Ana M. Cuadro

A V-shaped cationic dye for nonlinear optical bioimaging

A symmetric cationic molecule with D-π-A(+)-π-D architecture was synthesized with high two-photon absorption cross-section (σ(2) ≈ 1140 GM). Application as a marker in fluorescence microscopy of living cells revealed its presence inside the cell staining vesicular shape organelles in the cytoplasm. Fluorescence lifetime imaging microscopy shows that it is also able to penetrate within the nucleus.

Ring-Closing Metathesis Reactions on Azinium Salts: Straightforward Access to Quinolizinium Cations and Their Dihydro Derivatives

The ring-closing metathesis reaction of 1-butenyl-2-vinylpyridinium salts and 2-butenyl-1-vinylpyridinium salts using Grubbs second generation and Hoveyda-Grubbs catalysts proved to be an efficient approach to 3,4-dihydro- and 1,2-dihydroquinolizinium salts and the corresponding quinolizinium derivatives by an improved thermal oxidation in the presence of Pd/C without solvent. A comparative study showed that the quinolizinium system was obtained in better yields through the 3,4-dihydroquinolizinium route, thus allowing the synthesis of quinolizinium derivatives or improvements in the yields of some examples reported previously.

Synthesis of N- (Aminoethyl) Azoles Under Phase Transfer Catalysis

Abstract A convenient procedure is reported for the N-alkylation of azoles with 2-chloroethylamine under phase-transfer catalysis conditions.

Donor-(π-bridge)-azinium as D-π-A+ one-dimensional and D-π-A+-π-D multidimensional V-shaped chromophores

Heteroaromatic cations reacted with N-heteroarylacetylenes under Sonogashira conditions to allow easy access to potential single donor D-π-A(+) and V-shaped D-π-A(+)-π-D chromophores, where the acceptor moiety A is the π-deficient pyridinium cation and the donor moiety is represented by different π-excessive N-heterocycles. The β hyperpolarizabilities were measured using hyper-Rayleigh scattering experiments and the experimental data are supported by a theoretical analysis that combines a variety of computational procedures, including Density Functional Theory (DFT) and correlated Hartree-Fock-based methods (RCIS(D)).

Synthesis and biological evaluation of 2,6-di-tert-butylphenol hydrazones as 5-lipoxygenase inhibitors

Abstract The preparation of hydrazone derivatives of 3,5-di- tert -butyl-4-hydroxybenzaldehyde and the inhibition of 5-lipoxygenase (5-LO) by these compounds is discussed.

Synthesis of highly stabilised ylides from N- [2- (1,3-benzazolylmethyl)]pyridinium salts

Abstract A series of new stable ylides has been synthesized by the reaction of N-[2-(1,3-benzazolylmethyl)]-pyridinium salts with electrophiles such as carbon disulphide, isothiocyanate derivatives, phenylisocyanate and benzoyl chloride in a two-phase system. Preparation of pyridinium ketene dithioacetal derivatives and attempts to transform them into N-(diheteroarylmethyl)pyridinium ylides are also described.

Nonlinear emission of quinolizinium-based dyes with application in fluorescence lifetime imaging.

Charged molecules based on the quinolizinum cation have potential applications as labels in fluorescence imaging in biological media under nonlinear excitation. A systematic study of the linear and nonlinear photophysics of derivatives of the quinolizinum cation substituted by either dimethylaniline or methoxyphenyl electron donors is performed. The effects of donor strength, conjugation length, and symmetry in the two-photon emission efficiency are analyzed in detail. The best performing nonlinear fluorophore, with two-photon absorption cross sections of 1140 GM and an emission quantum yield of 0.22, is characterized by a symmetric D-π-A(+)-π-D architecture based on the methoxyphenyl substituent. Application of this molecule as a fluorescent marker in optical microscopy of living cells revealed that, under favorable conditions, the fluorophore can be localized in the cytoplasmatic compartment of the cell, staining vesicular shape organelles. At higher dye concentrations and longer staining times, the fluorophore can also penetrate into the nucleus. The nonlinearly excited fluorescence lifetime imaging shows that the fluorophore lifetime is sensitive to its location in the different cell compartments. Using fluorescence lifetime microscopy, a multicolor map of the cell is drafted with a single dye.

New route to pyrido[1,2-b]pyridazinium inner salts. Evidence of a 1,3-dipolar cycloaddition-ring expansion process

We wish to express our thanks to the Comision Interministerial de Ciencia y Tecnologia (CICYT, project PM97-004) and to the Ministerio de Educacion y Ciencia for a grant to one of us (J.V.M).2-Alkoxycarbonylpyridinium N-aminides behave as 1,3-dipoles when reacted with Michael acceptors, giving rise to the corresponding cycloadducts which, depending on their regioisomeric nature, subsequently undergo a ring expansion to give pyrido[1,2-b]pyridazinium inner salts.

2-Alkoxycarbonylcycloimmonium ylides, efficient 1,4-dipole equivalents in the synthesis of new conjugated betaines

We wish to express our thanks to the Comision Interministerial de Ciencia y Tecnologia (CICYT ) for financial support (Project PB90-0284), and to the Ministerio de Educacion y Ciencia by a grant to one of us (A.M.C)

Efficient synthesis of an indoloquinolizinium alkaloid selective DNA-binder by ring-closing metathesis.

Two total syntheses of the indolo[2,3-a]quinolizinium cation have been accomplished through the application of two ring-closing metathesis reactions to form the pyridinium ring. One of these approaches provides the tetracyclic cation in only five steps from commercially available harmane. Fluorescence-based thermal denaturation experiments, as well as spectrofluorimetric titration, circular dichroism measurements, and theoretical simulations, showed a consistent DNA-binding capacity by intercalation with a marked preference for AT-rich sequences.