ES2819307A1 - CHIRAL IONIC LIQUIDS BASED ON L-CARNITINE ESTERS AND THEIR USE AS CHIRAL SELECTORS IN DUAL SYSTEMS FOR THE SEPARATION OF ENANTHYOMERS BY CAPILLARY ELECTROPHORESIS (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

The present invention relates to a non-protic CIL based on L-carnitine esters of general structure I {IMAGE-01} in which - the cationic part is asymmetric formed by a differently substituted ammonium cation, in which the substituents are not all the same, derived from the corresponding ester (-COOR) of the chiral amino acid L-carnitine, - R is selected from alkyl of 1 to 5 carbon atoms, linear or branched, substituted or unsubstituted, benzyl, substituted or unsubstituted phenyl, heterocycles as well as heteroaryls, - the anionic part (A-) is formed by an inorganic or organic anion. Its procedure of obtaining and use in the separation of compounds, more specifically, of enantiomers by means of EKC. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

CHIRAL IONIC LIQUIDS BASED ON L-CARNITINE ESTERS AND ITS

USE AS CHIRAL SELECTORS IN DUAL SYSTEMS FOR

SEPARATION OF ENANTHYOMERS BY CAPILLARY ELECTROPHORESIS

TECHNICAL SECTOR

The present invention is framed in the field of obtaining ionic liquids and their use in dual systems of chiral selectors for the separation of enantiomers by Capillary Electrophoresis.

STATE OF THE ART

Capillary Electrophoresis (CE) is an analytical technique with enormous potential for the separation of enantiomers due to its interesting characteristics such as its high efficiency, low consumption of solvents and samples, and the possibility of adding a chiral selector to the mobile phase to carry out perform an enantiomeric separation. Chiral analysis is currently of enormous interest due to the different biological activity that the enantiomers of a chiral compound can present. The need to control the presence of the different enantiomers in samples of pharmacological, clinical, food or environmental interest requires the development of sensitive advanced analytical methodologies that allow these enantiomers to be individually determined.

Electrokinetic Chromatography (EKC) is a separation mode in the CE format in which a chiral selector is added to the mobile phase in order to interact differentially with each of the enantiomers of a chiral compound, giving rise to to their separation. There are a large number of chiral selectors that can be used in EKC such as cyclodextrins, macrocyclic antibiotics, proteins, polymeric micelles, crown ethers, etc. This gives EKC extraordinary versatility when it comes to carrying out chiral separation by this technique. The prediction of the most suitable chiral selector to carry out a chiral separation is still difficult despite the large number of studies that have been carried out to study the analyte-chiral selector interactions by different techniques. Therefore, on occasions, when it is not possible to find a suitable chiral selector to carry out After enantiomeric separation, the use of mixtures of chiral selectors constituting dual systems can be very useful. In this sense, ionic liquids have shown great potential as agents that are capable of producing important synergistic effects when used in combination with other chiral selectors. In fact, although ionic liquids have been used as unique chiral selectors in the separation medium in EKC [1,2], most of the work carried out has been based on the use of ionic liquid mixtures with other selectors. chirals, mainly with cyclodextrins and macrocyclic antibiotics [1, 2, 3].

Ionic liquids are organic salts with melting points below 100 ° C. They are made up of bulky organic cations, including ammonium, phosphonium, alkylimidazolium, pyridinium, pyrrolidinium cations and organic or inorganic anions such as hexafluorophosphate, tetrafluoroborate, triflate, etc.

Within the ionic liquids, those in which either the cationic part, or the anionic part or both, are chiral, in which case they are called chiral ionic liquids (CILs). Within the group of CILs, mention can be made of those whose cationic part is a chiral amino acid, the synthesis of different CILs within this group having been described in the literature [2,4, 5].

However, only some of the CILs synthesized and whose cationic part is a chiral amino acid, have been used in EKC as single chiral selectors or in dual systems with other chiral selectors giving rise to the enantiomeric separation of different compounds (Table 1).

Table 1. CILs whose cationic part is a chiral amino acid and which have been used as single chiral selectors or in dual systems of chiral selectors in EKC, or as chiral ligands in CE of ligand exchange.

Abbreviations: Ala: Alanine; Asn: Asparagine; Asp: Aspartic acid; CF ³ CO ^2- : trifluoroacetate, Cl-Dns: dansyl chloride; Ile: Isoleucine; Met: Methionine, NTÍ ² : bis ( trifluoromethylsufonyl) imide; Lac: Lactate; Phe: Phenylalanine, Phn: Phenylalaninamide, Pro: Proline, Ser: Serine; Thr: Threonine, Tyr: Tyrosine, Val: Valine.

