| abstract |
There is provided a compound of Formula (III) or Formula (IV), wherein A is selected from H, OH, halogen and hydrocarbyl D, E and F are each independently of each other an optional linker group; P, Q and R are independently of each other a ring system, wherein R4 and R5 are independently selected from H, alkyl, cycloalkyl, alkenyl, acyl and aryl, or combinations thereof, or together represent alkylene, wherein the or each alkyl or cycloalkyl or alkenyl or optionally contain one or more hetero atoms or groups. |