Enantiomeric Discrimination of Isoxazoline Fused β‐amino Acid Derivatives using (18‐Crown‐6)‐2,3,11,12‐tetracarboxylic Acid as a Chiral NMR Solvating Agent

(18‐Crown‐6)‐2,3,11,12‐tetracarboxylic acid is a useful chiral NMR solvating agent for isoxazoline‐fused β‐amino acid derivatives. Isoxazoline substrates are analyzed as their hydrochloride salts in methanol‐d₄. The crown ether and substrate associate through the formation of three hydrogen bonds between the protonated amine and crown ether oxygen atoms. Enantiomeric discrimination is observed for two or more resonances of every substrate. At least one of these resonances is free of overlap with other resonances in the spectrum and has large enough enantiomeric discrimination to enable the determination of enantiomeric purity. 2D COSY methods can be used to identify additional resonances that exhibit enantiomeric discrimination in the NMR spectrum. Chirality, 25:48‐53, 2013.© 2012 Wiley Periodicals, Inc.     

Development of HPLC Chiral Stationary Phases Based on (+)‐(18‐Crown‐6)‐2,3,11,12‐tetracarboxylic Acid and Their Applications

Crown ether‐based chiral stationary phases (CSPs) have been known to be useful for the resolution of racemic primary amino compounds. In particular, CSPs based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid have been reported to be useful for the resolution of secondary amino compounds as well as primary amino compounds. In this article, the process of developing various CSPs based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid to improve the chiral recognition efficiency and/or the stability of the CSPs and their applications to the resolution of various primary and nonprimary amino compounds are reviewed. Chirality 27:576–588, 2015. © 2015 Wiley Periodicals, Inc.     

Comparison of Chiral Separations of Aminophosphonic Acids and Their Aminocarboxylic Acid Analogs Using a Crown Ether Column

Crown ethers are capable of complexing with primary amines and have been utilized in chromatography to separate amino acid racemates. This application has been extended to resolve (1‐amino‐1‐phenylmethyl)phosphonic acid and (1‐aminoethyl)phosphonic acid racemates, along with their aminocarboxylic acid analogs (2‐phenylglycine and alanine, respectively), via a ChiroSil RCA crown ether based chiral stationary phase. Effects of the organic modifier, temperature, and acid type and concentration on retention and selectivity were also investigated. Trends in retention and selectivity varied between aminophosponic acids and their aminocarboxylic analogs. Computer modeling and ¹H NMR analyses were performed to potentially gain a better understanding of interactions of the aforementioned molecules with the ChiroSil RCA chiral stationary phase. Theoretical predictions of the most stable conformations for (R)‐ and (S)‐enantiomers were compared to elution order; it was found that the elution order agreed with molecular modeling such that the longest retention correlated with the predicted most stable complex between the enantiomer and crown ether. ¹H NMR demonstrated interactions of aminophosphonic and aminocarboxylic racemates with (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid in solution and was utilized to determine enantiomeric excess of (1‐amino‐1‐phenylmethyl)phosphonic acid after its enantioenrichment via crystallization through diastereomeric salt formation with the crown ether followed by filtration. Chirality 25:369–378, 2013. © 2013 Wiley Periodicals, Inc.     

Liquid chromatographic direct resolution of flecainide and its analogs on a chiral stationary phase based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid

Flecainide, an antiarrythmic agent, and its analogs were resolved on a high performance liquid chromatographic chiral stationary phase (CSP) based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid with the use of a mobile phase consisting of methanol‐acetonitrile‐trifluoroacetic acid‐triethylamine (80/20/0.1/0.3, v/v/v/v). The chiral resolution was quite successful, the separation factors (α) and the resolutions (R_S) for 20 analytes including flecainide being in the range of 1.19–1.82 and 1.73–6.80, respectively. The ortho‐substituent of the benzoyl group of analytes was found to cause decrease in the retention times of analytes probably because of the conformational deformation of analytes originated from the steric hindrance exerted by the ortho‐substituent. Chirality, 2010. © 2009 Wiley‐Liss, Inc.     

