Three new toxic norditerpenoid alkaloids from the low larkspur Delphinium nuttallianum

Three new N-(methylsuccinimido)anthranoyllycoctonine norditerpenoids, given the names bearline (1), 14-acetylbearline (2), and 16-deacetylgeyerline (3 ), were isolated from the extract of the low larkspur Delphinium nuttallian um. The structures of the individual alkaloids were determined by H-1 and C -13 NMR spectroscopy and HRMS. These alkaloids are structurally related to the neurotoxic alkaloid methyllycaconitine (4) and may be important in esta blishing the toxicity of low larkspurs to cattle. A mouse bioassay was used to measure the LD50 values for two of the new alkaloids (1 and 2), as suff icient quantities of 3 were not available for toxicity testing. A structura lly related alkaloid, geyerline (7), was isolated from D. geyeri in suffici ent quantities for toxicity testing. The toxicities of 1, 2, and 7 were fou nd to be comparable to that of 4, with calculated LD50 values in mice of 5. 7, 3.3, and 6.2 mg/kg, respectively.