Influenza remains a highly pathogenic and hardly controlled human infection. The ability of selecting drug-resistant variants necessitates the search and development of novel anti-influenza drugs. Herein, we describe the synthesis and evaluation of a series of novel 2-substituted 7,8-dihydro-6H-imidazo[2,1-b][1,3]benzothiazol-5-ones 3a-k for their virus-inhibiting activity against influenza A virus. The new analogues 3a-k prepared in two steps from commercially available cyclohexane-1,3-diones were fully characterized by their NMR and mass spectral data. Among the new derivatives screened for cytotoxicity and in vitro antiviral activity against influenza virus A/Puerto Rico/8/34 (H1N1) in MDCK cells, three analogues 3i-k containing a thiophene unit were found to exhibit high virus-inhibiting activity (high SI values) and a favorable toxicity profile. The compound 3j (CC 50 : >1000 μM, SI = 77) with higher potency is the best anti-influenza hit analogue for further structural optimization and drug development. The most active compounds did not inhibit viral neuraminidase and possess therefore other targets and mechanisms of activity than the currently used neuraminidase inhibitors.

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A series of new noscapinoids designed; synthesized and assessed whether its 3‐ylidenephthalide and isocoumarin conjugates improved cytotoxicity. Cu‐catalysed Sonogashira coupling of N‐propargyl noscapine with 2‐bromobenzoic acids followed by in‐situ substrate‐directed 5‐exo‐dig or 6‐endo‐dig cyclization produced 3‐ylidenephthalide 6 a–6 f and isocoumarin 7 a–7 h analogues in very good yields. In comparison to the lead drug, noscapine, all the newly synthesised derivatives exhibited strong cytotoxic potential in vitro with IC50 ranging from 5.4 μM to 39.5 μM across the evaluated panel of cancer cell lines, without harming normal cells (IC50 >300 μM).