Improved Synthesis of Asymmetric Curcuminoids and Their Assessment as Antioxidants |
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Authors: | Yang-Je Cheng Cai-Wei Li Cing-Ling Kuo Tzenge-Lien Shih Jih-Jung Chen |
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Institution: | 1.Department of Chemistry, Tamkang University, Tamsui Dist., New Taipei City 251301, Taiwan; (Y.-J.C.); (C.-L.K.);2.Institute of Traditional Medicine, National Yang Ming Chiao Tung University, Taipei 112304, Taiwan;3.Department of Pharmacy, College of Pharmaceutical Sciences, National Yang Ming Chiao Tung University, Taipei 112304, Taiwan;4.Department of Medical Research, China Medical University Hospital, China Medical University, Taichung 404332, Taiwan |
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Abstract: | In this paper, the syntheses of twelve asymmetric curcumin analogs using Pabon’s method are reported. Generally, the previously reported yields of asymmetric curcuminoids, such as 9a (53%), 9c (38%), and 9k (38%), have been moderate or low. Herein, we propose that the low yields were due to the presence of water and n-BuNH2 in the reaction media. To prove this formulated hypothesis, we have demonstrated that the yields can be improved by adding molecular sieves (MS) (4 Å) to the reaction mixture, thus reducing the interference of water. Therefore, improved yields (41–76%) were obtained, except for 9b (36.7%), 9g (34%), and 9l (39.5%). Furthermore, compounds 9b, 9d, 9e, 9f, 9g, 9h, 9i, 9j, and 9l are reported herein for the first time. The structures of these synthetic compounds were determined by spectroscopic and mass spectrometry analyses. The free radical scavenging ability of these synthetic asymmetric curcuminoids was evaluated and compared to that of the positive control butylated hydroxytoluene (BHT). Among the synthesized asymmetric curcuminoids, compounds 9a (IC50 = 37.57 ± 0.89 μM) and 9e (IC50 = 37.17 ± 1.76 μM) possessed effective 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging abilities, and compounds 9h (IC50 = 11.36 ± 0.65 μM) and 9i (IC50 = 10.91 ± 0.77 μM) displayed potent 2,2’-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radical scavenging abilities comparable to that of curcumin (IC50 = 10.14 ± 1.04 μM). Furthermore, all the synthetic asymmetric curcuminoids were more active than BHT. |
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Keywords: | asymmetric curcuminoids curcuminoids Pabon’ s method 2 4-pentanedione |
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