title: Steroid structure and function V. A-ring conformation in 17-hydroxy-6 alpha-methylprogesterone.
abstract: The molecular conformation of 17-hydroxy-6 alpha-methylprogesterone has been determined crystallographically and is compared with 17-hydroxy-progesterone, 17-acetoxyprogesterone and 17-acetoxy-6 alpha-methylprogesterone (MPA). The analysis demonstrates that the 6 alpha-methyl substituent is not sufficient by itself to induce inversion of the A-ring. Consequently, the inverted form observed in MPA and proposed to be responsible for high affinity binding to the progesterone receptor appears to be induced by the combined long range influence of 17 alpha-acetoxy substituent and the direct interaction of the 6 alpha-methyl group with the flexible A-ring.
mesh_terms: D003461:Crystallography; D006908:Hydroxyprogesterones; D008525:Medroxyprogesterone / Q000031:analogs & derivatives; D008958:Models, Molecular; D008968:Molecular Conformation; D013329:Structure-Activity Relationship
chemical_list: D006908:Hydroxyprogesterones; D008525:Medroxyprogesterone