prov:value
| - R4, R5, R6,R7, R2 ', R3 ', R5 ' or R6' must be other than hydrogen provided that R2 ' is not methyl; (ii) when R1 is methyl and one of Ra and Rb is methyl and the other is isooctyl, at least one of R4, R5, R6, R7, R3 ' or R5 1 ' must be other than hydrogen; (iii) if one of Ra and Rb is H or lower alkyl, the other of Ra and Rb is not lower alkyl; and (iv) if one of Ra or Rb is C(O)R, at least one o
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