Synthesis of New 13-O-Acylavermectin Bl Aglycones

Six new 13-O-acylavermectin Bl aglycones(3-8) were synthesized from avermectin B1 aglycone and their bioactivities were evaluated against Spodoptera exigua, Spodoptera eridania, Tetranychus urticae and Aphis fabae.     

A new strategy for synthesizing the steroids with side chains from steroidal sapogenins: synthesis of the aglycone of OSW-1 by using the intact skeleton of diosgenin

The protected aglycone of saponin OSW-1, a new antitumor natural product, was synthesized in 13 linear steps in 9.5% overall yield by utilizing the intact skeleton of diosgenin. This strategy demonstrated a higher efficiency than the routine synthesis of steroids with side chains.     

Mass spectrometric profiling of flavonoid glycoconjugates possessing isomeric aglycones

In fields such as food and nutrition science or plant physiology, interest in untargeted profiling of flavonoids continues to expand. The group of flavonoids encompasses several thousands of chemically distinguishable compounds, among which are a number of isobaric compounds with the same elemental composition. Thus, the mass spectrometric identification of these compounds is challenging, especially when reference standards are not available to support their identification. Many different types of isomers of flavonoid glycoconjugates are known, i.e. compounds that differ in their glycosylation position, glycan sequence or type of interglycosidic linkage. This work focuses on the mass spectrometric identification of flavonoid glycoconjugate isomers possessing the same glycan mass and differing only in their aglycone core. A non‐targeted HPLC‐ESI‐MS/MS profiling method using a triple quadrupole MS is presented herein, which utilizes in‐source fragmentation and a pseudo‐MS³ approach for the selective analysis of flavonoid glycoconjugates with isomeric/isobaric aglycones. A selective MRM‐based identification of the in‐source formed isobaric aglycone fragments was established. Additionally, utilizing the precursor scanning capability of the employed triple quadrupole instrument, the developed method enabled the determination of the molecular weight of the studied intact flavonoid glycoconjugate. The versatility of the method was proven with various types of flavonoid aglycones, i.e. anthocyanins, flavonols, flavones, flavanones and isoflavones, along with their representative glycoconjugates. The developed method was also successfully applied to a commercially available sour cherry sample, in which 16 different glycoconjugates of pelargonidin, genistein, cyanidin, kaempferol and quercetin could be tentatively identified, including a number of compounds containing isomeric/isobaric aglycones. Copyright © 2015 John Wiley & Sons, Ltd.     

Three‐dimensional structure of cyclic antibiotic teicoplanin aglycone using NMR distance and dihedral angle restraints in a DMSO solvation model

The three‐dimensional solution conformation of teicoplanin aglycone was determined using NMR spectroscopy. A combination of NOE and dihedral angle restraints in a DMSO solvation model was used to calculate an ensemble of structures having a root mean square deviation of 0.17 Å. The structures were generated using systematic searches of conformational space for optimal satisfaction of distance and dihedral angle restraints. Comparison of the NMR‐derived structure of teicoplanin aglycone with the X‐ray structure of a teicoplanin aglycone analog revealed a common backbone conformation with deviation of two aromatic side chain substituents. Experimentally determined backbone ¹³C chemical shifts showed good agreement with those computed at the density functional level of theory, providing a cross validation of the backbone conformation. The flexible portion of the molecule was consistent with the region that changes conformation to accommodate protein binding. The results showed that a hydrogen‐bonded DMSO molecule in combination with NMR‐derived restraints together enabled calculation of structures that satisfied experimental data. Copyright © 2015 John Wiley & Sons, Ltd.     

A structural study of the naringin-β-cyclodextrin complex

The structure of the inclusion complex formed between naringin (naringenin-7-O--neohesperidoside) and-cyclodextrin (BCD) was studied in detail by UV and NMR spectroscopic techniques and potentiometry. A binding constant value of 1016±150M^–1 was arrived at from UV studies. Potentiometric studies showed that pK values of 4-OH and 5-OH were affected by and-cyclodextrins. One-dimensional difference NOE and spin-lattice relaxation time (T ₁) measurements indicated that the aglycone protion was affected more than the neohesperidoside portion. TheT ₁ values analysed for local motions indicated that _c values of complexed naringin was higher than that of free naringin. The internal rotation calculated for different groups showed _i values for the phenolic and dihydrobenzopyran portion decrease by a factor of 2. Also a value of 0.12–0.17 observed for the aglycone portion indicated that the coupling between guest and host is weak. All the studies have shown that the disposition in which the phenol group at 2 is inside the BCD cavity with 4-keto and 5-OH hydrogen bonded to the secondary hydroxyl groups at the rim of the wider end of the BCD cavity is the most probable one.     

