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The eradication of bacteria embedded in biofilms is among the most challenging obstacles in the management of chronic wounds. These biofilms are found in most chronic wounds ; moreover, the biofilm-embedded bacteria are considerably less susceptible to conventional antimicrobial treatment than the planktonic bacteria. Antimicrobial peptides and their mimics are considered attractive candidates in the pursuit of novel therapeutic options for the treatment of chronic wounds and general bacterial eradication. However, some limitations linked to these membrane-active antimicrobials are making their clinical use challenging. Novel innovative delivery systems addressing these limitations represent a smart solution. We hypothesized that incorporation of a novel synthetic mimic of an antimicrobial peptide in liposomes could improve its anti-biofilm effect as well as the antiinflammatory activity. The small synthetic mimic of an antimicrobial peptide, 7e-SMAMP, was incorporated into liposomes (~280 nm) tailored for skin wounds and evaluated for its potential activity against both biofilm formation and eradication of pre-formed biofilms. The 7e-SMAMP-liposomes significantly lowered inflammatory response in murine macrophages (~30 % reduction) without affecting the viability of macrophages or keratinocytes. Importantly, the 7e-SMAMP-liposomes completely eradicated biofilms produced by Staphylococcus aureus and Escherichia coli above concentrations of 6.25 μg/mL, whereas in Pseudomonas aeruginosa the eradication reached 75 % at the same concentration. Incorporation of 7e-SMAMP in liposomes improved both the inhibition of biofilm formation as well as biofilm eradication in vitro, as compared to non- formulated antimicrobial, therefore confirming its potential as a novel therapeutic option for bacteria-infected chronic wounds.

The asymmetric Rh‐catalyzed hydrocarboxylation of α,β‐unsaturated carbonyl compounds was originally developed by Mikami and co‐workers but gives only moderate enantiomeric excesses. In order to understand the factors controlling the enantioselectivity and to propose novel ligands for this reaction, we have used computational and experimental methods to study the Rh‐catalyzed hydrocarboxylation with different bidentate ligands. The analysis of the C−CO2 bond formation transition states with DFT methods shows a preference for outer‐sphere CO2 insertion, where CO2 can undergo a backside or frontside reaction with the nucleophile. The two ligands that prefer a frontside reaction, StackPhos and tBu‐BOX, display an intriguing stacking interaction between CO2 and an N‐heterocyclic ring of the ligand (imidazole or oxazoline). Our experimental results support the computationally predicted low enantiomeric excesses and highlight the difficulty in developing a highly selective version of this reaction.

Carbapenem resistance caused by metallo-β-lactamases is a serious global challenge that, if not tackled efficiently, is expected to lead to millions of deaths in the coming decades. Verona-integron encoded metallo-β-lactamase 2 (VIM-2) is a bacterial enzyme that has been reported from multidrug-resistant nosocomial isolates of Pseudomonas aeruginosa and other Gram-negative pathogens. As it hydrolyzes most β-lactams efficiently, including carbapenems, it is a major threat to current antimicrobial chemotherapies. So far, there is no clinically applicable inhibitor for this enzyme. In this work, the backbone NMR resonance assignment of VIM-2 is disclosed, opening up NMR investigations of this clinically important enzyme and its potential inhibitors for solutions, enabling a rational improvement of inhibitor candidates. Making use of the assignment, we identified the active enantiomer of a VIM-2 inhibitor candidate as well as its possible binding site and Kd, utilizing NMR chemical shift titration experiments.

The development of green Buchwald–Hartwig aminations has long been considered challenging, due to the high sensitivity of the reaction to the environment. Here we show that food-grade and waste vegetable oils, triglycerides originating from animals, and natural waxes can serve as excellent green solvents for Buchwald–Hartwig amination. We further demonstrate that amphiphiles and trace ingredients present in triglycerides as additives have a decisive effect on the yields of Buchwald–Hartwig aminations.

An amphipathic barbiturate mimic of the marine eusynstyelamides is reported as a promising class of antimicrobial agents. We hereby report a detailed analysis of the structure-activity relationship for cationic amphipathic N,N′ -dialkylated-5,5-disubstituted barbiturates. The influence of various cationic groups, hydrocarbon linkers and lipophilic side chains on the compounds’ antimicrobial potency and haemolytic activity was studied. A comprehensive library of 58 compounds was prepared using a concise synthetic strategy. We found cationic amine and guanidyl groups to yield the highest broad-spectrum activity and cationic trimethylated quaternary amine groups to exert narrow-spectrum activity against Gram-positive bacteria. n-Propyl hydrocarbon linkers proved to be the best compromise between potency and haemolytic activity. The combination of two different lipophilic side chains allowed for further fine-tuning of the biological properties. Using these insights, we were able to prepare both, the potent narrow-spectrum barbiturate 8a and the broad-spectrum barbiturates 11lG, 13jA and 13jG, all having low or no haemolytic activity. The guanidine derivative 11lG demonstrated a strong membrane disrupting effect in luciferase-based assays. We believe that these results may be valuable in further development of antimicrobial lead structures.

