Synthesis and Biological Evaluation of a Series of Liver-Selective Phosphonic Acid Thyroid Hormone Receptor Agonists and Their Prodrugs

Phosphonic acid (PA) thyroid hormone receptor (TR) agonists were synthesized to exploit the poor distribution of PA-based drugs to extrahepatic tissues and thereby to improve the therapeutic index. Nine PAs showed excellent TR binding affinities (TR beta(1), K-i < 10 nM), and most of them demonstrated significant cholesterol lowering effects in a cholesterol-fed rat (CFR) model. Unlike the corresponding carboxylic acid analogue and T-3, PA 22c demonstrated liver-selective effects by inducing maximal mitochondrial glycerol-3-phosphate dehydrogenase activity in rat liver while having no effect in the heart. Because of the low oral bioavailability of PA 22c, a series of prodrugs was synthesized and screened for oral efficacy in the CFR assay. The liver-activated cyclic 1-(3-chlorophenyl)-1,3-propanyl prodrug (MB07811) showed potent lipid lowering activity in the CFR (ED50 0.4 mg/kg, po) and good oral bioavailability (40%, rat) and was selected for development for the treatment of hypercholesterolemia.