| abstract |
A compound, which is a compound of formula (I) or a salt thereof: ** Formula ** wherein ring A is optionally substituted phenyl, ring B is phenyl or thienyl, each optionally substituted, R1 and R2 are each independently H or (C1-6) alkyl, X is O, S, S (O) or S (O) 2, and CH2 at - (CH2) n- is optionally replaced by O or S, and n is 4 or 5. |