Selenium derivatives of thyroxine and tri-iodothyronine

Selenium derivatives of thyroxine and tri-iodothyronine having the formula:

• ##STR3## wherein either
• (a)
• R.sub.1 is OH
• R.sub.2 is --CO--CX.sub.1 X.sub.2 X.sub.3,
• at least one of X.sub.1, X.sub.2 and X.sub.3 is --A.sub.p (SeQ).sub.q,
• A is saturated alkylene of 1 of 4 carbon atoms,
• Q is alkyl or alkenyl of 1 to 6 carbon atoms, cycloalkyl, aryl or aralkyl,
• p is 0 or 1,
• q is 1 or 2,
• one of X.sub.1, X.sub.2 and X.sub.3 may be amino and
• any other of X.sub.1, X.sub.2 or X.sub.3 is H, and
• M is H or I;
• or
• (b)
• R.sub.2 is H,
• R.sub.1 is --NZ--CY.sub.1 Y.sub.2 Y.sub.3,
• at least one of Y.sub.1, Y.sub.2 and Y.sub.3 is --A--(SeQ)q,
• one of Y.sub.1, Y.sub.2 and Y.sub.3 may be --COR.sub.4 where R.sub.4 is OH,
• any other of Y.sub.1, Y.sub.2 and Y.sub.3 may be H,
• Z is H or --A--(SeQ)q,
• A is saturated alkylene of 1 to 4 carbon atoms,
• Q is alkyl or alkenyl or 1 to 6 carbon atoms,
• cycloalkyl, aryl or aralkyl,
• q is 1 or 2, and
• M is H or I.