•A newly designed steviol glycoside modified-silica stationary phase-Click TE-RA.•Thiol-ene click chemistry strategy was employed for immobilization of rebaudioside A.•Click TE-RA with special structure could be used both in HILIC and HILIC/RPLC mixed-modes.•Click TE-RA showed excellent selectivity and efficient retention for polar compounds in HILIC.A diterpene glycoside compound, rebaudioside A (commonly abbreviated as RA), was immobilized onto porous silica surface through “thiol-ene” click chemistry strategy. The successful immobilization of the RA on the silica support was confirmed by FT-IR and elemental analysis. Chromatographic characteristics of the new stationary phase, named Click TE-RA, were evaluated by a set of diverse analytes such as carbohydrates, nucleosides, and organic acids in hydrophilic interaction liquid chromatography (HILIC) mode. The effects of water content, buffer pH and concentration were investigated and a typical HILIC retention feature of Click TE-RA was observed at high organic modifier content. The Click TE-RA stationary phase was further studied by a series of glycoside compounds. Tunable retention mechanisms from hydrophilic to hydrophobic interactions were observed. Separation of very polar compounds including oligosaccharides, nucleic acid bases and nucleosides using Click TE-RA in HILIC mode was successfully accomplished. In addition, separation of saponins both in HILIC and reversed-phase liquid chromatography (RPLC) modes was performed, demonstrating the presence of orthogonality between two different modes on Click TE-RA column. The multiple interactions induced by polar sugar group and hydrophobic aglycone group allowed this Click TE-RA to serve as a multi-mode stationary phase in two-dimensional liquid chromatography.

•Comprehensive qualitative and quantitative analysis of an alkaloid fraction purified from Piper longum L.•18 standard compounds and 25 minor amide alkaloids were identified.•A method based on relative response factor was used for quantitative analysis.•The quality of alkaloid fraction was efficiently improved after appropriate purification.In a previous research, an alkaloid fraction and 18 alkaloid compounds were prepared from Piper longum L. by series of purification process. In this paper, a qualitative and quantitative analysis method using ultra-high performance liquid chromatography-diode array detector–mass spectrometry (UHPLC-DAD–MS) was developed to evaluate the alkaloid fraction. Qualitative analysis of the alkaloid fraction was firstly completed by UHPLC-DAD method and 18 amide alkaloid compounds were identified. A further qualitative analysis of the alkaloid fraction was accomplished by UHPLC–MS/MS method. Another 25 amide alkaloids were identified according to their characteristic ions and neutral losses. At last, a quantitative method for the alkaloid fraction was established using four marker compounds including piperine, pipernonatine, guineensine and N-isobutyl-2E,4E-octadecadienamide. After the validation of this method, the contents of above four marker compounds in the alkaloid fraction were 57.5 mg/g, 65.6 mg/g, 17.7 mg/g and 23.9 mg/g, respectively. Moreover, the relative response factors of other three compounds to piperine were calculated. A comparative study between external standard quantification and relative response factor quantification proved no remarkable difference. UHPLC-DAD–MS method was demonstrated to be a powerful tool for the characterization of the alkaloid fraction from P. longum L. and the result proved that the quality of alkaloid fraction was efficiently improved after appropriate purification.

In this study, an off-line two-dimensional (2-D) supercritical fluid chromatography (SFC) × ultra-high performance liquid chromatography (UHPLC) method with high orthogonality was developed for the analysis of the practical amide alkaloids fraction from P. longum L. The effects of SFC parameters such as column type, organic modifier, temperature and back-pressure on separation were systematically evaluated. Different selectivity was observed for different columns (BEH, BEH 2-EP, XAmide and CSH FP). An investigation was then carried out of the orthogonality of different columns and systems following a geometric approach with a set of amide alkaloid samples. The orthogonality between a CSH FP column and a BEH column reached 50.79%, which was much higher than that for the other columns. While the orthogonality between SFC and UHPLC based on an XAmide column and an HSS T3 column reached 69.84%, which was the highest of all the combinations. At last, the practical amide alkaloids fraction was analyzed with an off-line 2-D chromatography SFC × UHPLC system. In total, at least 340 peaks were detected by this method. Rapid separation in these two dimensions and easy post treatment of SFC facilitated this 2-D system for the separation of complex samples.

