OBJECTIVE:Liposomes are promising delivery systems for pharmaceutical applications and have been used in medicine in the recent past. Preparation of liposomes requires reliable characterization and quantification of the phospholipid components for which the traditional cumbersome molybdate method is used frequently. The objective was to improve relative and absolute quantification of lipid components from liposomes. METHODS:A reliable method for quantification of lipid composition in liposome formulations in the 1-10 μmol range with 1H- and 31P NMR spectroscopy at 600 MHz has been developed. The method is based on three crystalline small-molecule standards (Ph3PO4, (Tol)3PO4, and Ph3PO) in CDCl3. RESULTS:Excellent calibration linearity and chemical stability of the standards was observed. The method was tested in blind fashion on liposomes containing POPC, PEG-ceramide and a pH-sensitive trans-aminocyclohexanol-based amphiphile (TACH).1 Relative quantification (percentage of components) as well as determination of absolute lipid amount was possible with excellent reproducibility with an average error of 5%. Quantification (triplicate) was accomplished in 15 min based on 1H NMR and in 1 h based on 31P NMR. Very little change in mixture composition was observed over multiple preparative steps. CONCLUSION:Liposome preparations containing POPC, POPE, DOPC, DPPC, TACH, and PEG-ceramide can be reliably characterized and quantified by 1H NMR and 31P NMR spectroscopy at 600 MHz in the μmol range.

An efficient synthesis for a new conformationally locked chiral cis-1,2-diaminocyclohexane scaffold has been developed. The conformational lock allows for convenient symmetrical derivatization of the amino groups through the reductive amination strategy. A series of optically pure chiral ligands based on the cis-DACH scaffold has been generated to demonstrate a proof-of-concept for these ligands as chiral catalysts in the asymmetric Henry reaction. Excellent yields with moderate enantioselectivity were demonstrated at room temperature, with an increase in enantioselectivity at lower temperatures, showing the potential of this new type of cis-DACH ligand.

Conformational energy (A-value) of the 4-phenyl-1,2,3- triazolyl group was estimated as 2.0 kcal mol–1 (8.5 kJ mol–1) using 1H NMR-based conformational study for a set of (4-phenyl-1,2,3-triazol-1-yl)cyclohexanes. This provides a reasonable estimation also for the conformational energy of 1,2,3-triazolyl group itself and its substituted analogues.

The number of applications found for crown ether-based materials continues to expand. Many of these applications feature dicyclohexano-18-crown-6 (DC18C6). The number of its derivatives, however, is very limited. To provide a suitable starting structure for the preparation of diverse functionalized DC18C6, the trans-syn-trans and trans-anti-trans isomers of dicyclohexeno-18-crown-6 have been synthesized for the first time through a convenient three-step synthetic procedure, yielding both isomers simultaneously. An efficient chromatographic separation resulted in the isolation of the pure isomers, and single crystal X-ray crystallography determined the solid-state structure of these crown ethers.

— The formation of complexes from anionic liposomes with a pH-sensitive molecular switch (flipid) and a cationic polypeptide (polylysine) embedded in the membrane with a degree of polymerization of 90, 660, and 1360 was investigated. Liposomes in the complex retain their integrity in a buffer solution with a pH of 7; The resulting complexes are resistant to dissociation in a physiological solution containing 0.15 M NaCl. Lowering the pH of the solution to 5 causes the formation of defects in the lipid bilayer by changing the conformation of the flipid, which leads to the release of the encapsulated substance from the liposomes into the surrounding solution. In this case, complexation increases both the rate of release of the encapsulated substance and the amount of the substance moving from the liposomes to the external solution. The results obtained are of interest for encapsulation and controlled drug delivery.

A series of trans-2-(azaarylsulfanyl)cyclohexanol derivatives, structurally similar to previously studied trans-2-amino-cyclohexanols, were synthesized through epoxide ring opening under basic conditions with sodium tetraborate as a catalyst. 1H NMR spectroscopy was used to elucidate the conformational equilibrium in various solvents and its acid-induced change due to stabilization of the conformer with the azaarylsulfanyl and hydroxy groups in equatorial position by an intramolecular hydrogen bond and electrostatic interactions.

