2,3-di-O-methoxymethyl-6-O-tert-butyldimethylsilyl-beta-cyclodextrin, a useful stationary phase for gas chromatographic separation of enantiomers

Enantiomeric analysis of γ(δ)-lactones by reversed phase high performance liquid chromatography using amylose tris(5-chloro-2-methylphenylcarbamate) as stationary phase

A Chiralpak AY-3R column was investigated for analytical enantiomeric separation of twelve racemic γ(δ)-lactones using reversed phase high performance liquid chromatography. Main influence factors, including organic modifier, flow rate and column temperature, were optimized. Five kinds of γ(δ)-lactones were successfully enantioseparated using the established method: γ-nonanolactone, δ-decalactone, δ-undecalactone, δ-dodecalactone and δ-tetradecalactone. Under optimized conditions, enantiomeric peak resolution (Rs) for the five γ(δ)-lactones reached more than 1.09, 1.08, 1.54, 1.43, and 1.11, respectively. Their chromatographic elution behavior was investigated using Van't Hoff equation and Van Deemter equation. It was found that an exothermic process occurred during enantiomeric separation of γ(δ)-lactones using this chromatographic column, and it showed a typical Van Deemter curve. Finally, this method was applied in enantiomeric ratio analysis of γ(δ)-lactones contents for purchased butter samples, and results confirmed the predominant content of the (R)-configuration of δ-dodecalactone in natural animal butter, while in margarine, an equal proportion of (R/S)-configuration of δ-dodecalactone was detected.

Study of Volatile Secondary Metabolites Present in Piper carpunya Leaves and in the Traditional Ecuadorian Beverage Guaviduca

Piper carpunya Ruiz & Pav. is an aromatic shrub native to Ecuador, the leaves of which are used to prepare the traditional beverage Guaviduca. Different health benefits are attributed to the guaviduca beverage, which is consumed as a traditional and folk medicine. In this study, fresh P. carpunya leaves were collected in the winter and summer and subjected to hydrodistillation for the extraction of the essential oil. The guaviduca beverage was prepared by infusion in water and the volatile compounds were isolated by liquid–liquid extraction. Chemical composition and enantioselective analyses were performed by gas chromatography. The antibacterial activity was assayed against Gram-positive and Gram-negative bacteria. The scavenging radical properties of the essential oil was evaluated by 2,2-diphenyl-1-picrylhydryl (DPPH) and 2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. The acetylcholinesterase inhibitory activity was measured using the spectrophotometric method. The chemical analysis allowed us to identify more than 98% of the compounds in all samples. The main constituent of the essential oil was 1,8-cineole (25.20 ± 1.31%) in P. carpunya collected in winter and (17.45 ± 2.33%) in P. carpunya collected in summer, while in the beverage, there was 14 mg/L. Safrole was identified in the essential oil (PCW 21.91 ± 2.79%; PCS 13.18 ± 1.72%) as well as in the beverage (2.43 ± 0.12 mg/L). Enantioselective analysis was used to investigate the enantiomeric ratio and excess of four chiral components. The essential oil presented a strong activity against Klebsiella pneumoniae with a MIC of 500 μg/mL and a very strong anticholinesterase activity with an IC₅₀ of 36.42 ± 1.15 µg/mL.

Facile synthesis of per(6-O-tert-butyldimethylsilyl)-α-, β-, and γ-cyclodextrin as protected intermediates for the functionalization of the secondary face of the macrocycles

Per(6-O-tert-butyldimethylsilyl)-α-, β- and γ-cyclodextrin derivatives are well-known as synthetic intermediates that enable the selective mono-, partial, or perfunctionalization of the secondary face of the macrocycles. Although silylation of the primary rim is readily achieved by treatment with tert-butyldimethylsilyl chloride in the presence of pyridine (either alone or mixed with a co-solvent), the reaction typically results in a mixture containing both under- and oversilylated byproducts that are difficult to remove. To address this challenge in preparing a pure product in high yield, we describe an approach that centers on the addition of a controlled excess of silylating agent to avoid the presence of undersilylated species, followed by the removal of oversilylated species by column chromatography elution with carefully designed solvent mixtures. This methodology works well for 6-, 7-, and 8-member rings (α-, β-, and γ-cyclodextrins, respectively) and has enabled us to repeatedly prepare up to ⁓35 g of ≥98% pure product (as determined by HPLC) in 3 d. We also provide procedures for lower-scale reactions, as well as an example of how the β-cyclodextrin derivative can be used for functionalization of the secondary face of the molecule.

