Strong cation exchange column allow for symmetrical peak shape and increased sample loading in the separation of basic compounds

Decoloration and alkaloid enrichment of Dactylicapnos scandens extracts based on the use of strong anion-exchange resins in tandem with strong cation-exchange silica-based materials

Alkaloids are natural bioactive ingredients but are usually present in low amounts in plant extracts. In addition, the dark color of plant extracts increases the difficulty in separation and identification of alkaloids. Therefore, effective decoloration and alkaloid enrichment methods are necessary for purification and further pharmacological studies of alkaloids. In this study, a simple and efficient strategy is developed for the decoloration and alkaloid enrichment of Dactylicapnos scandens (D. scandens) extracts. In feasibility experiments, we evaluated two anion-exchange resins and two cation-exchange silica-based materials with different functional groups using a standard mixture composed of alkaloids and nonalkaloids. By virtue of its high adsorbability of nonalkaloids, the strong anion-exchange resin PA408 is considered a better choice for the removal of nonalkaloids, and the strong cation-exchange silica-based material HSCX was selected for its great adsorption capacity for alkaloids. Furthermore, the optimized elution system was applied for the decoloration and alkaloid enrichment of D. scandens extracts. Nonalkaloid impurities in the extracts were removed by the use of PA408 in tandem with HSCX treatment, and the total alkaloid recovery, decoloration and impurity removal ratios are determined to be 98.74%, 81.45% and 87.33%, respectively. This strategy can contribute to further alkaloid purification and pharmacological profiling of D. scandens extracts, as well as other plants with medicinal value.

Optimized Chromatographic Determination of Naphazoline and Chlorpheniramine in Eye/Nose Drops Using Cation-exchange Column

A simple and efficient liquid chromatographic method has been developed and validated for the simultaneous determination of naphazoline and chlorpheniramine in eye/nose drops, in presence of naphazoline degradation product and naphthalene acetic acid (NAPD). The separation was achieved within 6.0 min, employing a mixture of 53.5% v/v water-acetonitrile containing 78.70 mM/L sodium dihydrogen orthophosphate adjusted to pH 5.30 as isocratic mobile phase, pumped at 1.0 mL/min through a strong cation-exchange column (10 μm particle size), the analytes were monitored at 230 nm. Statistical experimental designs and graphic representations (response surface methodology) were used for optimizing the chromatographic separation. The linearity plots were linear over concentration range up to 125% of the analytes nominal concentrations (100%) with regression coefficients (r) > 0.99, method's accuracy (RSD < 2.0%), repeatability and intermediate precision (RSD < 2.0%) were verified. System suitability parameters were also within the acceptable range. The validated method was successfully employed for the routine analysis of eye/nose drops.

Liquid chromatographic separation of alkaloids in herbal medicines: Current status and perspectives

Alkaloids are a widespread group of basic compounds in herbal medicines and have attracted great interest due to various pharmaceutical activities and desirable druggability. Their distinctive structures make chromatographic separation fairly difficult. Peak tailing, poor resolution, and inferior column-to-column reproducibility are common obstacles to overcome. In order to provide a valuable reference, the methodologies and/or strategies on liquid chromatographic separation of alkaloids in herbal medicines proposed from 2012 to 2019 are thoroughly summarized.

Ultra-high performance separation of basic compounds on reversed-phase columns packed with fully/superficially porous silica and hybrid particles by using ultraviolet transparent hydrophobic cationic additives

The use of the tetrabutylammonium additive was investigated in the ultra-high performance reversed-phase liquid chromatographic elution of basic molecules of pharmaceutical interest. When added to the mobile phase at low pH, the hydrophobic tetrabutylammonium cation interacts with the octadecyl chains and with the residual silanols, thus imparting a positive charge to the stationary phase, modulating retention and improving peak shape of protonated basic solutes. Two sources of additive were tested: a mixture of tetrabutylammonium hydroxide/trifluoroacetic acid and tetrabutylammonium hydrogen sulfate. Retention and peak shape of 11 basic pharmaceutical compounds were evaluated on commercially available ultra-fast columns packed with octadecyl stationary phases (Ascentis Express C18 2.0 µm, Acquity BEH C18 1.7 µm, Titan C18 1.9 µm). All columns benefit from the use of additive, especially tetrabutylammonium hydrogen sulfate, providing very symmetric peaks with reasonable retention times. Focusing on the probe compounds amitriptyline and sertraline, efficiency and asymmetry values were investigated at increasing retention factor. The trend is very different to that obtained in reversed-phase conditions and the effect lies in the complex molecular interaction mechanisms based on hydrophobic and ion exchange interactions as well as electrostatic repulsion.

