Angel Alvarez-Larena

Design, selection, and characterization of thioflavin-based intercalation compounds with metal chelating properties for application in Alzheimer's disease.

Metal chelation is considered a rational therapeutic approach for interdicting Alzheimers amyloid pathogenesis. At present, enhancing the targeting and efficacy of metal-ion chelating agents through ligand design is a main strategy in the development of the next generation of metal chelators. Inspired by the traditional dye Thioflavin-T, we have designed new multifunctional molecules that contain both amyloid binding and metal chelating properties. In silico techniques have enabled us to identify commercial compounds that enclose the designed molecular framework (M1), include potential antioxidant properties, facilitate the formation of iodine-labeled derivatives, and can be permeable through the blood-brain barrier. Iodination reactions of the selected compounds, 2-(2-hydroxyphenyl)benzoxazole (HBX), 2-(2-hydroxyphenyl)benzothiazole (HBT), and 2-(2-aminophenyl)-1H-benzimidazole (BM), have led to the corresponding iodinated derivatives HBXI, HBTI, and BMI, which have been characterized by X-ray diffraction. The chelating properties of the latter compounds toward Cu(II) and Zn(II) have been examined in the solid phase and in solution. The acidity constants of HBXI, HBTI, and BMI and the formation constants of the corresponding ML and ML2 complexes [M = Cu(II), Zn(II)] have been determined by UV-vis pH titrations. The calculated values for the overall formation constants for the ML2 complexes indicate the suitability of the HBXI, HBTI, and BMI ligands for sequestering Cu(II) and Zn(II) metal ions present in freshly prepared solutions of beta-amyloid (Abeta) peptide. This was confirmed by Abeta aggregation studies showing that these compounds are able to arrest the metal-promoted increase in amyloid fibril buildup. The fluorescence features of HBX, HBT, BM, and the corresponding iodinated derivatives, together with fluorescence microscopy studies on two types of pregrown fibrils, have shown that HBX and HBT compounds could behave as potential markers for the presence of amyloid fibrils, whereas HBXI and HBTI may be especially suitable for radioisotopic detection of Abeta deposits. Taken together, the results reported in this work show the potential of new multifunctional thioflavin-based chelating agents as Alzheimers disease therapeutics.

Ruthenium(II) complexes containing both arene and functionalized phosphines. Synthesis and catalytic activity for the hydrogenation of styrene and phenylacetylene

Abstract The [RuCl2(η6-arene)]2 complex reacts with PPh2R (R=H, Py, CH2Py, CCPh, CCtBu and CCp-Tol) ligands in CH2Cl2 to give neutral P-coordinated ruthenium(II) complexes [RuCl2(p-cymene)PPh2R]. The structure of [RuCl2(p-cymene)PPh2H] and [RuCl2(p-cymene)PPh2Py] complexes has been established by X-ray diffraction. The neutral P-coordinated complexes [RuCl2(p-cymene)PPh2Py] and [RuCl2(p-cymene)PPh2CH2Py] react with NaBF4 in CH2Cl2–MeOH mixture to give [RuCl(η6-p-cymene)PPh2Py]BF4 and [RuCl(η6-p-cymene)PPh2CH2Py]BF4 complexes, in which PPh2Py and PPh2CH2Py act as bidentate ligands. The structure of [RuCl(η6-p-cymene)PPh2Py]BF4 was determined by X-ray diffraction. The reaction of [RuCl2(η6-arene)]2 with PPh2CCPPh2 led to the [RuCl2(p-cymene)]2PPh2CCPPh2 complex, in which the diphosphine ligand bridges two [RuCl2(p-cymene)] units. [RuCl2(p-cymene)PPh2Py] and [RuCl(η6-p-cymene)PPh2Py]BF4 are suitable catalyst precursors for the hydrogenation of styrene and phenylacetylene.