Guanine-rich DNA sequences can undergo self-assembly into unique G-quadruplex structures that interfere with the binding of proteins to the same DNA region. The formation of DNA G-quadruplexes requires monovalent cations (Na+ and K+) or small molecules known as G-quadruplex (G4) ligands. Phenanthroline is a type of G4 ligand scaffold known for its coordination with metal ions to form complexes with a large aromatic surface area, which aptly stack with G-quartets. In this report, we have investigated the side chain effect on G-quadruplex recognition by evaluating a series of 5-substituted phenanthroline-based metal complexes (Phen-Ni) binding to telomeric G-quadruplex DNA. Results from biophysical methods including fluorescence and circular dichroism (CD) thermal denaturation, CD titration, and the fluorescent intercalator displacement (FID) assay suggest that several Phen-Ni complexes bind to G-quadruplex DNA with submicromolar G4DC50 values. Arylsulfanyl groups at the 5 position of 1,10-phenanthroline are the best side chains regarding binding affinity and selectivity towards G-quadruplex DNA. Most of the G-quadruplex binding Phen-Ni complexes can inhibit telomerase activity in vitro as indicated by the telomeric repeat amplification protocol (TRAP) assay and such inhibition is clearly concentration dependent. Our results here provide a guidance of utilizing 5-substituted phenanthroline derivatives as a viable and facile approach to design novel G4 ligands.

A series of trans-2-aminocyclohexanol derivatives have been explored as powerful conformational pH triggers. On protonation of the amino group, a conformer with equatorial position of ammonio and hydroxy groups becomes predominant because of an intramolecular hydrogen bond and electrostatic interactions. The energy of these interactions was estimated to be above 10kJ/mol and in some models exceeded 20 kJ/mol (strong enough to twist a ring in tert-butyl derivatives). As a result of this conformational flip, all other substituents are forced to change their orientation. If the substituents are designed to perform certain geometry-dependent functions, for example, as cation chelators or as lipid tails, such acid-induced transition may be used to control the corresponding molecular properties. The pH sensitivity of conformational equilibria was explored by H-1 nuclear magnetic resonance spectroscopy (NMR), and the titration curves were used for estimation of the pK(a) values of protonated compounds that varied from 2.6 to 8.5 (in d(4)-methanol) depending on the structure of amino group. Thus, trans-2-aminocyclohexanols can be also used as conformational pH indicators in organic solvents.

The report presents a first example of a regio- and stereospecific Lewis acid-catalyzed aminolysis of 1-benzyl-3,4-epoxypiperidine leading to trans-3-amino-1-benzylpiperidin-4-ols, in contrast with other Lewis acid-catalyzed reactions leading to trans-4-amino-l-benzylpiperidin-3-ols. The reaction is performed at room temperature using the reagents prepared by interaction of a hard Lewis acid - diisobutylaluminum hydride (DIBAL-H) with primary and secondary amines. The obtained products are potential intermediates on the way to stereochemical analogues of the antitumor piperidine alkaloid pseudodistomin D. (C) 2017 Elsevier Ltd. All rights reserved.

Binding of pH-sensitive anionic liposomes to a star-shaped polycation provides accumulation of plenty of liposomes in a small volume and an increase in the rate and maximal amount of the pH-triggered content release.

Lipidic amphiphiles equipped with the trans-2-aminocyclohexanol (TACH) moiety are promising pH-sensitive conformational switches ("flipids") that can trigger a lipid bilayer perturbation in response to increased acidity. Because pH-sensitivity was shown to improve the efficiency of several gene delivery systems, we expected that such flipids could significantly enhance the gene transfection by lipoplexes. Thus a series of novel lipids with various TACH-based head groups and hydrocarbon tails were designed, prepared and incorporated into lipoplexes that contain the cationic lipid 1,2-dioleoyl-3-trimethylammonio-propane (DOTAP) and plasmid DNA encoding a luciferase gene. B16F1 and HeLa cells were transfected with such lipoplexes in both serum-free and serum-containing media. The lipoplexes consisting of TACH-lipids exhibited up to two orders of magnitude better transfection efficiency and yet similar toxicity compared to the ones with the conventional helper lipids 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) or cholesterol. Thus, the TACH-lipids can be used as novel helper lipids for efficient gene transfection with low cytotoxicity.