Diastereoselective and Scalable Synthesis of 6-(S)-Hydroxycannabidivarin

The synthesis of 6-(S)-hydroxycannabidivarin was required to assess its biological activity in the treatment of neurological disorders. A novel and scalable synthesis has been developed where the key step involves a Friedel-Crafts alkylation of phloroglucinol with (1S,2R,5R)-2-hydroxy-2-methyl-5-(prop-1-en-2-yl)cyclohex-3-en-1-ylbenzoate. Careful optimization of the reaction conditions identified trifluoromethanesulfonic acid in isopropyl acetate as the best catalyst/solvent combination, providing optimum regioselectivity, diastereoselectivity, and yield for this step. This enabled the multigram synthesis of 6-(S)-hydroxycannabidivarin in 10 steps from S-(+)-carvone.

Chiral Pyrrolidinium Ionic Liquids with (-)-Borneol Fragment in the Cation - Synthesis, Physicochemical Properties and Application in Diels-Alder Reaction

A series of chiral pyrrolidinium salts containing (1 S)-endo-(-)-born-2-yloxymethyl substituent in the structure of the cation and six different anions: chloride, tetrafluoroborate [BF4 ]- , hexafluorophosphate [PF6 ]- , trifluoromethanesulfonate [OTf]- , bis(trifluoromethylsulfonyl)imide [NTf2 ]- , bis(pentafluoroethylsulfonyl)imide [NPf2 ]- and perfluorobutanesulfonate [C4 FS]- were efficiently prepared and extensively characterized. The enantiomeric purity of them was confirmed by NMR analysis with a chemical shift reagent. All salts were characterized with the specific rotation, the solubility in commonly used solvents, thermal properties, including phase transition temperatures and thermal stability. Salts with [PF6 ]- , [C4 FS]- , [NTf2 ]- and [NPf2 ]- anions were classified as chiral ionic liquids (CILs). Moreover, salts with [NTf2 ]- and [NPf2 ]- anions were in the liquid state at room temperature and below. Therefore, density and dynamic viscosity, the surface tension and the contact angle on three different surfaces were also measured for them. Additionally, these chiral ionic liquids were tested as solvents in Diels-Alder reaction.

Evaluation of new L-amino acids triethanolammonium salts usability for controlling protease activity

Twenty new triethanolammonium amino acid salts (TEA AA) have been prepared from triethanolammonium hydroxide and L-amino acids. The physicochemical properties of TEA AA depended on the applied amino acid. Five of the synthesised salts, i.e. mono- and bis-salts of L-glutamic acid, L-aspartic acid, and TEA salt of l-glutamine were solids with melting points between 127.32 °C to 171.51 °C. The other TEA AA exhibited glass transition temperatures from -68.45 °C for TEA Ser to -6.27 °C for TEA Trp and were assigned as amino acid ionic liquids (AAILs). The TEA His was characterised by the highest thermal stability, with an average temperature of 5 % weight loss at 186.4 °C, whereas the lowest stability was determined for TEA Asp (107.5 °C). The developed salts were tested as reaction medium additives for proteolytic enzymes (papain, subtilisin, bromelain). Most AAILs showed an inhibitory effect on tested proteases but with different mechanisms related to the enzyme substrate specificity and structural diversity. The TEA Ser was the most effective competitive inhibitor (K_i = 0.24 10^-4 mol/L) for bromelain, while TEA Val uncompetitive inhibitor for papain (K_i = 0.25 10^-4 mol/L). The developed TEA AA salts exhibit potential as enzyme-controlling agents for use in industrial processes.

The application of amino acid ionic liquids as additives in the ultrasound-assisted extraction of plant material

The aim of the present study was to determine the antioxidant activity of the aqueous extracts from Lycopodium clavatum, Cetraria islandica and Dipsacus fullonum obtained using aqueous solutions of ionic liquids by the ultrasound-assisted extraction (IL-UAE) method. Triethanolammonium salts [TEAH]⁺[AA]⁻ of four amino acids of different hydrophobicity – isoleucine – Ile, methionine – Met, threonine – Thr and arginine – Arg, were chosen as ionic liquids, because they are based on natural, bio-renewable raw materials, such as amino acids and contain a pharmaceutically and cosmetically acceptable counterion of triethanolamine. Triethanolammonium salts were synthesized, identified by spectroscopic methods (NMR and FT-IR) and characterized by thermal methods (DSC and TGA). The 2.5% w/v aqueous solutions of triethanolammonium amino acid salts were used as the solvents in combination with ultrasound assisted extraction (UAE). The estimation of antioxidant properties was carried out using the DPPH, FRAP and CUPRAC assays. Total polyphenol content was measured using the reagent Folin–Ciocalteu. The results showed that the use of [TEAH]⁺[Thr]⁻ or [TEAH]⁺[Met]⁻ aqueous solutions increased the antioxidant activity of extracts in comparison to that achieved for extracts with pure water. The use of [TEAH]⁺[Thr]⁻ as an additive for ultrasound-assisted extraction was characterized by obtaining plant extracts with the highest antioxidant potential, even 2.4-fold. The use of the AAIL-UAE method allowed obtaining higher amounts of polyphenols compared to pure water extracts, even 5.5-fold. The used method allowed the extraction of thermosensitive natural compounds, shortened the extraction time and lowered energy consumption.

