Taxane Diterpenoids from the Root Bark of Taiwanese Yew Taxus Mairei

Nineteen compounds including taxumairol R (1) , taxinine M (2) , taxacin (3) , paclitaxel (4) , 10‐deacetyltaxol A (5) , 10‐deacetyl‐7‐epi‐taxol (6) , 7‐epi‐taxol (7) , taxol C, 10‐deacetyltaxol C, 7β‐xylosyl‐10‐deacetyltaxol (8) , taxamairin A (9) , taxinine A, 14β‐hydroxytaxusin (10) , 5α‐hydroxy‐7β,9α,10β, 13α‐tetraacetoxy‐4(20), 11‐taxadiene, 1‐dehydroxybaccatin‐VI, 1β‐dehydroxybaccatin‐IV, baccatin IV, baccatin VI and ponasterone A have been isolated and identified from the root bark of Taxus mairei. Among them, compound 1 was a new taxoid and compounds 11 and 7β‐xylosyl‐10‐deacetyltaxol pentaacetate were new derivatives prepared from 14β‐hydroxytaxusin (10) and 8 , respectively. Their structures and assignment were established on the basis of 2D‐NMR analysis and chemical methods.     

Facile Synthesis of 7‐epi‐Taxane and Its Derivatives and Preliminary Evaluation of Anticancer Activity

7‐epi‐Taxane has been achieved efficiently in gram scale from natural taxane via inversion of the 7‐hydroxyl group simply using Ag₂O as catalyst and DMF as solvent. The catalyst could be quantitatively recovered by filtration without loss of catalytic activity. This condition is also applicable to the direct epimerization of taxane derivatives (e.g., docetaxel and paclitaxel) to 7‐epi‐taxane derivatives (e.g., 7‐epi‐docetaxel and 7‐epi‐paclitaxel). Furthermore, 33 ester derivatives of 7‐epi‐taxane with different amino acid moieties at the position of C‐13 were successfully synthesized via esterification without protecting C‐7‐OH. Bioassay results revealed that compounds 13 and 18 have good selectivity against prostatic cancer cell line DU145, with IC₅₀ value as low as 15.9 nmol/L for 18 .     

Separation and purification of two taxanes and one xylosyl‐containing taxane from Taxus wallichiana Zucc.: A comparison between high‐speed countercurrent chromatography and reversed‐phase flash chromatography

10‐Deacetylbaccatin III, an important semisynthetic precursor of paclitaxel and docetaxel, can be extracted from Taxus wallichiana Zucc. A process for the isolation and purification of 10‐deacetylbaccatin III ( 1 ), baccatin III ( 2 ), and 7β‐xylosyl‐10‐deacetyltaxol ( 3 ) from the leaves and branches of Taxus wallichiana Zucc. via macroporous resin column chromatography combined with high‐speed countercurrent chromatography or reversed‐phase flash chromatography was developed in this study. After fractionation by macroporous resin column chromatography, 80% methanol fraction was selected based on high‐performance liquid chromatography and liquid chromatography with mass spectrometry qualitative analysis. A solvent system composed of n‐hexane, ethyl acetate, methanol, and water (1.6:2.5:1.6:2.5, v/v/v/v) was used for the high‐speed countercurrent chromatography separation at a flow rate of 2.5 mL/min. The reversed‐phase flash chromatography separation was performed using methanol/water as the mobile phase at a flow rate of 3 mL/min. The high‐speed countercurrent chromatography separation produced compounds 1 (10.2 mg, 94.4%), 2 (2.1 mg, 98.0%), and 3 (4.6 mg, 98.8%) from 100 mg of sample within 110 min, while the reversed‐phase flash chromatography separation purified compounds 1 (9.8 mg, 95.6%) and 3 (4.9 mg, 97.9%) from 100 mg of sample within 120 min.     

