Natural product synthesis with unnatural results:: Characterization of a novel fused imidazolidinone tetrahydropyrroloindole ring system by long-range 1H-15N 2D-NMR

Synthetic efforts towards the indole alkaloid natural product roquefortine C resulted in the formation of an unknown intermediate. Elucidation of the structure of this molecule relied on the use of long-range H-1-N-15 2D-NMR. Computational predictions were used to facilitate the location of weak responses in long-range H-1-C-13 HMBC spectra. These methods provided conclusive evidence that this compound possessed a novel tetracycle. The complete H-1, C-13, and N-15 chemical shift assignments of this unique fused imidazolidinone tetrahydropyrroloindole derivative are reported.