| http://www.w3.org/ns/prov#value | - One of R4 and R5 may be a hydrogen atom and another may be an unsubstituted alkyl group, preferably, one of R4 and R5 is a hydrogen atom and another is a t-butyl group; or one of R4 and R5 may be a hydrogen atom and another may be a phenylalkyl group, preferably, one of R4 and R5 is a hydrogen atom and another is a benzyl group.
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