Synthesis of tritium labelled 24‐epibrassinolide

Abstract

Abstract Deuterium and tritium 5,7,7‐tris‐labelled 24‐epibrassinolide were prepared by base catalyzed exchange reaction using 24‐epicastasterone tetraacetate 1 or bis‐isopropylidenedioxy‐24‐epicastasterone 8 and labelled water. Baeyer‐Villiger oxidation of the obtained labelled 6‐ketones 2 and 3 with CF 3 CO 3 H gave after alkaline deacetylation of the resulting 4 and 5 the desired tris‐labelled 24‐epibrassinolides 6 and 7 , respectively, or starting from 9 under simultaneous oxidation and deprotection in one step the same final products.