Structure-activity relationships of norditerpenoid alkaloids occurring in toxic larkspur (Delphinium) species.

Fourteen norditerpenoid alkaloids present in larkspur (Delphinium) species associated with cattle poisoning on grazing land in the western United States have been toxicologically assessed in a mouse bioassay. Toxicity data for these alkaloids have established the tertiary nitrogen atom and anthranilic acid esterification as important structural features necessary to impart toxicity to lycoctonine-type norditerpenoid alkaloids. Variation in C-14 functionality of the toxic alkaloids is also a factor that influences toxicity in these compounds. The relationship of the structure-activity information of this study to previous in vitro neuromuscular studies is discussed.