Chiral NMR discrimination of amines: analysis of secondary, tertiary, and prochiral amines using (18-crown-6)-2,3,11,12-tetracarboxylic acid

Enantiomeric discrimination is observed in the 1H and 13C NMR spectra of secondary and tertiary amines in the presence of (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid (1). Nonequivalence of the resonances of prochiral nuclei in primary and secondary amines is also observed when they associate with 1. The amines are added in their neutral form and are protonated by the carboxylic acid groups of 1 to produce the corresponding ammonium and carboxylate ions. Secondary amines associate with 1 through two hydrogen bonds and an ion pair interaction. Tertiary amines can only form one hydrogen bond to accompany the ion pairing. Chiral discrimination in the 1H and 13C NMR spectra of a series of aryl-containing secondary amines is of sufficient magnitude to determine enantiomeric purities. The discrimination in the spectra of tertiary amines with 1 is smaller, but 13C NMR spectra provided enough distinction for the determination of enantiomeric purity.     

Preparation and Studies of Chiral Stationary Phases Containing Enantiopure Acridino‐18‐Crown‐6 Ether Selectors

The enantiomeric separation ability of the newly prepared chiral stationary phases containing acridino‐18‐crown‐6 ether selectors was studied by high‐performance liquid chromatography (HPLC). The chiral stationary phases separated the enantiomers of selected protonated primary aralkylamines efficiently. The best results were found for the separation of the mixtures of enantiomers of NO₂‐PEA. Chirality 26:651–654, 2014. © 2014 Wiley Periodicals, Inc.     

Enantiomeric separation of Novel Psychoactive Substances by capillary electrophoresis using (+)‐18‐crown‐6‐tetracarboxylic acid as chiral selector

In the recent years, hundreds of Novel Psychoactive Substances (NPS) have entered both the European and the global drug market. These drugs, which are mainly used for recreational matters, have caused serious social problems. Every year, the spectrum of these misused drugs is enlarged by new derivatives, which are produced by modifications of basic structures of already well‐known substances. Additionally, a lot of them possess a stereogenic center which leads to 2 enantiomeric forms. The fact that the pharmacological effects and potencies of the enantiomers of these chiral NPS may differ can be assumed from a broad spectrum of active pharmaceutical ingredients. For this reason, analytical method development regarding enantiomeric separation for these classes of substances is of great pharmaceutical and medical interest. The aim of this work was to create an easy‐to‐prepare chiral capillary electrophoresis method for the enantioseparation of NPS which contains a primary amino group by means of (+)‐18‐crown‐6‐tetracarboxylic acid as chiral selector. Novel Psychoactive Substances were purchased at various Internet stores or represent samples seized by Austrian police. The effects of selector concentration, the electrolyte composition, and the addition of organic modifiers to the background electrolyte on enantioseparation were investigated. Under optimized conditions, the use of 20‐mM (+)‐18‐crown‐6‐tetracarboxylic acid, 10‐mM Tris, and 30‐mM citric acid buffer at pH 2.10 turned out to be effective. Fifteen of 24 tested NPS were resolved in their enantiomers within 15 minutes. It was found that all NPS were traded as racemic mixtures.     

High‐Performance Liquid Chromatographic Enantioseparation of Unusual Isoxazoline‐Fused 2‐Aminocyclopentanecarboxylic Acids on (+)‐(18‐Crown‐6)‐2,3,11,12‐Tetracarboxylic Acid‐Based Chiral Stationary Phases

The enantiomers of four unusual isoxazoline‐fused 2‐aminocyclopentanecarboxylic acids were directly separated on chiral stationary phases containing (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid as chiral selector. The nature of the alcoholic modifier (MeOH, EtOH, IPA) exerted a great effect on the retention, whereas the selectivity and resolution did not change substantially. Two types of dependence of retention on alcohol content were detected: k₁ increased continuously with increasing alcohol content or a U‐shaped retention curve was observed. A comparison of the chromatographic data obtained with HCOOH, AcOH, TFA, HClO₄, H₂SO₄, or H₃PO₄ as acidic modifier at a constant concentration demonstrated that in most cases, larger k values were obtained on the application of AcOH or HCOOH, and an increase of the acid content resulted in a decrease of retention. Some mechanistic aspects of the chiral recognition process are discussed with respect to the structures of the analytes and selector. The sequence of elution of the enantiomers was determined in all cases. Chirality 24:817‐824, 2012. © 2012 Wiley Periodicals, Inc.     

