Mikhail V. Pugachev

Synthesis and antibacterial activity of novel phosphonium salts on the basis of pyridoxine.

A series of 13 phosphonium salts on the basis of pyridoxine derivatives were synthesized and their antibacterial activity against clinically relevant strains was tested in vitro. All compounds were almost inactive against gram-negative bacteria and exhibited structure-dependent activity against gram-positive bacteria. A crucial role of ketal protection group in phosphonium salts for their antibacterial properties was demonstrated. Among synthesized compounds 5,6-bis[triphenylphosphonio(methyl)]-2,2,8-trimethyl-4H-[1,3]dioxino[4,5-c]pyridine dichloride (compound 20) was found to be the most effective towards Staphylococcus aureus and Staphylococcus epidermidis strains (MIC 5μg/ml). The mechanism of antibacterial activity of this compound probably involves cell penetration and interaction with genomic and plasmid DNA.

Bis-phosphonium salts of pyridoxine: the relationship between structure and antibacterial activity.

A series of 23 novel bis-phosphonium salts based on pyridoxine were synthesized and their antibacterial activities were evaluated in vitro. All compounds were inactive against gram-negative bacteria and exhibited the structure-dependent activity against gram-positive bacteria. The antibacterial activity enhanced with the increase in chain length at acetal carbon atom in the order n-Pr>Et>Me. Further increasing of length and branching of alkyl chain leads to the reduction of antibacterial activity. Replacement of the phenyl substituents at the phosphorus atoms in 5,6-bis(triphenylphosphonio(methyl))-2,2,8-trimethyl-4H-[1,3]-dioxino[4,5-c]pyridine dichloride (compound 1) with n-butyl, m-tolyl or p-tolyl as well as chloride anions in the compound 1 with bromides (compound 14a) increased the activity against Staphylococcus aureus and Staphylococcus epidermidis up to 5 times (MICs=1-1.25 μg/ml). But in practically all cases chemical modifications of compound 1 led to the increase of its toxicity for HEK-293 cells. The only exception is compound 5,6-bis[tributylphosphonio(methyl)]-2,2,8-trimethyl-4H-[1,3]dioxino[4,5-c]pyridine dichloride (10a) which demonstrated lower MIC values against S. aureus and S. epidermidis (1 μg/ml) and lower cytotoxicity on HEK-293 cells (CC(50)=200 μg/ml). Compound 10a had no significant mutagenic and genotoxic effects and was selected for further evaluation. It should be noted that all bis-phosphonium salt based on pyridoxine were much more toxic than vancomycin.

New Derivatives of Pyridoxine Exhibit High Antibacterial Activity against Biofilm-Embedded Staphylococcus Cells.

Opportunistic bacteria Staphylococcus aureus and Staphylococcus epidermidis often form rigid biofilms on tissues and inorganic surfaces. In the biofilm bacterial cells are embedded in a self-produced polysaccharide matrix and thereby are inaccessible to biocides, antibiotics, or host immune system. Here we show the antibacterial activity of newly synthesized cationic biocides, the quaternary ammonium, and bisphosphonium salts of pyridoxine (vitamin B6) against biofilm-embedded Staphylococci. The derivatives of 6-hydroxymethylpyridoxine were ineffective against biofilm-embedded S. aureus and S. epidermidis at concentrations up to 64 μg/mL, although all compounds tested exhibited low MICs (2 μg/mL) against planktonic cells. In contrast, the quaternary ammonium salt of pyridoxine (N,N-dimethyl-N-((2,2,8-trimethyl-4H-[1,3]dioxino[4,5-c]pyridin-5-yl)methyl)octadecan-1-aminium chloride (3)) demonstrated high biocidal activity against both planktonic and biofilm-embedded bacteria. Thus, the complete death of biofilm-embedded S. aureus and S. epidermidis cells was obtained at concentrations of 64 and 16 μg/mL, respectively. We suggest that the quaternary ammonium salts of pyridoxine are perspective to design new synthetic antibiotics and disinfectants for external application against biofilm-embedded cells.