Purification of tertiary and quaternary alkaloids from Rhizoma Corydalis using reversed-phase/weak cation-exchange mixed-mode class separation combined with preparative C18 and silica based strong cation-exchange chromatography

A new optimization strategy for purification of alkaloids from Rhizoma Corydalis using preparative liquid chromatography was developed, featuring a selective separation of different types of alkaloids into different parts by a reversed-phase/weak cation-exchange mixed-mode column (named C18WCX) at first. The total alkaloids of Rhizoma Corydalis were divided into four fractions with fraction III and IV corresponding to the tertiary type medium bases and the quaternary type strong bases, respectively. For fraction III, a conventional C18 column was used to isolate tertiary alkaloids using acetonitrile and 0.1% phosphoric acid (adjusted with triethylamine to pH 6.0) as mobile phases. High selectivity and symmetrical peak shapes of tertiary alkaloids were obtained, resulting in six main tertiary alkaloids isolated in a single run. As strong bases, quaternary alkaloids often suffer from serious peak tailing problem on conventional C18 columns. Therefore, a silica-based strong cation-exchange (SCX) column was used for purification of fraction IV. On the SCX column, good peak shapes in high sample loading were achieved. Five main quaternary alkaloids were isolated and identified from the fraction in one-step. The procedures presented effective for the preparative isolation and purification of alkaloids from Rhizoma Corydalis.

A novel two-dimensional liquid chromatography - Mass spectrometry method for direct drug impurity identification from HPLC eluent containing ion-pairing reagent in mobile phases

In this study, a novel two dimensional liquid chromatography - mass spectrometry (2D-LC-MS) method with use of a weak anion exchange column between the 1st DLC RP column and the 2nd DLC RP column (RP1-WAX-RP2) was developed and applied to identify drug impurities from MS incompatible mobile phases containing sodium 1-octanesulfonate and non-volatile buffer. The 1st DLC conditions follow exactly the original standard HPLC method recorded in Chinese Pharmacopeia (ChP), European Pharmacopeia (EP) or US Pharmacopeia (USP). An impurity fraction was collected with a built-in sample loop (100 μL) and transferred to the WAX column where 1-octanesulfonate and phosphate were trapped and removed. While, the impurity and other cations were eluted to the 2nd D column (RP2) for separation and identification by connected IT-TOF MS. Methods were programmed and applied to identify impurities in two generic drugs, sulpiride (hydrophilic drug with logP 0.57) and dobutamine (hydrophobic drug with logP 3.6). The results indicate that the methods based on RP1-WAX-RP2 column configuration offer a feasible solution for direct impurity identification in generic drug product or API without needs of off-line desalting from the MS incompatible mobile phases containing ion-pairing reagent and non-volatile buffer.

A non-derivative method for the quantitative analysis of isosteroidal alkaloids from Fritillaria by high performance liquid chromatography combined with charged aerosol detection

A non-derivative method was developed for the qualitative and quantitative analysis of isosteroidal alkaloids from Fritillaria thunbergii. During method development the performance of two universal detectors, the charged aerosol detector (CAD) and evaporative light scattering detector (ELSD), were evaluated. The CAD was found to be 30 to 55 times more sensitive than ELSD enabling the measurement of low levels of reference compound impurities that could not be detected by ELSD. The peak area percent of the reference compound, peimisine, obtained by CAD was 50.10%, but 91.66% by ELSD showing that CAD is suitable to estimate the presence of impurities. The CAD showed good reproducibility with overall intra- and inter-day peak area RSD values of less than 1.8% and 2.7%, respectively and had a linear dynamic range of up to 4 orders of magnitude (0.06-44mg/L) for peimine and peiminine. The optimized method was used for the quantitative analysis of peimine and peiminine from F. thunbergii.

Ion-exchange vs reversed-phase chromatography for separation and determination of basic psychotropic drugs

Ion exchange chromatography, an alternative to reversed-phase (RP) chromatography, is described in this paper. We aimed to obtain optimal conditions for the separation of basic drugs because silica-based RP stationary phases show silanol effect and make the analysis of basic analytes hardly possible. The retention, separation selectivity, symmetry of peaks and system efficiency were examined in different eluent systems containing different types of buffers at acidic pH and with the addition of organic modifiers: methanol and acetonitrile. The obtained results reveal a large influence of the salt cation used for buffer preparation and the type of organic modifier on the retention behavior of the analytes. These results were also compared with those obtained on an XBridge C18 column. The obtained results demonstrated that SCX stationary phases can be successfully used as alternatives to C18 stationary phases in the separation of basic compounds. The most selective and efficient chromatographic systems were applied for the quantification of some psychotropic drugs in fortified human serum samples.

