Preparative isolation and purification of rupestonic acid from the Chinese medicinal plant Artemisia rupestris L. by high-speed counter-current chromatography

Synthesis of an aggregation-induced emission-based fluorescent probe based on rupestonic acid

Chinese herbal medicine and Chinese patent medicine have been widely applied for cancer care in China. Rupestonic acid, an active ingredient of Artemisia rupestris L., has recently been confirmed to have certain anti-tumor effects in vitro. In this study, we employed the application of a commonly devoted triphenylamine as a fluorophore and the addition of 2,4-thiazolidinedione as a bridge to integrate rupestonic acid into the AIE system to create an fluorescent probe with anti-tumor properties. The spectral, cytotoxic, and cellular imaging properties of the probe were measured. Its promising responses make possible the application of the probe in antitumor theragnostic systems.

Asymmetric Synthesis of Rupestonic Acid and Pechueloic Acid

In this report, the originally proposed rupestonic acid (5) and pechueloic acid (3) were efficiently synthesized. The chiral lactone 13, recycled from the degradation of saponin glycosides, was utilized to prepare the key chiral fragment 11. During the exploration of this convergent assembly strategy, the ring-closing metathesis (RCM), SmI₂-prompted intermolecular addition, and [2,3]-Wittig rearrangement proved to be effective transformations for the synthesis of subunits.

Structure-activity relationship studies of 1-(1'-hydroxyalkyl)rupestonic acid methyl esters against influenza viruses

A series of 1-(1'-hydroxyalkyl)rupestonic acid methyl esters were synthesized via the condensation of methyl rupestonate with various aldehydes in the presence of LDA. This mixed aldol reaction was highly stereoselective and all the new compounds were elucidated by detailed NMR and MS analyses. The absolute configurations of the newly formed stereocenters were further confirmed by X-ray crystallographic analysis of 3d, the results of which were found to be opposite to the prediction based on Zimmerman-Traxler's and Houk's models. All the compounds synthesized were then evaluated for their in vitro inhibitory activities against influenza A (H1N1 and H3N2) and B viruses. The data showed that 3p displayed the highest activity against influenza A H1N1 (IC₅₀=0.69μg/mL) and H3N2 (IC₅₀=0.69μg/mL) viruses, which were even better than Ribavirin and Oseltmivir. On the other hand, both 3c and 3o were found to show comparable activities with the reference drugs in inhibiting both influenza A and B viruses. Further studies will focus on reducing the cytotoxicity of the hits reported in this work.

Nitric Oxide Inhibitory Dimeric Sesquiterpenoids from Artemisia rupestris

Twelve new dimeric sesquiterpenoids (1-12) were isolated from the dried whole plants of Artemisia rupestris. Their structures were determined using MS and NMR data, and the absolute configurations were elucidated on the basis of experimental and calculated ECD spectra. Compounds 1-9 are presumably formed via biocatalyzed [2+2] or [4+2] cycloaddition reactions. Stereoselectivity of the [4+2] Diels-Alder reaction dictated the formation of endo-products. The dimeric sesquiterpenoids exhibited moderate inhibition on NO production stimulated by lipopolysaccharide in BV-2 microglial cells, with IC50 values in the range 17.0-71.8 μM.

New sesquiterpene and thiophene derivatives from Artemisia rupestris

A new sesquiterpene, rupestrisin A (1), and three new thiophene derivatives, rupestrienes A-C (2-4), were isolated from Artemisia rupestris. Their structures were determined by analyses of MS and NMR spectroscopic data, and the absolute configuration of 1 was established by calculated ECD spectra using time-dependent density functional theory. In in vitro bioassays, compounds 1-4 showed inhibitory effects on LPS-stimulated NO production in BV-2 microglial cells with IC50 values of 24.3, 20.3, 8.5, and 5.3 μM, respectively.

Counter-current chromatography for the separation of terpenoids: a comprehensive review with respect to the solvent systems employed

Natural products extracts are commonly highly complex mixtures of active compounds and consequently their purification becomes a particularly challenging task. The development of a purification protocol to extract a single active component from the many hundreds that are often present in the mixture is something that can take months or even years to achieve, thus it is important for the natural product chemist to have, at their disposal, a broad range of diverse purification techniques. Counter-current chromatography (CCC) is one such separation technique utilising two immiscible phases, one as the stationary phase (retained in a spinning coil by centrifugal forces) and the second as the mobile phase. The method benefits from a number of advantages when compared with the more traditional liquid-solid separation methods, such as no irreversible adsorption, total recovery of the injected sample, minimal tailing of peaks, low risk of sample denaturation, the ability to accept particulates, and a low solvent consumption. The selection of an appropriate two-phase solvent system is critical to the running of CCC since this is both the mobile and the stationary phase of the system. However, this is also by far the most time consuming aspect of the technique and the one that most inhibits its general take-up. In recent years, numerous natural product purifications have been published using CCC from almost every country across the globe. Many of these papers are devoted to terpenoids-one of the most diverse groups. Naturally occurring terpenoids provide opportunities to discover new drugs but many of them are available at very low levels in nature and a huge number of them still remain unexplored. The collective knowledge on performing successful CCC separations of terpenoids has been gathered and reviewed by the authors, in order to create a comprehensive document that will be of great assistance in performing future purifications.

