A new class of pyrazino[1,2-a]benzimidazole derivatives possessing the SO 2 Me pharmacophore at the para position of the C-3 phenyl ring was designed, synthesized, and tested for their cyclooxygenase-2 (COX-2) inhibitory, anti-cancer and anti-platelet aggregation activities. In vitro COX-1/COX-2 inhibition studies showed that 2-(4methylphenyl)-1-methylene-3-(4-(methylsulfonyl)phenyl)-1,2-dihydropyrazino-[1,2a]benzimidazole (5g) was the most potent COX-2 inhibitor (IC 50 = 0.08 μM) and 2-(3,4,5-trimethoxyphenyl)-1-methylene-3-(4-(methylsulfonyl)phenyl)-1,2-dihydropyrazino-[1,2-a]benzimidazole (5m) had the highest selectivity index (SI > 909).Cytotoxicity of the synthesized compounds was also determined against the MCF-7 cell line. Most compounds were cytotoxic against MCF-7 cells and our results showed that compound 5m exhibited the highest anti-proliferative activity compared to the reference compound, cisplatin. Our data also indicated that compound 5k was the most potent platelet aggregation inhibitor according to aggregometry test results. K E Y W O R D S anti-cancer, anti-platelet aggregation, COX-2 inhibitory, docking study, MCF-7, pyrazinobenzimidazole 1 | INTRODUCTION Nonsteroidal anti-inflammatory drugs (NSAIDs) continue to be one of the most widely used prescription and over-the-counter medications. These drugs interfere with inflammatory mediators (prostaglandins) biosynthesis by inhibiting cyclooxygenase (COX) The pharmacologic effects of NSIADs are attributed to inhibition of COX-1 and COX-2 enzymes. COX-1 produces prostaglandins involved in normal cellular activity such as maintenance of kidney functions and gastric mucosa protection; COX-2 produces prostaglandins at inflammatory sites. [1] Most NSAIDs inhibit both COX-1 and COX-2, but with varying degrees of selectivity. The evidence shows that antiinflammatory activities of NSAIDs are due to the inhibition of COX-2, whereas the ulcerogenic adverse effects are associated with the inhibition of COX-1. The differences in the amino acid sequence of COX-1 and COX-2 binding sites provided valuable strategy for the design of selective COX-2 inhibitors. The main difference involves the presence of a second pocket within COX binding site, which is more available in COX-2, whereas restricted in COX-1 due to the extra steric bulk of Ile 523 in COX-1. The larger volume of COX-2 active site allows larger molecules to enter the active site and inhibit COX-2, selectively. [2] Based upon this, many selective COX-2 inhibitors have been designed and entered the market. These medicines have fewer Arch Pharm Chem Life Sci. 2019;352:e1800265.wileyonlinelibrary.com/journal/ardp

A new class of peptide derivatives possessing SO Me and N pharmacophores at the para position of a phenyl ring bound to different aromatic amino acids were synthesized based on solid-phase synthesis methodology, and evaluated as selective cyclooxygenase-2 (COX-2) inhibitors. One of the analogues, i.e., compound 2a as the representative of this series, was recognized as the highest selective COX-2 inhibitor with a COX-2 selectivity index of >500. The structure-activity relationships (SARs) acquired indicated that compound 2a containing a 4-(methylsulfonyl)benzoyl group as a pharmacophore and tyrosine as a ring bearing amino acid in the second position and glutamic acid as the C-terminal amino acid can give the essential geometry to provide selective COX-2 inhibitory activity. Antiproliferative activity of the synthesized peptides (1a-7b) was also determined against four different human cancer cell lines, including MCF-7, HepG2, A549, and HeLa. According to our results, A549, HepG2, and MCF7 seemed to be more sensitive cell lines than HeLa cells encountering these compounds, which gave inhibitory action with IC values from 4.8 to 64.4 µM. In this regard, compounds 3a and 2b displayed the best inhibitory activity against the cell lines. Moreover, a good correlation was observed between the antiproliferative potency and the COX-2 inhibitory activity of compounds 1a, 2a, 2b, and 5b. Such findings suggest that one of the mechanism of anticancer activity of these peptides may be through the COX-2 inhibitory action.