Ryania insecticide: structural assignments of four natural 8ax-hydroxy-10-epiryanoids

Four 8ax-hydroxy-10-epiryanoids isolated from ryania, the botanical insecticide, were established by 1H NMR spectroscopy to consist of three known compounds (A, D, and F) and a new ryanoid (E). Earlier structural assignments of A and D with a methoxy substituent at C-4 are not consistent with their 1H and 13C NMR spectra or with the conversion of A to the corresponding diketone on oxidation with periodate, a known reaction of the C-4, C-12 diol group of ryanodine. The revised structures are 8ax-hydroxy-10-(O-methyl)-10-epiryanodine for A and 8ax-hydroxy-10-(O-methyl)-10-epidehydroryanodine for D. NOESY experiments in chloroform but not in other solvents indicate that the pyrrole-2-carboxylate group of A lies in a different spatial orientation than that of ryanodine relative to the rest of the molecule. The new ryanoid (E) is characterized as 18-hydroxy-A, i.e., 8ax,18-dihydroxy-10-(O-methyl)-10-epiryanoidine. Evidence is detailed for the assignment of F as 8ax-hydroxy-10-epidehydroryanodine, and more complete spectral data support the previously assigned structures of C1 and C2 in the ryanodine and anhydroryanodine series, respectively