Supercritical Fluid Chromatography--Theoretical Background and Applications on Natural Products

Simultaneously characterization of multiple constituents in Valeriana jatamansi Jones using an online supercritical fluid extraction-high-performance liquid chromatography/supercritical fluid chromatography-mass spectrometry system

Valeriana jatamansi Jones is a commonly used traditional Chinese medicine, boasting rich effective compositions with versatile chemical structures and wide polarity, including iridoids, chlorogenic acid, and flavonoids. Previous reports indicate that conventional high-performance liquid chromatography (HPLC) analytical methods have proven inefficient performance in comprehensively characterizing components in Valeriana jatamansi. In the present study, a hybrid online analytical platform combining supercritical fluid extraction with both conventional HPLC separation (reverse phase) and supercritical fluid chromatography (normal phase) has been established and validated. This system can provide online extraction with two different chromatographic separation modes to increase separation ability and has been connected to a mass spectrometer to acquire high-resolution mass spectrometry data. Then, the online platform was applied to screening components in Valeriana jatamansi. A total of 117 compounds were identified, including five lignans, 18 organic acids, six flavonoids, and 88 iridoids. Thirty-three compounds were reported from Valeriana jatamansi for the first time. These results enrich our understanding of the components of Valeriana jatamansi and prove that the developed online platform in this study is a robust approach for accelerating working efficiency in comprehensively analyzing complicated samples.

1H NMR-Based Biochemometric Analysis of Morus alba Extracts toward a Multipotent Herbal Anti-Infective

Mulberry Diels-Alder-type adducts (MDAAs) derived from the white mulberry tree were discovered recently as dual inhibitors of influenza viruses and pneumococci. For the development of a natural product based remedy for respiratory infections, the aim was to (i) identify the most prolific natural source of MDAAs, (ii) develop a protocol to maximize the content of MDAAs in Morus alba extracts, (iii) unravel constituents with the highest anti-infective potential within multicomponent mixtures, and (iv) select and characterize a hit extract as a candidate for further studies. Validated quantitative UPLC-PDA analysis of seven MDAAs (1-7) revealed the root bark as the best starting material and pressurized liquid extraction (PLE) as the optimum technique for extraction. Extracts enriched in MDAAs of a total content above 20% exerted a potent dual anti-influenza virus and antipneumococcal activity. For a detailed analysis of the most bioactive chemical features and molecules within the extracts, ¹H NMR-based heterocovariance analysis (HetCA) was used. According to the multivariate statistical analysis procedure conducted, MDAAs exclusively accounted for the in vitro anti-influenza viral effect. The anti-infective profile of one hit extract (MA60) investigated showed a good tolerance by lung cells (A549, Calu-3) and pronounced in vitro activities against influenza viruses, S. pneumoniae, S. aureus, and inflammation.

Quality evaluation of Panax notoginseng (Burk.) F.H. Chen using supercritical fluid chromatography-mass spectrometry and chemical pattern recognition

An efficient supercritical fluid chromatography-mass spectrometry (SFC-MS) method was developed for the quality evaluation of Panax Notoginseng (Burk) F.H. Chen (P. notoginseng) by combination with chemical pattern recognition (CPR). Design of experiments (DoE) was applied to obtain optimal SFC-MS conditions. Several CPR methods including hierarchical cluster analysis (HCA), principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were employed to establish a classification model based on the peak areas and contents of 12 components in P. notoginseng in order to evaluate the quality difference according to the collecting time (Chunqi and Dongqi) and medicinal parts (fibrous root, rhizome, branch root, and main root). PLS-DA has proved to be a satisfactory method with accurate discrimination of the selected samples. The characteristic variables based on the variable importance in projection (VIP) values were selected using PLS-DA. Three characteristic components (ginsenoside Rg₂, ginsenoside Rg₁, ginsenoside Rb₁) with higher VIP values (>1) were chosen to further build the CPR model. Subsequently, the model was verified by testing another set of samples and the results indicated that the established model was satisfactory. PLS-DA models based on the peak areas of the 12 selected analytes in 30 batches of P. notoginseng could give accurate classification. The obtained results demonstrate that the developed method using SFC-MS and PLS-DA has a great potential for the quality assessment of P. notoginseng.

