Spirolactones are a class of functional group in organic chemistry featuring a cyclic ester attached spiro to another ring system. The name is also used to refer to a class of synthetic steroids, called steroid-17α-spirolactones, 17α-spirolactosteroids, or simply 17α-spirolactones, which feature their spirolactone group at the C17α position.[1] [2] [3] They are antimineralocorticoids, or antagonists of the mineralocorticoid receptor (which is activated predominantly by the mineralocorticoid steroid hormone aldosterone), and have been employed clinically as potassium-sparing diuretics.[4] [5] Some also possess progestogenic and/or antiandrogen properties, which have both contributed to side effects and been utilized for medical indications (e.g., spironolactone as an antiandrogen, and drospirenone as a progestin).[6] The spirolactones were developed by G. D. Searle & Company in the 1950s and thereafter and were denoted as "SC" compounds (e.g., SC-9420 for spironolactone).
The spirolactones include the marketed drugs spironolactone (SC-9420; Aldactone), canrenone (SC-9376; Cantaren, Luvion), potassium canrenoate (SC-14266; Venactone, Soldactone), eplerenone (SC-66110, CGP-30083; Inspra), and drospirenone (ZK-30595; Yasmin). Spirolactones that were not ever marketed include SC-5233, SC-8109, SC-11927 (Catatoxic Steroid 1; CS-1), spiroxasone, prorenone (SC-23133), prorenoate potassium (SC-23992), 7α-thiospironolactone (SC-24813), mexrenone (SC-25152, ZK-32055), dicirenone (SC-26304), 7α-thiomethylspironolactone (SC-26519), mexrenoate potassium (SC-26714), spirorenone (ZK-35973), ZK-91587 (15β,16β-methylenemexrenone), mespirenone (ZK-94679), and ZK-97894 (7α-thiomethylmespirenone). Oxprenoate potassium (RU-28318) is not a spirolactone by definition but is a closely related antimineralocorticoid that was never marketed.
SC-5233 (6,7-dihydrocanrenone), the C17α propanoic acid lactone of testosterone (androst-4-en-17β-ol-3-one), is the unsubstituted parent or prototype compound of the spirolactones, and is one of a few of the simplest members of the series along with SC-8109 (the 19-demethyl analogue of SC-5233) and canrenone (the 1,2-didehydro analogue of SC-5233).[7] Spironolactone is a derivative of SC-5233 with a 7α-acetylthio group (that is, SC-5233 is 7α-desthioacetylspironolactone).