Margarita Romero-Ávila

Synthesis and biological activity of furostanic analogues of brassinosteroids bearing the 5α-hydroxy-6-oxo moiety

Two furostanic analogues of brassinosteroids bearing the 5alpha-hydroxy-6-oxo moiety were synthesized and their biological activity studied using the bean second internode elongation test. One of the compounds produced significant stimulation at doses of 2.5 and 5ng/plant.

Revisiting 23-iodospirostanes. New facts and full characterization.

In addition to a previous report, the reaction of tigogenin acetate with ICl in refluxing CHCl(3) produced the hitherto unknown 23R-iodotigogenin acetate, bearing an axial iodine atom at C-23 and its already reported 23S-epimer. The same treatment of sarsasapogenin acetate led to a single diasteromer characterized as 23S-iodosarsasapogenin acetate. A full characterization of the obtained compound including (1)H, (13)C NMR, MS and X-ray diffraction is provided.

Optical properties of two fluorene derived BODIPY molecular rotors as fluorescent ratiometric viscosity probes

BODIPY-derived molecular fluorescent rotors are one of the most useful families of fluorescent probes for the quantitative measurement of microviscosity. Here, we report the photophysical properties of two molecular rotors as ratiometric viscosity sensors, meso-(4-(9H-fluoren-2-yl)ethynyl)phenyl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (1) and meso-(5-(9H-fluoren-2-yl)ethynyl)thiophen-2-yl-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (2) having two independent chromophores; one (fluorene) is not influenced by viscosity and is used to determine concentration properties, and the other chromophore (BODIPY) acts as a molecular rotor. The fluorescence ratiometric calibration against microviscosity for the most sensitive probe (1), was obtained in a wide linear dynamic range. The sensitivity of the spectroscopic observables for 1 and 2 towards solvent viscosity and the typical analytical interfering solvent polarity and polarizability parameters were investigated by means of two different solvent scales, namely Lippert–Mataga and Catalan, finding consistent results. Quantum chemical calculations were conducted to analyze the probe mechanism in terms of Natural Transition Orbitals (NTOs) and the spatial extent of charge transfer excitations.

Experimental–Theoretical Approach to the Adsorption Mechanisms for Anionic, Cationic, and Zwitterionic Surfactants at the Calcite–Water Interface

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.

Hypervalent-iodine induced quasi-Favorskii C-ring contraction of 12-oxosteroids: A shortcut to C-norsteroids

Treatment of 12-oxosteroids with PhI(OAc)(2) and KOH in refluxing methanol triggers a quasi-Favorskii C-ring contraction leading to the corresponding 11α-alcoxycarbonyl-C-norsteroids in moderate yields. This constitutes the first one-step synthetic alternative to C-norsteroids starting from 12-oxosteroids.

Synthesis of 24-phenyl-24-oxo steroids derived from bile acids by palladium-catalyzed cross coupling with phenylboronic acid. NMR characterization and X-ray structures

Palladium-catalyzed cross coupling of phenyboronic acid with acetylated bile acids in which the carboxyl functions have been activated by formation of a mixed anhydride with pivalic anhydride afforded moderate to good yield of 24-phenyl-24-oxo-steroids. Unambiguous assignments of the NMR signals were made with the aid of combined 1D and 2D NMR techniques. X-ray diffraction studies confirmed the obtained structures.

Engineering organic semiconducting solids. Multicomponent access to crystalline 3-(4-aryl-1,2,3-triazolyl)coumarins

Crystalline 3-(4-aryl-1,2,3-triazol-1-yl)coumarins (ATCs) were prepared from commercial materials using a four-component methodology as a key step. In the present work, a feasible and environmentally friendly route to the title compounds was developed through the reaction between salicylaldehydes, ethyl bromoacetate, phenylacetylenes and sodium azide under mild conditions, with short reaction times and a simple workup. Crystalline solids are readily accessed from the featured products via solution processing and their arrays in the solid state were elucidated through SXRD; these molecules display a periodic overlap of π-systems, which facilitates carrier transport in organic electronic devices. Semiconductor band gaps for the obtained solids were derived through plane-wave DFT and compared with reference systems known to display superior performance in organic electronics. Thus ATCs represent attractive systems for research and implementation in molecular materials, a task which will be facilitated by the concise route herein described.