Water‐soluble calix[4]resorcinarenes as chiral NMR solvating agents for bicyclic aromatic compounds

Water‐soluble calix[4]resorcinarenes with proline, 3‐hydroxyproline, and 4‐hydroxyproline substituent groups are evaluated as chiral NMR solvating agents on a series of bicyclic aromatic compounds with naphthyl, indole, dihydroindole, and indane rings. The substrates interact with the calixresorcinarene through insertion of the aromatic ring into the cavity. Most of the substrates are analyzed as cationic species, although one anionic species is analyzed. All of the substrates exhibit enantiomeric discrimination in the ¹H‐NMR spectrum with one or more of the calixresorcinarenes. In most cases, the hydroxyproline derivatives are more effective at causing enantiodifferentiation than the corresponding proline derivative. Presumably, the hydroxyl group on the proline moieties is involved in interactions with the substituent groups of the substrate that are important in creating chiral recognition. The enantiomeric discrimination in the ¹H‐NMR spectrum is large enough for many resonances to permit the analysis of enantiomeric purity. Chirality 2009. © 2009 Wiley‐Liss, Inc.     

Liquid Chromatographic Resolution of Mexiletine and Its Analogs on Crown Ether‐Based Chiral Stationary Phases

Mexiletine, an effective class IB antiarrhythmic agent, and its analogs were resolved on three different crown ether‐based chiral stationary phases (CSPs), one (CSP 1 ) of which is based on (+)‐(18‐crown‐6)‐2,3,11,12‐tetracarboxylic acid and the other two (CSP 2 and CSP 3 ) are based on (3,3’‐diphenyl‐1,1’‐binaphthyl)‐20‐crown‐6. Mexiletine was resolved with a resolution (R_S) of greater than 1.00 on CSP 1 and CSP 3 containing residual silanol group‐protecting n‐octyl groups on the silica surface, but with a resolution (R_S) of less than 1.00 on CSP 2 . The chromatographic behaviors for the resolution of mexiletine analogs containing a substituted phenyl group at the chiral center on the three CSPs were quite dependent on the phenoxy group of analytes. Namely, mexiletine analogs containing 2,6‐dimethylphenoxy, 3,4‐dimethylphenoxy, 3‐methylphenoxy, 4‐methylphenoxy, and a simple phenoxy group were resolved very well on the three CSPs even though the chiral recognition efficiencies vary with the CSPs. However, mexiletine analogs containing 2‐methylphenoxy group were not resolved at all or only slightly resolved. Among the three CSPs, CSP 3 was found to show the highest chiral recognition efficiencies for the resolution of mexiletine and its analogs, especially in terms of resolution (R_S). Chirality 26:272–278, 2014. © 2014 Wiley Periodicals, Inc.     

Crystallographic studies for the chiral recognition of the novel chiral stationary phase derived from (+)‐(R)‐18‐crown‐6 tetracarboxylic acid

Chiral discrimination observed in high‐performance liquid chromatography (HPLC) with the novel chiral stationary phase (CSP‐18C6I) derived from (+)‐(R)‐18‐crown‐6 tetracarboxylic acid [(+)‐18C6H₄] was investigated by X‐ray crystallographic analysis of the complex composed of the R‐enantiomer of 1‐(1‐naphthyl)ethylamine (1‐NEA) and (+)‐18C6H₄. Mixtures of 1‐NEA (the R‐ or S‐enantiomer) and (+)‐18C6H₄ were dissolved in methanol‐water (1:1) solution and allowed to stand for crystallization. The R‐enantiomer crystallized with (+)‐18C6H₄ as a co‐crystal, although the S‐enantiomer did not. This result was in good agreement with the enantiomer elution order of 1‐NEA in CSP‐18C6I. The apparent binding constants (K_a) of the enantiomers to the (+)‐18C6H₄ obtained from ¹H‐NMR experiments also supported the above‐mentioned result. The X‐ray crystal structure of the 1:1 complex of the R‐enantiomer and (+)‐18C6H₄ indicated the four sets of hydrogen bond association between the naphthylethylammonium cation and oxygen of polyether ring or carbonyl group of (+)‐18C6H₄. Chirality 11:173–178, 1999. © 1999 Wiley‐Liss, Inc.     