A supercritical fluid workflow for the quality assessment of herbal drugs and commercial preparations from Rhodiola rosea

INTRODUCTION

Preparations from the Rhodiola rosea are experiencing an increase in popularity: extracts of dried roots and rhizomes are used as adaptogen to treat stress, fatigue, and weakness. To meet high pharmaceutical standards, fast and reliable methods to assess phytochemical variations in respect of quality control are needed.

OBJECTIVE

The aim of this study was to extract and quantify seven characteristic secondary metabolites of R. rosea, namely p-tyrosol (1), rosin (2), rosiridin (3), salidroside (4), rosarin (5), rosavin (6), and tricin-5-O-β-d-glucopyranoside (7) in 24 herbal drugs and seven commercial preparations using a newly established supercritical fluid workflow.

METHODS

The developed protocol allowed for an exhaustive extraction of compounds 1-7 using 60% carbon dioxide (CO₂ ) and 40% methanol. The constituents were analysed on an ultra-high-performance supercritical fluid chromatography (UHPSFC) instrument using a charged surface hybrid fluoro-phenyl (CSH FP) column (3.0 mm × 100 mm, 1.7 μm; mobile phase: CO₂ and methanol).

RESULTS

The seven compounds were separated in a remarkably short time (< 3.5 minutes). For their quantitation, good results in terms of selectivity, linearity (R²  ≥ 0.99), precision (intraday ≤ 3.03%, interday ≤ 5.17%) and accuracy (recovery rates 96.6-102.4%) were achieved using selected ion recording on a Quadrupole Dalton (QDa) mass detector.

CONCLUSION

The quantitative analysis of the investigated herbal drugs showed a highly differing metabolite pattern which was also observed in the investigated commercial products. None of the commercial dietary products met the declared content of rosavins and salidroside. The developed and validated protocol offers a novel and reliable method to assess the quantitative composition of Rhodiola herbal drugs and preparations.

Quantitative Analysis of Prenylated Constituents in Commercial Hops Samples Using Ultrahigh-Performance Supercritical Fluid Chromatography

The importance of hops (the flowers of Humulus lupulus) as food and an herbal remedy is reflected by a large number of analytical methods published. However, supercritical fluid chromatography, a highly efficient, rapid, and "green" separation technique, has not been considered for hops samples so far. This prompted us to establish the first supercritical fluid chromatography-based protocol for the separation, identification, and quantitation of five prenylated constituents of hops. Hulupinic acid ( 1: ), a prominent oxidation product of hop acids, three flavanones, i.e., 8-prenylnaringenin ( 2: ), 6-prenylnaringenin ( 3: ), and isoxanthohumol ( 4: ), as well as the chalcone xanthohumol ( 5: ) could be baseline separated in less than 5 minutes using a Viridis BEH 2-EP column (3.0 × 100 mm; 1.7 µm particle size) and a mobile phase consisting of CO₂ and isopropanol. Good results regarding selectivity, accuracy (recovery rates: 85.0 - 113.1%), precision (intra-day ≤ 2.1%, inter-day ≤ 3.5%), and linearity (R² ≥ 0.99) were obtained for both photodiode array and mass detection. The lowest detection limit at 220 nm was at 0.1 µg/mL ( 1, 3: , and 4: ), with mass detection even at 0.001 µg/mL ( 4: ). As an application example of the validated method, the five hops constituents were quantified in three dietary supplements, one herbal medicinal product, and two batches of hop flowers (Lupuli flos). In most samples analyzed, the major component was 5: (0.01 - 1.02%), whereas the major component in Lupuli flos samples was compound 1: (0.12 - 0.21%). This protocol offers a fast and environmentally friendly alternative to liquid chromatography for the quality control of hops.

