Solvent and alkyl substitution effects on charge-transfer mediated triplet state generation in BODIPY dyads: a combined computational and experimental study.

Donor-acceptor dyads based on BODIPYs have been recently employed to enhance the formation of triplet excited states with the process of spin-orbit charge transfer intersystem crossing (SOCT-ISC) which does not require introduction of transition metals or other heavy atoms into the molecule. In this work we compare two donor-acceptor dyads based on meso-naphthalenyl BODIPY by combining experimental and computational investigations. The photophysical and electrochemical characterization reveals a significant effect of alkylation of the BODIPY core, disfavoring the SOCT-ISC mechanism for the ethylated BODIPY dyad. This is complemented with a computational investigation carried out to rationalize the influence of ethyl substituents and solvent effects on the electronic structure and efficiency of triplet state population via charge recombination (CR) from the photoinduced electron transfer (PeT) generated charge-transfer (CT) state. Time dependent-density functional theory (TD-DFT) calculations including solvent effects and spin-orbit coupling (SOC) calculations uncover the combined role played by solvent and alkyl substitution on the lateral positions of BODIPY.

Circularly Polarized Luminescence from New Heteroleptic Eu(III) and Tb(III) Complexes.

The complexes [Eu(bpcd)(tta)], [Eu(bpcd)(Coum)], and [Tb(bpcd)(Coum)] [tta = 2-thenoyltrifluoroacetyl-acetonate, Coum = 3-acetyl-4-hydroxy-coumarin, and bpcd = N,N'-bis(2-pyridylmethyl)-trans-1,2-diaminocyclohexane-N,N'-diacetate] have been synthesized and characterized from photophysical and thermodynamic points of view. The optical and chiroptical properties of these complexes, such as the total luminescence, decay curves of the Ln(III) luminescence, electronic circular dichroism, and circularly polarized luminescence, have been investigated. Interestingly, the number of coordinated solvent (methanol) molecules is sensitive to the nature of the metal ion. This number, estimated by spectroscopy, is >1 for Eu(III)-based complexes and <1 for Tb(III)-based complexes. A possible explanation for this behavior is provided via the study of the minimum energy structure obtained by density functional theory (DFT) calculations on the model complexes of the diamagnetic Y(III) and La(III) counterparts [Y(bpcd)(tta)], [Y(bpcd)(Coum)], and [La(bpcd)(Coum)]. By time-dependent DFT calculations, estimation of donor-acceptor (D-A) distances and of the energy position of the S1 and T1 ligand excited states involved in the antenna effect was possible. These data are useful for rationalizing the different sensitization efficiencies (ηsens) of the antennae toward Eu(III) and Tb(III). The tta ligand is an optimal antenna for sensitizing Eu(III) luminescence, while the Coum ligand sensitizes better Tb(III) luminescence {ϕovl = 55%; ηsens ≥ 55% for the [Tb(bpcd)(Coum)] complex}. Finally, for the [Eu(bpcd)(tta)] complex, a sizable value of glum (0.26) and a good quantum yield (26%) were measured.

Design, Pharmacological Characterization, and Molecular Docking of Minimalist Peptidomimetic Antagonists of α4ß1 Integrin.

Integrin receptors mediate cell-cell interactions via the recognition of cell-adhesion glycoproteins, as well as via the interactions of cells with proteins of the extracellular matrix, and upon activation they transduce signals bi-directionally across the cell membrane. In the case of injury, infection, or inflammation, integrins of ß2 and α4 families participate in the recruitment of leukocytes, a multi-step process initiated by the capturing of rolling leukocytes and terminated by their extravasation. In particular, α4ß1 integrin is deeply involved in leukocyte firm adhesion preceding extravasation. Besides its well-known role in inflammatory diseases, α4ß1 integrin is also involved in cancer, being expressed in various tumors and showing an important role in cancer formation and spreading. Hence, targeting this integrin represents an opportunity for the treatment of inflammatory disorders, some autoimmune diseases, and cancer. In this context, taking inspiration from the recognition motives of α4ß1 integrin with its natural ligands FN and VCAM-1, we designed minimalist α/ß hybrid peptide ligands, with our approach being associated with a retro strategy. These modifications are expected to improve the compounds' stability and bioavailability. As it turned out, some of the ligands were found to be antagonists, being able to inhibit the adhesion of integrin-expressing cells to plates coated with the natural ligands without inducing any conformational switch and any activation of intracellular signaling pathways. An original model structure of the receptor was generated using protein-protein docking to evaluate the bioactive conformations of the antagonists via molecular docking. Since the experimental structure of α4ß1 integrin is still unknown, the simulations might also shed light on the interactions between the receptor and its native protein ligands.

