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(3H)-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.