salts featuring synthetically useful functionality are readily accessible by nickel-catalyzed C-S cross-coupling of (hetero)aryl iodides and thiourea. Convenient, chromatography-free isolation of these salts is achieved by precipitation, allowing the methodology to be applied directly to large scales. Thiophenols are liberated from the corresponding isothiouronium salts upon treatment with a weak base, enabling an in situ release/S-functionalization strategy that entirely negates the need to isolate, purify or manipulate these noxious reagents.

Ring-Closing Synthesis of Dibenzothiophene Sulfonium Salts and Their Use as Leaving Groups for Aromatic 18F-Fluorination

Herein, we report a novel intramolecular ring-closing reaction of biaryl thioethers that give access to highly functionalized dibenzothiophene sulfonium salts under mild conditions. The resulting precursors react regioselectively with [¹⁸F]fluoride to give [¹⁸F]fluoroarenes in predictable radiochemical yields. The strategy expands the available radiochemical space and provides superior labeling efficiency for clinically relevant PET tracers.

Reductively-labile sulfonate ester protecting groups that are rapidly cleaved by physiological glutathione

Sulfonates are frequently used to endow water solubility on hydrophobic molecules, but the repertoire of sulfonate protecting groups remains limited. Here we describe the first sulfonate esters that can be unmasked by the mild reducing conditions found in live mammalian cells. Self-immolative cleavage releases the sulfonate and the two-electron reduction product of a thioquinone methide.

Discotic liquid crystals of transition metal complexes, 53†: synthesis and mesomorphism of phthalocyanines substituted by m-alkoxyphenylthio groups

We have successfully synthesized a series of novel octakis([Formula: see text]-alkoxyphenylthio)phthalocyaninato copper(II) complexes, ([Formula: see text]-C[Formula: see text]OPhS)[Formula: see text]PcCu ([Formula: see text] = 2, 4, 6, 8, 10, 12, 14, 16: 1b~1i), by our developed method to reveal their mesomorphism. The phase transition behavior and mesophase structures have been established by using a polarizing optical microscope, a differential scanning calorimeter, and a temperature-dependent small angle X-ray diffractometer. Interestingly, the very short chain-substituted derivatives, ([Formula: see text]-C[Formula: see text]OPhS)[Formula: see text]PcCu (1a) and ([Formula: see text]-C[Formula: see text]OPhS)[Formula: see text]PCu (1b), show a hexagonal ordered columnar (Col[Formula: see text] mesophase, whereas each of the other longer-chain-substituted derivatives, ([Formula: see text]-C[Formula: see text]OPhS)[Formula: see text]PcCu ([Formula: see text] = 4~16: 1c~1i), shows only rectangular ordered columnar (Col[Formula: see text] mesophase(s). In contrast to the present longer-chain-substituted phenylthio derivatives, each of the previous longer-chain-substituted phenoxy derivatives, ([Formula: see text]-C[Formula: see text]OPhO)[Formula: see text]PcCu ([Formula: see text] = 10–20), shows a different columnar mesophase of Col[Formula: see text]. We discuss this difference of mesomorphism from the viewpoint of the different steric hindrance originated by the peripheral substituents, PhO and PhS groups. Moreover, we could estimate the optical band gaps of ([Formula: see text]-C[Formula: see text]OPhO)[Formula: see text]PcCu and ([Formula: see text]-C[Formula: see text]OPhS)[Formula: see text]PcCu (1f) from absorption edge of the Q-bands to be 1.79 eV and 1.70 eV, respectively. Therefore, the phenylthio-substituted derivative gave a narrower band gap byca. 0.1 eV in comparison with the phenoxy-substituted derivative.

Mild Ti-mediated transformation of t-butyl thio-ethers into thio-acetates

We report a straightforward method for the rapid conversion of thio-ethers to thio-acetates using TiCl4, in good to excellent yields. The reaction conditions tolerate a variety of functional groups, including halide, nitro, ether, thiophene and acetylene functionalities. A catalytic variant of this reaction is also described.

