BIOACTIVE RYANOIDS FROM NUCLEOPHILIC ADDITIONS TO 4,12-SECO-4,12-DIOXORYANODINE

Ryanoids are the most potent inhibitors known for the calcium-release channel (ryanodine receptor), and they are also botanical insecticides . Twenty-two new ryanoids are described in which the C-4, C-12 bond is ruptured or replaced with an oxygen bridge and in which substituents at C-4 and C-12 are modified to have a wide range of polarities. They are obtained by nucleophilic additions to the 4,12-seco-4,12-dioxo com pounds or diketones prepared from ryanodine and dehydroryanodine by pe riodate oxidation. Structures of the new compounds are distinguished b y changes in NMR chemical shifts of C-13 and H-1 nuclei in the regions of C-4 and C-12. The new ryanoids are compared with ryanodine as inhi bitors of [H-3] ryanodine binding using a rabbit muscle sarcoplasmic r eticulum preparation alone or with ATP and a mouse brain receptor with ATP. They are also examined as knockdown agents for houseflies pretre ated with a cytochrome P450 oxidase inhibitor to suppress detoxificati on and then injection with the ryanoid. The diketones have very weak b inding activity in the receptor assays and very low toxicity to flies. Activity approaching that of ryanodine in both the receptor and fly a ssays is obtained for ketals with small groups at C-12 and polar subst ituents such as OH or NHOH at C-4. The oximes range from low to modera te potency. Addition of thiols to the vinyl group of dehydroryanodine gives three thioethers all of low biological activity. With most ryano ids addition of ATP to the muscle system increases its sensitivity to near that found for the brain receptor with ATP; possible exceptions a re compounds with phenyl substituents. Activity at the calcium-release channel generally follows housefly toxicity although the hydrazine an d hydroxyamine adducts are much weaker than expected perhaps due to di ssociation under the assay conditions.