Development of safe, renewable, cheap and versatile solvents is a longstanding challenge in chemistry. We show here that vegetable oils and related systems can become prominent solvents for organic synthesis. Suzuki–Miyaura, Hiyama, Stille, Sonogashira and Heck cross-couplings proceed with quantitative yields in a range of vegetable oils, fish oil, butter and waxes used as solvents. Appropriate methodologies for high-throughput screening and sustainable isolation techniques applicable for vegetable oils and related lipids are presented.

We report a series of synthetic cationic amphipathic barbiturates inspired by the pharmacophore model of small antimicrobial peptides (AMPs) and the marine antimicrobials eusynstyelamides. These N,N'-dialkylated-5,5-disubstituted barbiturates consist of an achiral barbiturate scaffold with two cationic groups and two lipophilic side chains. Minimum inhibitory concentrations of 2-8 μg/mL were achieved against 30 multi-resistant clinical isolates of Gram-positive and Gram-negative bacteria, including isolates with extended spectrum β-lactamase-carbapenemase production. The guanidine barbiturate 7e (3,5-di-Br) demonstrated promising in vivo antibiotic efficacy in mice infected with clinical isolates of Escherichia coli and Klebsiella pneumoniae using a neutropenic peritonitis model. Mode of action studies showed a strong membrane disrupting effect and was supported by nuclear magnetic resonance and molecular dynamics simulations. The results express how the pharmacophore model of small AMPs and the structure of the marine eusynstyelamides can be used to design highly potent lead peptidomimetics against multi-resistant bacteria.

As pioneered by Corey and Chaykovsky, sulfoxonium ylides have had widespread application in organic synthesis for more than a half century. In most of the reactions, sulfoxonium ylides were used to react with electrophiles. Under suitable reaction conditions these ylides can generate metal carbenoids and react with nucleophiles. By combining the typical reactivity of sulfoxonium ylides with transition-metal catalysis, a growing number of investigations have expanded their application in organic synthesis. This review provides an update on the preparation of sulfoxonium ylides and their applications in carbenoid transfer reactions.1 Introduction2 Preparation of Sulfoxonium Ylides3 Investigation for Carbenoid Formation from Sulfoxonium Ylide 4 X–H (X = N, O, S, C) Functionalization Reactions5 Polymerizaton of Carbenoids Generated from Sulfoxonium Ylides6 Conclusion and Perspective

Phorbazoles are polychlorinated heterocyclic secondary metabolites isolated from a marine sponge and several of these natural products have shown inhibitory activity against cancer cells. In this work, a synthesis of the trichlorinated phorbazole B using late stage electrophilic chlorination was developed. The synthesis relied on the use of an oxazole precursor, which was protected with an iodine in the reactive 4-position, followed by complete chlorination of all pyrrole positions. Attempts to prepare phorbazole A and C, which contain a 3,4-dichlorinated pyrrole, were unsuccessful as the desired chlorination pattern on the pyrrole could not be obtained. The identities of the dichlorinated intermediates and products were determined using NMR techniques including NOESY/ROESY, 1,1-ADEQUATE and high-resolution CLIP-HSQMBC.

Solvents constitute the largest component for many chemical processes and substitution of nonrenewable solvents is a longstanding goal for green chemistry. Here, we show that Pd-catalyzed carbonylative couplings, such as carbonylative crosscouplings, aminocarbonylations, and alkoxycarbonylations, can be successfully realized using renewable solvents. The present research covers not only well-established renewable solvents, such as 2-methyltetrahydrofuran (2MeTHF), limonene, and dimethyl carbonate, but also recently introduced biomass-derived 1,1-diethoxyethane, isosorbide dimethyl ether, eucalyptol, rose oxide, γ-terpinene, and α-pinene. The carbonylative coupling of boronic acids and aryl bromides works well in limonene. Aminocarbonylation gave excellent results in dimethyl carbonate, α-pinene, and limonene, while alkoxycarbonylation was successful in 2MeTHF, α-pinene, γ-terpinene, and dimethyl carbonate. The developed methods based on renewable solvents can be used for the synthesis of commercial drug Trimetozine and an analogue of Itopride.