Linker Hydrophilicity Modulates the Anticancer Activity of RGD-Cryptophycin Conjugates.

Most anticancer agents are hydrophobic and can easily penetrate the tumor cell membrane by passive diffusion. This may impede the development of highly effective and tumor-selective treatment options. A hydrophilic ß-glucuronidase-cleavable linker was used to connect the highly potent antimitotic agent cryptophycin-55 glycinate with the αv ß3 integrin ligand c(RGDfK). Incorporation of the self-immolative linker containing glucuronic acid results in lower cytotoxicity than that of the free payload, suggesting that hydrophilic sugar linkers can preclude passive cellular uptake. In vitro drug-release studies and cytotoxicity assays demonstrated the potential of this small molecule-drug conjugate, providing guidance for the development of therapeutics containing hydrophobic anticancer drugs.

Metallaphotoredox catalysis with organic dyes.

The use of organic dyes to promote organic reactions by photoredox catalysis is continuously expanding and was recently reviewed by Nicewicz. The synthesis of new dyes, their application in flow photoredox reactions, and their use in stereoselective and multicomponent transformations have considerably expanded the repertoire of application of organic dyes in photoredox mediated reactions. The low costs of these dyes, their tailored synthesis and availability in combination with the development of new concepts and careful catalytic cycle design (made possible by the application of fine theoretical investigations and deep understanding) are guiding the widespread application of organic dyes in the metallaphotoredox catalysis area. Developments and recent applications of different metal catalyzed processes mediated by organic dyes are covered by this review.

Selective detection of α4ß1 integrin (VLA-4)-expressing cells using peptide-functionalized nanostructured materials mimicking endothelial surfaces adjacent to inflammatory sites.

Persistent accumulation of immune cells mediated by α4ß1 integrin (VLA-4) is a hallmark of the inflammatory diseases and of chronic inflammation observed in the affected tissues of autoimmune diseases. Aiming at exploring new methods for monitoring the course of the inflammatory processes, we designed the first peptide-functionalized nanostructured devices capable to mimic the high-density multivalency binding between the α4ß1 integrin-expressing cells and the ligands overexpressed on the endothelial surfaces, in the proximity of the sites of inflammation. Specifically, we describe the first examples of monolayers constituted by dye-loaded zeolite L crystals, coated with α4ß1 integrin peptide ligands, and we analyze the adhesion of model Jurkat cells in comparison to non-α4ß1 integrin-expressing cells. In particular, the peptidomimetic diphenylurea-Leu-Asp-Val-diamine allows significant and selective detection of α4ß1 integrin-expressing Jurkat cells, after very rapid incubation time, supporting the possible implementation in a diagnostic device capable to detect the desired cells from biological fluids, obtainable from patients in a noninvasive way.

Design and Pharmacological Characterization of α4ß1 Integrin Cyclopeptide Agonists: Computational Investigation of Ligand Determinants for Agonism versus Antagonism.

α4ß1 integrin is a cell adhesion receptor deeply involved in the migration and accumulation of leukocytes. Therefore, integrin antagonists that inhibit leukocytes recruitment are currently regarded as a therapeutic opportunity for the treatment of inflammatory disorder, including leukocyte-related autoimmune diseases. Recently, it has been suggested that integrin agonists capable to prevent the release of adherent leukocytes might serve as therapeutic agents as well. However, very few α4ß1 integrin agonists have been discovered so far, thus precluding the investigation of their potential therapeutic efficacy. In this perspective, we synthesized cyclopeptides containing the LDV recognition motif found in the native ligand fibronectin. This approach led to the discovery of potent agonists capable to increase the adhesion of α4 integrin-expressing cells. Conformational and quantum mechanics computations predicted distinct ligand-receptor interactions for antagonists or agonists, plausibly referable to receptor inhibition or activation.

Design of α/ß-Hybrid Peptide Ligands of α4ß1 Integrin Equipped with a Linkable Side Chain for Chemoselective Biofunctionalization of Microstructured Materials.

