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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Fabian Hammerle1, Johannes Fiala1, Anja Höck1,2
1Department of Department of Pharmacognosy, Institute of Pharmacy, CCB - Centrum of Chemistry and Biomedicine, CMBI - Center for Molecular Biosciences, University of Innsbruck, 6020 Innsbruck, Austria.
Abstract:
The photoantimicrobial potential of four mushroom species (i.e., Cortinarius cinnabarinus, C. holoxanthus, C. malicorius, and C. sanguineus) was explored by studying the minimal inhibitory concentrations (MIC) via a light-modified broth microdilution assay based on the recommended protocols of the European Committee on Antimicrobial Susceptibility Testing (EUCAST). The extracts were tested against Candida albicans, Escherichia coli, and Staphylococcus aureus under blue (λ = 428 and 478 nm, H = 30 J/cm2) and green light (λ = 528 nm, H = 30 J/cm2) irradiation. Three extracts showed significant photoantimicrobial effects at concentrations below 25 microg/mL. Targeted isolation of the major pigments from C. sanguineus led to the identification of two new potent photoantimicrobials, one of them (i.e., dermocybin) being active against S. aureus and C. albicans under green light irradiation [PhotoMIC530 = 39.5 microM (12.5 microg/mL) and 2.4 microM (0.75 microg/mL), respectively] and the other one (i.e., emodin) being in addition active against E. coli in a low micromolar range [PhotoMIC428 = 11.1 microM (3 microg/mL)]. Intriguingly, dermocybin was not (photo)cytotoxic against the three tested cell lines, adding an additional level of selectivity. Since both photoantimicrobials are not charged, this discovery shifts the paradigm of cationic photosensitizers.
Insights
Mushroom extracts show potent photoantimicrobial activity against bacteria and fungi. New compounds, dermocybin and emodin, demonstrate selective antimicrobial effects under light irradiation.
Area of Science:
- Mycology
- Photobiology
- Antimicrobial Resistance
Background:
- The rise of antimicrobial resistance necessitates novel therapeutic strategies.
- Mushroom extracts are a potential source of bioactive compounds with antimicrobial properties.
- Photoantimicrobial therapy offers a light-activated approach to combat microbial infections.
Purpose of the Study:
- To investigate the photoantimicrobial potential of four *Cortinarius* mushroom species.
- To identify and characterize novel photoantimicrobial compounds from mushroom extracts.
- To evaluate the efficacy and selectivity of these compounds against pathogenic microbes.
Main Methods:
- Minimal inhibitory concentrations (MIC) determined using a modified broth microdilution assay.
- Extracts tested against *Candida albicans*, *Escherichia coli*, and *Staphylococcus aureus*.
- Irradiation with blue (428/478 nm) and green (528 nm) light.
Main Results:
- Three mushroom extracts exhibited significant photoantimicrobial effects below 25 µg/mL.
- Dermocybin and emodin isolated from *C. sanguineus* showed potent activity.
- Dermocybin active against *S. aureus* and *C. albicans*; emodin active against *E. coli* and *C. albicans*.
- Dermocybin displayed no photo-cytotoxicity against tested cell lines.
Conclusions:
- Mushroom-derived compounds can serve as effective photoantimicrobials.
- Dermocybin and emodin represent promising, non-charged photoantimicrobial agents.
- This discovery challenges existing paradigms regarding cationic photosensitizers in antimicrobial therapy.
