Paenimacrolidin, a novel macrolide antibiotic from Paenibacillus sp. F6-B70 active against methicillin-resistant Staphylococcus aureus.
Bottom Line: Elucidation of the structure by nuclear magnetic resonance and infrared spectroscopy revealed that the active compound, paenimacrolidin (PAM), was a novel 22-membered macrolide with side-chains.The antibiotic capacity of PAM was compromised by its instability, which can be overcome significantly with addition of an anti-oxidant.To our knowledge, this is the first report of the isolation of an active macrolide from paenibacilli, which may be a promising source of novel antibiotics.
Affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, China. email@example.comShow MeSH
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Mentions: The analysis of the 1H NMR, 13C NMR and HMQC spectra of PAM enabled us to assign all the protons to their bonding carbons. Two subunits comprising C‐2 to C‐23 including the methyl group carbons C‐32 and C‐33, and C‐25 to C‐30 indicated by the bold lines (Fig. 3) were mainly established by 1H–1H COSY spectra. The assembly of the two subunits, C‐atoms and hetero‐atoms, was achieved based on clear HMBC findings (Fig. 3). The chemical shift of carbon C‐21 (δH 5.18 p.p.m.; δc 80.3 p.p.m.) and the required ring double‐bond equivalents indicated a ring closure between C‐21 and C‐1 to construct a 22‐membered macrolide, which was confirmed by the cross‐peak of H‐21/C‐1 in the HMBC spectrum. The correlations of the H‐31/C‐23, H‐31/C‐24 and H‐31/C‐25 indicated the presence of a triene moiety, and the absorption maximum at 277 nm (logε 4.57) exhibited in the UV spectrum supported this conclusion. Large coupling constants (Table 2) showed the carbon–carbon double bonds Δ6,7 and Δ22,23 of PAM to have E geometries, as shown in Fig. 3. The geometry of Δ26,27 was determined as Z by the small coupling constant. The E geometry of Δ24,25 was deduced by the NOESY correlation between H‐31 and H‐25. The overlapping proton signals of Δ15,16 and Δ18,19 made it difficult to calculate their coupling constants, so the NOESY spectra were applied to establish the geometry of Δ15,16 and Δ18,19. The proton signal of H‐14 at δ 2.28 corresponded with that of H‐16 (δ 5.34), suggesting the E geometry of Δ15,16. The configuration of Δ18,19 as Z was also solved by the corresponding NOESY correlation of H‐32/H‐17. In summary, the structure of PAM was elucidated as a 22‐membered macrolide with a side‐chain, which was a unique highly unsaturated moiety with a conjugated triene and a terminal double bond.
Affiliation: Institute of Microbiology, College of Life Sciences, Zhejiang University, Hangzhou, China. firstname.lastname@example.org