Levothyroxine

Levothyroxine is the optically pure L-enantiomer of thyroxine, featuring a 1,2,3,4,5,6-hexaiodo-1,4-benzoquinone core linked to a 3,5-diiodo-L-tyrosine moiety via an ether bridge. The molecule contains an amino group at C-3, a ketone at C-4, and four iodine atoms conjugated to aromatic rings, conferring high metabolic stability. As the sole stereoisomer of the parent drug, it retains full thyromimetic activity through T3-mediated nuclear receptor binding. This compound serves as an HPLC reference standard for quantifying thyroid hormone analogs in pharmaceutical formulations.