We have synthesized a tritiated form of 14α-hydroxy-β-cholest-7-ene-3, 6-dione (5β-diketol) of high specific activity (1.74 TBq/mmol) from 7-dehydrocholesterol in seven steps with stereoselective introduction of the A/B cis ring junction as the key reaction. We have examined the ability of endocrine glands (prothoracic glands) of Locusta migratoria to use this molecule as a precursor of 3-dehydroecdysone and of ecdysone biosynthesis. A very ...