Larkspur chemistry: Toxic alkaloids in tall larkspurs

Abstract

Three species of tall larkspur (Delphinium barbeyi (Huth), Delphinium occidentale (Wats.) Wats, and Delphinium glaucescens) that are toxic to cattle were chemically analyzed to determine “total alkaloid” content. D. barbeyi and D. occidentale contained more “total alkaloids” than D. glaucescens. The “total alkaloid” content of all plant tissues in the 3 species declined as the growing season progressed. Variation in the occurrence of specific diterpenoid alkaloids was established by gas chromatographic analysis of D. barbeyi plant tissues at different phenological growth stages. Highest yields of specific alkaloids were found in early growth stage plant tissues. Deltaline was the most prominent diterpenoid alkaloid in D. barbeyi and 14-0-acetyldictyocarpine is a new diterpenoid alkaloid with high occurrence in this plant. The toxicity of specific diterpenoid alkaloids obtained from the tall larkspurs evaluated in a mouse bioassay showed methyllcaconitine to be highly toxic. Other diterpenoid alkaloids isolated from the 3 Iarkspurs showed much lower levels of toxicity compared to methyllycaconitine