Search

We report the synthesis of α‐trifluoromethylacrylates from α‐trifluoroborylacrylates via a stereoretentive radical trifluoromethylation with inexpensive reagents NaSO2CF3 and TBHP at room temperature. Under these conditions, a wide substrate scope afforded the (E)‐diastereomer exclusively in moderate to good yield. The utility of the reaction products is demonstrated in the synthesis of phenyl‐4H‐pyran, a potent and selective class of IKCa channel blockers. [ABSTRACT FROM AUTHOR]

A method for the regioselective reduction of the terminal double bond of 1,1-disubstituted allenes has been developed. In the presence of a palladium catalyst, tetrahydroxydiboron and stoichiometric water, allene semireduction proceeds in high yield to afford Z -alkenes selectively. [ABSTRACT FROM AUTHOR]

Within these, Modes B A b and B C b , in which the boron atom acts as a Lewis acid, have been widely explored, [6] SP , sp [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] whereas reports on the phosphorus atom acting as a Lewis base (Mode B B b ) are scarce. [37] In Ph SB 2 sb PBpin, despite the presence of tricoordinate boron and phosphorus centers, there is negligible -dative interaction between the phosphorus lone pair and the p-orbital on the boron. Keywords: pinacol diphenylphosphinoboronate; boroles; borafluorenes; antiaromaticity; Lewis acid EN pinacol diphenylphosphinoboronate boroles borafluorenes antiaromaticity Lewis acid 2193 2196 4 10/31/23 20231127 NES 231127 Graph Phosphinoboranes [1][52][2] (R SB 2 sb P-BR SB 2 sb ) feature trivalent and tricoordinate P and B atoms linked covalently and are valence isoelectronic with aminoboranes (R SB 2 sb N-BR SB 2 sb ; Scheme 1a). Upon coordination, the P(1)-B(2) bonds of the Ph SB 2 sb PBpin elongate slightly [ B 1 b : 1.953(2) A , B 2 b : 1.9432(18) A , cf. free Ph SB 2 sb PBpin: 1.9274(14) A ]. [Extracted from the article]

A facile method for the preparation of β-boryl-α-silyl aryl acrylamides using phenyllithium, dimethylphenylsilylpinacolborane, and propargylamides is reported. A key feature of this transition metal-free reaction is the Brønsted base deprotonation of aryl secondary propargylamide to produce a Lewis base that activates the B−Si bond, which is followed by a sequential intramolecular α-silylation- trans-β-borylation. The reaction proceeds in complete regio- and stereoselectivity. A wide variety of N- and aryl-substituted propargylamides afford trans-1,2-vinylborasilanes in high yield. The vicinal borasilane products undergo a variety of subsequent chemoselective transformations. [ABSTRACT FROM AUTHOR]

Copper(II)-catalyzed silylation of substituted alkynylcarbonyl compounds was investigated. Through the activation of Me2PhSiBpin in water at room temperature and open atmosphere, vinylsilanes conjugated to carbonyl groups are synthesized in high yield. A surprising diastereodivergent access to olefin geometry was discovered using a silyl conjugate addition strategy: aldehydes and ketones were Z selective while esters and amides were exclusively transformed into the E products. [ABSTRACT FROM AUTHOR]

Copper(II)-catalyzed silylation of substituted alkynylcarbonyl compounds was investigated. Through the activation of Me2PhSiBpin in water at room temperature and open atmosphere, vinylsilanes conjugated to carbonyl groups are synthesized in high yield. A surprising diastereodivergent access to olefin geometry was discovered using a silyl conjugate addition strategy: aldehydes and ketones were Z selective while esters and amides were exclusively transformed into the E products. [ABSTRACT FROM AUTHOR]

