prov:value
| - more preferably, R4 is a radical of hydrogen, C1-C6 alkyl, aryl, heteroaryl, aryl-C1-C4 alkyl, heteroaryl-C1-C4 alkyl or R20???Z20???C2-C4 alkyl radical, wherein the aryl and heteroaryl radicals are optionally substituted by 1-2 radicals of hydroxy, C1-C4 alkoxy, C1-C4 alkylthiol, amino, C1-C4 alkylamino, di(C1-C4 alkyl)amino, acetylamino, halo, C1-C4 alkyl, trifluoromethyl or trifluoromethoxy;
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