Design of ß-Keto Esters with Antibacterial Activity: Synthesis, In Vitro Evaluation, and Theoretical Assessment of Their Reactivity and Quorum-Sensing Inhibition Capacity.

This work proposes the design of ß-keto esters as antibacterial compounds. The design was based on the structure of the autoinducer of bacterial quorum sensing, N-(3-oxo-hexanoyl)-l-homoserine lactone (3-oxo-C6-HSL). Eight ß-keto ester analogues were synthesised with good yields and were spectroscopically characterised, showing that the compounds were only present in their ß-keto ester tautomer form. We carried out a computational analysis of the reactivity and ADME (absorption, distribution, metabolism, and excretion) properties of the compounds as well as molecular docking and molecular dynamics calculations with the LasR and LuxS quorum-sensing (QS) proteins, which are involved in bacterial resistance to antibiotics. The results show that all the compounds exhibit reliable ADME properties and that only compound 7 can present electrophile toxicity. The theoretical reactivity study shows that compounds 6 and 8 present a differential local reactivity regarding the rest of the series. Compound 8 presents the most promising potential in terms of its ability to interact with the LasR and LuxS QS proteins efficiently according to its molecular docking and molecular dynamics calculations. An initial in vitro antimicrobial screening was performed against the human pathogenic bacteria Pseudomonas aeruginosa and Staphylococcus aureus as well as the phytopathogenic bacteria Pseudomonas syringae and Agrobacterium tumefaciens. Compounds 6 and 8 exhibit the most promising results in the in vitro antimicrobial screening against the panel of bacteria studied.

Isocyanides as Acceptor Groups in MHAT Reactions with Unactivated Alkenes.

The use of isocyanides as acceptor groups in metal-hydride hydrogen atom transfer (MHAT) coupling reactions with nonactivated alkenes to form heterocycles is described. Monosubstituted alkenes couple and cyclize directly, whereas more substituted alkenes proceed via a two-step, one-pot procedure involving MHAT reductive cyclization followed by a MHAT Minisci coupling upon the addition of acid. To highlight the utility of the methodology, a diverse variety of substituted heterocycles such as phenanthridines, indoles, and isoquinolines were prepared.

Four-Step Synthesis of (-)-4-epi-Presilphiperfolan-8α-ol by Intramolecular Iron Hydride Atom Transfer-Mediated Ketone-Alkene Coupling and Studies to Access trans-Hydrindanols with a Botryane Scaffold.

From an (R)-(+)-pulegone-derived building block that incorporates the stereo-defined tertiary carbon bearing a methyl group, as found in the targeted sesquiterpenoid, a four-step synthesis of (-)-4-epi-presilphiperfolan-8-α-ol was achieved. The key processes involved are a ring-closing metathesis leading to a bridged alkene-tethered ketone and its subsequent FeIII -mediated metal-hydride atom transfer (MHAT) transannular cyclization. This synthetic method, implying an irreversible addition of a carbon-centered radical upon a ketone by means of a hydrogen atom transfer upon the alkoxy radical intermediate, was also applied in the synthesis of trans-fused hydrindanols structurally related to botrydial compounds.

Base-Mediated Nitrophenyl Reductive Cyclization for the Synthesis of Hexahydro-2,6-methano-1-benzazocines.

A Diels-Alder reaction leading to 4-nitrophenylcyclohexanones followed by a newly developed base-mediated reductive cyclization of the resulting ketone tethered to the nitrobenzene moiety gives access to the hexahydro-2,6-methano-1-benzazocine ring system present in several biologically interesting natural products such as aspernomine. The scope of the reaction was explored with eight substituted nitrobenzenes, obtaining yields of up to 87%. The highest cytotoxicity was observed in benzazocine 4h, bearing an enone moiety, which was active against eight cancer cell lines.

Accounting for population structure in genomic predictions of Eucalyptus globulus.

Genetic groups have been widely adopted in tree breeding to account for provenance effects within pedigree-derived relationship matrices. However, provenances or genetic groups have not yet been incorporated into single-step genomic BLUP ("HBLUP") analyses of tree populations. To quantify the impact of accounting for population structure in Eucalyptus globulus, we used HBLUP to compare breeding value predictions from models excluding base population effects and models including either fixed genetic groups or the marker-derived proxies, also known as metafounders. Full-sib families from 2 separate breeding populations were evaluated across 13 sites in the "Green Triangle" region of Australia. Gamma matrices (Γ) describing similarities among metafounders reflected the geographic distribution of populations and the origins of 2 land races were identified. Diagonal elements of Γ provided population diversity or allelic covariation estimates between 0.24 and 0.56. Genetic group solutions were strongly correlated with metafounder solutions across models and metafounder effects influenced the genetic solutions of base population parents. The accuracy, stability, dispersion, and bias of model solutions were compared using the linear regression method. Addition of genomic information increased accuracy from 0.41 to 0.47 and stability from 0.68 to 0.71, while increasing bias slightly. Dispersion was within 0.10 of the ideal value (1.0) for all models. Although inclusion of metafounders did not strongly affect accuracy or stability and had mixed effects on bias, we nevertheless recommend the incorporation of metafounders in prediction models to represent the hierarchical genetic population structure of recently domesticated populations.

