Hiroshi Tomoda

Two new 2-benzylfuran compounds, designated as paramyfurans A (1) and B (2), and a new dihydrocoumarin compound, designated as paramylactone (3), along with abscisic acid (4), were isolated from the culture broth of the fungal strain Paramyrothecium sp. BF-1049. The planar structures of 1, 2, and 3 were elucidated based on spectroscopic analyses, including 1D and 2D NMR. Compound 3 was further separated into its enantiomers, namely (+)-paramylactone ((+)-3) and (−)-paramylactone ((−)-3), by HPLC using a chiral column. Their absolute stereochemistry was determined by comparing calculated and experimental ECD spectra. Compounds 1–4 exhibited cytotoxic activity against three mesothelioma cell lines (NCI-H2452, NCI-H2052, and Y-MESO-27), with IC₅₀ values ranging from 0.68 to 19.86 μM.

Fungal cyclotetrapeptide nectriatide and its synthetic linear derivatives (nectriatide-based compounds, NCTs), having no antifungal activity, potentiated the antifungal activity of amphotericin B (AmB) against Candida albicans. The mechanism of action was investigated using fluorescein-conjugated and biotin-tagged probes. Microscopy revealed fluorescent probe localization at the C. albicans cell surface. The biotinyl probe binding assay toward membrane lipids showed the highest affinity for ergosterol but no affinity for cholesterol. Ergosterol binding was confirmed by a liposome disruption assay. LC–MS quantification of AmB in C. albicans revealed that NCTs increased the level of binding of AmB to C. albicans. These results indicate that NCTs bind to ergosterol on the fungal plasma membrane, subsequently localizing AmB, explaining the observed potentiation of AmB fungicidal activity.

Two new α-pyrone compounds designated marinapyrones A (1) and B (2) were isolated along with the known related compound micropyrone B (3) from the culture broth of rhizosphere-derived actinomycete strain W21-0103. The structures of 1 and 2 were elucidated by spectroscopic data analyses, including 1D and 2D NMR. Compounds 1-3 exhibited weak antioxidant activity in a radical scavenging assay.

Nectriatide, a fungal cyclotetrapeptide, was previously found to enhance the antifungal activity of amphotericin B (AmB), with nectriatide linear derivatives (NLDs) exhibiting even stronger potentiation. Although we showed that NLDs have an affinity for ergosterol in vitro, the precise mechanism underlying these interactions within living fungal cells remained elusive. Here, we demonstrate for the first time a label-free, single-cell Raman microspectroscopic imaging approach to visualize how NLD-1 colocalizes with ergosterol in Saccharomyces cerevisiae. Our results revealed clear evidence of NLD-1 localization in ergosterol-rich regions, indicating direct interaction. Furthermore, antifungal-enhancing effect of NLD-1 was markedly reduced in ERG4-deficient S. cerevisiae─supporting its specific recognition of ergosterol. This unprecedented real-time, in situ visualization of an AmB potentiator in living yeast cells not only provides new insights into the mechanism of AmB enhancement but also sets the stage for broader applications in understanding other antifungal synergies at the molecular level.

The total synthesis and structural determination of shodoamide C (1), a compound that enhances the activity of amphotericin B against Candida albicans, have been achieved. A synthetic strategy for compound 1 facilitated the efficient synthesis of all 16 stereoisomers, allowing for the identification of the four previously unknown stereocenters of 1 through the chiral recycle HPLC analyses. All stereoisomers of 1 showed similar activity, indicating that their stereochemistries minimally influenced it.

Fungal cyclotetrapeptide nectriatide and its synthetic linear derivatives (nectriatide-based compounds, NCTs), having no antifungal activity, potentiated antifungal activity of amphotericin B (AmB) against Candida albicans . The mechanism of action was investigated using fluorescein-conjugated and biotin-tagged probes. Microscopy revealed fluorescent-probe localization at the C. albicans cell membrane. The biotinyl probe binding assay towards membrane lipids showed the highest affinity for ergosterol but no affinity for cholesterol. Ergosterol binding was confirmed by a liposome disruption assay. LC-MS quantification of AmB in C. albicans revealed that NCTs increased AmB binding to C. albicans . These results indicate that NCTs bind to ergosterol on the fungal plasma membrane, subsequently localizing AmB, explaining the observed potentiation of AmB fungicidal activity.

Celludinones A and B, isolated from the fungus Talaromyces cellulolyticus BF-0307, were inhibitors of sterol O-acyltransferase (SOAT). Further searches for their congeners in the culture broth of the fungus by LC/UV and LC/MS analysis resulted in the discovery of four structurally related compounds, including a new dihydroisobenzofuran named celludinone C (1). The structure of 1, including its absolute stereochemistry, was elucidated by 1D/2D NMR and electronic circular dichroism (ECD) spectra. All of these compounds inhibited both SOAT1 and 2, with IC₅₀ values ranging from 8.5 to 30 µM.

Ali A, Passitta M, Rante H, Wahyudin E, Djide NJN, Politan RJ, Nur EA, Shigeno S, Ohte S, Kobayashi K, Hosoda K, Tomoda H, Ohshiro T. 2024. Antibiotic production by an endophytic Streptomyces isolated from the medicinal plant Poikilospermum suaveolens. Biodiversitas 25: 2221-2229. This study investigates the antibiotic production potential of endophytic actinomycetes isolated from Poikilospermum suaveolens plants. Samples were collected from various parts of the plant in karst ecosystems. Endophytic actinomycetes were cultured and screened for antimicrobial activity using agar diffusion and liquid microdilution methods. One of the 11 isolated strains exhibited significant antibiotic activity against clinically relevant organisms identified as belonging to the Streptomyces genus, specifically Streptomyces mirabilis strain NRRL ISP-5169. Submerged fermentation of this strain over 9 days showed strong antagonistic effects against Gram-positive bacteria. Spectroscopic analyses confirmed the presence of actinomycin D as the bioactive compound. This study provides on the previously unexplored potential of endophytic actinomycetes from P. suaveolens as a promising resource for antibiotic discovery.

During our screening for anti-mycobacterial agents against Mycobacterium avium complex (MAC), two new polycyclic tetramate macrolactams (PTMs), named hydroxycapsimycin (1) and brokamycin (2), were isolated along with the known PTM, ikarugamycin (3), from the culture broth of marine-derived Streptomyces sp. KKMA-0239. The relative structures of 1 and 2 were elucidated by spectroscopic data analyses, including 1D and 2D NMR. Furthermore, the absolute configuration of 1 was confirmed by a single-crystal X-ray diffraction analysis. Compounds 2 and 3 exhibited moderate antimycobacterial activities against MAC, including clinically isolated drug-resistant M. avium.