The present invention aims to obtain an optical isomer of DCP-LA, which shows more superior activity and is suitable for clinical utilization, and provide an agent having a superior PKC-ε activation action, a prophylactic and/or therapeutic agent for neurotransmitter release disorders, and a prophylactic and/or therapeutic agent for neuropsychiatric diseases, which contain the isomer as an active ingredient.A compound represented by the following formula: or a pharmaceutically acceptable salt thereof, and a selective PKC-ε activator containing same as an active ingredient, and is the like.