Graphene oxide was found to be an efficient and reusable acid catalyst for the esterification reaction. A wide range of aliphatic and aromatic acids and alcohols were compatible with the standard conditions and afforded the corresponding products in good yields. The heterogeneous catalyst can be easily recovered and recycled in dichloroethane solvent with good catalytic activity.
New TLC, HPLC and LC/MS methods were developed for the rapid separation, characterization and quantitation of thiophenes in Radix Echinopsis, a herbal medicine, which has been used in China for long history. Nineteen commercial batches of this herb were analyzed by TLC and HPLC. Only five batches were derived from correct species. The other 14 batches were identified as its adulterating species, Radix Rhapontici, as they did not contain characteristic thiophenes of Echinopsis species. By LC/MS, 16 thiophenes were identified from the methanol extracts of Radix Echinopsis and Radix Rhapontici according to their fragmentation behaviors in MS/MS. In addition, a fully validated HPLC method was established to determine the contents of α-terthienyl in Radix Echinopsis. The contents ranged from 2.7 to 5.2 mg/g for five tested samples. The methods in this paper were simple and reliable, and could be used for the comprehensive quality control of Radix Echinopsis.
High performance liquid chromatography was coupled with UV detection for simultaneous quantification of lopinavir (LPV) and ritonavir (RTV) in human plasma. This assay was sensitive, accurate and simple, and only used 200 μL of plasma sample. Samples were liquid-liquid extracted, and diazepam was used as an internal standard. The chromatographic separation was achieved on a C18 reversed-phase analytic column with a mobile phase of acetonitrile-sodium dihydrogen phosphate buffer (10 mmol L−1, pH 4.80) (60:40, v/v). UV detection was conducted at 205 nm and the column oven was set at 40°C. Calibration curves were constructed between 0.5–20 μg mL−1 for LPV and 0.05–5 μg mL−1 for RTV. The relative standard deviations were 2.16%–3.20% for LPV and 2.12%–2.60% for RTV for intra-day analysis, and 2.34%–4.04% for LPV and 0.31%–4.94% for RTV for inter-day analysis. The accuracy was within 100%±10%. The mean extraction recoveries were 79.17%, 52.26% and 91.35% for RTV, LPV and diazepam, respectively. This method was successfully applied to human plasma samples from patients orally administered a salvage regimen of lopinavir-ritonavir tablets.
Flavonoids, as an important class of natural products, are the main bioactive constituents of a lot of medicinal or dietary plants. They have been reported to show extensive benefits to human health, including antioxidant, anti-inflammatory, and anti-cancer activities. In most cases, flavonoids are present in plants as a series of analogues with similar structures and physico-chemical properties. This chemical complexity renders the quality control of flavonoid-containing herbal products problematic. Therefore, rapid, accurate and sensitive analytical techniques for flavonoids are of significance. This review summarizes the advances in sample extraction, chromatographic separation, detection, and structural analysis of flavonoids in medicinal and dietary herbs since 2005. Emphasis will be put on the qualitative and quantitative analysis of flavonoids in botanical extracts by high-performance liquid chromatography (HPLC) and liquid chromatography coupled with mass spectrometry (LC/MS). New techniques like UPLC, HILIC, and 2D-HPLC have significantly improved the separation capabilities of HPLC. The versatile LC/MS does not only allow fast and accurate structural analysis of flavonoids in complicated mixtures, but also provides a rapid and sensitive technique for the quantitative detection of flavonoids in herbal extracts and even in biological matrices. These techniques will be widely used for the chemical analysis of flavonoids and for the quality control of related herbal products. Keywords: Flavonoids, HPLC, LC/MS, separation, detection, structural analysis, medicinal and dietary herb, benzo-Y-pyrone, flavones, chalcones, C-glycosides,, safflower, carthamin, anti-inflammatory, anti-cancer
Carduus acanthoides is a traditional Tibetan herbal medicine for the treatment of hematemesis, hematuria, and menorrhagia. Despite its multiple biological activities, comprehensive chemical analysis of this herb has not been reported, so far. In this study, chemical constituents of C. acanthoides were analyzed by ultra-performance liquid chromatography coupled with diode array detection and time-of-flight mass spectrometry (UPLC/DAD/qTOF-MS). The methanol extract of C. acanthoides was separated on an ACQUITY HSS T3 column (1.8 μm, 150 mm × 2.1 mm) and eluted with acetonitrile–water (containing 0.1% formic acid). Constituents were identified by UV and HRMS in the negative ion mode. A total of 69 compounds were identified from C. acanthoides, including 35 flavonoids, 17 quinic acids, 7 phenolic acid glycosides, 5 phenylethanoid glycosides, 3 coumarins, and 2 phenolic acids. Among them, 31 compounds were unambiguously characterized by comparing with reference standards. Furthermore, a UPLC/UV (340 nm) method was established to simultaneously determine 3 quinic acids and 6 flavonoids, including neochlorogenic acid (9), chlorogenic acid (16), cryptochlorogenic acid (18), kaempferol 3-O-rhamnoside-7-O-glucoside (32), luteolin 7-O-glucosyl-(1→2)-glucoside (34), luteolin 7-O-glucoside (38), luteolin 7-O-6′′′-O-acetyl-glucosyl-(1→2)-glucoside (44), kaempferol 3-O-rhamnoside (55), and chrysoeriol 7-O-6′′′-O-acetyl-glucosyl-(1→2)-glucoside (56). All analytes showed good linearity (r2 ≥ 0.998) with an LOD of 0.077–0.120 μg mL−1. These nine compounds accounted for 2.1–3.5‰ of the herb.
Previous data established 4'-deoxyflavone glycosides (4'-DFGs) as important pharmaceutical components in the roots of rare medical plants like Scutellaria baicalensis Georgi. Extracting these compounds from plants involves land occupation and is environmentally unfriendly. Therefore, a modular ("plug-and-play") yeast-consortium platform is developed to synthesize diverse 4'-DFGs de novo. By codon-optimizing glycosyltransferase genes from different organisms for Pichia pastoris, six site-specific glycosylation chassis are generated to be capable of biosynthesizing 18 different 4'-DFGs. Cellular factories showed increased 4'-DFG production (up to 18.6-fold) due to strengthened synthesis of UDP-sugar precursors and blocked hydrolysis of endogenous glycosides. Co-culturing upstream flavone-synthesis-module cells with downstream glycoside-transformation-module cells alleviated the toxicity of 4'-deoxyflavones and enabled high-level de novo synthesis of 4'-DFGs. Baicalin is produced at the highest level (1290.0 mg L
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