Biotransformation of 3-(2',4',5'-triethoxybenzoyl) propionic acid, a new biliary smooth muscle relaxant with choleretic activity, in rats.

1. By the combined use of deuterium labelling and gas chromatographic-mass spectrometric analysis, the metabolite pattern of 3-[2',4',5'-triethoxybenzoyl) propionic acid (triethoxybenzoylpropionic acid), a new biliary smooth muscle relaxant with choleretic activity, has been determined in the rat. 2. The metabolites excreted in urine and/or bile were isolated and characterized as follows: the parent drug, 3-(2',5'-diethoxy-4'-hydroxybenzoyl)propionic acid (metabolite II),3-(2'-ethoxy-4'-hydroxy-5'-methoxybenzoyl)propionic acid or 3-(2'-ethoxy-5'-hydroxy-4'-methoxybenzoyl)propionic acid (III), 3-(2',4'-diethoxy-5'-hydroxybenzoyl)propionic acid (V) and 3-[2',4'-diethoxy-5'-(2-hydroxyethoxy)benzoyl]propionic acid (VI). 3. The primary route of biotransformation of triethoxybenzoylpropionic acid in the rat was either O-de-ethylation at the C-4' and C-5' positions or beta-hydroxylation of the ethoxy group at the C-5' position in the parent molecule. 4. All these excreted products except metabolite VI were eliminated both unconjugated and in conjugates (probably glucuronides and/or sulphates). 5. The rat excreted mainly metabolites V and VI in the urine and parent drug, metabolites V and VI in the bile.