Patent ID: 8236827

Claim:
A compound of formula (I): or a pharmaceutically acceptable salt thereof, wherein: R 1 , R 2 and R 3 are independently H or lower alkyl; R 4 , R 5 , R 6 , R 7 and R 8 are independently H, halo, lower alkyl or —O-lower alkyl, provided that at least one is —O-lower alkyl; or at least one pair of R 4 to R 8 , the members of which pair are adjacent to one another on the ring, are conjoined to form —O—(CR 14 R 15 ) n —O—, where n is 1 or 2 and R 14 and R 15 are independently H or lower alkyl, and the remainder of R 4 to R 8 are independently H, halo, lower alkyl or —O-lower alkyl; and R 9 , R 10 , R 11 , R 12 and R 13 are independently H, halo, lower alkyl or —O— lower alkyl, provided that at least one pair of R 9 to R 13 , the members of which pair are adjacent to one another on the ring, are conjoined to form —O—(CR 16 R 17 ) m —O—, where m is 1 or 2 and R 16 and R 17 are independently H or lower alkyl, and the remainder of R 9 to R 13 are independently H, halo, lower alkyl or —O-lower alkyl.