Simple Resolution of Enantiomeric NMR Signals of α‐Amino Acids by Using Samarium(III) Nitrate With L‐Tartarate

Readily available L‐tartaric acid, which is a bidentate ligand with two chiral centers forming a seven‐membered chelate ring, was applied to the chiral ligand for the chiral nuclear magnetic resonance (NMR) shift reagent of samarium(III) formed in situ. This simple method does not cause serious signal broadening in the high magnetic field. Enantiomeric ¹³C and ¹H NMR signals and enantiotopic ¹H NMR signals of α‐amino acids were successfully resolved at pH 8.0 and the 1:3 molar ratio of Sm(NO₃)₃:L‐tartaric acid. It is elucidated that the enantiomeric signal resolution is attributed to the anisotropic magnetic environment for the enantiomers induced by the chiral L‐tartarato samarium(III) complex rather than differences in stability of the diastereomeric substrate adducts. The present ¹³C NMR signal resolution was also effective for the practical simultaneous analysis of plural kinds of DL‐amino acids. Chirality 27:353–357, 2015.© 2015 Wiley Periodicals, Inc.     

Solution NMR resonance assignment strategies for β‐barrel membrane proteins

Membrane proteins in detergent micelles are large and dynamic complexes that present challenges for solution NMR investigations such as spectral overlap and line broadening. In this study, multiple methods are introduced to facilitate resonance assignment of β‐barrel membrane proteins using Opa₆₀ from Neisseria gonorrhoeae as a model system. Opa₆₀ is an eight‐stranded β‐barrel with long extracellular loops (～63% of the protein) that engage host receptors and induce engulfment of the bacterium. The NMR spectra of Opa₆₀ in detergent micelles exhibits significant spectral overlap and resonances corresponding to the loop regions had variable line widths, which interfered with a complete assignment of the protein. To assign the β‐barrel residues, trypsin cleavage was used to remove much of the extracellular loops while preserving the detergent solubilized β‐barrel. The removal of the loop resonances significantly improved the assignment of the Opa₆₀ β‐barrel region (97% of the resonances corresponding to the β‐barrel and periplasmic turns were assigned). For the loop resonance assignments, two strategies were implemented; modulating temperature and synthetic peptides. Lowering the temperature broadened many peaks beyond detection and simplified the spectra to only the most dynamic regions of the loops facilitating 27 loop resonances to be assigned. To further assign functionally important and unstructured regions of the extracellular loops, a synthetic 20 amino acid peptide was synthesized and had nearly complete spectral overlap with the full‐length protein allowing 17 loop resonances to be assigned. Collectively, these strategies are effective tools that may accelerate solution NMR structure determination of β‐barrel membrane proteins.     

Preparative Enantioseparation of β‐Substituted‐2‐Phenylpropionic Acids by Countercurrent Chromatography With Substituted β‐Cyclodextrin as Chiral Selectors

Preparative enantioseparation of four β‐substituted‐2‐phenylpropionic acids was performed by countercurrent chromatography with substituted β‐cyclodextrin as chiral selectors. The two‐phase solvent system was composed of n‐hexane‐ethyl acetate‐0.10 mol L‐1 of phosphate buffer solution at pH 2.67 containing 0.10 mol L^‐1 of hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) or sulfobutylether‐β‐cyclodextrin (SBE‐β‐CD). The influence factors, including the type of substituted β‐cyclodextrin, composition of organic phase, concentration of chiral selector, pH value of the aqueous phase, and equilibrium temperature were optimized by enantioselective liquid–liquid extraction. Under the optimum separation conditions, 100 mg of 2‐phenylbutyric acid, 100 mg of tropic acid, and 50 mg of 2,3‐diphenylpropionic acid were successfully enantioseparated by high‐speed countercurrent chromatography, and the recovery of the (±)‐enantiomers was in the range of 90–91% for (±)‐2‐phenylbutyric acid, 91–92% for (±)‐tropic acid, 85–87% for (±)‐2,3‐diphenylpropionic acid with purity of over 97%, 96%, and 98%, respectively. The formation of 1:1 stoichiometric inclusion complex of β‐substituted‐2‐phenylpropionic acids with HP‐β‐CD was determined by UV spectrophotometry and the inclusion constants were calculated by a modified Benesi‐Hildebrand equation. The results showed that different enantioselectivities among different racemates were mainly caused by different enantiorecognition between each enantiomer and HP‐β‐CD, while it might be partially caused by different inclusion capacity between racemic solutes and HP‐β‐CD. Chirality 27:795–801, 2015. © 2015 Wiley Periodicals, Inc.     

