Application of silver ion in the separation of macrolide antibiotic components by high-speed counter-current chromatography

Three macrolide antibiotic components – ascomycin, tacrolimus and dihydrotacrolimus – were separated and purified by silver ion high-speed counter-current chromatography (HSCCC). The solvent system consisted of n-hexane–tert-butyl methyl ether–methanol–water (1:3:6:5, v/v) and silver nitrate (0.10 mol/l). The silver ion acted as a π-complexing agent with tacrolimus because of its extra side double bond compared with ascomycin and dihydrotacrolimus. This complexation modified the partition coefficient values and the separation factors of the three components. As a result, ascomycin, tacrolimus and dihydrotacrolimus were purified from 150 mg extracted crude sample with purities of 97.6%, 98.7% and 96.5%, respectively, and yields over 80% (including their tautomers). These results cannot be achieved with the same solvent system but without the addition of silver ion.     

Purification of quinoline yellow components using high-speed counter-current chromatography by stepwise increasing the flow-rate of the mobile phase

Quinoline yellow (Color Index No. 47005) consists of multiple components that show a large difference in their partition coefficients (K), ranging from 0.03 to 3.3 in the solvent system tert.-butyl methyl ether (MTBE)-1-butanol-acetonitrile-aqueous 0.1 M trifluoroacetic acid (TFA). Consequently, it requires an excessively long elution time for the simultaneous separation of all components by the standard high-speed counter-current chromatography technique, which uses a constant flow-rate of the mobile phase. In order to overcome this problem, we increased the flow-rate of the mobile phase stepwise from 0.1 to 2.0 mL/min. Using this new procedure, six components (0.2-6.1 mg) were successfully isolated from 25 mg of a commercial quinoline yellow preparation in a single run using a two-phase solvent system composed of MTBE-1-butanol-acetonitrile-aqueous 0.1 M TFA (1:3:1:5, v/v). The purified components were analyzed by high-performance liquid chromatography, electrospray ionization mass spectrometry, and nuclear magnetic resonance spectroscopy.     

Application of stereocontrolled aldol coupling to synthesis of segments of immunosuppressants FK-506 and rapamycin

The sector comprising C24-C34 of FK-506 containing five of the stereogenic centers in this macrolide was synthesized from (−)-quinic acid. Aldol coupling of the C24-C34 unit with a methyl ketone representing C20-C23 of FK-506 proceeded with complete Felkin stereoselectivity to afford the C20-C34 portion of the immunosuppressant. A chelate transition state invoking coordination of a lithium enolate with a trityl ether is proposed to explain this stereoselectivity. The strategy adopted for construction of the C26-C34 moiety of FK-506 was extended to the C34-C42 subunit of rapamycin. A Mukaiyama asymmetric anti-aldol coupling was used to set in place the vicinal diol functionality at C27,28 in the C26-C33 segment of this macrolide.     

Development of Abraham model correlations for describing the transfer of molecular solutes into propanenitrile and butanenitrile from water and from the gas phase

Experimental solubilities were measured for 20 crystalline organic solutes dissolved in propanenitrile and for 13 crystalline organic solutes dissolved in butanenitrile at 298.15 K. Infinite dilution activity coefficient data for solutes dissolved in propanenitrile and butanenitrile have been compiled from the published chemical and engineering literature and converted into gas-to-liquid partition coefficients and water-to-organic solvent partition coefficients through standard thermodynamic relationships. Abraham model correlations were developed for describing solute transfer into both propanenitrile and butanenitrile by combining our measured solubility data with the partition coefficients that we calculated from the published activity coefficient data. The derived Abraham model correlations were found to back-calculate the observed partition coefficients and molar solubility data to within 0.14 log units.     

Solvent system selection in counter-current chromatography using conductor-like screening model for real solvents

The aim of this investigation was to minimize the experimental effort for solvent system selection in counter-current chromatography. The separation mechanism in counter-current chromatography is based exclusively on the partitioning of the solute between the two liquid phases. Therefore, a quantum chemical method combined with statistical thermodynamics (conductor-like screening model for real solvents, COSMO-RS) was used for the prediction of the partition coefficient. A comparison of the experimental and predicted data for five model solutes systems demonstrated the potential of the use of COSMO-RS as a screening tool for the solvent system selection.     

