Abstract
The strain Streptomyces osmaniensis CA-244599 isolated from the Comoros islands was submitted to liquid-state fermentation coupled to in situ solid-phase extraction with amberlite XAD-16 resin. Elution of the trapped compounds on the resin beads by ethyl acetate afforded seven metabolites, osmanicin (1), streptazolin (2), streptazone C (3), streptazone B1 (4), streptenol C (5), nocardamine (6) and desmethylenylnocardamine (7). Osmanicin (1) is a newly reported unusual scaffold combining streptazolin (2) and streptazone C (3) through a Diels-Alder type reaction. Experimental evidence excluded the spontaneous formation of 1 from 2 and 3. The isolated compounds were evaluated for their ability to inhibit elastase using normal human diploid fibroblasts. Compound 1 exhibited the most potent activity with an IC50 of 3.7 μM.
Highlights
The Streptomyces genus belongs to the gram-positive actinobacteria phylum and is among the most prolific producers of diverse and bioactive secondary metabolites
The strain was confirmed as Streptomyces by molecular analysis according to its 16S rRNA and tentatively assigned to the species S. osmaniensis by following phylogenetic analysis (Figure 1)
The compounds were eluted from the resin by ethyl acetate followed by methanol, and analyzed by HPLC coupled with PDA, LSD, MS detectors and were evaluated for their activity in cell-based (BJ cells) assays at the concentration of 1 and 10 μg/mL (Figure 2)
Summary
The Streptomyces genus belongs to the gram-positive actinobacteria phylum and is among the most prolific producers of diverse and bioactive secondary metabolites. These metabolites belong to different structural classes, including polyketides, peptides, terpenoids, alkaloids and hydrazides [1], which exhibit a wide range of biological activities such as antibiotic (vancomycin, erythromycin and tetracycline), antifungal (amphotericin B), anticancer (mitomycin C), antiparasitic (ivermectin) and immunosuppressive (rapamycin) activities [2]. Streptomyces species from terrestrial and marine ecosystems have been intensively investigated in recent decades, there still remains a pool of unexplored diversity of secondary metabolites. This discovery pipeline is continuously fed through innovative experimental strategies [3]. In the frame of the current work, we describe the scale-up isolation and characterization of a new elastase inhibitor together with six previously described metabolites that have potential applications in the cosmetic industry
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