Complex sentence: For the film, Warner Brothers intended to cast the more bankable Edward G. Robinson as Duke; but Howard informed the studio that he would not appear in the movie version without Bogart as his co-star.
Split into simpler sentences: For the film, Warner Brothers intended to cast the more bankable Edward G. Robinson as Duke. However, Howard informed the studio that he would not appear in the movie version without Bogart as his co-star.