Synthesis of perfluoroalkylated xylitol ethers and esters: new surfactants for biomedical uses

Rotamers in Crystal Structures of Xylitol, D-Arabitol and L-Arabitol

Rotamers are stereoisomers produced by rotation (twisting) about σ bonds and are often rapidly interconverting at room temperature. Xylitol-massively produced sweetener-(2R,3r,4S)-pentane-1,2,3,4,5-pentol) forms rotamers from the linear conformer by rotation of a xylitol fragment around the C2-C3 bond (rotamer 1) or the C3-C4 bond (rotamer 2). The rotamers form two distinguishable structures. Small differences in geometry of rotamers of the main carbon chain were confirmed by theoretical calculations; however, they were beyond the capabilities of the X-ray powder diffraction technique due to the almost identical unit cell parameters. In the case of rotamers of similar compounds, the rotations occurred mostly within hydroxyl groups likewise rotations in L-arabitol and D-arabitol, which are discussed in this work. Our results, supported by theoretical calculations, showed that energetic differences are slightly higher for rotamers with rotations within hydroxyl groups instead of a carbon chain.

Synthesis, emulsification and self-assembly properties of sugar-containing semifluorinated amphiphiles

Surfactants with two and three monosaccharide-based heads and a perfluoroalkyl tail have been synthesized. Perfluoroalkyl C3-symmetric triol and C2-symmetric diol were conveniently prepared via Cu-catalyzed azide-alkyne cycloaddition between a fluorous alkyne and tertiary and secondary azides, respectively. Glycosylation of the perfluoroalkyl diol and triol led to orthoester-type structures, which were evaluated for their capacity to stabilize aqueous emulsions of highly fluorinated anesthetics. The self-assembly properties of the tri-sugar amphiphile were examined by transmission electron microscopy.

Cytotoxic activity of triazole-containing alkyl β-D-glucopyranosides on a human T-cell leukemia cell line

BACKGROUND

Simple glycoside surfactants represent a class of chemicals that are produced from renewable raw materials. They are considered to be environmentally safe and, therefore, are increasingly used as pharmaceuticals, detergents, and personal care products. Although they display low to moderate toxicity in cells in culture, the underlying mechanisms of surfactant-mediated cytotoxicity are poorly investigated.

RESULTS

We synthesized a series of triazole-linked (fluoro)alkyl β-glucopyranosides using the copper-catalyzed azide-alkyne reaction, one of many popular "click" reactions that enable efficient preparation of structurally diverse compounds, and investigate the toxicity of this novel class of surfactant in the Jurkat cell line. Similar to other carbohydrate surfactants, the cytotoxicity of the triazole-linked alkyl β-glucopyranosides was low, with IC50 values decreasing from 1198 to 24 μM as the hydrophobic tail length increased from 8 to 16 carbons. The two alkyl β-glucopyranosides with the longest hydrophobic tails caused apoptosis by mechanisms involving mitochondrial depolarization and caspase-3 activation.

CONCLUSIONS

Triazole-linked, glucose-based surfactants 4a-g and other carbohydrate surfactants may cause apoptosis, and not necrosis, at low micromolar concentrations via induction of the intrinsic apoptotic cascade; however, additional studies are needed to fully explore the molecular mechanisms of their toxicity. Graphical AbstractTriazole-linked, glucose-based surfactants cause apoptosis, and not necrosis, at low micromolar concentrations via induction of the intrinsic apoptotic cascade.

Synthesis, surface properties, and biocompatibility of 1,2,3-triazole-containing alkyl β-D-xylopyranoside surfactants

We are interested in the development of surfactants derived from hemicellulosic biomass, as they are potential components in pharmaceuticals, personal care products, and other detergents. Such surfactants should exhibit low toxicity in mammalian cells. In this study we synthesized a series of alkyl or fluoroalkyl β-xylopyranosides from azides and an alkyne using the copper-catalyzed azide-alkyne (CuAAC) 'click' reaction in 4 steps from xylose. The purified products were evaluated for both their surfactant properties, and for their biocompatibility. Unlike other carbohydrate-based surfactants, liquid-crystalline behavior was not observed by differential scanning calorimetry. The triazole-containing β-xylopyranosides with short (6 carbons) and long (>12 carbons) chains exhibited no toxicity at concentrations ranging from 1 to 1000 μM. Triazole-containing β-xylopyranosides with 8, 10, or 12 carbons caused toxicity via apoptosis, with CC50 values ranging from 26-890 μM. The two longest chain compounds did form stable monolayers at the air-water interface over a range of temperatures, although a brief transition to an the unstable monolayer was observed.