Patents CN105152950, CN105152949 and CN105061236 deal with the synthesis of ionic liquids in which the cationic part is an amino acid, such as tyrosine, phenylalanine, lysine, leucine or alanine, which does not coincide with that of the present invention (L- ester carnitine). In patent application US2009145197 other amino acids are mentioned as cationic part, one of them being D-carnitinanitrile, which also does not coincide with the L-carnitine ester.

One of the problems solved by the present invention is to provide a process for obtaining CILs derived from L-carnitine esters as chiral selectors, whose synthesis had not been previously described, from aqueous solutions of said esters with silver, sodium salts. or potassium derived from the corresponding inorganic or organic anions in a simple and inexpensive way.

The ClLs of the invention are useful in the separation of enantiomers of chiral compounds of food, pharmaceutical, cosmetic, agrochemical or environmental interest, and in the quality control of products from these sectors.

DESCRIPTION OF THE INVENTION

A first aspect of the present invention refers to a non-protic chiral ionic liquid (CIL) based on L-carnitine esters of general structure I

in which:

- the cationic part is asymmetric formed by a differently substituted ammonium cation, in which the substituents are not all the same, derived from the corresponding ester (-COOR) of the chiral amino acid L-carnitine. - R is selected from alkyl of 1 to 5 carbon atoms, linear or branched, substituted or unsubstituted, benzyl, substituted or unsubstituted phenyl, heterocycles as well as heteroaryls,

- the anionic part (A-) is formed by an inorganic or organic anion.

The group R according to particular embodiments is selected from methyl, ethyl, propyl, isopropyl, tert-butyl, n-butyl, pentyl, benzyl, phenyl, a phenyl group substituted by introducing one or two substituents, the same or different, selected from , nitro, halo, alkyl, alkoxy, hydroxy, trifluoromethyl, cyanide, heterocycles, and heteroaryls. Among the inorganic anions, the chiral ionic liquid can be selected from halides (chlorides (Cl-), bromide (Br-), Iodide (I-)), hexafluorophosphate (PF6-) and tetrafluoroborates (BF ⁴ -).

Among the organic anions, the chiral ionic liquid can be acetate (AcO-), triflate (TfO-), taurinate, tetracyanoborate (B (CN) ⁴ -), n-octyl sulfate, docusate, L-lactate, amino acids, bis ( trifluoromethylsufonyl) imide (NTf ² ), bis (pentafluoroethylsulfonyl) imide, tricyanomethane anion, tris (pentafluoroethyl) trifluorophosphate (FAP), as well as other organic anions described in references [5] ( Chira! ionio Liquids: A compendium of synthesis and applications) and [20] (Ionic liquids in analytical chemistry).

According to particular embodiments, the anionic part comprises an anion selected from a halide, hexafluorophosphate or tetrafluoroborate, acetate, triflate, tetracyanoborate, n-octyl sulfate, docusate, L-lactate, amino acids, bis (trifluoromethylsulfonyl) imide (NTf ² ) or bis (pentafluoroethylsulfonyl) imide.

As is well known, the polarity and the hydrophobic and hydrophilic characters, physicochemical properties, such as conductivity, volatility, vapor pressure, thermal stability, and their corresponding miscibility in organic solvents as in water of the different ionic liquids resides fundamentally in the combination that exists between the cation and the selected anion. From these combinations, different CILs are obtained with different properties as chiral selectors or as components of dual systems of chiral selectors [2].

In a preferred embodiment of the present invention, the cationic part of the CIL is the methyl ester of L-carnitine and the anionic part is any one of the inorganic or organic anions described above.

In another preferred embodiment, the anion is bis (trifluoromethylsufonyl) imide (NTf ² ).

The present invention also relates to an intermediate compound of general formula II

wherein X- is a halide anion and "R" has the same meaning as indicated above for the compounds of formula I. Preferably the anion X- is a chloride.

The present invention also relates to a dual system for the separation of chemical compounds comprising a chiral ionic liquid defined above and a second component which is a chiral selector. Preferably, the chiral selector is a cyclodextrin.

