Dilatatin, the first example of a C-allosylated natural product

Abstract Dilatatin, the xanthone- C -glycoside previously isolated from the filmy fern Hymenophyllum dilatatum , is identified as 2- C -β- d -allopyranosyl-1,3,6,7-tetrahydroxyxanthone. The glycosyl moiety is demonstrated to be allopyranose by 13 C NMR spectroscopy using synthetic β- d -allopyranosyl-2,4,6-trimethoxybenzene as a model.