| Abstract |
Chemical investigation of the cyanobacterium Microcystis aeruginosa NIES-4285 led to the isolation of six new natural products, microginins 705 (1), 719 (2), 733A (3), 733B (4), and 733C (5), and anabaenopeptin 885 (7), and three known compounds, anabaenopeptins 871 (6), B (8), and F (9). Planar structures and absolute configurations for 1-7 were determined by 2D NMR, HRMS, and Marfey's analyses. Microginin 733C (5), and anabaenopeptins 871 (6) and 885 (7) contained a unique residue of 2-amino-5-(4-hydroxyphenyl)pentanoic acid (Ahppa): doubly homologated tyrosine (di-hTyr). The biosynthetic origin of this nonproteinogenic amino acid di-hTyr was investigated, and it was found that MaHphABCDE are involved in the production of di-hTyr. In addition, biochemical characterization of aminotransferase MaHphE showed that it is a promiscuous enzyme. This result expanded the biocatalytic toolbox for amino acid homologation.
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