Carbapenem-resistant Gram-negative pathogens are a critical public health threat and there is an urgent need for new treatments. Carbapenemases (β-lactamases able to inactivate carbapenems) have been identified in both serine β-lactamase (SBL) and metallo-β-lactamase (MBL) families. The recent introduction of SBL carbapenemase inhibitors has provided alternative therapeutic options. Unfortunately, there are no approved inhibitors of MBL-mediated carbapenem-resistance and treatment options for infections caused by MBL-producing Gram-negatives are limited., Carbapenem-resistant Gram-negative pathogens are a critical public health threat and there is an urgent need for new treatments. Carbapenemases (β-lactamases able to inactivate carbapenems) have been identified in both serine β-lactamase (SBL) and metallo-β-lactamase (MBL) families. The recent introduction of SBL carbapenemase inhibitors has provided alternative therapeutic options. Unfortunately, there are no approved inhibitors of MBL-mediated carbapenem-resistance and treatment options for infections caused by MBL-producing Gram-negatives are limited. Here, we present ZN148, a zinc-chelating MBL-inhibitor capable of restoring the bactericidal effect of meropenem and in vitro clinical susceptibility to carbapenems in >98% of a large international collection of MBL-producing clinical Enterobacterales strains (n = 234). Moreover, ZN148 was able to potentiate the effect of meropenem against NDM-1-producing Klebsiella pneumoniae in a murine neutropenic peritonitis model. ZN148 showed no inhibition of the human zinc-containing enzyme glyoxylase II at 500 μM, and no acute toxicity was observed in an in vivo mouse model with cumulative dosages up to 128 mg/kg. Biochemical analysis showed a time-dependent inhibition of MBLs by ZN148 and removal of zinc ions from the active site. Addition of exogenous zinc after ZN148 exposure only restored MBL activity by ∼30%, suggesting an irreversible mechanism of inhibition. Mass-spectrometry and molecular modeling indicated potential oxidation of the active site Cys221 residue. Overall, these results demonstrate the therapeutic potential of a ZN148-carbapenem combination against MBL-producing Gram-negative pathogens and that ZN148 is a highly promising MBL inhibitor that is capable of operating in a functional space not presently filled by any clinically approved compound.

The copper-NHC-catalyzed carboxylation of organoboranes with CO2 was investigated using computational and experimental methods. The DFT and DLPNO-CCSD(T) results indicate that nonbenzylic substrates are converted via an inner-sphere carboxylation of an organocopper intermediate, whereas benzylic substrates may simultaneously proceed along both inner- and outer-sphere CO2 insertion pathways. Interestingly, the computations predict that two conceptually different carboxylation mechanisms are possible for benzylic organoboranes, one being copper-catalyzed and one being mediated by the reaction additive CsF. Our experimental evaluation of the computed reactions confirms that carboxylation of nonbenzylic substrates requires copper catalysis, whereas benzylic substrates can be carboxylated with and without copper.

Metallo-β-lactamases (MBLs) are an emerging cause of bacterial antibiotic resistance by hydrolysing all classes of β-lactams except monobactams, and the MBLs are not inhibited by clinically available serine-β-lactamase inhibitors. Two of the most commonly encountered MBLs in clinical isolates worldwide – the New Delhi metallo-β-lactamase (NDM-1) and the Verona integron-encoded metallo-β-lactamase (VIM-2) – are included in this study. A series of several NH-1,2,3-triazoles was prepared by a three-step protocol utilizing Banert cascade reaction as the key step. The inhibitor properties were evaluated in biochemical assays against the MBLs VIM-2, NDM-1 and GIM-1, and VIM-2 showed IC50 values down to nanomolar range. High-resolution crystal structures of four inhibitors in complex with VIM-2 revealed hydrogen bonds from the triazole inhibitors to Arg228 and to the backbone of Ala231 or Asn233, along with hydrophobic interactions to Trp87, Phe61 and Tyr67. The inhibitors show reduced MIC in synergy assays with Pseudomonas aeruginosa and Escherichia coli strains harbouring VIM enzymes. The obtained results will be useful for further structural guided design of MBL inhibitors.

Structural features of proton-deficient heteroaromatic natural products, such as the breitfussins, can severely complicate their characterization by NMR spectroscopy. For the breitfussins in particular, the constitution of the five-membered oxazole central ring cannot be unequivocally established via conventional NMR methods when the 4′-position is halogenated. The level of difficulty is exacerbated by 4′-iodination, as the accuracy with which theoretical NMR parameters are determined relies extensively on computational treatment of the relativistic effects of the iodine atom. It is demonstrated in the present study, that the structure of a 4′-iodo breitfussin analog can be unequivocally established by anisotropic NMR methods, by adopting a reduced singular value decomposition (SVD) protocol that leverages the planar structures exhibited by its conformers., Structural features of proton-deficient heteroaromatic natural products, such as the breitfussins, can severely complicate their characterization by NMR spectroscopy.