Synthesis, thermal properties, and cytotoxicity evaluation of hydrocarbon and fluorocarbon alkyl β-D-xylopyranoside surfactants

Alkyl β-d-xylopyranosides are highly surface active, biodegradable surfactants that can be prepared from hemicelluloses and are of interest for use as pharmaceuticals, detergents, agrochemicals, and personal care products. To gain further insights into their structure-property and structure-activity relationships, the present study synthesized a series of hydrocarbon (-C(6)H(13) to -C(16)H(33)) and fluorocarbon (-(CH(2))(2)C(6)F(13)) alkyl β-d-xylopyranosides in four steps from d-xylose by acylation or benzoylation, bromination, Koenigs-Knorr reaction, and hydrolysis, with the benzoyl protecting group giving better yields compared to the acyl group in the Koenigs-Knorr reaction. All alkyl β-d-xylopyranosides formed thermotropic liquid crystals. The phase transition of the solid crystalline phase to a liquid crystalline phase increased linearly with the length of the hydrophobic tail. The clearing points were near constant for alkyl β-d-xylopyranosides with a hydrophobic tail ⩾8, but occurred at a significantly lower temperature for hexyl β-d-xylopyranoside. Short and long-chain alkyl β-d-xylopyranosides displayed no cytotoxicity at concentration below their aqueous solubility limit. Hydrocarbon and fluorocarbon alkyl β-d-xylopyranosides with intermediate chain length displayed some toxicity at millimolar concentrations due to apoptosis.

Evaluation of antimicrobial effectiveness of C-8 xylitol monoester as an alternative preservative for cosmetic products

Xylitol is a natural sugar derived from plants, fruits and vegetables, whose antimicrobial properties are described in the literature. This study aimed to evaluate the antimicrobial effectiveness of C-8 xylitol monoester, for its use as a preservative in cosmetic formulations. The minimum inhibitory concentration (MIC) was determined by the broth macrodilution method, and the antimicrobial effectiveness of C-8 xylitol monoester was determined by using challenge test method. The results obtained in the determination of minimum inhibitory concentration are between 1.0% and 1.25% for Staphylococcus aureus, Escherichia coli and Candida albicans and between 1.0% and 1.5% for Pseudomonas aeruginosa and Aspergillus niger. The amount of 1% of C-8 xylitol monoester was added to the lotion used in the challenge test, observing a rapid decline in the number of CFU g(-1) in stages of evaluation after contamination of the product by all bacteria. The same occurs in relation to C. albicans, which shows a 90% reduction in the number of CFU g(-1). Regarding A. niger, similar reduction is observed when pH value of the lotion is adjusted from 5.5 to 7.0. The results indicate that under the tests conditions, C-8 xylitol monoester has antimicrobial activity and could be considered as an alternative preservative for cosmetic formulations.

Hydrophobic tail length, degree of fluorination and headgroup stereochemistry are determinants of the biocompatibility of (fluorinated) carbohydrate surfactants

A series of hydrocarbon and fluorocarbon carbohydrate surfactants with different headgroups (i.e., gluco-, galacto- and maltopyranoside) and (fluorinated) alkyl tails (i.e., C7 and C14 to C19) was synthesized to investigate trends in their cytotoxicity and haemolytic activity, and how surfactant-lipid interactions of selected surfactants contribute to these two measures of biocompatibility. All surfactants displayed low cytotoxicity (EC50 = 25 to >250 microM) and low haemolytic activity (EC50 = 0.2 to >3.3 mM), with headgroup structure, tail length and degree of fluorination being important structural determinants for both endpoints. The EC50 values of hydrocarbon and fluorocarbon glucopyranoside surfactants displayed a "cut-off" effect (i.e., a maximum with respect to the chain length). According to steady-state fluorescence anisotropy studies, short chain (C7) surfactants partitioned less readily into model membranes, which explains their low cytotoxicity and haemolytic activity. Interestingly, galactopyranosides were less toxic compared to glucopyranosides with the same hydrophobic tail. Although both surfactant types only differ in the stereochemistry of the 4-OH group, hexadecyl gluco- and galactopyranoside surfactants had similar apparent membrane partition coefficients, but differed in their overall effect on the phase behaviour of DPPC model membranes, as assessed using steady-state fluorescence anisotropy studies. These observations suggest that highly selective surfactant-lipid interactions may be responsible for the differential cytotoxicity and, possible, haemolytic activity of hydrocarbon and fluorocarbon carbohydrate surfactants intended for a variety of pharmaceutical and biomedical applications.

Perfluorocarbon compounds as vehicles for pulmonary drug delivery

Drug delivery to the diseased lung is hindered by the buildup of fluid and shunting of blood flow away from the site of injury. The use of perfluorocarbon compounds (PFCs) as drug delivery vehicles has been proposed to overcome these obstacles. This drug delivery approach is based on the unique properties of PFCs. For example, PFCs can homogeneously fill the lung and recruit airways by replacing edematous fluid. Analogously, drugs administered with a PFC vehicle are expected to be homogeneously distributed throughout the lung. At the same time, intrapulmonary administration of the drug will achieve higher drug concentrations in the lung than conventional approaches, while reducing systemic exposure. Unfortunately, PFCs are poor solvents for typical drug molecules. To overcome this obstacle, several approaches, such as dispersions, prodrugs, solubilizing agents and (micro)emulsions, are under investigation to develop homogeneous PFC-drug mixtures suitable for intrapulmonary administration.

Novel perfluoroalkylated derivatives of d-galactopyranose and xylitol for biomedical uses. Hemocompatibility and effect on perfluorocarbon emulsions

6-O-(4,4,5,5,6,6,7,7,7-Nonafluoro-2-hydroxyheptyl)-, 6-O-(4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-2-hydroxynonyl)-, and 6-O-(4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoro-2-hydroxyundecyl)-d-galactopyranose (9, 10, and 11, resp.) were prepared by a two-step synthesis including the reaction of 1,2:3,4-di-O-isopropylidene-alpha-d-galactopyranose with 2-[(perfluoroalkyl)methyl]oxiranes under catalysis with BF(3).Et(2)O. Similarly, 1-O-(4,4,5,5,6,6,7,7,7-nonafluoro-2-hydroxyheptyl)-, 1-O-(4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluoro-2-hydroxynonyl)-, 1-O-(4,4,5,5,6,6,7,7,8,8,9,9,10,10,11,11,11-heptadecafluoro-2-hydroxyundecyl)-dl-xylitol (18, 19, and 20, resp.) were prepared by a two-step synthesis from the corresponding 1,2:3,4-di-O-isopropylidene-dl-xylitol. Most of the both types of fluoroalkylated carbohydrate derivatives 9-11 and 18-20 generally displayed very low level of hemolytic activity and excellent co-emulsifying properties on testing on perfluorodecalin-Pluronic F-68 microemulsions.

Novel amphiphilic fluoroalkylated derivatives of xylitol, D-glucose and D-galactose for medical applications: hemocompatibility and co-emulsifying properties

1-O-(4,4,5,5,6,6,7,7,8,8,9,9,9-Tridecafluorononyl)xylitol 6 was synthesized as a novel standard compound for the assessment of hemocompatibility and co-emulsifying properties in microemulsions for biomedical uses. 3-O-(1,1,2,4,4,5,7,7,8,8,9,9,9-Tridecafluoro-5-trifluoro-methyl-3,6-dioxanonyl)-D-glucose 9 and 6-O-(1,1,2,4,4,5,7,7,8,8,9,9,9-tridecafluoro-5-trifluoromethyl-3,6-dioxanonyl)-D-galactose 12 were synthesized by nucleophilic addition of protected carbohydrates to perfluorinated vinyl oligoether. Biological tests revealed very good hemocompatibility and co-emulsifying properties for the amphiphiles 6, 9 and 12.

Carbohydrate- and related polyol-derived fluorosurfactants: an update

A short review of recent literature is presented on the synthesis, biological properties, colloid and surface chemistry, and applications of carbohydrate- and related polyol-derived amphiphiles with perfluoroalkyl hydrophobes.

Formation and properties of Langmuir and Gibbs monolayers: a comparative study using hydrogenated and partially fluorinated amphiphilic derivatives of mannitol

The synthesis and surface behavior of a series of nine new hydrogenated nonionic surfactants and their fluorinated analogs, derived from D-mannitol are described. Adsorption monolayers (Gibbs monolayers) were studied by surface pressure (H) measurements as a function of time. For the spread monolayers (Langmuir monolayers), the measurements of surface pressure versus molecular area (A) were performed. For the most hydrophobic amphiphiles at low concentrations, the adsorption at the air/water interface from the bulk solution required extremely long times to attain equilibrium. The A values for two compounds which could be studied in both adsorbed and spread monolayers provided data allowing a direct comparison of the properties of the two types of films formed at the air/water interface. In spite of different mechanisms of formation of Langmuir and Gibbs monolayers, their characteristic parameters were identical, proving the equivalence of these two types of structures.

Amphiphilic sugar phosphates with single or double perfluoroalkylated hydrophobic chains for use in oxygen and drug delivery systems

New anionic amphiphiles with a phosphate ester junction between the fluorophilic-lipophilic tail and the sugar-based hydrophilic head were synthesized and evaluated. The single hydrophobic chain surfactants 1 a, b and 2a allowed the preparation of stable and fine highly concentrated emulsions of perfluorodecalin or perfluoroocytl bromide, either when used alone or in conjunction with egg yolk phospholipids (EYP). Surfactants 3d, 5d, 6d and 6e, with two hydrophobic chains, one fluorinated the other not, gave liposomal structures, and displayed encapsulation properties for carboxyfluorescein. The phosphodiesters tested cause no significant inhibition of the growth and viability of Namalva cell cultures (0.1-1 g/L range). Single chain phosphodiesters manifest no detectable hemolytic activity (at 100 g/L for 1a) whereas double chain compounds do moderately (ca 20% hemolysis at 20 g/L). The maximum tolerated dose compatible with the survival of all of a series of 10 intravenously injected mice is in 130 mg/kg body weight range.

