Phytochemistry of the gum copal tree, Trachylobium verrucosum(gaertn.) oliv. The first natural α-hydroxychalcone and 2,3-cis- and 2,3-trans-3-methoxyflavanones
Besides high concentrations of (+)-2,3-trans-3,4-trans- and (+)-2,3-trans-3,4-cis-mopanols and -peltogynols, the heartwood of Trachylobium verrucosum contains α,2′,3,4,4′-pentahydroxychalcone and 3-O-methyl-2,3-cis-and -2,3-trans-fustins, representing the first natural α-hydroxychalcone and also the first 3-methoxyflavanones and 3-oxygenated-2,3-cis-flavanone, as prominent metabolites. They are associated with low concentrations of 2-benzyl-2-hydroxybenzo[b]furan-3(2H)-one and 3-hydroxyflavone analogues.
Mechanistic aspects of the synthesis of 2′-hydroxy-α,3,4,4′-tetramethoxy-trans-chalcone from (±)-3,3′,4′,7-tetra-O-methyl-2,3-trans-fustin and via the crossed aldol condensation, and its novel conversion into both 3,3′,4′,7-tetra-O-methyl-2,3-cis- and -2,3-trans-fustins are discussed. Fisetin tetramethyl ether is converted by photolysis into both mopanin and peltogynin trimethyl ethers.