Conversion of Phenylalanine and Tropic Acid into Tropane Alkaloids by Duboisia leichhardtii Root Cultures

Abstract

Summary 14C-labelled phenylalanine and tropic acid, which are possible precursors of the acid moiety of the tropane alkaloids, hyoscyamine and scopolamine, were fed to Duboisia leicbhardtii root cultures. 14C-phenylalanine was efficiently incorporated into tropane alkaloids and more than 50 % of the total radioactivity extractable from the tissues and the medium was recovered in the alkaloidal fraction after 1 week in culture. On the other hand, less than 1 % of 14C-tropic acid was converted to tropane alkaloids even after 3 weeks in culture. Formation of labelled hyoscyamine, scopolamine and apoatropine was confirmed by TLC-autoradiography and that of the former two was also confirmed by enzymatic hydrolysis. A change in the ratio of radioactivity of scopolamine to hyoscyamine over 3 weeks of culture was traced, indicating that the root cultures sustained the ability to convert hyoscyamine to scopolamine for at least 21 days, although biosynthesis of hyoscyamine in the roots stopped after the first 7 days in culture. A possible reason why little 14C-tropic acid was incorporated into tropane alkaloids is discussed.