Photochemische Studien, 62. Untersuchungen zur Photostabilität von Halometason und Prednicarbat in kristallinem Zustand sowie Kristallstruktur von Halometason

Photochemical Studies, 62. — Investigation on the Photostability of Halometasone and Prednicarbate in the Crystal State and Crystal Structure of Halometasone UV irradiation of halometasone ( 1 ) in the crystal state yields three photoproducts: 2‐chloro‐6α,‐9‐difluoro‐11β, 17α‐dihydroxy‐16α‐methyl‐3‐oxoandrosta‐1,4‐diene‐17β‐carbaldehyde ( 3 ), 2‐chloro‐6α,9‐difluoro‐11β‐hydroxy‐16α‐methylandrosta‐1,4‐diene‐3,17‐dione ( 4 and the dimerization product 2ξ‐chloro‐2ξ‐(2‐chloro‐6α,9‐difluoro‐11β,2→‐trihydroxy‐16α‐methyl‐3,20‐dioxopregna‐1,4‐dien‐21‐yl)‐6α,9‐difluoro‐11β,17, 21‐trihydroxy‐16α‐methylpregna‐4‐ene‐3,20‐dione ( 5 ). The structure of 5 is determined by the molecular packing of 1 in the crystal, as shown by an X‐ray analysis of 1 . Two photo‐products are formed after irradiation of prednicarbate ( 2 ): 11β, 17‐dihydroxy‐21‐propionyloxypregna‐1,4‐diene‐3,20‐dione ( 6 ) and 17‐(ethoxycarbonyloxy)‐11β,21‐dihydroxypregna‐1,4‐diene‐3,20‐dione ( 7 ).