Oxidosqualene cyclase involved in the biosynthesis of bryonolic acid. Converts oxidosqualene to isomultiflorenol. (S)-2,3-epoxysqualene = isomultiflorenol In cultured cells, IMS1 mRNA expression is high between days 16 and 20 and precedes the accumulation of bryonolic acid. Belongs to the terpene cyclase/mutase family.