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

Abstract The synthesis of analogs ( 8 , 12 , 14 ) 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 ( 7 ) 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, 8 , 12 , 14 , in good yields, respectively. Precursor analog 12 was then converted to carthamin analog 14 by oxidative decarboxylation by treatment with potassium permanganate as well as the natural specimen.