Foldamers controlled by functional triamino acids: structural investigation of α/γ-hybrid oligopeptides.

Peptide-like foldamers controlled by normal amide backbone hydrogen bonding have been extensively studied, and their folding patterns largely rely on configurational and conformational constraints induced by the steric properties of backbone substituents at appropriate positions. In contrast, opportunities to influence peptide secondary structure by functional groups forming individual hydrogen bond networks have not received much attention. Here, peptide-like foldamers consisting of alternating α,ß,γ-triamino acids 3-amino-4-(aminomethyl)-2-methylpyrrolidine-3-carboxylate (AAMP) and natural amino acids glycine and alanine are reported, which were obtained by solution phase peptide synthesis. They form ordered secondary structures, which are dominated by a three-dimensional bridged triazaspiranoid-like hydrogen bond network involving the non-backbone amino groups, the backbone amide hydrogen bonds, and the relative configuration of the α,ß,γ-triamino and α-amino acid building blocks. This additional stabilization leads to folding in both nonpolar organic as well as in aqueous environments. The three-dimensional arrangement of the individual foldamers is supported by X-ray crystallography, NMR spectroscopy, chiroptical methods, and molecular dynamics simulations.

Factors, associated with elevated concentration of soluble carbonic anhydrase IX in plasma of women with cervical dysplasia.

Precancerous lesions of human cervix uteri have a tendency for regression or progression. In cervical intraepithelial neoplasia grade 2 (CINII) case there is an uncertainty if a lesion will progress or regress. The carbonic anhydrase IX (CAIX) enzyme is overexpressed in cervical cancer which is more sensitive to radiotherapy. CAIX is associated with poor prognosis in solid hypoxic tumors. The aim of this study was to determine factors related to elevated soluble CAIX (s-CAIX) in high-grade intraepithelial lesion (HSIL) cases. METHODS: Patients diagnosed with HSIL (N = 77) were included into the research group whereas without HSIL (N = 72)-the control group. Concentration of the soluble CAIX (s-CAIX) in plasma was determined by the DIANA ligand-antibody-based method. C. trachomatis was detected from cervical samples by PCR. Primary outcomes were risk factors elevating s-CAIX level in HSIL group. Non-parametric statistical analysis methods were used to calculate correlations. RESULTS: The s-CAIX level in patients with HSIL was elevated among older participants (rs = 0.27, p = 0.04) and with C. trachomatis infection (p = 0.028). Among heavy smokers with HSIL, the concentration of s-CAIX was higher in older women (rs = 0.52, p = 0.005), but was not related to the age of heavy smokers' controls (τ = 0.18 p = 0.40). CONCLUSION: The concentration of s-CAIX was higher among older, heavy smoking and diagnosed with C. trachomatis patients. All these factors increased the risk for HSIL progression.

Unified Total Synthesis of Diverse Meroterpenoids from Ganoderma Applanatum.

A unified approach to meroterpenoids applanatumols B, V, W, X, and Y produced by the medicinal fungus Ganoderma applanatum and 2'-epi-spiroapplanatumine O is presented. The key synthetic sequence consists of a tandem anionic ketone allylation/oxy-Cope rearrangement/α-oxygenation furnishing an α-aminoxy ketone and a persistent radical effect-based 5-exo-trig cyclization leading to the trisubstituted cyclopentane core. The relative configuration of applanatumol V has to be revised. Some compounds display significant cytotoxic and antioxidant properties.

Sulfonyl Nitrene and Amidyl Radical: Structure and Reactivity.

Photocatalytic generation of nitrenes and radicals can be used to tune or even control their reactivity. Photocatalytic activation of sulfonyl azides leads to the elimination of N2 and the resulting reactive species initiate C-H activations and amide formation reactions. Here, we present reactive radicals that are generated from sulfonyl azides: sulfonyl nitrene radical anion, sulfonyl nitrene and sulfonyl amidyl radical, and test their gas phase reactivity in C-H activation reactions. The sulfonyl nitrene radical anion is the least reactive and its reactivity is governed by the proton coupled electron transfer mechanism. In contrast, sulfonyl nitrene and sulfonyl amidyl radicals react via hydrogen atom transfer pathways. These reactivities and detailed characterization of the radicals with vibrational spectroscopy and with DFT calculations provide information necessary for taking control over the reactivity of these intermediates.