Selection of a nonaqueous two-phase solvent system for fractionation of xylo-oligosaccharide prebiotics using a conductor-like screening model for real solvents

Fractionation of xylo-oligosaccharides (XOS) using a liquid–liquid solvent system can be a difficult endeavor due to the high solubility of XOS in water. Use of a nonaqueous solvent system is a solution for XOS fractionation. XOS are gaining attention as a prebiotic food additive and are abundant in agricultural residues. We describe the use of a molecular modeling approach to determine which solvents and at what volume ratio to use for XOS fractionation. The conductor-like screening model for real solvents was used to predict the partition coefficients of xylose and two major functional XOS—xylobiose and xylotriose, based on the structure of the compounds and the composition of solvents in a panel of nonaqueous biphasic solvent systems. Eleven common solvents used in countercurrent chromatography were used to build 12 biphasic solvents model systems that were then evaluated and compared using shake flask experiments to determine which could fractionate the three XOS from a mixture. The model and experimental results indicate that a heptane/n-butanol/acetonitrile system at a volume ratio of 9:4:5 would result in a partition coefficient close to the region of optimal separation for a countercurrent chromatography fractionation.     

High-speed counter-current chromatography of apple procyanidins

Apple procyanidins were separated by high-speed counter-current chromatography using a type-J multilayer coil planet centrifuge. Several two-phase solvent systems with a wide range of hydrophobicities from a non-polar hexane system to polar n-butanol systems were evaluated their performance in terms of the partition coefficient and the retention of the phase. The best separation of procyanidins B and C was achieved with a two-phase solvent system composed of n-butanol-methyl tert.-butyl ether-acetonitrile-0.1% trifluoroacetic acid (2:4:3:8) using the lower phase as a mobile at a flow-rate of 1.0 ml/min.     

Preparative purification of tetrabromotetrachlorofluorescein and phloxine B by centrifugal counter-current chromatography.

A centrifugal counter-current chromatographic method for preparative purification of commercial tetrabromotetrachlorofluorescein and Phloxine B (D&C Red Nos. 27 and 28, respectively) was developed. Ethyl acetate-n-butanol-0.01 M ammonium acetate (1:1:2) was used as the two-phase solvent system. Each purification trial involved 50 mg of sample and yielded 22 mg (+/- 2 mg) of pure dye. The purity of the product was measured by high-performance liquid and thin-layer chromatography and was found to be 99.9%. The partition coefficients of these compounds were found to be highly concentration-dependent in the two-phase solvent system used. If this problem can be circumvented, then the counter-current chromatographic method can be extended for use with gram quantities of dye.     

Nuclear magnetic resonance-based solvent system selection for counter-current chromatography separation of compounds present in the same high-performance liquid chromatography peak: Flavonoids in barley seedlings as an example

Partition coefficient is a key parameter for counter-current chromatography separation. High-performance liquid chromatography (HPLC) is the most commonly used tool for the screening of partition coefficients. However, HPLC technology is not applicable to the compounds present in the same chromatographic peak. Nuclear magnetic resonance (NMR) technology could easily distinguish compounds according to their characteristic absorption even if they exist in the same HPLC peak. In this study, two flavonoids present in the same HPLC peak were successfully purified by counter-current chromatography with a solvent system screened by NMR to show the great potential of NMR technology in the screening of the partition coefficient of co-efflux compounds. Through NMR screening, an optimized ethyl acetate/n-buthanol/water (7:3:10, v/v/v) system was applied in this study. As a result, two flavonoids, including 4.8 mg of 3′-methoxyl-6′’’-O-feruloylsaponarin and 9.8 mg of 6′’’-O-feruloylsaponarin were separated from 15 mg of the mixture. There is only one methoxy group difference between the two flavonoids. This study provides a new strategy for the screening of counter-current chromatography solvent systems and broadens the application scope of counter-current chromatography.     