Synthesis, NMR Characterization and Crystal Structure of Methyl 3α,7α-Dihydroxy-12-oxo-5β-cholanate

The crystal structure and NMR characterization of methyl 3α,7α-dihydroxy-12-oxo-5β-cholanate are described. The title compound which was obtained from methyl cholanate in a 3-step synthetic sequence that does not alter the starting chirality, crystallizes in the monoclinic system with P 21 space group. While despite the substitution pattern rings A, B and C adopt chair conformations, the 5 membered D ring, that bears the side chain attached to C-17, shows a twisted conformation on C-13–C-14. In the crystal array, classical hydrogen bond interactions O–H···H and intermolecular contacts C–H···O of hydrogen bond type are observed.Graphical AbstractThe crystal structure and NMR characterization of Methyl α,7α-dihydroxy-12-oxo-5β-cholanate are described.

Downregulation of SnoN oncoprotein induced by antibiotics anisomycin and puromycin positively regulates transforming growth factor-β signals.

BACKGROUND SnoN and Ski proteins function as Smad transcriptional corepressors and are implicated in the regulation of diverse cellular processes such as proliferation, differentiation and transformation. Transforming growth factor-β (TGF-β) signaling causes SnoN and Ski protein degradation via proteasome with the participation of phosphorylated R-Smad proteins. Intriguingly, the antibiotics anisomycin (ANS) and puromycin (PURO) are also able to downregulate Ski and SnoN proteins via proteasome. METHODS We explored the effects of ANS and PURO on SnoN protein downregulation when the activity of TGF-β signaling was inhibited by using different pharmacological and non-pharmacological approaches, either by using specific TβRI inhibitors, overexpressing the inhibitory Smad7 protein, or knocking-down TβRI receptor or Smad2 by specific shRNAs. The outcome of SnoN and Ski downregulation induced by ANS or PURO on TGF-β signaling was also studied. RESULTS SnoN protein downregulation induced by ANS and PURO did not involve the induction of R-Smad phosphorylation but it was abrogated after TGF-β signaling inhibition; this effect occurred in a cell type-specific manner and independently of protein synthesis inhibition or any other ribotoxic effect. Intriguingly, antibiotics seem to require components of the TGF-β/Smad pathway to downregulate SnoN. In addition, SnoN protein downregulation induced by antibiotics favored gene transcription induced by TGF-β signaling. CONCLUSIONS ANS and PURO require TGF-β/Smad pathway to induce SnoN and Ski protein downregulation independently of inducing R-Smad2 phosphorylation, which facilitates TGF-β signaling. GENERAL SIGNIFICANCE Antibiotic analogs lacking ribotoxic effects are useful as pharmacological tools to study TGF-β signaling by controlling Ski and SnoN protein levels.

On the Brassard's rule of regioselectivity in Diels–Alder reactions between haloquinones and polar dienes

The [4 + 2] polar Diels–Alder reaction between nucleophilic dienes and haloquinones proceeds with remarkably high regioselectivity. In the present work, we simulated diene–dienophile bimolecular encounters in a model stoichiometric reaction between haloquinones and Brassards diene, using Monte Carlo sampling; the energetics of the stacking modes was then studied through DFT calculations. QTAIM analysis for the theoretical electron density was applied to describe contacts between π-systems, foreseeing chemically-productive paths for pre-cycloaddition assemblies associated with the experimental regioisomer. Upon thermally-triggered cycloaddition, Brassards rule of selectivity manifests: only certain stacked microstates consolidate asynchronously into cycloadducts. The halogen atom tunes electron density at the reactive centers, as confirmed by NMR and calculations. Unidimensional energy landscapes were derived to capture energetic profiles of the studied reaction. The model systems were synthesized with high regioselectivity, delving further into the role of halogen substituents.