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Benzylidene-bis-(4-Hydroxycoumarin) and Benzopyrano-Coumarin Derivatives: Synthesis, 1H/13C-NMR Conformational and X-ray Crystal Structure Studies and In Vitro Antiviral Activity Evaluations

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Author(s): Davorka Završnik | Samija Muratović | Damjan Makuc | Janez Plavec | Mario Cetina | Ante Nagl | Erik De Clercq | Jan Balzarini | Mladen Mintas

Journal: Molecules
ISSN 1420-3049

Volume: 16;
Issue: 7;
Start page: 6023;
Date: 2011;
Original page

Keywords: 4-hydroxycoumarin | benzopyranocoumarin | antiviral activity | 1H/13C-NMR conformational study | X-ray diffraction

ABSTRACT
We report on the synthesis of 4-hydroxycoumarin dimers 1–15 bearing an aryl substituent on the central linker and fused benzopyranocoumarin derivatives 16–20 and on their in vitro broad anti-DNA and RNA virus activity evaluations. The chemical identities and structure of compounds 1–20 were deduced from their homo- and heteronuclear NMR measurements whereas the conformational properties of 5, 14 and 20 were assessed by the use of 1D difference NOE enhancements. Unequivocal proof of the stereostructure of compounds 7, 9, 16 and 18 was obtained by single crystal X-ray diffraction method. The X-ray crystal structure analysis revealed that two 4-hydroxycoumarin moieties in the 4-trifluoromethylphenyl- and 2-nitrophenyl derivatives (compounds 7 and 9, respectively) are intramolecularly hydrogen-bonded between hydroxyl and carbonyl oxygen atoms. Consequently, the compounds 7 and 9 adopt conformations in which two 4-hydroxy-coumarin moieties are anti-disposed. Antiviral activity evaluation results indicated that the 4-bromobenzylidene derivative of bis-(4-hydroxycoumarin) (compound 3) possesses inhibitory activity against HSV-1 (KOS), HSV-2 (G), vaccinia virus and HSV-1 TK- KOS (ACVr) at a concentration of 9–12 μM and at a minimum cytotoxic concentration (MCC) greater than 20 μM. Compounds 4–6, 8, and 20 were active against feline herpes virus (50% effective concentration, EC50 = 5–8.1 μM), that is at a 4-7-fold lower concentration than the MCC.
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