Herpes simplex virus DNA polymerase is a heterodimer composed of UL30, a catalytic subunit, and UL42, a processivity subunit. Mutations that decrease DNA binding by UL42 decrease long chain DNA synthesis by the polymerase. The crystal structure of UL42 bound to the C terminus of UL30 revealed an extensive positively charged surface ("back face"). We tested two hypotheses, 1) the C terminus of UL30 affects DNA binding and 2) the positively charged back face mediates DNA binding. Addressing the first hypothesis, we found that the presence of a peptide corresponding to the UL30 C terminus did not result in altered binding of UL42 to DNA. Addressing the second hypothesis, previous work showed that substitution of four conserved arginine residues on the basic face with alanines resulted in decreased DNA affinity. We tested the affinities for DNA and the stimulation of long chain DNA synthesis of mutants in which the four conserved arginine residues were substituted individually or together with lysines and also a mutant in which a conserved glutamine residue was substituted with an arginine to increase positive charge on the back face. We also engineered cysteines onto this surface to permit disulfide cross-linking studies. Last, we assayed the effects of ionic strength on DNA binding by UL42 to estimate the number of ions released upon binding. Our results taken together strongly suggest that the basic back face of UL42 contacts DNA and that positive charge on this surface is important for this interaction. [ABSTRACT FROM AUTHOR]

DNA glycosylases must interrogate millions of base pairs of undamaged DNA in order to locate and then excise one damaged nucleobase. The nature of this search process remains poorly understood. Here we report the use of disulfide cross-linking (DXL) technology to obtain structures of a bacterial DNA glycosylase, MutM, interrogating undamaged DNA. These structures, solved to 2.0 angstrom resolution, reveal the nature of the search process: The protein inserts a probe residue into the helical stack and severely buckles the target base pair, which remains intrahelical. MutM therefore actively interrogates the intact DNA helix while searching for damage. [ABSTRACT FROM AUTHOR]

Using an N-oleoyl ethanolamide scaffold, a series of phosphate polar head group analogues of LPA comprised of various α-substituted phosphonates and thiophosphates was prepared. In a broken cell GTP[γ35S] binding assay, agonist activity was evaluated at the three LPA receptors of the endothelial differentiation gene (Edg) family. This study has resulted in the discovery of a nonhydrolyzable LPA1-selective agonist (11). Additionally, thiophosphate 19 bears an isosteric phosphate mimetic that confers agonism at the LPA1 receptor but not LPA2. [Copyright &y& Elsevier]

Trialkyl phosphines PMe3 and PEt3 catalyze the 1,2‐cis‐diboration of 1,3‐butadiynes to give 1,2‐diboryl enynes. The products were utilized to synthesize 1,1,2,4‐tetraaryl enynes using a Suzuki‐Miyaura protocol and can readily undergo proto‐deborylation. [ABSTRACT FROM AUTHOR]

We report an organocatalytic trans hydroboration of 3-substituted-propiolonitriles. In the presence of catalytic amounts of tributylphosphine and pinacolborane, regioselective hydroboration of the internal triple bond proceeded in a stereoselective fashion under mild conditions to afford the corresponding (E)-1,2-vinylcyanoborane derivatives. The mechanism is proposed to occur through a 1,2-phosphine addition instead of a canonical 1,4-conjugate addition pathway. [ABSTRACT FROM AUTHOR]

Semaglutide is an anti-diabetes and weight loss drug that decreases food intake, slows gastric emptying, and increases insulin secretion. Patients begin treatment with low-dose semaglutide and increase dosage over time as efficacy plateaus. With increasing dosage, there is also greater incidence of gastrointestinal side effects. One reason for the plateau in semaglutide efficacy despite continued low food intake is due to compensatory actions whereby the body becomes more metabolically efficient to defend against further weight loss. Mitochondrial uncoupler drugs decrease metabolic efficiency, therefore we sought to investigate the combination therapy of semaglutide with the mitochondrial uncoupler BAM15 in diet-induced obese mice. Mice were fed high-fat western diet (WD) and stratified into six treatment groups including WD control, BAM15, low-dose semaglutide without or with BAM15, and high-dose semaglutide without or with BAM15. Combining BAM15 with either semaglutide dose decreased body fat and liver triglycerides, which was not achieved by any monotherapy, while high-dose semaglutide with BAM15 had the greatest effect on glucose homeostasis. This study demonstrates a novel approach to improve weight loss without loss of lean mass and improve glucose control by simultaneously targeting energy intake and energy efficiency. Such a combination may decrease the need for semaglutide dose escalation and hence minimize potential gastrointestinal side effects. [ABSTRACT FROM AUTHOR]

