Meleagrin, a New FabI Inhibitor from <i>Penicillium chryosogenum</i> with at Least One Additional Mode of Action

<div><p>Bacterial enoyl-acyl carrier protein reductase (FabI) is a promising novel antibacterial target. We isolated a new class of FabI inhibitor from <i>Penicillium chrysogenum</i>, which produces various antibiotics, the mechanisms of some of them are unknown. The isolated FabI inhibitor was determined to be meleagrin by mass spectroscopy and nuclear magnetic resonance spectral analyses, and its more active and inactive derivatives were chemically prepared. Consistent with their selective inhibition of <i>Staphylococcus aureus</i> FabI, meleagrin and its more active derivatives directly bound to <i>S. aureus</i> FabI in a fluorescence quenching assay, inhibited intracellular fatty acid biosynthesis and growth of <i>S. aureus</i>, and increased the minimum inhibitory concentration for <i>fabI</i>-overexpressing <i>S. aureus</i>. The compounds that were not effective against the FabK isoform, however, inhibited the growth of <i>Streptococcus pneumoniae</i> that contained only the FabK isoform. Additionally no resistant mutant to the compounds was obtained. Importantly, <i>fabK</i>-overexpressing <i>Escherichia coli</i> was not resistant to these compounds, but was resistant to triclosan. These results demonstrate that the compounds inhibited another target in addition to FabI. Thus, meleagrin is a new class of FabI inhibitor with at least one additional mode of action that could have potential for treating multidrug-resistant bacteria.</p></div

Direct binding of the derivatives of meleagrin with <i>_{Staphylococcus aureus}</i> FabI by fluorescence quenching assay.

<p>(A) The more active derivative (<b>5</b>), (B) The inactive derivative (<b>7</b>), (C) triclosan (TCL) as a positive control, and (D) kanamycin (Km) as a negative control.</p

MOESM1 of Improvement of the pharmacological activity of menthol via enzymatic β-anomer-selective glycosylation

Additional file 1. Structural elucidation, LC–MS and HR-ESIMS data of (−)-menthol β-glucoside, (−)-menthol β-galactoside, and (−)-menthol N-acetylglucosamine. Lineweaver–Burk plot of (−)-menthol glucosylation by BLC with respect to menthol (Figure S1). LC–MS analysis of (−)-menthol glycosylation reaction by BLC with UDP-d-galactose (Figure S2) and UDP-d-N-acetylglucosamine (Figure S3). 1H NMR spectra of synthesized (−)-menthol α-glucoside and (−)-menthol β-glucoside (Figure S4). 1H and 13C NMR spectra of (−)-menthol β-glucoside (Figure S5) and (−)-menthol β-galactoside (Figure S6) prepared by BLC-catalyzed glycosylation reactions. HMBC data of the menthol glucoside and menthol galactoside prepared by BLC-catalyzed glycosylation reactions (Figure S7). Topical cooling test (Table S1)

Comparison of the inhibitory effects of meleagrin (1) and its derivatives against <i>Staphylococcus aureus</i> and <i>E. coli</i> FabI, bacterial growth, and [¹⁴C] acetate and [¹⁴C] leucine incorporation into membrane fatty acids.

a<p><i>S. aureus</i> RN4220; ^b<i>E. coli</i> KCTC 1924; ^c<i>S. pneumoniae</i> KCTC 3932.</p

Frequency of resistance to meleagrin (1) and its more active derivative.

<p>Frequency of resistance to meleagrin (1) and its more active derivative.</p

The mechanism of inhibition of <i>_{Staphylococcus aureus}</i> FabI by meleagrin respective to t-o-NAC thioester (A) and NADPH (B), and <i>_Ki</i> determination of meleagrin (C).

<p>The mechanism of inhibition of <i>_{Staphylococcus aureus}</i> FabI by meleagrin respective to t-o-NAC thioester (A) and NADPH (B), and <i>_Ki</i> determination of meleagrin (C).</p

Reduced susceptibility of <i>fabI</i>-overexpressing <i>Staphylococcus aureus</i> to meleagrin (1) and its derivatives.

<p>Reduced susceptibility of <i>fabI</i>-overexpressing <i>Staphylococcus aureus</i> to meleagrin (1) and its derivatives.</p

Unchanged susceptibility of <i>fabK</i>-overexpressing <i>E. coli</i> to meleagrin (1) and its derivative (MIC, μg/mL).

a<p>3% arabinose was treated.</p

Effects of meleagrin (1) on incorporation of radiolabeled precursors into <i>S. aureus</i> and <i>S. pneumoniae</i>.

a<p><i>S. aureus</i> RN4220; ^b<i>S. pneumoniae</i> KCTC 3932. ^cReference antibacterials used for inhibition of acetate, thymidine, uridine, isoleucine, and N-acetyl-d-glucosamine incorporation are triclosan, norfloxacin, rifampin, chlorampenicol, and vancomycin, respectively. ^dReference antibacterials in <i>S. pneumoniae</i> were the same as in <i>S. aureus</i>, except cerulenin was used instead of triclosan for acetate inhibition.</p

Flavimycins A and B, Dimeric 1,3-Dihydroisobenzofurans with Peptide Deformylase Inhibitory Activity from <i>Aspergillus flavipes</i>

Flavimycins A (<b>1</b>) and B (<b>2</b>), novel dimeric 1,3-dihydroisobenzofurans, were isolated as inhibitors of peptide deformylase from cultures of <i>Aspergillus flavipes</i>. Their chemical structures were established by NMR and MS data analysis. Compounds <b>1</b> and <b>2</b> exist as epimeric mixtures at C-1 through fast hemiacetal–aldehyde tautomerism. Compounds <b>1</b> and <b>2</b> inhibited <i>Staphylococcus aureus</i> peptide deformylase with IC₅₀ values of 35.8 and 100.1 μM, respectively. Consistent with their PDF inhibition, <b>1</b> showed two times stronger antibacterial activity than <b>2</b> on <i>S. aureus</i> including MRSA, with MIC values of 32–64 μg/mL