José E. Rodríguez-Borges

Chiral bis(oxazoline) and pyridyl alcoholate dioxo-molybdenum(VI) complexes: synthesis, characterization and catalytic examinations

Abstract A group of chiral molybdenum(VI) complexes comprising MoO2Cl2L**, MoO2Cl(THF)L* and MoO2L2* [L**=chiral bis(oxazoline) and L*=chiral 2′-pyridyl alcoholate] have been prepared in good yields by reaction of the solvent substituted complex MoO2Cl2(THF)2 with one or two equivalents of chiral ligand. Optically active aminoalcohols (L*) were obtained by reaction of the appropriate organolithium compound with (−)-menthone, (+)-8-phenylisomenthone, (−)-8-phenylmenthone, (+)-camphor and (−)-thujone. The molybdenum complexes were characterized by multinuclear NMR (1H, 13C, 17O, 95Mo) spectroscopy, IR spectroscopy and elemental analysis. 95Mo-NMR data reflected the donor capability of the organic ligands, whereas 1H-NMR and IR data were comparatively indifferent to the changes in the Lewis base ligand. The complexes were evaluated as catalysts for the asymmetric epoxidation of trans-β-methylstyrene by tert-butylhydroperoxide. The bis(oxazoline) complexes showed good catalytic activity but had low optical yields. Complexes of the type MoO2Cl(THF)L* (L*=chiral 2′-pyridyl alcoholate) also exhibited high catalytic activity and enantiomeric excesses of up to 23%. The corresponding MoO2L2* alcoholate complexes were considerably less active with comparable optical yields.

Chiral dioxomolybdenum(VI) complexes for enantioselective alkene epoxidation

Chiral dioxomolybdenum(VI) complexes of the type MoO2Cl2(L*) (L* = oxime), MoO2(THF)2L* (L*= cis-p-menthane-3,8diol) and MoO2Cl(THF)L* (L*=8-phenylthioneomenthol and 8-phenylthioisoneomenthol) have been prepared in good yields by reacting MoO2Cl2(THF)2 with the appropriate chiral organic bidentate O,O-, O,N- and O,S-ligands. The complexes were characterised by solution NMR ( 1 H, 13 C, 95 Mo) and IR spectroscopy as well as elementary analysis, and were evaluated as catalysts in solution for the asymmetric epoxidation of cis--methylstyrene by tert-butylhydroperoxide (TBHP). The cis-diol complex shows high catalytic activity and enantiomeric excesses of up to 25%. An attempt was made to immobilise the complex MoO2(THF)Cl[(−)-8-phenylthioneomenthol] within the channels of MCM-41 mesoporous silica by using a tethering ligand [L=NC(CH2)3Si(OEt)3]. The material was characterised by powder X-ray diffraction (XRD), IR spectroscopy and magic-anglespinning (MAS) NMR ( 13 C, 29 Si). Catalytic examinations demonstrated that it was active in the epoxidation of cyclooctene by TBHP.

Identification of Ubiquitin-specific Protease 9X (USP9X) as a Deubiquitinase Acting on Ubiquitin-Peroxin 5 (PEX5) Thioester Conjugate

Background: The mammalian deubiquitinase that hydrolyzes the ubiquitin-PEX5 thioester conjugate was unknown. Results: USP9X was found to be the most active deubiquitinase acting on ubiquitin-PEX5. Conclusion: We propose that USP9X participates in the PEX5-mediated peroxisomal protein import pathway. Significance: The unbiased biochemical strategy described here will be useful to identify deubiquitinases acting on other substrates. Peroxin 5 (PEX5), the peroxisomal protein shuttling receptor, binds newly synthesized peroxisomal matrix proteins in the cytosol and promotes their translocation across the organelle membrane. During the translocation step, PEX5 itself becomes inserted into the peroxisomal docking/translocation machinery. PEX5 is then monoubiquitinated at a conserved cysteine residue and extracted back into the cytosol in an ATP-dependent manner. We have previously shown that the ubiquitin-PEX5 thioester conjugate (Ub-PEX5) released into the cytosol can be efficiently disrupted by physiological concentrations of glutathione, raising the possibility that a fraction of Ub-PEX5 is nonenzymatically deubiquitinated in vivo. However, data suggesting that Ub-PEX5 is also a target of a deubiquitinase were also obtained in that work. Here, we used an unbiased biochemical approach to identify this enzyme. Our results suggest that ubiquitin-specific protease 9X (USP9X) is by far the most active deubiquitinase acting on Ub-PEX5, both in female rat liver and HeLa cells. We also show that USP9X is an elongated monomeric protein with the capacity to hydrolyze thioester, isopeptide, and peptide bonds. The strategy described here will be useful in identifying deubiquitinases acting on other ubiquitin conjugates.

Studies on olefin epoxidation with t-BuOOH catalysed by dioxomolybdenum(VI) complexes of a novel chiral pyridyl alcoholate ligand

The chiral dioxomolybdenum(VI) complexes [MoCl{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}(O)2(THF)] and [Mo{(1R,2S,5S)-8-trimethylsilyloxy-1-(2-pyridyl)mentholato}2(O)2] have been prepared in good yields by reaction of the solvent substituted complex [MoCl2O2(THF)2] with one or two equivalents of chiral 2′-pyridyl alcohol. The optically active aminoalcohol was obtained by reaction of 2-pyridyllithium with (−)-(2S,5S)-8-trimethylsilyloxymenthone. The complexes are active catalysts in the homogeneous epoxidation of cyclic and linear olefins, dienes and terpenes by t-BuOOH. They present remarkable activity and excellent product selectivity in cyclooctene epoxidation (cyclooctene oxide was obtained in quantitative yield). In the case of limonene, regioselectivity is high in favour of the epoxidation of the internal cyclic double bond. Ring opening activity was also observed for α-pinene oxide, producing campholenic aldehyde and epoxy campholenic aldehyde.

