The present invention is directed to compounds represented by the following structural Formula (I), (a) R1 is selected from the group consisting of hydrogen, substituted or unsubstituted group selected from C.sub.1-C.sub.8 alkyl, aryl-C.sub.0-4-alkyl, heteroaryl-C.sub.0-4-alkyl, C.sub.3-C.sub.6 cycloalkylaryl-C.sub.0-2-alkyl, and --CH.sub.2--C(O)--R17-R18, wherein R17 is O or NH and R18 is optionally substituted benzyl; (b) R2 is selected from the group consisting of C.sub.1-C.sub.6 alkyl, C.sub.1-C.sub.6 alkenyl, aryl-C.sub.0-4-alkyl, heteroaryl-C.sub.0-4-alkyl, C.sub.1-C.sub.4 alkyl sulfonamide, C.sub.1-C.sub.4 alkyl amide, OR10 and C.sub.3-C.sub.6 cycloalkyl; (c) W is O or S; (d) X is an optionally substituted C.sub.1-C.sub.5 alkylene linker wherein one carbon atom of the linker may optionally be replaced with O, NH, S, and optionally two carbons together may form a double bond; (e) Y is selected from the group consisting of C, O, S, NH and a single bond; and (f) E is selected from the group consisting of C(R3)(R4)A, A, and a substituted or unsubstituted group selected from the group consisting of (CH.sub.2)n COOR19. ##STR00001##