The Identification and Dereplication of Natural Products From Cyanobacteria
thesisposted on 06.08.2019, 00:00 by Jr. Julio C Soriagalvarro
Cyanobacteria are prolific producers of secondary metabolites that contain unique chemical features and biological activities. In this thesis, we demonstrate the utility of untargeted MS/MS, GNPS, and 1H NMR spectroscopy in dereplicating known cytotoxic constituents directly from the active fractions of the freshwater cyanobacterium cf. Spirulina sp. UIC 10531. In addition, bioassay-guided fractionation was used to discover novel secondary metabolites from the freshwater cyanobacterium Desmonostoc sp. UIC 10056. Desmothiazolamide A and B were isolated by semi-preparative HPLC and the structures were elucidated by a combination of HRMS and 1D and 2D NMR. The configurations of the amino acid residues were assigned after acid hydrolysis using Marfey’s method. Both desmothiazolamide A and B are members of the class of compounds known as cyclamides, which are characterized as macrocyclic hexapeptides that contain heterocyclic rings (oxazole and thiazole moieties as well as their reduced derivatives) intercalated between amino acid residues. A wide variety of biological activities have been reported for cyclamides including antialgal, phytotoxic, sedative, multi-drug-resistance-reversing, antiparasitic, and antimalarial properties. However, no activity was observed for desmothiazolamide A and B when evaluated for antiproliferative activity against human cancer cell lines (HT-29, MDA-MB-435, MDA-MB-231, and OVCAR3) and antibacterial activity against Mycobacterium tuberculosis and Pseudomonas aeruginosa.