Tackling poison and leach: catalysis by dangling thiol-palladium functions within a porous metal-organic solid

Self-standing thiol (-SH) groups within a Zr(IV)-based metal-organic framework (MOF) anchor Pd(II) atoms for catalytic applications: the spatial constraint prevents the thiol groups from sealing off/poisoning the Pd(II) center, while the strong Pd-S bond precludes Pd leaching, enabling multiple cycles of heterogeneous catalysis to be executed.

A general approach to the synthesis of 5-S-functionalized pyrimidine nucleosides and their analogues

A palladium-catalyzed C–S coupling reaction has been used as a key step for the introduction of S-functionality at the C-5 position of the cytosine and uracil nucleosides and their analogues.

Discovery of (2S)-1-[4-(2-{6-amino-8-[(6-bromo-1,3-benzodioxol-5-yl)sulfanyl]-9H-purin-9-yl}ethyl)piperidin-1-yl]-2-hydroxypropan-1-one (MPC-3100), a purine-based Hsp90 inhibitor

Modulation of Hsp90 (heat shock protein 90) function has been recognized as an attractive approach for cancer treatment, since many cancer cells depend on Hsp90 to maintain cellular homeostasis. This has spurred the search for small-molecule Hsp90 inhibitors. Here we describe our lead optimization studies centered on the purine-based Hsp90 inhibitor 28a containing a piperidine moiety at the purine N9 position. In this study, key SAR was established for the piperidine N-substituent and for the congeners of the 1,3-benzodioxole at C8. These efforts led to the identification of orally bioavailable 28g that exhibits good in vitro profiles and a characteristic molecular biomarker signature of Hsp90 inhibition both in vitro and in vivo. Favorable pharmacokinetic properties along with significant antitumor effects in multiple human cancer xenograft models led to the selection of 28g (MPC-3100) as a clinical candidate.

A practical, one-pot synthesis of highly substituted thiophenes and benzo[b]thiophenes from bromoenynes and o-alkynylbromobenzenes

An efficient synthesis of thiophenes and benzo[b]thiophenes has been developed from easily available bromoenynes and o-alkynylbromobenzene derivatives. This novel one-pot procedure involves a Pd-catalyzed C-S bond formation using a hydrogen sulfide surrogate followed by a heterocyclization reaction. Moreover, in situ functionalization with selected electrophiles further expands the potential of this methodology to the preparation of the corresponding highly substituted sulfur heterocycles.

A new odorless procedure for the synthesis of 2'-deoxy-6-thioguanosine and its incorporation into oligodeoxynucleotides

6-S-[2-[(2-ethylhexyl)oxycarbonyl]ethyl)}-3',5'-O-bis(tert-butyldimethylsilyl)-2'-deoxy-6-thiogua nosine (2) was synthesized in high yield from the corresponding 6-O-mesitylenesulfonyl derivative by the reaction with 2-ethylhexyl 3-mercapto-propionate. The phosphoramidite precursor derived from 2 was successfully applied to an automated DNA synthesizer to produce 2'-deoxy-6-thioguanosine containing ODN. The results showed that 2-ethylhexyl 3-mercaptopropionate is useful as an odor less reagent and also as an S-protecting group of 2'-deoxy-6-thioguanosine.

A general and efficient approach to aryl thiols: CuI-catalyzed coupling of aryl iodides with sulfur and subsequent reduction

A CuI-catalyzed coupling reaction of aryl iodides and sulfur powder takes place in the presence of K(2)CO(3) at 90 degrees C. The coupling mixture is directly treated with NaBH(4) or triphenylphosphine to afford aryl thiols in good to excellent yields. A wide range of substituted aryl thiols that bear methoxy, hydroxyl, carboxylate, amido, keto, bromo, and fluoro groups can be assembled through this procedure.

Peptide/protein-polymer conjugates: synthetic strategies and design concepts

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.

General and practical synthesis of benzothiazoles

The carbon-sulfur bond formation of aryl bromides and triflates catalyzed by a new catalyst system, Pd2(dba)3/xantphos, has been demonstrated. Based on this finding, a novel and practical synthesis of benzothiazoles has been developed. This new methodology allows for the assembly of a wide range of benzothiazoles.