Cytotoxic Effects on Breast Cancer Cell Lines of Chalcones Derived from a Natural Precursor and Their Molecular Docking Analysis.

This study aimed to determine the in vitro cytotoxicity and understand possible cytotoxic mechanisms via an in silico study of eleven chalcones synthesized from two acetophenones. Five were synthesized from a prenylacetophenone isolated from a plant that grows in the Andean region of the Atacama Desert. The cytotoxic activity of all the synthesized chalcones was tested against breast cancer cell lines using an MTT cell proliferation assay. The results suggest that the prenyl group in the A-ring of the methoxy and hydroxyl substituents of the B-ring appear to be crucial for the cytotoxicity of these compounds. The chalcones 12 and 13 showed significant inhibitory effects against growth in MCF-7 cells (IC50 4.19 ± 1.04 µM and IC50 3.30 ± 0.92 µM), ZR-75-1 cells (IC50 9.40 ± 1.74 µM and IC50 8.75 ± 2.01µM), and MDA-MB-231 cells (IC50 6.12 ± 0.84 µM and IC50 18.10 ± 1.65 µM). Moreover, these chalcones showed differential activity between MCF-10F (IC50 95.76 ± 1.52 µM and IC50 95.11 ± 1.97 µM, respectively) and the tumor lines. The in vitro results agree with molecular coupling results, whose affinity energies and binding mode agree with the most active compounds. Thus, compounds 12 and 13 can be considered for further studies and are candidates for developing new antitumor agents. In conclusion, these observations give rise to a new hypothesis for designing chalcones with potential cytotoxicity with high potential for the pharmaceutical industry.

Single-step genomic BLUP enables joint analysis of disconnected breeding programs: an example with Eucalyptus globulus Labill.

Single-step GBLUP (HBLUP) efficiently combines genomic, pedigree, and phenotypic information for holistic genetic analyses of disjunct breeding populations. We combined data from two independent multigenerational Eucalyptus globulus breeding populations to provide direct comparisons across the programs and indirect predictions in environments where pedigreed families had not been evaluated. Despite few known pedigree connections between the programs, genomic relationships provided the connectivity required to create a unified relationship matrix, H, which was used to compare pedigree-based and HBLUP models. Stem volume data from 48 sites spread across three regions of southern Australia and wood quality data across 20 sites provided comparisons of model accuracy. Genotyping proved valuable for correcting pedigree errors and HBLUP more precisely defines relationships within and among populations, with relationships among the genotyped individuals used to connect the pedigrees of the two programs. Cryptic relationships among the native range populations provided evidence of population structure and evidence of the origin of landrace populations. HBLUP across programs improved the prediction accuracy of parents and genotyped individuals and enabled breeding value predictions to be directly compared and inferred in regions where little to no testing has been undertaken. The impact of incorporating genetic groups in the estimation of H will further align traditional genetic evaluation pipelines with approaches that incorporate marker-derived relationships into prediction models.

Phloem sap metabolites vary according to the interactive effects of nutrient supply and seasonal conditions in Eucalyptus globulus (Labill).

Improving the efficiency of fertilizer application is paramount to both the sustainability and profitability of forest plantations. Therefore, developing reliable, cost-effective tools to assess tree nutritional status is of great interest. This investigation sought to assess the use of phloem sap-derived metabolites as an indicator of nutritional status on a background of seasonal water availability of Eucalyptus globulus (Labill) trees grown under field conditions. Phloem is a central conduit for long-distance transport and signaling in plants and offers great promise in reflecting plant-scale resource limitations. Changes in the abundance of solutes and isotopes in phloem sap are sensitive to environmental cues. With a focus on both water and nutrient availability, we characterize patterns in phloem sugars, amino acids and the abundance of carbon isotopes in phloem sap obtained from E. globulus among different seasons and fertilizer treatments. Phloem-derived total amino acid concentration was found to increase with an increasing nitrogen (N) supply; however, this response was lost with the concurrent addition of phosphorus and at the highest level of N supply. Significant seasonal variation in all measured parameters was also detected, highlighting the need for caution in making quantitative relationships with growth. Broader implications of the interactive effects of both water supply and multi-nutrient additions and relationships with growth are discussed.

