title: Unequivocal 13C NMR assignment of cyclohexadienyl rings in bromotyrosine-derived metabolites from marine sponges.
abstract: Bromotyrosine-derived compounds are commonly isolated from Verongida sponges and are a major class of marine natural products. Here we report on the unequivocal (13)C NMR assignment of the brominated carbons at positions C-2 and C-4 of the cyclohexadiene ring, two carbons whose resonances are often incorrectly assigned. Interpretation of HMBC data acquired for a series of known bromotyrosine analogues, which included ianthesine E(1), aerothionin (2), 11-hydroxyaerothionin (3), and 11,19-dideoxyfistularin-3 (4), allowed us to unequivocally assign the carbons in question, C-2 and C-4, through the observance of unique HMBC correlations from the C-1 hydroxyl proton. Here we present the complete 2D NMR data sets recorded in DMSO-d(6) for 2-4 that were used to confirm the assignment and establish the working model. Using this model, a survey of the literature revealed that many members of this structure class had been wrongly assigned. This paper serves to reassign those compounds whose (13)C NMR assignment at positions C-2 and C-4 of the cyclohexadiene ring should be reversed.
authors.affiliation: Eskitis Institute, Griffith University, Brisbane, QLD 4111, Australia.
authors.forename: John A
authors.initials: JA
authors.lastname: Kalaitzis
authors.forename: Rohan A
authors.initials: RA
authors.lastname: Davis
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Quinn
mesh_terms: D000818:Animals; D002247:Carbon Isotopes; D053138:Cyclohexenes / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D011161:Porifera / Q000737:chemistry*; D012015:Reference Standards; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D053138:Cyclohexenes; C475724:bromotyrosine; D014443:Tyrosine