A compound of Formula (I) or a pharmaceutically acceptable salt thereof, where R1 can be hydro, methoxy, difluoromethoxy or trifluoromethoxy R2 can be hydro, methoxy, trifluoromethoxy or trifluoromethyl and R3 can be hydro or methoxy. The compound of formula (I) can inhibit glutaminase, e.g., GLS1.