Based on chiral N-(1-phenylethyl) glycines, a series of peptoid chiral stationary phases (CSPs) terminated with achiral alkyl group (diisopropyl, t-butyl or n-butyl) and varied in absolute configuration of selector were investigated with nine axially chiral analytes. It is very interesting to observe that selectors with heterogeneous configuration form, such as S-R-R, S-R-S, S-S-R, generally performed better than S-S-S selectors. Moreover, longer S-R-S-R-S selector did not outperform the S-R-S one obviously, with several separations declined. In addition to the result that the elution order of most enantiomers depends on the asymmetric center adjacent to the terminus of selector, we presume that the moieties around this chiral center are the most important absorbing sites for chiral discrimination; the terminal group and other chiral blocks in selector may assist enantiorecognition by constructing appropriate conformation. Various terminal alkyl groups also resulted in a few differences in enantioselectivity.Highlights► Peptoid CSPs varied in absolute configuration were investigated. ► Homogeneous chiral sides in peptoid selector were proved unnecessary. ► CSP with heterogeneous configuration form exhibited specific selectivity. ► The chiral residue next to the terminus was important for chiral recognition. ► Longer peptoid chain was not an essential condition for enantiorecognition.

•Stereomeric peptoid CSPs containing different chiral units were investigated.•Configuration of CSP affects enantiorecognition abilities significantly.•CSP with mixed selectors combines certain selectivities of individual CSPs.•Elution orders on these CSPs help to attribute effective interaction sites.•Excellent separation of VANOL implies the potential preparative application.In this study, we investigated six stereomeric peptoid chiral stationary phases (CSPs) successively combining N′-phenyl-proline amide, α-phenylethyl amine, 2-aminocyclohexyl phenylcarbamate and another α-phenylethyl amine under normal phase mode. CSPs 1–4 with R-S-(R,R)-S, R-S-(S,S)-S, R-R-(R,R)-R and R-R-(S,S)-R configuration exhibited much different enantiorecognition abilities. Overall, CSPs 1 and 2 performed better for the 55 analytes tested. CSP 5 with mixed selectors combined partial selectivities of CSPs 1 and 2. CSP 6 as enantiomeric counterpart of CSP 2 exhibited similar enantioseparation ability and reversal elution orders for analytes resolved. For several biaryl type analytes, CSP 6 even outperformed commercial Chiralpak AD-H and Chiralcel OD-H. Excellent resolution of 3,3′-diphenyl-2,2′-bi-1-naphthalol (VANOL) on CSP 6 illustrated its potential application in preparative enantioseparation. Eluting orders of enantiomers on stereomeric CSPs also provided us further insight into enantiorecognition of some analytes.

A comprehensive off-line two-dimensional liquid chromatography (2D-LC) method coupling normal phase liquid chromatography (NPLC) and reversed phase liquid chromatography (RPLC) was developed for separation and purification of amide alkaloids from Piper longum L. In the first dimension, the crude alkaloid fractions were separated in NPLC mode and 20 fractions were collected. Then fractions 5–20 were selected for further purification in RPLC mode in the second dimension. The purities of RPLC fractions with similar structures were all identified accurately by ultra performance liquid chromatography (UPLC). In total, 28 compounds with high purity were obtained and their structures were comprehensively characterized by electrospray ionization-mass spectrometry (ESI-MS) and nuclear magnetic resonance (NMR) spectroscopy. The results demonstrate that this 2D NPLC × RPLC method with good orthogonality (58.3%) was effective for the preparative separation and purification of amide alkaloids from Piper longum L.

Highlights•Carbohydrate separation using HILIC was systematically evaluated.•Column temperature, selectivity and surface charge property played critical roles.•Complementary selectivity among different columns was beneficial to separation.•Buffer salt with proper pH and concentration was necessary to ionic carbohydrates.•A guidance for analysts during method development for carbohydrates’ separation.A strategy was developed to rapidly evaluate chromatographic properties of hydrophilic interaction chromatography (HILIC) columns for separating carbohydrates. Seven HILIC columns (Silica, Diol, TSK Amide-80, XAmide, Click Maltose, Click β-CD, and Click TE-Cys columns) were evaluated by using three monosaccharide and seven disaccharides as probes. The influence of column temperature on the peak shape and tautomerization of carbohydrates, as well as column selectivity were investigated. The influence of surface charge property on the retention was also studied by using glucose, glucuronic acid, and glucosamine, which indicated that buffer salt concentration and pH value in mobile phase was necessary to control the ionic interactions between ionic carbohydrates and HILIC columns. According to evaluation results, the XAmide column was selected as an example to establish experimental schemes for separation of complex mixtures of oligosaccharide.Graphical abstractA strategy was developed to rapidly evaluate chromatographic properties of hydrophilic interaction chromatography (HILIC) columns for separation of carbohydrates by using three monosaccharide and seven disaccharides as probes.

