NEW MATERIAL: A compd. represented by formula I (wherein R1 is a lower alkyl or a lower alkoxy-lower alkyl, R2 is a lower alkyl or a phenyl-lower alkyl, R3 and R6 are each H or F, R4 and R5 are each H or a lower alkoxy and (n) is 1, 2 or 3) and its acid addition salt.

EXAMPLE: Methoxyacetic acid [1R,2R]-(-)-6-fluoro-1,2,3,4-tetrahydro-1- isopropyl-2-[2-methoxy-[3,4-(methylenedioxy)phenetylamino]ethyl]-2-naphthyl.

USE: Useful for multiple resistance to tumor cell propagation suppression and the lowering of chloroquine resistance in malaria.

PROCESS: A novel compd. represented by formula II is O-acylated to obtain the compd. represented by formula I. As a proper acylating agent, there are an acid halide and an acid anhydride.