title: Application of 13C-labeling and 13C-13C COSY NMR experiments in the structure determination of a microbial natural product.
abstract: The elucidation of the structures of complex natural products bearing many quaternary carbons remains challenging, even in this advanced spectroscopic era. (13)C-(13)C COSY NMR spectroscopy shows direct couplings between (13)C and (13)C, which comprise the backbone of a natural product. Thus, this type of experiment is particularly useful for natural products bearing consecutive quaternary carbons. However, the low sensitivity of (13)C-based NMR experiments, due to the low natural abundance of the (13)C nucleus, is problematic when applying these techniques. Our efforts in the (13)C labeling of a microbial natural product, cyclopiazonic acid (1), by feeding (13)C-labeled glucose to the fungal culture, enabled us to acquire (13)C-(13)C COSY NMR spectra on a milligram scale that clearly show the carbon backbone of the compound. This is the first application of (13)C-(13)C COSY NMR experiments for a natural product. The results suggest that (13)C-(13)C COSY NMR spectroscopy can be routinely used for the structure determination of microbial natural products by (13)C-enrichment of a compound with (13)C-glucose.
authors.affiliation: Natural Products Research Institute, College of Pharmacy, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 151-742, Republic of Korea.
authors.forename: Yun
authors.initials: Y
authors.lastname: Kwon
authors.forename: Sunghyouk
authors.initials: S
authors.lastname: Park
authors.forename: Jongheon
authors.initials: J
authors.lastname: Shin
authors.forename: Dong-Chan
authors.initials: DC
authors.lastname: Oh
mesh_terms: D001231:Aspergillus flavus / Q000254:growth & development*; D001688:Biological Products / Q000737:chemistry* / Q000302:isolation & purification; D002247:Carbon Isotopes; D066241:Carbon-13 Magnetic Resonance Spectroscopy / Q000379:methods*; D007211:Indoles / Q000737:chemistry* / Q000302:isolation & purification; D007553:Isotope Labeling; D015394:Molecular Structure
chemical_list: D001688:Biological Products; D002247:Carbon Isotopes; D007211:Indoles; C000543:cyclopiazonic acid