A compound of formula (I) wherein Y is oxygen or sulfur, and X1, X2 and X3 are independently of each other hydrogen, halogen, hydroxy or linear or branched (C1-6)-alkoxy, or hydroxy-(C1-6)alkyl or (C1-6)alkoxy-(C1-6)alkyl, mono- or dihalogenated (C1-6)-alkyl, amino(C1-6)-alkyl, hydroxy(C1-6)-alkyl, with one of the two provisos that: (1) at least of X1, X2 and X3 is other than hydrogen, and (2) X2 is other than hydroxy, when X1 and X3 are hydrogen.
