Solvent-Dependent Structures of Natural Products Based on the Combined Use of DFT Calculations and 1H-NMR Chemical Shifts.

Detailed solvent and temperature effects on the experimental 1H-NMR chemical shifts of the natural products chrysophanol (1), emodin (2), and physcion (3) are reported for the investigation of hydrogen bonding, solvation and conformation effects in solution. Very small chemical shift of │Δδ│ < 0.3 ppm and temperature coefficients │Δδ/ΔΤ│ ≤ 2.1 ppb/K were observed in DMSO-d6, acetone-d6 and CDCl3 for the C(1)-OH and C(8)-OH groups which demonstrate that they are involved in a strong intramolecular hydrogen bond. On the contrary, large chemical shift differences of 5.23 ppm at 298 K and Δδ/ΔΤ values in the range of -5.3 to -19.1 ppb/K between DMSO-d6 and CDCl3 were observed for the C(3)-OH group which demonstrate that the solvation state of the hydroxyl proton is a key factor in determining the value of the chemical shift. DFT calculated 1H-NMR chemical shifts, using various functionals and basis sets, the conductor-like polarizable continuum model, and discrete solute-solvent hydrogen bond interactions, were found to be in very good agreement with the experimental 1H-NMR chemical shifts even with computationally less demanding level of theory. The 1H-NMR chemical shifts of the OH groups which participate in intramolecular hydrogen bond are dependent on the conformational state of substituents and, thus, can be used as molecular sensors in conformational analysis. When the X-ray structures of chrysophanol (1), emodin (2), and physcion (3) were used as input geometries, the DFT-calculated 1H-NMR chemical shifts were shown to strongly deviate from the experimental chemical shifts and no functional dependence could be obtained. Comparison of the most important intramolecular data of the DFT calculated and the X-ray structures demonstrate significant differences for distances involving hydrogen atoms, most notably the intramolecular hydrogen bond O-H and C-H bond lengths which deviate by 0.152 tο 0.132 Å and 0.133 to 0.100 Å, respectively, in the two structural methods. Further differences were observed in the conformation of -OH, -CH3, and -OCH3 substituents.

A novel strategy for phosphopeptide enrichment using lanthanide phosphate co-precipitation.

Reversible phosphorylation of proteins is a common theme in the regulation of important cellular functions such as growth, metabolism, and differentiation. The comprehensive understanding of biological processes requires the characterization of protein phosphorylation at the molecular level. Although, the number of cellular phosphoproteins is relatively high, the phosphorylated residues themselves are generally of low abundance due to the sub-stoichiometric nature. However, low abundance of phosphopeptides and low degree of phosphorylation typically necessitates isolation and concentration of phosphopeptides prior to mass spectrometric analysis. In this study, we used trivalent lanthanide ions (LaCl(3), CeCl(3), EuCl(3), TbCl(3), HoCl(3), ErCl(3), and TmCl(3)) for phosphopeptide enrichment and cleaning-up. Due to their low solubility product, lanthanide ions form stable complexes with the phosphate groups of phosphopeptides and precipitate out of solution. In a further step, non-phosphorylated compounds can easily be removed by simple centrifugation and washing before mass spectrometric analysis using Matrix-assisted laser desorption/ionisation-time of flight. The precipitation method was applied for the isolation of phosphopeptides from standard proteins such as ovalbumin, α-casein, and ß-casein. High enrichment of phosphopeptides could also be achieved for real samples such as fresh milk and egg white. The technology presented here represents an excellent and highly selective tool for phosphopeptide recovery; it is easily applicable and shows several advantages as compared with standard approaches such as TiO(2) or IMAC.

In vitro and computational studies on the antiglycation activity of compounds isolated from antidiabetic Tetracera alnifolia stem bark.

The continuous search for new compounds in natural-based plants is a promising strategy for the prevention of diseases. This work examined antiglycation activity compounds isolated from the antidiabetic extract of T. alnifolia stem bark via in vitro and computational [molecular dynamics (MD)] approach. Phytochemical investigation of ethyl acetate fraction and the application of spectroscopic methods led to the isolation and elucidation of 3 compounds: quercetin (1), kaempferol (2), and gallic acid (3). Compounds 1, 2 and 3 were then screened for antioxidant and antiglycation activities. Results show that the ethanol extract of T. alnifolia demonstrated good antioxidant activity compared to the standard gallic acid. There was a significant reduction in fasting blood glucose level progressively in diabetic rats, for 21 days compared to diabetic control. Consequently, the antiglycation activity of ethyl acetate fraction had the highest antiglycation activities, followed by dichloromethane (DCM) fraction. Compounds isolated from ethyl acetate fraction, exhibited the highest antiglycation effect for kaempferol followed by quercetin, while gallic acid had the least antiglycation effect. The root mean square of deviation (RMSD) and MM/GBSA energies obtained from molecular dynamics agree with the in vitro antiglycation activity with the sequence of structural stability in the order; kaempferol > quercetin > gallic acid. Therefore, findings from these results suggest that compounds isolated from T. alnifolia possess antiglycation activity.Communicated by Ramaswamy H. Sarma.

