Phosphonopeptides Revisited, in an Era of Increasing Antimicrobial Resistance.

Given the increase in resistance to antibacterial agents, there is an urgent need for the development of new agents with novel modes of action. As an interim solution, it is also prudent to reinvestigate old or abandoned antibacterial compounds to assess their efficacy in the context of widespread resistance to conventional agents. In the 1970s, much work was performed on the development of peptide mimetics, exemplified by the phosphonopeptide, alafosfalin. We investigated the activity of alafosfalin, di-alanyl fosfalin and ß-chloro-L-alanyl-ß-chloro-L-alanine against 297 bacterial isolates, including carbapenemase-producing Enterobacterales (CPE) (n = 128), methicillin-resistant Staphylococcus aureus (MRSA) (n = 37) and glycopeptide-resistant enterococci (GRE) (n = 43). The interaction of alafosfalin with meropenem was also examined against 20 isolates of CPE. The MIC50 and MIC90 of alafosfalin for CPE were 1 mg/L and 4 mg/L, respectively and alafosfalin acted synergistically when combined with meropenem against 16 of 20 isolates of CPE. Di-alanyl fosfalin showed potent activity against glycopeptide-resistant isolates of Enterococcus faecalis (MIC90; 0.5 mg/L) and Enterococcus faecium (MIC90; 2 mg/L). Alafosfalin was only moderately active against MRSA (MIC90; 8 mg/L), whereas ß-chloro-L-alanyl-ß-chloro-L-alanine was slightly more active (MIC90; 4 mg/L). This study shows that phosphonopeptides, including alafosfalin, may have a therapeutic role to play in an era of increasing antibacterial resistance.

Synthesis and Evaluation of Novel 7- and 8-Aminophenoxazinones for the Detection of ß-Alanine Aminopeptidase Activity and the Reliable Identification of Pseudomonas aeruginosa in Clinical Samples.

A series of novel 8-aminophenoxazin-3-one and 7-aminophenoxazin-3-one chromogens and their corresponding ß-alanine derivatives were synthesized and evaluated for their ability to detect ß-alanyl aminopeptidase activity in bacteria known to hydrolyze ß-alanine derivatized substrates. The results provided insight into the structural requirements for effective visualization of enzymatic activity and the mechanism of formation of phenoxazinon-3-ones. 8-Aminophenoxazin-3-one substrates 23c, 23d, and 23e were prepared in good to high overall yield and were selective for ß-alanyl aminopeptidase activity in bacteria, producing a lighter agar background coloration facilitating visualization of colored colonies, with variable localization to the colonies, but had lower sensitivities for the detection of Pseudomonas aeruginosa in comparison to the analogous 7-aminophenoxazin-3-one substrates. The synthetic methodology employed here allows the preparation of a range of substrates for evaluation and the establishment of structure-activity relationships. For example, the 2-pentyl substituted aminophenoxazin-3-one 22b performed with analogous sensitivity to the corresponding 1-pentyl-7-aminophenoxazin-3-one substrate 1 used commercially, highlighting that the position of the pentyl substituent can be varied while maintaining detection sensitivity.