Efficient synthesis of analogs of safflower yellow B, carthamin, and its precursor: two yellow and one red dimeric pigments in safflower petals

The synthesis of analogs (, , ) of two yellow pigments, safflower yellow B and the precursor of carthamin, and carthamin itself, a red pigment, which are produced in safflower (Carthamus tinctrious L.) petals and, which have a common dimeric quinochalcone structure, is reported. The key compound for the synthesis of these analogs, (p-hydroxycinnamoyl)filicinic acid () was synthesized in six steps from phloroglucinol in a total yield of 39%, which was reacted with 2,3,4,5,6-penta-O-acetyl-aldehydo-d-glucose, glyoxylic acid, and ethyl orthoformate in the presence of base to afford the corresponding analog, , , , in good yields, respectively. Precursor analog was then converted to carthamin analog by oxidative decarboxylation by treatment with potassium permanganate as well as the natural specimen.