New polyphenolic compounds with xanthylium skeletons formed through reaction between (+)-catechin and glyoxylic acid

The reaction between (+)-catechin and glyoxylic acid was studied in a model solution system. The major (+)-catechin carboxymethine-linked I dimer was isolated and shown to proceed to new polyphenolic compounds exhibiting abso rption maxima around 440 and 460 nm. Three yellow pigments were obtained by incubation of the 8-8 colorless isomer. One was the previously reported xa nthylium compound NJ2 with a maximum at 440 nm. The other two, showing abso rption maxima at 460 nm, were obtained separately by incubation of the colo rless dimer in hydroethanolic or methanolic medium. Structural elucidation of these two new yellow pigments was achieved by means of MS and 1D and 2D NMR techniques and showed that they were, respectively, ethyl and methyl es ters of NJ2. The fact that these compounds were not obtained when NJ2 was i ncubated in hydromethanolic or ethanolic medium showed that esterification took place before the formation of the xanthylium chromophores. The detecti on of the esterified colorless compounds and the corresponding xanthene int ermediates confirmed the postulated mechanism. New pigments exhibiting a st rong absorption at 560 nm were also observed.