Solubility and Thermodynamic Properties of A Hexanediamine Derivative in Pure Organic Solvents and Nonaqueous Solvent Mixtures

The solubility of N,N′-Bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine in seven pure solvents (acetonitrile, acetone, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate and isobutyl acetate) and two binary solvent mixtures (acetone?+?acetonitrile and methyl acetate?+?acetonitrile) were measured from 273.15 to 303.15 K at atmospheric pressure by a dynamic method. The solubility data in these pure solvents were correlated by the modified Apelblat model, the Wilson model and the NRTL model, and that in the binary solvents mixture were fitted to the CNIBS/R–K model and the NRTL model. Furthermore, the mixing thermodynamic properties in pure and binary solvent systems were calculated and are discussed, based on the NRTL model. Finally, the applicability of the model of Zhang et al. (Ind Eng Chem Res 51:6933–6938, 2012) in correlating solubility data versus dielectric constant was extended from organic solvent–water mixtures to pure organic solvents and nonaqueous organic solvent mixtures. It was found that the dissolution behavior of a compound in the binary solvent mixtures can be predicted to some extent from those in pure solvents.     

PH-Zone-refining counter-current chromatography of lappaconitine from Aconitum sinomontanum nakai I. Separation of prepurified extract

pH-Zone-refining counter-current chromatography was applied to the separation of diterpenoid alkaloids from a crude sample from a crude prepurified sample containing lappaconitine at about 90% purity using a multilayer coil planet centrifuge. The experiment was performed with a two-phase solvent system composed of methyl tert.-butyl ether-tetrahydrofuran-distilled water (2:2:3, v/v) where triethylamine (10 mM) was added to the upper organic stationary phase as a retainer and hydrochloric acid (10 mM) to the aqueous mobile phase as an eluter. The separation of 10.5 g of the sample yielded 9.0 g of lappaconitine at a high purity of over 99% as determined by HPLC.     

Experimental and predicted solubilities of 3,4-dichlorobenzoic acid in select organic solvents and in binary aqueous–ethanol mixtures

Experimental solubilities are reported for 3,4-dichlorobenzoic acid dissolved in methyl butyrate, and in 16 alcohol, 5 alkyl acetate, 5 alkoxyalcohol and 6 ether solvents. Solubilities were also measured in nine binary aqueous–ethanol solvent mixtures at 298.15?K. The measured solubility data were correlated with the Abraham solvation parameter model. Mathematical expressions based on the Abraham model predicted the observed molar solubilities to within 0.12 log units.     

Optimisation of the derivatization in cellulose-type chiral selectors for enantioseparation by centrifugal partition chromatography

Cellulose was chemically modified with hydrophobic dodecanoyl groups followed by 3,5-dimethylphenylcarbamoyl substituents forming mixed ester/carbamate derivatives in order to improve the solubility in lipophilic solvents compared to the corresponding homosubstituted cellulose tris(3,5-dimethylphenylcarbamate). Two mixed derivatives of different degree of substitution were prepared, tested as chiral selectors (CSs) in counter-current chromatography (CCC) and compared to the homo-substituted derivative. Alternatively, cellulose tris(3,5-dichlorophenylcarbamate), was synthesised and tested with the same purpose. The racemic drugs pindolol and warfarin were used as test compounds. Biphasic organic/aqueous solvent systems, composed of methyl isobutyl ketone, t-butyl methyl ether or ethyl acetate and aqueous ammonium acetate or sodium phosphate buffer, were used. Centrifugal partition chromatography, a variety of CCC, in the classical elution mode and the pH-zone-refining displacement mode was applied. The enantioseparation of pindolol and warfarin was achieved in the latter conditions. The presence of dodecanoyl chains on the CS increased solubility in the organic solvents used. The selectivity of the mixed dodecanoyl/3,5-dimethylphenylcarbamoyl cellulose derivative with low degree of dodecanoyl groups (degree of substitution 0.3/degree of substitution 2.6, respectively) was similar to that of the homo-substituted derivative. Furthermore, the loading capacity for pindolol was increased by a factor of three compared to cellulose tris(3,5-dimethylphenylcarbamate). Nevertheless, the increasing degree of substitution with dodecanoyl groups on the CS, although improved solubility in the stationary phase, contributed negatively to the enantioselectivity, where warfarin was more affected than pindolol.     

