Isolation and constitution of quercetagitrin, a glucoside of quercetagetin

Summary

Quercetagitrin, a monoglucoside of quercetagetin, has for the first time been isolated from the flowers of the African Marigold (Tagetes erecta). It is not a 3-glucoside since it gives a red precipitate with lead acetate and does not undergo easy hydrolysis with acids. Further it is easily oxidised in cold alkali, and after methylation the products of decomposition yield veratric acid. The glucose group, therefore, is not present in the side phenyl nucleus. By complete methylation and subsequent hydrolysis of the glucoside, a pentamethyl quercetagetin is obtained. This ether is a new compound, and differs from 3∶6∶7∶3′∶4′-pentamethyl quercetagetin in all its properties, and hence the free hydroxyl group in it is in either the 6th or the 7th position. The allyl ether of this new pentamethyl quercetagetin smoothly undergoes the Claisen Rearrangement, indicating thereby that the ortho-position with respect to the allyloxy group is unsubstituted. Hence the allyl ether should be 3∶5∶6∶3′∶4′-pentamethyl-7-allyl quercetagetin, and the new pentamethyl ether should have the constitution of 3∶5∶6∶3′∶4′-pentamethyl quercetagetin. Consequently quercetagitrin is the 7-glucoside of quercetagetin.