Biocatalytic Synthesis of Homochiral 2-Hydroxy-4-butyrolactone Derivatives by Tandem Aldol Addition and Carbonyl Reduction.

Chiral 2-hydroxy acids and 2-hydroxy-4-butyrolactone derivatives are structural motifs often found in fine and commodity chemicals. Here, we report a tandem biocatalytic stereodivergent route for the preparation of these compounds using three stereoselective aldolases and two stereocomplementary ketoreductases using simple and achiral starting materials. The strategy comprises (i) aldol addition reaction of 2-oxoacids to aldehydes using two aldolases from E. coli, 3-methyl-2-oxobutanoate hydroxymethyltransferase (KPHMT Ecoli ), 2-keto-3-deoxy-l-rhamnonate aldolase (YfaU Ecoli ), and trans-o-hydroxybenzylidene pyruvate hydratase-aldolase from Pseudomonas putida (HBPA Pputida ) and (ii) subsequent 2-oxogroup reduction of the aldol adduct by ketopantoate reductase from E. coli (KPR Ecoli ) and a Δ1-piperidine-2-carboxylate/Δ1-pyrroline-2-carboxylate reductase from Pseudomonas syringae pv. tomato DSM 50315 (DpkA Psyrin ) with uncovered promiscuous ketoreductase activity. A total of 29 structurally diverse compounds were prepared: both enantiomers of 2-hydroxy-4-butyrolactone (>99% ee), 21 2-hydroxy-3-substituted-4-butyrolactones with the (2R,3S), (2S,3S), (2R,3R), or (2S,3R) configuration (from 60:40 to 98:2 dr), and 6 2-hydroxy-4-substituted-4-butyrolactones with the (2S,4R) configuration (from 87:13 to 98:2 dr). Conversions of aldol adducts varied from 32 to 98%, while quantitative conversions were achieved by both ketoreductases, with global isolated yields between 20 and 45% for most of the examples. One-pot one-step cascade reactions were successfully conducted achieving isolated yields from 30 to 57%.

Synthesis of γ-Hydroxy-α-amino Acid Derivatives by Enzymatic Tandem Aldol Addition-Transamination Reactions.

Three enzymatic routes toward γ-hydroxy-α-amino acids by tandem aldol addition-transamination one-pot two-step reactions are reported. The approaches feature an enantioselective aldol addition of pyruvate to various nonaromatic aldehydes catalyzed by trans-o-hydroxybenzylidene pyruvate hydratase-aldolase (HBPA) from Pseudomonas putida. This affords chiral 4-hydroxy-2-oxo acids, which were subsequently enantioselectively aminated using S-selective transaminases. Three transamination processes were investigated involving different amine donors and transaminases: (i) l-Ala as an amine donor with pyruvate recycling, (ii) a benzylamine donor using benzaldehyde lyase from Pseudomonas fluorescens Biovar I (BAL) to transform the benzaldehyde formed into benzoin, minimizing equilibrium limitations, and (iii) l-Glu as an amine donor with a double cascade comprising branched-chain α-amino acid aminotransferase (BCAT) and aspartate amino transferase (AspAT), both from E. coli, using l-Asp as a substrate to regenerate l-Glu. The γ-hydroxy-α-amino acids thus obtained were transformed into chiral α-amino-γ-butyrolactones, structural motifs found in many biologically active compounds and valuable intermediates for the synthesis of pharmaceutical agents.

Webcam autofocus mechanism used as a delay line for the characterization of femtosecond pulses.

In this work, we present an electromagnetic focusing mechanism (EFM), from a commercial webcam, implemented as a delay line of a femtosecond laser pulse characterization system. The characterization system consists on a second order autocorrelator based on a two-photon-absorption detection. The results presented here were performed for two different home-made femtosecond oscillators: Ti:sapph @ 820 nm and highly chirped pulses generated with an Erbium Doped Fiber @ 1550 nm. The EFM applied as a delay line represents an excellent alternative due its performance in terms of stability, resolution, and long scan range up to 3 ps. Due its low power consumption, the device can be connected through the Universal Serial Bus (USB) port. Details of components, schematics of electronic controls, and detection systems are presented.