One-step separation and purification of rupestonic acid and chrysosptertin B from Artemisia rupestris L. by high-speed counter-current chromatography

INTRODUCTION

Artemisia rupestris L. is a well-known traditional Chinese medicinal plant in Xinjiang. Rupestonic acid is the main active ingredient of A. rupestris L., and has been chosen as a 'marker compound' for the chemical evaluation or quality control of A. rupestris L. and its products. Although HSCCC separation method was developed before, the separation was performed with two steps using the same solvent system, which were time-consuming and waste of the solvents.

OBJECTIVE

To develop a simple HSCCC method for the separation and purification of rupestonic acid in a single run.

METHODOLOGY

The measurement of partition coefficient (K) was introduced to select the two-phase solvent system. The simple HSCCC method was established according to the selected solvent system for separation and purification of rupestonic acid. The purity of target compound was test by HPLC and the structure was identified by MS, (1)H NMR and (13)C NMR.

RESULTS

A total of 72.3 mg of rupestonic acid and 53.5 mg of chrysosptertin B with over 95% purity were yielded from 500 mg extracts of Artemisia rupestris L. in one-step separation.

CONCLUSION

The rupestonic acid was separated in a single run by HSCCC.

Preparative isolation and purification of isobenzofuranone derivatives and saponins from seeds of Nigella glandulifera Freyn by high-speed counter-current chromatography combined with gel filtration

Although the medicinal plant and food Nigella glandulifera Freyn has been researched for decades, isobenzofuranones have never been isolated before. Two isobenzofuranone derivatives and two saponins were successfully separated and purified from seeds of N. glandulifera Freyn by high-speed counter-current chromatography (HSCCC) with the optimized two-phase solvent system, n-hexane-ethyl acetate-methanol-water (7:3:5:5, v/v). Salfredin B(11) (22.1mg, HPLC purity 95.3%), 5, 7-dihydroxy-6-(3-methybut-2-enyl) isobenzofuran-1(3H)-one (18.9mg, HPLC purity 97.3%) and crude sample 2 (555mg) were separated from 600mg of ethyl acetate extract of N. glandulifera Freyn. Following a cleaning-up step by chromatography on Sephadex LH-20, hederagenin (12mg) and 3-O-[beta-d-xylopyranosyl-(1-->3)-alpha-l-rhamnopyranosyl-(1-->2)-alpha-l-arabinopyranosyl]-hederagenin (45mg) were separated from sample 2. All of the fractions before peak II were collected and subjected to a Sephadex LH-20 column and eluted by methanol, two of triterpene saponins (12mg of hederagenin and 45mg of 3-O-[beta-d-xylopyranosyl-(1-->3)-alpha-l-rhamnopyranosyl-(1-->2)-alpha-l-arabinopyranosyl]-hederagenin) were isolated. The structures of peak fractions were identified by IR, electron ionization MS, (1)H NMR and (13)C NMR. 5, 7-Dihydroxy-6-(3-methybut-2-enyl) isobenzofuran-1(3H)-one was isolated for the first time from higher plant and salfredin B11 was isolated for the first time in this plant.

Natural product isolation

Since the 1990s, interest in natural product research has increased considerably. Following several outstanding developments in the areas of separation methods, spectroscopic techniques, and sensitive bioassays, natural product research has gained new attention for providing novel chemical entities. This updated review deals with sample preparation and purification, recent extraction techniques used for natural product separation, liquid-solid and liquid-liquid isolation techniques, as well as multi-step chromatographic operations. It covers examples of papers published since the NPR review 'Modern separation methods' by Marston and Hostettmann,1 with major emphasis on methods developed and the research undertaken since 2000.

APPLICATION OF PREPARATIVE HIGH-SPEED COUNTERCURRENT CHROMATOGRAPHY FOR SEPARATION OF ELATINE FROM DELPHINIUM SHAWURENSE

Preparative separation of elatine in Delphinium shawurense was achieved for the first time using high-speed countercurrent chromatography (HSCCC). The separation was performed with a solvent system composed of ethyl acetate-chloroform-methanol-water (3:0.1:2:3, v/v) using the lower organic phase as a mobile phase under a revolution speed of 800 rpm. This yielded 72 mg of elatine at over 97% purity with an approximately 95% recovery. The chemical structure was identified by MS and NMR.