prov:value
| - Thus a preferred sub-group of compounds of formula (I) are compounds of formula (II) where R1, R2, R3 and R4 are as defined above and R66 is C1-6 alkyl in particular methyl and R67 is selected from hydrogen, halogen, alkyl of 1-6 carbon atoms, alkenyl of 2-6 carbon atoms, alkynyl of 2-6 carbon atoms, azido, hydroxyalkyl of 1-6 carbon atoms, halomethyl, alkoxymethyl of 2-7 carbon atoms, alkanoyloxy
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