In carbohydrate chemistry, the stereoselective synthesis of 1,2-cis-glycosides remains a formidable challenge. This complexity is comparable to the synthesis of 1,2-cis-β-D-mannosides, primarily due to the adverse anomeric and Δ-2 effects. Over the past decades, to attain β-stereoselectivity in D-rhamnosylation, researchers have devised numerous direct and indirect methodologies, including the hydrogen-bond-mediated aglycone delivery (HAD) method, the synthesis of β-D-mannoside paired with C6 deoxygenation, and the combined approach of 1,2-trans-glycosylation and C2 epimerization. This review elaborates on the advancements in β-D-rhamnosylation and its implications for the total synthesis of tiacumicin B and other physiologically relevant glycans.
Glycosides ; Mannosides ; Glycosylation ; Stereoisomerism

To elucidate the chemical material basis of Rhododendron nivale, this study comprehensively used various chromatographic techniques to isolate and obtain five new meroterpenoid enantiomers(1a/1b-5a/5b) from the ethyl acetate extract of R. nivale. A variety of spectral analytical methods, such as high-resolution mass spectrometry(HRMS), nuclear magnetic resonance spectroscopy(NMR), and infrared(IR) spectrum, were used to evaluate the structure, combined with the measurement and calculation of electronic circular dichroism(ECD). The new compounds 1a/1b-4a/4b were named as(±)-nivalones A-B(1a/1b-2a/2b) and(±)-nivalnoids C-D(3a/3b-4a/4b), along with one known enantiomer(±)-anthoponoid G(5a/5b). Human neuroblastoma cells(SH-SY5Y cells) induced by hydrogen peroxide(H_2O_2) were used as oxidative stress models to evaluate the protective activity of the isolated compounds against oxidative damage to nerve cells. It was found that compounds 2a and 3a had a certain protective effect on nerve cells against H_2O_2-induced oxidative damage at concentrations of 50 μmol·L~(-1), which increased the cell survival rate from 44.02%±2.30% to 67.82%±1.12% and 62.20%±1.87%, respectively. Other compounds did not show a significant ability to protect cells from oxidative damage. These findings enrich the chemical constituents of R. nivale and provide valuable information for identifying the structure of its meroterpenoids.
Humans ; Rhododendron/chemistry* ; Neuroblastoma ; Oxidative Stress ; Magnetic Resonance Spectroscopy ; Stereoisomerism ; Molecular Structure

Two new neolignans and one new lignan (1-3) were obtained from the roots of Paeonia lactiflora. Their structures were unambiguously elucidated based on extensive spectroscopic analysis, single-crystal X-ray crystallography, and the calculated and experimental electronic circular dichroism (ECD) spectra. Compound 1 was a racemic mixture and successfully resolved into the anticipated enantiomers via chiral-phase HPLC. Compound 3 demonstrated moderate inhibitory activity against human carboxylesterase 2A1 (hCES2A1) with an IC₅₀ value of 7.28 ± 0.94 μmol·^-1.
Chromatography, High Pressure Liquid ; Humans ; Lignans/chemistry* ; Paeonia ; Plant Roots/chemistry* ; Stereoisomerism

This study investigated the chemical components from the florets of Carthamus tinctorius. Five compounds were isolated from C. tinctorius by column chromatography with silica gel and toyopearl HW-40 F, preparative thin-layer chromatography(TLC), and semi-preparative reverse phased high performance liquid chromatography(RP-HPLC). Their structures were identified by mass spectrometry(MS), one-dimension nuclear magnetic resonance(1 D-NMR), two-dimension nuclear magnetic resonance(2 D-NMR), and single-crystal X-ray diffraction as(-)-(2S,3S,5S,7S,10R)-eudesma-4(15)-en-2,3,11-triol(1 a),(+)-(2R,3R,5R,7R,10S)-eudesma-4(15)-en-2,3,11-triol(1 b), rosin(2),(+)-syringaresinol(3), and(E)-1-(4'-hydroxyphenyl)-but-1-en-3-one(4). Compounds 1 a and 1 b are a pair of enantiomeric sesquiterpenoids. Compound 1 a is a new eudesmene and is named(-)-plucheol A. Compound 1 a at 100 μmol·L~(-1) showed significant antioxidant activity against ABTS~(+·) and DPPH·, with the scavenging rates of 30.98%±4.17% and 27.52%±1.24%, respectively, while compound 1 b was inactive. In addition, compounds 1 a and 1 b showed no obvious anti-inflammatory activity.
Carthamus tinctorius/chemistry* ; Chromatography, High Pressure Liquid/methods* ; Sesquiterpenes/chemistry* ; Stereoisomerism ; Mass Spectrometry ; Molecular Structure

