Simulation Reveals the Chameleonic Behavior of Macrocycles.

Conformational analysis is central to the design of bioactive molecules. It is particularly challenging for macrocycles due to noncovalent transannular interactions, steric interactions, and ring strain that are often coupled. Herein, we simulated the conformations of five macrocycles designed to express a progression of increasing complexity in environment-dependent intramolecular interactions and verified the results against NMR measurements in chloroform and dimethyl sulfoxide. Molecular dynamics using an explicit solvent model, but not the Monte Carlo method with implicit solvation, handled both solvents correctly. Refinement of conformations at the ab initio level was fundamental to reproducing the experimental observations─standard state-of-the-art molecular mechanics force fields were insufficient. Our simulations correctly predicted the intramolecular interactions between side chains and the macrocycle and revealed an unprecedented solvent-induced conformational switch of the macrocyclic ring. Our results provide a platform for the rational, prospective design of molecular chameleons that adapt to the properties of the environment.

Excitation- and Emission-Wavelength-Based Multiplex Spectroscopy Using Red-Absorbing Near-Infrared-Emitting Lanthanide Complexes.

Multiplex imaging in the red and near-infrared (NIR) should be an enabling tool for the real-time investigation of biological systems. Currently available emitters have short luminescent lifetimes, broad absorption and emission bands, and small Stokes shifts, which limits multiplexing in this region to two colors. NIR-emitting luminescent lanthanide (Ln) complexes carrying hydroporphyrin (chlorin) sensitizing antennae are excitable in the red through the narrow, intense and tunable chlorin absorptions. Both emission- and excitation-based multiplexing are possible, the former by exciting the same antenna appended to different Lns, the latter by attaching different chlorins with nonoverlapping absorptions to the same Ln. The combination of excitation and emission spectroscopies allows for the straightforward differentiation of up to four different complexes.

Furan- and Thiophene-Based Auxochromes Red-shift Chlorin Absorptions and Enable Oxidative Chlorin Polymerizations.

The de novo syntheses of chemically stable chlorins with five-membered heterocyclic (furane, thiophene, formylfurane and formylthiophene) substituents in selected meso- and ß-positions are reported. Heterocycle incorporation in the 3- and 13-positions shifted the chlorin absorption and emission to the red (up to λem =680 nm), thus these readily incorporated substituents function analogously to auxochromes present in chlorophylls, for example, formyl and vinyl groups. Photophysical, theoretical and X-ray crystallographic experiments revealed small but significant differences between the behavior of the furan- and the thiophene-based auxochromes. Four regioisomeric bis-thienylchlorins (3,10; 3,13, 3,15 and 10,15) were oxidatively electropolymerized; the chlorin monomer geometry had a profound impact on the polymerization efficiency and the electrochemical properties of the resulting material. Chemical co-polymerization of 3,13-bis-thienylchlorin with 3-hexylthiophene yielded an organic-soluble red-emitting polymer.

Rational Synthesis of 2-Bromoporphyrins and 2,12-Dibromoporphyrins.

Bromoporphyrins were prepared by the metal-mediated self-condensation of brominated 1-formyldipyrromethanes. Depending on the conditions, Mg(II)-2,12-dibromoporphyrin and Mg(II)-2-bromoporphyrin could be obtained in up to 11% and 17% isolated yield, respectively. Zn(II) was also a viable templating metal. The positions of the bromine substituents were confirmed by 2D-NMR spectroscopic analysis and the X-ray crystal structure of a derivative. Suzuki and Sonogashira reactions of the bromoporphyrins yielded 2-substituted or 2,12-disubstituted porphyrins with red-shifted absorption and emission spectra. This method provides access to the minimalist core of ß-mono- and ß,ß'-disubstituted porphyrins from readily available starting materials.

Unexpected effect of halogenation on the water solubility of small organic compounds.

Halogenation is an indispensable method in the structural modification of lead compounds. It is known to increase lipophilicity and is hence used to improve membrane permeability and thus bioavailability. In this study, we compare the water solubility (logS) of organohalogen compounds and their non-halogenated parent compounds using the molecular matched pair (MMP) analysis method. Unexpectedly, 19.9% of the compounds increased their water solubility upon halogenation. Iodination was observed to have the greatest effect on solubility, followed by chlorination, bromination, and fluorination. Introducing amino, hydroxyl and carboxyl groups into organohalogens improves their aqueous solubilities, whereas introducing a trifluoromethyl group has the opposite effect. According to our quantum chemical calculations, the increased water solubility upon halogenation is, at least partially, attributed to an increased polarity and polarizability. These results improve our understanding of the influence of halogenation on bioactivity.

