Yanbin Lu

Ionic liquid-based microwave-assisted extraction of phenolic alkaloids from the medicinal plant Nelumbo nucifera Gaertn.

An ionic liquid-based microwave-assisted extraction (ILMAE) approach has been successfully applied to the effective extraction of the phenolic alkaloids present in samples of the medicinal plant Nelumbo nucifera Gaertn. The ionic liquids investigated comprised a range of four anions, four 1-alkyl-3-methylimidazolium derivatives differing in hydrophobic chain length. The results indicate that varying the anion has apparent effects on the overall extraction efficiency. In addition, the influence of some microwave parameters, such as irradiation power, extraction time and solid-liquid ratio, are also investigated. Under the optimized conditions, the proposed approach has been evaluated in comparison with the conventional heat-reflux extraction (HRE) and regular MAE. The reduction of the extraction times (from 2h to 90s) and remarkable higher efficiency (20-50% improved) supports the suitability of the proposed approach. In addition, the proposed method is validated by the recovery, correlation coefficient (R(2)), and reproducibility (RSD, n=5), which are in the range of 98-105%, 0.9994-0.9998, and 1.2-5.4%, respectively.

Screening of Complex Natural Extracts by Countercurrent Chromatography Using a Parallel Protocol

In countercurrent chromatography (CCC) the choice of the liquid system is the heart of any separation. It corresponds to the selection of the mobile phase and the stationary phase at the same time. Any change in one phase composition induces a change in the other phase composition which renders the choice of the appropriate liquid system difficult and lengthy. A scale of compositions of the heptane-ethyl acetate-methanol-water quaternary liquid system was referred to by letters from A to Z and called the Arizona (AZ) liquid system. Each composition of the AZ system has the same heptane/ethyl acetate and methanol/water volume ratios. It is shown that there is a continuous polarity change from the hydrophilic A composition (ethyl acetate-water) to the hydrophobic Z (heptane-methanol) mixture by measuring the distribution constant K(D) of a known test mixture. For all compounds, the log K(D) is linearly increasing with the water content of the lower aqueous phase of the composition used. The slopes of the log K(D) versus percent H(2)O have very different values which means that the chromatographic selectivity changes with liquid system compositions. The AZ system was associated to the elution-extrusion method to design a procedure to identify rapidly the appropriate solvent composition able to fractionate correctly a complex natural extract. With the use of an integrated three-coil CCC column (40 mL each coil) able to test three AZ compositions in parallel, it is shown that the optimum AZ composition is found in half a day using less than a liter total volume of solvents. Two natural extracts are rapidly screened using the proposed protocol. An extract of Piper longum L. of intermediate polarity was fractionated in five usable portions using the 3/2/3/2 (Q) composition of the AZ system. A polar extract of Polygonum cuspidatum was also separated in five fractions using the 1/6/1/6 (D) composition. In both cases, a 140 mL CCC column was used for a direct scale-up transfer with the same liquid system. Purified fractions were subjected to an antioxidant activity assay and liquid chromatography with UV and mass spectrometry detection (LC-UV/MS) analysis to determine the molecular weight, number, and quantity of compounds in the active fractions. Four fractions of P. cuspidatum showed excellent antioxidant activity. They were rapidly produced at the milligram level by the 140 mL CCC column and fractionated by semipreparative high-performance liquid chromatography (HPLC) in individual compounds that were each identified by NMR and MS and reevaluated for confirmation of bioactivity. The rapid screening CCC protocol associated to the preparative capability of CCC allows for a fast identification and characterization of active compounds in natural products.

