Sulfobutylation of Beta-Cyclodextrin Enhances the Complex Formation with Mitragynine: An NMR and Chiroptical Study

Mitragynine (MTR), the main indole alkaloid of the well-known plant kratom (Mitragyna speciosa), is one of the most studied natural products nowadays, due to its remarkable biological effects. It is a partial agonist on the opioid receptors, and as such relieves pain without the well-known side-effects of the opioids applied in the clinical practice. MTR and its derivatives therefore became novel candidates for drug development. The poor aqueous solubility and low bioavailability of drugs are often improved by cyclodextrins (CyDs) as excipients through host-guest type complex formation. Among the wide variety of CyDs, sulfobutylether-beta-cyclodextrin (SBEβCyD) is frequently used and official in the European and U.S. Pharmacopoeia. Herein, the host-guest complexation of MTR with βCyD and SBEβCyD was studied using chiroptical and NMR spectroscopy. It was found by NMR measurements that MTR forms a rather weak (logβ11 = 0.8) 1:1 host-guest complex with βCyD, while the co-existence of the 2MTR∙SBEβCyD and MTR∙SBEβCyD species was deducted from 1H NMR titrations in the millimolar MTR concentration range. Sulfobutylation of βCyD significantly enhanced the affinity towards MTR. The structure of the formed inclusion complex was extensively studied by circular dichroism spectroscopy and 2D ROESY NMR. The insertion of the indole moiety was confirmed by both techniques

Comparative analysis of the full set of methylated β-cyclodextrins as chiral selectors in capillary electrophoresis

The chiral separation ability of the full library of methylated-β-cyclodextrins towards pharmacologically significant racemic drugs including basic compounds was studied by chiral capillary electrophoresis. The syntheses of all the methylated, single isomer β-cyclodextrins were revised and optimized and the aqueous solubility of the derivatives was unambiguously established. The three most relevant commercially available methylated isomeric mixtures were also included in the screening, so a total of ten various methylated CDs were investigated. The effects of the selector concentration on the enantiorecognition properties at acidic pH was investigated. Among the dimethylated β-cyclodextrins, the heptakis (2,6-di-O-methyl)-β-cyclodextrin isomer (2,6-DIMEB) resulted the most versatile chiral selector. Terbutaline was selected as a model compound for the in-depth investigation of host-guest enantiodiscrimination ability. The association constants between the two terbutaline enantiomers and 2,6-DIMEB were determined in order to support that the enantioseparation is driven by differences is host-guest-binding. The migration order of the enantiomers was confirmed by performing spiking experiments with the pure enantiomers. 1D and 2D NMR spectroscopy was applied to the 2,3-, and 2,6-DIMEB/terbutaline systems to rationalize at molecular level the different enantioseparation ability of the dimethylated β-cyclodextrin selectors. This article is protected by copyright. All rights reserved

Structural characterization of fondaparinux interaction with per-6-amino-beta-cyclodextrin: an NMR and MS study

The highly anionic synthetic pentasaccharide fondaparinux (FDPX) – representing the antithrombin binding sequence of heparin – is in clinical use as a potent anticoagulant. Contrary to the unfractionated heparin, FDPX lacks potent antidote completely reversing its anticoagulant activity, therefore it is of great importance to identify new structures exhibiting strong intermolecular interactions towards FDPX. The polycationic heptakis(6-amino-6-deoxy)-beta-cyclodextrin (NH2-β-CD) can serve as an excellent model compound to mimic these interactions between the oppositely charged oligosaccharides. Herein, extensive NMR spectroscopic and nano-electrospray ionization mass spectrometric (nESI-MS) studies were conducted to understand the molecular-level interactions in the FDPX - NH2-β-CD systems. NMR experiments were performed at pD 7.4 and 2.0. Job’s method of continuous variation and 1H NMR titration experiments suggested the formation of FDPX∙NH2-β-CD complex at pD 7.4, while the presence of multiple complexes was assumed at pD 2.0. Stability constants were determined by separate 1H NMR titrations, yielding log β11=3.65 ± 0.02 at pD 7.4, while log β11 ≥ 4.9 value suggested a high-affinity system at pD 2.0. 2D NOESY NMR studies indicated spatial proximities between the anomeric resonance α-l-iduronic acid residue and the cyclodextrin’s methylene unit in the proximity of the cationic amino function. Acidic degradation of FDPX was investigated by NMR and MS for the first time in detail confirming that desulfation occurs involving one to two sulfate moieties. The desulfation of FDPX was inhibited by the cationic cyclodextrin in the case of equimolar ratio at pD 2.0. This is the first report on the stabilizing effect of cyclodextrin complexation on heparin degradation

