Variable-temperature ¹H-NMR studies on two C-glycosylflavones.

Two known C-glycosylflavones, swertisin and embinoidin, were isolated from the leaves of Anthurium aripoense, and characterized by room temperature 1D and 2D NMR experiments. At this temperature, the ¹H- and ¹³C-NMR spectra of these C-glycosylflavones revealed doubling of signals, which suggested the presence of two rotamers in solution. Variable-temperature (VT) ¹H-NMR studies supported this hypothesis. The T-ROESY data, in addition to the theoretical (MM2) calculations utilizing the Chem3D Pro software, confirmed the hypothesis that the two rotamers interchange via rotation about the C-glycosidic bond.

Toxicity-structure activity evaluation of limonoids from Swietenia species on Artemia salina.

CONTEXT: Many plant extracts and compounds are being investigated for their cytotoxicity and hence their medicinal or therapeutic properties. Reports of toxicity studies with limonoid analogs have been sparse and have involved mainly crude extracts. In this study, individual natural limonoids have been isolated and their toxicity manipulated via semisynthesis. OBJECTIVE: The lethality of limonoid analogs from Swietenia macrophylla King and Swietenia aubrevilleana Stehlé & Cusin (Meliaceae) against Artemia salina Leach was determined. MATERIALS AND METHODS: Four known natural limonoids were isolated from the dry ground seeds of S. macrophylla and S. aubrevilleana, modified using acylation and hydrolysis reactions and tested in A. salina lethality assays at 1-400 ppm. A 50% lethal concentration (LC(50)) was determined by probit analysis. RESULTS: Higher levels of toxicity were achieved in most of the prepared analogs compared with the parent natural limonoids. The compound showing the highest toxicity with LC(50) 3.9 ppm was 3-O-benzoyl-3-detigloylisoswietenine (20). Other analogs with high toxicity were 6-O-benzoylswietenolide (7), 6-O-benzoylswietenine (17), and 3,6-O,O-dipropionylswietenolide (9), which showed LC(50) values of 4.3, 7.5, and 28.5 ppm, respectively. DISCUSSION AND CONCLUSIONS: Toxicity can be improved via semisynthesis. The compounds exhibiting high toxicity (low LC(50)) may be good candidates for cytotoxicity studies.

The use of coupled HSQC spectra to aid in stereochemical assignments of molecules with severe proton spectral overlap.

INTRODUCTION: A simple glycoside with only 13 carbons exhibited extensive overlapping of four of the glycosidic protons, causing extreme difficulty in the determination of the stereochemistry of the pyranose unit. However, acquisition of a high-resolution coupled heteronuclear single-quantum coherence (HSQC) spectrum overcame this problem. This spectrum provides a useful method for determining vicinal proton coupling constants between strongly coupled protons. OBJECTIVE: To show the potential of high-resolution coupled HSQC spectra in overcoming spectral overlap. METHODOLOGY: The sample was obtained by methanol extraction, followed by fractionation and column chromatography of the dried leaves of Montrichardia arborescens (Araceae). NMR spectra were obtained on 1.5 mg of sample dissolved in 120 µL of CD3OD containing 0.1% trimethylsilyl (TMS) as internal standard. A gradient-selected HSQC spectrum was obtained using standard Varian library pulse sequences in phase sensitive mode. The high-resolution coupled HSQC spectrum focused on the saccharide region with a 1025 Hz ¹H spectral window, a 6300 Hz ¹³C spectral window, 1024 data points, a 0.3 Hz relaxation delay, 384 time increments (linear predicted to 4096), and 80 scans per time increment. RESULTS: The use of a high-resolution coupled HSQC spectrum allowed determination of the coupling patterns of the various pyranose protons with sufficient accuracy. This enabled completion of the assignments and identification of the pyranose unit as glucose. CONCLUSION: The study has shown the effectiveness of the use of a high-resolution coupled HSQC spectrum in the assignment of molecules with severe spectral overlap.

Limonoids from Meliaceae with lipid peroxidation inhibitory activity.

In this study the antioxidant activity of natural limonoids from Meliaceae swietenolide (1), 3,6-O,O-diacetylswietenolide (2), swietenine (3), swietemahonin G (4) and 2-hydroxyswietenine (5) were investigated along with the semi-synthetic analogues (6-25) of compounds 1, 3-4. Lipid peroxidation (LPO) inhibitory assays revealed 85.6, 13.3, 77.3, 61.2 and 24.6% inhibition for the natural compounds 1-5. Excellent antioxidant activity was seen for the semi-synthetic analogues 10 (98.3%), 16-17, 21-22 and 25 (100%), which were more active than the positive controls BHA (91.3%) and TBHQ (95.7%).

In vitro antagonistic activity of monoterpenes and their mixtures against 'toe nail fungus' pathogens.

The antibiotic effect of the active ingredients in Meijer medicated chest rub (eucalyptus oil, camphor and menthol) as well as the inactive ingredients (thymol, oil of turpentine, oil of nutmeg and oil of cedar leaf) were studied in vitro using the fungal pathogens responsible for onychomycosis, such as the dermatophytes Tricophyton rubrum, Trichophyton mentagrophytes, Microsporum canis, Epidermophyton fl occosum and Epidermophyton stockdale. The zones of inhibition data revealed that camphor (1). menthol (2). thymol (3). and oil of Eucalyptus citriodora were the most efficacious components against the test organisms. The MIC(100) for mixtures of these four components in various carrier solvents revealed that formulations consisting of 5 mg/mL concentrations of each have a potential to be efffective in controlling onychomycosis.

New erythrolides from the Caribbean gorgonian octocoral Erythropodium caribaeorum.

Seven new briarane diterpenes, erythrolides K-Q (1-7), as well as the known compounds erythrolides A, B, C, F, and J have been isolated from samples of the Caribbean gorgonian Erythropodium caribaeorumcollected at Buccoo Reef and Flying Reef, Tobago. The structures of the new compounds were determined by high-resolution 1H and 13C NMR spectroscopy utilizing COSY, HMBC, HMQC, and NOESY experiments. The structures of erythrolides K and P were confirmed and their relative stereochemistry determined by X-ray crystallographic analysis.