Preparative isolation of arylbutanoid‐type phenol [(‐)‐rhododendrin] with peak tailing on conventional C18 column using middle chromatogram isolated gel column coupled with reversed‐phase liquid chromatography

Reversed‐phase liquid chromatography coupled with middle chromatogram isolated gel column was employed for the efficient preparative separation of the arylbutanoid‐type phenol [(‐)‐rhododendrin] from Saxifraga tangutica. Universal C18 (XTerra C18) and XCharge C18 columns were compared for (‐)‐rhododendrin fraction analysis and preparation. Although tailing and overloading occurred on the XTerra C18 column, the positively charged reversed‐phase C18 column (XCharge C18) overcame these drawbacks, allowing for favorable separation resolution, even when loading at a on a preparative scale (3.69 mg per injection). The general separation process was as follows. First, 365.0 mg of crude (‐)‐rhododendrin was enriched from 165 g Saxifraga tangutica extract via a middle chromatogram isolated gel column. Second, separation was performed on an XTerra C18 preparative column, from which 73.8 mg of the target fraction was easily obtained. Finally, the 24.0 mg tailing peak of (‐)‐rhododendrin on XTerra C18 column was selectively purified on the XCharge C18 analytical column. These results demonstrate that the tailing nonalkaloid peaks can be effectively used for preparative isolation on XCharge C18 columns.     

Isocratic Separation of Dansylated Biogenic Amines on a C8‐Bonded Silica Column under the LC Elution of Methanol‐Based Mobile Phase

Under the elution of methanol‐based mobile phase, the isocratic resolution of 12 biogenic amines, including 1 aromatic, 2 heterocyclic and 9 aliphatic amines, as the dansylated derivatives has been accomplished in less than 25 minutes on a 15 cm C₈‐bonded column. The resolution can not be reproduced on other examined alkyl‐bonded phases (e.g., C₄ and C₁₈) under the same chromatographic conditions, or in the reversed‐phase mode. The retention, mainly as a result of hydrophobic interaction between analyte and stationary phase, can be adjusted by varying the percentage of methanol in the mobile phase. Also, incorporating acetic acid as additive to the mobile phase to protonate the analyte and silanol groups that are little shielding on the surface of silica gel reduces the dipole‐dipole interaction, and thus the retention scale, which in turn deteriorates the resolution. Furthermore, the elution reversal is plausible for some of analytes as a greater percent of acetic acid is used in the elution. Values of correlation coefficients (R²) range between 0.9995 and 0.9996, indicating good linearity.     

C18‐bound porous silica monolith particles as a low‐cost high‐performance liquid chromatography stationary phase with an excellent chromatographic performance

Ground porous silica monolith particles with an average particle size of 2.34 μm and large pores (363 Å) exhibiting excellent chromatographic performance have been synthesized on a relatively large scale by a sophisticated sol–gel procedure. The particle size distribution was rather broad, and the d(0.1)/d(0.9) ratio was 0.14. The resultant silica monolith particles were chemically modified with chlorodimethyloctadecylsilane and end‐capped with a mixture of hexamethyldisilazane and chlorotrimethylsilane. Very good separation efficiency (185 000/m) and chromatographic resolution were achieved when the C₁₈‐bound phase was evaluated for a test mixture of five benzene derivatives after packing in a stainless‐steel column (1.0 mm × 150 mm). The optimized elution conditions were found to be 70:30 v/v acetonitrile/water with 0.1% trifluoroacetic acid at a flow rate of 25 μL/min. The column was also evaluated for fast analysis at a flow rate of 100 μL/min, and all the five analytes were eluted within 3.5 min with reasonable efficiency (ca. 60 000/m) and resolution. The strategy of using particles with reduced particle size and large pores (363 Å) combined with C₁₈ modification in addition to partial‐monolithic architecture has resulted in a useful stationary phase (C₁₈‐bound silica monolith particles) of low production cost showing excellent chromatographic performance.     

Determination of a hydrophilic paclitaxel derivative, 7‐xylosyl‐10‐deacetylpaclitaxel in rat plasma by LC–MS/MS

A LC‐MS/MS method for the determination of a hydrophilic paclitaxel derivative 7‐xylosyl‐10‐deacetylpaclitaxel in rat plasma was developed to evaluate the pharmacokinetics of 7‐xylosyl‐10‐deacetylpaclitaxel in the rats. 7‐Xylosyl‐10‐deacetylpaclitaxel and docetaxel (IS for 7‐xylosyl‐10‐deacetylpaclitaxel) were extracted from rat plasma with acetic ether and analyzed on a Hypersil C₁₈ column (4.6 × 150 mm i.d., particle size 5 µm) with the mobile phase of ACN/0.05% formic acid (50:50, v/v). The analytes were detected using an ESI MS/MS in the multiple reaction monitoring mode. The standard curves for 7‐xylosyl‐10‐deacetylpaclitaxel in plasma were linear (r >0.999) over the concentration range of 2.0–1000 ng/mL with a weighting of 1/concentration². The method showed a satisfactory sensitivity (2.0 ng/mL using 50 µL plasma), precision (CV ≤ 10.1%), accuracy (relative error ?12.4 to 12.0%), and selectivity. This method was successfully applied to the pharmacokinetic study of 7‐xylosyl‐10‐deacetylpaclitaxel in rat plasma after intravenous administration of 7‐xylosyl‐10‐deacetylpaclitaxel to female Wistar rats. Copyright © 2008 John Wiley & Sons, Ltd.     

Imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide for the determination of m‐cresol in synthetic and real samples

m‐Cresol‐imprinted silica nanoparticles coated with N‐propylsilylmorpholine‐4‐carboxamide have been developed that contain specific pockets for the selective uptake of m‐cresol. Silica nanoparticles were synthesized by a sol–gel process followed by functionalization of their surface with N‐propylsilylmorpholine‐4‐carboxamide. The formation of m‐cresol‐imprinted silica nanoparticles was confirmed by UV‐Vis spectrophotometry, infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. Electron microscopic studies revealed the formation of monodispersed imprinted silica nanoparticles with spherical shape and an average size of 83 nm. The developed nanoparticles were filled in a syringe and used for the extraction of m‐cresol from aqueous samples followed by quantification using high‐performance liquid chromatography with diode array detection. Various adsorption experiments showed that developed m‐cresol‐imprinted silica nanoparticles exhibited a high adsorption capacity and selectivity and offered a fast kinetics for rebinding m‐cresol. The chromatographic quantification was achieved using mobile phase consisting of acetonitrile/water (70:30 v/v) at an isocratic flow rate of 1.0 mL/min using a reversed‐phase C₁₈ column and detection at λ_max = 275 nm. The limits of detection and quantification were 1.86 and 22.32 ng/mL, respectively, for the developed method. The percent recoveries ranged from 96.66–103.33% in the spiked samples. This combination of this nanotechnique with molecular imprinting was proved as a reliable, sensitive and selective method for determining the target from synthetic and real samples.     

Preparative separation and enrichment of four taxoids from Taxus chinensis needles extracts by macroporous resin column chromatography

An environment‐friendly method was established for the preparative separation and enrichment of four taxoids, namely 10‐deacetylbaccatin III (10‐DAB III), 7‐xylosyl‐10‐deacetyltaxol (7‐xyl‐10‐DAT), cephalomannine and paclitaxel from Taxus chinensis needles extracts. Characteristics of seven widely used macroporous resins for four taxoids were compared, AB‐8 resin offered better adsorption and desorption capacities than others. AB‐8 resin column chromatography was used to study the desorption process for four taxoids. The optimum parameters for desorption were 30% ethanol 5 RV for removing impurities, following 15 RV for 10‐DAB III, after the desorption of impurities with 35% ethanol 10 RV, 45% ethanol 30 RV for 7‐xyl‐10‐DAT, then 65% ethanol 10 RV for cephalomannine and paclitaxel, the flow rate was 6 RV/h. After separation on AB‐8 resin column chromatography, the contents of 10‐DAB III, 7‐xyl‐10‐DAT, cephalomannine and paclitaxel in the product reached 4.58, 13.17, 1.36 and 3.08%, respectively, which were 7.63‐, 3.68‐, 6.18‐ and 6.55‐fold to those in T. chinensis needles extracts. The recovery yields were 94.96, 77.32, 88.09 and 95.25%. In general, the AB‐8 resin column chromatography has the advantages of lower cost, high efficiency and simple procedure. Therefore, it may provide scientific references for the preparative separation and enrichment of taxoids from other T. species.     

固相合成甲胺基阿维菌素苯甲酸盐

To implement the solid phase synthesis of 4““-epi-methylamino-4““-deoxyavermecfin B1 benzoate, tert-butyldimethylsilylchloride was chosen for the first solution synthesis. Then a novel silyl chloride resin 1, achieved from hydroxymethyl polystyrene resin and dimethyldichlorosilane, was used successfully for the attachment of avermectin B1 2. Through oxidation, amination formation, cleavage, and benzoate formation, resin bounded avermectin B1 9 gave 4““-epi-methylamino-4““-deoxyavermectin B1 benzoate 3.     

