Qualitative and Dynamical Analysis of a Bionomic Fishery Model with Prey Refuge.

Predation and escaping from predation through hiding are two fundamental phenomena in ecology. The most common approach to reducing the chance of predation is to use a refuge. Here, we consider a three species fishery model system with prey refuge induced by a Holling type-II functional response.

Appearance of Temporal and Spatial Chaos in an Ecological System: A Mathematical Modeling Study.

The ecological theory of species interactions rests largely on the competition, interference, and predator-prey models. In this paper, we propose and investigate a three-species predator-prey model to inspect the mutual interference between predators. We analyze boundedness and Kolmogorov conditions for the non-spatial model.

Stereoretentive Etherification of an α-Aryl-β-amino Alcohol Using a Selective Aziridinium Ring Opening for the Synthesis of AZD7594.

A selective aziridinium ring-opening was used to etherify an α-aryl-β-amino alcohol with stereochemical retention. This transformation was achieved in a biphasic system to address phenoxide solubility and the formation of a sulfonate ester impurity. The protecting group strategy was directed by a stability study of the activated α-aryl-β-amino alcohol in this system.

Rhodium(III)-catalyzed C-H activation/annulation with vinyl esters as an acetylene equivalent.

The behavior of electron-rich alkenes in rhodium-catalyzed C-H activation/annulation reactions is investigated. Vinyl acetate emerges as a convenient acetylene equivalent, facilitating the synthesis of sixteen 3,4-unsubstituted isoquinolones, as well as select heteroaryl-fused pyridones. The complementary regiochemical preferences of enol ethers versus enol esters/enamides is discussed.

Restoration and recovery of damaged eco-epidemiological systems: application to the Salton Sea, California, USA.

In this paper, we have proposed and analysed a mathematical model to figure out possible ways to rescue a damaged eco-epidemiological system. Our strategy of rescue is based on the realization of the fact that chaotic dynamics often associated with excursions of system dynamics to extinction-sized densities. Chaotic dynamics of the model is depicted by 2D scans, bifurcation analysis, largest Lyapunov exponent and basin boundary calculations.

Diastereoselective alkylation reactions of 1-methylcyclohexa-2,5-diene-1-carboxylic acid.

The deprotonation and alkylation of 1-methylcyclohexa-2,5-diene-1-carboxylic acid has been investigated under a range of conditions. In all cases, the formation of compounds 14 was found to be completely stereoselective, although compound 14c was formed as an impurity when alkyl iodides were used as electrophiles, and doubly-alkylated compounds 17 were formed in some cases when alkyl bromides were used.

Synthesis of the louisianin alkaloid family via a 1,2,4-triazine inverse-electron-demand Diels-Alder approach.

Isolated in 1995, the four members of the louisianin family (A, B, C and D) are simple pyridine and 2-pyridone alkaloids that display both antibacterial and anticancer activity. Herein we describe the synthesis of all four members of the louisianin family, from a conveniently prepared 1,2,4-triazine and via a common tetrasubstituted pyridine intermediate. This study includes the synthesis of louisianin B in both racemic form and as the (-)-enantiomer.

Facile and general synthesis of quaternary 3-aminooxindoles.

A novel approach to the valuable quaternary 3-aminooxindole skeleton is reported on the basis of intramolecular arylation of enolates of substituted amino acids. The reaction tolerates dialkyl- and arylalkylamines as well as a range of carbon substituents (primary and secondary alkyl, aryl). The cyclization of N-indolyl-substituted substrates is accompanied by direct C-H arylation of the indole, leading to indolo-fused benzodiazepines.

Improved methodologies for the preparation of highly substituted pyridines.

[reaction: see text] Two separate strategies have been developed for the preparation of highly substituted pyridines from 1,2,4-triazines via the inverse-electron-demand Diels-Alder reaction: a microwave-promoted, solvent-free procedure and a tethered imine-enamine (TIE) approach. Both routes avoid the need for a discrete aromatization step and offer significant advantages over the classical methods, giving a wide variety of tri-, tetra-, and penta-substituted pyridines in high, optimized yields.

Tandem oxidation processes using manganese dioxide: discovery, applications, and current studies.

"One-pot" processes in which alcohol oxidations are combined with further elaboration of the carbonyl intermediate are reviewed. Sequential processes are briefly discussed, but most attention is centered on tandem processes; that is, oxidations carried out in the presence of a nucleophilic trapping agent, rather than those in which the trapping agent is added after the oxidation is complete. As part of this Account, a comprehensive review of the discovery of tandem oxidation processes (TOP) will be given together with applications in alkene-forming reactions, cyclopropanations, and imine, oxime, amine, and heterocycle formation.

Tandem oxidation processes: a combined phosphorus- and sulfur-ylide approach to polysubstituted cyclopropanes.

