caa a22 4500 445325674 CHVBK 20180317142719.0 cr unu---uuuuu 170323e20110501xx s 000 0 eng 10.1007/s10858-011-9499-z doi (NATIONALLICENCE)springer-10.1007/s10858-011-9499-z García Víctor Departamento de Química de Productos Naturales y Biotecnología, Instituto de Productos Naturales de Canarias, Avda. Francisco Sánchez, 3, 38206, La Laguna, Tenerife, Canary Islands aut Acid epimerization of 20-keto pregnane glycosides is determined by 2D-NMR spectroscopy [Elektronische Daten] [Víctor García] Carbohydrates influence many essential biological events such as apoptosis, differentiation, tumor metastasis, cancer, neurobiology, immunology, development, host-pathogen interactions, diabetes, signal transduction, protein folding, and many other contexts. We now report on the structure determination of pregnane glycosides isolated from the aerial parts of Ceropegia fusca Bolle (Asclepiadaceae). The observation of cicatrizant, vulnerary and cytostatic activities in some humans and animals of Ceropegia fusca Bolle, a species endemic to the Canary Islands, encouraged us to begin a pharmacological study to determine their exact therapeutic properties. High resolution 1H-NMR spectra of pregnane glycosides very often display well-resolved signals that can be used as starting points in several selective NMR experiments to study scalar (J coupling), and dipolar (NOE) interactions. ROESY is especially suited for molecules such that ωτc~1, where τc are the motional correlation times and ω is the angular frequency. In these cases the NOE is nearly zero, while the rotating-frame Overhauser effect spectroscopy (ROESY) is always positive and increases monotonically for increasing values of τc. The ROESY shows dipolar interactions cross peaks even in medium-sized molecules which are helpful in unambiguous assignment of all the interglycosidic linkages. Selective excitation was carried out using a double pulsed-field gradient spin-echo sequence (DPFGSE) in which 180° Gaussian pulses are sandwiched between sine shaped z-gradients. Scalar interactions were studied by homonuclear DPFGSE-COSY and DPFGSE-TOCSY experiments, while DPFGSE-ROESY was used to monitor the spatial environment of the selectively excited proton. Dipolar interactions between nuclei close in space can be detected by the 1D GROESY experiment, which is a one-dimensional counterpart of the 2D ROESY method. The C-12 and C-17 configurations were determined by ROESY experiments. The Author(s), 2011 Epimerization nationallicence Glycosides nationallicence NMR nationallicence Oligosaccharides nationallicence Journal of Biomolecular NMR Springer Netherlands 50/1(2011-05-01), 91-97 0925-2738 50:1<91 2011 50 10858 https://doi.org/10.1007/s10858-011-9499-z text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s10858-011-9499-z text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- García Víctor Departamento de Química de Productos Naturales y Biotecnología, Instituto de Productos Naturales de Canarias, Avda. Francisco Sánchez, 3, 38206, La Laguna, Tenerife, Canary Islands aut NATIONALLICENCE 773 0- Journal of Biomolecular NMR Springer Netherlands 50/1(2011-05-01), 91-97 0925-2738 50:1<91 2011 50 10858 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer