Towards novel efficient monomeric surfactants based on serine, tyrosine and 4-hydroxyproline: synthesis and micellization properties

The synthesis of some novel monomeric serine- and tyrosine-based cationic and 4-hydroxyproline-based anionic surfactants, having a long lipophilic alkyl chain directly attached to the nitrogen atom of the amino acid, is described. The most efficient synthetic methodologies were established: reductive amination of the corresponding ‘fatty’ aldehydes, followed by methylation and deprotection (serine and tyrosine) to obtain the cationic surfactants; or reductive amination followed by saponification (4-hydroxyproline) to obtain the anionic ones. All the compounds were obtained in good to excellent yields. An assessment of their micellization properties and surface activity by tensiometry showed fairly good performance levels.     

Liquid chromatographic resolution of racemic amines,amino alcohols and related compounds on a chiral crown ether stationary phase

A chiral stationary phase (CSP) based on diphenyl-substituted 1,1'-binaphthyl crown ether was applied in resolving various racemic amines, amino alcohols and alpha-aminocarbonyl compounds including pharmaceutically important compounds such as amphetamine analogues, mexiletine, norepinephrine and norephedrine. The resolution was quite successful. In order to find out the effects of mobile phase additives on the chromatographic resolution behaviors, four selected racemic compounds were resolved on the CSP with the variation of the type and content of organic, acidic and cationic modifiers in aqueous mobile phase and with the variation of column temperature. The resolution behaviors were quite dependent on the type and the content of organic, acidic and cationic modifiers in aqueous mobile phase and on column temperature.     

Enantiomer separation by capillary electrophoresis using DEAE-dextran and aminoglycosidic antibiotics

Summary Diethylaminoethyl (DEAE) dextran hydrochloride and three kinds of aminoglycosidic antibiotics; fradiomycin sulfate, kanamycin sulfate and streptomycin sulfate, were employed as chiral selectors in capillary electrophoresis, enantiomer separation. These selectors are cationic or basic because of amino functionality and therefore used for enantiomer separation of acidic compounds. To avoid adsorption of the basic or cationic selectors on the capillary inner surface, a coated capillary was employed. Among those tested, enantiomers of binaphthyl compounds and synthetic intermediates of diltiazem analogues were separated. Methanol addition was effective for the improvement of peak shape and resolution.     

Simultaneous analysis of cationic, anionic, and neutral compounds using monolithic CEC columns

A new capillary electrochromatography (CEC) column for the simultaneous analysis of cationic, neutral, and anionic compounds using CEC-ESI-MS is described. Three different silica monolith columns were prepared by changing the poly(ethylene glycol) (PEG) contents for comparison of the separation property of these columns. Different separation programs were used for the simultaneous separation of different charged compounds under the same conditions. The column prepared with 80 mg of PEG separated typical compounds within 15 min using 1 M formic acid as the electrolyte. The analytes migrated in the order of cationic, neutral, and anionic compounds, which means that the migration order was mainly determined by the electrophoresis. The hydrodynamic flow by pressure from the inlet side was significant for a stable analysis to be achieved. The effect of the composition of the sheath liquid was also examined. All analytes (14 amino acids, thiourea, urea, citric acid, and ATP) were detectable when 1% acetic acid in 50% (v/v) methanol was used as the sheath liquid.     

Solid-phase synthesis of fullerene-peptides

The solid-phase synthesis of peptides (SPPS) containing [60]fullerene-functionalized amino acids is reported. A new amino acid, fulleropyrrolidino-glutamic acid (Fgu), is used for the SPPS of a series of analogues of different length based on the natural Leu(5)-Enkephalin and on cationic antimicrobial peptides. These fullero-peptides were prepared on different solid supports to analyze the influence of the resin on the synthesis. Optimized protocols for the coupling and deprotection procedures were determined allowing the synthesis of highly pure peptides in sufficient quantities for evaluation of biological activities. In particular, to avoid side reactions of the fullerene moiety with bases and nucleophiles, the removal of the protecting groups was performed under inert conditions (nitrogen or argon in the dark). We have encountered serious problems with the recovery of the crude compounds, especially when Fgu was inserted in the proximity of the resin core as fullero-peptides tend to remain embedded inside the resin. Eventually, all of the fullero-peptides were easily purified, and the cationic peptides were tested for their antimicrobial activities. They displayed a specific activity against the Gram-positive bacterium S. aureus and also lysed erythrocytes. The availability of a fullero-amino acid easily useable in the SPPS of fullero-peptides may thus open the way to the synthesis of new types of biologically active oligomers.     

Immobilization of cationic polymer particles having active ester groups onto solid surfaces

Monodispersed cationic polymer particles with sulfonium groups and active ester groups at their surfaces were prepared by emulsifier-free emulsion copolymerization of styrene (ST) with a water-soluble active ester monomer, methacryloyloxyphenyldimethylsulfonium methylsulfate (MAPDS). The cationic polymer particle monolayers were fabricated on unmodified and aminated glass plates by electrostatic interactions and chemical reactions, respectively. The polymer particles were immobilized onto unmodified glass plates at relatively regular intervals in the absence of electrolytes, and the morphology of particle monolayers on the glass plates was changed with solid content of latex, electrolyte and cationic surfactant concentration. The polymer particles were immobilized onto aminated glass plate as aggregates by controlling the pH of latex and electrolyte concentration. Remaining active ester groups of the particle monolayers were confirmed to react easily with primary amino compounds.     

pH-Sensitive surfactants from lysine: assessment of their cytotoxicity and environmental behavior

The toxicity and environmental behavior of new pH-sensitive surfactants from lysine are presented. Three different chemical structures are studied: surfactants with one amino acid and one alkyl chain, surfactants with two amino acids on the polar head and one alkyl chain, and gemini surfactants. The pH sensitivity of these compounds can be tuned by modifying their chemical structures. Cytotoxicity has been evaluated using erythrocytes and fibroblast cells. The toxic effects against these cells depend on the hydrophobicity of the molecules as well as their cationic charge density. The effect of hydrophobicity and cationic charge density on toxicity is different for each type of cells. For erythrocytes, the toxicity increases as hydrophobicity and charge density increases. Nevertheless, for fibroblasts cationic charge density affects cytotoxicity in the opposite way: the higher charge density, the lower the toxicity. The effect of the pH on hemolysis has been evaluated in detail. The aquatic toxicity was established using Daphnia magna . All surfactants yielded EC(50) values considerably higher than that reported for cationic surfactants based on quaternary ammonium groups. Finally, their biodegradability was evaluated using the CO(2) headspace test (ISO 14593). These lysine derivatives showed high levels of biodegradation under aerobic conditions and can be classified as "readily biodegradable compounds".     

Synthesis of certain 2-substituted-1H-benzimidazole derivatives as antimicrobial and cytotoxic agents

A series of 2-substituted-1H-benzimidazole derivatives were synthesized and evaluated for antimicrobial, antifungal and cytotoxic activities. The results showed that all tested compounds showed potent antimicrobial activity against some species of Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli, Salmonella typhi) and fungi (Candida albicans) with minimum inhibitory concentrations (MICs) lower than 0.016 μg/mL. In contrast, all tested compounds were inactive against Staphylococcus aureus (Gram-positive bacterium). The final targets were also tested for their antitumor activity in vitro on cervical carcinoma (HeLa) cell line. Eight of the test compounds displayed more potent cytotoxic effect than doxorubicin at nanomolar concentrations. Compounds 2c and 3c exerted the strongest cytoyoxic effect with IC(50) 15 and 13 nM, respectively.     

Design and activity of cationic fullerene derivatives as inhibitors of acetylcholinesterase

Four different regioisomers of cationic bis-N,N-dimethylfulleropyrrolidinium salts have been prepared and evaluated as inhibitors of the enzymatic activity of acetylcholinesterase. These fullerene-based derivatives were found to be noncompetitive inhibitors of acetylthiocholine hydrolysis. Molecular modelling was used to describe the possible interactions between the fullerene cage and the amino acids surrounding the cavity of the enzyme. The cationic C(60) derivatives used in this study represent a new class of molecules potentially able to modulate the enzymatic activity of acetylcholinesterase.     

Synthesis and evaluation of beta-carbolinium cations as new antimalarial agents based on pi-delocalized lipophilic cation (DLC) hypothesis

Several beta-carbolines including naturally occurring substances and their corresponding cationic derivatives were synthesized and evaluated for antimalarial (antiplasmodial) activity in vitro and in vivo. A tetracyclic carbolinium salt was elucidated for antileishmanial and antitrypanosomal activities in vitro as well as antiplasmodial activity. Quarternary carbolinium cations showed much higher potencies in vitro than electronically neutral beta-carbolines and a good correlation was observed between pi-delocalized lipophilic cationic (DLC) structure and antimalarial efficacy. beta-Carbolinium compounds exhibit medium suppressive activity in vivo against rodent malaria.     

Preparation of chitosan functionalized monolithic silica column for hydrophilic interaction liquid chromatography

A novel cationic hydrophilic interaction monolithic stationary phase based on the chemical modification of carboxymethyl chitosan (CMCH) to the monolithic silica skeleton using carbodiimide as an activation reagent was prepared for performing capillary liquid chromatography. The amino and hydroxy moieties of CMCH functioned as both the ion-exchange sites and polar providers. The performance of the column was studied by the separation of polar acidic compounds. The chitosan functionalized monolithic silica column showed good selectivity for nucleosides, nucleotides, aromatic acids and aliphatic acids. The mechanism for the separation of these compounds was also studied. The results showed that these compounds were separated primarily based on the hydrophilic interaction mechanism.     

Synthesis of cationic porphyrin modified amino acids

Derivatives of amino acids bearing a porphyrin moiety on a side chain were synthesized by coupling a porphyrin to a glutamic acid side chain; the utility of these compounds was demonstrated by their use in solid-phase synthesis of a peptide bearing a cationic porphyrin and by studying its DNA-binding properties.     

Polymerization of 1-azabicyclo[4.2.0]octane with chiral tricyclic amino acid esters for obtaining biomedical materials

<正>The cationic ring-opening polymerization of 1-azabicyclo[4.2.0]octane,commonly called conidine(1) was studied with some chiral tricyclic amino acid esters(6a-6f) as acylation agents to obtain optically active biopolymers(8a-8f) of the different masses.The structures of the new compounds were confirmed by FT-IR,UV and NMR,and the distribution index of the molecular weights of the polymers was determined from SEC measurements.     

Erufosine (ErPC3) Cationic Prodrugs as Dual Gene Delivery Reagents for Combined Antitumor Therapy

Sixteen cationic prodrugs of the antitumor alkylphospholipid (APL) erufosine were rationally synthesized to provide original gene delivery reagents with improved cytotoxicity profile. The DNA complexation properties of these cationic lipids were determined and associated transfection rates were measured. Furthermore, the self-assembly properties of the pro-erufosine compounds were investigated and their critical aggregation concentration was determined. Their hydrolytic stability under pH conditions mimicking the extracellular environment and the late endosome milieu was measured. Hemolytic activity and cytotoxicity of the compounds were investigated. The results obtained in various cell lines demonstrate that the prodrugs of erufosine display antineoplastic activity similar to that of the parent antitumor drug but are not associated with hemolytic toxicity, which is a dose-limiting side effect of APLs and a major obstacle to their use in anticancer therapeutic regimen. Furthermore, by using lipoplexes prepared from a prodrug of erufosine and a plasmid DNA encoding a pro-apoptotic protein (TRAIL), evidence was provided for selective cytotoxicity towards tumor cells while nontumor cells were resistant. This study demonstrates that the combination approach involving well tolerated erufosine cationic prodrugs and cancer gene therapy holds significant promise in tumor therapy.     

Ionization behavior of amino lipids for siRNA delivery: determination of ionization constants, SAR, and the impact of lipid pKa on cationic lipid-biomembrane interactions

Ionizable amino lipids are being pursued as an important class of materials for delivering small interfering RNA (siRNA) therapeutics, and research is being conducted to elucidate the structure-activity relationships (SAR) of these lipids. The pK(a) of cationic lipid headgroups is one of the critical physiochemical properties of interest due to the strong impact of lipid ionization on the assembly and performance of these lipids. This research focused on developing approaches that permit the rapid determination of the relevant pK(a) of the ionizable amino lipids. Two distinct approaches were investigated: (1) potentiometric titration of amino lipids dissolved in neutral surfactant micelles; and (2) pH-dependent partitioning of a fluorescent dye to cationic liposomes formulated from amino lipids. Using the approaches developed here, the pK(a) values of cationic lipids with distinct headgroups were measured and found to be significantly lower than calculated values. It was also found that lipid-lipid interaction has a strong impact on the pK(a) values of lipids. Lysis of model biomembranes by cationic lipids was used to evaluate the impact of lipid pK(a) on the interaction between cationic lipids and cell membranes. It was found that cationic lipid-biomembrane interaction depends strongly on lipid pK(a) and solution pH, and this interaction is much stronger when amino lipids are highly charged. The presence of an optimal pK(a) range of ionizable amino lipids for siRNA delivery was suggested based on these results. The pK(a) methods reported here can be used to support the SAR screen of cationic lipids for siRNA delivery, and the information revealed through studying the impact of pK(a) on the interaction between cationic lipids and cell membranes will contribute significantly to the design of more efficient siRNA delivery vehicles.     

Synthesis and characterization of peptide-cationic steroid antibiotic conjugates

[reaction: see text] New cationic steroid antibiotics have been prepared by conjugating tripeptides to a triamino analogue of cholic acid. These compounds were synthesized on a solid phase in an indexed library that was screened for antibacterial activity against Gram-negative and Gram-positive bacteria. Selected compounds were synthesized on a larger scale, and minimum inhibition concentrations were measured. These results correlated very well with the screening of the indexed library of antibiotics. The most active antibiotics demonstrate a marked improvement over a related and well characterized cationic steroid antibiotic.     