A new manganese dioxide-mediated tandem oxidation process (TOP) has been developed which, by suitable combination of stabilised phosphorus- and sulfur-ylides, allows the direct conversion of allylic alcohols or alpha-hydroxyketones into polysubstituted cyclopropanes.

Tandem oxidation processes for the preparation of functionalized cyclopropanes.

[reaction: see text] A novel manganese dioxide-mediated tandem oxidation process (TOP) has been developed which allows the direct conversion of allylic alcohols into cyclopropanes, the intermediate aldehydes being trapped in situ with a stabilized sulfur-ylide. This methodology has been applied successfully to a variety of allylic alcohols and to a formal synthesis of the simple, naturally occurring lignan, (+/-)-picropodophyllone.

Cascade reactions of substituted 1,2,4-triazines: rapid access to nitrogen-containing polycycles.

A new and straightforward methodology for the construction of complex nitrogen-containing polycycles has been developed. This methodology exploits easily prepared 1,2,4-triazines as substrates for a pericyclic reaction cascade, forming the polycycles in good to excellent yield in a single operation.

A versatile and stereocontrolled route to pyranose and furanose C-glycosides.

[reaction: see text] The alpha,beta-unsaturated-gamma,delta-epoxyester 1 is a novel and versatile precursor to a wide variety of C-glycosides. For instance, treatment of Z-1 or E-1 with palladium(0) affords, stereospecifically, beta- or alpha-C-furanosides, respectively. In contrast, reaction of Z-1 or E-1 with base gives, stereoselectively, the beta- or alpha-C-pyranosides, respectively.

Tandem oxidation processes for the preparation of nitrogen-containing heteroaromatic and heterocyclic compounds.

alpha-hydroxy ketones undergo manganese dioxide-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines to give quinoxalines or dihydropyrazines, respectively, in a one-pot procedure which avoids the need to isolate the highly reactive dicarbonyl intermediates. The scope and limitations of these procedures are outlined and modifications to this procedure are discussed in which reduction is carried out in the same reaction vessel, generating piperazines, or oxidation, leading to pyrazines.

Highly substituted pyridines via tethered imine-enamine (TIE) methodology.

A tethered imine-enamine methodology has been developed for the direct conversion of 1,2,4-triazines into highly substituted pyridines via the inverse electron demand Diels-Alder reaction which avoids the need for a discrete aromatisation step. This TIE methodology has also been applied in one pot reaction cascades involving 1,2,4-triazines and utilising MnO(2)-mediated tandem oxidation processes (TOPs).

Preparation of quinoxalines, dihydropyrazines, pyrazines and piperazines using tandem oxidation processes.

Alpha-hydroxyketones undergo MnO2-mediated oxidation followed by in situ trapping with aromatic or aliphatic 1,2-diamines to give quinoxalines or dihydropyrazines, respectively, in a one pot procedure which avoids the need to isolate the highly reactive 1,2-dicarbonyl intermediates. Modifications of the procedure allow the formation of pyrazines and piperazines.

Further observations on a low-molecular-weight natriuretic substance in the urine of normal man.

Large quantities of the low-molecular-weight natriuretic material (F4), which appears after the salts when fractionated on G-25 Sephadex column, were obtained from the urine of normal man on a normal diet. The natriuretic substance in F4 was (1) untrafiltrable through a membrane with a claimed molecular-weight cut-off of 500 daltons (Amicon UMO5); (2) soluble in more polar organic solvents; (3) totally soluble in 95% acetone when specific activity was doubled; (4) relatively resistant to heating at 100 degrees C for 1 hour at a pH of 10, and to heating at 110 degrees C in 6 N hydrochloric acid for up to 90 hours under anaerobic conditions, and treatment with nitrous acid; it was less resistant to these procedures when extracted into 95% acetone; (5) not destroyed by trypsin, chymotrypsin, pronase, pepsin, leucine aminopeptidase, and subtilysin, nor was it destroyed by pepsin, leucine aminopeptidase, subtilysin, carboxypeptidase A and B, and aminopeptidase M, or by monoamine oxidase, aryl sulphatase, and beta-glucuronidase when extracted into 95% acetone. The natriuretic substance in the 95% acetone-soluble F4 was totally destroyed by incubation with prolidase.

Two natriuretic substances in extracts of urine from normal man when salt-depleted and salt-loaded.

When the extra-cellular fluid volume is expanded, the subsequent rise in urinary sodium excretion that occurs is due in part to a change in the concentration of some circulating natriuretic substance. Two natriuretic substances with different characteristics on Sephadex chromatography have been previously been identified separately by different workers. Extracts prepared from the urine of 31 normal subjects were tested for these two natriuretic materials in the normal conscious water-loaded rat.