Influence of oligonucleotides structures for separation of diastereomers by capillary electrophoresis method using polyvinylpyrrolidone 1,300,000

In the field of oligonucleotides drug discovery, phosphorothioate (PS) modification has been recognized as an effective tool to overcome the nuclease digestion, and generates 2n of possible diastereomers, where n equals the number of PS linkages. However, it is also well known that differences in drug efficacy and toxicity are caused by differences in stereochemistry of oligonucleotides. Therefore, the development of a high-resolution analytical method that enables stereo discrimination of oligonucleotides is desired. Under this circumstance, capillary electrophoresis (CE) using polyvinylpyrrolidone (PVP) is considered as one of the useful tools for the separation analysis of diastereomers. In this study, we evaluated the several oligonucleotides with the structural diversities in order to understand the separation mechanism of the diastereomers by CE. Especially, five kinds of 2'-moieties were deeply examined by CE with PVP 1,300,000 polymer solution. We found that different trend of the peak shapes and the peak resolution were observed among these oligonucleotides. For example, the better peak resolution was observed in 6 mer PS3-DNA compared to the rigid structure of 6 mer PS3-LNA. As for this reason, the computational simulation revealed that difference of accessible surface area caused by the steric structure of thiophosphate in each oligonucleotide is one of the key attributes to explain the separation of the diastereomers. In addition, we achieved the separation of sixteen peak tops of the diastereomers in 6 mer PS4-DNA, and the complete separation of fifteen diastereomers in 6 mer PS4-RNA. These knowledge for the separation of the diastereomers by CE will be expected to the quality control of the oligonucleotide drugs.

Non-enzymatic reactions in biogenesis of fungal natural products

Fungi have long been regarded as abundant sources of natural products (NPs) exhibiting significant biological activities. Decades of studies on the biosynthesis of fungal NPs revealed that most of the biosynthetic steps are catalyzed by sophisticated enzymes encoded in biosynthetic gene clusters, whereas some reactions proceed without enzymes. These non-enzymatic reactions complicate biosynthetic analysis of NPs and play important roles in diversifying the structure of the products. Therefore, knowledge on the non-enzymatic reactions is important for elucidating the biosynthetic mechanism. This review focuses on non-enzymatic reactions we recently encountered during biosynthetic studies of four types of NPs (viridicatins, Sch210972, lentopeptins, and lentofuranine).

The phosphylated butyrylcholinesterase-derived tetrapeptide GlyGluSerAla proves exposure to organophosphorus agents with enantioselectivity

We herein present for the first time the phosphylated (*) tetrapeptide (TP)-adduct GlyGluSer198*Ala generated from butyrylcholinesterase (BChE) with proteinase K excellently suited for the verification of exposure to toxic organophosphorus nerve agents (OPNA). Verification requires bioanalytical methods mandatory for toxicological and legal reasons. OPNA react with BChE by phosphonylation of the active site serine residue (Ser198) forming one of the major target protein adducts for verification. After its enzymatic cleavage with pepsin, the nonapeptide (NP) PheGlyGluSer*AlaGlyAlaAlaSer is typically produced as biomarker. Usually OPNA occur as racemic mixtures of phosphonic acid derivatives with the stereocenter at the phosphorus atom, e.g. (±)-VX. Both enantiomers react with BChE, but the adducted NP does not allow their chromatographic distinction. In contrast, the herein introduced TP-adducts appeared as two peaks when using a stationary reversed phase (1.8 µm) in micro-liquid chromatography-electrospray ionisation tandem-mass spectrometry (µLC-ESI MS/MS) analysis. These two peaks represent diastereomers of the (+)- and (-)-OPNA adducted to the peptide that comprises chiral L-amino acids exclusively. Concentration- and time-dependent effects of adduct formation with (±)-VX and its pure enantiomers (+)- and (-)-VX as well as with (±)-cyclosarin (GF) were investigated in detail characterising enantioselective adduct formation, stability, ageing and spontaneous reactivation. The method was also successfully applied to samples from a real case of pesticide poisoning as well as to samples of biomedical proficiency tests provided by the Organisation for the Prohibition of Chemical Weapons.

