A method for enhancing learning and memory or treating amnesia. The method includes administrating to a subject in need thereof a compound of the formula (I): A is H, R, or  each of Ar1, Ar2, and Ar3, independently, is phenyl, thienyl, furyl, or pyrrolyl; each of R1, R2, R3, R4, R5, and R6, independently, is H, nitro, halogen, R, OH, OR, C(O)OH, C(O)OR, C(O)SH, C(O)SR, C(O)NH2, C(O)NHR, C(O)NRR′, ROH, ROR′, RSH, RSR′, ROC(O)R′OH, NHR, NRR′, RNHR′, or RNR′R″; or R1 and R2 together, R3 and R4 together, or R5 and R6 together are ORO; wherein each of R, R′, and R″, independently is C1˜C6 alkyl; and n is 1, 2, or 3. The compound is in an effective amount for enhancing learning and memory or treating amnesia.