Preparative isolation and purification of antioxidative stilbene oligomers from Vitis chunganeniss using high‐speed counter‐current chromatography in stepwise elution mode

Preparative high-speed counter-current chromatography (HSCCC) was successfully applied to the isolation and purification of three stilbene oligomers from Vitis chunganeniss using stepwise elution with a pair of two-phase solvent systems composed of n-hexane-ethyl acetate-methanol-water at (2:5:2:5, v/v) and (1:2:1:2, v/v). The preparative HSCCC separation was performed on 800 mg of crude sample yielding hopeaphenol (21.1 mg), amurensin G (37.2 mg) and vitisin A (95.6 mg) in a one-step separation, with purities over 95% as determined by HPLC. The structures of these three compounds were identified by MS, (1)H NMR and (13)C NMR. In addition, their antioxidant activities were screened by DPPH assay, where vitisin A showed strong antioxidant activity. Further EPR experiments with spin-trapping technique demonstrated that vitisin A is a potent and selective singlet oxygen quencher, which may be used in singlet oxygen-mediated diseases as a pharmacological agent.

Rapid screening of bioactive components from Zingiber cassumunar using elution-extrusion counter-current chromatography

Elution-extrusion counter-current chromatography (EECCC) takes full advantages of the liquid nature of the stationary phase. It effectively extends the solute hydrophobicity window that can be studied and renders the CCC technique particularly suitable for rapid analysis of complex samples. In this paper, EECCC was used to screen the crude ethanol extract of Zingiber cassumunar and to isolate milligram-amounts of bioactive components. The two column volume (2V(C)) EECCC method was applied to rapidly optimize the composition of the biphasic liquid system in both reversed- and normal-phase separation mode. With the n-hexane/ethyl acetate/methanol/water 1/1/1/1 (v/v) system, 100mg of crude Z. cassumunar extract were fractionated on a 140 mL-capacity semi-preparative hydrodynamic CCC column and 0.5 g on a 1600 mL column for large-scale preparation. Satisfactory separation efficiency was achieved in both cases, producing milligram-amounts of four phenylbutenoids over 90% pure and of a mixture of diastereoisomers (phenylbutenoid dimers). However, the global throughputs of the two columns were 8 and 11 mg/h, not very different. This is due to the fact that the 1600 mL column could not retain the liquid stationary phase as well as the smaller 140 mL column. It was necessary to work at much lower flow rate than calculated. Methanol was added as a post-column clarifying reagent for stable continuous UV detection. A lipophilic biphasic liquid system composed of n-hexane/acetonitrile/water (5/3/2, v/v) allowed to resolve the pair of diastereoisomers with the larger preparative instrument producing 35 mg of the (+/-)-trans form 99.1% pure and 28 mg of the (+/-)-cis isomer 98.1% pure. Compared with classical elution, the EECCC approach exhibits strong separation efficiency and great potential to be a high-throughput separation technique in the case of complex samples.

Integrated Countercurrent Extraction of Natural Products: A Combination of Liquid and Solid Supports

An integrated online column-switching countercurrent chromatography (CCC) with a solid-phase trapping/preconcentration interface is presented. The interface is systematically evaluated in terms of sorbent type, column size, and kinetic factor from the view of the unique CCC process. Results indicate that satisfactory trapping efficiency can be achieved using a 25 mm x 10 mm i.d. column packed with Oasis HLB materials. In addition to the analyte focusing effect, large volume injection is avoided, thereby allowing the use of totally different biphasic liquid systems to enhance the system orthogonality. The present integrated system simply combines the liquid and solid supports and is successfully applied in a one-step preparative separation of four antioxidative compounds from the ethyl acetate extract of traditional Chinese herbal medicine Rubia cordifolia L. (Rubiaceae), exhibiting great advantages in peak resolution, peak capacity, and instrument integration compared with conventional CCC separations.

Rapid and preparative separation of traditional Chinese medicine Evodia rutaecarpa employing elution-extrusion and back-extrusion counter-current chromatography: Comparative study