The present invention also refers to a procedure for obtaining the ClLs described and comprising the following steps:

a) formation of the intermediate compound of general formula II by a reaction of a halide of L-carnitine (III), in alcoholic acid medium at 40-120 ° C until the disappearance of the starting material, for a time between 3 to 24 hours and subsequent elimination of the alcoholic medium,

b) optionally, an exchange of the corresponding halide anion, preferably chloride, in derivative II obtained in step (a) in an aqueous medium, with a salt selected from a silver salt, sodium salts, potassium salts and lithium salts derived from corresponding inorganic or organic anion represented as A- in formula I, or with the acid corresponding to said anion.

For the purposes of the present invention, the anion exchange reaction is carried out through a process called anionic metathesis, thus generating the corresponding CILs. This step comprises the treatment of stoichiometric amounts of the corresponding halide (II) salt with a salt selected from silver salts, sodium salts, potassium salts and lithium salts derived from the corresponding inorganic or organic anion represented as A- in formula I derived from the corresponding inorganic or organic anions represented as A- in formula I, such as salts derived from bromide (Br-), iodide (I-)), hexafluorophosphate (PF6 -) [16], tetrafluoroborate derivatives (BF ⁴ -), acetate (AcO-), triflate (TfO-), tetracyanoborate (B (CN) ⁴ -), n-octyl sulfate, Docusate, L-lactate, amino acids, bis (trifluoromethylsufonyl) imide (NTf ² ) [17] , bis (pentafluoroethylsulfonyl) imide, acetate (CH ³ CO ² -), trifluoroacetate (CF ³ CO ² -),

- or with the corresponding free acid of the appropriate anion.

In step a) the L-carnitine (III) halide can be of commercial origin, and is preferably chloride.

"Medium alcoholic acid" means that an alcohol is used, which can be any, and is preferably selected from methanol, ethanol, isopropanol, n-butanol, tert - butanol, preferably methanol, and an acid which is preferably hydrochloric acid.

The alcohol used in the alcoholic medium in step a) is removed under reduced pressure, comprised between 20 and 200 mbar, after the reaction has ended.

According to particular embodiments, the reaction temperature of step a) is between 40 and 100 ° C. According to additional particular embodiments, the reaction temperature of step a) is between 40 and 90 ° C.

According to particular embodiments, the reaction time of step a) is between 3 and 15 hours. According to additional particular embodiments, the reaction time of step a) is between 3 and 8 hours.

The anionic metathesis reaction of step b) is carried out in an aqueous medium by treating one equivalent of the compound of general formula II with one equivalent of a silver salt, sodium salts, potassium salts and lithium salts derived from the corresponding anion. inorganic or organic, preferably with lithium salts, at temperatures between 15 and 50 ° C, more preferably between 15 ° C and 30 ° C, even more preferably at 20 ° C, generating as a by-product of reaction water or the corresponding salts of halide.

Particular embodiments of the procedure are shown represented in the following diagram:

A: NO3-, BF4-, NTF2-,

CH3COO-, CH3CH2OHCO2-, etc ...

Some additional alternatives for the synthesis of chiral ionic liquids are described for example in [15].

The present invention also relates to the use of the chiral ionic liquids defined above in the chemical, medical or pharmaceutical industry. Preferably refers to the use of ClLs in separation of chiral products. Most preferably it relates to the use of CILs as chiral selectors, and more preferably as components of dual systems of chiral selectors in EKC to improve the obtained resolution of the enantiomers of chiral compounds of interest. CILs are used as components of a dual system consisting of another chiral selector as a second component for the separation of chiral compounds, more preferably amino acids. The dual systems are constituted by a CIL and another chiral selector such as a cyclodextrin.

According to particular embodiments, the separation is an enantiomeric separation of amino acids by Capillary Electrophoresis. A specific embodiment relates to the separation of the amino acids homocysteine and cysteine.

According to additional particular embodiments, the ionic liquid is [L-carnitine] [NTf ² ] and is at a concentration between 1 and 20 mM in the separation process.

According to additional particular embodiments, the dual system comprises gammacyclodextrin in a concentration of 2 mM.

According to additional particular embodiments in the separation process, the dual system comprises acetate buffer pH 5.0, phosphate at pH 6.0 and 7.0, or borate buffer at pH 9.0.

