prov:value
| - Preferably R1, R2, R3, R4, and R5 independently represents an alkyl group having 1 to 6 carbon atoms, more preferably a methyl, ethyl, n-propyl, butyl, or methoxymethyl group; or an aryl group, particularly a phenyl or naphthyl group; or both R1 and R2 are ???(CH2CH2CH2)??? as a part of two fused 6-membered rings.
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