With repeated silica gel, octadecyl silica(ODS), and Sephadex LH-20 column chromatography, normal-phase and reverse-phase high performance liquid chromatography(HPLC), etc., a pair of new enantiomers and 5 known compounds were separated from the 95% ethanol extract of Chloranthus multistachys. These compounds were identified by the nuclear magnetic resonance spectroscopy(including 1 D-NMR and 2 D-NMR), single-crystal X-ray diffraction, circular dichroism(CD) spectroscopy, mass spectrometry(MS), and some other methods as(1R,4R,5R,8S,10R)-chloraeudolide H(1 a),(1S,4S,5S,8R,10S)-chloraeudolide H(1 b), hydroxyisogermafurenolide(2), 4α-hydroxy-5α,8β(H)-eudesm-7(11)-en-8,12-olide(3), chloraniolide A(4), chlorantene D(5), 4α,8β-dihydroxy-5α(H)-eudesm-7(11)-en-8,12-olide(6). Compounds 1 a and 1 b are a pair of new eudesmane-type sesquiterpene enantiomers, and compounds 2-4 were isolated from C. multistachys for the first time.
Chromatography, High Pressure Liquid ; Magnetic Resonance Spectroscopy ; Mass Spectrometry ; Molecular Structure ; Sesquiterpenes ; Stereoisomerism

The L(+)-form of tartaric acid (L(+)-TA) exists extensively in nature, and is widely used in the food, chemical, textile, building, and pharmaceutical industries (Su et al., 2001). The main method for L(+)-TA production is microbial transformation by cis-epoxysuccinate hydrolase (CESH), which can catalyze the asymmetric hydrolysis of cis-epoxysuccinic acid or its salts to TA or tartrate (Bao et al., 2019). Seventeen species containing CESH have been isolated so far. However, most species for L(+)-TA production have been reported from bacteria (Xuan and Feng, 2019). The only fungus isolated from soil by our lab recently, that could be used as catalyst for the process under acidic condition, is Aspergillus niger WH-2 (Bao et al., 2020). In order to find strains with new characteristics, this study attempted to isolate a new CESH source from fungi and investigate its application value.
Aspergillus niger/metabolism* ; Biomass ; Catalysis ; Fermentation ; Hydrogen-Ion Concentration ; Hydrolases/chemistry* ; Hydrolysis ; Industrial Microbiology ; Magnetic Resonance Spectroscopy ; Penicillium/metabolism* ; Phylogeny ; Soil ; Species Specificity ; Stereoisomerism ; Tartrates/chemistry* ; Temperature ; Textiles

Methamphetamine （MAMP） is a kind of amphetamine-type stimulants （ATS） which contains one chiral carbon atom in its structure. Therefore a pair of enantiomers, S-（+）-MAMP and R-（-）-MAMP exist. R type and S type methamphetamines possess similar physicochemical properties, but has largely different pharmacological and toxic effects. S-（+）-MAMP is the main component of addictive drug "Ice" at present, seriously affecting human health and public safety. The separation analysis and mechanism of toxic effects discussions on MAMP are the current research focuses. This paper reviews the research progress of separation analysis methods and toxic effects of methamphetamine enantiomers to provide reference for forensic study and forensic practice.
Central Nervous System Stimulants ; Humans ; Methamphetamine/chemistry* ; Stereoisomerism ; Substance Abuse Detection

Two cyclopeptides, celogentin L (1) and its epimer lyciumin A (2) were firstly isolated from Celosia argentea L.. The planar structures of the two compounds were fully determined by spectroscopic data, including 1D-, 2D-NMR, and HR-ESI/MS. The absolute configurations of amino acid components were assigned via chiral-phase HPLC analyses after acid hydrolysis. Furthermore, the configuration of C-N linkage at the glycine Cα was elucidated by extensive analyses of 2D-NMR and comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Cytotoxicity of the two compounds against human alveolar epithelial A549, hepatocellular carcinoma HepG2, and cervical cancer Hela cell lines was assayed. Although both of them were inactive in these cells, the present findings add new facets for the chemistry of Celosia argentea.
A549 Cells ; Cell Survival ; drug effects ; Celosia ; chemistry ; Chemistry Techniques, Analytical ; HeLa Cells ; Hep G2 Cells ; Humans ; Molecular Conformation ; Molecular Structure ; Peptides, Cyclic ; chemistry ; isolation & purification ; toxicity ; Seeds ; chemistry ; Stereoisomerism

OBJECTIVETo investigate the permeation-enhancing effect of dl-linalool, d-linalool, and l-linalool on model drugs across excised rat skin and the effect of linalool on the ceramides in stratum corneum lipids.

