Thioxo amino acid pyrrolidides and thiazolidides: new inhibitors of proline specific peptidases

Aminopeptidase P (APP), dipeptidyl peptidase II (DP II), dipeptidyl peptida se IV (DP IV) and prolyl oligopeptidase (POP) are proline specific peptidas es. Hence, they are able to cleave peptide bonds containing the imino acid proline. Amino acid pyrrolidides (Pyrr) and thiazolidides (Thia) are well-k nown product analogue inhibitors of DP IV and POP. For the first time we de scribe the influence of a thioxo amide bond, incorporated into these compou nds, on the inhibition of the proline specific peptidases. Taking into acco unt the substrate specificity of these peptidases, we have synthesized Xaa- psi[CS-N]-Pyrr and Xaa-psi[CS-N]-Thia of the amino acids Ala, Phe, Val and Ile. The inhibition constants were determined for the above mentioned proli ne specific peptidases isolated from different sources. As a result, the se rine proteases DP II, DP IV and POP were inhibited competitively, whereas m etal-dependent APP displayed a linear mixed-type inhibition with inhibition constants up to 10(-4) M. Thioxylation of Xaa-Pyrr and Xaa-Thia led to a s light decrease of inhibition of DP IV and POP compared to Xaa-Pyrr and Xaa- Thia, though the inhibition constants were still in the range up to 10(-7) M. As Xaa-Thia exist as two isomers, we investigated isomer specific inhibi tion with regard to DP IV. Thus, our studies have revealed that DP IV was o nly inhibited by the Z isomer of the Xaa-psi[CS-N]-Thia. For the first time , Xaa-Pyrr and Xaa-Thia were characterized as inhibitors of DP II with inhi bition constants in the micromolar range. In contrast to DP IV inhibition, the Xaa-psi[CS-N]Pyrr and Xaa-psi[CS-N]-Thia have proven to be more potent inhibitors of DP II than the corresponding Xaa-Pyrr and Xaa-Thia. Thus, the se Xaa-psi[CS-N]-Thia are new potent inhibitors especially suitable for DP II with K-i values ranging in the upper nanomolar concentration. (C) 2000 E lsevier Science B.V. All rights reserved.