Chemical synthesis and hepatic biotransformation of 3 alpha,7 alpha-dihydroxy-7 beta-methyl-24-nor-5 beta-cholan-23-oic acid, a 7-methyl derivative of norchenodeoxycholic acid: studies in the hamster

Abstract

A new bile acid analogue, 3 alpha,7 alpha-dihydroxy-7 beta-methyl-24-nor-5 beta-cholan-23-oic acid (7-Me-norCDCA) was synthesized from the methyl ester of norursodeoxycholic acid, and its hepatic biotransformation was defined in the hamster. To synthesize 7-Me-norCDCA, the 3 alpha-hydroxyl group of methyl norursodeoxycholate was protected as the hemisuccinate, and the 7 beta-hydroxyl group was oxidized with CrO3 to form the 7-ketone. A Grigard reaction with methyl magnesium iodide followed by alkaline hydrolysis gave 7-Me-norCDCA (greater than 70% yield). The structure of the new compound was confirmed by proton magnetic resonance and mass spectrometry. After intraduodenal administration of the 14C-labeled compound into the anesthetized biliary fistula hamster, it was rapidly and efficiently secreted into the bile; 80% of radioactivity was recovered in 2 h. After intravenous infusion, the compound was efficiently extracted by the liver and secreted into the bile (greater than 75% in 3 h). Most (93%) of the biliary radioactivity was present in biotransformation products. The major biotransformation product (48.7 +/- 6.0%) was a new compound, assigned the structure of 3 alpha,5 beta,7 alpha- trihydroxy-7 beta-methyl-24-nor-5 beta-cholan-23-oic acid (5 beta-hydroxy-7- Me-norCDCA). In addition, conjugates of 7-Me-norCDCA with taurine (13.7 +/- 5.0%), sulfate (10.3 +/- 3.0%), or glucuronide (5.1 +/- 1.7%) were formed. 7-Me-norCDCA was strongly choleretic in the hamster; during its intravenous infusion, bile flow increased 2 to 3 times above the basal level, and the calculated choleretic activity of the compound (and its metabolic products) was much greater than that of many natural bile acids, indicating that the compound induced hypercholeresis. It is concluded that the biotransformation and physiological properties of 7-Me-norCDCA closely resemble those of norCDCA. Based on previous studies, the major biological effect of the 7-methyl group in 7-Me-norCDCA is to prevent its bacterial 7-dehydroxylation in the distal intestine.