Application of 13C-labeling and 13C–13C COSY NMR experiments in the structure determination of a microbial natural product

다국어 초록 (Multilingual Abstract)

The elucidation of the structures of complexnatural products bearing many quaternary carbons remainschallenging, even in this advanced spectroscopic era.
13C–13C COSY NMR spectroscopy shows direct couplingsbetween 13C and 13C, which comprise the backbone of anatural product. Thus, this type of experiment is particularlyuseful for natural products bearing consecutive quaternarycarbons. However, the low sensitivity of 13C-basedNMR experiments, due to the low natural abundance of the13C nucleus, is problematic when applying these techniques.
Our efforts in the 13C labeling of a microbial naturalproduct, cyclopiazonic acid (1), by feeding 13C-labeledglucose to the fungal culture, enabled us to acquire13C–13C COSY NMR spectra on a milligram scale thatclearly show the carbon backbone of the compound. This isthe first application of 13C–13C COSY NMR experimentsfor a natural product. The results suggest that 13C–13CCOSY NMR spectroscopy can be routinely used for thestructure determination of microbial natural products by13C-enrichment of a compound with 13C-glucose.

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