A method has been developed for the facile Cu(II)-catalyzed protoboration of monosubstituted allenes in aqueous media under atmospheric conditions. The reaction occurs site selectively, favoring internal alkene protoboration to afford 1,1-disubstituted vinylboronic acid derivatives (up to 93 : 7) with modest to good yields. The method has been applied to a variety of phenylallene derivatives as well as alkylsubstituted allenes. [ABSTRACT FROM AUTHOR]

The diboration of substituted propargylic alcohols has been achieved using a bimetallic Pd/Cu catalyst system. The in situ formation of a pentrafluoroboronic acid intermediate sufficiently activates the C–O bond towards dual catalysis affording (Z)-allyl, vinyldiboronates stereoselectively. [ABSTRACT FROM AUTHOR]

Review: [70 refs. [ABSTRACT FROM AUTHOR]

An operationally simple and mild protocol is developed for the hydrosilylation of α,β-alkynyl carbonyl compounds. [ABSTRACT FROM AUTHOR]

We demonstrate the creation of anisotropic patchy silver nanospheroids (AgNSs) using linearly polarized UV light and a photo-uncaging o-nitrobenzyl-based ligand, which anchors to the AgNSs by two gold-sulfur bonds. Exposure to a 1 J/cm² dose of UV light induces a photo-uncaging reaction in the ligand that reveals a primary amine on the surface. By using linearly polarized UV light, we meter the exposure dose such that only the poles of the nanoparticle receive a full dose, limiting the photo-uncaging reaction primarily to the particle's plasmonic hot spots. We reveal this anisotropy by preferentially adhering negatively charged gold nanospheres (AuNSs) to the AgNSs' poles by using the electrostatic attraction between them and the positively charged primary amines generated by photo-uncaging. When the assembly is performed onto silver particles that are immobilized on a substrate, it results in nanoscale structures with a strong tendency to align with the polarization of the exposing light. This manifests in polarimetric spectroscopy as a linear dichroism aligned with the polarization direction. [ABSTRACT FROM AUTHOR]

The reaction is applied to a variety of α,β-unsaturated carbonyl compounds like esters, aldehydes or linear and cyclic ketones. [ABSTRACT FROM AUTHOR]

Human African trypanosomiasis (HAT) is a lethal, vector-borne disease caused by the parasite Trypanosoma brucei . Therapeutic strategies for this neglected tropical disease suffer from disadvantages such as toxicity, high cost, and emerging resistance. Therefore, new drugs with novel modes of action are needed. We screened cultured T. brucei against a focused kinase inhibitor library to identify promising bioactive compounds. Among the ten hits identified from the phenotypic screen, AZ960 emerged as the most promising compound with potent antiparasitic activity (IC 50 = 120 nM) and was shown to be a selective inhibitor of an essential gene product, T. brucei extracellular signal-regulated kinase 8 (TbERK8). We report that AZ960 has a K i of 1.25 μM for TbERK8 and demonstrate its utility in establishing TbERK8 as a potentially druggable target in T. brucei . [ABSTRACT FROM AUTHOR]

We report a tri-n-butyl phosphine catalyzed regio- and stereo-selective hydroboration of ynamides to yield (Z)-β-borylenamides in good yields. Surprisingly, a formal cis addition to the triple bond was observed as confirmed by NMR and X-ray crystallography. 31P NMR studies suggest that a zwitterionic vinylphosphonium intermediate is key in the mechanism. The resulting products were further transformed to β-CF3 enamides via stereoretentive trifluoromethylation. [ABSTRACT FROM AUTHOR]

We report a transition metal‐free, regio‐ and stereo‐selective, phosphine‐catalyzed method for the trans hydroboration of 1,3‐diynes with pinacolborane that affords (E)‐1‐boryl‐1,3‐enynes. The reaction proceeds with excellent selectivity for boron addition to the external carbon of the 1,3‐diyne framework as unambiguously established by NMR and X‐ray crystallographic studies. The reaction displays a broad substrate scope including unsymmetrical diynes to generate products in high yield (up to 95 %). Experimental and theoretical studies suggest that phosphine attack on the alkyne is a key process in the catalytic cycle. [ABSTRACT FROM AUTHOR]

