Enantioseparation of vesamicol and novel vesamicol analogs by high-performance liquid chromatography on different chiral stationary phases

Chiral resolution of serial potent and selective σ1 ligands and biological evaluation of (-)-[18F]TZ3108 in rodent and the nonhuman primate brain

Twelve optically pure enantiomers were obtained using either crystallization or chiral high performance liquid chromatography (HPLC) separation methodologies to resolve six racemic sigma-1 (σ₁) receptor ligands. The in vitro binding affinities of each enantiomer for σ₁, σ₂ receptors and vesicular acetylcholine transporter (VAChT) were determined. Out of the 12 optically pure enantiomers, five displayed very high affinities for σ₁ (K_i<2nM) and high selectivity for σ₁ versus σ₂ and VAChT (>100-fold). The minus enantiomer, (-)-14a ((-)-TZ3108) (K_i-σ1=1.8±0.4nM, K_i-σ2=6960±810nM, K_i-VAChT=980±87nM), was chosen for radiolabeling and further in vivo evaluation in rodents and nonhuman primates (NHPs). A biodistribution study in Sprague Dawley rats showed brain uptake (%ID/gram) of (-)-[¹⁸F]TZ3108 reached 1.285±0.062 at 5min and 0.802±0.129 at 120min. NHP microPET imaging studies revealed higher brain uptake of (-)-[¹⁸F]TZ3108 and more favorable pharmacokinetics compared to its racemic counterpart. Pretreatment of the animal using two structurally different σ₁ ligands significantly decreased accumulation of (-)-[¹⁸F]TZ3108 in the brain. Together, our in vivo evaluation results suggest that (-)-[¹⁸F]TZ3108 is a promising positron emission tomography (PET) tracer for quantifying σ₁ receptor in the brain.

Surface-site reactivity in small-molecule adsorption: A theoretical study of thiol binding on multi-coordinated gold clusters

BACKGROUND

The adsorption of organic molecules on metal surfaces has a broad array of applications, from device engineering to medical diagnosis. The most extensively investigated class of metal-molecule complexes is the adsorption of thiols on gold.

RESULTS

In the present manuscript, we investigate the dependence of methylthiol adsorption structures and energies on the degree of unsaturation at the metal binding site. We designed an Au20 cluster with a broad range of metal site coordination numbers, from 3 to 9, and examined the binding conditions of methylthiol at the various sites.

CONCLUSION

We found that despite the small molecular size, the dispersive interactions of the backbone are a determining factor in the molecular affinity for various sites. Kink sites were preferred binding locations due to the availability of multiple surface atoms for dispersive interactions with the methyl groups, whereas tip sites experienced low affinity, despite having low coordination numbers.

Stereoselective oxidation of regioisomeric octadecenoic acids by fatty acid dioxygenases

Seven Z-octadecenoic acids having the double bond located in positions 6Z to 13Z were photooxidized. The resulting hydroperoxy-E-octadecenoic acids [HpOME(E)] were resolved by chiral phase-HPLC-MS, and the absolute configurations of the enantiomers were determined by gas chromatographic analysis of diastereoisomeric derivatives. The MS/MS/MS spectra showed characteristic fragments, which were influenced by the distance between the hydroperoxide and carboxyl groups. These fatty acids were then investigated as substrates of cyclooxygenase-1 (COX-1), manganese lipoxygenase (MnLOX), and the (8R)-dioxygenase (8R-DOX) activities of two linoleate diol synthases (LDS) and 10R-DOX. COX-1 and MnLOX abstracted hydrogen at C-11 of (12Z)-18:1 and C-12 of (13Z)-18:1. (11Z)-18:1 was subject to hydrogen abstraction at C-10 by MnLOX and at both allylic positions by COX-1. Both allylic hydrogens of (8Z)-18:1 were also abstracted by 8R-DOX activities of LDS and 10R-DOX, but only the allylic hydrogens close to the carboxyl groups of (11Z)-18:1 and (12Z)-18:1. 8R-DOX also oxidized monoenoic C(14)-C(20) fatty acids with double bonds at the (9Z) position, suggesting that the length of the omega end has little influence on positioning for oxygenation. We conclude that COX-1 and MnLOX can readily abstract allylic hydrogens of octadecenoic fatty acids from C-10 to C-12 and 8R-DOX from C-7 and C-12.