Aberration effects on femtosecond pulses generated by nonideal achromatic doublets.

There are three main effects that affect the femtosecond pulse focusing process near the focal plane of a refractive lens: the group velocity dispersion (GVD), the propagation time difference (PTD), and the aberrations of the lens. In this paper we study in detail these effects generated by nonideal achromatic doublets based on a Fourier-optical analysis and Seidel aberration theory considering lens material, wavelength range, lens surface design, and temporally and spatially uniform and Gaussian intensity distributions. We show that the residual chromatic aberration in achromatic lenses, which has been neglected so far, has a considerable effect on the focusing of pulses shorter than 20 fs in the spectral range between the UV and IR, 300 to 1100 nm, and is particularly important in the blue and UV spectral range. We present a general fitted function for an estimation of the pulse stretching parameter, which depends only on the numerical aperture and focal length of the doublet as well as the wavelength of the carrier of the pulse.

Artificio radiográfico para el estudio del estado periodontal. Comportamiento óseo perimplantario y otros enfoques diagnósticos / Radiographic artifact for the study of periodontal status. Periimplant osseous behavior and other diagnostic approaches

En el presente trabajo se trata de ampliar, mediante un método de filtración localizada en sectores precisos de la película radiográfica, un medio que facilite la visualización de estructuras con bajo porcentaje mineral, las que por su condición de baja densidad, frente a valores de radiación corrientes, pierden su posibilidad de impresionar la película radiográfica surgiendo como consecuencia, la falta de información al respecto (AU)

Artificio radiográfico para el estudio del estado periodontal. Comportamiento óseo perimplantario y otros enfoques diagnósticos / Radiographic artifact for the study of periodontal status. Periimplant osseous behavior and other diagnostic approaches

En el presente trabajo se trata de ampliar, mediante un método de filtración localizada en sectores precisos de la película radiográfica, un medio que facilite la visualización de estructuras con bajo porcentaje mineral, las que por su condición de baja densidad, frente a valores de radiación corrientes, pierden su posibilidad de impresionar la película radiográfica surgiendo como consecuencia, la falta de información al respecto

Tomografía de senos maxilares con equipos radiográficos panorámicos / Tomography of maxillary sinus with panoramic radiography equipment

Basado en los principios de la mecánica funcional de los equipos panorámicos y tratando de aprovechar su semejanza dinámica con los aparatos tomográficos lineales, se efectuaron ciertas modificaciones en ellos, sin alterar sus estructuras, lo que permitió lograr radiografías con enfoque tomográfico. Estos ensayos se hicieron en tomas frontales de Seno Maxilar, con óptimos resultados. Con esta metodología se lograría la doble funcionalidad de Panorámicos y Tomógrafos, en especial para aquellos aparatos que no han sido construídos con tales fines y daría la posibilidad de ampliar estos estudios a otras zonas de los maxilares (AU)

Tomografía de senos maxilares con equipos radiográficos panorámicos / Tomography of maxillary sinus with panoramic radiography equipment

Basado en los principios de la mecánica funcional de los equipos panorámicos y tratando de aprovechar su semejanza dinámica con los aparatos tomográficos lineales, se efectuaron ciertas modificaciones en ellos, sin alterar sus estructuras, lo que permitió lograr radiografías con enfoque tomográfico. Estos ensayos se hicieron en tomas frontales de Seno Maxilar, con óptimos resultados. Con esta metodología se lograría la doble funcionalidad de Panorámicos y Tomógrafos, en especial para aquellos aparatos que no han sido construídos con tales fines y daría la posibilidad de ampliar estos estudios a otras zonas de los maxilares