Chromatographic and spectroscopic methods for the determination of solvent properties of room temperature ionic liquids

Room temperature ionic liquids are novel solvents with favorable environmental and technical features. Synthetic routes to over 200 room temperature ionic liquids are known but for most ionic liquids physicochemical data are generally lacking or incomplete. Chromatographic and spectroscopic methods afford suitable tools for the study of solvation properties under conditions that approximate infinite dilution. Gas-liquid chromatography is suitable for the determination of gas-liquid partition coefficients and activity coefficients as well as thermodynamic constants derived from either of these parameters and their variation with temperature. The solvation parameter model can be used to define the contribution from individual intermolecular interactions to the gas-liquid partition coefficient. Application of chemometric procedures to a large database of system constants for ionic liquids indicates their unique solvent properties: low cohesion for ionic liquids with weakly associated ions compared with non-ionic liquids of similar polarity; greater hydrogen-bond basicity than typical polar non-ionic solvents; and a range of dipolarity/polarizability that encompasses the same range as occupied by the most polar non-ionic liquids. These properties can be crudely related to ion structures but further work is required to develop a comprehensive approach for the design of ionic liquids for specific applications. Data for liquid-liquid partition coefficients is scarce by comparison with gas-liquid partition coefficients. Preliminary studies indicate the possibility of using the solvation parameter model for interpretation of liquid-liquid partition coefficients determined by shake-flask procedures as well as the feasibility of using liquid-liquid chromatography for the convenient and rapid determination of liquid-liquid partition coefficients. Spectroscopic measurements of solvatochromic and fluorescent probe molecules in room temperature ionic liquids provide insights into solvent intermolecular interactions although interpretation of the different and generally uncorrelated "polarity" scales is sometimes ambiguous. All evidence points to the ionic liquids as a unique class of polar solvents suitable for technical development. In terms of designer solvents, however, further work is needed to fill the gaps in our knowledge of the relationship between ion structures and physicochemical properties.     

A simple method to optimize the HSCCC two-phase solvent system by predicting the partition coefficient for target compound

A simple method was developed to optimize the solvent ratio of the two-phase solvent system used in the high-speed counter-current chromatography (HSCCC) separation. Some mathematic equations, such as the exponential and the power equations, were established to describe the relationship between the solvent ratio and the partition coefficient. Using this new method, the two-phase solvent system was easily optimized to obtain a proper partition coefficient for the CCC separation of the target compound. Furthermore, this method was satisfactorily applied in determining the two-phase solvent system for the HSCCC preparation of pseudolaric acid B from the Chinese herb Pseudolarix kaempferi Gordon (Pinaceae). The two-phase solvent system of n-hexane/EtOAc/MeOH/H(2)O (5:5:5:5 by volume) was used with a good partition coefficient K = 1.08. As a result, 232.05 mg of pseudolaric acid B was yielded from 0.5 g of the crude extract with a purity of 97.26% by HPLC analysis.     

Isavuconazole: Thermodynamic Evaluation of Processes Sublimation,Dissolution and Partition in Pharmaceutically Relevant Media

A temperature dependence of saturated vapor pressure of isavuconazole (IVZ), an antimycotic drug, was found by using the method of inert gas-carrier transfer and the thermodynamic functions of sublimation were calculated at a temperature of 298.15 K. The value of the compound standard molar enthalpy of sublimation was found to be 138.1 ± 0.5 kJ·mol⁻¹. The IVZ thermophysical properties—melting point and enthalpy—equaled 302.7 K and 29.9 kJ mol⁻¹, respectively. The isothermal saturation method was used to determine the drug solubility in seven pharmaceutically relevant solvents within the temperature range from 293.15 to 313.15 K. The IVZ solubility in the studied solvents increased in the following order: buffer pH 7.4, buffer pH 2.0, buffer pH 1.2, hexane, 1-octanol, 1-propanol, ethanol. Depending on the solvent chemical nature, the compound solubility varied from 6.7 × 10⁻⁶ to 0.3 mol·L⁻¹. The Hansen s approach was used for evaluating and analyzing the solubility data of drug. The results show that this model well-described intermolecular interactions in the solutions studied. It was established that in comparison with the van’t Hoff model, the modified Apelblat one ensured the best correlation with the experimental solubility data of the studied drug. The activity coefficients at infinite dilution and dissolution excess thermodynamic functions of IVZ were calculated in each of the solvents. Temperature dependences of the compound partition coefficients were obtained in a binary 1-octanol/buffer pH 7.4 system and the transfer thermodynamic functions were calculated. The drug distribution from the aqueous solution to the organic medium was found to be spontaneous and entropy-driven.