Accepted manuscript version. Published version available at https://doi.org/10.1055/s-0036-1591755. The synthesis of two marine natural products containing a 3-alkylidene-6-arylidene-2,5-diketopiperazine scaffold by employing two consecutive aldol condensations starting with 1,4-diacetyl-2,5-diketopiperazine is reported. The target compounds contain a phenol or an imidazole group as aryl substituents, respectively, and suitable conditions for the aldol condensation of 1-acyl-3-alkylidene-2,5-diketopiperazine with the required functionalised aromatic aldehydes were developed. Provided the optimal base was used, introduction of the phenol group did not require use of a protecting group. Boc-protection was beneficial for introduction of the imidazole group, and conditions for carrying out the aldol condensation and Boc-deprotection in one step were identified. The stereochemistry of the target compounds was confirmed by NMR analysis.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Catalysis, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acscatal.7b02306. CO2 is a promising and sustainable carbon feedstock for organic synthesis. New catalytic protocols for efficient incorporation of CO2into organic molecules are continuously being reported. However, little progress has been made in the enantioselective conversion of CO2to form enantioenriched molecules. In order to allow CO2to become a versatile carbon source in academia and in the fine chemical and pharmaceutical industries, the development of enantioselective approaches is essential. Here we discuss general strategies for CO2activation and for generation of enantioenriched molecules, alongside selected examples of reactions involving asymmetric incorporation of CO2. The main product classes considered are carboxylic acids and derivatives (C–CO2bonds) and carbonates, carbamates, and polycarbonates (C–OCO bonds). Similarities to asymmetric hydrogenation are discussed, and some strategies for developing novel enantioselective CO2reactions are outlined.

Source at https://doi.org/10.1016/j.ejmech.2019.111671. The rapid emergence and spread of multi-resistant bacteria have created an urgent need for new antimicrobial agents. We report here a series of amphipathic α,α-disubstituted β-amino amide derivatives with activity against 30 multi-resistant clinical isolates of Gram-positive and Gram-negative bacteria, including isolates with extended spectrum β-lactamase – carbapenemase (ESBL-CARBA) production. A variety of halogenated aromatic side-chains were investigated to improve antimicrobial potency and minimize formation of Phase I metabolites. Net positive charge and cationic character of the derivatives had an important effect on toxicity against human cell lines. The most potent and selective derivative was the diguanidine derivative 4e with 3,5-di-brominated benzylic side-chains. Derivative 4e displayed minimum inhibitory concentrations (MIC) of 0.25–8 μg/mL against Gram-positive and Gram-negative reference strains, and 2–32 μg/mL against multi-resistant clinical isolates. Derivative 4e showed also low toxicity against human red blood cells (EC50 > 200 μg/mL), human hepatocyte carcinoma cells (HepG2: EC50 > 64 μg/mL), and human lung fibroblast cells (MRC-5: EC50 > 64 μg/mL). The broad-spectrum antimicrobial activity and low toxicity of diguanylated derivatives such as 4e make them attractive as lead compounds for development of novel antimicrobial drugs.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Medicinal Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see [insert ACS Articles on Request author-directed link to Published Work, see https://doi.org/10.1021/acs.jmedchem.9b01006. In this work, we demonstrate that the indole-oxazole-pyrrole framework of the breitfussin family of natural products is a promising scaffold for kinase inhibition. Six new halogenated natural products, breitfussin C–H (3 – 8) were isolated and characterized from the Arctic, marine hydrozoan Thuiaria breitfussi. The structures of two of the new natural products were also confirmed by total synthesis. Two of the breitfussins (3 and 4) were found to selectively inhibit the survival of several cancer cell lines, with the lowest IC50 value of 340 nM measured against the drug-resistant triple negative breast cancer cell line MDA-MB-468, while leaving the majority of the tested cell lines not or significantly less affected. When tested against panels of protein kinases, 3 gave IC50 and Kd values as low as 200 and 390 nM against the PIM1 and DRAK1 kinases, respectively. The activity was confirmed to be mediated through ATP competitive binding in the ATP binding pocket of the kinases. Furthermore, evaluation of potential off-target and toxicological effects, as well as relevant in vitro ADME parameters for 3 revealed that the breitfussin scaffold holds promise for the development of selective kinase inhibitors.

Sulfoxonium ylides have recently gained prominence as safe carbenoid precursors in metal-catalyzed reactions. The stability and reactivity of sulfoxonium ylides depend on the substitution of the ylide carbon. The reactivity of vinyl-substituted sulfoxonium ylides is different and offers several advantages over known stabilized sulfoxonium ylides in the case of carbenoid transfer reactions. Herein, we provide an overview of early efforts in this area, with particular emphasis on our own recent development of sulfoxonium ylide-derived vinyl carbenoid transformations for N-Heterocycles.1 Introduction2 Classification of Sulfoxonium Ylides3 Synthesis of Vinyl Sulfoxonium Ylides4 [3+2] Annulation of Vinyl Sulfoxonium Ylides5 [4+1] Annulation of Vinyl Sulfoxonium Ylides6 Conclusion

This is the peer reviewed version of the following article: Vaitla, J., Bayer, A. & Hopmann, K.H. (2018). Iron‐Catalyzed Carbenoid Transfer Reactions of Vinyl Sulfoxonium Ylides: An Experimental and Computational Study. Angewandte Chemie International Edition, 57(49), 16180-16184, which has been published in final form at https://doi.org/10.1002/anie.201810451. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. A method for the generation of unprecedented vinyl carbenoids from sulfoxonium ylides has been developed and applied in the synthesis of a diverse array of heterocycles such as indolizines, pyrroles, 3‐pyrrolin‐2‐ones, and furans. The reactions proceed by FeBr2 catalysis under mild reaction conditions with a broad substrate scope. A reaction pathway involving iron carbenoids is proposed based on a series of control experiments and DFT calculations.