A rapid and sensitive LC–MS/MS method for quantification of quercetin‐3‐O‐β‐d‐glucopyranosyl‐7‐O‐β‐d‐gentiobioside in plasma and its application to a pharmacokinetic study

A rapid and sensitive LC–MS/MS method with good accuracy and precision was developed and validated for the pharmacokinetic study of quercetin‐3‐O‐β‐d ‐glucopyranosyl‐7‐O‐β‐d ‐gentiobioside (QGG) in Sprague–Dawley rats. Plasma samples were simply precipitated by methanol and then analyzed by LC–MS/MS. A Venusil® ASB C₁₈ column (2.1 × 50 mm, i.d. 5 μm) was used for separation, with methanol–water (50:50, v/v) as the mobile phase at a flow rate of 300 μL/min. The optimized mass transition ion‐pairs (m/z) for quantitation were 787.3/301.3 for QGG, and 725.3/293.3 for internal standard. The linear range was 7.32–1830 ng/mL with an average correlation coefficient of 0.9992, and the limit of quantification was 7.32 ng/mL. The intra‐ and inter‐day precision and accuracy were less than ±15%. At low, medium and high quality control concentrations, the recovery and matrix effect of the analyte and IS were in the range of 89.06–92.43 and 88.58–97.62%, respectively. The method was applied for the pharmacokinetic study of QGG in Sprague–Dawley rats. Copyright © 2016 John Wiley & Sons, Ltd.     

Determination of docetaxel in rat plasma and its application in the comparative pharmacokinetics of Taxotere and SID530, a novel docetaxel formulation with hydroxypropyl‐β‐cyclodextrin

In this study, a sensitive, simple and reliable method for the quantification of docetaxel in rat plasma was developed and validated using liquid chromatography–tandem mass spectrometry (LC‐MS/MS). The plasma samples were prepared by protein precipitation, and paclitaxel was used as an internal standard (IS). Chromatographic separation was achieved using a Gemini C₁₈ column (2.0 × 150 mm, 5 µm) with a mobile phase consisting of 0.1% formic acid–acetonitrile (30:70, v/v). The precursor–product ion pairs used for multiple reaction monitoring were m/z 808.5 → 527.5 (docetaxel) and m/z 854.2 → 286.5 (IS, paclitaxel). A calibration curve for docetaxel was constructed over the range 1–1000 ng/mL. The developed method was specific, precise and accurate, and no matrix effect was observed. The validated method was applied in a comparative pharmacokinetic study in which two docetaxel formulations, SID530, a new parenteral formulation of docetaxel with hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD), and Taxotere, were administered to rats at a dose of 5 mg/kg. For SID530 and Taxotere, the mean C₀ values were 1494 and 1818 ng/mL, respectively, and the AUC_last values were 837 and 755 h ng/mL, respectively. These two formulations did not show any statistical differences with regard to the pharmacokinetic parameters, thus establishing that the SID530 and Taxotere products are pharmacokinetically comparable in male rats. Copyright © 2012 John Wiley & Sons, Ltd.     

Rapid preparative isolation of erythrocentaurin from Enicostemma littorale by medium‐pressure liquid chromatography,its estimation by high‐pressure thin‐layer chromatography,and its α‐amylase inhibitory activity

Erythrocentaurin is a relatively simple natural product present among the members of Gentianaceae. A preparative method for the isolation of erythrocentaurin from the ethyl acetate fraction of Enicostemma littorale using medium‐pressure liquid chromatography has been reported. The method consisted of a simple step gradient from 10 to 20% ethyl acetate in n‐hexane. Using a 70 × 460 mm Si60 column, this method is capable of processing 20 g of material in <3 h (purity ≈ 97%). The recovery of erythrocentaurin was 87.77%. Estimation of erythrocentaurin in extracts and fractions based on high‐pressure thin‐layer chromatography was carried out on silica gel 60 F₂₅₄ plates with toluene/ethyl acetate/formic acid (80:18:2 v/v/v) as the mobile phase. The densitometric analysis was performed at 230 nm. A well‐separated compact band of erythrocentaurin appeared at R_f 0.54 ± 0.04. The analytical method showed good linearity in the concentration range of 200–1500 ng/band with a correlation coefficient of 0.99417. The limits of detection and quantification were found to be ≈60 and ≈180 ng/band, respectively. Erythrocentaurin exhibited a concentration‐dependent α‐amylase inhibition (IC₅₀ 1.67 ± 0.28 mg/mL). The outcome of the study should be considered for pharmacokinetic and biotransformation studies involving E. littorale.     

