Enantioselective Synthesis of Cyclobutylboronates via a Copper‐Catalyzed Desymmetrization Approach

The first catalytic enantioselective synthesis of cyclobutylboronates, by using a chiral copper(I) complex, is reported. A broad variety of cyclobutanes have been prepared with consistently high levels of diastereo‐ and enantiocontrol. Moreover, this method constitutes the first report of an enantioselective desymmetrization of meso‐cyclobutenes to prepare chiral cyclobutanes.     

Inhibitory effects of lupene-derived pentacyclic triterpenoids from Bursera simaruba on HSV-1 and HSV-2 in vitro replication

The cytotoxicity and antiviral properties of Bursera simaruba against herpes simplex viruses (HSV-1 and HSV-2) were investigated through a bioactivity-guided isolation protocol. The plant material was fractionated using solvent-solvent partitioning, size-exclusion and thin-layer chromatography. The antiviral compounds present in the most active fractions were identified by means of LC-MS and NMR. Three different methods were compared during the evaluation of antiviral activity of samples. Four lupene-related pentacyclic triterpenes were found to be responsible for the anti-herpesvirus effects of B. simaruba and were isolated from this species for the first time. The selective indexes (SI) of B. simaruba-derived samples ranged from 7.7 to 201.9.     

New approach to the Positron equation by means of the algebraic structure of the ideals

Starting from the electron Lagrangian density and expanding it with a more general idempotent than the one used by Hestenes, we achieve to show how the algebraic structure of the ideals draws a distinction between electrons and positrons without any need of the charge conjugation. A remarkable fact, consequence of the formalism used, is evidenced by the magnetization density discriminating the sign of the charge of the particles involved.     

Vertical and oblique fault detection in explicit surfaces

The purpose of this paper is to study the problem of detection of vertical and oblique faults in explicit surfaces. First, we characterize the finite jump discontinuities of a univariate function in terms of the divergence of sequences related to the slopes of least-squares polynomial approximations of the function. Then, we propose an algorithm to locate the finite jump discontinuities of a univariate function and its first derivative from a finite set of scattered data values of the function. As a consequence, we derive a method to detect vertical and oblique faults in explicit surfaces when the data sets are distributed along lines. We finally present some numerical and graphical examples.     

Synthesis, mesomorphic properties and structural study by semi-empirical calculations of amides containing the 1,3,4-thiadiazole unit

The synthesis and liquid crystalline properties of a new series of amides (series 2a-f , 3a-d and 4a-d ) incorporating pyridine and 1,3,4-thiadiazole rings are reported. No homologues of the series 2 show mesomorphic properties. In the series 3 only the highest homologues ( 3d ) displays an enantiotropic SmA mesophase; the compound 3c exhibits a monotropic SmA mesophase, and the homologues 3a , b display no liquid crystal properties. The amides 4b-d display an enantiotropic SmA phases and the first homologue ( 4a ) exhibit only crystalisotropic transition. These series are compared with previously reported Schiff's bases and amide analogues. A structural study by AM1 semi-empirical calculation is also described.     

Critical Objective Size and Calmness Modulus in Linear Programming

This paper introduces the concept of critical objective size associated with a linear program in order to provide operative point-based formulas (only involving the nominal data, and not data in a neighborhood) for computing or estimating the calmness modulus of the optimal set (argmin) mapping under uniqueness of nominal optimal solution and perturbations of all coefficients. Our starting point is an upper bound on this modulus given in Cánovas et al. (4). In this paper we prove that this upper bound is attained if and only if the norm of the objective function coefficient vector is less than or equal to the critical objective size. This concept also allows us to obtain operative lower bounds on the calmness modulus. We analyze in detail an illustrative example in order to explore some strategies that can improve the referred upper and lower bounds.     

An efficient synthesis of gamma-amino acids and attempts to drive its enantioselectivity

Addition of carboxylic acid dianions to bromoacetonitrile lead, in good yields,to the corresponding gamma-cyanoacids, which on hydrogenation yielded gamma-amino acids. This two step methodology improves upon previously described results. Poor e.e's resultedfrom our attempts to drive the enantioselectivity of this transformation by chiral amide induction.     

Electrochemical degradation of tetracycline in artificial urine medium

The electrochemical degradation of tetracycline hydrochloride (TeC) was comparatively investigated in artificial urine and chloride-containing media using a one-compartment filter-press flow cell composed of a Ti/Ru_0.3Ti_0.7O₂ dimensionally stable anode. The effect of the current density (10–40 mA cm^?2) on the removal levels attained for TeC and total organic carbon (TOC) (in both media), as well as for urea and creatinine in artificial urine medium, was assessed. The TeC removal rate in the artificial urine medium was much lower than in chloride-containing medium, probably due to the higher consumption of the electrogenerated active chlorine species by the urea and creatinine in the artificial urine medium. Moreover, the obtained removal levels for the urea and creatinine were negligible at current densities lower than 30 mA cm^?2. As TOC abatement was also very small, it is possible that TeC oxidation leads to intermediate compounds. Thus, if current densities less than 20 mA cm^?2 are applied, TeC can be selectively removed.