Accepted manuscript version. Publisher's version available at http://doi.org/10.1039/c6ob01219a. A practical and efficient methodology for the preparation of 2-aminoethyl α,α-disubstituted β-amino amides in three steps from methyl cyanoacetate has been developed. The key step in the synthesis was the chemoselective reduction of the nitrile group in presence of an amide and aryl halide functionalities. Reduction with RANEY® Nickel catalyst, either with molecular hydrogen (8–10 bar) or under transfer hydrogenation conditions, necessitated in situ protection of the resulting amines with Boc2O, whereas aryl bromide containing nitriles could be chemoselectively reduced with ZnCl2/NaBH4 without debromination. The developed protocol involved only one chromatographic purification step and can be performed at gram scale.

The present study describes the synthesis and biological studies of a small series of head-to-tail cyclic tetrapeptides of the general structure c(Lys-β

Accepted manuscript version of the following article: Pavlovic, L., Vaitla, J., Bayer, A. & Hopmann, K.H. (2018). Rhodium-Catalyzed Hydrocarboxylation: Mechanistic Analysis Reveals Unusual Transition State for Carbon–Carbon Bond Formation. Organometallics, 37(6), 941-948. Published version available at https://doi.org/10.1021/acs.organomet.7b00899. The mechanism of rhodium-COD-catalyzed hydrocarboxylation of styrene derivatives and α,β-unsaturated carbonyl compounds with CO2 has been investigated using density functional theory (PBE-D2/IEFPCM). The calculations support a catalytic cycle as originally proposed by Mikami and co-workers including β-hydride elimination, insertion of the unsaturated substrate into a rhodium–hydride bond, and subsequent carboxylation with CO2. The CO2 insertion step is found to be rate limiting. The calculations reveal two interesting aspects. First, during C–CO2 bond formation, the CO2 molecule interacts with neither the rhodium complex nor the organozinc additive. This appears to be in contrast to other CO2 insertion reactions, where CO2–metal interactions have been predicted. Second, the substrates show an unusual coordination mode during CO2 insertion, with the nucleophilic carbon positioned up to 3.6 Å away from rhodium. In order to understand the experimentally observed substrate preferences, we have analyzed a set of five alkenes: an α,β-unsaturated ester, an α,β-unsaturated amide, styrene, and two styrene derivatives. The computational results and additional experiments reported here indicate that the lack of activity with amides is caused by an overly high barrier for CO2 insertion and is not due to catalyst inactivation. Our experimental studies also reveal two putative side reactions, involving oxidative cleavage or dimerization of the alkene substrate. In the presence of CO2, these alternative reaction pathways are suppressed. The overall insights may be relevant for the design of future hydrocarboxylation catalysts.

Accepted manuscript version. Published version available at https://doi.org/10.1021/acs.orglett.7b03413. A convenient strategy for the synthesis of sulfur ylides via rhodium-catalyzed coupling of in situ generated iodonium ylides with sulfides or sulfoxides has been developed. A wide range of sulfur ylides were obtained in moderate to good yields from inexpensive sulfur compounds and active methylene compounds with a short reaction time (MW, 5–10 min) or 12–16 h at rt. Furthermore, these sulfoxonium ylides were used as novel acceptor/acceptor carbenes for N–H insertion reactions.

This work has received support from the Research Council of Norway through a Centre of Excellence Grant (Grant No. 179568/V30) and project grants (Grant No. 214095, 177558) and the European Research Council starting grant (Grant No. 279619). The work has also received support from the Norwegian Supercomputing program NOTUR (Grant No. NN4654K).

The first total synthesis of breitfussin A and B is described. The approach features two palladium-catalyzed cross-couplings installing the indole and pyrrole onto the oxazole core and selective lithiation/iodination of a common indole-oxazole fragment providing 2,4-diiodinated or 2-iodinated oxazoles as potential precursors for breitfussin A and B, respectively. An unexpected acid promoted deiodination was utilized in the synthesis of breitfussin B. Comparison of the synthetic material with previously reported spectral data of isolated breitfussin A and B verified the structure of the breitfussin framework.

