2H-Pyrazino[1,2-a]pyrimidine-1(6H)-carboxylic acid, hexahydro-6-[2-[(4-methyl-1-piperazinyl)amino]-2-oxoethyl]-4,7-dioxo-8- (phenylmethyl)-, [3,5-bis(trifluoromethyl)phenyl]methyl ester