Epoxidation in Vivo of Hyoscyamine to Scopolamine Does Not Involve a Dehydration Step

Hyoscyamine is epoxidized to scopolamine via 6beta-hydroxyhyoscyamine in several solanaceous plants. 6,7-Dehydrohyoscyamine has been proposed to be an intermediate in the conversion of 6beta-hydroxyhyoscyamine to scopolamine on the basis of the observation that this unsaturated alkaloid is converted to scopolamine when fed to a Datura scion. To determine whether a dehydration step is involved in scopolamine biosynthesis, [6-(18)O]6beta-hydroxyhyoscyamine was prepared from l-hyoscyamine and (18)O(2) using hyoscyamine 6beta-hydroxylase obtained from root cultures of Hyoscyamus niger L. When [6-(18)O]6beta-hydroxyhyoscyamine was fed to shoot cultures of Duboisia myoporoides R. B(R)., the labeled alkaloid was converted to scopolamine which retained (18)O in the epoxide oxygen. It is concluded that 6beta-hydroxyhyoscyamine is converted in vivo to scopolamine without a dehydration step.