The Radiochemical Centre Limited

Gavin Murray Cree

Anthony Leonard Riley

Reginald Monks

Novel Selenium derivatives of thyroxine and tri-iodothyronine have the formula: ##STR1## wherein M is I or H and either (a) R.sub.1 is OH or a carboxyl protecting group and R.sub.2 contains at least one Se, preferably .sup.75 Se, atom or (b) R.sub.2 is H or an amino protecting group and R.sub.1 contains at least one Se, preferably .sup.75 Se, atom. The compounds are useful in dual isotope assays of thyroid function.

Selenium derivatives of thyroxine and tri-iodothyronine

Novel selenium-75 derivatives of cholesterol have the formula ##STR1## (I) where X is hydrogen or acyl, Y is alkyl and n is 0 or 1. They are useful for visualizing the adrenal glands of mammals.

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Gavin Murray Cree