Polycyclic polyprenylated acylphloroglucinols (PPAPs) comprise a large group of compounds of mostly plant origin. The best-known compound is hyperforin from St. John's wort with its antidepressant, antitumor and antimicrobial properties. Chemical synthesis of PPAP variants allows the generation of compounds with improved activity and compatibility. Here we studied two synthetic PPAP-derivatives, PPAP 23 and PPAP 53, as to their antimicrobial activity. While PPAP 23 is insoluble in water, PPAP 53, the sodium salt, is water-soluble. In vitro, both compounds exhibited good and comparable activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium. Both compounds had no adverse effects on Galleria mellonella wax moth larvae, even at high concentrations. However, they were unable to protect the larvae from infection with S. aureus because components of the larval coelom neutralized the antimicrobial activity; a similar neutralizing effect was also seen with serum albumin. In a septic arthritis model triggered by S. aureus PPAP23 decreased the formation of abscesses and bacterial load in kidneys, and in a mouse skin abscess model topical treatment with PPAP 53 resulted in an approximately two-fold reduction in S. aureus counts. PPAP 23 and PPAP 53 also showed high growth inhibiting activity against anaerobic Gram-positive pathogenic gut bacteria such as Clostridium perfringens and Clostridium difficile. Based on these results, we envision potential application of PPAP 23 and PPAP 53 in the topical treatment of wound infections with Gram+ pathogens, and their oral use in intestinal infections with C. difficile.

Polycyclic polyprenylated acylphloroglucinols (PPAPs) comprise a large group of compounds of mostly plant origin. The best-known compound is hyperforin from St. John’s wort with its antidepressant, antitumor and antimicrobial properties. The chemical synthesis of PPAP variants allows the generation of compounds with improved activity and compatibility. Here, we studied the antimicrobial activity of two synthetic PPAP-derivatives, the water-insoluble PPAP23 and the water-soluble sodium salt PPAP53. In vitro, both compounds exhibited good activity against methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin-resistant Enterococcus faecium. Both compounds had no adverse effects on Galleria mellonella wax moth larvae. However, they were unable to protect the larvae from infection with S. aureus because components of the larval coelom neutralized the antimicrobial activity; a similar effect was also seen with serum albumin. In silico docking studies with PPAP53 revealed that it binds to the F1 pocket of human serum albumin with a binding energy of −7.5 kcal/mol. In an infection model of septic arthritis, PPAP23 decreased the formation of abscesses and S. aureus load in kidneys; in a mouse skin abscess model, topical treatment with PPAP53 reduced S. aureus counts. Both PPAPs were active against anaerobic Gram-positive gut bacteria such as neurotransmitter-producing Clostridium, Enterococcus or Ruminococcus species. Based on these results, we foresee possible applications in the decolonization of pathogens.