CE is a separation technique known to any expert in this field that allows the separation of a large number of molecules of different characteristics and nature. The separation is carried out in a capillary containing an electrolyte medium or separation buffer, as well as the molecules to be separated, eg amino acids. The separation is based on the different mobility of the analytes with different mass / charge ratio under the application of an electric field that originates when establishing a potential difference between the ends of the capillary. The separation of the analytes can be improved by optimizing different experimental variables such as temperature, applied voltage, separation buffer, among others. This technique is characterized by a very low consumption of reagents, solvents and samples in relation to other separation techniques. Therefore, it is considered an analytical technique clean and respectful with the environment. Analytes can be detected by different systems such as UV-Vis, fluorescence, Mass Spectrometry, etc.

In the case where the analytes are separated based on their differential interaction with a chiral selector present in the separation medium, the CE mode is called Electrokinetic Chromatography (EKC).

In a preferred embodiment of the present invention, the ionic liquid is [L-Carnitine] [NTf ² ] and is at a concentration between 1mM and 20mM in the separation buffer in EKC, more preferably the concentration is between 1mM and 10 mM and more preferably 5 mM.

In a preferred embodiment of the present invention, the EKC separation is carried out under the following experimental conditions: using a voltage of 20 kV, at a temperature of 20 ° C; the sample is preferably injected by pressure (hydrodynamic injection), more preferably at a pressure of about 50 mbar, and even more preferably for about 4 seconds; furthermore, preferably a capillary with an internal diameter of 50 µm and a total length of 50 cm with a neutral buffer is used.

The buffer used in the present invention is any at a pH higher than the pKa of the amino acids and known to anyone skilled in capillary electrophoresis, preferably at a pH of between 7.0 and 9.0 and more preferably a phosphate buffer is used.

The analytes to be separated in the present invention could be protein and non-protein amino acids.

Through separation, the enantiomers of a chiral compound can be determined individually, with application to quality control of drugs, foods or other samples.

In the description and claims of the present invention, the word "comprises" and its variants are not intended to exclude other technical characteristics, additives, components or steps. For those skilled in this field, other objects, advantages and characteristics of the invention will emerge in part of the description and part of the practice of the invention. For illustrative purposes, the following figures and examples are presented below and are not intended to be limiting of the present invention.

DESCRIPTION OF THE FIGURES

Figure 1. Enantiomeric separation of the amino acid homocysteine (Hcy) using the gamma-cyclodextrin [L-Carnitine] [NTf ² ] system as a chiral selector.

Figure 2. Enantiomeric separation of the protein amino acid cysteine (Cys) using gamma-cyclodextrin as a chiral selector.

Figure 3. Enantiomeric separation of the amino acid homocysteine (Hcy) using the gamma-cyclodextrin [L-Carnitine] [NTf ² ] system as a chiral selector.

Figure 4. Enantiomeric separation of the protein amino acid cysteine (Cys) using the gamma-cyclodextrin [L-Carnitine] [NTf ² ] system as a chiral selector.

EXAMPLES

General instrumental reagents, materials and methods

L-carnitine hydrochloride (98%, CAS: 6645-46-1), lithium salt derived from bis (trifluoromethane) sulfonamide (99.85%, CAS: 90076-65-6), 1.25 M HCl solution in methanol and methanol. All reagents were purchased from Sigma-Aldrich Chemistry. All reagents used were used without any extra purification. The nuclear magnetic resonance (NMR) spectra were recorded using deuterated solvents (DMSO-O6 or CD ³ OD), as indicated in each case, in a Varian spectrometer - 300 MHz or 500 MHz. Tetramethylsilane ( TMS). The chemical shifts (5) are indicated in parts per million (ppm) and the residual undeuterated solvents are used as internal references for the proton (3.36 ppm for CD ³ OD and 2.49 for DMSO-da) and for the carbon (39.9 ppm for DMSO-da). In 1H-NMR the coupling constants (J) are indicated in Hertz (Hz) and the multiplicities are represented as follows: s (singlet), d (doublet), t (triplet), m (multiplet), and br (as a wide signal). Low resolution mass spectra were obtained using Agilent Technologies 6120 Quadrupole LC-MS with electrospray ionization (ESI) with the Agilent Technologies 1260 Infinity LC system using the SeQuantZic-Hilic column (Merck-Millipore) with dimensions 150 mm x 4.6 mm , 5 pm. Agilent Technologies software was used to process the data. The mass spectrum (MS) is indicated as the ratio of units of mass / charge (m / z). The analysis was carried out using a flow of 1mL / min keeping the temperature of the column at 25 ° C. The detector was set at 277.4 nm ± 16 nm. The mobile phase is made up of mobile phase A (200 mM ammonium acetate, pH 5.2, without EDTA) and mobile phase B (80% Acetonitrile and 20% ammonium acetate solution), using an isocratic method.