Antibacterial effects of quaternary bis-phosphonium and ammonium salts of pyridoxine on Staphylococcus aureus cells: A single base hitting two distinct targets?

We studied the effects of quaternary bis-phosphonium and bis-ammonium salts of pyridoxine with lipophilic substituents on the survival and morphology of Staphylococcus aureus cells. We found that, while originating from the same base, they exhibit considerably different antimicrobial mechanisms. In the presence of Ca2+ ions the MIC and MBC values of ammonium salt increased 100-fold, suggesting that Ca2+ ions can successfully impede the membrane Ca2+ ions exchange required for ammonium salt incorporation. In contrast, in the presence of quaternary phosphonium salt, the artificial capsular-like material was formed around the cells and the filamentous and chain-like growth of the cells was observed suggesting the disruption of the cell division mechanisms. Altogether, both pyridoxine derivatives successfully inhibited the growth of gram-positive bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis) and Escherichia coli considerably, while demonstrated nearly no effect against Klebsiella pneumoniae and Pseudomonas aeruginosa. We suggest that due to their effects on distinct and likely complementary targets the derivatives of pyridoxine represent potentially perspective antibacterials with complicated adaptation and thus with lower risk of drug resistance development.

Synthesis and in vitro antitumor activity of novel alkenyl derivatives of pyridoxine, bioisosteric analogs of feruloyl methane

Two series of novel pyridoxine-based azaheterocyclic analogs of feruloyl methane (Dehydrozingerone, DZG) were synthesized, and their biological activity against a panel of tumor and normal cell lines was evaluated in vitro. The most active compounds possessed expressed cytotoxic activity, which was comparable to cytotoxic activity of doxorubicin and significantly higher than that of DZG, and a remarkable selectivity for the studied cancer cell lines as compared to the normal cells. The leading compound and DZG initiated arrest of the cell cycle in the G2/M phase, preventing normal division and further transition of daughter cells to the G0/G1 phase. Similar to DZG, but with higher efficiency, the leading compound was able to inhibit migration activity and, therefore, invasiveness of tumor cells. It also increased concentration of reactive oxygen species in tumor cells, induced depolarization of mitochondrial membranes and initiated apoptosis accompanied by disruption of integrity of cytoplasmic cell membranes. By contrast to DZG, the leading compound did not possess antioxidant properties. The obtained data make the described chemotype a promising starting point for the development of new anticancer agents.

Synthesis and Antitumor Activity of Novel Pyridoxine-Based Bioisosteric Analogs of trans-Stilbenes

A series of trans-6-phenylethenyl substituted pyridoxine derivatives, novel bioisosteric analogs of drugs based on trans-stilbene scaffold, were synthesized using the Wittig reaction of a bis-triphenylphosphonium pyridoxine derivative with various aromatic aldehydes. Two compounds demonstrated high activity against the estrogen-dependent MCF-7 (breast cancer) cell line with IC50 in the range of 1.9–7.9 µM and very good selectivity for other studied normal and tumor cells, including the estrogen receptor negative MDA-MB-231 breast cancer cells. The active compounds possessed an intense blue fluorescence, and this feature allowed us to effectively visualize them in cytoplasm and in nucleus. The obtained results make the described chemotype a promising starting point for the development of new anticancer agents for the therapy of estrogen-dependent malignancies.

Synthesis of a new quaternary phosphonium salt: NMR study of the conformational structure and dynamics.

A novel phosphonium salt based on pyridoxine was synthesized. Conformational analysis of the compound in solution was performed using dynamic NMR experiments and calculations. The obtained results revealed some differences in the conformational transitions and the energy parameters of the conformational exchange of the studied compound in comparison to previously reported data for other phosphorus‐containing pyridoxine derivatives. It was shown that increasing the substituent at the C‐11 carbon leads to greater differences in the populations of stable states and the corresponding equilibrium energies. Copyright