prov:value
| - d from the group consisting of hydrogen, methyl, ethyl, propyl, and phenyl, with the proviso that R1 and R2 are selected to provide at least one tertiary oxycarbonyl containing moiety and/or at least one R is a substituent which is directly linked to a carbon which is directly joined to oxygen and is selected from the group consisting of methyl, ethyl, propyl, isopropyl, butyl and isobutyl, and wh
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