Crystal structure of thioflavin-T and its binding to amyloid fibrils: insights at the molecular level

Combining X-ray data on thioflavin-T and theoretical calculations on its binding to a peptide model for Abeta(1-42) fibrils gives evidence of main stabilizing interactions, which influence the dihedral angle between the two moieties of thioflavin-T and thereby its fluorescence properties; these results shed new light on possible strategies for the design of dyes to bind amyloid fibrils more specifically.

Enantioselective synthetic approaches to cyclopropane and cyclobutane β-amino acids: synthesis and structural study of a conformationally constrained β-dipeptide

Abstract Synthetic approaches to carbocyclic compounds, namely cyclopropane and cyclobutane β-amino acids, are presented. One of them is based on enzymatic desymmetrization of meso diesters, leading to the enantioselective production of cis-hemiesters, which afforded β-amino acids through Curtius rearrangements. The enantiomeric excess for the cyclobutane derivatives was 91% whereas the cyclopropanes were obtained in 63% ee. According to another strategy, an enantiomerically pure cyclopropane trans-β-amino acid, bearing a quaternary center, has been synthesized from a homochiral precursor easily available from d -glyceraldehyde. The preparation and structural investigation of the first synthesized cyclobutane containing dipeptide is also described. A hairpin-like conformation of this molecule in the solid state has been demonstrated by X-ray structural analysis, showing crystal packing induced by the presence of the rigid cyclobutane moiety and the formation of intermolecular hydrogen bonds. NMR experiments confirmed that these molecules also tend to produce aggregates in solution. On the contrary, theoretical calculations suggest that intramolecular interactions are important in the gas phase, as expected.

An Alternative to the Classical α‐Arylation: The Transfer of an Intact 2‐Iodoaryl from ArI(O2CCF3)2

The α-arylation of carbonyl compounds is generally accomplished under basic conditions, both under metal catalysis and via aryl transfer from the diaryl λ(3)-iodanes. Here, we describe an alternative metal-free α-arylation using ArI(O2CCF3)2 as the source of a 2-iodoaryl group. The reaction is applicable to activated ketones, such as α-cyanoketones, and works with substituted aryliodanes. This formal C-H functionalization reaction is thought to proceed through a [3,3] rearrangement of an iodonium enolate. The final α-(2-iodoaryl)ketones are versatile synthetic building blocks.

Cobalt(II) complexes with pyrazole-derived ligands: crystal structure of {bis[3-phenyl-5-(2-pyridyl) pyrazole]aquachlorocobalt(II)}chloride monohydrate

Abstract The synthesis of the new pyrazole-derived ligands 3-phenyl-5-(2-pyridyl) pyrazole (HL0) and 3-phenyl-5-(6-methyl-(2-pyridyl))pyrazole (HL1) and their Co(II) complexes is reported. Elemental analyses, conductivity measurements and IR and UV–Vis spectroscopies defined all complexes. 1H and 13C NMR spectroscopies were also used in the characterization of ligands. The crystal and molecular structures of [Co(HL0)2Cl(H2O)]Cl·H2O, consisting of discrete ions and water molecules linked by hydrogen bonds, are also reported. The hexacoordinated metal atom is bonded to two pyridinic nitrogens, two pyrazolic nitrogens (one of each nitrogen belonging to two different ligands), one chlorine atom and one water molecule, forming a distorted octahedral environment. The ligands are not exactly planar and the arrangement of ligands is cis, with a dihedral angle between the two mean planes of ligands of 89.21(6)°. The degree of distortion from regular octahedral geometry is compared to that of closely related structures.

Camphor-derived alcohols as chiral auxiliaries for asymmetric Pauson-Khand bicyclizations. Enantioselective synthesis of α-methoxyenones

Abstract The intramolecular Pauson-Khand reaction of enol and ynol ethers of Oppolzers camphor-derived neopentyloxy alcohols is described. Bicyclic products are obtained in yields of up to 65% and with diastereoselectivities as high as 94:6 under very mild reaction conditions. The absolute configurations of the major stereoisomers obtained when (1R, 2S, 3R, 4S)-3-neopentyloxy-1,7,7-trimethylbicyclo- [2.2.1]heptan-2-ol is used as a chiral auxiliary are rationalized on the basis of the theoretically predicted preferential conformations of model precursors. A simple procedure for obtaining auxiliary-free, enantiopure bicyclic α-methoxyenones is also presented.