Sodium hydrogen phosphate was obtained from Panreac Química S.A. (Barcelona, Spain). Sodium hydroxide, boric acid, pentane, the amino acids DL-homocysteine (Hcy), L-homocysteine, and the derivatizing agent 9-fluorenylmethoxycarbonyl chloride (FMOC) were purchased from Sigma-Aldrich Química (Madrid, Spain). Acetonitrile grade HPLC was obtained from Scharlau (Barcelona, Spain). The chiral selector gammacyclodextrin, as well as the amino acids DL-cysteine (Cys) and L-cysteine obtained from Fluka (Buchs, Switzerland). The solutions were made with purified ultrapure water through a Millipore Milli-Q system (Bedford, MA, USA). All solutions were filtered before being injected into the capillary electrophoresis system with 0.45 pm pore diameter nylon syringe filters purchased from Scharlau (Barcelona, Spain).

Preparation of amino acid solutions

Amino acids are derivatized for subsequent UV detection following a previously described procedure [18]. Briefly, 200 pL of a solution of the derivatizing agent dissolved in Acetonitrile (30 mM) was mixed with 200 pL of a solution of the amino acid to be studied (10 mM). The reaction was kept at room temperature for 2 minutes. The excess derivatizing agent was removed by adding 500 pL of pentane and the final solution was diluted 10 times with Milli-Q water before injecting into the system.

Capillary Electrophoresis

The analyzes were carried out on an Agilent 7100 capillary electrophoresis equipment (Agilent Technologies, Waldbronn, Germany) with a UV-DAD detector. Fused silica capillaries (Polymicro Technologies, Phoenix, AZ, USA) with an internal diameter of 50 pm and an effective length of 50 cm (58.5 cm total length) were used. Between injections, conditioning was carried out with 0.1M sodium hydroxide (1 bar) for 2 minutes, Milli-Q water (1 bar) for 1 minute and separation buffer (1 bar) for 3 minutes. The separation was carried out using a temperature of 20 ° C, applying a voltage of 20 kV and UV detection at a wavelength of 210 nm with a bandwidth of 4 nm. The sample was pressure injected at 50 mbar for 4 s. A 50 mM phosphate buffer (pH 7.0) was used for enantiomeric separation of amino acids.

Synthesis and characterization of ionic liquids

By way of use, the following illustrative examples are described, which are not intended to be limiting:

a) The preparation of halides of the methyl ester derived from L-carnitine according to step (a) of the process of the present invention (Example 1).

b) The preparation of the corresponding CYL containing bis (trifluoromethylsulfonyl) imide (NTf ² ) as anion (Example 2) from the L-carnitine methyl ester chloride, obtained in step a).

The synthesized CILs have been characterized by different techniques, including 1H and 13C Nuclear Magnetic Resonance (NMR), HPLC-MS and elemental analysis.

EXAMPLE 1. Methyl (S) -2-hydroxy-4-trimethylammonium-butyrate chloride

A solution of L-carnitine (III) chloride (0.40 g, 2.00 mmol, 1.0 eq.) In methanol (3 mL) was treated with a 1.25 M solution of HCl in methanol (1 mL ). The resulting mixture was heated at 80 ° C for 3 hours. When the reaction was complete, the solvent was evaporated in vacuo affording the chloride derivative of methyl (S) -2-hydroxy-4-trimethylammonium butyrate (420 mg, 98%) as a white solid. 1H-NMR (CD ³ OD) 5 (ppm): 4.25 (m, J = 6.0 Hz, 1H); 3.42 (s, 3H); 3.18 (d, J = 8.5 Hz, 2H); 2.95 (s, 9H); 2.30 (d, J = 8.5 Hz, 2H).

13C-NMR (CD ³ OD) 5 (ppm): 176.8; 62.5; 53.6; 53.5; 53.4; 50.9; 39.6. Analysis by HPLC-MS ( positive mode): tR = 1.023 min (m / z 176.2 (M + H) +).

EXAMPLE 2. CYL derived from L-carnitine methyl ester with Bis (trifluoromethane) sulfonamide [L-Carnitine] [NTf 2 ] anion.