Thermodynamic origin of the chiral recognition of tryptophan on teicoplanin and teicoplanin aglycone stationary phases

The D-, L-tryptophan binding and the chiral recognition properties of the teicoplanin and teicoplanin aglycone (TAG) chiral stationary phase (CSPs) were compared at various column temperatures. The solute adsorption isotherms (bi-Langmuir model) were determined for both the two CSPs using the perturbation method. It was demonstrated that the sugar units were involved in the reduction of the apparent enantioselectivity through two phenomena: (i) the inhibition of some enantioselective contacts with low-affinity binding regions of the aglycone and (ii) a decrease in the stereoselective properties of the aglycone high-affinity binding pocket. The phenomenon (ii) was governed by both a decrease in the ratio of the enantiomer adsorption constant and a strong reduction of the site accessibility for D- and L-tryptophan. In addition, a temperature effect study was performed to investigate the chiral recognition mechanism at the aglycone high-affinity pocket. An enthalpy-entropy compensation analysis derived from the Grunwald model as well as the comparison with the literature data demonstrated that the enantioselective binding mode was dependent on an interface dehydration process. The change in the enantioselective process observed between the TAG and teicoplanin CSP was characterized by a difference of ca. 2-3 ordered water molecules released from the species interface.     

Structural characterization of the ligstroside aglycone isoforms in virgin olive oils by liquid chromatography–high‐resolution Fourier‐transform mass spectrometry and H/Dexchange

A systematic structural characterization of the isomeric forms related to ligstroside aglycone (LA), one of the most relevant secoiridoids contained in virgin olive oils, was performed using reverse phase liquid chromatography with electrospray ionization Fourier‐transform single and tandem mass spectrometry, operated in negative ion mode (RPLC‐ESI(?)‐FTMS and FTMS/MS). The high mass resolution and accuracy provided by the adopted orbital trap mass analyzer enabled the recognition of more than 10 different isomeric forms of LA in virgin olive oil extracts. They were related to four different types of molecular structure, two of which including a dihydropyranic ring bearing one or two aldehydic groups, whereas the others corresponded to dialdehydic open‐structure forms, differing just for the position of a C═C bond. The contemporary presence of enolic or dienolic tautomers associated to most of these compounds, stable at room temperature (23°C), was also assessed through RPLC‐ESI‐FTMS analyses operated under H/D exchange conditions, ie, by using D₂O instead of H₂O as co‐solvent of acetonitrile in the RPLC mobile phase. As discussed in the paper, the results obtained for LA indicated a remarkable structural similarity with oleuropein aglycone (OA), the most abundant secoiridoid of olive oil, whose isoforms had been previously characterized using the same analytical approach.     

Chiral recognition by enantioselective liquid chromatography: Mechanisms and modern chiral stationary phases

An overview of the state-of-the-art in LC enantiomer separation is presented. This tutorial review is mainly focused on mechanisms of chiral recognition and enantiomer distinction of popular chiral selectors and corresponding chiral stationary phases including discussions of thermodynamics, additivity principle of binding increments, site-selective thermodynamics, extrathermodynamic approaches, methods employed for the investigation of dominating intermolecular interactions and complex structures such as spectroscopic methods (IR, NMR), X-ray diffraction and computational methods. Modern chiral stationary phases are discussed with particular focus on those that are commercially available and broadly used. It is attempted to provide the reader with vivid images of molecular recognition mechanisms of selected chiral selector–selectand pairs on basis of solid-state X-ray crystal structures and simulated computer models, respectively. Such snapshot images illustrated in this communication unfortunately cannot account for the molecular dynamics of the real world, but are supposed to be helpful for the understanding. The exploding number of papers about applications of various chiral stationary phases in numerous fields of enantiomer separations is not covered systematically.     

Swerilactones E-G, three unusual lactones from Swertia mileensis

Swerilactones E (1), F (2), and G (3), three unusual lactones with a phenyl group, were isolated from the traditional Chinese herb of Swertia mileensis. Their structures were determined based on extensive spectroscopic analysis and X-ray single crystal crystallography. Our anti-HBV assay on the Hep G 2.2.15 cell line in vitro showed that compounds 1 and 2 exhibited significant inhibitory activities against the secretion of HBsAg with IC₅₀ of 0.22 and 0.70 mM and HBeAg with IC₅₀ of 0.52 and >6.78 mM, respectively.     

Insignin A, A Novel C_21-Steroidal Aglycone from Biondia insignis

The genus Biondia having six species is exclusively distributed in China. But none of them was investigated in the aspect of phytochemistry before this work. From the view of plant taxonomy, the genus Biondia in the Trib. Asclepiadeae is close to the genus Cynanchum, and the plants of the latter mainly contain C21-steroids. In order to investigate whether the plants of the genus Biondia have C21-steroidal compounds and what kind of skeleton they may have, the whole plant of Biondia insigni…