This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Siriwardena group designed and synthesized a series of novel polyhydroxylated sulfonium salts that have proven to be excellent biological tools with which to study the modes-of-action of various glycosidases. Although the structures of a host of these exotic derivatives have been established by single-crystal X-ray studies, structural elucidation of others based on the analyses of NMR spectral data alone has not always been straightforward. One such example is a sulfonium salt analog of the potent natural mannosidase inhibitor, swainsonine. Our original analysis had identified six potential structures of which one was selected as the most likely on the basis of NMR data and other arguments. However, the structure elucidation and conformational behavior of this salt is complex and could only be defined with confidence by application of a combined quantum mechanical-NMR approach developed by the Woods group. In this approach, quantum NMR data and NOE intensities were calculated for all theoretically possible structures and conformers, and these were compared with the corresponding, accurately determined, experimental NMR values.
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