The determination of enantiomer composition of 1‐((3‐chlorophenyl)‐(phenyl)methyl) amine and 1‐((3‐chlorophenyl)(phenyl)‐methyl) urea (Galodif) by NMR spectroscopy,chiral HPLC,and polarimetry

For the first time, a method for enantiomer resolution of the anticonvulsant Galodif (1‐((3‐chlorophenyl)(phenyl)methyl) urea) by chiral HPLC was developed, whereas the enantiomeric composition of 1‐((3‐chlorophenyl)(phenyl)methyl) amine—precursor in Galodif synthesis—cannot be resolved by this method. However, starting 1‐((3‐chlorophenyl)(phenyl)methyl) amine quantitatively forms diastereomeric N‐((3‐chlorophenyl)(phenyl)methyl)‐1‐camphorsulfonamides in reaction with chiral (1R)‐(+)‐ or (1S)‐(?)‐camphor‐10‐sulfonyl chlorides. The diastereomeric ratio of obtained camphorsulfonamides can be easily determined by NMR ¹H and ¹³C spectroscopy. The DFT calculations of specific rotation of Galodif enantiomers showed good agreement with experimental data. The absolute configuration of enantiomers was proposed for the first time.     

Isostructural unbranched alkyl‐chains as tools for stabilizing β‐turn structure

To investigate the structural role played by isostructural unbranched alkyl‐chains on the conformational ensemble and stability of β‐turn structures, the conformational properties of a designed model peptide: Plm‐Pro‐Gly‐Pda ( 1 , Plm: H₃C—(CH₂)₁₄—CONH—; Pda: —CONH— (CH₂)₁₄—CH₃) have been examined and compared with the parent peptide: Boc‐Pro‐Gly‐NHMe ( 2 , Boc: tert‐butoxycarbonyl; NHMe: N‐methylamide). The characteristic ¹³C NMR chemical‐shifts of the Pro C^β and C^γ resonances ascertained the incidence of an all‐trans peptide‐bond in low polarity deuterochloroform solution. Using FTIR and ¹H NMR spectroscopy, we establish that apolar alkyl‐chains flanking a β‐turn promoting Pro‐Gly sequence impart definite incremental stability to the well‐defined hydrogen‐bonded structure. The assessment of ¹H NMR derived thermodynamic parameters of the hydrogen‐bonded amide‐NHs via variable temperature indicate that much weaker hydrophobic interactions do contribute to the stability of folded reverse turn structures. The far‐UV CD spectral patterns of 1 and 2 in 2,2,2‐trifluoroethanol are consistent with Pro‐Gly specific type II β‐turn structure, concomitantly substantiate that the flanking alkyl‐chains induce substantial bias in enhanced β‐turn populations. In view of structural as well as functional importance of the Pro‐Gly mediated secondary structures, besides biochemical and biological significance of proteins lipidation via myristoylation or palmytoilation, we highlight potential convenience of the unbranched Plm and Pda moieities not only as main‐chain N‐ and C‐terminal protecting groups but also to mimic and stabilize specific isolated secondary and supersecondary structural components frequently observed in proteins and polypeptides. © 2013 Wiley Periodicals, Inc. Biopolymers 99: 419–426, 2013.     

β‐Amino acids containing peptides and click‐cyclized peptide as β‐turn mimics: a comparative study with ‘conventional’ lactam‐ and disulfide‐bridged hexapeptides

The increasing interest in click chemistry and its use to stabilize turn structures led us to compare the propensity for β‐turn stabilization of different analogs designed as mimics of the β‐turn structure found in tendamistat. The β‐turn conformation of linear β‐amino acid‐containing peptides and triazole‐cyclized analogs were compared to ‘conventional’ lactam‐ and disulfide‐bridged hexapeptide analogs. Their 3D structures and their propensity to fold in β‐turns in solution, and for those not structured in solution in the presence of α‐amylase, were analyzed by NMR spectroscopy and by restrained molecular dynamics with energy minimization. The linear tetrapeptide Ac‐Ser‐Trp‐Arg‐Tyr‐NH₂ and both the amide bond‐cyclized, c[Pro‐Ser‐Trp‐Arg‐Tyr‐D ‐Ala] and the disulfide‐bridged, Ac‐c[Cys‐Ser‐Trp‐Arg‐Tyr‐Cys]‐NH₂ hexapeptides adopt dominantly in solution a β‐turn conformation closely related to the one observed in tendamistat. On the contrary, the β‐amino acid‐containing peptides such as Ac‐(R)‐β³‐hSer‐(S)‐Trp‐(S)‐β³‐hArg‐(S)‐β³‐hTyr‐NH₂, and the triazole cyclic peptide, c[Lys‐Ser‐Trp‐Arg‐Tyr‐βtA]‐NH₂, both specifically designed to mimic this β‐turn, do not adopt stable structures in solution and do not show any characteristics of β‐turn conformation. However, these unstructured peptides specifically interact in the active site of α‐amylase, as shown by TrNOESY and saturation transfer difference NMR experiments performed in the presence of the enzyme, and are displaced by acarbose, a specific α‐amylase inhibitor. Thus, in contrast to amide‐cyclized or disulfide‐bridged hexapeptides, β‐amino acid‐containing peptides and click‐cyclized peptides may not be regarded as β‐turn stabilizers, but can be considered as potential β‐turn inducers. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