Heat shock induces a massive but differential inactivation of SUMO-specific proteases.

Covalent conjugation of the small ubiquitin-like modifier (SUMO) to proteins is a highly dynamic and reversible process. Cells maintain a fine-tuned balance between SUMO conjugation and deconjugation. In response to stress stimuli such as heat shock, this balance is altered resulting in a dramatic increase in the levels of SUMO conjugates. Whether this reflects an activation of the conjugation cascade, a decrease in the activity of SUMO-specific proteases (SENPs), or both, remains unknown. Here, we show that from the five human SENPs detected in HeLa cells (SENP1/2/3/6/7) the activities of all but one (SENP6) were largely diminished after 30min of heat shock. The decreased activity is not due to changes in their steady-state levels. Rather, in vitro experiments suggest that these SENPs are intrinsically heat-sensitive, a property most likely emerging from their catalytic domains. Heat shock inactivation seems to be a specific property of SENPs because numerous members of the related deubiquitinase family of cysteine proteases are not affected by this stress condition. Overall, our results suggest that SENPs are particularly sensitive to heat shock, a property that may be important for the adaptation of cells to this stress condition.

A short, efficient synthesis of the chiral auxiliary (+)-8-phenylneomenthol

Abstract (+)-8-Phenylneomenthol 2, the structure of which was confirmed by X-ray analysis of its 3,5-dinitrobenzoate, was efficiently prepared from commercially available (−)-8-phenylmenthol 3 by oxidation with the Sarett reagent, followed by L-Selectride reduction of the (+)-8-phenylmenthone 6 thus formed.

Comparison of adipocere formation in four soil types of the Porto (Portugal) district.

Four typical soils of the Porto (Portugal) area were characterized and used to study the decomposition of buried pieces of pork meat under controlled laboratory experiments (an 8 month experiment with a relatively high soil moisture and a 1 month experiment with relatively low soil moisture). The soils types were: organic, sandy, gravel and clay-gravel soils. Soils were characterized for their grain size distribution, pH, water content, organic matter percentage and mineral composition. Four free fatty acids (myristic, palmitic, oleic and stearic) were analysed (using a methodology based on an extraction step followed by a derivatization reaction and high performance liquid chromatography analysis) in soil samples as a sign of adipocere formation. The direct sensorial analysis of the buried sample residues and the free fatty acids profiles of the sampled soils showed that sandy and clay-gravel soils (in a low moisture environment) slowed the normal decomposition process promoting the formation of adipocere. Nevertheless, this apparent soil effect is indirect and a consequence of the different water retention and permeability of the soils. Thus, the water content of the soils is a crucial factor for adipocere formation.

Synthesis and characterization of all stereoisomers of 8-phenylmenthol

Abstract New, improved and/or specific syntheses of the diastereoisomers of (−)-8-phenylmenthol are described. The configurations of these products, usable as chiral auxiliaries, were confirmed by X-ray diffractometry of their 3,5-dinitrobenzoates.

Comparative study to predict toxic modes of action of phenols from molecular structures.

Quantitative structure–activity relationship models for the prediction of mode of toxic action (MOA) of 221 phenols to the ciliated protozoan Tetrahymena pyriformis using atom-based quadratic indices are reported. The phenols represent a variety of MOAs including polar narcotics, weak acid respiratory uncouplers, pro-electrophiles and soft electrophiles. Linear discriminant analysis (LDA), and four machine learning techniques (ML), namely k-nearest neighbours (k-NN), support vector machine (SVM), classification trees (CTs) and artificial neural networks (ANNs), have been used to develop several models with higher accuracies and predictive capabilities for distinguishing between four MOAs. Most of them showed global accuracy of over 90%, and false alarm rate values were below 2.9% for the training set. Cross-validation, complementary subsets and external test set were performed, with good behaviour in all cases. Our models compare favourably with other previously published models, and in general the models obtained with ML techniques show better results than those developed with linear techniques. We developed unsupervised and supervised consensus, and these results were better than our ML models, the results of rule-based approach and other ensemble models previously published. This investigation highlights the merits of ML-based techniques as an alternative to other more traditional methods for modelling MOA.

Synthesis of novel 1-alkyl-8-substituted-3-(3-methoxypropyl) xanthines as putative A2B receptor antagonists

In order to identify a high-affinity, selective antagonist for the A(2B) subtype adenosine receptor, more than 40 1,8-disubstituted-3-(3-methoxypropyl) xanthines were prepared and evaluated for their binding affinity at recombinant human adenosine receptors, mainly of the A(2A) and A(2B) subtypes. Some of the 1-ethyl-3-(3-methoxypropyl)-8-aryl substituted derivatives 15(a-m) showed moderate-to-high affinity at human A(2B) receptors, with compound 15d showing A(2B) selectivity over the other A receptors assayed (A(1), A(2A), A(3)) of 34-fold or over.