Copper-catalyzed asymmetric conjugate additions are powerful reactions that allow the formation of single-enantiomer building blocks in a few steps. However, highly enantioselective conjugate addition to five-membered-ring substrates is more challenging and is often neglected. Here, we report catalytic asymmetric 1,4-addition of alkylzirconocenes, formed in situ from readily available alkenes, to cyclopent- 4-ene-1,3-dione monoacetals. Good to high enantioselectivities are observed and the procedure tolerates various functional groups. [ABSTRACT FROM AUTHOR]

Chikungunya virus (CHIKV) is a re-emerging arbovirus in the alphavirus genus. Upon infection, it can cause severe joint pain that can last years in some patients, significantly affecting their quality of life. Currently, there are no vaccines or anti-viral therapies available against CHIKV. Its spread to the Americas from the eastern continents has substantially increased the count of the infected by millions. Thus, there is an urgent need to identify therapeutic targets for CHIKV treatment. A potential point of intervention is the sphingosine-1-phosphate (S1P) pathway. Conversion of sphingosine to S1P is catalyzed by Sphingosine kinases (SKs), which we previously showed to be crucial pro-viral host factor during CHIKV infection. In this study, we screened inhibitors of SKs and identified a novel potent inhibitor of CHIKV infection—SLL3071511. We showed that the pre-treatment of cells with SLL3071511 in vitro effectively inhibited CHIKV infection with an EC50 value of 2.91 µM under both prophylactic and therapeutic modes, significantly decreasing the viral gene expression and release of viral particles. Our studies suggest that targeting SKs is a viable approach for controlling CHIKV replication. [ABSTRACT FROM AUTHOR]

We report a chemoselective, phosphine‐catalyzed semireduction of primary and secondary propiolamides. In the presence of stoichiometric pinacolborane and catalytic n‐tributylphosphine, a variety of propiolamides were successfully converted to the corresponding acrylamides in excellent yield with (E)‐stereoselectivity. The reaction condition is tolerant of various functional groups including alkene, alkyne, ketone, or ester. Deuterium labeling studies established that the hydride from activated pinacolborane is added to the α‐carbon and the proton on the amide nitrogen is abstracted by the ß‐carbon to furnish the (E)‐acrylamides. DFT calculations revealed a clear energetic driving force for the (E)‐ over the (Z)‐isomer. [ABSTRACT FROM AUTHOR]

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon–boron bond into a carbon–X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon–boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon–boron bonds. [ABSTRACT FROM AUTHOR]

Most cellular RNAs engage in intrastrand base-pairing that gives rise to complex three-dimensional folds. This self-pairing presents an impediment toward binding of the RNA by nucleic acid-based ligands. An important step in the discovery of RNAtargeting ligands is therefore to identify those regions in a folded RNA that are accessible toward the nucleic acid-based ligand. Because the folding of RNA targets can involve interactions between nonadjacent regions and employ both Watson-Crick and non-Watson-Crick base-pairing, screening of candidate binder ensembles is typically necessary. Microarray-based screening approaches have shown great promise in this regard and have suggested that achieving complete sequence coverage would be a valuable attribute of a next generation system. Here, we report a custom microarray displaying a library of RNA-interacting polynucleotides comprising all possible 2'-OMe RNA sequences from 4- to 8-nucleotides in length. We demonstrate the utility of this array in identifying RNA-interacting polynucleotides that bind tightly and specifically to the highly conserved, functionally essential template/pseudoknot domain of human telomerase RNA and that inhibit telomerase function in vitro. [ABSTRACT FROM AUTHOR]

Using bis(pinacolato)diboron, catalytic amounts of CuII, and various amine bases in water under atmospheric conditions at rt, acyclic and cyclic α,β-unsaturated ketones and esters are β-borylated in up to 98% yield. Mechanistic investigations using UV–vis spectroscopy, 11B NMR, and solvent kinetic isotope effect suggest that the role of the amine is not only to coordinate to CuIIbut also to activate a nucleophilic water molecule to form the reactive sp2–sp3diboron complex. [ABSTRACT FROM AUTHOR]