Traditional Chinese medicines (TCMs) have attracted much attention in recent years. Elution-extrusion and/or back-extrusion counter-current chromatography (EECCC/BECCC) both take full advantage of the liquid nature of the stationary phase. They effectively extend the solute hydrophobicity window that can be studied and rendered the CCC technique particularly suitable for rapid analysis of complex samples. In this paper, a popular traditional Chinese medicine, Evodia rutaecarpa, was used as the target complex mixture for extrusion CCC separations. With a carefully selected biphasic liquid system (n-hexane/ethyl acetate/methanol/water, 3/2/3/2, v/v) and optimized conditions (V(CM)=V(C), mobile phase flow rate: 3mL/min in descending mode, sample loading: 100mg), five fractions could be obtained in only 100min on a 140-mL capacity CCC instrument using both elution- and back-extrusion methods. Each fraction was analyzed and identified compared with the data of major standards using LC/MS. Moreover, the performance of both extrusion protocols was systematically compared and summarized. EECCC could be operated continuously and was found extremely suitable for high-throughput separation; however, post-column addition of a clarifying reagent is recommended to smooth the UV-signal during the extrusion process. Considering BECCC, the practical operation is very simple by just switching a 4-port valve to change the flow direction. The change of flowing direction should be done after a sufficient amount of mobile phase has flushed the column in the classical mode so that solutes with small and medium distribution constants have been eluted. Otherwise, a significant portion of the solutes will stay in the mobile phase inside the column, mix together and produce a broad peak showing in the mobile phase eluting after the stationary phase extrusion. Compared with classical CCC or other preparative separation tools, extrusion CCC approaches exhibit distinguished superiority in the modernization process of traditional Chinese medicines.

Determination of Anti-Tumor Constitute Mollugin from Traditional Chinese Medicine Rubia cordifolia: Comparative Study of Classical and Microwave Extraction Techniques

Abstract Rubia cordifolia is a common traditional Chinese medicine (TCM) used for centuries for the treatment of cough, inflammation of the joints, uterine hemorrhage, and uteritis. Mollugin is a major active component present in R. cordifolia and recognized as a potential anti-tumor compound. In this work, a microwave-assisted extraction (MAE) method has been developed for extracting mollugin from R. cordifolia. Several variables that can potentially affect the extraction yield, namely extracting solvent, microwave power, extraction time, and solid-liquid ratio were optimized. The separation and quantitative determination of mollugin was carried out by HPLC with UV detection at 254 nm. Under appropriate MAE conditions, such as extraction time of 4 min, ethanol concentration of 70% (v/v), microwave power of 460 W, and solid-liquid ratio of 1:20 (g/mL), the extraction yield of mollugin from R. cordifolia with MAE was higher than conventional extraction methods such as Soxhlet extraction, heat reflux extraction, and ultrasonic-assisted extraction. Due to the considerable saving in time and its higher extraction yield, the proposed MAE procedure was obviously a more rapid and effective sample preparation technique.

Preparative isolation and purification of two amides from Mallotus lianus Croiz by high‐speed counter‐current chromatography

High-speed counter-current chromatography (HSCCC) was applied to the preparative isolation and purification of two amides from Mallotus lianus Croiz. In a single HSCCC separation, using the two-phase solvent system composed of n-hexane/ethyl acetate/methanol/water (5:1:5:1 v/v), 247.5 mg of the enriched crude sample was separated to afford 10.3 mg of N-isobutyl-2E,4E,12Z-octadecatrienamide and 15.7 mg of (7Z,10Z,18Z)tricosa-7,10,18-trienamide, a novel compound, with the purities of 98.0 and 94.6%, respectively. The HSCCC fractions were analyzed by HPLC and chemical structures of the compounds were identified by 1D- and 2D-NMR, ESI-, and GC-MS.

Differentiation of configurations of the phenylbutenoid dimer derivatives from Zingiber cassumunar by tandem mass spectrometry

High-performance liquid chromatography/electrospray tandem mass spectrometry was developed to distinguish isomers and compounds of similar structures with different configurations in the rhizomes of Z. cassumunar. Energy-resolved breakdown curves were utilized to differentiate four compounds. Compounds 2 (3R,4S) and 4 (3R,4R) were a pair of stereoisomers which could be distinguished easily by breakdown curves. The breakdown curve of compound 1 was identical to that of compound 2, which suggested that the configuration of compound 1 was (3R,4S) or (3S,4R). The breakdown curve of compound 3 was completely different from those of compounds 1, 2 and 4, and it might be that the configuration of the double bond of compound 3 was different from the other three compounds. Hence, the described method using breakdown curves has great potential in the distinguishing of isomers and compounds of similar structure with different configurations.