Natural Products, Traditional Uses and Pharmacological Activities of the Genus Biebersteinia (Biebersteiniaceae)

Medicinal plants have been known as a rich source of natural products (NPs). Due to their diverse chemical structures and remarkable pharmacological activities, NPs are regarded as important repertoires for drug discovery and development. Biebersteinia plant species belong to the Biebersteiniaceae family, and have been used in folk medicines in China and Iran for ages. However, the chemical properties, bioactivities and modes of action of the NPs produced by medicinal Biebersteinia species are poorly understood despite the fact that there are only four known Biebersteinia species worldwide. Here, we reviewed the chemical classifications and diversity of the various NPs found in the four known Biebersteinia species. We found that the major chemical categories in these plants include flavonoids, alkaloids, phenylpropanoids, terpenoids, essential oils and fatty acids. We also discussed the anti-inflammatory, analgesic, antibacterial, antioxidant, antihypertensive and hypoglycemic effects of the four Biebersteinia species. We believe that the present review will facilitate the exploration of traditional uses and pharmacological properties of Biebersteinia species, extraction of the NPs and elucidation of their molecular mechanisms, as well as the development of novel drugs based on the reported properties and mode-of-action.

Signal enhancement in supercritical fluid chromatography-diode-array detection with multiple injection

To circumvent the detrimental effects of large‐volume injection with fixed‐loop injector in modern supercritical fluid chromatography, the feasibility of performing multiple injection was investigated. By accumulating analytes from a certain number of continual small‐volume injections, compounds can be concentrated on the column head, and this leads to signal enhancement compared with a single injection. The signal to noise enhancement of different compounds appeared to be associated with their retention on different stationary phases and with type of sample diluent. The diethylamine column gave the best signal to noise enhancement when acetonitrile was used as sample diluent and the 2‐picolylamine column showed the best overall performance with water as the sample diluent. The advantage of multiple injection over one‐time large‐volume injection was proven with sulfanilamide, with both acetonitrile and water as sample diluents. The multiple injection approach exhibited comparable within‐ and between‐day precision of retention time and peak area with those of single injections. The potential of the multiple injection approach was demonstrated in the analysis of sulfanilamide‐spiked honey extract and diclofenac‐spiked ground water sample. The limitations of this approach were also discussed.

Quantitative determination of major alkaloids in Cinchona bark by Supercritical Fluid Chromatography

Chinoline alkaloids found in Cinchona bark still play an important role in medicine, for example as antimalarial and antiarrhythmic drugs. For the first time Supercritical Fluid Chromatography has been utilized for their separation. Six respective derivatives (dihydroquinidine, dihydroquinine, quinidine, quinine, cinchonine and cinchonidine) could be resolved in less than 7 min, and three of them quantified in crude plant extracts. The optimum stationary phase showed to be an Acquity UPC² Torus DEA 1.7 μm column, the mobile phase comprised of CO₂, acetonitrile, methanol and diethylamine. Method validation confirmed that the procedure is selective, accurate (recovery rates from 97.2% to 103.7%), precise (intra-day ≤2.2%, inter-day ≤3.0%) and linear (R² ≥ 0.999); at 275 nm the observed detection limits were always below 2.5 μg/ml. In all of the samples analyzed cinchonine dominated (1.87%-2.30%), followed by quinine and cinchonidine. Their total content ranged from 4.75% to 5.20%. These values are in good agreement with published data, so that due to unmatched speed and environmental friendly character SFC is definitely an excellent alternative for the analysis of these important natural products.

Techniques for extraction and isolation of natural products: a comprehensive review

Natural medicines were the only option for the prevention and treatment of human diseases for thousands of years. Natural products are important sources for drug development. The amounts of bioactive natural products in natural medicines are always fairly low. Today, it is very crucial to develop effective and selective methods for the extraction and isolation of those bioactive natural products. This paper intends to provide a comprehensive view of a variety of methods used in the extraction and isolation of natural products. This paper also presents the advantage, disadvantage and practical examples of conventional and modern techniques involved in natural products research.

