Discovery of a New Class of Sortase A Transpeptidase Inhibitors to Tackle Gram-Positive Pathogens: 2-(2-Phenylhydrazinylidene)alkanoic Acids and Related Derivatives

Abstract

A FRET-based random screening assay was used to generate hit compounds as sortase A inhibitors that allowed us to identify ethyl 3-oxo-2-(2-phenylhydrazinylidene)butanoate as an example of a new class of sortase A inhibitors. Other analogues were generated by changing the ethoxycarbonyl function for a carboxy, cyano or amide group, or introducing substituents in the phenyl ring of the ester and acid derivatives. The most active derivative found was 3-oxo-2-(2-(3,4dichlorophenyl)hydrazinylidene)butanoic acid (2b), showing an IC50 value of 50 µM. For a preliminary assessment of their antivirulence properties the new derivatives were tested for their antibiofilm activity. The most active compound resulted 2a, which showed inhibition of about 60% against S. aureus ATCC 29213, S. aureus ATCC 25923, S. aureus ATCC 6538 and S. epidermidis RP62A at a screening concentration of 100 µM.

Keywords: 2-(2-phenylhydrazinylidene)alkanoic acid derivatives; FRET; biofilms; sortase A.

Figure 1

Structure of phenylhydrazinylidene derivatives 1a and 2.

Scheme 1

Synthetic route for compounds 1a–h, 5a–h, 6a and 7a.

Figure 2

Reported NH chemical shift values of the geometrical structures of compounds 1a,f, ethyl (2-phenylhydrazinylidene)mesoxalate (8) and 2-(2-phenylhydrazinylidene)propanedinitrile (9).

Figure 3

Dimeric structure 10 of (2E)-3-oxo-2-(2-phenylhydrazinylidene)butanenitrile (6a) and structures of (2Z)-3-oxo-2-(2-phenylazohydrazinylidene)butanamide 7a and (2Z)-acids 5a–h.