METHODSIn vitro skin permeation studies were performed with Valia-Chien diffusion cells, and the permeation samples were analyzed by high performance liquid chromatography with chiral stationary phase. Infrared spectroscopy was used to investigate the effect of linalool on stratum corneum lipids.

RESULTSWhen the donor vehicles added with 1% dl-linalool, 1% d-linalool, or 1% l-linalool, the steady-state skin permeation rate of naproxen was (2.47±0.63), (1.53±0.54), (1.73±0.48) μg·cm(-2)·h(-1), respectively, which is 2.49, 1.55, and 1.75 times (all P<0.05) compared with control group [(0.99±0.42)μg·cm(-2)·h(-1)], and the differences were statistically significant (all P<0.05). The permeation-enhancing effect of dl-linalool on naproxen was found significantly greater than that of d-linalool and l-linalool (both P<0.05). Compared with the control group, the stratum corneum treated with dl-linalool shifted to higher wave number on 2.09 cm(-1) of asymmetric CH2 stretching vibrations in attenuated total reflection-fourier transform infrared spectroscopy analysis. However, stratum corneum treated with d-linalool and l-linalool did not display this phenomenon.

CONCLUSIONThe disturbing degree of dl-linalool on stratum corneum lipids (ceramides) is different from that of linalool enantiomers, suggesting their different enhancing effect on the same drug.

Animals ; Lipids ; Monoterpenes ; Naproxen ; Rats ; Skin ; Skin Absorption ; Spectroscopy, Fourier Transform Infrared ; Stereoisomerism

OBJECTIVETo observe the effect of natural type ginsenoside Rg2 (Rg2) and its stereoisomers [20 (R)-Rg2 and 20 (S)-Rg2] at different concentrations on oxygen-glucose deprivation/ reperfusion (OGD/R) induced cortical neuronal injury model in vitro, and to explore the mechanism, and compare their differences of action.

METHODSCortical neurons after 7-day culture were randomly divided into 5 groups, i.e., the control group, the model group, the Rg2 group, 20 (R) -Rg2 group, and 20 (S) - Rg2 group. Cortical neurons in the Rg2 group, 20 (R)-Rg2 group, and 20(S)-Rg2 group were pretreated with 20, 40, and 80 μmol/L Rg2, 20 (R) -Rg2, and 20 (S) -Rg2 for 24 h to prepare OGD/R model. The cell survival rate, the activity of Caspase-3, the intracellular Ca2+ concentration, contents of superoxide dismutase (SOD) and malondialdehyde (MDA) were detected 24 h later.

RESULTSCompared with the control group, cell survival rates and activities of SOD obviously decreased, the activity of Caspase-3, Ca2+ fluorescent optical gray value, and contents of MDA significantly increased with statistical difference (P < 0.05). Compared with the model group, cell survival rates and activities of SOD obviously increased, the activity of Caspase-3, Ca2+ fluorescent optical gray value, and contents of MDA significantly decreased in 20 μmol/L Rg2 group, 40 μmol/L 20 (R) -Rg2 group, and 80 μmol/L 20 (S) -Rg2 group (P < 0.05). Compared with 20(S)-Rg2 group, cell survival rates increased and contents of MDA significantly decreased in 20, 40, and 80 μmol/L Rg2 and 20 (R)-Rg2 groups (P < 0.05). The activity of Caspase-3 decreased and contents of SOD increased in 80 μmol/L 20 (R)-Rg2 group, and 40, 80 μmol/L Rg2 groups (P < 0.05). Ca2+ fluorescent optical gray value decreased in 40, 80 μmol/L Rg2 and 20 (R)-Rg2 groups (P < 0.05). Compared with 20 (R)-Rg2 group, Ca2+ fluorescent optical gray value decreased in 80 μmol/L Rg2 group (P < 0.05); contents of SOD increased in 40 and 80 μmol/L Rg2 groups (P < 0.05); contents of MDA decreased in 20, 40, and 80 μmol/L Rg2 groups (P < 0.05).

CONCLUSIONSRg2 and its stereoisomers could improve cell vitality of cortical neurons against OGD/R induced injury. This might be related to improving anti-apoptotic capacities and antioxidant abilities, and reducing Ca2+ inflow. Besides, the neuroprotective effect of 20 (R) -Rg2 was better than that of 20 (S) -Rg2, but inferior to that of Rg2.

Antioxidants ; metabolism ; Apoptosis ; Calcium ; metabolism ; Caspase 3 ; metabolism ; Cell Survival ; Cells, Cultured ; Ginsenosides ; pharmacology ; Glucose ; Humans ; Malondialdehyde ; metabolism ; Neurons ; drug effects ; Neuroprotective Agents ; pharmacology ; Oxygen ; Random Allocation ; Reperfusion Injury ; Stereoisomerism ; Superoxide Dismutase ; metabolism