Novel 6-aryl-1,4-dihydrobenzo[d]oxazine-2-thiones as potent, selective, and orally active nonsteroidal progesterone receptor agonists

The functional activity of 6-aryl benzoxazinone-based progesterone (PR) antagonists changed to PR agonism when the 2-carbonyl group was replaced by a 2-thiocarbonyl moiety. Based on this finding novel 6-aryl benzoxazine-2-thiones were synthesized and evaluated as PR agonists in various in vitro and in vivo assays. Several analogues had sub-nanomolar in vitro potency and showed excellent oral activities in rats. Compounds 15 and 29 had similar potencies to medroxyprogesterone acetate (MPA) in the in vitro T47D Alkaline Phosphatase assay and in vivo rat decidualization model. In contrast to MPA, 29 was highly selective (>500-fold) for PR over glucocorticoid and androgen receptors.