Leandro H. Andrade

Continuous flow synthesis of chiral amines in organic solvents: immobilization of E. coli cells containing both ω-transaminase and PLP.

E. coli cells containing overexpressed (R)-selective ω-transaminase and the cofactor PLP were immobilized on methacrylate beads suitable for continuous flow applications. The use of an organic solvent suppresses leaching of PLP from the cells; no additional cofactor was required after setting up the packed-bed reactor containing the biocatalyst (ω-TA-PLP). Non-natural ketone substrates were transformed in flow with excellent enantioselectivity (>99% ee). Features of this novel system include high-throughput (30-60 min residence time), clean production (no quench, workup, or purification required), high enzyme stability (the packed-bed reactor can be continuously operated for 1-10 days), and excellent mass recovery.

Bioreduction of fluoroacetophenones by the fungi Aspergillus terreus and Rhizopus oryzae

The enantioselective bioreduction of a number of fluoroacetophenones was carried out with whole cells of Rhizopus oryzae CCT 4964, Aspergillus terreus CCT 3320 and Aspergillus terreus CCT 4083 giving the corresponding alcohols in good yield and high enantioselectivity. Initial results with these fungi indicated that some of them are promising biocatalysts for deracemization reactions of secondary alcohols.

Plasmonic Nanorattles as Next-Generation Catalysts for Surface Plasmon Resonance-Mediated Oxidations Promoted by Activated Oxygen

Nanorattles, comprised of a nanosphere inside a nanoshell, were employed as the next generation of plasmonic catalysts for oxidations promoted by activated O2 . After investigating how the presence of a nanosphere inside a nanoshell affected the electric-field enhancements in the nanorattle relative to a nanoshell and a nanosphere, the SPR-mediated oxidation of p-aminothiophenol (PATP) functionalized at their surface was investigated to benchmark how these different electric-field intensities affected the performances of Au@AgAu nanorattles, AgAu nanoshells and Au nanoparticles having similar sizes. The high performance of the nanorattles enabled the visible-light driven synthesis of azobenzene from aniline under ambient conditions. As the nanorattles allow the formation of electromagnetic hot spots without relying on the uncontrolled aggregation of nanostructures, it enables their application as catalysts in liquid phase under mild conditions using visible light as the main energy input.

Lipase-Catalyzed Highly Enantioselective Kinetic Resolution of Boron-Containing Chiral Alcohols

The first application of enzymes as catalysts to obtain optically pure boron compounds is described. The kinetic resolution of boron-containing chiral alcohols via enantioselective transesterification catalyzed by lipases was studied. Aromatic, allylic, and aliphatic secondary alcohols containing a boronate ester or boronic acid group were resolved by lipase from Candida antartica (CALB), and excellent E values (E > 200) and high enantiomeric excesses (up to >99%) of both remaining substrates and acetylated product were obtained.

Impact of hydrocarbons, PCBs and heavy metals on bacterial communities in Lerma River, Salamanca, Mexico: Investigation of hydrocarbon degradation potential.

Freshwater contamination usually comes from runoff water or direct wastewater discharges to the environment. This paper presents a case study which reveals the impact of these types of contamination on the sediment bacterial population. A small stretch of Lerma River Basin, heavily impacted by industrial activities and urban wastewater release, was studied. Due to industrial inputs, the sediments are characterized by strong hydrocarbon concentrations, ranging from 2 935 to 28 430μg·kg(-1) of total polyaromatic hydrocarbons (PAHs). These sediments are also impacted by heavy metals (e.g., 9.6μg·kg(-1) of Cd and 246μg·kg(-1) of Cu, about 8 times the maximum recommended values for environmental samples) and polychlorinated biphenyls (ranging from 54 to 123μg·kg(-1) of total PCBs). The bacterial diversity on 6 sediment samples, taken from upstream to downstream of the main industrial and urban contamination sources, was assessed through TRFLP. Even though the high PAH concentrations are hazardous to aquatic life, they are not the only factor driving bacterial community composition in this ecosystem. Urban discharges, leading to hypoxia and low pH, also strongly influenced bacterial community structure. The bacterial bioprospection of these samples, using PAH as unique carbon source, yielded 8 hydrocarbonoclastic strains. By sequencing the 16S rDNA gene, these were identified as similar to Mycobacterium goodii, Pseudomonas aeruginosa, Pseudomonas lundensis or Aeromonas veronii. These strains showed high capacity to degrade naphthalene (between 92 and 100% at 200mg·L(-1)), pyrene (up to 72% at 100mg·L(-1)) and/or fluoranthene (52% at 50mg·L(-1)) as their only carbon source on in vitro experiments. These hydrocarbonoclastic bacteria were detected even in the samples upstream of the city of Salamanca, suggesting chronical contamination, already in place longer before. Such microorganisms are clearly potential candidates for hydrocarbon degradation in the treatment of oil discharges.

