Progesterone metabolite. Isoln from pregnant mares' urine: Brooks et al., Biochem. J. 51, 694 (1952). Prepn by catalytic reduction of allopregnane-3,20-dione: Marker et al., GB 512940 (1939 to Parke, Davis); by hydrogenation of pregn-5-ene-3β-ol-20-one: Klyne, Barton, J. Am. Chem. Soc. 71, 1500 (1949); by hydrogenation of pregn-5-ene-3β,20β-diol: Klyne, Miller, J. Chem. Soc. 1950, 1972.