Ryanoid insecticides: structural examination by fully coupled two-dimensional 1H–13C shift correlation nuclear magnetic resonance spectroscopy

Abstract

The two-dimensional pulse sequence, (π/2, ¹H)–Δt₁–(π/2, ¹H; π/2, ¹³C)–acquire, for ‘fully coupled’¹H–¹³C shift correlation n.m.r. has been applied to structural analysis of ryanodine (1) and 9,21-didehydroryanodine (2)(a new botanical insecticide from Ryania speciosa). This procedure allowed total assignment of the ¹³C n.m.r. spectra using one-, two-, and three-bond ¹H–¹³C couplings, stereochemical assignments of protons, and some conformational data via relative ³J_cH couplings. The structure (2) defined by n.m.r. was confirmed by reductive conversion into ryanodine (1) and 9-epi-ryanodine (3).