Environmentally Friendly Procedure Based on Supercritical Fluid Chromatography and Tandem Mass Spectrometry Molecular Networking for the Discovery of Potent Antiviral Compounds from Euphorbia semiperfoliata

A supercritical fluid chromatography-based targeted purification procedure using tandem mass spectrometry and molecular networking was developed to analyze, annotate, and isolate secondary metabolites from complex plant extract mixture. This approach was applied for the targeted isolation of new antiviral diterpene esters from Euphorbia semiperfoliata whole plant extract. The analysis of bioactive fractions revealed that unknown diterpene esters, including jatrophane esters and phorbol esters, were present in the samples. The purification procedure using semipreparative supercritical fluid chromatography led to the isolation and identification of two new jatrophane esters (13 and 14) and one known (15) and three new 4-deoxyphorbol esters (16-18). The structure and absolute configuration of compound 16 were confirmed by X-ray crystallography. This compound was found to display antiviral activity against Chikungunya virus (EC₅₀ = 0.45 μM), while compound 15 proved to be a potent and selective inhibitor of HIV-1 replication in a recombinant virus assay (EC₅₀ = 13 nM). This study showed that a supercritical fluid chromatography-based protocol and molecular networking can facilitate and accelerate the discovery of bioactive small molecules by targeting molecules of interest, while minimizing the use of toxic solvents.

Fast and improved separation of major coumarins in Ammi visnaga (L.) Lam. by supercritical fluid chromatography

The first supercritical fluid chromatography method for the determination of five major coumarins (dihydrosamidin, visnadin, samidin, khellin, and visnagin) in Ammi visnaga fruits is described. Their baseline separation was possible in less than 5 min by using a UPC² HSS C₁₈ SB column with 1.8 μm particle size and a mobile phase comprising CO₂ , methanol, acetonitrile, and diethylamine. The type of stationary phase used was of particular relevance because, except for the selected one, the others did not resolve the two structural isomers dihydrosamidin and visnadin. Method validation confirmed that the procedure is linear (R² ≥ 0.9996) in a concentration range from 6 to 480 μg/mL, it is accurate (recovery rates: 97.2-103.6%) and precise (intraday deviation ≤ 6.6%, intraday deviation ≤ 1.7%); injecting 1 μL of standard solution, the determined limit of detection was below 1.9 μg/mL for all compounds. The analysis of different A. visnaga samples revealed their similar compositions, and khellin (0.75-1.01%) and visnagin (0.18-0.46%) were the dominant coumarins. Visnadin and dihydrosamidin, the individual quantification of which is described for the first time, were present at concentrations below 0.14%.

Determination of coumarins in the roots of Angelica dahurica by supercritical fluid chromatography

The fact that supercritical fluid chromatography (SFC) offers many desirable features is known for a long time. Yet, the number of applications on natural products is still limited, because robust and user-friendly instrumentation became available just a few years ago. As coumarins hardly have been studied by this technique we developed the first SFC assay for their determination in crude plant material. After method optimization eight standard compounds, including simple coumarins, linear and angular furanocoumarins, could be baseline separated in 6min using an Acquity UPC(2) CSH Fluoro-Phenyl 1.7μm column with supercritical CO2, methanol and diethylamine as mobile phase. Method validation confirmed that the assay is linear (R(2)≥0.9995), precise (intra-day variation≤5.8%; inter-day variation≤4.4%) and accurate (recovery rates from 96.5 to 104.2%). Detection limits determined at 300nm were below 2ng on-column, and the method showed to be well suited for the analysis of coumarins in Angelica dahurica roots. It was observed that qualitative as well as quantitative composition vary significantly. In all samples Imperatorin (0.09-0.28%) was the major coumarin, followed either by Isoimperatorin or Oxypeucedanin; the total coumarin content ranged from 0.16 to 0.77%. The results were in good agreement to published data, so that because of its speed and green nature SFC is definitely an interesting alternative for the analysis of this important class of natural products.