Isolation and characterization of water-soluble intermediates of blue pigments transformed from geniposide of Gardenia jasminoides

Gardenia blue dye was obtained through the reaction of methylamine with genipin, the aglycone of geniposide isolated from the fruits of Gardenia jasminoides. The resulting blue pigments were passed through Bio-Gel P-2 resin yielding five fractions, GM1 -GM5. Four fractions (GM1-GM4) were all blue pigments, and the first eluted higher molecular weight fraction GM1 had a higher tinctorial strength than the later eluted lower molecular weight fractions, GM2-GM4. The last eluted GM5 fraction with lambda(max) of 292 nm was colorless and was confirmed as the true intermediate of the blue pigments on the basis of UV-vis spectrophotometric evidence. The GM5 fraction was composed of two epimeric isomers, and their structures were characterized by H-1 NMR, H-1-H-1 COSY, C-13 NMR, and HMQC and HMBC spectral measurements.