Arg-Gly-Asp (RGD)-binding integrins, e.g., αvß3, αvß1, αvß5 integrins, are currently regarded as privileged targets for the delivery of diagnostic and theranostic agents, especially in cancer treatment. In contrast, scarce attention has been paid so far to the diagnostic opportunities promised by integrins that recognize other peptide motifs. In particular, α4ß1 integrin is involved in inflammatory, allergic, and autoimmune diseases, therefore, it represents an interesting therapeutic target. Aiming at obtaining simple, highly stable ligands of α4ß1 integrin, we designed hybrid α/ß peptidomimetics carrying linkable side chains for the expedient functionalization of biomaterials, nano- and microparticles. We identified the prototypic ligands MPUPA-(R)-isoAsp(NHPr)-Gly-OH (12) and MPUPA-Dap(Ac)-Gly-OH (13) (MPUPA, methylphenylureaphenylacetic acid; Dap, 2,3-diamino propionic acid). Modification of 12 and 13 by introduction of flexible linkers at isoAsp or Dap gave 49 and 50, respectively, which allowed for coating with monolayers (ML) of flat zeolite crystals. The resulting peptide-zeolite MLs were able to capture selectively α4ß1 integrin-expressing cells. In perspective, the α4ß1 integrin ligands identified in this study can find applications for preparing biofunctionalized surfaces and diagnostic devices to control the progression of α4ß1 integrin-correlated diseases.

Green synthesis of bioactive oligopeptides promoted by recyclable nanocrystalline hydroxyapatite.

Aim: The pharmaceutical industry is showing renewed interest in therapeutic peptides. Unfortunately, the chemical synthesis of peptides remains very expensive and problematic in terms of environmental sustainability. Hence, making peptides 'greener' has become a new front line for the expansion of peptide market. Results: We developed a mechanochemical solvent-free peptide bond-forming protocol using standard reagents and nanocrystalline hydroxyapatite as a bio-compatible, reusable inorganic base. The reaction was also conducted under ultra-mild, minimal solvent-grinding conditions, using common laboratory equipment. Conclusion: The efficacy of the described protocol was validated with the convenient preparation of endomorphin-1, H-Tyr-Pro-Trp-Phe-NH2, the endogenous ligand of the µ-opioid receptor, currently regarded as a lead for the discovery of painkillers devoid of harmful side effects.

DS-70, a novel and potent α4 integrin antagonist, is an effective treatment for experimental allergic conjunctivitis in guinea pigs.

BACKGROUND AND PURPOSE: Allergic conjunctivitis is an eye inflammation that involves the infiltration of immune cells into the conjunctiva via cell surface-adhesion receptors, such as integrin α4 ß1 . These receptors interact with adhesion molecules expressed on the conjunctival endothelium and may be a target to treat this disease. We synthesized DS-70, a novel α/ß-peptidomimetic α4 integrin antagonist, to prevent the conjunctival infiltration of immune cells and clinical symptoms in a model of allergic conjunctivitis. EXPERIMENTAL APPROACH: In vitro, DS-70 was pharmacologically characterized using a scintillation proximity procedure to measure its affinity for α4 ß1 integrin, and its effect on cell adhesion mediated by different integrins was also evaluated. The effects of DS-70 on vascular cell adhesion molecule-1 (VCAM-1)-mediated degranulation of a human mast cell line and an eosinophilic cell line, which both express α4 ß1 , and on VCAM-1-mediated phosphorylation of ERK 1/2 in Jurkat E6.1 cells were investigated. Effects of DS-70 administered in the conjunctival fornix of ovalbumin-sensitized guinea pigs were evaluated. KEY RESULTS: DS-70 bound to integrin α4 ß1 with nanomolar affinity, prevented the adhesion of α4 integrin-expressing cells, antagonized VCAM-1-mediated degranulation of mast cells and eosinophils and ERK 1/2 phosphorylation. Only 20% was degraded after an 8 h incubation with serum. DS-70 dose-dependently reduced the clinical symptoms of allergic conjunctivitis, conjunctival α4 integrin expression and conjunctival levels of chemokines and cytokines in ovalbumin-sensitized guinea pigs. CONCLUSIONS AND IMPLICATIONS: These findings highlight the role of α4 integrin in allergic conjunctivitis and suggest that DS-70 is a potential treatment for this condition.