Chemical Modulation of Peptoids: Synthesis and Conformational Studies on Partially Constrained Derivatives

The high conformational flexibility of peptoids can generate problems in biomolecular selectivity as a result of undesired off-target interactions. This drawback can be counterbalanced by restricting the original flexibility to a certain extent, thus leading to new peptidomimetics. By starting from the structure of an active peptoid as an apoptosis inhibitor, we designed two families of peptidomimetics that bear either 7-substituted perhydro-1,4-diazepine-2,5-dione 2 or 3-substituted 1,4-piperazine-2,5-dione 3 moieties. We report an efficient, solid-phase-based synthesis for both peptidomimetic families 2 and 3 from a common intermediate. An NMR spectroscopic study of 2a,b and 3a,b showed two species in solution in different solvents that interconvert slowly on the NMR timescale. The cis/trans isomerization around the exocyclic tertiary amide bond is responsible for this conformational behavior. The cis isomers are more favored in nonpolar environments, and this preference is higher for the six-membered-ring derivative 3a,b. We propose that the hydrogen-bonding pattern could play an important role in the cis/trans equilibrium process. These hydrogen bonds were characterized in solution, in the solid state (i.e., by using X-ray studies), and by molecular modeling of simplified systems. A comparative study of a model peptoid 10 containing the isolated tertiary amide bond under study outlined the importance of the heterocyclic moiety for the prevalence of the cis configuration in 2a and 3a. The kinetics of the cis/trans interconversion in 2a, 3a, and 10 was also studied by variable-temperature NMR spectroscopic analysis. The full line-shape analysis of the NMR spectra of 10 revealed negligible entropic contribution to the energetic barrier in this conformational process. A theoretical analysis of 10 supported the results observed by NMR spectroscopic analysis. Overall, these results are relevant for the study of the peptidomimetic/biological-target interactions.

Synthesis and structural characterisation of new binuclear Pd(II) complexes with both bridging and terminal pyrazolate ligands

Abstract Dinuclear pyrazolato-bridged Pd(II) complexes Pd2L40 and Pd2L41 have been prepared by reacting Pd(Ac)2 and one equivalent of HL0 (3-phenyl-5-(2-pyridyl)pyrazole) or HL1 (3-phenyl-5-(6-methyl-(2-pyridyl))pyrazole. The new complexes have been characterised by elemental analyses, IR, 1H NMR and in the case of PdL14 by single crystal X-ray diffraction methods. This structure shows two palladium atoms bridged by two L1 ligands. The square-planar geometry of each Pd atom is completed by a bidentate chelating L1 ligand. The six-membered dipalladacycle formed by the two Pd atoms and the two bridging pyrazolato ligands adopts a distorted boat-like conformation.

The formation of [RuCl(p-cymene)(Me2HPz)(PPh2OR)]Cl (Me2HPz=3, 5-dimethylpyrazole; R=H, Me and p-Tol) complexes from the cleavage of the P-N bond of a P-coordinated P(Me2Pz)Ph2 ligand by ROH molecules in a ruthenium(II) complex. Crystal structure of [RuCl(p-cymene)(Me2HPz)(PPh2OH)]Cl

Abstract The complex [RuCl2(p-cymene)]2 reacts with 1-(3,5-dimethyl)pyrazolyldiphenylphosphine (P(Me2Pz)Ph2) to give the complex RuCl2(p-cymene)(P(Me2Pz)Ph2). This compound reacts with ROH molecules (R=H, Me and p-Tol) to give [RuCl(p-cymene)(Me2HPz)(PPh2OR)]Cl (R=H, Me and p-Tol) complexes, which contain both Me2HPz and PPh2OR coordinated molecules.