A two-step procedure for deprotection of alkylpinacolyl boronate esters via transesterification with diethanolamine followed by hydrolysis was successfully developed with the advantages of tolerance to various functional groups, short reaction time, and ease of product isolation. [ABSTRACT FROM AUTHOR]

Interest in peptides incorporating boronic acid moieties is increasing due to their potential as therapeutics; diagnostics for a variety of diseases such as cancer. The utility ot peptide boronic acids may be expanded with access to vast libraries that can be deconvoluted rapidly and economically. Unfortunately, current detection protocols using mass spec-trometry are laborious and confounded by boronic acid trimerizjtion, which requires time-consuming analysis of dehydration products. These issues are exacerbated when the peptide sequence is unknown, as with de novo sequencing, and especially when multiple boronic acid moieties are present. Thus, a rapid, reliable, and simple method tor peptide identification is of utmost importance. Herein, we report the identification and sequencing of linear and branched peptide boronic acids containing up to five boronic acid groups by matrix-assisted laser desorption/ionization mass spectrometry (MALDl-MS). Protocols for preparation of pinacol boronic esters were adapted for efficient MALDl analysis of peptides. Additionally, a novel peptide boronic add detection strategy was developed in which 2,5-dihydroxybenzoic acid (DHB) served as both matrix and derivatizing agent in a convenient, in situ, on-plate esterification. Finally, we demonstrate that DHH-modified peptide boronic acids from a single bead can be analyzed by MALDI-MSMS analysis, validating our approach for the identification and sequencing of branched peptide boronic acid libraries. [ABSTRACT FROM AUTHOR]

Summary: Processivity factors tether the catalytic subunits of DNA polymerases to DNA so that continuous synthesis of long DNA strands is possible. The human cytomegalovirus DNA polymerase subunit UL44 forms a C clamp-shaped dimer intermediate in structure between monomeric herpes simplex virus UL42, which binds DNA directly via a basic surface, and the trimeric sliding clamp PCNA, which encircles DNA. To investigate how UL44 interacts with DNA, calculations were performed in which a 12 bp DNA oligonucleotide was docked to UL44. The calculations suggested that UL44 encircles DNA, which interacts with basic residues both within the cavity of the C clamp and in flexible loops of UL44 that complete the “circle.” The results of mutational and crosslinking studies were consistent with this model. Thus, UL44 is a “hybrid” of UL42 and PCNA: its structure is intermediate between the two and its mode of interaction with DNA has elements of both. [Copyright &y& Elsevier]

Metabolic disorders such as type 2 diabetes, fatty liver disease, hyperlipidemia, and obesity commonly co-occur but clinical treatment options do not effectively target all disorders. Calorie restriction, semaglutide, rosiglitazone, and mitochondrial uncouplers have all demonstrated efficacy against one or more obesity-related metabolic disorders, but it currently remains unclear which therapeutic strategy best targets the combination of hyperglycaemia, liver fat, hypertriglyceridemia, and adiposity. Herein we performed a head-to-head comparison of 5 treatment interventions in the female db/db mouse model of severe metabolic disease. Treatments included ∼60 % calorie restriction (CR), semaglutide, rosiglitazone, BAM15, and niclosamide ethanolamine (NEN). Results showed that BAM15 and CR improved body weight and liver steatosis to levels superior to semaglutide, NEN, and rosiglitazone, while BAM15, semaglutide, and rosiglitazone improved glucose tolerance better than CR and NEN. BAM15, CR, semaglutide, and rosiglitazone all had efficacy against hypertriglyceridaemia. These data provide a comprehensive head-to-head comparison of several key treatment strategies for metabolic disease and highlight the efficacy of mitochondrial uncoupling to correct multiple facets of the metabolic disease milieu in female db/db mice. • Mitochondrial uncouplers such as BAM15 increase energy expenditure. • BAM15, 3 FDA-approved drugs and calorie restriction were tested in female db/db mice. • Glucose tolerance was completely restored by BAM15, semaglutide, and rosiglitazone. • Body weight and liver fat were most decreased by BAM15 and calorie restriction. • BAM15-treated mice had body composition with the greatest lean:fat mass ratio. [ABSTRACT FROM AUTHOR]

