Potential COX-2 inhibitors modulating NF-κB/MAPK signaling pathways: Design, synthesis and evaluation of anti-inflammatory activity of Pterostilbene-carboxylic acid derivatives with an oxime ether moiety.

In this work, a series of novel Pterostilbene-oxime ether-carboxylic acid (POC) derivatives (d1-d10, e1-e10 and 1-13) were designed, synthesized, and characterized by spectroscopic techniques. In order to further determine the absolute configuration of these compounds, one of them, compound d3, was investigated by X-ray single crystal diffraction method. d3 had a triclinic crystal with P-1 space group, and its CHCH and CHN was confirmed as E configuration. A strong hydrogen bond was formed between the hydrogen atom in CHCH moiety and the nitrogen atom in CHN moiety, which was a vital factor in the formation and stability of E configuration in the CHCH and CHN. The safety and anti-inflammatory activities of compounds (d1-d10, e1-e10 and 1-13) in vitro were evaluated. At 20 μM, compounds (d1-d10, e1-e10 and 1-13 were non-toxic and exhibited weak to strong inhibitory effects on the LPS-induced NO release. Among them, five compounds (1, 2, 7, 8 and 9) showed excellent anti-inflammatory effects with IC₅₀ (NO) values ranging from 9.87 to 19.78 μM, as well as strong COX-2 inhibitory abilities with IC₅₀ (COX-2) values ranging from 85.44 to 140.88 nM. Moreover, there was a rough positive correlation between their anti-inflammatory properties and the COX-2 inhibitory abilities. Compounds (1, 2, 7, 8 and 9) smoothly docked with COX-2 protein (PDB ID: 5KIR) to form stable complexes with strong hydrogen bonds, with an affinity range of -8.3 to -9.9 kcal/mol. SAR indicated that the amidation of POC at R₂ position was more favorable for enhancing the compound's biological actives than esterification. In addition, the 4-fluobenzyl substitution at R₂ position of the oxime ether moiety can obviously enhance the activity of above amide derivates. Introducing acyl groups (CO(CH₂)_nCH₃, n = 2, 4 and 6) into NH(CH₂)₃OH group to form ester chain is disadvantageous for activity enhancing, moreover, the longer the carbon chain, the poorer the activity. The strongest COX-2 inhibitor (IC₅₀ (COX-2) = 85.44 ± 3.88 nM), compound 7, exerted as anti-inflammatory activities (IC₅₀ (NO) = 9.87 ± 1.38 μM) by down-regulating the expression of COX-2 and iNOS, and modulating NF-κB/MAPK signaling pathways.