L-[3-13C]Phenylalanine andL-[3-13C]tyrosine were administered toMorusalbacell cultures, to produce intermolecular Diels–Alder type adducts of a prenylchalcone and a 2-arylbenzofuran such as chalcomoracin (1) as well as the adducts of two molecules of prenylchalcones such as kuwanon J (2) in high yields. The13C NMR spectra of1and2isolated from the cultures revealed that both amino acids were incorporated intact into chalcomoracin (1) and kuwanon J (2). This is the first example of direct NMR evidence for the almost equivalent incorporation of phenylalanine and tyrosine into the shikimate metabolites. This finding suggests the participation of a biosynthetic route from phenylalanine viatrans-cinnamate top-coumarate and from tyrosine top-coumarate in this plant.