[Display omitted] Sphingosine-1-phosphate (S1P) is a chemotactic lipid that influences immune cell positioning. S1P concentration gradients are necessary for proper egress of lymphocytes from the thymus and secondary lymphoid tissues. This trafficking is interdicted by S1P receptor modulators, and it is expected that S1P transporter (Spns2) inhibitors, by reshaping S1P concentration gradients, will do the same. We previously reported SLF1081851 as a prototype Spns2 inhibitor, which provided a scaffold to investigate the importance of the oxadiazole core and the terminal amine. In this report, we disclose a structure–activity relationship study by incorporating imidazole as both a linker and surrogate for a positive charge in SLF1081851. In vitro inhibition of Spns2-dependent S1P transport in HeLa cells identified 7b as an inhibitor with an IC 50 of 1.4 ± 0.3 µM. The SAR studies reported herein indicate that imidazolium can be a substitute for the terminal amine in SLF1081851 and that Spns2 inhibition is highly dependent on the lipid alkyl tail length. [ABSTRACT FROM AUTHOR]

We report the first trans phosphinoboration of internal alkynes. With an organophosphine catalyst, alkynoate esters and the phosphinoboronate Ph2P‐Bpin are efficiently converted into the corresponding trans‐α‐phosphino‐β‐boryl acrylate products in moderate to good yield with high regio‐ and Z‐selectivity. This reaction operates under mild conditions and demonstrates good atom economy, requiring only a modest excess of the phosphinoboronate. X‐ray crystallography experiments allowed structural assignment of the unprecedented and densely functionalized (Z)‐α‐phosphino‐β‐boryl acrylate products. [ABSTRACT FROM AUTHOR]

We report the first trans phosphinoboration of internal alkynes. With an organophosphine catalyst, alkynoate esters and the phosphinoboronate Ph2P‐Bpin are efficiently converted into the corresponding trans‐α‐phosphino‐β‐boryl acrylate products in moderate to good yield with high regio‐ and Z‐selectivity. This reaction operates under mild conditions and demonstrates good atom economy, requiring only a modest excess of the phosphinoboronate. X‐ray crystallography experiments allowed structural assignment of the unprecedented and densely functionalized (Z)‐α‐phosphino‐β‐boryl acrylate products. [ABSTRACT FROM AUTHOR]

A mild and efficient copper-catalyzed borylation of electron deficient allenoates using an sp2–sp3mixed hybridized diboron regioselectively installs a boron moiety on the β-position with exclusive (Z)-double bond geometry. [ABSTRACT FROM AUTHOR]

The NaOtBu‐catalyzed mixed 1,1‐diboration of terminal alkynes using the unsymmetrical diboron reagent BpinBdan (pin = pinacolato; dan = 1,8‐diaminonaphthalene) proceeds in a regio‐ and stereoselective fashion affording moderate to high yields of 1,1‐diborylalkenes bearing orthogonal boron protecting groups. It is applicable to gram‐scale synthesis without loss of yield or selectivity. The mixed 1,1‐diborylalkene products can be utilized in Suzuki–Miyaura cross‐coupling reactions which take place selectivly at the C–B site. DFT calculations suggest the NaOtBu‐catalyzed mixed 1,1‐diboration of alkynes occurs through deprotonation of the terminal alkyne, stepwise addition of BpinBdan to the terminal carbon followed by protonation with tBuOH. Experimentally observed selective formation of (Z)‐diborylalkenes is supported by our theoretical studies. [ABSTRACT FROM AUTHOR]