[Research progress of anti-influenza virus agents].

Influenza is a major threat to millions of people worldwide. Vaccines and antiviral agents are two main options available to reduce the impact of the influenza virus, while anti-influenza agents are the most effective means to prevent the transmission of the highly contagious virus and to treat the epidemics of disease. At present, four anti-influenza agents have been approved by the FDA for the treatment of influenza, including two M2 protein ion channel inhibitors-amantadine and rimantadine and two neuraminidase inhibitors-zanamivir and oseltamivir. Arbidol hydrochloride, launched in Russia, is a potent inhibitor of influenza virus, too. Neuraminidase inhibitors could be classified generally by structure into six different kinds: sialic acid derivatives, benzoic acid derivatives, cyclohexene derivatives, cyclopentane derivatives, pyrrolidine derivatives and natural products. In this paper, recent progress in the research of the action mechanisms and structure-activity relationships of these anti-influenza virus agents were reviewed.

Investigation of the demetallation of 10-aryl substituted synthetic chlorins under acidic conditions.

The acidic demetallation of a series of sparsely substituted Zn(II) chlorins is reported. The chlorins were functionalized in the 10-position with substituents ranging from strongly electron donating mesityl and p-methoxyphenyl to electron-withdrawing p-nitrophenyl and pentafluorophenyl groups. The demetallation kinetics were investigated using UV-Visible absorption spectroscopy. Demetallation was carried out by exposing the metallochlorins dissolved in CH2Cl2 to an excess of trifluoroacetic acid. Reasonable correlation was found between the Hammett constant of the 10-substituent and the rate constant of the loss of the metal ion. The largest differences were observed between the p-methoxyphenyl and p-nitrophenyl-substituted Zn(II) chlorins, undergoing loss of Zn(II) with pseudo first order rate constants of 0.0789 × 10-3 and 3.70 × 10-3 min-1, respectively. Taken together, these data establish the dramatic influence even subtle changes can have in altering the electronic properties of chlorins, which in turn impacts metallochlorin function.

Regioselective synthesis of 4azido-Neu2en5,7Ac(2)1Me and its intramolecular transformation to 4azido-Neu2en5,9Ac(2)1Me.

Methyl 5-N-acetyl-7-O-acetyl-4-azido-2,3-didehydro-2,4-dideoxy-neuraminic acid (4azido-Neu2en5,7 Ac(2)1Me) was synthesized regioselectively starting from 4azido-Neu2en5Ac1Me in high yield. The transformation of 4azido-Neu2en5,7Ac(2)1Me to the corresponding thermodynamically stable 4azido-Neu2en5,9Ac(2)1Me via intramolecular acetyl migration was confirmed by single-crystal X-ray diffraction analysis. The proposed rearrangement mechanism is discussed.

Directly linked hydroporphyrin dimers.

Directly linked hydroporphyrin (chlorin) dimers were accessed regioselectively from bromochlorins. Versatile 15-borylated chlorins were prepared in excellent yield via Miyaura borylation. Suzuki coupling yielded meso-meso-linked homo- and heterodimers, and meso-ß-linked dimers. The photophysical and electrochemical properties of the dimers are reported.

Synthesis and characterisation of lanthanide-hydroporphyrin dyads.

Fluorescence spectroscopy is in many ways the ideal tool for the interrogation of complex biological systems, as it is non-invasive, sensitive, and offers high spatiotemporal resolution. For biomedical imaging luminescent probes absorbing and emitting in the red-to-near infrared (NIR) region are best suited to maximise tissue penetration and minimise damage to cellular components. NIR-emitting lanthanides (Ln) sensitised with red-absorbing antennae are promising candidates for these applications, assuming the challenges of poor photophysical properties and tedious syntheses of the complexes are overcome. Chlorins are porphyrin-type tetrapyrroles with intense red absorption. Recently chlorins have been shown to sensitise Yb and Nd emission when incorporated into Ln-complexes. Here we expand on our previous work, and explore the effect of chlorin structure, metallation state, chlorin-Ln-complex linker length and mode of attachment on the properties of chlorin-Ln complexes. As chlorin absorption bands are ∼20 nm fwhm and readily tunable, a deeper understanding of structure-property relationships would enable the use of chlorin-Ln complexes in multicolour imaging using antenna-specific excitation. A detailed description of antenna and complex syntheses and photophysical characterisation is given. A number of challenges were identified, which will have to be addressed in future studies to enable multicolour imaging using the NIR-emitting lanthanides.