Metallo-β-lactamases (MBLs) threaten the effectiveness of β-lactam antibiotics, including carbapenems, and are a concern for global public health. β-Lactam/β-lactamase inhibitor combinations active against class A and class D carbapenemases are used, but no clinically useful MBL inhibitor is currently available. Tripoli metallo-β-lactamase-1 (TMB-1) and TMB-2 are members of MBL subclass B1a, where TMB-2 is an S228P variant of TMB-1. The role of S228P was studied by comparisons of TMB-1 and TMB-2, and E119 was investigated through the construction of site-directed mutants of TMB-1, E119Q, E119S, and E119A (E119Q/S/A). All TMB variants were characterized through enzyme kinetic studies. Thermostability and crystallization analyses of TMB-1 were performed. Thiol-based inhibitors were investigated by determining the 50% inhibitory concentrations (IC 50 ) and binding using surface plasmon resonance (SPR) for analysis of TMB-1. Thermostability measurements found TMB-1 to be stabilized by high NaCl concentrations. Steady-state enzyme kinetics analyses found substitutions of E119, in particular, substitutions associated with the penicillins, to affect hydrolysis to some extent. TMB-2 with S228P showed slightly reduced catalytic efficiency compared to TMB-1. The IC 50 levels of the new thiol-based inhibitors were 0.66 μM (inhibitor 2a) and 0.62 μM (inhibitor 2b), and the equilibrium dissociation constant ( K D ) of inhibitor 2a was 1.6 μM; thus, both were more potent inhibitors than l -captopril (IC 50 = 47 μM; K D = 25 μM). The crystal structure of TMB-1 was resolved to 1.75 Å. Modeling of inhibitor 2b in the TMB-1 active site suggested that the presence of the W64 residue results in T-shaped π-π stacking and R224 cation-π interactions with the phenyl ring of the inhibitor. In sum, the results suggest that residues 119 and 228 affect the catalytic efficiency of TMB-1 and that inhibitors 2a and 2b are more potent inhibitors for TMB-1 than l -captopril.

β-Lactam antibiotics are of utmost importance when treating bacterial infections in the medical community. However, currently their utility is threatened by the emergence and spread of β-lactam resistance. The most prevalent resistance mechanism to β-lactam antibiotics is expression of β-lactamase enzymes. One way to overcome resistance caused by β-lactamases, is the development of β-lactamase inhibitors and today several β-lactamase inhibitors e.g. avibactam are approved in the clinic. Our focus is the oxacillinase-48 (OXA-48), an enzyme reported to spread rapidly across the world and commonly identified in Escherichia coli and Klebsiella pneumoniae. To guide inhibitor design, we used diversely substituted 3-aryl and 3-heteroaryl benzoic acids to probe the active site of OXA-48 for useful enzyme-inhibitor interactions. In the presented study, a focused fragment library containing 3-substituted benzoic acid derivatives were synthesised and biochemically characterized. Based on crystallographic data from fragment-enzyme complexes, the fragments could be classified into R1 or R2 44 binders by their overall binding conformation in relation to the binding of the R1 and R2 45 side groups of imipenem. Moreover, binding interactions attractive for future inhibitor design were found and their usefulness explored by the rational design and evaluation of merged inhibitors from orthogonally binding fragments. The best inhibitors among the resulting 3,5-disubstituted benzoic acids showed inhibitory potential in the low micromolar range (IC50 = 2.9 µM). For these inhibitors, the complex X-ray structures revealed non-covalent binding to Arg250, Arg214 and Tyr211 in the active site and the interactions observed with the mono-substituted fragments were also identified in the merged structures.

Accepted manuscript version, licensed CC BY-NC-ND 4.0. " . Published version available in European Journal of Medicinal Chemistry. 135:159-173. Bacterial resistance is compromising the use of β-lactam antibiotics including carbapenems. The main resistance mechanism against β-lactams is hydrolysis of the β-lactam ring mediated by serine- or metallo-β-lactamases (MBLs). Although several inhibitors of MBLs have been reported, none has been developed into a clinically useful inhibitor. Mercaptocarboxylic acids are among the most prominent scaffolds reported as MBL inhibitors. In this study, the carboxylate group of mercaptocarboxylic acids was replaced with bioisosteric groups like phosphonate esters, phosphonic acids and NH-tetrazoles. The influence of the replacement on the bioactivity and inhibitor binding was evaluated. A series of bioisosteres of previously reported inhibitors was synthesized and evaluated against the MBLs VIM-2, NDM-1 and GIM- 1. The most active inhibitors combined a mercapto group and a phosphonate ester or acid, with two/three carbon chains connecting a phenyl group. Surprisingly, also compounds containing thioacetate groups instead of thiols showed low IC50 values. High-resolution crystal structures of three inhibitors in complex with VIM-2 revealed hydrophobic interactions for the diethyl groups in the phosphonate ester (inhibitor 2b), the mercapto bridging the two active site zinc ions, and tight stacking of the benzene ring to the inhibitor between Phe62, Tyr67, Arg228 and His263. The inhibitors show reduced enzyme activity in Escherichia coli cells harboring MBL. The obtained results will be useful for further structural guided design of MBL inhibitors.

