Conformational control and photoenolization of pyridine-3-carboxaldehydes in the solid state: stabilization of photoenols via hydrogen bonding and electronic control

Reversible Shifting of a Chemical Equilibrium by Light: The Case of Keto-Enol Tautomerism of a β-Ketoester

Manipulating the equilibrium between a ketone and an enol by light opens up ample opportunities in material chemistry and photopharmacology. By incorporating β-ketoester into the ethene bridge of a photoactive diarylethene, we achieved reversible light-induced tautomerization to give thermally stable enol. In a pristine state, the tautomeric equilibrium is almost completely shifted toward the ketone. Photocyclization of diarylethene results in a new equilibrium containing a significant fraction of the enol tautomer.

"Inherently Chiral" Ionic-Liquid Media: Effective Chiral Electroanalysis on Achiral Electrodes

To achieve enantioselective electroanalysis either chiral electrodes or chiral media are needed. High enantiodiscrimination properties can be granted by the "inherent chirality" strategy of developing molecular materials in which the stereogenic element responsible for chirality coincides with the molecular portion responsible for their specific properties, an approach recently yielding outstanding performances as electrode surfaces. Inherently chiral ionic liquids (ICILs) have now been prepared starting from atropisomeric 3,3'-bicollidine, synthesized from inexpensive reagents, resolved into antipodes without need of chiral HPLC and converted into long-chain dialkyl salts with melting points below room temperature. Both the new ICILs and shorter family terms, solid at room temperature, employed as low-concentration additives in achiral ILs, afford impressive enantioselection for the enantiomers of different probes on achiral electrodes, regularly increasing with additive concentration.

Structure activity relationship studies of natural product chemokine receptor CCR5 antagonist anibamine toward the development of novel anti prostate cancer agents

Recent studies have indicated that the CCR5 chemokine receptor may be a potential target for treating prostate cancer. Thus, development of CCR5 antagonists may provide novel prostate cancer therapy. Anibamine, a novel pyridine quaternary alkaloid isolated from Aniba sp., was found to effectively compete with (125)I-gp120 in binding to the chemokine receptor CCR5, with an IC(50) = 1 μM. Anibamine is the first natural product reported as a CCR5 antagonist, and thus provides a novel structural skeleton unique from other lead compounds that have generally been identified from high-throughput screening efforts. In order to refine the lead compound's structure and improve the therapeutic index of anibamine derivatives as potential anti prostate cancer agents, the approach of "deconstruction-reconstruction-elaboration" was applied in the structure-activity relationship studies of this work. Here, we report the design, syntheses and anti prostate cancer activities of anibamine and 17 analogues. The results from the in vitro and in vivo studies described here show that this class of compounds has potential to provide novel leads as anti prostate cancer agents.

Rational design of highly active and selective ligands for the alpha5beta1 integrin receptor

The inhibition of integrin function is a major challenge in medicinal chemistry. Potent ligands are currently in different stages of clinical trials for the antiangiogenic therapy of cancer and age-related macula degeneration (AMD). The subtype alpha5beta1 has recently been drawn into the focus of research because of its genuine role in angiogenesis. In our previous work we could demonstrate that the lack of structural information about the receptor could be overcome by a homology model based on the X-ray structure of the alphavbeta3 integrin subtype and the sequence similarities between both receptors. In this work, we describe the rational design and synthesis of high affinity alpha5beta1 binders, and the optimisation of selectivity against alphavbeta3 by means of extensive SAR studies and docking experiments. A first series of compounds based on the tyrosine scaffold resulted in affinities in the low and even subnanomolar range and selectivities of 400-fold against alphavbeta3. The insights about the structure-activity relationship gained from tyrosine-based ligands could be successfully transferred to ligands that bear an aza-glycine scaffold to yield alpha5beta1 ligands with affinities of approximately 1 nm and selectivities that exceed 10(4)-fold. The ligands have already been successfully employed as selective alpha5beta1 ligands in biological research and might serve as lead structures for antiangiogenic cancer therapy.