Synthesis of D-glucose 3- and 6-[2-(perfluoroalkyl)ethyl] phosphates: a new type of anionic surfactant for biomedical use

D-Glucose 3- and 6-[sodium 2-(perfluoro-hexyl or -octyl)ethyl phosphates) have been synthesized by condensation of 1,2,3,4,-tetra-O-acetyl-beta-D-glucopyranose and 1,2:5,6-di-O-isopropylidene-alpha-D-glucofuranose with 2-(perfluoroalkyl)ethylphosphoroditriazolides followed by O-deacetylation or deacetalation. The structures of the compounds were established on the basis of 1H-, 19F-, 31P-, and 13C-NMR data. These salts display strong surface activities and appear to have good biocompatibility.

Overview of progress in the fluorocarbon approach to in vivo oxygen delivery

The development of fluorocarbon-based oxygen carriers has experienced rapid progress over the past few years. Fluosol has been approved for use during percutaneous transluminal coronary angioplasty (PTCA) for high-risk patients. Its clinical evaluation is being pursued as an adjunct to cancer therapy and for treatment of myocardial infarction in conjunction with thrombolytic therapy. O2-delivery efficacy has been achieved with the development of the new highly concentrated (4 to 5 times more concentrated than Fluosol), fluid, emulsions of perfluorooctyl bromide (perflubron), trade-named Oxygen. The stability of fluorocarbon emulsions has also improved considerably and the new emulsions can be stored unfrozen and are ready for use. The side-effect profile of these emulsions has been characterized as being the normal response of the body's phagocytes to the injection of particles, a response that is considered physiological rather than pathological in nature; it involves some products of arachidonic acid metabolism and can be controlled pharmacologically. Means of further stabilizing fluorocarbon emulsions, involving molecular-diffusion-controlling additives or fluorinated surfactants, including mixed fluorocarbon-hydrocarbon compounds, have been devised. Increased control over in vivo particle recognition, intravascular persistence and side effects, and at adapting emulsion characteristics to specific applications, is being investigated. The range of therapeutic applications is expanding. The concentrated emulsions will be able to serve as a temporary red blood cell substitute in many situations. Acute normovolemic hemodilution with fluorocarbon emulsions, used in conjunction with homologous predonation and other blood-sparing techniques, should afford greater flexibility, increase the margin of safety, and reduce or alleviate the need for autologous blood transfusion during surgical procedures. Fluorocarbon applications in the cardiovascular field include use during PTCA, for cardioplegia and reperfusion, and the treatment of myocardial infarction. Significant tumor growth delay has been achieved when concentrated emulsions are used in conjunction with cancer radio- or chemotherapy. Liquid ventilation has potential as a unique treatment for the adult and infant respiratory distress syndromes and for drug delivery. The radiopaque and versatile perflubron can also be used in contrast agents for diagnosis with computed X-ray tomography, magnetic resonance imaging and ultrasound, allowing the early detection and staging of cancer. Other potential applications investigated include the treatment of cerebral ischemia, organ and limb preservation, use as a tamponade during retinal repair, etc.

Stability and stabilization of fluorocarbon emulsions destined for injection

The factors that have an impact on the stability, and the mechanisms of degradation of fluorocarbon emulsions suited for intravascular use, are briefly reviewed. Various ways of prolonging shelf stability are discussed. The effectiveness of perfluoroalkylated surfactants and/or co-surfactants as stabilizers is demonstrated. New means of stabilizing fluorocarbon-in-water emulsions using molecular dowels are presented.

Fluorocarbon-based in vivo oxygen transport and delivery systems

The approval of Fluosol, a fluorocarbon emulsion for oxygenating the myocardium during the transluminal coronary angioplasty procedure, is a landmark in the field of injectable oxygen carriers, the so-called blood substitutes. This review discusses the advances made since this first emulsion was initially developed about 12 years ago. Attention is focused on the progress achieved in the preparation and selection of new, better-defined and faster-excreted fluorocarbons, and better surfactants, improved emulsions, knowledge of structure/property relationships along with an improved understanding of the physiologic response to their administration. These advances have led to the development of a second generation of highly concentrated, fluid and stable injectable oxygen carriers suitable for a broad range of clinical applications. Prospects for further progress and future generations of emulsions are also outlined.