Effects of synthetic trypsin inhibitors on the growth of Escherichia coli

Derivatives of aryl-4-guanidinomethylbenzoate and N-aryl-4-guanidinomethylbenzamide as new antibacterial agents: synthesis and bioactivity

AIM

The aim of the present study was to design, synthesize, and evaluate novel antibacterial agents, derivatives of aryl-4-guanidinomethylbenzoate and N-aryl-4-guanidinomethylbenzamide.

METHODS

A total of 44 derivatives of aryl-4-guanidin-omethylbenzoate (series A) and N-aryl-4-guanidinomethylbenzamide (series B) were synthesized and their antibacterial activities were assessed in vitro against a variety of Gram-positive and Gram-negative bacteria by an agar dilution method.

RESULTS

Twelve compounds showed potent bactericidal effects against a panel of Gram-positive germs, including methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), vancomycin-intermediate Staphylococcus aureus (VISA), and methicillin-resistant coagulase-negative staphylococci (MRCNS), with minimum inhibitory concentrations (MIC) ranging between 0.5 and 8 microg/mL, which were comparable to the MIC values of several marketed antibiotics. They exhibited weak or no activity on the Gram-negative bacteria tested. In addition, these compounds displayed high inhibitory activities towards oligopeptidase B of bacterial origin.

CONCLUSION

In comparison with the previously reported MIC values of several known antibiotics, the derivatives of aryl-4-guanidinomethylbenzoate and N-aryl-4-guanidinomethylbenzamide showed comparable in vitro bactericidal activities against VRE and VISA as linezolid. Their growth inhibitory effects on MRSA were similar to vancomycin, but were less potent than linezolid and vancomycin against MRCNS. This class of compounds may have the potential to be developed into narrow spectrum antibacterial agents against certain drug-resistant strains of bacteria.

High-level expression and purification of Escherichia coli oligopeptidase B

Oligopeptidase B (OpdB) of Escherichia coli, previously called protease II, has a trypsin-like specificity, cleaving peptides at lysine and arginine residues and belongs to the prolyl oligopeptidase family of new serine peptidases. In this study, we report the fusion expression of E. coli oligopeptidase B with an N-terminal histidine tag using pET28a as the expression vector. Although most of the recombinant OpdB was produced as inclusion bodies, the solubility of the recombinant protease increased significantly when the expression temperature shifted from 37 to 30 degrees C. Recombinant OpdB (approximately 10 mg) could be purified from the soluble fraction of the crude extract of 1L log-phase E. coli culture containing 1.5 g wet bacterial cells. The purified OpdB has a molecular weight of approximately 80 kDa and a specific activity of 4.8 x 10(4) U/mg. OpdB could also be purified from the inclusion bodies with a lower yield. The recombinant enzyme was very stable under 40 degrees C. By comparison of the substrate specificity of the purified OpdB with that of OpdA, another trypsin-like protease in E. coli, we found that Boc-Glu-Lys-Lys-MCA is a specific substrate for E. coli OpdB. We also found that compared to OpdA, OpdB is much more sensitive to GMCHA-OPh(t)Bu, a synthetic trypsin inhibitor that can retard the growth of E. coli.

Antibacterial effects of esters of guanidino- and amidino-acids trypsin inhibitors

Inhibitory effects of various esters of trans-4-guanidinomethylcyclohexanecarboxylic acid and the 4-tert- butylphenyl esters of amidinopiperidine-4-alkanoic, trans-4- amidinocyclohexanealkanoic, trans-4-guanidinoethylcyclohexanecarboxylic and trans-4-guanidinocyclohexanealkanoic acids, all trypsin inhibitors, on the growth of E. coli, B. subtilis, S. aureus and S. epidermidis were examined. 4-tert-Butylphenyl esters strongly inhibited the growth of E. coli and the order of the inhibitory effects correlated with that for the inhibitory effects on proteinase In, which appears immediately before initiation of DNA synthesis in E. coli and closely correlates with the onset of DNA synthesis. No correlation was observed between the inhibitory effects and Ki values for trypsin. The 4-tert-butylphenyl esters also strongly inhibited B. subtilis, S. aureus and S. epidermidis, and the order, of the inhibitory effects on these bacteria roughly coincided with that on E. coli. The order of the inhibitory effects of each ester, on these bacteria was S. epidermidis > S. aureus > B. subtilis > E. coli. Among the esters examined, the biphenyl ester of trans-4-guanidinoethylcyclohexanecarboxylic acid was the most inhibitory on these four bacteria and proteinase In. Hydrolysis of tert-butyloxycarbonyl-L-valyl-L-prolyl-L-arginine 4-methylcoumarin-7-amide, which is a substrate for proteinase In, in crude extracts of E. coli, B. subtilis and S. epidermidis was examined. The order of this activity in these bacteria was E. coli > B. subtilis > S. epidermidis.