Abstract: In this study, docosahexaenoic acid (DHA) and astaxanthin were applied as reaction substrates to synthesize DHA astaxanthin ester The optimal reaction conditions were determined as follows: 250 mg of astaxanthin 282 mg of DHA, 5 mL of anhydrous acetone, 100 mg of 4-dimethylaminopyridine (DMAP) and, 100 mg of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDCI), were reacted in a nitrogen atmosphere under dark conditions with magnetic stirring at 25 ℃ for 3 h. As identified by liquid chromatography-mass spectrometry (LC-MS), the synthesized products were composed of free astaxanthin, DHA astaxanthin monoester and DHA astaxanthin diester. Each of these components was analyzed by HPLC-DAD and quantified by peak area normalization method. The results showed that under optimum conditions, DHA astaxanthin esters accounted for 95.67% of the total products, mainly DHA astaxanthin diester (77.46%), DHA astaxanthin monoester (18.21%) and small amounts of free astaxanthin (3.24%). DHA astaxanthin diesters and DHA astaxanthin monoesters were separated by silica gel column chromatography with increasing solvent polarity from 100:0 to 92:8 (petroleum ether:acetone, V/V). Finally, the purity of the purified DHA astaxanthin diesters and DHA astaxanthin monoesters were (98.2 ± 0.5)% and (94.0 ± 0.6)%, respectively.

Key words: astaxanthin, DHA astaxanthin ester, synthesis, isolation and identification, mass spectroscopy