Evaluation of separation properties of a modified strong cation exchange material named MEX and its application in 2D-MEX × C18 system to separate peptides from scorpion venom

Peptides from scorpion venom represent one of the most promising sources for drug discovery in some specific disease.

Discovery of N-methyltetrahydroprotoberberines with κ-opioid receptor agonists-opioid receptor agonist activities from corydalis yanhusuo W. T. Wang by using two-dimensional liquid chromatography

ETHNOPHARMACOLOGICAL RELEVANCE

The need for an efficacious analgesic without unwanted side effects is urgent. κ-opioid receptor agonists are known to exhibit potent analgesic effects and elicited fewer side effects than other opioid agonists. Thus in this study we chose the κ-opioid receptor as the target to identify the active components from traditional Chinese medicines (TCMs).

MATERIALS AND METHODS

The κ-opioid receptor was expressed in human embryonic kidney-293 T cells (HEK293T). Fluorometric Imaging Plate Reader (FLIPR) assay was used for the determination of Ca(2+) response when κ-opioid receptor was activated. A novel 2D separation system employing C18HCE as the first dimension and a strong cation exchange column (SCX) as the second dimension was conducted for the purification of the active principles.

RESULTS

With the aid of HPLC-based activity profiling, activities could be linked to two peaks from Corydalis yanhusuo W. T. Wang (C. yanhusuo) extract. Two N-methyltetrahydroprotoberberines with κ-opioid receptor agonist activities were isolated for the first time from C. yanhusuo by using 2D-LC.

CONCLUSIONS

Our study suggests that N-methyltetrahydroprotoberberines may serve as a new scaffold for κ-opioid receptor ligands. The strategy that we adopted can be applied to other naturally-occurring active alkaloids acting at different receptors.

A novel analgesic isolated from a traditional Chinese medicine

BACKGROUND

Current pain management is limited, in particular, with regard to chronic pain. In an attempt to discover novel analgesics, we combined the approach developed to characterize traditional Chinese medicine (TCM), as part of the "herbalome" project, with the reverse pharmacology approach aimed at discovering new endogenous transmitters and hormones.

RESULTS

In a plant used for centuries for its analgesic properties, we identify a compound, dehydrocorybulbine (DHCB), that is effective at alleviating thermally induced acute pain. We synthesize DHCB and show that it displays moderate dopamine receptor antagonist activities. By using selective pharmacological compounds and dopamine receptor knockout (KO) mice, we show that DHCB antinociceptive effect is primarily due to its interaction with D2 receptors, at least at low doses. We further show that DHCB is effective against inflammatory pain and injury-induced neuropathic pain and furthermore causes no antinociceptive tolerance.

CONCLUSIONS

Our study casts DHCB as a different type of analgesic compound and as a promising lead in pain management.

Overloading study of basic compounds with a positively charged C18 column in liquid chromatography

While tailing and overloading of basic compounds remain problematic on most RP columns, a new kind of positively charged RP column named XCharge C18 was found to be superior good for the separation of alkaloids in our practical use. In this work, the surface charge property of the XCharge C18 column was evaluated by the retention of NO(3)(-) under different pH values and buffer concentrations. A considerable and pH-dependent positive charge was confirmed on the column. Then overloading behaviors of bases were systematically studied using amitriptyline as a basic probe. Good peak shapes (Tf<1.5) and extra high loadability with a C(0.5) of about 30,000 mg/L were observed on the column, with commonly used 0.1% formic acid as mobile phase additive. However, increasing the ionic strength of buffer with phosphates led to tailing peaks at high sample amount and sharp decline in loadability (C(0.5) of 2000-3000 mg/L), although it brought higher column efficiency at low sample amount. Higher pH also induced worse performance and lower loadability. The overall results demonstrated the importance of an appropriate level of ionic repulsion for the XCharge C18 column to achieve the good performance for bases, which could be explained by the multiple-site adsorption theory as ionic repulsion would shield the solute from occupying high-energy sites deeper in C18 layer.