Iron-Catalyzed Radical Intermolecular Addition of Unbiased Alkenes to Aldehydes.

The intermolecular reductive radical coupling of aldehydes with nonactivated alkenes, employing metal hydride atom transfer (MHAT) catalysis with a combination of FeII and FeIII salts, is described. This constitutes the first use of aldehydes as viable acceptor groups in MHAT reactions. The insights gained in this study led to the reexamination of the previously reported intramolecular version of the reaction, and the addition of FeII salts allowed the development of a more efficient second-generation approach.

Iron Hydride Radical Reductive Alkylation of Unactivated Alkenes.

Iron-catalyzed hydrogen atom transfer-mediated intermolecular C-C coupling reactions between alkenes and tosylhydrazones, followed by in situ cleavage of the tosylhydrazine intermediates using Et3N, are described. The process involves a new strategic bond disconnection resulting in the reductive alkylation of nonactivated alkenes. The reaction is operationally simple, proceeds under mild conditions, and has a wide substrate scope.

Decahydroquinoline Ring 13C NMR Spectroscopic Patterns for the Stereochemical Elucidation of Phlegmarine-Type Lycopodium Alkaloids: Synthesis of (-)-Serralongamine A and Structural Reassignment and Synthesis of (-)-Huperzine K and (-)-Huperzine M (Lycoposerramine Y).

Analysis of 13C NMR spectroscopic data of the phlegmarine subset of Lycopodium alkaloids revealed spectral patterns that allowed the stereochemical arrangement of the four stereogenic carbons in the decahydroquinoline core to be established. A relatively simple predictive set of chemical shift combinations is reported, providing a tool for the challenging stereochemical assignment of phlegmarine-type alkaloids. Based on the chemical shifts in their NMR spectroscopic profiles, the alkaloids huperzine K and huperzine M, formally reported as cis derivatives, were structurally reassigned as trans-decahydroquinolines. The NMR spectroscopic data for huperzine M were identical to those reported for lycoposerramine Y and, hence, also implied the configurational reassignment of the latter. The revised structures of the above alkaloids were confirmed by enantioselective total synthesis. Additionally, the synthesis of (-)-serralongamine A via a common intermediate precursor is reported.

Synthesis of cis-hydrindan-2,4-diones bearing an all-carbon quaternary center by a Danheiser annulation.

A straightforward synthetic entry to functionalized hydrindane compounds based on a rapid assembly of the core nucleus by a Danheiser cycloaddition is reported. Valuable bicyclic building blocks containing the fused five and six-membered carbocyclic ring system can be achieved in only four steps from a simple acyclic ß-keto ester.

Radical Cyclization of Alkene-Tethered Ketones Initiated by Hydrogen-Atom Transfer.

An unprecedented C-C coupling reaction between alkenes and ketones by hydrogen-atom transfer, using Fe(acac)3 and PhSiH3 in EtOH, is described. This mild protocol features high site selectivity and allows the construction of sterically congested structures containing tertiary alcohols and quaternary centers. The overall process introduces a novel strategic bond disconnection for ring-closing reactions.

The evolution of a stereoselective synthesis of the C1-C16 fragment of bryostatins.

The development of a synthesis of the C1-C16 fragment of bryostatins in which the key step is a stereoselective oxy-Michael reaction used to assemble the cis-2,6-disubstituted tetrahydropyran with the exocyclic alkene already installed, is described. Following early work using Stille reactions to prepare precursors for oxy-Michael reactions, a more efficient route was devised based on a ketophosphonate-aldehyde condensation to prepare the key dienone. Synthesis of the aldehyde required for the ketophosphonate condensation involved the highly stereoselective addition of a diorganocuprate derived from allylmagnesium bromide and copper(i) iodide to the methyl 5-hydroxyhex-2-ynoate prepared by ring-opening of a protected glycidol using lithiated methyl propiolate. Ester reduction, selective alcohol protection and oxidative cleavage of the terminal double bond gave the required aldehyde. The ketophosphonate was prepared in 13 steps from (R)-pantolactone using a synthesis based on a chelation controlled aldol condensation and an anti-selective reduction of a 3-hydroxyketone. Following the ketophosphonate-aldehyde reaction, selective deprotection followed by treatment with base effected the oxy-Michael reaction that gave the cis-2,6-disubstituted tetrahydropyran via thermodynamic control. Subsequent functional group manipulation led to the synthesis of a hydroxy ester that corresponded to the C1-C16 fragment of the bryostatins in 23 steps from (R)-pantolactone. The synthesis was repeated using slightly different protecting groups for a study of a ring-closing metathesis approach to the bryostatins.

