title: Structure and absolute stereochemistry of phormidolide, a new toxic metabolite from the marine cyanobacterium Phormidium sp.
abstract: The extract from a laboratory culture of an Indonesian isolate of the cyanobacterium Phormidium sp. displayed inhibitory activity in a Ras-Raf protein interaction assay. Assay-guided fractionation led to the isolation of both active and inactive materials of novel structure. The major inactive metabolite, phormidolide, was nevertheless highly toxic to brine shrimp (LC(50) = 1.5 microM), and hence, its structure was elucidated using various spectroscopic methods, primarily NMR. A series of partial structures were developed from standard experiments and then assembled using GHMBC, 2D INADEQUATE, and ACCORD-ADEQUATE data obtained on a (13)C-enriched sample. The relative stereochemistry at phormidolide's 11 chiral centers was established using the J-based configuration analysis method in concert with the G-BIRD(R)-HSQMBC NMR experiment. Absolute stereochemistry was determined on a bis-acetonide derivative using the variable temperature Mosher ester method. The robust number of NMR restraints provided from determination of most homonuclear and heteronuclear coupling constants in phormidolide, along with an abundance of NOE information, allowed construction of a refined lowest energy three-dimensional structure in Macromodel. Phormidolide is one of only a few macrolide-type natural products to be reported from marine cyanobacteria.
authors.affiliation: College of Pharmacy, Oregon State University, Corvallis, Oregon 97331, USA.
authors.forename: R Thomas
authors.initials: RT
authors.lastname: Williamson
authors.forename: Anna
authors.initials: A
authors.lastname: Boulanger
authors.forename: Alexandra
authors.initials: A
authors.lastname: Vulpanovici
authors.forename: Mary A
authors.initials: MA
authors.lastname: Roberts
authors.forename: William H
authors.initials: WH
authors.lastname: Gerwick
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry*; D018942:Macrolides / Q000737:chemistry*; D008386:Marine Biology; D008958:Models, Molecular; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors; D013237:Stereoisomerism; D014118:Toxins, Biological / Q000737:chemistry*; D018631:ras Proteins / Q000037:antagonists & inhibitors
chemical_list: D018942:Macrolides; D014118:Toxins, Biological; C475799:phormidolide; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins