prov:value
| - (a) R1 is ???OR6, in particular wherein R6 is C1-6alkyl, such as methyl, ethyl, or tert-butyl and most preferably where R6 is hydrogen; (b) R1 is ???NHS(???O)2R7, in particular wherein R7 is C1-6alkyl, C3-C7cycloalkyl, or aryl, e.g. wherein R7 is methyl, cyclopropyl, or phenyl; or (c) R1 is ???NHS(???O)2R7, in particular wherein R7 is C3-7cycloalkyl substituted with C1-6alkyl, preferably wherein R
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