Abstract
Five new phenolic siderophores 1–5 were isolated from the organic extract of a culture broth in a modified SGG medium of Pseudomonas sp. UIAU-6B, obtained from sediments collected from the Oyun river in North Central Nigeria. The structure of the new compounds, pseudomonin A–C (1–3) and pseudomobactin A and B (4 and 5) isolated alongside two known compounds, pseudomonine (6) and salicylic acid (7), were elucidated based on high-resolution mass spectrometry, 1D and 2D NMR analyses. The absolute configuration of the threonine residue in compounds 1–5 was determined by Marfey analysis. The antimicrobial evaluation of compound 4 exhibited the most potent activity against vancomycin-sensitive Enterococcus faecium VS144754, followed by 3 and 5, with MIC values ranging from 8 to 32 µg/mL. Compounds 2 and 3 exhibited moderate activity against Mycobacterium tuberculosis H37Rv, with MIC values of 7.8 and 15.6 µg/mL, respectively. Plausible biosynthetic hypotheses toward the new compounds 1–5 were proposed.
Highlights
The introduction of antimicrobial drugs in the mid-20th century has had an unprecedented positive impact on human health, but the current threat of multiple drug resistance may well roll back all these past achievements [1]
UIAU-6B in modified SGG medium indicated the presence of some interesting peaks with molecular ions which gave no hits when they were searched in natural product databases (Antibase)
The two known compounds, pseudomonine (6) and salicylic acid (7) were isolated as the major constituents of the extracts and their structures were determined by analysis of HRESIMS, 1D and 2D NMR data which were comparable with those reported in the literature [28,36,37]
Summary
The introduction of antimicrobial drugs in the mid-20th century has had an unprecedented positive impact on human health, but the current threat of multiple drug resistance may well roll back all these past achievements [1]. The two known compounds, pseudomonine (6) and salicylic acid (7) were isolated as the major constituents of the extracts and their structures were determined by analysis of HRESIMS, 1D and 2D NMR data (see Figure 1 and Supporting Information File 1 for details) which were comparable with those reported in the literature [28,36,37].
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