Improved binding affinity and interesting selectivities of aminopyrimidine-bearing carbohydrate receptors in comparison with their aminopyridine analogues

Synthesis and crystal structures of two solvates of 1-{[2,6-bis-(hy-droxy-meth-yl)-4-methyl-phen-oxy]meth-yl}-3,5-bis-{[(4,6-di-methyl-pyridin-2-yl)amino]meth-yl}-2,4,6-tri-ethyl-benzene

In the crystal structures of the formamide monosolvate (1a) and the n-propanol/H2O solvate/hydrate (1b) of the title compound, C38H50N4O3 (1), the tripodal host mol-ecule adopts a conformation in which the substituents attached to the central benzene ring are arranged in an alternating order above and below the ring plane. As a result of the different nature of the involved guest species, the crystal components in 1a create a three-dimensional supra-molecular architecture, while the crystal structure of 1b consists of two-dimensional supra-molecular aggregates extending parallel to the crystallographic ab plane.

Compounds Derived from 9,9-Dialkylfluorenes: Syntheses, Crystal Structures and Initial Binding Studies (Part II)

New representatives of 2,4,7-trisubstituted 9,9-dialkyl-9H-fluorenes were prepared and used for crystallographic investigations as well as initial binding studies towards metal ions and carbohydrates. The binding studies, which included ¹ H NMR spectroscopic titrations and fluorescence measurements, demonstrated the ability of the tested fluorene-based compounds to act as complexing agents for ionic and neutral substrates. Depending on the nature of the subunits of the fluorene derivatives, "turn on" or "turn off" fluorescent chemosensors can be developed. Compounds composed of 4,6-dimethylpyridin-2-yl-aminomethyl moieties have the potential to be used as sensitive "turn-on" chemosensors for some metal ions.

Cycloalkyl Groups as Building Blocks of Artificial Carbohydrate Receptors: Studies with Macrocycles Bearing Flexible Side-Arms

The cyclopentyl group was expected to act as a building block for artificial carbohydrate receptors and to participate in van der Waals contacts with the carbohydrate substrate in a similar way as observed for the pyrrolidine ring of proline in the crystal structures of protein-carbohydrate complexes. Systematic binding studies with a series of 1,3,5-trisubstituted 2,4,6-triethylbenzenes bearing various cycloalkyl groups as recognition units provided indications of the involvement of these groups in the complexation process and showed the influence of the ring size on the receptor efficiency. Representatives of compounds that exhibit a macrocyclic backbone and flexible side arms were now chosen as further model systems to investigate whether the previously observed effects represent a general trend. Binding studies with these macrocycles towards β-D-glucopyranoside, an all-equatorial substituted carbohydrate substrate, included 1H NMR spectroscopic titrations and microcalorimetric investigations. The performed studies confirmed the previously observed tendency and showed that the compound bearing cyclohexyl groups displays the best binding properties.

Synthesis and crystal structure of 1,3-bis{[N,N-bis(2-hydroxyethyl)amino]methyl}-5-{[(4,6-dimethylpyridin-2-yl)amino]methyl}-2,4,6-triethylbenzene

In the crystal structure of the title compound, C30H50N4O4, the two bis(hydroxyethyl)amino moieties and the 2,4-dimethylpyridinylamino unit of the molecule are located on one side of the central benzene ring, while the ethyl substituents are oriented in the opposite direction. The dihedral angle between the planes of the aromatic rings is 73.6 (1)°. The conformation of the molecule is stabilized by intramolecular O—H...O (1.86–2.12 Å) and C—H...N (2.40, 2.54 Å) hydrogen bonds. Dimers of inversion-related molecules represent the basic supramolecular entities of the crystal structure. They are further connected via O—H...O hydrogen bonding into undulating layers extending parallel to the crystallographic bc plane. Interlayer interaction is accomplished by weak C—H...π contacts.

Binding modes of methyl α-d-glucopyranoside to an artificial receptor in crystalline complexes

Compared to the numerous X-ray crystal structures of protein-carbohydrate complexes, the successful elucidation of the crystal structures of complexes between artificial receptors and carbohydrates has been very rarely reported in the literature. In this work, we describe the binding modes of two complexes formed between methyl α-d-glucopyranoside and an artificial receptor belonging to the class of compounds consisting of a 1,3,5-trisubstituted 2,4,6-trialkylbenzene scaffold. It is particularly noteworthy that these two complexes are present in one crystal structure, as was observed by us for the first time in the case of the recently reported three crystal structures of the complexes with methyl β-d-glucopyranoside, each containing two different receptor-carbohydrate complexes. The noncovalent interactions stabilizing the new complexes are compared with those observed in the aforementioned crystalline complexes with methyl β-d-glucopyranoside.

