. . . . "yl 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, cyano, halo, C1-C4 alkyl, trifluoromethyl or trifluoromethoxy; and R4 is a radical of hydrogen, C1-C4 alkyl, aryl, heteroaryl, aryl-C1-C4 alkyl, heteroaryl-C1-C4 alkyl or R20???Z20???C2-C4 alkyl radical; and wherein R20 is a h" .