HEXACYCLIC INDOLE ALKALOIDS - THE STRUCTURE OF CUANZINE AS AN EXPERIMENTAL TEST OF MOLECULAR MECHANICS CALCULATIONS

The conformational space of cuanzine was explored by employing MM2 force field for energy calculations and minimization. Location of the global minimum on the potential energy surface furnished a geometry which resembles the literature reported X-ray conformation of vincamine 3. Moreover, the global minimum of structure 1 was found at a higher energy value than the global minimum of its C(16) epimer 8, suggesting that the previous assignment of structure 1 to natural cuanzine should be revised into 8. Reinterpretation of the 1H NMR data reinforced this suggestion which was ultimately confirmed by X-ray analysis of cuanzine hydrochloride.