Preparative isolation of flavonoid compounds from Oroxylum indicum by high‐speed counter‐current chromatography by using ionic liquids as the modifier of two‐phase solvent system

A preparative high‐speed counter‐current chromatography method for isolation and purification of flavonoid compounds from Oroxylum indicum was successfully established by using ionic liquids as the modifier of the two‐phase solvent system. Two flavonoid compounds including baicalein‐7‐O‐diglucoside and baicalein‐7‐O‐glucoside were purified from the crude extract of O. indicum by using ethyl acetate–water–[C₄mim][PF₆] (5:5:0.2, v/v) as two‐phase solvent system. 36.4 mg of baicalein‐7‐O‐diglucoside and 60.5 mg of baicalein‐7‐O‐glucoside were obtained from 120 mg of the crude extract. Their purities were 98.7 and 99.1%, respectively, as determined by HPLC area normalization method. The chemical structures of the isolated compounds were identified by ¹H‐NMR and ¹³C‐NMR.     

Evaluation of an amide‐based stationary phase for supercritical fluid chromatography

A relatively new stationary phase containing a polar group embedded in a hydrophobic backbone (i.e., ACE ® C18‐amide) was evaluated for use in supercritical fluid chromatography. The amide‐based column was compared with columns packed with bare silica, C₁₈ silica, and a terminal‐amide silica phase. The system was held at supercritical pressure and temperature with a mobile phase composition of CO₂ and methanol as cosolvent. The linear solvation energy relationship model was used to evaluate the behavior of these stationary phases, relating the retention factor of selected probes to specific chromatographic interactions. A five‐component test mixture, consisting of a group of drug‐like molecules was separated isocratically. The results show that the C₁₈‐amide stationary phase provided a combination of interactions contributing to the retention of the probe compounds. The hydrophobic interactions are favorable; however, the electron donating ability of the embedded amide group shows a large positive interaction. Under the chromatographic conditions used, the C₁₈‐amide column was able to provide baseline resolution of all the drug‐like probe compounds in a text mixture, while the other columns tested did not.     

Liquid chromatographic enantioseparation of (RS)‐etodolac using (S)‐levofloxacin and determination of absolute configuration of the diastereomeric derivatives

(RS)‐Etodolac was isolated from commercial tablets and was purified and characterized to be used as racemic standard. A pair of diastereomeric derivatives was synthesized using (S)‐levofloxacin as a chiral derivatizing reagent. The derivatization reaction was carried out under conditions of stirring at room temperature (30°C for 1.5 h) as well as under microwave irradiation; the derivatives obtained by the two methods were compared. Reaction conditions for derivatization were optimized with respect to mole ratio of chiral derivatizing reagent and (RS)‐etodolac. No racemization was observed throughout the study. Separation of diastereomeric derivatives was successful using C₁₈ column and a binary mixture of methanol and triethyl ammonium phosphate buffer of pH 4.5 (80:20, v/v) as mobile phase at a flow rate of 1 mL min^?1 and UV detection at 223 nm. An efficient approach for recognizing chirality and determining the absolute configuration of the diastereomeric derivatives of (RS)‐etodolac is described, which in turn is a measure of the enantiomeric purity of (RS)‐etodolac since the diastereomeric derivatives were separated and isolated using preparative thin‐layer chromatography.     

An LC–MS/MS method for simultaneous determination of 1,5‐dicaffeoylquinic acid and 1‐O‐acetylbritannilactone in rat plasma and its application to a pharmacokinetic study

A selective and sensitive liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was developed for the simultaneous quantitative determination of 1,5‐dicaffeoylquinic acid (1,5‐DCQA) and 1‐O‐ acetylbritannilactone (1‐O‐ ABL) in rat plasma. Chromatographic separation was performed on a Zorbax Eclipse XDB‐C₁₈ column using isocratic mobile phase consisting of methanol–water–formic acid (70:30:0.1, v /v/v) at a flow rate of 0.25 mL/min. The detection was achieved using a triple‐quadrupole tandem MS in selected reaction monitoring mode. The calibration curves of all analytes in plasma showed good linearity over the concentration ranges of 0.850–213 ng/mL for 1,5‐DCQA, and 0.520–130 ng/mL for 1‐O‐ ABL, respectively. The extraction recoveries were ≥78.5%, and the matrix effect ranged from 91.4 to 102.7% in all the plasma samples. The method was successfully applied for the pharmacokinetic study of the two active components in the collected plasma following oral administration of Inula britannica extract in rats.     