A solution of methyl (S) -2-hydroxy-4-trimethylammonium-butyrate chloride (358 mg, 1.68 mmol, 1.0 eq.) In distilled water (2 mL) was treated with an equimolar solution of the lithium salt derived from bis (trifluoromethane) sulfonamide ((Tf) ² NLi) (482.8 g, 1.68 mmol, 1.0 eq.) in distilled water (1 mL). The corresponding reaction mixture was stirred at room temperature (25 ° C) for 3 hours. After this time, in the The reaction mixture was observed to form two phases that were separated by means of an extraction funnel and the phase below was collected and dried under vacuum overnight (45 ° C, 150 mbar), yielding 361 mg (47%) of [L-Carnitine] [NTf ² ] as a thick, colorless oil. 1H-NMR (CD ³ OD) 5 (ppm) 4.25 (m, J = 6.0 Hz, 1H); 3.42 (s, 3H); 3.18 (d, J = 8.5 Hz, 2H); 2.95 (s, 9H); 2.30 (d, J = 8.5 Hz, 2H). Analysis by HPLC-MS (positive mode): ír = 1.023 min (m / z 176.2 (M + H) +). Anal. Calcd. for C ¹⁰ H ¹⁸ N ² O ⁷ S ² F ⁶ : C, 26.3; H, 4; F, 25; N, 6.1; S, 14.1. Found: C, 25.29; H, 4.14; N, 6.20; S, 14.40. Elemental analysis tests were performed using an oxygen dose of 30.

Use of CILs based on L-carnitine methyl ester for enantiomeric separation of amino acids by capillary electrophoresis

The use of CILs based on the methyl ester of L-carnitine in a dual system together with gamma-cyclodextrin was evaluated for the enantiomeric separation of protein and non-protein amino acids, more preferably for the amino acids homocysteine and cysteine. A higher enantiomeric Rs was obtained with the addition of these nanoadditives to the separation medium. The experimental conditions used were the following: capillary with an internal diameter of 50 pm and an effective length of 50 cm (total length 58.5 cm); capillary temperature, 20 ° C; applied voltage, 20 kV; injection by pressure, 50 mbar for 4 s; UV detection at 210 nm (4 nm bandwidth) and 50 mM phosphate separation buffer at pH 7.0. The concentrations of the chiral selectors were 2 mM for the gamma-cyclodextrin and 5 mM for the ionic liquid. Under these conditions, two peaks corresponding to the enantiomers of the amino acids were obtained. To try to improve the separation, some electrophoretic conditions were optimized. Thus, different pH and separation buffers were tested. The following were tested: acetate buffer pH 5.0, phosphate pH 6.0 and 7.0 and borate buffer pH 9.0. The best separation was obtained for the phosphate buffer at pH 7.0. In addition, different concentrations of gamma-cyclodextrin were tested in a range of 1-15 mM, obtaining the best separation at a concentration of 10 mM for homocysteine and 2 mM for cysteine (Figures 1 and 2). In order to obtain a higher enantiomeric resolution, the ionic liquid [L-Carnitine] [NTf ² ] was added to the separation medium. Different ionic liquid concentrations (1-20 mM) were tested by setting the concentration of gamma-cyclodextrin at 2 mM. A concentration of 5 mM of [L-Carnitine] [NTf ² ] allowed the best separation of amino acids (Figures 3 and 4).

REFERENCES

[1] Q. Zhang, TrACTrens Anal. Chem. 2018, 100, 145-154.

[2] M. Greño, M.L. Marina, M. Catro-Puyana, Critical Rew. Anal. Chem. 2018, 48, 429 446.

[3] C.P. Kapnissi-Christodoulou, I.J. Stavrou, M.C. Mavroudi, J. Chromatogr. As of 2014, 1363, 2-10.

[4] J. Ding, D.W. Armstrong, Chirality 2005, 17, 281-292.

[5] T. Payagala, D.W. Armstrong, Chirality 2012, 24, 17-53.

[6] I.J. Stavrou, C.P. Kapnissi-Christodoulou, Electrophoresis 2013, 34, 524-530.

[7] C.A. Hadjistasi, I.J. Stavrou, R-I, Stefan Van-staden, H.Y. Aboul-Enein, C.P. Kapnissi-Christodoulou, Chirality 2013, 25, 556-560.

[8] J. Zhang, Y. Du, Q. Zhang, J. Chen, G. Xu, T. Yu, X. Hua, J. Chromatogr. As of 2013, 1316, 119-126.

