1. [14C]Endrin, administered orally to rabbits, is excreted in the faeces as unchanged endrin (50% of that administered) and in the urine as a mixture of polar metabolites. 2. The major biotransformation is hydroxylation at the methylene bridge (C-12) to yield anti-12-hydroxyendrin. syn-Hydroxylation at C-12 also occurs. 3. The hydroxylated metabolites are excreted mainly as their sulphate conjugates. 4. Glucuronide conjugates are also excreted. anti-12-Hydroxyendrin is rapidly conjugated in vitro on incubation with rabbit liver microsomal glucuronyl transferase and UDPGA. 5. Comparative aspects of the metabolism of endrin in rats and rabbits are discussed.

SuininavyThe first synthesis of a 9-hydroxylated derivative of HEOD (dieldrin) has been accomplished in three steps starting from hexachlorocyclopentadiene and 7-benzoyloxybicyclo [2,2,1]hepta-2,5-diene.

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The first syntheses of syn-12-hydroxydieldrin, syn-12-hydroxyendrin and anti-12-hydroxyendrin have been accomplished by debenzoylation and epoxidation of three isomeric adduction products of hexachlorocyclopentadiene and 1,7,7-trinorborna-2,5-dien-7-yl benzoate. A third known metabolite of endrin, lZketoendrin, and a putative metabolite of dieldrin, lZketodieldrin, were prepared from the corresponding alcohols by oxidation with chromium trioxide. Characterisation of the three debenzoylated intermediates as syn-12-hydroxyaldrin, and syn-and anti-12-hydroxyisodrin constitutes the first syntheses of these three possible metabolites of aldrin and isodrin.

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