prov:value
| - where R1, R2, R3, and R4 independently are a hydrogen atom, a lower alkyl, aryl, benzyl, halogen, hydroxyl, alkoxyl, thiol, thioether, amino, nitro, carboxyl, formate, formamido or phosphido group, or adjacent substituents (i.e., R1???R2, R2???R3, R3???R4) are substituted oxygen groups that together form a cyclic acetal or ketal; and R5 is a hydrogen atom, a alkoxyl, alkyl, hydrogen, halo, aryl, o
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