Compounds of Formula (Ia) wherein R is a C6-C12 substituted or unsubstituted aryl, a C6-C12 substituted or unsubstituted heteroaryl, a C1-C6 substituted or unsubstituted alkyl or —NR′R′, Q is C(O), O, NR′, S, S(O)2, C(O)2(CH2)p Y is C(O), O, NR′, S, S(O)2, C(O)2(CH2)p Z is H or C1-C4 alkyl, R′ is H, C(O), S(O)2, C(O)2, a C6-C12 substituted or unsubstituted aryl, a C6-C12 substituted or unsubstituted heteroaryl or a C1-C6 substituted or unsubstituted alkyl, when substituted, aryl, heteroaryl and alkyl are substituted with halogen, C6-C12 heteroaryl, —NR′R′ or COOZ, which have diagnostic and therapeutic properties, such as the treatment and management of prostate cancer and other diseases related to NAALADase inhibition, Radiolabels can be incorporated into the structure through a variety of prosthetic groups attached at the X amino acid side chain via a carbon or hetero atom linkage.