[3] The initial discovery of spirorenone was deemed a great success, as no compound with greater antimineralocorticoid activity had been developed since spironolactone in 1957.

[4] Moreover, spirorenone itself has virtually no affinity for the androgen receptor while its progestogenic activity shows species differences, being somewhat greater than that of spironolactone in rabbits but absent in mice and rats.

[3] However, it was serendipitously and unexpectedly found that low doses of spirorenone lowered testosterone levels in men during clinical studies.

Though this transformation has also been accomplished by chemical means, microbiological oxidation by Botryodiplodia malorum apparently proves superior to give PC44520204 (2).

Addition of the dianion from propargyl alcohol to the carbonyl group at position 17 adds the required carbon atoms for the future lactone [82543-17-7] (7).