Conformational Exploration of Enflurane in Solution and in a Biological Environment.

Enflurane is a fluorinated volatile anesthetic, whose bioactive conformation is not known. Actually, a few studies have reported on the conformations of enflurane in nonpolar solution and gas phase. The present computational and spectroscopic (infrared and NMR) work shows that three pairs of isoenergetic conformers take place in the gas phase, neat liquid, polar, and nonpolar solutions. According to docking studies, a single conformation is largely preferred over its isoenergetic isomers to complex with the active site of Integrin LFA-1 enzyme (PDB code: 3F78 ), where the widely used anesthetic isoflurane (a constitutional isomer of enflurane) is known to bind. Weak hydrogen bonding from an electrostatic interaction between the CHF2 hydrogen and the central CF2 fluorines was not found to rule the conformational isomerism of enflurane. Moreover, intramolecular interactions based on steric, electrostatic, and hyperconjugative effects usually invoked to describe the anomeric effect are not responsible for the possible bioactive conformation of enflurane, which is rather governed by the enzyme induced fit.

Pycnanthulignenes A-D, antimicrobial cyclolignene derivatives from the roots of Pycnanthus angolensis.

Investigation of the constituents of Pycnanthus angolensis roots has resulted in the isolation of four new cyclolignene derivatives, named pycnanthulignene A (1), pycnanthulignene B (2), pycnanthulignene C (3), and pycnanthulignene D (4), and six known compounds, 4,5-dimethoxy-3',4'-methylenedioxy-2,7'-cycloligna-7,7'-diene, 2,7-dimethoxy-3,6-dimethylnaphthalene, 4'-methoxy-4,5-methylenedioxy-2,7'-cyclolign-7-ene, genkwainin, 8-hydroxykanzakiflavone-2, and formononetin. The structures of these compounds were established using spectroscopic methods. Compounds 1 and 3 showed significant antimicrobial activities against a panel of drug-resistant pathogens.

The implications of (2S,4S)-hydroxyproline 4-O-glycosylation for prolyl amide isomerization.

The conformations of peptides and proteins are often influenced by glycans O-linked to serine (Ser) or threonine (Thr). (2S,4R)-4-Hydroxyproline (Hyp), together with L-proline (Pro), are interesting targets for O-glycosylation because they have a unique influence on peptide and protein conformation. In previous work we found that glycosylation of Hyp does not affect the N-terminal amide trans/cis ratios (K(trans/cis)) or the rates of amide isomerization in model amides. The stereoisomer of Hyp--(2S,4S)-4-hydroxyproline (hyp)--is rarely found in nature, and has a different influence both on the conformation of the pyrrolidine ring and on K(trans/cis). Glycans attached to hyp would be expected to be projected from the opposite face of the prolyl side chain relative to Hyp; the impact this would have on K(trans/cis) was unknown. Measurements of (3)J coupling constants indicate that the glycan has little impact on the C(gamma)-endo conformation produced by hyp. As a result, it was found that the D-galactose residue extending from a C(gamma)-endo pucker affects both K(trans/cis) and the rate of isomerization, which is not found to occur when it is projected from a C(gamma)-exo pucker; this reflects the different environments delineated by the proline side chain. The enthalpic contributions to the stabilization of the trans amide isomer may be due to disruption of intramolecular interactions present in hyp; the change in enthalpy is balanced by a decrease in entropy incurred upon glycosylation. Because the different stereoisomers--Hyp and hyp--project the O-linked carbohydrates in opposite spatial orientations, these glycosylated amino acids may be useful for understanding of how the projection of a glycan from the peptide or protein backbone exerts its influence.

Antiplasmodial Limonoids from Trichilia rubescens (Meliaceae).

Two new limonoids, named rubescins D-E (1-2) along with eight known compounds, including five havanensin type limonoids, TS1 (3), TS3 (4), rubescins A-C (5-7) and three known phytosterols, ß-sitosterol, stigmasterol and its 3ß-O-glucopyranoside derivative were isolated from the roots and stem bark of Trichilia rubescens, collected from Cameroon. The structures of the new compounds were determined by detailed analyses of 1D and 2D NMR spectra, in combination with high-resolution mass spectrometry data and by comparison with related data from literature. Anti-plasmodial activities of some of the isolated limonoids 1, 2, 4, 6 and 7 were evaluated against erythrocytic stages of strain 3D7 Plasmodium falciparum. Compounds 2 and 4 exhibited significant anti-plasmodial in vitro activity with IC50 values of 1.13 and 0.79 µM, respectively.

Antimicrobial activities of the CH2Cl2-CH3OH (1:1) extracts and compounds from the roots and fruits of Pycnanthus angolensis (Myristicaceae).

This study was designed at evaluating the antimycobacterial, antibacterial and antifungal activities of the CH2Cl2-CH3OH (1:1) extracts and isolated compounds, namely 3,4-dimethoxy-3',4'-methylenedioxy-7,7'-epoxylignan (1), genkwainin (2), pycnanthulignene C (3), 4,5-dimethoxy-3',4'-methylenedioxy-2,7'-cycloligna-7,7'-diene (4), pycnanthulignene A (5) from the roots, and calycosin (6), biochanin A (7) and prunetin (8), from the fruits of Pycnanthus angolensis. The microplate alamar blue assay and the broth microdilution method were used to determine the minimal inhibitory concentration (MIC) and minimal microbicidal concentration of the samples. The H+-ATPase-mediated proton pumping assay was used to evaluate one of the possible mechanisms of action of the extracts and isolated compounds. The results of MIC determinations showed that the extract from roots was able to prevent the growth of all the studied organisms, including mycobacteria, fungi, and Gram-positive and Gram-negative bacteria. All tested compounds showed antimicrobial activities to different extents, compound 1 and 8 exhibiting the best antimicrobial spectrum, with 92.3% of the tested organisms being sensitive. The results obtained in this study also showed that the extracts as well as most of the compounds were able to inhibit the H(+)-ATPase activity. The overall results provided evidence that P. angolensis and some of its components might be potential sources of antimicrobial drugs against tuberculosis, bacterial and fungal diseases.