Confirmation of the Revised Structure of Samoquasine A and a Proposed Structural Revision of Cherimoline.

The identity of the natural product samoquasine A has remained obscure since its isolation from custard apple seeds in 2000. One of the proposed structures, benzo[ f]phthalazin-4(3 H)-one, was prepared in two steps by regioselective ortho-lithiation/formylation of N, N-diisopropyl-2-naphthylamide, followed by cyclization with hydrazine, but was shown to be different from the natural product. Perlolidine, another candidate structure, was synthesized by a novel route involving a β-selective Heck reaction of butyl vinyl ether. Both perlolidine and samoquasine A are converted by trimethylsilyldiazomethane into the same N-methyl derivative. In addition, the 13C NMR spectra of perlolidine and another structurally mis-assigned natural product, cherimoline, are almost identical. Thus, both samoquasine A and cherimoline are actually perlolidine.