In Vitro Study of Antiviral Properties of Compounds Based on 1,4-Dioxane Derivative of Closo-Decaborate Anion with Amino Acid Ester Residues Against Influenza Virus A/IIV-Orenburg/83/2012(H1N1)pdm09

New derivatives of the <i>closo</i>-decaborate anion [B₁₀H₉-O(CH₂)₂O(CH₂)₃C(O)-L-OCH₃]^2- (An) (<b>1</b>: L = Trp; <b>2</b>: L = His; <b>3</b>: L = Met; <b>4</b>: L = Ala(2-oxopyrrolidin-3-yl) (Pld) were synthesized and isolated as tetraphenylphosphonium salts (Ph₄P)₂An. Anions <b>1</b>^2-; <b>2</b>^2-; <b>3</b>^2-, and <b>4</b>^2- contain a pendant functional group from the L-tryptophan methyl ester, L-histidine methyl ester, L-methionine methyl ester, or methyl 2-amino-3-(2-oxopyrrolidin-3-yl)propanoate (-Trp-OCH₃, -His-OCH₃, -Met-OCH₃, or -Pld-OCH₃) residue, respectively, bonded with the boron cluster anion through the oxybis[(ethane-2,1-diyl)oxy] spacer. This pacer is formed as a result of the nucleophilic opening of the attached dioxane molecule in the [B₁₀H₉O(CH₂)₄O]^- starting derivative. Sodium salts of the target compounds were isolated and used in biological experiments. It was established that among compounds Na₂An (An = <b>1</b>-<b>4</b>), not all are capable of inhibiting the cytopathic effect of the virus in vitro. Sodium salts Na₂An have a low toxic effect on a monolayer of continuous canine embryonic kidney (MDCK) cell line. Compounds Na₂<b>1</b> and Na₂<b>2</b> had IC₅₀ of 5.0 and 20.0 μg/mL, respectively, while for compounds Na₂<b>3</b> and Na₂<b>4</b>, IC₅₀ values could not be achieved at the concentrations studied. The studies performed for molecular docking of the anionic part of <b>1</b>^2- and <b>2</b>^2- with the transmembrane domain of viroporin M2 show some differences in the location of these two ligands inside the M2 canal pore.