Chirality: An Important Phenomenon Regarding Biosynthesis, Perception, and Authenticity of Flavor Compounds

Chirality plays an important role in flavor research. This will be outlined using selected examples from the key areas analysis, authenticity assessment, biogenesis, and odor perception. Developments of analytical techniques, in particular the use of chiral stationary phases in capillary gas chromatography, enabled the determination of naturally occurring configurations of chiral volatiles at trace levels. Thus, knowledge of pathways and enzymes involved in the biogenesis of chiral substances was acquired, and enantioselective analysis has become a prominent tool in the authenticity assessment of flavorings. Increasing information is also available on structure-odor relationships of chiral flavor compounds and the influence of their configurations on odor thresholds and odor properties. A substantial extension of these data sets and a further understanding of the role of chirality in the perception of aroma compounds is expected from studies on the enantioselectivity of odorant receptor systems. Developments in these areas will be put into a historical perspective, recent progress will be emphasized, and data gaps will be described.

Analysis and Sensory Evaluation of the Stereoisomers of a Homologous Series (C5-C10) of 4-Mercapto-2-alkanols

A homologous series of 4-mercapto-2-alkanols (C5-C10) was used to investigate the impact of the stereochemistry on the sensory properties of a class of naturally occurring polyfunctional thiols having a 1,3-oxygen-sulfur functionality. Stereoisomers were obtained via syntheses of racemic mixtures and subsequent lipase-catalyzed kinetic resolutions. Analytical separations of the stereoisomers were achieved by capillary gas chromatography (GC) using chiral stationary phases. The absolute configurations were assigned via NMR analysis. Sensory evaluations by means of GC/olfactometry revealed odor threshold minima for the medium-chain homologues (C7-C9) of the 4-mercapto-2-alkanol stereoisomers. Except for the C5 homologue, the lowest odor thresholds were determined for the (2R,4R)-configured stereoisomers. The variability in odor qualities was mainly determined by the chain length. None of the 4-mercapto-2-alkanol stereoisomers showed consistent odor qualities for all homologues.

Enantioselective analysis of secondary alcohols and their esters in purple and yellow passion fruits

The enantiomeric compositions of the acetates, butanoates, hexanoates, and octanoates of the secondary alcohols 2-pentanol, 2-heptanol, and 2-nonanol were determined in yellow (Passiflora edulis f. flavicarpa) and purple (Passiflora edulis Sims) passion fruits. The compounds were isolated by means of simultaneous distillation-extraction. Enantiodifferentiation was performed via multidimensional gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-beta-cyclodextrin as chiral stationary phase. The series of homologous 2-alkyl esters, which are typical constituents of purple passion fruits, were shown to be present as nearly optically pure (R)-enantiomers. The proportions of the (S)-enantiomers varied in different batches and were dependent on the alcohol moieties of the esters. For minor amounts of esters detected in yellow fruits, the (R)-enantiomers were also dominating. However, the enantiomeric excesses were significantly lower than in the purple variety. Enantioselective analysis of the free alcohols revealed that 2-heptanol exhibited opposite configurations in purple and yellow passion fruits. A similar phenomenon was observed for 2-pentanol, which was present in the yellow fruits as a nearly racemic mixture. Data determined in extracts obtained by other techniques (liquid-liquid extraction, vacuum headspace technique) showed that the isolation procedure had no significant impact on the enantiomeric ratios.