Assigning stereodiversity of the 27-Me group of furostane-type steroidal saponins via NMR chemical shifts |
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Authors: | Agrawal Pawan K |
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Affiliation: | Natural Product Incorporation, 7963 Anderson Park Lane, Westerville, OH 43081, USA. pkagrawal11@hotmail.com |
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Abstract: | Applicability of (13)C and (1)H NMR chemical shifts for the assignment of the 25R/25S configuration of the 27-methyl group in the case of furostane-type steroidal saponins has been investigated. A comparative study of (13)C NMR data suggest that chemical shift values for C-20, C-21, C-22, C-23, C-24, C-25, C-26 and C-27 resonances were not much influenced by R/S configuration of the 27-Me group, thus reflecting limited application of (13)C NMR chemical shifts for such stereochemical determinations. In contrast, (1)H NMR chemical shifts (delta(a), delta(b)) for geminal protons of glycosyloxy methylene (H(2)-26) exhibit pronounced dependence and the difference (Delta(ab)=delta(a)-delta(b)) among their chemical shifts [Delta(ab)= or <0.48 for 25R; Delta(ab)= or >0.57 for 25S] seems to be of general applicability for ascertaining 25R/25S orientation of the 27-methyl group of furostane-type steroidal saponins. |
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Keywords: | Furostane Steroidal saponin 13C NMR 1H NMR Stereochemistry |
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