Predicted Structure Rewrites History

Researchers have successfully predicted that the structure of a natural product reported two dozen years ago was assigned incorrectly and have used both theoretical and experimental means to prove that it is so (J. Am. Chem. Soc., DOI: 10.1021/ja3089394). Structural reassignments with theoretical origins are not commonplace. In most cases, reassignments instead originate with unsuccessful efforts to synthesize a compound with a misassigned structure. In this case, a Spanish group isolated a natural product they called aquatolide from a flowering Mediterranean plant and used experimental NMR data to structurally analyze it in 1989 (Tetrahedron Lett.,1989,30, 2851). Interested in the molecule’s ladderlike structure, Dean J. Tantillo of the University of California, Davis, was studying the compound recently and found discrepancies between the reported structure and chemical shift predictions made by computational NMR. Subsequent theoretical and experimental analysis by Tantillo, his UC Davis colleague Jared T. Shaw, and coworkers revealed that the correct structure is very different from the one reported originally. The original structure was consistent with the data on which it was based, but other possible structures also matched. One lesson, Shaw says, is that “extensive analysis combining theory and measurement may be needed before assigning the structures of complex natural products.”