Pyridyl and pyridazinyl substituted thyronine compounds having selective thyromimetic activity

A compound of structure (I) ##STR50## in which, R.sup.1 is --CH.sub.2 CR.sup.2 R.sup.3 NR.sup.4 R.sup.5 or YCOR.sup.6 ;

• R.sup.2 is hydrogen or C.sub.1-4 alkyl;
• R.sup.3 is hydrogen or --COR.sup.6 ;
• R.sup.4 is hydrogen or C.sub.1-4 alkyl;
• R.sup.5 is hydrogen, C.sub.1-4 alkyl or C.sub.1-4 alkanoyl;
• R.sup.6 is hydroxy, C.sub.1-4 alkoxy, or --NR.sup.4 R.sup.5 ;
• Y is a bond or C.sub.1-4 alkylene;
• R.sup.7 and R.sup.8 are the same or different and are each hydrogen, halogen, C.sub.1-4 alkyl, nitro or amino,
• X is oxygen, sulphur, or CH.sub.2 ;
• R.sup.9 is hydroxy or C.sub.1-4 alkoxy, aryl C.sub.1-4 alkoxy, C.sub.1-4 alkanoyloxy, aryl C.sub.1-4 alkanoyloxy, arylsulphonyloxy, alkylsulphonyloxy, or O-glucuronide;
• R.sup.10 is hydrogen or C.sub.1-4 alkyl;
• and
• Ar is 5-hydroxy-2-pyridyl, 6-oxo-3(1H)-pyridyl, or a 6-oxo-3(1H)-pyridazinyl group,
• or a pharmaceutically acceptable salt thereof.