Protection of CCl4-Induced Liver and Kidney Damage by Phenolic Compounds in Leaf Extracts of Cnestis ferruginea (de Candolle).

BACKGROUND: The chemoprevention of chemically-induced hepatotoxicity is a crucial means of minimizing susceptibility to hepatic carcinogenesis and plants remain a rich source of anti-hepatotoxicants with antioxidant properties. OBJECTIVE: The protective role of defatted-methanol (MECF) and ethyl acetate fractions (EF), obtained from Leaves of Cnestis ferruginea in rats induced with carbon tetrachloride (CCl4) toxicity was investigated. MATERIALS AND METHODS: Adult male Wistar rats were orally administered MECF or EF (125 - 500 mg/kg bwt/5mL) or silymarin (25 mg/kg bwt/5 mL) separately for three days before intervention with an intraperitoneal dose of CCl4. Biomarkers of liver and kidney toxicity as well as Ca(2+) regulation were evaluated. RESULTS: Pre-treatment with MECF and EF significantly (P < 0.05) decreased the activities of serum alanine and aspartate aminotransferases, levels of urea, creatinine and cholesterol. A significantly (P < 0.05) enhanced Ca(2+) -ATPase activity and lowered levels of membrane cholesterol: Phospholipid ratio were observed in liver microsomes of pre-treated as compared to CCl4 -only treated rats. Rat liver superoxide dismutase activity was enhanced by 125 mg/kg and 250 mg/kg of EF and MECF, while decreases were observed at 500 mg/kg. MECF and EF, like silymarin, attenuated CCl4 -induced hepatotoxicity, microsomal membrane Ca(2+) -ATPase inactivation and renal dysfunction. Phytochemistry of MECF revealed the presence of anthraquinones, cardiac and flavone glycosides, tannins and trihydroxyl phenol. CONCLUSION: These findings suggest that the mechanism of hepatoprotection elicited by MECF and EF, involve its antioxidative properties and regulation of Ca(2+) homeostasis.

Iridoid glycoside from the leaves of Clerodendrum volubile beauv. shows potent antioxidant activity against oxidative stress in rat brain and hepatic tissues.

AIM: This study aims at reporting the isolation, structure elucidation, and antioxidant potentials of ajugoside from C. volubile leaves in sodium nitroprusside (SNP)-induced oxidative stressed rat brain and hepatic tissues. MATERIALS AND METHOD: An iridoid monoterpene, ajugoside was isolated from the n-butanol fraction of C. volubile and evaluated for its antioxidant protective potential on brain and liver tissues of male Wister rats in an ex vivo model. Two molar concentrations (6.4 × 10(-4) M and 1.28 × 10(-3) M) of the metabolite and SNP were incubated with the tissues homogenate at 37°C for 2 hr prior to the test and assayed for catalase, superoxide dismutase (SOD) activities, and lipid peroxidation. α tocopherol (6.4 × 10(-4) M) was used as standard. RESULTS: Both molar concentrations exhibited high catalase activity in the tissues. However, 6.4 × 10(-4) M ajugoside exhibited a very high SOD activity (liver: 96.45 and brain: 96.30%) and inhibition of lipid peroxidation (liver: 88.11 and brain: 93.27%) compared to the standard. 1.28 × 10(-3) M ajugoside also exhibited good activities but lower than that of the standard and 6.4 × 10(-4) M ajugoside. DISCUSSION AND CONCLUSION: Ajugoside showed potent antioxidant activities as evidenced by the synergistic high activities of SOD and catalase as well as inhibition of lipid peroxidation in the studied tissues.

New cholinesterase inhibiting bisbenzylisoquinoline alkaloids from Cocculus pendulus.

Phytochemical investigation on Cocculus pendulus (J. R. & G. FORST.) resulted in the isolation of two new and three known bisbenzylisoquinoline alkaloids. The structures of the new alkaloids, kurramine-2'-beta-N-oxide (1) and kurramine-2'-alpha-N-oxide (2), were elucidated with the help of spectroscopic techniques. The cholinesterase inhibitory activities of these bisbenzylisoquinoline alkaloids are reported here for the first time.

Synthesis of coumarin derivatives with cytotoxic, antibacterial and antifungal activity.

The synthesis and selective biological screening of 7-hydroxy-4-methyl-2H-chromen-2-one (2), 7-hydroxy-4,5-dimethyl-2H-chromen-2-one (15) and some of their derivatives were carried out. Compound 13 was found to be most potent cytotoxic agent with LD50 = 126.69 microg/ml. In antibacterial assay the compounds showed a broad spectrum of activities. Compound 11 exhibited a very high degree of plant growth inhibition at three levels of concentration. Compound 4 showed very promising antifungal activity against Candida albicans. Compounds 12 and 13 demonstrated excellent antioxidant activity.