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).