Photochromism of Photoenolizable Ketones in Quinoline and 1,8-Naphthyridine Series Studied by Time-Resolved Absorption Spectroscopy

For the two photochromic molecules, 3-benzoyl-2-benzyl-1-methyl-1H-quinolin-4-one (QC1) and 3-benzoyl-1,2-dibenzyl-1H-1,8-naphthyridin-4-one (QC18a) as well as the nonphotochromic 3-benzoyl-1-benzyl-2-methyl-1H-1,8-naphthyridin-4-one (QC18b), the full photochemical mechanism, which is based on the photoenolization process, has been elucidated using stationary and time-resolved spectroscopy techniques. After photoexcitation, the S1(n,pi*)-T1(n,pi*) ISC process involving the exocyclic carbonyl chromophore is demonstrated to occur. Subsequently, gamma-hydrogen transfer proceeds very rapidly to give rise to the triplet photoenol with a probable 1,4-biradical structure. For all three molecules, the biradical is clearly detected and proved quantitatively to be the direct precursor of the colored form (photochromic compounds) or ground state starting material (nonphotochromic compound). Solvent effects for the three molecules studied may suggest the existence of intramolecular hydrogen bonding in both biradical and colored form species. Structural effects on the gamma-hydrogen transfer rate and biradical decay are related to the photochromic performances.

Fine-Tuning of Relative Metal–Metal Distances within Highly Ordered Chiral 2D Nanopatterns

The two-dimensional nanopatterning of a series of neutral alkoxy/alkyl-functionalised bis(salicylaldehydato)/bis(aldiminato)copper(II) and -palladium(II) complexes at a liquid/solid (highly oriented pyrolytic graphite, HOPG) interface has been studied by scanning tunnelling microscopy (STM). The relative metal-metal distances were tuned stepwise in two dimensions by ligand design. Exchange of the carbonyl O-atom for NH or N-alkyl units effects different intermolecular interactions such as weak hydrogen bonds and steric effects that determine, together with the van der Waals forces between the alkyl chains, the relative arrangements of the complexes. Further variation of the length and position of the alkoxy side chains as well as the exchange of CuII for PdII affords an absolute fine-tuning of the surface structures. Highly resolved STM images of the resultant highly ordered adlayers allow us to establish detailed models of the molecular 2D arrays and to classify them into three basic chiral pattern types. Homochirality within the individual domains is induced by the highly regular deposition of the prochiral complexes from the same enantiotopic face. In the case of the C12 O-substituted bis(salicylaldiminato) (NH) Cu(II) complex Cu5, a secondary structure occurs as a racemic mixture of two chiral surface species deposited in a distinct alternating order.

Substituent Electronic Effects on the Persistence and Absorption Spectra of (Z)-o-Xylylenols. A Nanosecond Laser Flash Photolysis Study

[reaction: see text] A systematic investigation on a broad set of aldehydes reveals that the lifetimes of (Z)-photoenols can be modulated by variation of the substituents. We have found that the lifetimes of (Z)-enols (in benzene) can be varied by more than 1 order of magnitude with a judicious choice of the substituents that exert mesomeric and inductive effects as, for example, in the case of pentamethylbenzaldehyde (tau = 35 ns) and dicyanomesitaldehyde (tau = 760 ns). This study thus points to the fact that the electronic factors in conjunction with hydrogen bonding stabilization can considerably broaden the uni- as well as bimolecular chemistry based on photoenolization. Further, we have shown that the photoenols exhibit dramatic shifts in their absorption properties with variation of the substituents; although the photoenols have long been considered to be colored, their absorption properties have not been heretofore comprehensively examined.

Structure controlled self-assembly of Cu(ii) salicylic aldehyde and aldimine derivative complexes

The order of self-assembled monolayers of Cu(II) salicylic aldehyde and aldimine complexes has been gradually changed by ligand substitution and the resulting nanostructures have been studied at the graphite/liquid interface using scanning tunneling microscopy.