Development of a novel method for analysing N-acetyl-DL-leucine enantiomers in human fingernail by UPLC-ESI-MS/MS and the evaluation in diabetes mellitus

BACKGROUND

Recent research has been reported that N-acetyl-leucine content is significantly reduced in the saliva of diabetic patients, but no reports of detection in human nails have been found. This study aims to develop a novel method for the chiral separation of N-acetyl-DL-leucine (Ac-DL-Leu) in human fingernails to investigate the differences between healthy volunteers (HVs), prediabetes (PDs) and diabetic patients (DPs), and to verify its effectiveness in early warning of diabetes.

METHOD

Chiral resolution was performed using DBD-Apy pre-column derivatization on a C18 column (2.1 × 150 mm, 1.9 μm) at 40 ^oC, and detected by UPLC-ESI-MS/MS.

RESULTS

The resolution and the limit of detection (LOD) of Ac-DL-Leu were 1.75 and 1.50 fmol, respectively. The linear range of Ac-DL-Leu was 10-2000 fmol and the determination coefficient (R²) was above 0.9997. The recovery of Ac-DL-Leu in human nails was 96.92-105.69%. The contents of Ac-D-Leu and Ac-L-Leu were analyzed in 18 HVs, 13 PDs and 16 DPs fingernails. The results showed that their contents were significantly lower in DPs than in PDs and HVs (p < 0.0001).

CONCLUSIONS

A method for evaluating the effectiveness of Ac-DL-Leu enantiomers in human fingernails as a biomarker for diabetes was firstly developed.

Diastereomer- and enantiomer-selective accumulation and depuration of 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexanes (DBE-DBCHs) and 1,2,5,6-tetrabromocyclooctanes (TBCOs) in earthworms (Eisenia fetida)

Due to the regulation of hexabromocyclododecane (HBCD), much attention has been paid to its potential substitutes, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane (DBE-DBCH) and 1,2,5,6-tetrabromocyclooctane (TBCO). DBE-DBCH and TBCO contain several diastereomers and enantiomers, which may exhibit different environmental behaviors and biological effects. In this study, the accumulation and depuration of individual DBE-DBCH and TBCO diastereomers by earthworms (Eisenia fetida) from diastereomer-contaminated soils were evaluated. The accumulation and depuration kinetics of DBE-DBCH and TBCO diastereomers followed one-compartment first-order kinetics. The biota soil accumulation factor (BSAF) of β-DBE-DBCH (2.74 g_oc g_lip^-1) was 1.26 times that of α-DBE-DBCH (2.18 g_oc g_lip^-1), while the BSAF of β-TBCO (2.15 g_oc g_lip^-1) was 1.62 times that of α-TBCO (1.3 g_oc g_lip^-1), showing the diastereomer-specific accumulation of DBE-DBCH and TBCO. DBE-DBCH and TBCO diastereomers appeared to be transformed in earthworm-soil systems; however, no evidence of bioisomerization of the four diastereomers in earthworms was found, and no potential metabolites of debromination and hydroxylation were detected. Furthermore, the selective enrichment of E₁-α-DBE-DBCH and E₁-β-DBE-DBCH (E₁ represents the first enantiomer eluted) occurred in earthworms as the enantiomer fractions (EFs) for α-DBE-DBCH (0.562-0.763) and β-DBE-DBCH (0.516-0.647) were significantly greater than those in the technical products (0.501 for α-DBE-DBCH and 0.497 for β-DBE-DBCH, p < 0.05), especially in the depuration stage. The results demonstrated the diastereomer- and enantiomer-selective accumulation of DBE-DBCH and the diastereomer-selective accumulation of TBCO in the earthworm.

