| http://www.w3.org/ns/prov#value | - readily removable when necessary. [0057] It is preferred that R1 is a hydrogen atom or a group selected from unsubstituted or substituted alkyl, for example methyl, trifluoromethyl, 3-methylsulfonamidopropyl, methyl- or phenyl-sulfonylmethyl, carboxy-tetrafluoroethyl; unsubstituted or substituted aryl, for example phenyl, 3,5-di-chlorophenyl, o-methane-sulfonamidophenyl, 4-methanesulfonylphenyl, 2
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