This review summarizes the current status of knowledge on asymmetric iridium-catalyzed direct hydrogenations of acyclic and cyclic imines. An overview of the most interesting catalysts with respect to selectivity, activity and substrate scope is given, including a discussion of the effects of different reaction conditions on the enantioselectivity of imine reduction. A detailed analysis of proposed imine hydrogenation mechanisms is presented, revealing that a significant number of recent proposals suggest outer sphere mechanisms, implying that the substrate does not bind to the metal centre during the hydrogenation reaction. An intriguing question is how a high enantioselectivity can be achieved in such systems. Generally, the factors governing the stereocontrol of iridium-catalyzed direct imine hydrogenation are little studied. The mechanistic proposals that have been put forward to explain the enantiodiscrimination of selected complexes are reviewed here, showing that the stereocontrol appears to be governed by weak non-bonding interactions between the substrate and the chiral catalyst complex. These selectivity-determining interactions might be modified through coordination of solvent, additive, or product molecules to the iridium complex, providing a rationale for the effect of solvent or additives on the enantioselectivity.

Recent experimental studies of iridium-phosphinooxazoline-mediated alkene hydrogenation indicated two dihydride species as resting states, with the minor isomer assumed to give rise to the major pr...

Accepted manuscript version. Published version available at https://doi.org/10.1002/anie.201610520. Metal carbenes can undergo a myriad of synthetic transformations. Sulfur ylides are potential safe precursors of metal carbenes. Herein, we report cascade reactions that involve carbenoids derived from sulfoxonium ylides for the efficient and regioselective synthesis of indoles and pyrroles. The tandem action of iridium and Brønsted acid catalysts enables rapid assembly of the heterocycles from unmodified anilines or readily accessible enamines under microwave irradiation. The key mechanistic steps are the catalytic transformation of the sulfoxonium ylide into an iridium–carbene complex, followed by N−H or C−H functionalization of an aniline or enamine, respectively, and a final acid‐catalyzed cyclization. The present method was successfully applied to the synthesis of the densely functionalized pyrrole subunit of atorvastatin.

Cyclotrimerizations of ethynyl N-methyliminodiacetic acid (MIDA) boronate (1) with 1,6-diynes 2 have been studied, using three different catalysts (based on ruthenium, rhodium, and iridium) and variable reaction conditions. Successful cyclotrimerization reactions were obtained with both Cp*RuCl(cod) and Rh(cod)2BF4/BINAP as pre-catalysts in THF or acetone. Ruthenium-catalyzed cyclotrimerization of an unsymmetrically bromo-substituted diyne (2f) with 1 was successfully scaled up (2 g) and included in a total synthesis strategy toward potential selective inhibitors of tyrosine kinase 2.

The authors gratefully acknowledge the financial support from the Research Council of Norway (grant number 165850/V30) and the University of Tromso for a scholarship to N. K.

A study on transition metal catalyzed alkyne cyclotrimerization of unsymmetrically bromo-substituted diynes with ethynyltrimethylsilane was carried out to prepare bicyclic bromobenzene key intermediates for the total synthesis of five potential tyrosine kinase 2 inhibitors. Two different pre-catalysts (Cp*RuCl(cod) and [Rh(cod)2]BF4/BINAP) and different reaction conditions have been examined.

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal of Medicinal Chemistry, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.jmedchem.6b00660. The spread of antibiotic resistant bacteria is a global threat that shakes the foundations of modern healthcare. β-Lactamases are enzymes that confer resistance to β-lactam antibiotics in bacteria, and there is a critical need for new inhibitors of these enzymes for combination therapy together with an antibiotic. With this in mind, we have screened a library of 490 fragments to identify starting points for the development of new inhibitors of the class D β-lactamase oxacillinase-48 (OXA-48) through surface plasmon resonance (SPR), dose-rate inhibition assays, and X-ray crystallography. Furthermore, we have uncovered structure–activity relationships and used alternate conformations from a crystallographic structure to grow a fragment into a more potent compound with a KD of 50 μM and an IC50 of 18 μM.

Phosphine-oxazoline (PHOX)-based iridium complexes have emerged as useful tools for enantioselective hydrogenation of unfunctionalized alkenes and imines. The mechanistic details of the asymmetric hydrogenation process, however, are poorly understood. Several different mechanisms have been put forward for hydrogenation of unfunctionalized alkenes, but it remains unclear which of these provide an accurate description of the hydrogenation reaction. The mechanistic aspects of Ir-(PHOX)-mediated hydrogenation of imines are little explored, and no detailed mechanism has been formulated to date. Here we provide a comprehensive quantum mechanical study of Ir-(PHOX)-mediated hydrogenation of both alkene and imine substrates. Our results support previous findings by Brandt et al., clearly favoring an Ir(III)/Ir(V) reaction cycle for Ir-(PHOX)-mediated hydrogenation of unfunctionalized alkenes. An important aspect of this reaction mechanism is the orientation of the metal-coordinated alkene substrate, which determi...

The present study describes the synthesis and biological studies of a small series of head-to-tail cyclic tetrapeptides of the general structure c(Lys‐β2,2‐Xaa‐Lys) containing one lipophilic β2,2-a ...

