Abstract
Sanctolide A (1), a 14-membered polyketide–nonribosomal peptide (PK–NRP) hybrid macrolide, was isolated from the cultured cyanobacterium Oscillatoria sancta (SAG 74.79). The planar structure was determined using various spectroscopic techniques including HRESIMS, and 1D and 2D NMR analyses. The relative configuration was assigned by J-based configurational analysis in combination with NOE correlations. The absolute configuration was determined by Mosher ester and enantioselective HPLC analyses. The structure of sanctolide A (1) features a rare N-methyl enamide and a 2-hydroxyisovaleric acid, which are incorporated to form a 14-membered macrolide ring structure, comprising a new type of cyanobacterial macrolides derived from a PKS–NRPS hybrid biosynthetic pathway.
Highlights
Sanctolide A (1), a 14-membered polyketide-nonribosomal peptide (PK-NRP) hybrid macrolide, was isolated from the cultured cyanobacterium Oscillatoria sancta (SAG 74.79)
Polyketide-nonribosomal peptide (PK-NRP) hybrids represent a major class of cyanobacterial secondary metabolites.[4]
A major group of cyanobacterial PK-NRP hybrid metabolites is lipopeptides, where linear or cyclic peptides contain one lipophilic residue of polyketide origin such as β-amino acid and N-acyl residues.[2]. Another subclass of cyanobacterial PK-NRP hybrid metabolites is comprised of macrolides whose building blocks are mainly acetates with one or two amino acids incorporated into their macrolide ring structures
Summary
Sanctolide A (1), a 14-membered polyketide-nonribosomal peptide (PK-NRP) hybrid macrolide, was isolated from the cultured cyanobacterium Oscillatoria sancta (SAG 74.79). Keywords cyanobacteria; Oscillatoria sancta; 14-membered macrolide; PK-NRP hybrid; brine shrimp toxicity In our continuing search for biologically active secondary metabolites from cultured cyanobacteria, the cell extract of Oscillatoria sancta (SAG 74.79) was initially evaluated for its activity in a brine shrimp toxicity assay and found to be active.
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