The interplay of sphingosine 1-phosphate (S1P) synthetic and degradative enzymes as well as S1P exporters creates concentration gradients that are a fundamental to S1P biology. Extracellular S1P levels, such as in blood and lymph, are high relative to cellular S1P. The blood-tissue S1P gradient maintains endothelial integrity while local S1P gradients influence immune cell positioning. Indeed, the importance of S1P gradients was recognized initially when the mechanism of action of an S1P receptor agonist used as a medicine for multiple sclerosis was revealed to be inhibition of T-lymphocytes' recognition of the high S1P in efferent lymph. Furthermore, the increase in erythrocyte S1P in response to hypoxia influences oxygen delivery during high altitude acclimatization. However, understanding of how S1P gradients are maintained is incomplete. For example, S1P is synthesized but is only slowly metabolized by blood yet circulating S1P turns over quickly by an unknown mechanism. Prompted by the counterintuitive observation that blood S1P increases markedly in response to inhibition S1P synthesis (by sphingosine kinase 2 (SphK2)), we studied mice wherein several tissues were made deficient in either SphK2 or S1P degrading enzymes. Our data reveal a mechanism whereby S1P is de-phosphorylated at the hepatocyte surface and the resulting sphingosine is sequestered by SphK phosphorylation and in turn degraded by intracellular S1P lyase. Thus, we identify the liver as the primary site of blood S1P clearance and provide an explanation for the role of SphK2 in this process. Our discovery suggests a general mechanism whereby S1P gradients are shaped. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Interaction of HIV-1 rev response element (RRE) RNA with its cognate protein, Rev, is critical for HIV-1 replication. Understanding the mode of interaction between RRE RNA and ligands at the binding site can facilitate RNA molecular recognition as well as provide a strategy for developing anti-HIV therapeutics. Our approach utilizes branched peptides as a scaffold for multivalent binding to RRE IIB (high affinity rev binding site) with incorporation of unnatural amino acids to increase affinity via non-canonical interactions with the RNA. Previous high throughput screening of a 46,656-member library revealed several hits that bound RRE IIB RNA in the sub-micromolar range. In particular, the lead compound, 4B3, displayed a K d value of 410 nM and demonstrated selectivity towards RRE. A ribonuclease protection assay revealed that 4B3 binds to the stem-loop structure of RRE IIB RNA, which was confirmed by SHAPE analysis with 234 nt long NL4-3 RRE RNA. Our studies further indicated interaction of 4B3 with both primary and secondary Rev binding sites. [ABSTRACT FROM AUTHOR]

Abstract A method for the semi-reduction of alkynoic acids through an α-borylation and subsequent protodeborylation mechanism has been developed. The transition metal-free protocol is achieved through the activation of bis(pinacolato)diboron by an in situ generated carboxylate moiety yielding aryl acrylic acids. Our studies demonstrate an unprecedented dual role for the carboxylate anion that involves the activation of the diboron reagent and a directing effect in the α-borylation. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

We quantitatively investigate lithographic patterning of a thiol-anchored self-assembled monolayer (SAM) of photocleavable o-nitrobenzyl ligands on gold through a multi-photon absorption process at 1.7 eV (730 nm wavelength). The photocleaving rate increases faster than the square of the incident light intensity, indicating a process more complex than simple two-photon absorption. We tentatively ascribe this observation to two-photon absorption that triggers the formation of a long-lived intermediate aci-nitro species whose decomposition yield is partially determined either by absorption of additional photons or by a local temperature that is elevated by the incident light. At the highest light intensities, thermal processes compete with photoactivation and lead to damage of the SAM. The threshold is high enough that this destructive process can largely be avoided, even while power densities are kept sufficiently large that complete photoactivation takes place on time scales of tens of seconds to a few minutes. This means that this type of ligand can be activated at visible and near infrared wavelengths where plasmonic resonances can easily be engineered in metal nanostructures, even though their single-photon reactivity at these wavelengths is negligible. This will allow selective functionalization of plasmon hotspots, which in addition to high resolution lithographic applications would be of benefit to applications such as Surface Enhanced Raman Spectroscopy and plasmonic photocatalysis as well as directed bottom-up nanoassembly. [ABSTRACT FROM AUTHOR]

Organoboron compounds are valuable synthetic intermediates that find application in a diverse variety of processes including both C-X and C-C bond-forming transformations. This has been achieved by using a variety of boron derivatives. Of these, boronate esters are probably the most versatile and, reflecting this, methods for the generation of boronate esters are of considerable current interest. Given the mild reaction conditions, good functional group tolerance, and low cost of the metal catalyst, the use of copper-boryl reagents is particularly attractive. In this review, methodologies in copper-boryl chemistry are discussed and the many different transformations possible are surveyed. [ABSTRACT FROM AUTHOR]