Two-dimensional liquid chromatography (2-D LC) has been widely used for the analysis of complex samples owing to its great improvement in separation selectivity and peak capacity. However, one 2-D LC system may not be enough to meet the separation requirements due to the complexity of certain samples and respective limitations of two separation modes. In this work, water extract of Scutellaria barbata D. Don, a traditional Chinese medicine, was fractionated into polar fraction and medium-polar fraction by means of solid phase extraction (SPE). The fraction preparation made it easy to select the corresponding combination of 2-D LC method from hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RP-LC). An off-line 2-D HILIC × HILIC to analyze the polar fraction and an off-line 2-D HILIC × RP-LC to analyze the medium-polar fraction were developed, respectively. In total, 749 peaks were detected: 206 peaks from the polar fraction by the 2-D HILIC × HILIC and 543 from the medium-polar fraction by the 2-D HILIC × RP-LC. The practical peak capacities obtained in both systems were 2698 and 2879, and the orthogonality reached 63.18% and 90.62%, respectively. The results demonstrated that the two systems were both highly orthogonal, and the peak capacities greatly increased.Highlights► Different 2D-LC modes were combined for the analysis of Scutellaria barbata D. Don. ► 206 peaks were detected in polar fraction by 2-D HILIC × HILIC. ► 543 peaks were detected in medium-polar fraction by 2-D HILIC × RP-LC.

The role of a terminal group of a peptoid selector in a chiral separation was investigated. Six chiral stationary phases (CSPs) with the terminal groups replaced by achiral alkyl groups (n-butyl, t-butyl and diisopropyl) and chiral groups ((1R, 2R)-2-aminocyclohexyl phenylcarbamate, N’-phenyl-L-proline amide and N’-phenyl-L-leucine amide) were synthesized. Achiral terminal groups with different steric hindrances did not broaden the enantioselectivity, but improved the separation factors for some analytes, probably due to the improvement of interactions between the analytes and peptoid chain. Introducing new chiral terminal groups proved an effective way to broaden the applicable spectrum of peptoid CSPs.Highlights► Preparation of new peptoid CSPs with achiral or chiral terminal groups. ► Improvement of enantioseparation by altering achiral terminal groups. ► Extending applicable spectrum by introducing new terminal chiral blocks.

A comprehensive off-line two-dimensional liquid chromatography (2D-LC) method coupling hydrophilic interaction liquid chromatography (HILIC) and reversed phase liquid chromatography (RPLC) was developed in this study to detect as many saponins as possible in extracts of Panax notoginseng. The orthogonality of the 2D HILIC × RPLC was up to 81%, and the peak capacity was 10200. In total, 224 saponins were found, and some of them were trace amounts. Besides, a screening table designed by adding molecular weights of possible aglycones and sugars was constructed to help rapidly characterize the saponins using MS information. Unfortunately, the structure of saponins could not be identified by using only MS information.

It is a new task to separate structure-related compounds into a fraction according to their structural characteristics in a complex traditional Chinese medicine (TCM). This method makes separation of the components of the sample simple and structural elucidation easy. In this study, selective separation of alkaloids in Rhizoma coptidis was realized on a “click” binaphthyl column possessing a planar conjugate structure. Three kinds of alkaloids, aporphine, tetrahydroprotoberberine and protoberberine in Rhizoma coptidis showed better retention than other compounds by virtue of π–π interactions with the stationary phase. Moreover, the “click” binaphthyl column could distinguish the aporphine and tetrahydroprotoberberine alkaloids possessing two benzene rings from the protoberberine alkaloids possessing three benzene rings. After separating on the “click” binaphthyl column, the fractions containing the alkaloids were collected and then analyzed with liquid chromatography-mass spectrometry (LC-MS). Totally, 23 alkaloids were identified, and among these alkaloids, three tetrahydroprotoberberine, two aporphine and seven protoberberine alkaloids were first found in Rhizoma coptidis. These newly found alkaloids are minor compounds, and they are always neglected without eliminating the interference of compounds in large amounts by pre-separation on the “click” binaphthyl column. The typical fragmentation pathways of each class of alkaloids were summarized to illustrate their structures. In the MS2 spectrum, the loss of a molecule of dimethylamine ((CH3)2NH) was observed as the characteristic loss of aporphine alkaloids. All the tetrahydroprotoberberine alkaloids would undergo the Retro-Diels–Alder (RDA) fragmentation reaction in the MS2 fragmentation. For protoberberine alkaloids, different characteristic fragmentations were observed with different skeleton structures.

