[14C] – radiolabeling of {[trans‐(8β)]‐6‐methyl‐1‐(1‐methylethyl) ergoline‐8‐carboxylic acid, 4‐methoxycyclohexyl ester (Z)‐2‐butenedioate [(1:1)]. A potent and selective 5ht2‐receptor antagonist

Abstract [14C]‐Labeled {[trans‐(8 β)]‐6‐methyl‐1‐(1‐methylethyl)ergoline‐8‐carboxylic acid, 4‐methoxycyclohexyl ester (Z)‐2‐butenedioate (1:1)} (LY281067) (10) was synthesized from unlabeled 6‐methyl‐1‐(1‐methylethyl)ergoline‐8‐carboxylic acid (2). The [14C] label was introduced into the carboxyl group attached to the 8 position of the ergoline nucleus. This site is stable to metabolism. The synthesis involves removal of the unlabeled carboxyl group from 2 and subsequent reinsertion of a [14C]‐labeled carboxyl group into the same position. The radiolabel is not introduced until near the end of the synthesis which allows for ease of handling and scale‐up of intermediates.