NMR studies of phakellins and isophakellins.

Phakellins 3 and 4 and isophakellins 5 and 6 are tetracyclic pyrrole-imidazole alkaloids. Their structure elucidation is herein reviewed using state-of-the-art NMR methods. Special emphasis has been given to the application of ADEQUATE NMR pulse sequences. Furthermore, (15)N NMR chemical shifts, proton T1 relaxation times, and (1)J(CH) coupling constants were determined.