Enantioselective organocatalytic phospha-Michael reaction of α,β-unsaturated ketones and diaryl phosphine oxides has been developed for the first time employing multifunctional organocatalysts. Optically active products bearing quaternary chiral carbon stereocenters were obtained in high yields with good to excellent enantioselectivities (up to 98% ee).

A general and direct organocatalytic asymmetric vinylogous Michael reaction of γ-butenolide with α,β-unsaturated ketones was investigated with a multifunctional primary amine salt as catalyst. The reaction enables straightforward access toward synthetically versatile γ-substituted butenolides from simple 2(5H)-furanone with satisfactory yields, diastereo- and enantioselectivities (up to 30:1 dr and 95–99% ee).

An unprecedented enantioselective Michael addition of various ketones to maleimides catalyzed by a simple bifunctional primary amine, monosulfonyl DPEN salt, is reported and provides the desired adducts in good to excellent yields (up to 99%) with excellent enantioselectivities (up to 99%).

The first highly efficient Michael addition of challenging α,α-disubstituted aldehydes to maleimides catalyzed by a simple bifunctional primary amine thiourea catalyst/benzoic acid system has been successfully developed to generate quaternary carbon centers in high yields (up to 99%) with excellent enantioselectivities (91–99%).

Catalyzed by the bifunctional tertiary amino–thiourea organocatalyst derived from epicinchona alkaloid, the asymmetric Michael addition of anthrone to enone was achieved in high yield with excellent enantioselectivity.

Monodisperse phenylene-bridged organosilica spheres show great potential as chromatographic stationary phase. In this paper, the tunable particle size of monodisperse phenylene-bridged organosilica spheres were prepared by co-condensing different proportion of 1,4-bis(triethoxysilyl)benzene (1,4-BTEB) and tetraethylorthosilicate (TEOS), and then pore size was expanded by two-step post-synthesis hydrothermal treatments using N,N-dimethyldecylamine (DMDA)/dodecylamine (DDA) and tris-(hydroxymethyl)-aminomethane (TRIS) in turn. Phenylene-bridged organosilica spheres with particle size of 3.0–3.5 μm and pore size of 85 Å were further surface modified by C18 group and tested in reversed-phase high performance liquid chromatography (RP-HPLC). The primary chromatographic results demonstrated that C18 bonded phenylene-bridged organosilica stationary phase has high retention and good chemical stability in the high pH mobile phase, which indicated that the phenylene-bridged organosilica can be used for HPLC packing supports.

A novel chitooligosaccharide stationary phase for hydrophilic interaction liquid chromatography (HILIC) was developed via click chemistry and showed great HILIC characteristics on separation of polar compounds and enrichment of glycopeptides.

The first highly efficient Michael addition of challenging α,α-disubstituted aldehydes to maleimides catalyzed by a simple bifunctional primary amine thiourea catalyst/benzoic acid system has been successfully developed to generate quaternary carbon centers in high yields (up to 99%) with excellent enantioselectivities (91–99%).

Enantioselective organocatalytic phospha-Michael reaction of α,β-unsaturated ketones and diaryl phosphine oxides has been developed for the first time employing multifunctional organocatalysts. Optically active products bearing quaternary chiral carbon stereocenters were obtained in high yields with good to excellent enantioselectivities (up to 98% ee).

A general and direct organocatalytic asymmetric vinylogous Michael reaction of γ-butenolide with α,β-unsaturated ketones was investigated with a multifunctional primary amine salt as catalyst. The reaction enables straightforward access toward synthetically versatile γ-substituted butenolides from simple 2(5H)-furanone with satisfactory yields, diastereo- and enantioselectivities (up to 30:1 dr and 95–99% ee).

A novel chitooligosaccharide stationary phase for hydrophilic interaction liquid chromatography (HILIC) was developed via click chemistry and showed great HILIC characteristics on separation of polar compounds and enrichment of glycopeptides.

Catalyzed by the bifunctional tertiary amino–thiourea organocatalyst derived from epicinchona alkaloid, the asymmetric Michael addition of anthrone to enone was achieved in high yield with excellent enantioselectivity.

An unprecedented enantioselective Michael addition of various ketones to maleimides catalyzed by a simple bifunctional primary amine, monosulfonyl DPEN salt, is reported and provides the desired adducts in good to excellent yields (up to 99%) with excellent enantioselectivities (up to 99%).