NMR study of the tautomeric behavior of N-(α-aminoalkyl)tetrazoles.

N-(α-Aminoalkyl)tetrazoles exist in solution as equilibrium mixtures of N1 and N2 tautomers. The position of equilibrium depends significantly on the polarity of the solvent and the substituents in the tetrazole ring. Interconversion between individual tautomers is shown to proceed via tight ion-pair intermediates in which intramolecular recombination is faster than the intermolecular crossover since the latter probably requires solvent separation of ion-pair intermediates.

Tautomerism in drug discovery.

The influence of tautomerism on the precise structure of drugs and thus of their potential to interact with biological systems is discussed from thermodynamic and kinetic aspects. The types of tautomerism encountered in the structure of drugs in current use are surveyed together with the effect of pH, solvent polarity, and temperature.

1H, 13C, and 15N NMR spectra of some pyridazine derivatives.

(1)H, (13)C, and (15)N NMR chemical shifts for pyridazines 4-22 were measured using 1D and 2D NMR spectroscopic methods including (1)H-(1)H gDQCOSY, (1)H-(13)C gHMQC, (1)H-(13)C gHMBC, and (1)H-(15)N CIGAR-HMBC experiments.

Synthesis and characterization of a redox-active ion channel supporting cation flux in lipid bilayers.

The synthesis, cation binding and transmembrane conductive properties of a novel synthetic ion channel containing a redox-active ferrocene unit are described. Fluorescence spectroscopy was used to demonstrate that the channel supports multiple ion coordination and association constants for 1:1 and 1:2 (channel:cation) coordination for both Na(+) and K(+) were evaluated. Experiments using a black lipid membrane preparation revealed that this compound functioned effectively as an ion channel for both Na(+) and K(+). Concomitant (23)Na NMR spectroscopy studies supported this finding and revealed a Na(+) flux, at least 5 times higher than ion transport rates by monensin. Furthermore, oxidation of the redox-active centre (Fe(2+) to Fe(3+)) effectively inhibited ion transport.

Interfacially Engineered Pyridinium Pseudogemini Surfactants as Versatile and Efficient Supramolecular Delivery Systems for DNA, siRNA, and mRNA.

This article presents the synthesis, self-assembly, and biological activity as transfection agents for pDNA, siRNA, and mRNA of novel pyridinium pseudogemini surfactants, interfacially engineered from the most efficient gemini surfactants and lipids generated in our amphiphile research program. Formulation of novel amphiphiles in water revealed supramolecular properties very similar to those of gemini surfactants, despite their lipidlike charge/mass ratio. This dual character was found also to enhance endosomal escape and significantly increase the transfection efficiency. We were also successful in identifying the parameters governing the efficient delivery of pDNA, siRNA, and mRNA, drawing valuable structure-activity and structure-property relationships for each nucleic acid type, and establishing DNA/siRNA/mRNA comparisons. Several supramolecular complexes identified in this study proved to be extremely efficient nucleic acid delivery systems, displaying excellent serum stability and tissue penetration in three-dimensional organoids.

Synthetic nucleic acid delivery systems: present and perspectives.

Self-assembled synthetic gene delivery systems represent the bottom-up approach to gene delivery and gene silencing, in which scientists are designing novel cationic and procationic amphiphiles that can pack, transport, and deliver nucleic acids to various targets in the body in a controlled manner. These supramolecular assemblies are safer than viruses, but they are lagging behind them in efficiency. We are presenting recent progress that has narrowed this gap through better understanding the delivery barriers and incorporation of this knowledge in the design of novel synthetic amphiphiles, formulations, and revolutionary screening and optimization processes. Structure-properties and structure-activity relationships were drawn within each amphiphile class, presenting the cellular and animal models used to generate them. We are also revealing pertinent in vitro/in vivo correlations that emphasize promising amphiphiles and successful formulation optimization efforts for efficient in vivo nucleic acid delivery, together with main organ targets and diseases treatable with these revolutionary technologies.

Ethylene bis-imidazoles are highly potent and selective activators for isozymes VA and VII of carbonic anhydrase, with a potential nootropic effect.

A series of ethylene bis-imidazoles was synthesized via a novel microwave-mediated synthesis. Biological testing on eight isozymes of carbonic anhydrase (CA) present in the human brain revealed compounds with nanomolar potency against CA VA and CA VII, also displaying excellent selectivity against other CA isozymes present in this organ.

"Single-single" amphiphilic janus dendrimers self-assemble into uniform dendrimersomes with predictable size.

An accelerated modular synthesis of six libraries containing 29 amphiphilic Janus dendrimers, employed to discover and predict functions via primary structures, is reported. These dendrimers were constructed from a single hydrophobic and a single hydrophilic dendron, interconnected with l-Ala to form two constitutional isomeric libraries, with Gly to produce one library, and with l-propanediol ester to generate two additional constitutional isomeric libraries. They are denoted "single-single" amphiphilic Janus dendrimers. Assemblies obtained by injection of their ethanol solution into water were analyzed by dynamic light scattering and cryogenic transmission electron microscopy. A diversity of complex structures including soft and hard dendrimersomes, cubosomes, solid lamellae, and rod-like micelles were obtained in water. It was discovered that the "single-single" amphiphilic Janus dendrimers containing three triethylene glycol groups in the hydrophilic dendron favored the formation of dendrimersomes. Assemblies in bulk analyzed by differential scanning calorimetry and powder X-ray diffraction revealed that the amphiphilic Janus dendrimers with melting point or glass transition below room temperature self-assemble into soft dendrimersomes in water, while those with higher temperature transitions produce hard assemblies. In the range of concentrations where their size distribution is narrow, the diameter of the dendrimersomes is predictable by the d-spacing of their assemblies in bulk. These results suggested the synthesis of Library 6 containing two simpler constitutional isomeric benzyl ester based amphiphilic Janus dendrimers that self-assemble in water into soft dendrimersomes and multidendrimersome dendrimersomes with predictable dimensions.

Regioselective syntheses of beta-N-linked glycoaminoacids and glycopeptides.

Acylation of tetra-O-pivaloyl-beta-D-galactopyranosylamine 2 by readily available N- (Cbz or Fmoc-alpha-aminoacyl) benzotriazoles under microwave irradiation proceeded diastereoselectively to give beta-N-glycoaminoacids 3a-d, (3c+3c') (compound numbers written within brackets represent a racemate or a diastereomeric mixture; compound numbers without brackets represent a single enantiomer) (83-92%), and glycosylated asparagine building block 9 (65%). N-Cbz-Protected peptidoylbenzotriazoles 4a-c similarly afforded beta-N-glycodipeptides 5a-c (76-81%). Regiospecific beta-N-linkage formation was established by 1D and 2D NMR techniques for 3b.

Efficient peptide coupling involving sterically hindered amino acids.

Hindered amino acids have been introduced into peptide chains by coupling N-(Cbz- and Fmoc-alpha-aminoacyl)benzotriazoles with amino acids, wherein at least one of the components was sterically hindered, to provide compounds 3a-e, (3c +3 c'), 5a-d, (5a + 5a'), 6a-c, (6b + 6b'), 8a-c, 9a-e, 10a-d, and (10a + 10a') in isolated yields of 41-95% with complete retention of chirality as evidenced by NMR and HPLC analysis. The benzotriazole activation methodology is a new route for the synthesis of sterically hindered peptides. (Note: compound numbers written within brackets represent diastereomeric mixtures or racemates; compound numbers without brackets represent enantiomers.).