Abstract
A number of new homogeneous metal catalysts have been studied for the deuteration and/or tritiation of a range of steroids. Sodium tetrachloropltinate (II) was the most satisfaatory of the catalysts examined. This aompound catalysed selective exchange of protons in ring A of aromatic type steroids such as 3βdesoxyestrone. oestrone and oestradiol. Conversion of the free steroids to their acetate or benzoate esters gave better labelling since the OH group in the free steroid reacts with the catalyst leading to precipitation of platinum from the homogeneous solution and a reduction in exchange rate. Steroids with hindered double bonds such as cholesterol, testosterone, pregnenolone, desoxycorticosterone acetate and progesterone do not exchange rapidly nor do the cardiac glycosides, digitoxin and digitoxigenin. Exchange with homogeneous platinum is more selective in isotope incorporation than with the corresponding heterogeneous platinum. A mechanism for the homogeneous exchange is proposed in terms of Οβbonded intermediates. The present data are a guide for predicting the isotopic hydrogen labelling behaviour of steroids with the recently discovered homogeneous platinum catalyst.