Synthese und1H-NMR-spektroskopische Untersuchungen neuer Curcuminanaloga

Highly diastereoselective annulation of 2-substituted 3-nitro-2H-chromenes with hemicurcuminoids and curcuminoids via a double and triple Michael reaction cascade

The K2CO3-catalysed double Michael addition of (E)-1,5-diaryl- and 1-alkyl-5-arylpent-4-ene-1,3-diones to 2-trifluoromethyl- and 2-phenyl-substituted 3-nitro-2H-chromenes in dichloromethane at room temperature for 48 h results in 10-aroyl(acyl)-7-aryl-6a-nitro-6,6a,7,8,10,10a-hexahydro-9H-benzo[c]chromen-9-ones in 75-98% yields as individual...

Catalyst-free Tandem 1,3-Dipolar Cycloaddition/Aldol Condensation: Diastereoselective Construction of the Azatetraquinane Skeleton

The one-pot regioselective and diastereoselective method for the synthesis of 5-(het)aroyl-7-(het)arylhexahydrobenzo[4,5]pentaleno[1,6a-b](thia)pyrrolizine-6,12-diones from accessible 1,5-di(het)arylpent-4-ene-1,3-diones or curcuminoids in 38-98% yield was developed. This reaction proceeds as a sequence of 1,3-dipolar cycloaddition of azomethine ylide generated in situ from ninhydrin and (thia)proline at the C═C bond of corresponding enedione, followed by spontaneous intramolecular aldol condensation and leads to the formation of an azatetraquinane scaffold.

An expedient synthesis of novel spiro[indenoquinoxaline-pyrrolizidine]-pyrazole conjugates with anticancer activity from 1,5-diarylpent-4-ene-1,3-diones through the 1,3-dipolar cycloaddition/cyclocondensation sequence

A highly regio- and stereoselective two-stage route for the synthesis of spiro[indenoquinoxaline-pyrrolizidine]-pyrazole hybrids with anticancer activity has been developed.

Borondifluoride complexes of hemicurcuminoids as bio-inspired push-pull dyes for bioimaging

Hemicurcuminoids are based on half of the π-conjugated backbone of curcuminoids. The synthesis of a series of such systems and their borondifluoride complexes is described. The electrochemical and photophysical properties of difluorodioxaborine species were investigated as a function of the nature of electron donor and acceptor groups appended at either terminal positions of the molecular backbone. The emissive character of these dipolar dyes was attributed to an intraligand charge transfer process, leading to fluorescence emission that is strongly dependent on solvent polarity. Quasi-quantitative quenching of fluorescence in high polarity solvents was attributed to photoinduced electron transfer. These dyes were shown to behave as versatile fluorophores. Indeed, they display efficient two-photon excited fluorescence emission leading to high two-photon brightness values. Furthermore, they form nanoparticles in water whose fluorescence emission quantum yield is less than that of the dye in solution, owing to aggregation-induced fluorescence quenching. When cos7 living cells were exposed to these weakly-emitting nanoparticles, one- and two-photon excited fluorescence spectra showed a strong emission within the cytoplasm that originated from the individual molecules. Dye uptake thus involved a disaggregation mechanism at the cell membrane which restored fluorescence emission. This off-on fluorescence switching allows a selective optical monitoring of those molecules that do enter the cell, which offers improved sensitivity and selectivity of detection for bioimaging purposes.

Theoretical study on physicochemical properties of curcumin

Curcumin is a yellow-orange pigment, which has attracted considerable attention due to its wide spectrum of biological and pharmacological activities. In spite of much effort devoted on curcumin, there still exist some open questions concerning its fundamental physicochemical properties. The present study suggests that the DFT and TD-DFT calculations are useful to answer these questions. Firstly, the thermodynamic as well as spectral parameters support that curcumin exists predominantly in enol form in solution. Secondly, the calculated absorption spectra of curcumin anions provides direct evidence that the lowest pK(a) of curcumin corresponds to the dissociation of enolic proton, which not only reconciles the controversy on this topic, but also has important implications on the proton-transfer/dissociation-associated radical-scavenging mechanisms of curcumin.

Induced circular dichroism spectra reveal binding of the antiinflammatory curcumin to human alpha1-acid glycoprotein

This paper reports the first experimental evidence on binding of the plant derived curcumin molecule to human alpha1-acid glycoprotein (AGP), an acute phase protein in blood. Oppositely signed induced circular dichroism (CD) bands measured in the visible spectral region in pH7.4 phosphate buffer indicate that the protein binds this natural polyphenol molecule in a left-handed chiral conformation. Decreasing of the intrinsic fluorescence of AGP upon addition of curcumin confirmed the binding to take place. Fluorescence quenching titration curve of AGP allowed to calculate the association constant of the ligand (Ka = 4 x 10(4) M(-1)). Modification of near UV CD spectrum of the protein suggests that curcumin induces changes in the tertiary structure of AGP, which leads to the decrease of binding affinity. By using rac-warfarin and amitriptyline, selective high affinity ligands of F1-S and A genetic variants of AGP, CD displacement experiments showed that curcumin is able to bind to both variants. Molecular docking calculations performed on curcumin-AGP and warfarin-AGP complexes suggest the existence of two alternative binding sites for curcumin; either at the open end of the central hydrophobic cavity or in a surface cleft of the protein.

Solvatochromic correlations and ground- and excited-state dipole moments of curcuminoid dyes

Experimental dipole moments of curcumin (1) and of its parent compound dicinnamoylmethane (2) were determined in dioxane and benzene, respectively. Theoretical dipole moments were calculated using a combination of the PPP method (pi-moment) and a vector sum of the sigma-bond moments (sigma-moment) as well as by the ZINDO/1 method. Solvatochromic correlations were used to obtain the experimental first excited singlet-state dipole moments. The experimental electronic absorption spectra were compared with the calculated transitions.