Asymmetric Synthesis of Octahydroindoles via a Domino Robinson Annulation/5-Endo Intramolecular Aza-Michael Reaction.

A straightforward, two-step asymmetric synthesis of octahydroindoles has been developed on the basis of two complementary strategies: (i) an organocatalyzed Michael reaction followed by a tandem Robinson-aza-Michael double cyclization catalyzed by PS-BEMP, and (ii) a diastereoselective cyclization, which formally constitutes a remote 1,6 asymmetric induction mediated by PS-BEMP. This allowed the construction of complex octahydroindoles with up to four stereocenters, excellent enantioselectivities (up to 95% ee), and complete diastereoselective control in a single-pot operation. DFT calculations were performed to understand the origin of this effect.

Synthesis of (±)-Serralongamine A and the Revised Structure of Huperzine N.

A revised structure for the Lycopodium alkaloid huperzine N is proposed and confirmed by synthesis. The key synthetic steps involve an epimerization of a cis-5-oxodecahydroquinoline to the corresponding trans isomer and a coupling, followed by a diastereoselective hydrogenation using Wilkinson's catalyst to incorporate the pyridylmethyl moiety. This route allowed the alkaloid serralongamine A to be synthesized for the first time, and two additional steps led to the revised structure of huperzine N, both products bearing an unusual decahydroquinoline stereostructure.

Approach to cis-Phlegmarine Alkaloids via Stereodivergent Reduction: Total Synthesis of (+)-Serratezomine E and Putative Structure of (-)-Huperzine N.

A unified strategy for the synthesis of the cis-phlegmarine group of alkaloids is presented, leading to the first synthesis of serratezomine E (1) as well as the putative structure of huperzine N (2). A contrasteric hydrogenation method was developed based on the use of Wilkinson's catalyst, which allowed the facial selectivity of standard hydrogenation to be completely overturned. Calculations were performed to determine the mechanism, and structures for huperzines M and N are reassigned.

Total synthesis of aignopsanes, a class of sesquiterpenes: (+)-aignopsanoic acid†A, (-)-methyl aignopsanoate†A, and (-)-isoaignopsanoic†A.

A general strategy for the synthesis of aignopsanes, a new family of sesquiterpene natural products of marine origin, is presented. The total synthesis of (+)-aignopsanoic acid A (1), (-)-methyl aignopsanoate A (2), and (-)-isoaignopsanoic A (3) has been achieved and their absolute configuration confirmed. (+)-Microcionin-1 (4), a structurally related furanosesquiterpene isolated in both enantiomeric forms from marine sponges, was also synthesized and its absolute configuration established in an unambiguous way. Interestingly, we report that (+)-microcionin-1 (4), can be converted by a simple oxidation process to aignopsanoic acid A (1). This transformation supports the hypothesis that (+)-microcionin-1 (4) may be an intermediate in the biosynthesis of aignopsanes.

A gram-scale route to phlegmarine alkaloids: rapid total synthesis of (-)-cermizine B.

The synthesis of the Lycopodium alkaloid (-)-cermizine B (1), which establishes its absolute configuration, is achieved by combining asymmetric organocatalysis and an uninterrupted eight-step reaction sequence, followed by a final reduction step. This "pot-economy" strategy provides access to the cis-phlegmarine stereoparent embedded in 1 for the first time, rapidly and on a gram-scale.

Synthetic and DFT studies towards a unified approach to phlegmarine alkaloids: aza-Michael intramolecular processes leading to 5-oxodecahydroquinolines.

A diastereoselective synthesis of cis-5-oxodecahydroquinolines is described in which three stereocenters are generated in a one-pot reaction. The reaction involves a lithium hydroxide-promoted Robinson annulation/intramolecular aza-Michael domino process from an achiral acyclic tosylamine-tethered ß-keto ester. The development and scope of this reaction was facilitated through the use of DFT-based mechanistic studies, which enabled the observed diastereodivergent course of the azacyclization to be rationalized. The varying stereochemistry and stability of the resulting decahydroquinolines was found to depend on whether a ß-keto ester or ketone were embedded in the substrates undergoing aminocyclization. This synthetic approach gave access not only to both diastereomeric cis-decahydroquinolines from the same precursor, but also to the corresponding trans isomers, through an epimerization processes of the corresponding N-unsubstituted cis-5-oxodecahydroquinolines. The described methodology provides advanced building-blocks with the three relative stereochemistries required for the total synthesis of phlegmarine alkaloids.