Enolate-Based Regioselective Anti-Beckmann C-C Bond Cleavage of Ketones.

The Baeyer-Villiger or Beckmann rearrangements are established methods for the cleavage of ketone derivatives under acidic conditions, proceeding for unsymmetrical precursors selectively at the more substituted site. However, the fragmentation regioselectivity cannot be switched and fragmentation at the less-substituted terminus is so far not possible. We report here that the reaction of ketone enolates with commercial alkyl nitrites provides a direct and regioselective way of fragmenting ketones into esters and oximes or ω-hydroxyimino esters, respectively. A comprehensive study of the scope of this reaction with respect to ketone classes and alkyl nitrites is presented. Control over the site of cleavage is gained through regioselective enolate formation by various bases. Oxidation of kinetic enolates of unsymmetrical ketones leads to the otherwise unavailable "anti-Beckmann" cleavage at the less-substituted side chain, while cleavage of thermodynamic enolates of the same ketones represents an alternative to the Baeyer-Villiger oxidation or the Beckmann rearrangement under basic conditions. The method is suited for the transformation of natural products and enables access to orthogonally reactive dicarbonyl compounds.

Design of Novel Uncharged Organic Superbases: Merging Basicity and Functionality.

ConspectusOne of the constant challenges of synthetic chemistry is the molecular design and synthesis of nonionic, metal-free superbases as chemically stable neutral organic compounds of moderate molecular weight, intrinsically high thermodynamic basicity, adaptable kinetic basicity, and weak or tunable nucleophilicity at their nitrogen, phosphorus, or carbon basicity centers. Such superbases can catalyze numerous reactions, ranging from C-C bond formation to cycloadditions and polymerization, to name just a few. Additional benefits of organic superbases, as opposed to their inorganic counterparts, are their solubility in organic reaction media, mild reaction conditions, and higher selectivity. Approaching such superbasic compounds remains a continuous challenge. However, recent advances in synthetic methodology and theoretical understanding have resulted in new design principles and synthetic strategies toward superbases. Our computational contributions have demonstrated that the gas-phase basicity region of 350 kcal mol-1 and even beyond is easily reachable by organosuperbases. However, despite record-high basicities, the physical limitations of many of these compounds become quickly evident. The typically large molecular weight of these molecules and their sensitivity to ordinary reaction conditions prevent them from being practical, even though their preparation is often not too difficult. Thus, obviously structural limitations with respect to molecular weight and structural complexity must be imposed on the design of new synthetically useful organic superbases, but strategies for increasing their basicity remain important.The contemporary design of novel organic superbases is illustrated by phosphazenyl phosphanes displaying gas-phase basicities (GB) above 300 kcal mol-1 but having molecular weights well below 1000 g·mol-1. This approach is based on a reconsideration of phosphorus(III) compounds, which goes along with increasing their stability in solution. Another example is the preparation of carbodiphosphoranes incorporating pyrrolidine, tetramethylguanidine, or hexamethylphosphazene as a substituent. With gas-phase proton affinities of up to 300 kcal mol-1, they are among the top nonionic carbon bases on the basicity scale. Remarkably, the high basicity of these compounds is achieved at molecular weights of around 600 g·mol-1. Another approach to achieving high basicity through the cooperative effect of multiple intramolecular hydrogen bonding, which increases the stabilization of conjugate acids, has recently been confirmed.This Account focuses on our efforts to produce superbasic molecules that embody many desirable traits, but other groups' approaches will also be discussed. We reveal the crucial structural features of superbases and place them on known basicity scales. We discuss the emerging potential and current limits of their application and give a general outlook into the future.

First Total Synthesis of Phytoprostanes with Prostaglandin-Like Configuration, Evidence for Their Formation in Edible Vegetable Oils and Orienting Study of Their Biological Activity.