The antioxidant activity of the aqueous extracts from Lycopodium clavatum, Cetraria islandica and Dipsacus fullonum obtained by ionic liquids and ultrasound-assisted extraction (IL-UAE) method was determined.

Ionic Liquid⁻Ultrasound-Based Extraction of Biflavonoids from Selaginella helvetica and Investigation of Their Antioxidant Activity

As a new and green solvent, ionic liquids (ILs) have received more attention during the green extraction and separation process for natural medicines. In this paper, IL-ultrasound-assisted extraction (IL-UAE) of total biflavonoids (TBFs) from Selaginella helvetica was firstly developed, and different ILs were employed and compared. Based on single-factor experiment, solid⁻liquid ratio (1:10⁻1:14 g/mL), IL concentration (0.6⁻1.0 mmol/mL), and extract temperature (40⁻60 °C) were further explored, according to response surface methodology (RSM), with TBF yields as the index. Moreover, antioxidant activity of TBF extract was analyzed by four methods, i.e., 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzth-iazoline-6-sulphonate (ABTS) free radical scavenging assay, ferric ion reducing power assay, and chelation of ferrous ions assay. The results indicated that [C₆mim]PF₆ had a high selectivity and efficiency. Moreover, important parameters for the extraction process were investigated and optimized. Through parameter optimization (0.8 mmol/L, 250 W, 40 min, 1:12.7 g/mL, and 47 °C), a yield of 18.69 mg/g biflavonoids was obtained from the extract of S. helvetica. Compared with ethanol-UAE, heat-reflux extraction, Soxhlet extraction, and percolation extraction, IL-UAE could not only obtain higher yield in a shorter time, but also reduce the solvent consumption. In addition, TBF extract showed potential antioxidant activity based on the above four antioxidant methods. In short, IL-UAE was first employed to develop a novel and green extraction method for TBF content, and this experiment provides valuable references for further utilization of S. helvetica.

Chiral protic imidazolium salts with a (−)-menthol fragment in the cation: synthesis, properties and use in the Diels–Alder reaction

New chiral protic imidazolium salts containing a (1R,2S,5R)-(−)-menthol substituent in the cation and four different anions (chloride, hexafluorophosphate, trifluoromethanesulfonate and bis(trifluoromethylsulfonyl)imide) were efficiently prepared and extensively characterized. Detailed NMR analysis was performed, and a comparison of the chemical shifts of the protons and carbons of the imidazolium cation as a function of the combined anion was discussed. The specific rotation, solubility in commonly used solvents, thermal properties including phase transition temperatures, and thermal stability were also determined. Three of the synthesized tertiary salts (Cl, PF₆ or OTf anion) were crystalline solids; 1-H-3-[(1R,2S,5R)-(−)-menthoxymethyl]-imidazolium bis(trifluoromethylsulfonyl)imide, (−)[H-Ment-Im][NTf₂] was a liquid at room temperature. The chiral protic salts were used in a Diels–Alder reaction as a test reaction, and the results were compared with those from aprotic chiral ionic liquids having the same chiral substituent in the cation (1R,2S,5R)-(−)-menthol with a bis(trifluoromethylsulfonyl)imide anion. Both protic and aprotic chiral salts, used in a Diels–Alder reaction, were pure (−)-enantiomers, which was determined by NMR with Δ-TRISPHAT tetrabutylammonium salt as a chiral shift reagent. Protic salts offered distinctly higher endo/exo ratios than aprotic ones, but an enantiomeric excess was not obtained. The stereoselectivity reached the same high level even after the fourth recycle of (−)[H-Ment-Im][NTf₂] in the reaction of ethyl-vinyl ketone with cyclopentadiene at temperature of −35 °C.

New chiral protic imidazolium salts from a natural (−)-menthol, their physicochemical properties and catalytic activity in a Diels–Alder reaction.