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Violacin A, a chromanone derivative, isolated from a fermentation broth of Streptomyces violaceoruber, has excellent anti-inflammatory potential. Herein, a biogenetically modeled approach to synthesize violacin A and twenty-five analogues was described, which involved the preparation of aromatic polyketide precursor through Claisen condensation and its spontaneous cyclization. The inhibitory effect on nitric oxide (NO) production of all synthetic molecules was evaluated by lipopolysaccharide (LPS)-induced Raw264.7 cells. The results revealed that introduction of aliphatic amine moieties on C-7 obviously improved the anti-inflammation effect of violacin A, and also the aromatic ether instead of ketone group at side chain was favorable to increase the activity. Among them, analogue 7a and 16d were screened as the most effective anti-inflammatory candidates. Molecular mechanism research revealed that 7a and 16d acquired anti-inflammatory ability due to the inhibition of NF-κB signaling pathway.

A concise total synthesis of an exceedingly potent anti-inflammatory agent violacin A as well as the preparation of thirty analogues of this lead from commercially available orcinol are described. Highlights of our synthetic efforts involve Friedel-Crafts acylation, the regioselective etherification and esterification of phenolic hydroxyl groups, and Baker-Venkatamaran rearrangement to form basic skeleton of violacin A. The deprotection reaction with Pd-catalytic was involved to avoid the elimination of the hemiacetal hydroxyl at C2. In addition, all synthetic compounds were screened for anti-inflammatory activity against nitric oxide (NO) production using lipopolysaccharide (LPS)-induced Raw264.7 cells. A range of violacin A derivatives 11b, 11d, 11f, 12e, 12g, 13g, 17d-g exhibited stronger anti-inflammatory effect than that of violacin A. Notably, halogeno-benzyloxy substituent at C-7 were favourable for anti-inflammatory activities of violacin A derivatives. Additionally, Western blot results indicated halogeno-benzyloxy derivatives inhibited pro-inflammatory cytokines releases correlated with the suppression of NF-κB signaling pathway.