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.