Expanding the potential of chiral chromatography for high-throughput screening of large compound libraries by means of sub-2µm Whelk-O 1 stationary phase in supercritical fluid conditions.

With the aim of exploring the potential of ultra-fast chiral chromatography for high-throughput analysis, the new sub-2 micron Whelk-O 1 chiral stationary phase (CSP) has been employed in supercritical fluid conditions to screen 129 racemates, mainly of pharmaceutical interest. By using a 5-cm long column (0.46cm internal diameter), a single co-solvent (MeOH) and a 7-min gradient elution, 85% of acidic and neutral analytes considered in this work have been successfully resolved, with resolution (Rs) larger than 2 in more than 65% of cases. Moreover, almost a half of basic samples that, for their own characteristics, are known to be difficult to separate on Whelk-O 1 CSP, have shown Rs greater than 0.3. The screening of the entire library could be accomplished in less than 24h (single run) with 63% of positive score. For well-resolved enantiomers (Rs roughly included between 1 and 3), we show that method transfer from gradient to isocratic conditions is straightforward. In many cases, isocratic ultra-fast separations (with analysis time smaller than 60s) have been achieved by simply employing, as isocratic mobile phase, the eluent composition at which the second enantiomer was eluted in gradient mode. By considering the extension and variety of the library in terms of chemico-physical and structural properties of compounds and numerousness, we believe that this work demonstrates the real potential of the technique for high-throughput enantioselective screening.

Synthesis, antimicrobial and anti-biofilm activities of novel Schiff base analogues derived from methyl-12-aminooctadec-9-enoate.

A novel library of Schiff base analogues (5a-q) were synthesized by the condensation of methyl-12-aminooctadec-9-enoate and different substituted aromatic aldehydes. The synthesized compounds were thoroughly characterized by spectroscopic techniques (FT-IR, (1)H NMR, (13)C NMR, ESI-MS and HRMS). The Schiff base analogues with different substitutions were screened for in vitro antibacterial activity against 7 different bacterial strains. Among these, the compounds with electron withdrawing substituent, namely chlorine (5a) and electron donating substituents, namely hydroxy (5 n) and methoxy (5 o), were found to exhibit excellent to good antimicrobial activities (MIC value 9-18 µM) against Staphylococcus aureus MTCC 96, Staphylococcus aureus MLS-16 MTCC 2940 and Bacillus subtilis MTCC 121. The products were also screened for anti-biofilm and MBC (Minimum Bactericidal Concentration) activities which exhibited promising activities.

N-benzoate-N' salicylaldehyde ethynelediamine: a new fluorescent sensor for Zn2+ ion by "off-on" mode.

Imbalance of zinc ion (Zn(2+)) in human body causes diseases like Alzheimer's and Parkinson's and therefore Zn(2+) estimation in biological fluids has diagnostic values. Fluorescence "off-on" sensors have advantages of high sensitivity and in situ application over other sensors. A new fluorescent "off-on" Zn(2+) sensor, N-benzoate-N' salicylaldehyde ethynelediamine (L), has been synthesisied. In 1:1(v/v) CH3OH:PBS (PBS = phosphate buffer solution), L shows ca. 20 times enhancement in fluorescence intensity on interaction with Zn(2+), due to snapping of photoinduced electron transfer (PET) process, which is selective over metal ions - Na(+), K(+), Ca(2+), Ni(2+), Cu(2+), Cd(2+), Hg(2+) and Pb(2+). These metal ions either individually or all together does not interfere the sensing ability of L towards Zn(2+). A 1:1 interaction between L and Zn(2+) ion with binding constant 10(4.25) has been established from spectroscopic data.

A convenient method for the enantiomeric separation of α-amino acid esters as benzophenone imine Schiff base derivatives.

A convenient liquid chromatographic method for the separation of α-amino acid esters as benzophenone Schiff base derivatives on coated chiral stationary phases (CSPs) (Chiralcel OD-H, Chiralcel OD, Chiralpak AD-H, Chiralpak AD, and Chiralpak AS) or covalently immobilized CSPs (Chiralpak IA, Chiralpak IB, and Chiralpak IC) derived from polysaccharide derivatives is described. Benzophenone imine derivatives of α-amino acid esters were readily prepared by stirring benzophenone imine and the hydrochloride salts of α-amino acid esters in 2-propanol. The chromatographic separations were conducted at a flow rate 1.0 mL/min and a detection wavelength of 254 nm; 0.5% 2-propanol/hexane (v/v) was used on CSPs. In general, the resolution of Chiralpak IC was superior to those of the other CSPs. In addition, the resolutions of other arylimine derivatives of α-amino acid esters and the effects of different mobile phases on the enantiomeric separation of α-amino acid esters as benzophenone imine derivatives on Chiralpak IC were investigated.

Development of a chemical strategy to produce rare aldohexoses from ketohexoses using 2-aminopyridine.

Rare sugars are monosaccharides that are found in relatively low abundance in nature. Herein, we describe a strategy for producing rare aldohexoses from ketohexoses using the classical Lobry de Bruyn-Alberda van Ekenstein transformation. Upon Schiff-base formation of keto sugars, a fluorescence-labeling reagent, 2-aminopyridine (2-AP), was used. While acting as a base catalyst, 2-AP efficiently promoted the ketose-to-aldose transformation, and acting as a Schiff-base reagent, it effectively froze the ketose-aldose equilibrium. We could also separate a mixture of Sor, Gul, and Ido in their Schiff-base forms using a normal-phase HPLC separation system. Although Gul and Ido represent the most unstable aldohexoses, our method provides a practical way to rapidly obtain these rare aldohexoses as needed.