Accepted manuscript version. Publisher's version available at http://dx.doi.org//10.1016/j.tet.2015.09.003. The first syntheses of tubastrine and 3-dehydroxy tubastrine are described. The target compounds were prepared in four consecutive steps from commercially available starting materials. The central scaffold was formed by a microwave-assisted C–N cross-coupling reaction between 1,3-bis(tert-butoxycarbonyl)-guanidine and (E)-((4-(2-iodovinyl)-1,2-phenylene)bis(oxy))bis(tert-butyldimethylsilane) and (E)-tert-butyl(4-(2-iodovinyl)phenoxy)–dimethylsilane, respectively. The aryl vinyl iodides were obtained by a Hunsdiecker–Borodin-type reaction of aryl acrylic acids, which were easily available from trans-caffeic acid or trans-p-coumaric acid.

This review summarizes the current status of knowledge on asymmetric iridium-catalyzed direct hydrogenations of acyclic and cyclic imines. An overview of the most interesting catalysts with respect to selectivity, activity and substrate scope is given, including a discussion of the effects of different reaction conditions on the enantioselectivity of imine reduction. A detailed analysis of proposed imine hydrogenation mechanisms is presented, revealing that a significant number of recent proposals suggest outer sphere mechanisms, implying that the substrate does not bind to the metal centre during the hydrogenation reaction. An intriguing question is how a high enantioselectivity can be achieved in such systems. Generally, the factors governing the stereocontrol of iridium-catalyzed direct imine hydrogenation are little studied. The mechanistic proposals that have been put forward to explain the enantiodiscrimination of selected complexes are reviewed here, showing that the stereocontrol appears to be governed by weak non-bonding interactions between the substrate and the chiral catalyst complex. These selectivity-determining interactions might be modified through coordination of solvent, additive, or product molecules to the iridium complex, providing a rationale for the effect of solvent or additives on the enantioselectivity.

Asymmetric hetero Diels–Alder (HDA) reactions of N-sulfinyldienophiles with bis(oxazoline)copper(II) and -zinc(II) triflatesare described. The cycloaddition with cyclic and acyclic 1,3-dienes has been studied. The copper catalyst was found to be more efficient. With 10 mol-% of catalyst loading, a pronounced enhancement in turnover, diastereoselectivity (54–>90 % de), and enantioselectivity (30–98 % ee) was obtained by the addition of 100 mol-% of TMSOTf. The role of the additive is unclear, but we hypothesize that it is involved in the breakdown of catalyst-sulfine aggregates assists in the release of catalyst from the HDA adducts. Mechanistic studies revealed a positive nonlinear effect with the zinc catalyst, assumed to arise from the formation of less reactive heterochiral complexes. The copper catalyst showed a nearly linear relationship between the enantioselectivity of the ligand tested and the HDA product formed. The relative configurations and, in one case, the absolute configuration of the HDA products were established by X-ray analysis. Finally, an enantioselective route to (3aR,6aS)-3,3a,4,6a-tetrahydrocyclopenta[d][1,3]oxazol-2-one, a precursor of the C-ring in agelastatin A, applying the asymmetric HDA reaction is described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Enantioselective hetero Diels–Alder (HDA) reactions of 1,3-cyclohexadiene with benzyl N-sulfinylcarbamate 1a and with N-sulfinyl-p-toluensulfonamide 1b promoted by chiral Ti(IV)-based Lewis acids are reported. The obtained yields and enantiomeric excesses obtained are heavily dependant on the mode of catalyst preparation. Acceptable reproducibility was obtained with Ti(IV)-catalysts prepared from Me2TiCl2 and chiral diols. Testing of various chiral diols gave the endo adduct in yields of up to 69% with 76% ee. The absolute configuration of the HDA products were established by chemical correlation and verified by X-ray crystallography.

The mechanism of the asymmetric dihydroxylation (AD) reaction has been hotly disputed. We have studied the stereochemical outcome of the AD reaction on a series of Cs-symmetric divinylcarbinol derivatives in order to shed light on the binding mode of the substrate to the osmium tetroxide−ligand complex. The product distribution is dependent on the size of the allylic substituent, and on the type and class of ligand. It is postulated that the diastereospecificity of the reactions originates from attractive forces between the substrate and the ligand. These interactions are independent of the interactions responsible for the enantioselectivity in the AD reaction.

Cyclotrimerizations of ethynyl N-methyliminodiacetic acid (MIDA) boronate (1) with 1,6-diynes 2 have been studied, using three different catalysts (based on ruthenium, rhodium, and iridium) and variable reaction conditions. Successful cyclotrimerization reactions were obtained with both Cp*RuCl(cod) and Rh(cod)2BF4/BINAP as pre-catalysts in THF or acetone. Ruthenium-catalyzed cyclotrimerization of an unsymmetrically bromo-substituted diyne (2f) with 1 was successfully scaled up (2 g) and included in a total synthesis strategy toward potential selective inhibitors of tyrosine kinase 2.

The new title Negishi-type cross-coupling reaction expands the scope of monobromophosphines, which are considered as poor substrates so far.