Publications (20) View all
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Article: Tetrachlorocarbonyliridates: water-soluble carbon monoxide releasing molecules rate-modulated by the sixth ligand.
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ABSTRACT: A new family of compounds is presented as potential carbon monoxide releasing molecules (CORMs). These compounds, based on tetrachlorocarbonyliridate(III) derivatives, were synthesized and fully characterized by X-ray diffraction, electrospray mass spectrometry, IR, NMR, and density functional theory calculations. The rate of CO release was studied via the myoglobin assay. The results showed that the rate depends on the nature of the sixth ligand, trans to CO, and that a significant modulation on the release rate can be produced by changing the ligand. The reported compounds are soluble in aqueous media, and the rates of CO release are comparable with those for known CORMs, releasing CO at a rate of 0.03-0.58 μM min(-1) in a 10 μM solution of myoglobin and 10 μM of the complexes.Inorganic Chemistry 02/2011; 50(6):2334-45. · 4.60 Impact Factor -
Article: Chemoenzymatic synthesis of alpha-hydroxy-beta-methyl-gamma-hydroxy esters: role of the keto-enol equilibrium to control the stereoselective hydrogenation in a key step.
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ABSTRACT: Alpha-hydroxy-beta-methyl-gamma-hydroxy esters not only are found in many natural products and potent drugs but also are useful intermediates in organic synthesis due to their highly functionalized skeleton that can be further manipulated and applied in the synthesis of many compounds with remarkable biological activities. This work was based on a chemoenzymatic approach to obtain these molecules with three contiguous stereogenic centers in a highly enantio- and diastereoselective way. Two distinct linear routes were proposed in which the key steps in both routes consisted of initial stereocontrolled ketoester bioreduction followed by unsaturated carbonyl bioreduction or reduction with Pd-C. Other key reactions in the synthesis include a Wasserman protocol for chain homologation and a Mannich-type olefination with maintenance of enantiomeric excess for all intermediates during the sequence. Whereas route A gave exclusively the skeleton with 3R,4R,5S configuration (99% ee and 11.5% global yield after 7 steps), route B gave the skeleton with 3R,4R,5S and 3R,4S,5R configurations (dr 1:12, 98% ee and 20% global yield after 5 steps).The Journal of Organic Chemistry 02/2010; 75(5):1410-8. · 4.45 Impact Factor -
Article: The Mechanism of Dephosphorylation of Bis(2,4-dinitrophenyl) Phosphate in Mixed Micelles of Cationic Surfactants and Lauryl Hydroxamic Acid
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ABSTRACT: Mixed micelles of cetyltrimethylammonium bromide (CTABr) or dodecyltrimethylammonium bromide (DTABr) and the α-nucleophile, lauryl hydroxamic acid (LHA) accelerate dephosphorylation of bis(2,4-dinitrophenyl)phosphate (BDNPP) over the pH range 4−10. With a 0.1 mole fraction of LHA in DTABr or CTABr, dephosphorylation of BDNPP is approximately 104-fold faster than its spontaneous hydrolysis, and monoanionic LHA− is the reactive species. The results are consistent with a mechanism involving concurrent nucleophilic attack by hydroxamate ion (i) on the aromatic carbon, giving an intermediate that decomposes to undecylamine and 2,4-dinitrophenol, and (ii) at phosphorus, giving an unstable intermediate that undergoes a Lossen rearrangement yielding a series of derivatives including N,N-dialkylurea, undecylamine, undecyl isocyanate, and carbamyl hydroxamate.The Journal of Organic Chemistry 10/2009; 74(21). · 4.45 Impact Factor -
Article: Coordinated nitroxyl anion is produced and released as nitrous oxide by the decomposition of iridium-coordinated nitrosothiols.
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ABSTRACT: The aqueous decomposition of the iridium coordinated nitrosothiols (RSNOs) trans-K[IrCl4(CH3CN)NOSPh] (1), and K2[IrCl5(NOECyS)] (2, ECyS = cysteine ethyl ester), was studied by MS analysis of the gaseous products, ESI-MS, NMR, and UV–Vis spectroscopy. Bent NO (NO−, nitroxyl anion), sulfenic acids and nitrite were observed as coordinated products in solution, while nitrous oxide (N2O) and nitrogen were detected in the gas phase. The formation of coordinated NO− and N2O, a nitroxyl dimerization product, allows us to propose the formation of free nitroxyl (HNO) as an intermediate. Complex 1 decomposes 300 times slower than free PhSNO does. In both cases (1 and 2) kinetic results show a first order decomposition behavior and a very negative ΔS≠, which strongly indicates an associative rate-determining step. A proposed decomposition mechanism, supported by the experimental data and DFT calculations, involves, as the first step, nucleophilic attack of H2O on to the sulfur atom of the coordinated RSNO, producing an NO− complex and free sulfenic acid, followed by two competing reactions: a ligand exchange reaction of this NO− with the sulfenic acid or, to a minor extent, coordination of N2O to produce an NO−/N2O complex which finally renders free N2 and coordinated NO2−. Some of the produced NO− is likely to be released from the metal center producing nitroxyl by protonation and finally N2O by dimerization and loss of H2O. In conclusion, the decomposition of these coordinated RSNOs occurs through a different mechanism than for the decomposition of free RSNOs. It involves the formation of sulfenic acids and coordinated NO−, which is released from the complexes and protonated at the reaction pH producing nitroxyl (HNO), and ultimately N2O.Inorganica Chimica Acta 01/2011; 366:85. · 1.85 Impact Factor -
Article: Brønsted acid catalyzed Morita-Baylis-Hillman reaction: a new mechanistic view for thioureas revealed by ESI-MS(/MS) monitoring and DFT calculations.
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ABSTRACT: A Morita-Baylis-Hillman (MBH) reaction catalyzed by thiourea was monitored by ESI-MS(/MS) and key intermediates were intercepted and characterized. These intermediates suggest that thiourea acts as an organocatalyst in all steps of the MBH reaction cycle, including the rate-limiting proton-transfer step. DFT calculations, performed for a model MBH reaction between formaldehyde and acrolein with trimethylamine as base and in the presence or the absence of thiourea, suggest that thiourea accelerates MBH reactions by decreasing the transition-state (TS) energies through bidentate hydrogen bonding throughout the whole catalytic cycle. In the rate-limiting proton-transfer step, the thiourea acts not as a proton shuttle, but as a Brønsted acid stabilizing the basic oxygen center that is formed in the TS.Chemistry 10/2009; 15(45):12460-9. · 5.93 Impact Factor
