A compound of formula (I) ##STR1## its tautomeric forms, its stereoisomers, its polymorphs, its pharmaceutically acceptable salts or its pharmaceutically acceptable solvates, wherein R.sup.3, R.sup.4, R.sup.5, and R.sup.6 are the same or different; R.sup.1 and R.sup.2 together represent along with carbon atoms to which they are attached an aromatic cyclic structure containing 5-6 ring atoms which may optionally be substituted; X represents a heteroatom selected from oxygen or sulfur; R.sup.7 represents hydrogen atom, hydroxy, alkoxy, halogen, lower alkyl group or optionally substituted aralkyl group or forms a bond together with R.sup.8 ; R.sup.8 represents hydrogen atom, hydroxy, alkoxy, halogen, lower alkyl group or optionally substituted aralkyl or R.sup.8 forms a bond together with R.sup.7 ; B represents an oxygen atom or a sulfur atom; Y represents an oxygen atom or a sulfur atom, n is an integer ranging from 1 to 4 and m is an integer of zero or one, compositions containing compounds of formula (I) and methods of use of the compounds are described.