Carbon-13 Nuclear Magnetic Resonance Spectroscopy of Naturally Occurring Substances.1,2 Lanosterol and Dihydrolanosterol.

✍ Scribed by G. Lukacs; F. Khuong-Huu; C.R. Bennett; Brian L. Buckwalter; Ernest Wenkert

• Publisher: Elsevier Science
• Year: 1972
• Tongue: French
• Weight: 171 KB
• Volume: 13
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)94087-0

✦ Synopsis

In continuation of our i3C nmr study of terpenic natural productsb2 the natural abundance "C nmr spectra of lanosterol (2). dihydrolanosterol (e) and related substances were recorded. Noise decoupled, single frequency off-resonance decoupled' and, whenever needed, noise off-resonance decoupled spectra5 yielded chemical shift data, differentiated carbon types and in the end led to the assignments in the Table. This constitutes the first cmr analysis of triterpenes. lb, 24.25-Ha tb 33 Comparison of the 6 values of laand lb with those of 2, 6-dimethyloctane4 -and 2-methyl-2-hepteneq respectively, permits assignment of the C-17 sidechain shifts. Chemical shift theory7 indicates the farthest downfield signals of non-protonated carbons to be olefinic C-8 and C-9 and the downfield methine to be C-3, thus leaving the remaining methine signals to C-5 and C-17. Conversion of dihydrolanosterol to its acetate (E) and ketone (2) and comparison of the ring A shifts of these derivatives with those of 5 and _l& yield the values of C-2, C-4 and the C-4 methyl groups.4lsl9 Finally, comparison of the spectra of la and 2 with the cmr spectrum of As(9)-sandaracopimaradienq (5) lo reveals the values of the C-10 angular methyl group, the C-10 quaternary carbon center and the C-l, C-6 and C -11 methylene functions.