Syntheses of Acyclic and Macrocyclic Compounds Derived from 9,9-Diethylfluorene (Part I)

A series of new 9,9-diethylfluorenes consisting of three side-arms each bearing a heterocyclic, bis(carboxymethyl)amino, bis(carbamoylmethyl)amino, bis(ethoxycarbonylmethyl)amino or an amino group were prepared on the basis of 2,4,7-tris(bromomethyl)-9,9-diethylfluorene. Imidazolyl, benzimidazolyl, pyrazolyl, pyrrolyl, 1,3-dioxoisoindolyl and pyridinium groups were taken into account as heterocyclic units, attached to the aromatic skeleton via -CH2-, -CH2NHCH2- or -CH2N=CH- linkers. In addition to the seventeen 2,4,7-trisubstituted 9,9-diethylfluorenes, two macrocyclic compounds were prepared on the basis of 2,7-bis(aminomethyl)-9,9-diethylfluorene. The excellent yield of the macrocyclization reaction is worth a special mention. Both the acyclic and the macrocyclic fluorene-based compounds have, among other things, the potential to act as artificial receptors for different substrates in analogy to the known receptors consisting of a benzene or biphenyl core.

Molecular Interrogation to Crack the Case of O-GlcNAc

The O-linked β-N-acetylglucosamine (O-GlcNAc) modification, termed O-GlcNAcylation, is an essential and dynamic post-translational modification in cells. O-GlcNAc transferase (OGT) installs this modification on serine and threonine residues, whereas O-GlcNAcase (OGA) hydrolyzes it. O-GlcNAc modifications are found on thousands of intracellular proteins involved in diverse biological processes. Dysregulation of O-GlcNAcylation and O-GlcNAc cycling enzymes has been detected in many diseases, including cancer, diabetes, cardiovascular and neurodegenerative diseases. Here, recent advances in the development of molecular tools to investigate OGT and OGA functions and substrate recognition are discussed. New chemical approaches to study O-GlcNAc dynamics and its potential roles in the immune system are also highlighted. It is hoped that this minireview will encourage more research in these areas to advance the understanding of O-GlcNAc in biology and diseases.

Hexaphenolic Rigid Cages Prepared by Self-Organization of C3 v Tridentates

Coordination cages were composed by self-organization of rigid C_{3 v}-symmetric heptaarene tridentates and Pd(II) precursors. The heptaarene framework involves one mesitylene, three phenol, and three pyridine moieties, which were connected by Suzuki coupling reactions. The treatment of the tridentates with Pd(dppp)(OTf)₂ or Pd(en)(NO₃)₂ in a 2:3 molar ratio furnished coordination cages, which was ascertained by crystallography, ¹H NMR and DOSY measurements, and ESI-TOFMS and UV-vis spectra. The cages have six phenolic hydroxy groups inside and were expected to incorporate hydrogen-bonding guest molecules such as saccharides. CD and DOSY measurements showed that octyl hexoside guests could be incorporated into the cage.

Conformations of benzene-based tripodal isatin-bearing compounds in the crystalline state

Studies of molecular conformations, examples of polymorphic forms, new solvates and analysis of supramolecular motifs giving interesting insights into molecular recognition phenomena are reported.

Carbohydrate receptors combining both a macrocyclic building block and flexible side arms as recognition units: binding properties of compounds with CH2OH groups as side arms

New representatives of compounds combining both a macrocyclic building block and two flexible side arms as recognition units were prepared and their binding properties toward selected carbohydrates were evaluated. The aim of this study was to examine the effects of the replacement of the heterocycle-bearing side arms by smaller units, such as hydroxy groups, on the binding capability. The design of this type of receptor was inspired by the participation of the side chain hydroxy group of serine and threonine in the biorecognition of carbohydrates. Such structural modifications enable the recognition of structure-activity relationships, which are of high importance in the development of carbohydrate receptors with predictable binding strength and selectivity.