Guttiferic acid, a novel rearrangement product from minor chromenoxanthone pigments of Garcinia morella Desr.

Morellic and isomorellic acids (2 and 3), present in the seed coat as well as resinous exudate of Garcinia morella Desr., are geometric isomers and structurally related to morellin (1), the major chromenoxanthone pigment. Both form crystalline complexes with pyridine and afford guttiferic acid (7), a novel skeletal rearrangement product, when heated with mild alkali. Structure of the latter has been deduced mainly by a comparative study of 1H and 13C NMR spectra of methyl morellate (5), methyl-O-methyl morellate (6), guttiferic acid (7) and dimethyl guttiferate (8).