Synthesis of a tritiated 3-dehydroecdysteroid putative precursor of ecdysteroid biosynthesis

We have synthesized a tritiated form of 5beta-cholest-7-ene-3,6-dione (5beta-diketone) of high specific activity (9.2 TBq/mmol) in ten steps from deoxychenocholic acid, which possesses the desired A/B cis ring junction (5beta-H configuration). We have conceived a synthetic pathway which permits labelling by tritiation at the final step and allowing for the introduction of the tritium label into both the side chain and the nucleus. We have examined the ability of insect endocrine glands (prothoracic glands) of Pieris Brassicae to use this molecule as a precursor of 3-dehydroecdysone and of ecdysone biosynthesis. No conversion can be detected. In the myriapod Lithobius forficatus only reduction of the 3-ketone can be observed. It seems that the 5beta-diketone is not an intermediate in the ecdysone biosynthetic pathway.