Phytoprostanes (PhytoP) are natural products, which form in plants under oxidative stress conditions from α-linolenic acid. However, their epimers with relative prostaglandin configuration termed phytoglandins (PhytoG) have never been detected in Nature, likely because of the lack of synthetic reference material. Here, the first asymmetric total synthesis of such compounds, namely of PhytoGF1α (9-epi-16-F1t -PhytoP) and its diastereomer ent-16-epi-PhytoGF1α (ent-9,16-diepi-16-F1t -PhytoP), has been accomplished. The synthetic strategy is based on radical anion oxidative cyclization, copper(I)-mediated alkyl-alkyl coupling and enantioselective reduction reactions. A UHPLC-MS/MS study using the synthesized compounds as standards indicates PhytoG formation at significant levels during autoxidation of α-linolenic acid in edible vegetable oils. Initial testing of synthetic PhytoGs together with F1 -PhytoP and 15-F2t -IsoP derivatives for potential interactions with the PGF2α (FP) receptor did not reveal significant activity. The notion that PUFA-derived oxidatively formed cyclic metabolites with prostaglandin configuration do not form to a significant extent in biological or food matrices has to be corrected. Strong evidence is provided that oxidatively formed PhytoG metabolites may be ingested with plant-derived food, which necessitates further investigation of their biological profile.

α,γ-Dioxygenated amides via tandem Brook rearrangement/radical oxygenation reactions and their application to syntheses of γ-lactams.

Pyrrolidones are common heterocyclic fragments in various biologically active compounds. Here, a two-step radical-based approach to γ-lactams bearing three to four stereocenters starting from epoxides, N-allylic silylacetamides and TEMPO is reported. The sequence starts with a new tandem nucleophilic substitution/Brook rearrangement/single electron transfer-induced radical oxygenation furnishing orthogonally protected α,γ-dioxygenated N-allylamides with wide scope, mostly good yields, and partly good diastereo- and enantioselectivity for defined combinations of chiral epoxides and chiral amides. This represents a very rare example of an oxidative geminal C-C/C-O difunctionalization next to carbonyl groups. The resulting dioxygenated allylic amides are subsequently subjected to persistent radical effect-based 5-exo-trig radical cyclization reactions providing functionalized pyrrolidones in high yields as diastereomeric mixtures. They converge to 3,4-trans-γ-lactams by base-mediated equilibration, which can be easily further diversified. Stereochemical models for both reaction types were developed.

First Total Syntheses of Novel Non-Enzymatic Polyunsaturated Fatty Acid Metabolites and Their Identification in Edible Oils.

Oxidative stress (OS) is an in vivo process leading to free radical overproduction, which triggers polyunsaturated fatty acid (PUFA) peroxidation resulting in the formation of racemic non-enzymatic oxygenated metabolites. As potential biomarkers of OS, their in vivo quantification is of great interest. However, since a large number of isomeric metabolites is formed in parallel, their quantification remains difficult without primary standards. Three new PUFA-metabolites, namely 18-F3t -isoprostane (IsoP) from eicosapentaenoic acid (EPA), 20-F4t -neuroprostane (NeuroP) from docosahexaenoic acid (DHA) and 20-F3t -NeuroP from docosapentaenoic acid (DPAn-3 ) were synthesized by two complementary synthetic strategies. The first one relied on a racemic approach to 18(RS)-18-F3t -IsoP using an oxidative radical anion cyclization as a key step, whereas the second used an enzymatic deracemization of a bicyclo[3.3.0]octene intermediate obtained from cyclooctadiene to pursue an asymmetric synthesis. The synthesized metabolites were applied in targeted lipidomics to prove lipid peroxidation in edible oils of commercial nutraceuticals.

Identification of Novel Carbonic Anhydrase IX Inhibitors Using High-Throughput Screening of Pooled Compound Libraries by DNA-Linked Inhibitor Antibody Assay (DIANA).

