Lupeol and pristimerin do not inhibit activation of the human sperm CatSper Ca(2+)-channel.

Opposing findings have been published on the regulation of the sperm-specific Ca 2+ channel CatSper (cation channel of sperm) in human sperm cells by the plant triterpenoids lupeol and pristimerin. While the original study on this topic found these triterpenoids to act as potent inhibitors of human CatSper, subsequent studies have failed to replicate such an inhibitory effect. It has been suggested that these issues could in part be due to purity issues and/or batch variation between the plant-derived extracts of lupeol and pristimerin obtained for the studies. The aim of this study was to elucidate this controversy by investigating the batches of lupeol and pristimerin used in our previous study with state-of-the-art 1H-, 13C- and 2D-nuclear magnetic resonance (NMR) methods to reveal potential purity and/or batch variation issues. When comparing the NMR-spectra obtained from 1H-NMR and 13C-NMR with previously published NMR-spectra for lupeol and pristimerin, we could confirm that both the lupeol and pristimerin batch were ≥95 % pure. These results confirm the validity of the findings in our previous study for lupeol and pristimerin, showing that lupeol and pristimerin do not inhibit activation of CatSper in human sperm. In conclusion, using 1H-, 13C- and 2D-NMR methods, we confirm that the lupeol and pristimerin batches used in our previous study were ≥95 % pure and thereby fail to identify any purity issues and/or batch variation that could explain the observed inability of lupeol and pristimerin to inhibit activation of CatSper in human sperm.

Self-Promoted Stereoselective Glycosylations - Past, Present, Future.

Self-promoted glycosylations have generally not received much attention, despite having the advantages of being easy to perform and often highly stereoselective. This account covers the work done in this field and the mechanistic aspects of self-promoted glycosylations are discussed, with a main focus on the stereoselectivity of the reactions. Most self-promoted glycosylations utilize trichloroacetimidate donors, but examples of self-promoted reactions with other donors have been described and will be discussed. Self-promoted glycosylation strategies can provide a basis for new stereoselective glycosylation methodologies.

Exploring the relationship between the conformation and pKa: can a pKa value be used to determine the conformational equilibrium?

Four substituted cis and trans-4,5-dihydroxyhexahydropyridazines that were expected to undergo pH induced conformational switching were synthesized and carefully investigated by NMR analyses and calculations. For two of the compounds a large difference in pKa existed between the two possible chair conformers and for one compound this resulted in conformational switching as a result of pH change. For the first time it is shown that the pKa directly reflects the conformational equilibrium of conformers.