prov:value
| - 1, 2, 3 or 4 heteroatoms in the ring which are independently N, S or O; and including N-oxides; X is a bond, or is one of the following groups: ##STR72## wherein Y is O, N--R6 or S; n' is 0, 1 or 2; R6 is H, lower alkyl, aryl, --C(O)--R11 or --C(O)--O--R11 ; R7 and R8 are the same or different and are independently H, alkyl, aryl, halogen, --O--R12, or R7 and R8 together can be oxygen to form a k
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