Abstract: Use of a compound of formula (I): wherein X is optionally substituted aminoalkyl, optionally substituted alkylene or an interactive group; Y and Z may be the same or different and are selected from N, O, S and C(R′) wherein R′ is hydrogen, optionally substituted alkyl or optionally substituted alkenyl; ---- is a double bond unless the attached Y or Z group is O or S in which case it is a single bond; and R1 to R11 may be the same or different and are selected from hydrogen, a sterically hindering group and an electron donating group; or any two of R1 to R11, Y, Z, NH and R′ may together with the carbon atoms to which they are attached form an optionally substituted ring which may contain heteroatoms, provided that at least one of R1 to R11 is an electron donating group and that when X is NCH3, Y and Z are N and R1, R2 and R4 to R11 are hydrogen, then R3 is not OH or OCH2CH3; and salts thereof, pharmaceutically acceptable derivatives thereof, pro-drugs thereof and/or tau