Glueball singularity,flavour loops and the Harari-Freund picture

We discuss several points concerning the structure of the cylinder term in the dual topological expansion. Using dual field theory as a guide, we concentrate on the possibility of a two-singularity scheme à la Harari-Freund. We start from results obtained previously at the lowest order in ?=N _f /N _c and study what can be the role of flavour-loop corrections in the real world where ?～1. It is argued that, in spite of the actual value of ?, precise mechanisms exist which can weaken the role of the flavour-loop corrections in the kinematical region where “soft” dynamics dominates. We also claim that theS-matrix at largeN _c (?≈-0) incorporates already many realistic features, and we refute some objections recently raised against the Harari-Freund picture.     

Simple cross-section model for elementary reactions

A simple reaction cross-section model has been obtained. It consists of hard spheres where the mass of the products has been introduced via angular momentum conservation. For exothermic reactions the cross section shows a maximum, providing that a threshold energy is present. The model has been applied to the alkali-atom—alkyl-oxide reactions, giving a simple understanding of the systematic trend of the cross section and the energy dependence of its maximum.     

Enantiodivergent synthesis of pyrrolo[2,1-a]isoquinolines based on diastereoselective Parham cyclization and alpha-amidoalkylation reactions

Enantiodivergent synthesis of C-10b-substituted pyrrolo[2,1-a]isoquinolines starting from an enantiomerically pure N-phenethylnorborn-5-en-endo-2,3-dicarboxyimide 3a, with a 2-exo-hydroxy-10-bornylsulfinyl group as a chiral auxiliary, has been developed. The key transformations are derived from diastereoselective intramolecular cyclization of aryllithiums and alpha-amidoalkylation reactions, with the ethylidene bridge of the norbornene moiety dictating the stereochemical outcome in both types of reactions. Thus, the organolithium addition-intramolecular alpha-amidoalkylation sequence on imide 3a afforded stereoselectively the R configuration at C-12b, whereas the tandem Parham cyclization-intermolecular alpha-amidoalkylation reactions on the corresponding iodinated imide 3b occurred with complete control of stereoselectivity, leading to the epimer at C-12b. Subsequent reductive removal of the chiral auxiliary and retro-Diels-Alder reaction afforded (10bS)- and (10bR)-pyrroloisoquinolines 1 in high yields and optical purities (>99% ee).     

Radical and palladium-catalyzed cyclizations to cyclobutenes: an entry to the BCD ring system of penitrem D

A novel approach toward the synthesis of the BCD ring system of penitrem D is described. The strategy capitalizes on the fast cyclization rates of aryl radicals into cyclobutenes and allows access to a variety of fused tricyclic structures. Radical/polar crossover reactions of precursors 24-29 promoted by samarium diiodide in the presence of HMPA and acetone allow access to the fully functionalized BCD ring system of penitrem D. The stereochemical implications of these processes are evaluated, and a Pd-mediated cyclization approach toward the penitrems is also introduced.     

Designing antibacterial compounds through a topological substructural approach

A novel application of TOPological Substructural MOlecular DEsign (TOPS-MODE) was carried out in antibacterial drugs using computer-aided molecular design. Two series of compounds, one containing antibacterial and the other containing non-antibacterial compounds, were processed by a k-means cluster analysis in order to design training and predicting series. All clusters had a p-level < 0.005. Afterward, a linear classification function has been derived toward discrimination between antibacterial and non-antibacterial compounds. The model correctly classifies 94% of active and 86% of inactive compounds in the training series. More specifically, the model showed a global good classification of 91%, i.e., 263 cases out of 289. In predicting series, the model has shown overall predictabilities of 91 and 83% for active and inactive compounds, respectively. Thereby, the model has a global percentage of good classification of 89%. The TOPS-MODE approach, also, similarly compares with respect to one of the most useful models for antimicrobials selection reported to date.     

Theoretical model of internal rotation in monosubstituted derivatives of furfural

The present work explores the effect of substitution in all free positions of furfural on conformational preferences of formyl group by using ab-initio calculations at the MP2/6-31G(p,d) level of theory. Theoretical modeling was made in vacuo. The selected substituents were -CH(3), NH(2), NO(2) and F groups in 3, 4, 5 and ipso carbonyl positions. Geometries of all derivatives were analyzed and it is ascertained that substitution has not important consequences on furan ring geometry. Differences of energy between OO-cis and trans conformers and energy barriers between them are described and extreme cases are explained. Interesting features appear in the cases of -NH(2) and -NO(2) groups, and particularly when the 3 and ipso carbonyl positions are substituted. Variations in energy barriers are correlated with variations in C2-C6 distances for the transition states and planar forms. Substitution effect on Mülliken charges are analyzed and related with internal rotation energy barriers and differences between conformers.