The DNA-linked inhibitor antibody assay (DIANA) has been recently validated for ultrasensitive enzyme detection and for quantitative evaluation of enzyme inhibitor potency. Here we present its adaptation for high-throughput screening of human carbonic anhydrase IX (CAIX), a promising drug and diagnostic target. We tested DIANA's performance by screening a unique compound collection of 2816 compounds consisting of lead-like small molecules synthesized at the Institute of Organic Chemistry and Biochemistry (IOCB) Prague ("IOCB library"). Additionally, to test the robustness of the assay and its potential for upscaling, we screened a pooled version of the IOCB library. The results from the pooled screening were in agreement with the initial nonpooled screen with no lost hits and no false positives, which shows DIANA's potential to screen more than 100,000 compounds per day.All DIANA screens showed a high signal-to-noise ratio with a Z' factor of >0.89. The DIANA screen identified 13 compounds with Ki values equal to or better than 10 µM. All retested hits were active also in an orthogonal enzymatic assay showing zero false positives. However, further biophysical validation of identified hits revealed that the inhibition activity of several hits was caused by a single highly potent CAIX inhibitor, being present as a minor impurity. This finding eventually led us to the identification of three novel CAIX inhibitors from the screen. We confirmed the validity of these compounds by elucidating their mode of binding into the CAIX active site by x-ray crystallography.

Tandem Anionic oxy-Cope Rearrangement/Oxygenation Reactions as a Versatile Method for Approaching Diverse Scaffolds.

Tandem anionic oxy-Cope rearrangement/radical oxygenation reactions provide δ,ϵ-unsaturated α-(aminoxy) carbonyl compounds, which serve as convenient precursors to diverse compound classes. Functionalized carbocycles are accessible by very rare all-carbon 5-endo-trig cyclizations, but also common 5-exo-trig radical cyclizations, based on the persistent radical effect. The tandem reactions can be further extended by highly diastereoselective allylation or reduction steps to give complex scaffolds.

Photochemical C-H Amination of Ethers and Geminal Difunctionalization Reactions in One Pot.

A mild, atom-economic, and metal-free α-C-H amination of ethers using relatively stable nonafluorobutanesulfonyl (nonaflyl, Nf) azide as the aminating reagent to give N-sulfonyl hemiaminals is reported. This enables unprecedented C(sp3 ) difunctionalization reactions, leading to diverse functionalized amino group containing compounds starting from simple ethers in one pot.

First total synthesis of ent-asperparaline C and assignment of the absolute configuration of asperparaline C.

The first asymmetric total synthesis of a member of the asperparaline family was accomplished and the unknown absolute configuration of asperparaline C has been determined to be all-(S). The key steps of the synthesis are an oxidative radical cyclization, a selective reduction of one of the tertiary amides, a singlet oxygen Diels-Alder reaction and a reductive spirocyclization.

Expansion of the fatty acyl reductase gene family shaped pheromone communication in Hymenoptera.

Fatty acyl reductases (FARs) are involved in the biosynthesis of fatty alcohols that serve a range of biological roles. Insects typically harbor numerous FAR gene family members. While some FARs are involved in pheromone biosynthesis, the biological significance of the large number of FARs in insect genomes remains unclear.Using bumble bee (Bombini) FAR expression analysis and functional characterization, hymenopteran FAR gene tree reconstruction, and inspection of transposable elements (TEs) in the genomic environment of FARs, we uncovered a massive expansion of the FAR gene family in Hymenoptera, presumably facilitated by TEs. The expansion occurred in the common ancestor of bumble bees and stingless bees (Meliponini). We found that bumble bee FARs from the expanded FAR-A ortholog group contribute to the species-specific pheromone composition. Our results indicate that expansion and functional diversification of the FAR gene family played a key role in the evolution of pheromone communication in Hymenoptera.

Unique Stereoselective Homolytic C-O Bond Activation in Diketopiperazine-Derived Alkoxyamines by Adjacent Amide Pyramidalization.