Separation of cannabinoids on three different mixed‐mode columns containing carbon/nanodiamond/amine‐polymer superficially porous particles

Three mixed‐mode high‐performance liquid chromatography columns packed with superficially porous carbon/nanodiamond/amine‐polymer particles were used to separate mixtures of cannabinoids. Columns evaluated included: (i) reversed phase (C₁₈), weak anion exchange, 4.6 × 33 mm, 3.6 μm, and 4.6 × 100 mm, 3.6 μm, (ii) reversed phase, strong anion exchange (quaternary amine), 4.6×33 mm, 3.6 μm, and (iii) hydrophilic interaction liquid chromatography, 4.6 × 150 mm, 3.6 μm. Different selectivities were achieved under various mobile phase and stationary phase conditions. Efficiencies and peak capacities were as high as 54 000 N/m and 56, respectively. The reversed phase mixed‐mode column (C₁₈) retained tetrahydrocannabinolic acid strongly under acidic conditions and weakly under basic conditions. Tetrahydrocannabinolic acid was retained strongly on the reversed phase, strong anion exchange mixed‐mode column under basic polar organic mobile phase conditions. The hydrophilic interaction liquid chromatography column retained polar cannabinoids better than the (more) neutral ones under basic conditions. A longer reversed phase (C₁₈) mixed‐mode column (4.6 × 100 mm) showed better resolution for analytes (and a contaminant) than a shorter column. Fast separations were achieved in less than 5 min and sometimes 2 min. A real world sample (bubble hash extract) was also analyzed by gradient elution.     

Resolution and isolation of enantiomers of (±)‐isoxsuprine using thin silica gel layers impregnated with l‐glutamic acid,comparison of separation of its diastereomers prepared with chiral derivatizing reagents having l‐amino acids as chiral auxiliaries

Thin silica gel layers impregnated with optically pure l ‐glutamic acid were used for direct resolution of enantiomers of (±)‐isoxsuprine in their native form. Three chiral derivatizing reagents, based on DFDNB moiety, were synthesized having l ‐alanine, l ‐valine and S‐benzyl‐l ‐cysteine as chiral auxiliaries. These were used to prepare diastereomers under microwave irradiation and conventional heating. The diastereomers were separated by reversed‐phase high‐performance liquid chromatography on a C₁₈ column with detection at 340 nm using gradient elution with mobile phase containing aqueous trifluoroacetic acid and acetonitrile in different compositions and by thin‐layer chromatography (TLC) on reversed phase (RP) C₁₈ plates. Diastereomers prepared with enantiomerically pure (+)‐isoxsuprine were used as standards for the determination of the elution order of diastereomers of (±)‐isoxsuprine. The elution order in the experimental study of RP‐TLC and RP‐HPLC supported the developed optimized structures of diastereomers based on density functional theory. The limit of detection was 0.1–0.09 µg/mL in TLC while it was in the range of 22–23 pg/mL in HPLC and 11–13 ng/mL in RP‐TLC for each enantiomer. The conditions of derivatization and chromatographic separation were optimized. The method was validated for accuracy, precision, limit of detection and limit of quantification. Copyright © 2014 John Wiley & Sons, Ltd.     

Comprehensive two‐dimensional monolithic liquid chromatography of polar compounds

Two‐dimensional liquid chromatography largely increases the number of separated compounds in a single run, theoretically up to the product of the peaks separated in each dimension on the columns with different selectivities. On‐line coupling of a reversed‐phase column with an aqueous normal‐phase (hydrophilic interaction liquid chromatography) column yields orthogonal systems with high peak capacities. Fast on‐line two‐dimensional liquid chromatography needs a capillary or micro‐bore column providing low‐volume effluent fractions transferred to a short efficient second‐dimension column for separation at a high mobile phase flow rate. We prepared polymethacrylate zwitterionic monolithic micro‐columns in fused silica capillaries with structurally different dimethacrylate cross‐linkers. The columns provide dual retention mechanism (hydrophilic interaction and reversed‐phase). Setting the mobile phase composition allows adjusting the separation selectivity for various polar substance classes. Coupling on‐line an organic polymer monolithic capillary column in the first dimension with a short silica‐based monolithic column in the second dimension provides two‐dimensional liquid chromatography systems with high peak capacities. The silica monolithic C₁₈ columns provide higher separation efficiency than the particle‐packed columns at the flow rates as high as 5 mL/min used in the second dimension. Decreasing the diameter of the silica monolithic columns allows using a higher flow rate at the maximum operation pressure and lower fraction volumes transferred from the first, hydrophilic interaction dimension, into the second, reversed‐phase mode, avoiding the mobile phase compatibility issues, improving the resolution, increasing the peak capacity, and the peak production rate.