Clobetasol Propionate Impurity (21-Chloro-16β-methyl-17-(1-oxopropoxy)pregna-1,4-diene-3,20-dione)

(8S,9S,10R,11S,13S,14S,16S,17R)-17-(2-chloroacetyl)-11-hydroxy-10,13,16-trimethyl-3-oxo-6,7,8,9,10,11,12,13,14,15,16,17-dodecahydro-3H-cyclopenta[a]phenanthren-17-yl propionate