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Bartolosides E–K from a Marine Coccoid Cyanobacterium

Afonso, Tiago B., Costa, M. Sofia, Rezende de Castro, Roberta, Freitas, Sara, Silva, Artur, Schneider, Maria Paula Cruz, Martins, Rosário, Leão, Pedro N.
Journal of natural products 2016 v.79 no.10 pp. 2504-2513
Cyanobacterium (genus), Synechocystis, carbon, glycolipids, glycosylation, multigene family, nuclear magnetic resonance spectroscopy, phylogeny
The glycosylated and halogenated dialkylresorcinol (DAR) compounds bartolosides A–D (1–4) were recently discovered from marine cyanobacteria and represent a novel family of glycolipids, encoded by the brt biosynthetic gene cluster. Here, we report the isolation and NMR- and MS-based structure elucidation of monoglycosylated bartolosides E–K (5–11), obtained from Synechocystis salina LEGE 06099, a strain closely related to the cyanobacterium that produces the diglycosylated 2–4. In addition, a genome region containing orthologues of brt genes was identified in this cyanobacterium. Interestingly, the major bartoloside in S. salina LEGE 06099 was 1 (above 0.5% dry wt), originally isolated from the phylogenetically distant filamentous cyanobacterium Nodosilinea sp. LEGE 06102. Compounds 5–11 are analogues of 1, with different alkyl chain lengths or halogenation patterns. Their structures and the organization of the brt genes suggest that the DAR-forming ketosynthase BrtD can generate structural diversity by accepting fatty acyl-derived substrates of varying length. Compound 9 features a rare midchain gem-dichloro moiety, indicating that the putative halogenase BrtJ is able to act twice on the same midchain carbon.