[9] J. Zhang, Y. Du, Q. Zhang, Y. Lei, Talanta 2014, 119, 193-201.

[10] M.C. Mavroudi, C.P. Kapnissi-Christodoulou, Electrophoresis 2015, 36, 2442-2450.

[11] I.J. Stavrou, Z.S. Breitbach, C.P. Kapnissi-Christodoulou, Electrophoresis 2015, 36, 3061-3068.

[12] A.G. Nicolaou, M.C. Mavroudi, I.J. Stavrou, C.A. Weatherly, C.P. Kapnissi-Christodoulou, Electrophoresis 2019, 40, 539-546.

[13] X. Mu, L-Qi, H. Zhang, Y. Shen, J. Qiao, H. Ma, Talanta 2012, 97, 349-354.

[14] J. Jiang, X. Mu, J. Qiao, Y. Su, L. Qi, Talanta 2017, 175, 451-456.

[15] R. Ratti, Advances in Chemistry 2014, Article ID 729842.

[16] a) J.G. Huddleston, R.D. Rogers, Chem. Comm. 1998, 16, 1765-1766. b) J. Fuller, R.T. Carlin, H.C. de Long, D. Haworth. J. Chem. Soc., Chem. Comm. 1994, 3, 299-300.

[17] a) P. Bonhote, A.-P. Dias, N. Papageorgiou, K. Kalyansundaram, M. Gratzel, Inorg. Chem. 1996, 35, 1168-1178. b) L. Cammarata, S.G. Kararian, P.A. Salter, T. Welton Phys. Chem. Chem. Phys. 2001, 3, 5192-5200.

[18] a) H. Wnag, P.E. Andersson, A. Engstrom, L.G. Blomberg, J.Chromatogr. A 1995, 704, 179-193. b) L. Sanchez-Hernandez, E. Dominguez-Vega, C. Montealegre, M. Castro-Puyana, M.L. Marina, A.L. Crego, Electrophoresis 2014, 35, 1244-1250.

[19] a) A.M. Rydzik, I.K.H. Leung, G.T. Kochan, A. Thalhammer, U. Oppermann, T.D.W. Claridge, C.J. Schofield, ChemBioChem 2012, 13, 1559-1563. b) R. Castagnani, F. De Angelis, E. De Fusco, F. Giannessi, D. Misitim, D. Meloni, M.O. Tinti, J. Org. Chem. 1995, 60, 8318-8319.

[20] P. Sun, DW Armstrong, Analytica Chimica Acta 2010, 661, 1-16.

THANKS

The authors are grateful for the funding received from the Ministry of Economy and Competitiveness (project CTQ2016-76368-P) and the Community of Madrid and European funds from the ESF and FEDER programs (project S2018 / BAA-4393, AVANSECAL-II-CM).

Claims (22)

1. A non-protic CIL based on asters of L-carnitine, [L-Carnitine] [NTf ² ], of general structure I

in which: - the cationic part is asymmetric formed by a differently substituted ammonium cation, in which the substituents are not all the same, derived from the corresponding ester (-COOR) of the chiral amino acid L-carnitine, - R is selected from alkyl of 1 to 5 carbon atoms, linear or branched, substituted or unsubstituted, benzyl, substituted or unsubstituted phenyl, heterocycles as well as heteroaryls, and - the anionic part (A-) is formed by an inorganic or organic anion. 2. A non-protic CYL according to claim 1, wherein R is selected from methyl, ethyl, propyl, isopropyl, n-butyl, te / f-butyl, pentyl, a phenyl group, benzyl, a phenyl group substituted by the introduction of one or two substituents, the same or different, selected from nitro, halo, alkyl, alkoxy, hydroxy, trifluoromethyl, cyanide, heterocycles and heteroaryls. 3. A non-protic CYL according to claim 1, wherein the anion A- is selected from halides, hexafluorophosphate, tetrafluoroborate, acetate, triflate, tetracyanoborate, noctil sulfate, docusate, L-lactate, amino acids, bis (trifluoromethylsufonyl) imide (NTf ² ), bis (pentafluoroethylsulfonyl) imide, tricyanomethane anion and tris (pentafluoroethyl) trifluorophosphate (FAP). 4. A non-protic CIL according to claim 1 of structure

and molecular formula C ¹⁰ H ¹⁸ N ² O ⁷ S ² F ⁶ . 5. An intermediate compound of general formula II