Separation of vigabatrin enantiomers using mixed-mode chromatography and its application to determine the vigabatrin enantiomer levels in rat plasma

Mixed-mode chromatography-comprising a mixed phase with reversed and ionic phases, enabling hydrophobic and ion-exchange interactions simultaneously-was applied to identify vigabatrin enantiomers by HPLC with pre-column fluorescence derivatization with 2,5-dioxopyrrolidin-1-yl (4-(((2-nitrophenyl)sulfonyl)oxy)-6-(3-oxomorpholino)quinoline-2-carbonyl)prolinate (Ns-MOK-(S)-Pro-OSu). The MOK-(S)-Pro-vigabatrin enantiomers were efficiently separated within 12 min (total analysis time per sample: 28 min, including washing and equilibrium time for the column). The mobile phase was H₂O/CH₃OH/10 mM ammonium formate (pH 2.0) (20/20/60, v/v/v). Column temperature was maintained at 60℃. The proposed HPLC method could successfully monitor plasma vigabatrin enantiomer levels in rats administered (±)-vigabatrin (50 mg/kg, p.o.).

Investigation of factors influencing the separation of diastereomers of phosphorothioated oligonucleotides

This study presents a systematic investigation of factors influencing the chromatographic separation of diastereomers of phosphorothioated pentameric oligonucleotides as model solutes. Separation was carried out under ion-pairing conditions using an XBridge C₁₈ column. For oligonucleotides with a single sulfur substitution, the diastereomer selectivity was found to increase with decreasing carbon chain length of the tertiary alkylamine used as an ion-pair reagent. Using an ion-pair reagent with high selectivity for diastereomers, triethylammonium, it was found the selectivity increased with decreased ion-pair concentration and shallower gradient slope. Selectivity was also demonstrated to be dependent on the position of the modified linkage. Substitutions at the center of the pentamer resulted in higher diastereomer selectivity compared to substitutions at either end. For mono-substituted oligonucleotides, the retention order and stereo configuration were consistently found to be correlated, with Rp followed by Sp, regardless of which linkage was modified. The type of nucleobase greatly affects the observed selectivity. A pentamer of cytosine has about twice the diastereomer selectivity of that of thymine. When investigating the retention of various oligonucleotides eluted using tributylammonium as the ion-pairing reagent, no diastereomer selectivity could be observed. However, retention was found to be dependent on both the degree and position of sulfur substitution as well as on the nucleobase. When analyzing fractions collected in the front and tail of overloaded injections, a significant difference was found in the ratio between Rp and Sp diastereomers, indicating that the peak broadening observed when using tributylammonium could be explained by partial diastereomer separation.

The relative toxicity of brodifacoum enantiomers

Brodifacoum (BDF) is a potent, long-acting anticoagulant rodenticide that can cause fatal poisoning in humans. The chemical structure of BDF includes 2 chiral carbons, resulting in 2 pairs of diastereomers, BDF-cis (R/S and S/R) and BDF-trans (R/R and S/S). However, the relative potency of these molecules is not known. The purpose of this study was to compare the in vitro and in vivo toxic effects of the 2 BDF diastereomer pairs. In adult Sprague-Dawley rats BDF-cis was significantly more toxic than BDF-trans (LD₅₀ values of 219 versus 316 μg/kg, respectively) while racemic BDF had intermediate potency (266 μg/kg). In adult New Zealand white rabbits, BDF-cis had a longer half-life than BDF-trans which could contribute to its observed increased toxicity. Lastly, BDF-cis (10 μM), but not BDF-trans, damaged cultured SH-SY5Y human neuroblastoma cells by attenuating mitochondrial reductive capacity. Taken together, these data suggest that different toxic manifestations of BDF poisoning in mammals could be attributed, in part, to differences in relative enantiomer concentrations present in racemic formulations of this commercially-available toxicant.

