title: Assigning stereodiversity of the 27-Me group of furostane-type steroidal saponins via NMR chemical shifts.
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.
authors.affiliation: Natural Product Incorporation, 7963 Anderson Park Lane, Westerville, OH 43081, USA. pkagrawal11@hotmail.com
authors.forename: Pawan K
authors.initials: PK
authors.lastname: Agrawal
mesh_terms: D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry*; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D011522:Protons; D012503:Saponins / Q000737:chemistry* / Q000302:isolation & purification; D013237:Stereoisomerism; D013256:Steroids / Q000737:chemistry* / Q000302:isolation & purification; D032444:Tribulus / Q000737:chemistry*
chemical_list: D011522:Protons; D012503:Saponins; D013256:Steroids; D008697:Methane