Studies on terrein as a new class of proteasome inhibitors

O proteassomo e uma protease intracelular multicatalitica envolvida na regulacao do ciclo e sinalizacao celular, apresentacao antigenica e apoptose. Uma vez que inibidores do proteassomo promovem morte celular por apoptose, esses tem sido propostos como novas drogas anti-tumorais. A terreina, um metabolito secundario secretado pelo fungo Aspergillus terreus, foi primeiramente descrita em 1935. Neste trabalho demonstramos que a terreina, isolada atraves da bioprospeccao de inibidores do proteassomo, mostrou efeito inibitorio das atividades do tipo quimiotripsina e tripsina da unidade catalitica do proteassomo 20S. Apesar da alta concentracao inibitoria determinada in vitro, aquela verificada apos incubacao de celulas em cultura na presenca de terreina (fibroblasto e tumor pulmonar humano) foi 4 vezes menor, o que sugere que o proteassomo seja um alvo intracelular especifico. A terreina promoveu morte celular por apoptose nas duas linhagens ensaiadas. Embora as concentracoes de terreina necessarias para desencadear apoptose nos modelos celulares aqui testados tenham sido altas (ordem de mM) quando comparadas com doses utilizadas de outros inibidores descritos recentemente (ordem de µM e nM), sua estrutura quimica nao esta relacionada a nenhum outro inibidor conhecido ate o momento. Concluimos que estes resultados apontam para a possibilidade de explorar a terreina como um novo fragmento molecular para o desenvolvimento de inibidores sinteticos do proteassomo. The proteasome is an intracellular multicatalytic protease involved in the cell cycle regulation, signaling response, antigen presentation and apoptosis. Since proteasome inhibitors promote cell death by apoptosis, they have been proposed as new anti-tumoral drugs. Terrein, a secondary metabolite secreted by the fungus Aspergillus terreus, was firstly described in 1935. In the present work we report that terrein isolated through the screening for inhibitors of the 20S proteasome showed inhibitory effect upon both chymotrypsin- and trypsin-like activities of the multicatalytic core particle, the 20S proteasome. Despite of the high inhibitory concentration determined in vitro, that verified by incubating cells (fibroblasts and a pulmonary tumor cell line) in the presence of terrein was 4-fold lower indicating the proteasome as a selective intracellular target. Moreover, terrein promoted apoptotic cell death on both fibroblasts and pulmonary tumor cell line tested. Although terrein concentrations (mM range) necessary to elicit apoptosis in the cellular models herein tried were high when compared to those (µM and nM range) of other inhibitors recently described, its chemical structure is not correlated to any other inhibitor reported thus far. Therefore, the present results point out for the possibility of exploring terrein as a new molecular fragment for the development of synthetic proteasome inhibitors.

Structure-activity relationships of hypervalent organochalcogenanes as inhibitors of cysteine cathepsins V and S.

A new series of organotelluranes were synthesized and investigated, and the structure-activity relationships in cysteine proteases inhibition were determined. It was possible to identify the relevance of structural components linked to the reactivity of these compounds as inhibitors. For example, dibromo-organotelluranes showed to be more reactive than dichloro-organotelluranes towards cysteine cathepsins V and S. Besides, no remarkable enantio-selectivity was verified. In general the achiral organotelluranes were more reactive than the chiral congeners against cysteine cathepsins V and S. A reactivity order for organochalcogenanes and cysteine cathepsins was proposed after the comparison of the inhibitory potencies of organotelluranes with the related organoselenanes.

Hypervalent organochalcogenanes as inhibitors of protein tyrosine phosphatases

A series of organochalcogenanes was synthesized and evaluated as protein tyrosine phosphatases (PTPs) inhibitors. The results indicate that organochalcogenanes inactivate the PTPs in a time- and concentration-dependent fashion, most likely through covalent modification of the active site sulfur-moiety by the chalcogen atom. Consequently, organochalcogenanes represent a new class of mechanism-based probes to modulate the PTP-mediated cellular processes.

Chemoenzymatic synthesis of organoselenium(IV) compounds and their evaluation as cysteine protease inhibitors

A series of organoselenium dihalides (organoselenanes) was synthesized from organoselenides using a chemoenzymatic approach. The organoselenanes have variations in their stereochemistry and in the halogen atom bonded to the selenium atom. Because of the unique selenium-thiol chemistry displayed by several organoselenium compounds, the organoselenanes were evaluated as new potential inhibitors of cysteine proteases (cathepsins S and V). By the analysis of the second-order rate constants of the inhibition of cathepsin S and V, it was possible to conclude that organoselenanes inhibited the cathepsin S faster than cathepsin V. It was observed higher inhibitory potencies for the dibromo organoselenanes derivatives than the dichloro analogues. In addition, the present data suggest the use of hypervalent selenium compounds as novel motifs for cysteine proteases inhibitors.

Bioreduction of substituted a-tetralones promoted by Daucus carota root

The bioreduction of a series of substituted a-tetralones, carried out using Daucus carota root (carrot), afforded the corresponding homochiral a-tetralols in variable conversions (9 to 90%) and excellent enantiomeric excesses. Two of the assayed a-tetralones were resistant to the bioreduction conditions. The absolute configurations of four a-tetralols were assigned as being (S), by comparison to the (S)-enantiomers obtained by kinetic resolution promoted by CALB-catalysed acetylation. Additionally, the new 5-methoxy-6-methyl-1-tetralone was synthesized in seven steps from 3-methylsalicylic acid.