in which: - the cationic part is asymmetric formed by a differently substituted ammonium cation, in which the substituents are not all the same, derived from the corresponding ester (-COOR) of the chiral amino acid L-carnitine, - R is selected from alkyl of 1 to 5 carbon atoms, linear or branched, substituted or unsubstituted, benzyl, substituted or unsubstituted phenyl, heterocycles as well as heteroaryls, and - the anionic part (X-) is a halide anion. 6. A dual system for separation of chemical compounds comprising a chiral ionic liquid defined in one of the preceding claims 1 to 4 and a second component which is a chiral selector. 7. A dual system according to claim 6, wherein the second chiral selector component is a cyclodextrin. 8. A method for obtaining the CILs defined in claims 1 to 4 comprising: a) formation of an ester of the amino acid L-carnitine, compound of general formula II, by a reaction of a halide of L-carnitine (III), in an alcoholic acid medium at 40-120 ° C until the disappearance of the starting material, for a time between 3 to 24 hours and subsequent elimination of the alcoholic medium,

b) optionally, an exchange of the halide anion of derivative II obtained in step (a) in aqueous medium, for the anion represented as A- in formula I, of a salt selected from silver salts, sodium salts, potassium salts and you go out of lithium, obtaining a CIL of formula I, or with the acid corresponding to said anion. 9. A process according to claim 8, in which step a) of formation of the intermediate compounds of formula II, esters of the amino acid L-carnitine, is carried out by reacting the L-carnitine chloride, of formula III, in alcoholic acid medium. The process according to claim 8, in which the anionic metathesis is carried out in an aqueous medium and comprises the treatment of stoichiometric amounts of derivative II with the corresponding silver, sodium, potassium or lithium salts of anions selected from bromide (Br -), Iodide (I-)), hexafluorophosphate (PF6 -) [16], derivatives of tetrafluoroborate (BF ⁴ -), acetate (AcO-), triflate (TfO-), tetracyanoborate (B (CN) ⁴ -), n-octyl sulfate, Docusate, L-lactate, amino acids, bis (trifluoromethylsufonyl) imide (NTf ² ), bis (pentafluoroethylsulfonyl) imide, acetate (CH ³ CO ² -), trifluoroacetate (CF ³ CO ² -). The process according to claim 8, wherein the metathesis reaction, step b), is carried out by selecting the lithium salt derived from bis (trifluoromethane) sulfonamide. 12. The method according to claim 8: i. wherein step b) comprises a treatment of a solution of L-carnitine methyl ester with stoichiometric amounts of bis (trifluoromethane) sulfonamide lithium salt in aqueous medium at room temperature for 5 hours; Y ii. separation of the CIL from the aqueous phase by decantation, obtaining the CIL [L-carnitine] [NTf ² ]. 13. Use of the CILs of general formula I defined in one of claims 1 to 4, in a process for separating chiral compounds. Use according to claim 13, in which the separation method is Capillary Electrophoresis and the CILs are components of a dual system of chiral selectors. 15. Use according to claim 13 or 14, wherein the ClLs comprise anions selected from bromide (Br-), Iodide (I-)), hexafluorophosphate (PF6-), tetrafluoroborate derivatives (BF ⁴ "), acetate ( AcO-), triflate (TfO-), tetracyanoborate (B (CN) ⁴ -), n-octyl sulfate, Docusate, L-lactate, amino acids, bis (trifluoromethylsufonyl) imide (NTf ² ), bis (pentafluoroethylsulfonyl) imide, acetate (CH ³ CO ² -), and trifluoroacetate (CF ³ CO ² -). 16. Use according to one of claims 13 to 15, wherein the anion is NTf ² . 17. Use according to one of Claims 13 to 16 for carrying out enantiomeric separations in Capillary Electrophoresis. 18. Use according to the preceding claim, in which the separation is an enantiomeric separation of amino acids in Capillary Electrophoresis. 19. Use according to the preceding claim, in which the amino acids are homocysteine and cysteine. Use according to one of Claims 13 to 19, in which the ionic liquid is [L-carnitine] [NTf ² ] and is at a concentration between 1 and 20 mM. 21. Use according to claim 14, in which the dual system comprises gammacyclodextrin in a concentration of 2 mM. 22. Use according to claim 14 wherein the dual system comprises acetate buffer pH 5.0, phosphate at pH 6.0 and 7.0, or borate buffer at pH 9.0.