The renal action of spirorenone and other 6 beta,7 beta; 15 beta,16 beta-dimethylene-17-spirolactones, a new type of steroidal aldosterone antagonists.

The aldosterone antagonistic activity in vivo and the affinity for mineralocorticoid receptors (MCR) in vitro of 3-(17 beta-hydroxy-6 beta,7 beta; 15 beta,16 beta-dimethylene-3-oxo-1, 4-androstadiene-17 alpha-yl) propionic acid gamma-lactone (spirorenone), a new aldosterone antagonist, and four of its derivatives were studied in comparison with spironolactone in rats. Spirorenone was 8.6 times as potent as spironolactone, but showed a lower affinity for the MCR than the standard. The C1/C2 saturated derivative (compound I) had 7.6 times the antialdosterone potency and 2 times the binding activity of spironolactone. The 17-spiroether derivative of spirorenone (compound II) showed a lower aldosterone antagonistic activity (1.7 the potency of spironolactone) as well as a lower affinity for the MCR (0.5 the affinity of spironolactone). The analogue with a 17 beta-hydroxyl group and a 17 alpha-hydroxypropyl side chain (compound III) possessed a very low binding capacity for MCR (1/10 of that of spironolactone) but still a 1.3 times higher antialdosterone activity than spironolactone. This result is probably due to a transformation of compound III to an active metabolite in vivo. Finally, the derivative with a reversed configuration of the 17-spirolactone ring (compound IV) had no biological activity in vivo and no affinity for the MCR. These results show that spirorenone or one of its active derivatives might lead to a new series of potent aldosterone antagonists.