Oxidovanadium(IV) Schiff base complex derived from vitamin B6: synthesis, characterization, and insulin enhancing properties.

A new Schiff base, [H(4)pydmedpt](2+)·2Cl(-), derived from one of the forms of vitamin B(6) has been synthesized by condensation of pyridoxal hydrochloride with N,N-bis[3-aminopropyl]-methylamine (medpt) and characterized by analytical and spectroscopic methods. The molecular structure is calculated by density functional theory (DFT) procedures, and the donor properties of each individual donor atom are evaluated by calculation of the Fukui function. One pot reaction of pyridoxal and medpt with vanadyl acetylacetonate yields the brown complex [V(IV)O(H(2)pydmedpt)](2+)·2Cl(-)1, which upon recrystallization from water crystallizes as [V(IV)O(pydmedpt)]·5H(2)O 2. The compounds are characterized by analytical and spectroscopic methods, 2 being also characterized by single crystal X-ray diffraction. It displays a slightly distorted octahedral geometry around the vanadium atom involving the coordination of N(amine), two N(imine), and O(phenolato) donors of the ligand. One of the phenolato oxygen donors is positioned trans to the terminal O-oxido atom with relatively short V-O(phenolate) {2.041(3) Å} and long V-O(oxido) {1.625(4) Å} bond distances when compared to other known compounds. The two different pK(a) values (6.0 and 7.9) obtained for 1 are due to protonation of the pyridine ring nitrogen atoms having different basic characters, this being also substantiated by theoretical calculation of the proton affinity of the O- and N- atoms of the molecule. The spin Hamiltonian parameters are obtained from the electron paramagnetic resonance (EPR) spectra, but the A(z) value (ca. 155 × 10(-4) cm(-1)) is lower than expected by applying the additivity rule for the present set of equatorial donor atoms (ca. 162-163 × 10(-4) cm(-1)), this being attributed to the strong trans V-O(phenolate) bond. The UV-vis transitions and EPR spectral parameters are calculated by DFT procedures, and both the calculated electronic transitions and the hyperfine coupling constants agree well with those experimentally observed. The inhibitory effect of 1 on FFA release and % glucose uptake determined with isolated rat adipocyte cells gave IC(50) and EC(50) values lower than for V(IV)OSO(4) and of the same order of magnitude of other reported insulin enhancing vanadium compounds.

Identification of AGE-precursors and AGE formation in glycation-induced BSA peptides.

The glycation of BSA leads to protein/peptide modifications that result in the formation of AGEs. AGEs react with the amino groups of N-terminal amino acid residues, particularly arginine and lysine residues. Enhanced AGE formation exists in the blood and tissues of diabetics, as well as in aging and other disorders. The Identification of AGEs is of great importance. Mass spectrometry has been applied to identify and structurally elucidate AGEs. Here, we report on the identification of AGE- peptides and AGE-precursors based on relative mass changes as a result of specific AGE formation. HPLC-ESIMS, ESI-MS/MS, and the Mascot database were used. The relative mass changes due to the specific type of AGE formation were added to the identified peptides followed by a manual search of the glycated samples, which resulted in the identification of seven peptides for the formation of five AGEs, namely CML, pyrraline, imidazolone A, imidazolone B, and AFGP. Four glycated peptides (FPK, ECCDKPLLEK, IETMR, and HLVDEPQNLIK) were identified in the formation of AGE-precursors.

First synthesis and isolation of the E- and Z-isomers of some new Schiff bases. Reactions of 6-azido-5-formyl-2-pyridone with aromatic amines.

Some novel Schiff bases have been prepared by reacting 6-azido-5-formyl-2-pyridone 1 with a series of aromatic amines 2a-f. 5-Arylaminomethylene-6-(E)-aryl-iminopyridones 3a-e were obtained by reaction of 1 with 2a-e at room temperature, whereas with 2f, the 6-azido-5-naphthalen-2-yl-iminomethylpyridone derivative 4 was formed. On the other hand, heating 1 with 2a-d at 140-150 degrees C yielded two sets of isomeric products, (E)-3a-d and (Z)-5a-d. Refluxing compounds (Z)-3a,c with hydroxyl-amine in methanol gave the corresponding hydroxyliminopyridones 8a,c. Heating of (E)-3a-d with excess POCl3 at reflux did not give the expected tricyclic compound 9, but rather the isomeric products (Z)-5a-d were obtained. The structures of all these products have been characterized using IR and 1H- and 13C-NMR spectroscopy.

Blue and ultraviolet light-absorbing opsin from the retinal pigment epithelium.

The retinal pigment epithelium (RPE) contains an abundant opsin that is distinct from rhodopsin and cone visual pigments and is able to bind the retinaldehyde chromophore. The putative retinal G protein-coupled receptor (RGR) was isolated in digitonin solution from bovine RPE microsomes and copurified consistently with a minor 34-kDa protein. The absorption spectrum of RGR revealed endogenous pH-sensitive absorbance in the blue and near-ultraviolet regions of light. Membrane-bound RGR was incubated with exogenously added all-trans-retinal and formed two long-lived pH-dependent photopigments with absorption maxima of 469 +/- 2.4 and 370 +/- 7.3 nm. The effects of hydrogen ion concentration suggest that the blue and near-UV photopigments are tautomeric forms of RGR, in which an all-trans-retinal Schiff base is protonated or unprotonated, respectively. The RPE pigment was also demonstrable by its reactivity to hydroxylamine in the dark. The retinaldehyde-RGR conjugate at neutral pH favors the near-UV pigment and is a novel light-absorbing opsin in the vertebrate eye.