Distinction of synthetic dl-α-tocopherol from natural vitamin E (d-α-tocopherol) by reversed-phase liquid chromatography. Enhanced selectivity of a polymeric C18 stationary phase at low temperature and/or at high pressure

Separation of diastereomers of dl-α-tocopherol was studied by reversed-phase liquid chromatography using three types of stationary phases, polymeric ODS, polymeric C30, and monomeric ODS. Polymeric ODS stationary phase (Inertsil ODS-P, 3mmID, 20cm) was effective for the separation of the isomers created by the presence of three chiral centers on the alkyl chain of synthetic dl-α-tocopherol. Considerable improvement of the separation of isomers was observed on ODS-P phase at high pressure and at low temperature. Complete separation of four pairs of diastereomers was achieved at 12.0°C, 536bar, while three peaks were observed when the separation was carried out either at 12.0°C at low pressure or at 20°C at 488bar. Higher temperature (30.0°C) with the ODS-P phase resulted in only partial separation of the diastereomers even at high pressure. Only slight resolution was observed for the mixture of diastereomers with the C30 stationary phase (Inertsil C30) at 12.0°C and 441bar, although the stationary phase afforded greater resolution for β- and γ-tocopherol than ODS-P. A monomeric C18 stationary phase did not show any separation at 12.0°C and 463bar. The results suggest that the binding site of the polymeric ODS-P phase is selective for flexible alkyl chains that provided the longest retention for the natural form, (R,R,R) form, and the enantiomer, (S,S,S) form, of dl-α-tocopherol.

D-Amino acids incorporation in the frog skin-derived peptide esculentin-1a(1-21)NH2 is beneficial for its multiple functions

Naturally occurring antimicrobial peptides (AMPs) represent promising future antibiotics. We have previously isolated esculentin-1a(1-21)NH2, a short peptide derived from the frog skin AMP esculentin-1a, with a potent anti-Pseudomonal activity. Here, we investigated additional functions of the peptide and properties responsible for these activities. For that purpose, we synthesized the peptide, as well as its structurally altered analog containing two D-amino acids. The peptides were then biophysically and biologically investigated for their cytotoxicity and immunomodulating activities. The data revealed that compared to the wild-type, the diastereomer: (1) is significantly less toxic towards mammalian cells, in agreement with its lower α-helical structure, as determined by circular dichroism spectroscopy; (2) is more effective against the biofilm form of Pseudomonas aeruginosa (responsible for lung infections in cystic fibrosis sufferers), while maintaining a high activity against the free-living form of this important pathogen; (3) is more stable in serum; (4) has a higher activity in promoting migration of lung epithelial cells, and presumably in healing damaged lung tissue, and (5) disaggregates and detoxifies the bacterial lipopolysaccharide (LPS), albeit less than the wild-type. Light scattering studies revealed a correlation between anti-LPS activity and the ability to disaggregate the LPS. Besides shedding light on the multifunction properties of esculentin-1a(1-21)NH2, the D-amino acid containing isomer may serve as an attractive template for the development of new anti-Pseudomonal compounds with additional beneficial properties. Furthermore, together with other studies, incorporation of D-amino acids may serve as a general approach to optimize the future design of new AMPs.

1,2-Dibromo-4-(1,2 dibromoethyl) cyclohexane (TBECH)-mediated steroid hormone receptor activation and gene regulation in chicken LMH cells

The incorporation of brominated flame retardants into industrial and household appliances has increased their occurrence in the environment, resulting in deleterious effects on wildlife. With the increasing restraints on available compounds, there has been a shift to using brominated flame retardants that has seen the production of alternative brominated flame retardants such as 1,2-dibromo-4-(1,2 dibromoethyl) cyclohexane (TBECH), which has been detected in the environment. In previous in silico and in vitro studies the authors have shown that TBECH can activate both the human androgen receptor (hAR) and the zebrafish AR (zAR) suggesting that it is a potential endocrine disruptor. The present study was aimed at determining the interaction of TBECH with the chicken AR (cAR). In the present study, TBECH bound to cAR, but in vitro activation assay studies using the chicken LMH cell line showed it had a potency of only 15% compared with testosterone. Sequence difference between ARs from different species may contribute to the different responses to TBECH. Further quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) analysis showed that TBECH interacted with and altered the expression of both thyroid receptors and estrogen receptors. In addition, the qRT-PCR analysis showed that TBECH altered the transcription pattern of genes involved in inflammatory, apoptotic, proliferative, DNA methylation, and drug-metabolizing pathways. This demonstrates that TBECH, apart from activating cAR, can also influence multiple biological pathways in the chicken.