Ryania insecticide: analysis and biological activity of 10 natural ryanoids

Ryania insecticide, the powdered stemwood of Ryania speciosa, was analyzed by HPLC and ¹H NMR for the content (ppm, w/w) of 10 ryanoids. The compounds were isolated and their potencies compared for toxicity to housefly adults (injection, piperonyl butoxide as a synergist), flour beetle larvae (dietary exposure), and mice (intraperitoneal) and for competition with [³H]ryanodine for binding to the Ca²⁺ release channel complex. Ryanodine (range 450-600 ppm) and 9,21-dehydroryanodine (650-700 ppm) are essentially equipotent and account for almost all of the biological activity of ryania in each of these systems. 9-Hydroxy-10-epiryanodine (7-17 ppm) and three 8_ax-hydroxy-10-epiryanodine derivatives [10-(O-methyl) (28-33 ppm), dehydro (30-64 ppm), and 10-(O-methyl)dehydro (22-32 ppm)] are very effective with houseflies but not in the other assays. 18-Hydroxyryanodine (<10 ppm), ryanodyl 3-(pyridine-3-carboxylate) (42-58 ppm), 8_ax,18-dihydroxy-10-(O-methyl)-10-epiryanodine (5-10 ppm), and 9-hydroxyanhydroryanodine (12-17 ppm) are all of low activity. The potency of a ryanoid at the Ca²⁺ release channel is a better predictor of toxicity to mice and beetle larvae than to housefly adults.