An improved method for determining enantiomeric excess by 13C‐NMR in chiral liquid crystal media

By using a combination of inverse gated ¹H decoupled ¹³C‐NMR experiments 1 with short acquisition times and NMR Cryo‐probe technology, the sample requirements and experimental times necessary to accurately measure enantiomeric excess of small chiral molecules has been reduced 16‐fold. Quality ¹³C‐NMR spectra can now be obtained from a 1 to 5 mg sample in 12 minutes. The enantiomeric excess determination achieved from the average integration of all the ¹³C‐resonances in the spectrum is comparable to enantiomeric excess measured by chiral SFC. The advantage of the NMR method is that enantiomeric excess can rapidly be measured in situ on practical amounts of enantioselective reaction products without the need for chromatographic separation or chemical modification and with substantially less solvent waste. Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Screening Approach for Chiral Separation of β‐Aminoketones by HPLC on Various Polysaccharide‐Based Chiral Stationary Phases

Nine β‐aminoketones were synthesized via Mannich reaction when benzaldehyde was condensed with some primary amines and acetophenone. The purified compounds were identified by using spectroscopic methods. The enantiomeric separation of these derivatives was carried out by high‐performance liquid chromatography (HPLC) using several coated and immobilized polysaccharide stationary phases, namely, Chiralcel^® OD‐H, Chiralcel^® OD, Chiralcel^® OJ, Chiralpak^® AD, Chiralpak^® IA, and Chiralpak^® IB using different mobile phases composed of n‐hexane and alcohol mixed in various ratios or pure ethanol or isopropanol. The retention behavior and selectivity of these chiral stationary phases were examined in isocratic normal phase mode. The results indicate that cellulose derivatives have higher enantioselectivity than amylose derivatives for the separation of racemic β‐amino ketones. Chirality 27:332–338, 2015. © 2015 Wiley Periodicals, Inc.     

Supramolecular interaction of 18‐crown‐6 ether with mesalazine and spectrofluorimetric determination of mesalazine in pharmaceutical formulations

The supramolecular interaction of protonated mesalazine (MSZ) and 18‐crown‐6 ether (18C6) has been examined by Ultraviolet–visible, FT‐IR and fluorescence spectroscopy. The formation of the inclusion complex has been confirmed based on the changes of the spectral properties. The MSZ–18C6 host–guest complex formed in (1:1) stoichiometry and the inclusion constant (K = 1.411 × 10² L mol^–1) was ascertained by the typical double reciprocal plots. Furthermore, the thermodynamic parameters (ΔG°, ΔH° and ΔS°) of (MSZ‐18C6) were obtained. Based on the remarkable enhancement of the fluorescence intensity of MSZ produced through complex formation, a simple, accurate, rapid and highly sensitive spectrofluorometric method for the determination of MSZ in aqueous solution in the presence of 18C6 was developed. The measurement of relative fluorescence intensity was carried with excitation at 298 nm, emission 410 nm. All variables affecting the reactions were studied and optimized. Beer's law was obeyed in the concentration range of 0.1–0.9 µg/mL. The absorbance was found to increase linearly with increasing concentration of MSZ. The molar absorptivity, Sandell sensitivity, limit of detection (LOD) and limit of quantification (LOQ) were calculated. The validity of the described method was assessed, and the method was successfully applied to the determination of MSZ in its pharmaceutical formulation. In addition, a solid inclusion complex was synthesized by the coprecipitation method. Copyright © 2015 John Wiley & Sons, Ltd.