Small molecule mitochondrial uncouplers transport protons from the mitochondrial inner membrane space into the mitochondrial matrix independent of ATP synthase, uncoupling nutrient metabolism from ATP generation. The therapeutic potential of mitochondrial uncouplers has been investigated for the treatment of metabolic diseases such as obesity and type 2 diabetes (T2D), ischemia-reperfusion injury, and neurodegenerative diseases. This communication will review the small molecule mitochondrial uncouplers reported to date and explore their potential as therapeutics. [ABSTRACT FROM AUTHOR]

Successful medicinal chemistry campaigns to discover and optimize sphingosine kinase inhibitors require a robust assay for screening chemical libraries and for determining rank order potencies. Existing assays for these enzymes are laborious, expensive and/or low throughput. The toxicity of excessive levels of phosphorylated sphingoid bases for the budding yeast, Saccharomyces cerevisiae, affords an assay wherein inhibitors added to the culture media rescue growth in a dose-dependent fashion. Herein, we describe our adaptation of a simple, inexpensive, and high throughput assay for assessing inhibitors of sphingosine kinase types 1 and 2 as well as ceramide kinase and for testing enzymatic activity of sphingosine kinase type 2 mutants. The assay was validated using recombinant enzymes and generally agrees with the rank order of potencies of existing inhibitors. [ABSTRACT FROM AUTHOR]

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with its five G-protein coupled receptors (S1P1-5) to regulate cell growth and survival and has been implicated in a variety of diseases including cancer and sickle cell disease. As the key mediators in the synthesis of S1P, sphingosine kinase (SphK) isoforms 1 and 2 have attracted attention as viable targets for pharmaceutical inhibition. In this article, we describe the design, synthesis, and biological evaluation of aminothiazole-based guanidine inhibitors of SphK. Surprisingly, combining features of reported SphK1 inhibitors generated SphK1/2 dual inhibitor 20l (SLC4011540) (hSphK1 K i = 120 nM, hSphK2 K i = 90 nM) and SphK2 inhibitor 20dd (SLC4101431) (K i = 90 nM, 100-fold SphK2 selectivity). These compounds effectively decrease S1P levels in vitro. In vivo administration of 20dd validated that inhibition of SphK2 increases blood S1P levels. [ABSTRACT FROM AUTHOR]

A substrate-assisted diboration of alkynamides using the unsymmetrical pinacolato-1,8-diaminonaphthalenato diboron (pinBBdan) is described. The transition-metal-free reaction proceeds in a regio- and stereoselective fashion to exclusively afford trans-vinyldiboronates in good to excellent yields. Notably, Bdan and Bpin are installed on the α- and β-carbon atoms, respectively. [ABSTRACT FROM AUTHOR]

A substrate-assisted diboration of alkynamides using the unsymmetrical pinacolato-1,8-diaminonaphthalenato diboron (pinBBdan) is described. The transition-metal-free reaction proceeds in a regio- and stereoselective fashion to exclusively afford trans-vinyldiboronates in good to excellent yields. Notably, Bdan and Bpin are installed on the α- and β-carbon atoms, respectively. [ABSTRACT FROM AUTHOR]

A branched peptide containing multiple boronic acids was found to bind RRE IIB selectively and inhibit HIV-1 p24 capsid production in a dose-dependent manner. Structure–activity relationship studies revealed that branching in the peptide is crucial for the low micromolar binding towards RRE IIB, and the peptide demonstrates selectivity towards RRE IIB in the presence of tRNA. Footprinting studies suggest a binding site on the upper stem and internal loop regions of the RNA, which induces enzymatic cleavage of the internal loops of RRE IIB upon binding. [ABSTRACT FROM AUTHOR]

[Display omitted] We report new mitochondrial uncouplers derived from the conversion of [1,2,5]oxadiazolo[3,4- b ]pyrazines to 1 H -imidazo[4,5- b ]pyrazines. The in situ Fe-mediated reduction of the oxadiazole fragment followed by cyclization gave access to imidazopyrazines in moderate to good yields. A selection of orthoesters also allowed functionalization on the 2-position of the imidazole ring. This method afforded a variety of imidazopyrazine derivatives with varying substitution on the 2, 5 and 6 positions. Our studies suggest that both a 2-trifluoromethyl group and N -methylation are crucial for mitochondrial uncoupling capacity. [ABSTRACT FROM AUTHOR]