Enantioseparation of solriamfetol and its major impurity phenylalaninol by capillary electrophoresis using sulfated gamma cyclodextrin

R-solriamfetol is a recently approved drug used for the treatment of excessive sleepiness associated with narcolepsy and sleep apnea. Herein, a capillary electrophoretic method was developed, enabling the simultaneous analysis of the API and its S-enantiomer in addition to the enantiomers of its major impurity phenylalaninol. Twenty-nine different cyclodextrins (CDs), including native, neutral, and charged ones were screened as potential chiral selectors, and the best results were obtained with sulfated CDs. Randomly sulfated-β-CD exhibited outstanding enantioresolution, the peaks of phenylalaninol enantiomers inserted between the two peaks of solriamfetol enantiomers, while sulfated-γ-CD (S-γ-CD) showed remarkable resolution values in a much shorter analysis time with the optimal enantiomer migration order. Among the single isomer sulfated CD derivatives, substituent dependent enantiomer migration order reversal could also be observed in the case of heptakis(6-O-sulfo)-β-CD (HS-β-CD) or heptakis(2,3-O-dimethyl-6-O-sulfo)-β-CD (HDMS-β-CD) with R-,S-solriamfetol, and heptakis(2,3-O-diacetyl-6-O-sulfo)-β-CD (HDAS-β-CD) resulting S-,R-solriamfetol migration order. The sulfated-γ-CD system was chosen for method optimization applying orthogonal experimental design. The optimized method (45 mM Tris-acetate buffer, pH 4.5, 4 mM S-γ-CD, 21°C, +19.5 kV) was capable for the baseline separation of solriamfetol and phenylalaninol enantiomers within 7 min. The optimized method was validated according to the ICH guidelines and successfully applied for the analysis of pharmaceutical preparation (Sunosi® 75 mg tablet), thus it may serve as a routine procedure for the laboratories of regulatory authorities as well as in Pharmacopoeias

Sulfobutylation of Beta-Cyclodextrin Enhances the Complex Formation with Mitragynine: An NMR and Chiroptical Study

Mitragynine (MTR), the main indole alkaloid of the well-known plant kratom (Mitragyna speciosa), is one of the most studied natural products nowadays, due to its remarkable biological effects. It is a partial agonist on the opioid receptors, and as such relieves pain without the well-known side-effects of the opioids applied in the clinical practice. MTR and its derivatives therefore became novel candidates for drug development. The poor aqueous solubility and low bioavailability of drugs are often improved by cyclodextrins (CyDs) as excipients through host-guest type complex formation. Among the wide variety of CyDs, sulfobutylether-beta-cyclodextrin (SBEβCyD) is frequently used and official in the European and U.S. Pharmacopoeia. Herein, the host-guest complexation of MTR with βCyD and SBEβCyD was studied using chiroptical and NMR spectroscopy. It was found by NMR measurements that MTR forms a rather weak (logβ11 = 0.8) 1:1 host-guest complex with βCyD, while the co-existence of the 2MTR∙SBEβCyD and MTR∙SBEβCyD species was deducted from 1H NMR titrations in the millimolar MTR concentration range. Sulfobutylation of βCyD significantly enhanced the affinity towards MTR. The structure of the formed inclusion complex was extensively studied by circular dichroism spectroscopy and 2D ROESY NMR. The insertion of the indole moiety was confirmed by both techniques