prov:value
| - O)n ; n is 0, 1 or 2; R' and R are each selected from the group consisting of hydrogen, lower alkyl, lower alkenyl, lower alkynyl, hydroxy lower alkyl, amino lower alkyl, C3-7 cycloalkyl, phenyl, di phenylmethylol, and lower alkyl substituted by one or two groups, provided that at least R' or R is other than hydrogen; and each X is hydrogen, or when Y is O and Z is S(???O)n simultaneously, then
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