New derivatives of the closo-decaborate anion [B₁₀H₉–O(CH₂)₂O(CH₂)₃C(O)–L–OCH₃]²⁻ (An) (1: L = Trp; 2: L = His; 3: L = Met; 4: L = Ala(2-oxopyrrolidin-3-yl) (Pld) were synthesized and isolated as tetraphenylphosphonium salts (Ph₄P)₂An. Anions 1²⁻; 2²⁻; 3²⁻, and 4²⁻ 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 = 1–4), 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 Na₂1 and Na₂2 had IC₅₀ of 5.0 and 20.0 μg/mL, respectively, while for compounds Na₂3 and Na₂4, IC₅₀ values could not be achieved at the concentrations studied. The studies performed for molecular docking of the anionic part of 1²⁻ and 2²⁻ with the transmembrane domain of viroporin M2 show some differences in the location of these two ligands inside the M2 canal pore.

The emergence of drug-resistant influenza virus strains necessitates the development of novel antiviral agents with unique mechanisms of action. This study presents the synthesis and in vitro evaluation of a new class of antiviral compounds: sodium salts of amino acid ester conjugates based on the closo-dodecaborate anion [B₁₂H₁₂]²⁻, linked via a tetrahydropyran-derived spacer (Na₂[B₁₂H₁₁O(CH₂)₆C(O)X], where X = L-Trp-OMe (Na₂2); L-His-OMe (Na₂3); L-Met-OMe (Na₂4); Pld-OMe (Na₂5)). The antiviral activity was assessed against contemporary, multidrug-resistant influenza A virus strains, including A/Cheboksary/125/2020 (H1N1)pdm09 and A/IIV-Orenburg/83/2012 (H1N1)pdm09. Cross-platform comparison revealed that the dodecaborate-tryptophan conjugate Na₂2 exhibited comparable efficacy to its lead decaborate analog against the Orenburg strain while demonstrating potent activity (IC₅₀ = 5.0 µg/mL) against the Cheboksary strain with reduced susceptibility to neuraminidase inhibitors (oseltamivir; zanamivir) and complete resistance to M2 channel blockers. The histidine-based conjugate Na₂3 also showed significant efficacy against the Cheboksary strain, while methionine and lactam derivatives (Na₂4; Na₂5) remained inactive. This work confirms boron clusters as versatile platforms for antiviral development and establishes structure–activity relationships crucial for optimizing both B₁₀ and B₁₂-based therapeutics against resistant influenza strains.

Objective: This study aimed to develop and evaluate stable pharmaceutical compositions based on squalene derived from both animal (shark liver) and plant (amaranth oil) sources. Methods: Oil-in-water nanoemulsions were prepared and stored at 4 °C for six months to evaluate stability. Key stability parameters, including droplet size and zeta potential, were determined using Dynamic Light Scattering (DLS). The immunogenicity of VLP-based rotavirus vaccine formulations containing these adjuvants was evaluated in a guinea pig model. Humoral and cellular immune responses were quantified using Enzyme-Linked Immunosorbent Assay (ELISA) for IgG titers, Neutralization Assays (NA) for virus-neutralizing activity, and the Lymphocyte Blast Transformation Reaction (LBTR) to assess cell-mediated immunity. Results: Both formulations exhibited high stability at 4 °C. Mean droplet diameters were 157 ± 3 nm (animal-derived) and 149 ± 3 nm (plant-derived), which were smaller than the commercial reference (174 ± 4 nm). Zeta potential values (-35 to -39 mV) confirmed robust colloidal stability. Immunization elicited potent responses; no statistically significant differences were observed between the two squalene sources regarding specific IgG titers (GM = 126 267) or virus-neutralizing activity (VNA GM = 640 vs 452.5, p > 0.05). Cellular immunity was induced by both adjuvants, yielding Proliferation Stimulation Index (PSI) values of 3.11 for the plant-derived formulation and 2.10 for the animal-derived variant. Conclusion: Plant-derived squalene from amaranth oil is a highly effective, sustainable alternative to shark-derived components, providing comparable stability and immunogenic potency for vaccine delivery. Keywords: pharmaceutical compositions, adjuvants, squalene, amaranth oil, nanoemulsions, virus-like particles, VLPs, vaccine formulations.

A series of novel substituted derivatives of the closo-decaborate anion [B₁₀H₁₀]²⁻ bearing alkoxy spacer chains of varying length derived from ring-opened crown ethers (12-crown-4, 15-crown-5, and 18-crown-6) with pendant L-amino acid methyl ester residues (L-tryptophan and L-histidine) have been synthesized. The synthetic approach involved the nucleophilic ring-opening of oxonium crown ether derivatives of the closo-decaborate anion followed by coupling with amino acid methyl esters via mixed anhydride activation. The obtained compounds were characterized by multinuclear NMR spectroscopy (¹H, ¹¹B, ¹³C), IR spectroscopy, elemental analysis, and electrospray ionization mass spectrometry (ESI-MS). The compounds were obtained as sodium salts and evaluated for their in vitro cytotoxic and antiviral properties against the influenza A virus strain A/Moscow/78/2020 (H1N1)pdm09, which contains the S31N mutation conferring resistance to adamantane-class drugs. Cytotoxicity was assessed on MDCK cells, and antiviral activity was determined by cell ELISA. The results revealed a clear structure–activity relationship: the length of the alkoxy spacer chain significantly influenced both antiviral activity and selectivity. The shortest spacer (derived from 12-crown-4) proved to be optimal, while elongation of the chain led to a decrease in antiviral potency. The compound containing a 12-crown-4-derived spacer and a tryptophan methyl ester residue exhibited the highest selectivity index (SI = 155) with low cytotoxicity (CC₅₀ = 155 µg/mL) and high antiviral activity (IC₅₀ = 1.0 µg/mL). Tryptophan-containing derivatives consistently outperformed their histidine analogues, confirming the key role of the indole side chain in antiviral activity. Overall, the closo-decaborate platform with crown ether-derived spacers and amino acid ester pendant groups represents a promising scaffold for the development of low-toxicity, highly selective inhibitors of influenza A virus replication. The compound with the 12-crown-4-derived spacer and a tryptophan methyl ester residue merits further investigation as the most promising among the synthesized samples.

(1) Background: Turbid biological formulations present a challenge for conventional optical protein analysis because scattering and particulate heterogeneity can distort analytical signals. (2) Methods: This study evaluated the limitations of ultraviolet–visible spectroscopy, intrinsic fluorescence, and dynamic light scattering for heterogeneous protein-containing systems and explored diffuse reflectance kinetics (DRK) as a non-destructive complementary approach. Bovine serum albumin model systems with and without particulate components were used to assess matrix-related effects, while a squalene-adjuvanted virus-like particle (VLP) formulation was investigated as a representative turbid biopharmaceutical system. DRK analysis was based on time-resolved diffuse-reflectance image sequences and numerical descriptors of spatiotemporal scattering dynamics. (3) Results: Conventional optical methods were strongly affected by turbidity, whereas selected DRK descriptors showed a concentration-dependent response in a squalene-containing emulsion matrix and acceptable repeatability under the investigated conditions. The results support the potential of DRK for comparative monitoring of apparent protein-related changes in turbid biological preparations. (4) Conclusions: Further validation using independent final vaccine batches and orthogonal reference methods is required before DRK can be considered for quantitative protein determination.