Synthesis and biological evaluation of modified pentapeptides as potent proteinase K inhibitors

This communication reports the first demonstration of synthesis and biological validation of modified pentapeptides, such as methoxysuccinyl-Ala-Ala-Ala-Pro-Leu-chloromethyl ketone 6b as a potent proteinase K inhibitor. The efficacy of MeOSuc-AAAPL-CH(2)Cl 6b analog in inhibiting the proteolytic activity of proteinase K was compared with the known MeOSuc-AAPV-CH(2)Cl analog. The examination of inhibitory activity using RT-PCR assay in the presence of proteinase K revealed that the MeOSuc-AAAPL-CH(2)Cl 6b inhibitor at a concentration of 0.05 mM allows a signal to be obtained for an exogenous target ('Xeno RNA') at 30 cycles (i.e., Ct=30), whereas the control MeOSuc-AAPV-CH(2)Cl requires a fivefold higher concentration (0.25 mM) to produce the same Ct. A plausible explanation for the higher efficiency of MeOSuc-AAAPL-CH(2)Cl 6b over control is proposed based on the molecular modeling studies.