Simple monocyclic diketopiperazine (DKP)-derived alkoxyamines exhibit unprecedented activation of a remote C-O bond for homolysis by amide distortion. The combination of strain-release-driven amide planarization and the persistent radical effect (PRE) enables a unique, irreversible, and quantitative trans→cis isomerization under much milder conditions than typically observed for such homolysis-limited reactions. This isomerization is shown to be general and independent of the steric and electronic nature of both the amino acid side chains and the substituents at the DKP nitrogen atoms. Homolysis rate constants are determined, and they significantly differ for both the labile trans diastereomers and the stable cis diastereomers. To reveal the factors influencing this unusual process, structural features of the kinetic trans diastereomers and thermodynamic cis diastereomers are investigated in the solid state and in solution. X-ray crystallographic analysis and computational studies indicate substantial distortion of the amide bond from planarity in the trans-alkoxyamines, and this is believed to be the cause for the facile and quantitative isomerization. Thus, these amino-acid-derived alkoxyamines are the first examples that exhibit a large thermodynamic preference for one diastereomer over the other upon thermal homolysis, and this allows controlled switching of configurations and configurational cycling.

Bioinspired total synthesis of tetrahydrofuran lignans by tandem nucleophilic addition/redox isomerization/oxidative coupling and cycloetherification reactions as key steps.

A very short three-step approach to trans,trans,trans-2,5-diaryl-3,4-dimethyltetrahydrofuran lignans is reported. The carbon skeleton is assembled in a single step based on an unprecedented tandem reaction consisting of 1,2-addition of aryllithium reagents to α,ß-unsaturated aldehydes, ruthenium-catalyzed redox isomerization of the resulting alkoxides to enolates and their dimerization triggered by single electron oxidation. The resulting 2,3-dialkyl-1,4-diketones form with moderate to good d/l-diastereoselectivity and are transformed to the target tetrahydrofuran lignans by reduction and diastereoselective cycloetherification.

Total Synthesis of ent-Pregnanolone Sulfate and Its Biological Investigation at the NMDA Receptor.

A unique asymmetric total synthesis of the unnatural enantiomer of pregnanolone, as well as a study of its biological activity at the NMDA receptor, is reported. The asymmetry is introduced by a highly atom-economic organocatalytic Robinson annulation. A new method for the construction of the cyclopentane D-ring consisting of CuI-catalyzed conjugate addition and oxygenation followed by thermal cyclization employing the persistent radical effect was developed. ent-Pregnanolone sulfate is surprisingly only 2.6-fold less active than the natural neurosteroid.

Total syntheses of all tri-oxygenated 16-phytoprostane classes via a common precursor constructed by oxidative cyclization and alkyl-alkyl coupling reactions as the key steps.

A unified strategy for the total synthesis of the methyl esters of all phytoprostane (PhytoP) classes bearing two ring-oxygen atoms based on an orthogonally protected common precursor is described. Racemic 16-F1t-, 16-E1-PhytoP and their C-16 epimers, which also occur as racemates in Nature, were successfully obtained. The first total synthesis of very sensitive 16-D1t-PhytoP succeeded, however, it quickly isomerized to more stable, but so far also unknown Δ13-16-D1t-PhytoP, which may serve as a more reliable biomarker for D-type PhytoP. The dioxygenated cyclopentane ring carrying the ω-chain with the oxygen functionality in the 16-position was approached by a radical oxidative cyclization mediated by ferrocenium hexafluorophosphate and TEMPO. The α-chain was introduced by a new copper-catalyzed alkyl-alkyl coupling of a 6-heptenyl Grignard reagent with a functionalized cyclopentylmethyl triflate.

Intermolecular Formation of Two C-C Bonds across Olefins Enabled by Boron-Based Relay Strategies.

Smooth handoff in the relay: Vinyl boronates enable the direct addition of nucleophilic and electrophilic or nucleophilic and radical-generating carbon reagents across the double bond with retention of the valuable boronate group. The key to the success of this difficult twofold C-C bond-formation strategy is the initial relay of the nucleophilic addition to boron and the rearrangement of a 1,2-metalate rearrangement, shuttling it to the carbon atom.

Sequential Oxidative and Reductive Radical Cyclization Approach toward Asperparaline C and Synthesis of Its 8-Oxo Analogue.

The most advanced approach, so far, to the asperparalines is developed. Consecutive oxidative and reductive radical cyclizations serve as the key steps to stereoselectively access the complex fully elaborated skeleton containing the cyclopentane and spiro-succinimide units.