Solid-phase synthesis of 89 polyamine-based cationic lipids for DNA delivery to mammalian cells

The ability of non-viral gene delivery systems to overcome extracellular and intracellular barriers is a critical issue for future clinical applications of gene therapy. In recent years much effort has been focused on the development of a variety of DNA carriers, and cationic liposomes have become the most common non-viral gene delivery system. Solid-phase synthesis was used to produce three libraries of polyamine-based cationic lipids with diverse hydrophobic tails. These were characterised, and structure-activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. Two of the cationic lipids produced high-efficiency transfection of human cells. Surprisingly, these two compounds were from the library with two headgroups and one aliphatic tail, a compound class regarded as detergent-like and little investigated for transfection. These cationic lipids are promising reagents for gene delivery and illustrate the potential of solid-phase synthesis methods for lipoplex discovery.     

New membranotropic cationic chlorins derived from pheophytin a: synthesis and evaluation of photodynamic activity

A series of new chlorins bearing the phytyl moiety and different number of cationic groups were synthesized based on pheophytin a. A comparative evaluation of dark cytotoxicity and photodynamic activity of the synthesized compounds was performed using mature mammalian erythrocytes. Both dark and photoinduced hemolytic activities of the synthesized compounds grow with increasing the number of the cationic group in the molecule.

     

Cationic surfactant-based polyfluorate salts: phase separation and analytical applications in the extraction and preconcentration of ionic species prior to liquid chromatography

The liquid-solid phase separation originating from the formation of cationic surfactant-based polyfluorate salts (CSBPS) has been explored for extracting and preconcentrating ionic species. Two cationic surfactants were tested; one with aliphatic hydrocarbon tail [Cetyltrimethylammonium bromide (CTAB)]and the other containing a heterocyclic ring [Hexadecylpyridinium bromide (HPyBr)]. Phase separation possibility was investigated with the use of hexafluorophosphates (PF6-) and tetrafluoroborates (BF4-). The effect of added acid, base and salt on the phase separation and analyte extraction was also investigated. In all cases the obtained phase diagrams consisted of two regions: a homogeneous liquid region and a solid-liquid region. Analytes of hydrophilic and hydrophobic nature such as amines, amino acids and organic chromophores were used as test compounds in both their anionic and cationic forms. The respective recoveries ranged from over 90% for anionic species and in the proximity of 50% for cationic species, remaining below 20% for neutral species. Extracts from alkaline aqueous and plasma samples spiked with tyrosine and phenylalanine were also subjected to HPLC separation with UV detection with satisfactory results. On line application was also enabled using a flow through-solid phase extraction-HPLC hyphenated apparatus, thus adding the element of automatization and increased reproducibility.     

Determination of total cationic and total anionic arsenic species in oyster tissue using microwave-assisted extraction followed by HPLC-ICP-MS

A microwave-assisted digestion procedure was developed in presence of concentrated nitric acid (2.0 ml) and 30% hydrogen peroxide (0.20 ml) using a closed pressurized microwave digestion system for the determination of total anionic and total cationic arsenic compounds reside in oyster tissue. At 450 W for 15 min digestion, 74% of anionic arsenic, and 31% of cationic arsenic (105% total arsenic) were retrieved. At 300 W microwave power, 68% of anionic and 30.5% of cationic arsenic (98.5% total arsenic), and 100 W, 63% of anionic and 31% of cationic arsenic (94% total arsenic) were extracted out. The methanol water mixture (9:1) was cull out, exclusively 31.6% of anionic and 29% of cationic arsenic compounds (60.6% total). The dimethylarsinoylriboside (phosphate-arsenosugar) was the predominant arsenic species, along with arsenobetaine (AB), dimethylarsinic acid (DMA), inorganic arsenic, methylarsonic acid (MA), arsenocholine (AC), trimethylarsineoxide (TMAO) and tetramethylarsonium ion (TMI). Some other arsenic compounds, those were not matched with the retention time of the available standards, were also detected. Arsenosugar was fragile and adequately transmuted to DMA (100%), AB and AC to TMAO (100%) when 450 W microwave power was applied for 15 min. The separation and quantification of arsenic compounds in the microwave digests and extracts, were carried out in anion (PRP-X100) and cation (LC-SCX) exchange columns using ICP-MS as arsenic specific detector. The procedure was also validated by determining the total cationic and total anionic arsenic compounds present in DORM 1.