R6 is hydrogen; C1-C5alkyl; C1-C5alkoxy; ???O???(C6-C10aryl); or R6 and Q together with a bivalent C3-C7alkylene radical which may be interrupted by one or more ???O??? and/or ???NR7??? or may be condensed with an aromatic ring, form a heterocyclic ring; and R7 is hydrogen; or C1C12alkyl; and most preferably wherein R6 is hydrogen.