Bartolosides E-K from a Marine Coccoid Cyanobacterium.

Area of Science:

• Marine Natural Products Chemistry
• Microbial Biochemistry
• Genomics

Background:

• Marine cyanobacteria produce diverse secondary metabolites.
• Bartolosides A-D (1-4) are novel glycosylated and halogenated dialkylresorcinols (DARs) encoded by the brt gene cluster.
• These compounds represent a unique class of glycolipids.

Purpose of the Study:

• To isolate and elucidate the structures of new bartolosides from Synechocystis salina.
• To investigate the brt biosynthetic gene cluster in Synechocystis salina.
• To understand the mechanisms of structural diversity in bartolosides.

Main Methods:

• Isolation and purification of compounds using chromatographic techniques.
• Structure elucidation via Nuclear Magnetic Resonance (NMR) and Mass Spectrometry (MS).
• Bioinformatic analysis of the brt gene cluster and its orthologues.

Main Results:

• Monoglycosylated bartolosides E-K (5-11) were isolated and characterized.
• Bartoloside 1 was identified as the major compound in Synechocystis salina, despite its original isolation from a different cyanobacterium.
• Structural analysis revealed variations in alkyl chain lengths and halogenation patterns, including a rare gem-dichloro moiety in compound 9.
• A genome region containing brt gene orthologues was identified in Synechocystis salina.

Conclusions:

• The DAR-forming ketosynthase BrtD contributes to structural diversity by accepting various fatty acyl-derived substrates.
• The halogenase BrtJ demonstrates the ability to perform multiple halogenation events on the same carbon.
• The findings provide insights into the biosynthesis and structural variability of this novel glycolipid family.