A new SiF-Dipropargyl glycerol scaffold as a versatile prosthetic group to design dimeric radioligands: synthesis of the [(18) F]BMPPSiF tracer to image serotonin receptors

A novel SiX-dipropargyl glycerol scaffold (X: H, F, or (18) F) was developed as a versatile prosthetic group that provides technical advantages for the preparation of dimeric radioligands based on silicon fluoride acceptor pre- or post-labeling with fluorine-18. Rapid conjugation with the prosthetic group takes place in microwave-assisted click conjugation under mild conditions. Thus, a bivalent homodimeric SiX-dipropargyl glycerol derivatized radioligand, [(18) F]BMPPSiF, with enhanced affinity was developed by using click conjugation. High uptake of the radioligand was demonstrated in 5-HT1A receptor-rich regions in the brain with positron emission tomography. Molecular docking studies (rigid protein-flexible ligand) of BMPPSiF and known antagonists (WAY-100635, MPPF, and MefWAY) with monomeric, dimeric, and multimeric 5-HT1A receptor models were performed, with the highest G score obtained for docked BMPPSiF: -6.766 as compared with all three antagonists on the monomeric model. Multimeric induced-fit docking was also performed to visualize the comparable mode of binding under in vivo conditions, and a notably improved G score of -8.455 was observed for BMPPSiF. These data directly correlate the high binding potential of BMPPSiF with the bivalent binding mode obtained in the biological studies. The present study warrants wide application of the SiX-dipropargyl glycerol prosthetic group in the development of ligands for imaging with enhanced affinity markers for specific targeting based on peptides, nucleosides, and lipids.

Practical synthesis of indoles and benzofurans in water using a heterogeneous bimetallic catalyst

This paper describes the preparation of indoles, azaindoles and benzofurans in pure water by using a new heterogeneous Pd–Cu/C catalyst through a cascade Sonogashira alkynylation–cyclization sequence. Details of the optimization studies and the substrate scope are discussed. This procedure allows the preparation of heterocycles with good yields and is tolerant to a wide variety of functional groups.

The colloidal state of tannins impacts the nature of their interaction with proteins: the case of salivary proline-rich protein/procyanidins binding

While the definition of tannins has been historically associated with its propensity to bind proteins in a nonspecific way, it is now admitted that specific interaction also occurs. The case of the astringency perception is a good example to illustrate this phenomenon: astringency is commonly described as a tactile sensation induced by the precipitation of a complex composed of proline-rich proteins present in the human saliva and tannins present in beverages such as tea or red wines. In the present work, the interactions between a human saliva protein segment and three different procyanidins (B1, B3, and C2) were investigated at the atomic level by NMR and molecular dynamics. The data provided evidence for (i) an increase in affinity compared to shortest human saliva peptides, which is accounted for by protein "wraping around" the tannin, (ii) a specificity in the interaction below tannin critical micelle concentration (CMC) of ca. 10 mM, with an affinity scale such that C2 > B1 > B3, and (iii) a nonspecific binding above tannin CMC that conducts irremediably to the precipitation of the tannins/protein complex. Such physicochemical findings describe in accurate terms saliva protein-tannin interactions and provide support for a more subtle description by oenologists of wine astringency perception in the mouth.

Sustainable Heck-Matsuda reaction with catalytic amounts of diazonium salts: an experimental and theoretical study

The palladium-catalyzed Heck-Matsuda reaction with a catalytic amount of an in-situ-generated diazonium salt proceeded under mild and sustainable conditions. The reaction proceeded at room temperature, under base-free conditions, and only generated tBuOH, H(2)O, and N(2) as by-products. Ortho-substituted diazonium salts were more-efficiently coupled to methyl acrylate than their corresponding para isomers, which required the addition of anisole as an additive. In support of these experimental data, we carried out theoretical studies to gain a deeper understanding of these reaction outcomes.

Towards a molecular interpretation of astringency: synthesis, 3D structure, colloidal state, and human saliva protein recognition of procyanidins

Astringency is a sensation in the mouth used in judging the quality of red wine. The rough, dry, and puckering sensation called astringency is the result of an interaction between tannins and saliva proteins, mainly proline-rich proteins (PRP), which leads to the formation and precipitation of a complex. A dry and rough sensation is then perceived in the mouth. To get an insight into astringency at the molecular level we investigated: (i) An efficient and iterative method for 4-8 procyanidin synthesis, which gives rise to all possible 4-8 procyanidins up to the tetramer with total control of degree of oligomerization and stereochemistry. (ii) The 3D-structural preferences, which take into account their internal movements, using 2D NMR and molecular modeling. (iii) The self-association process in water or hydroalcoholic solutions using diffusion NMR spectroscopy that gives the active proportion of tannins able to fix proteins. (iv) A comprehensive description of the PRP-procyanidin complex formation to get information about stoichiometry, binding site localization, and affinity constants for different procyanidins. The data collected suggest that the interactions are controlled by both procyanidin conformational and colloidal state preferences. All these results provide new insights into the molecular interpretation of tannin astringency.

Silicon-based chemistry: an original and efficient one-step approach to [18F]-nucleosides and [18F]-oligonucleotides for PET imaging

Take it eaSi! Nucleosides, dinucleotides, and one oligonucleotide, all modified by click chemistry, have for the first time been directly and very efficiently labeled with (18)F by using a silicon-based, one-step approach that opens the way for the development of a new class of positron emission tomography (PET) tracers (see graphic).

A useful, reliable and safer protocol for hydrogenation and the hydrogenolysis of O-benzyl groups: the in situ preparation of an active Pd(0)/C catalyst with well-defined properties

A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O-benzyl ethers has been developed. The method features the in situ preparation of an active Pd(0)/C catalyst from Pd(OAc)(2) and charcoal, in methanol. The mild reaction conditions (25°C) and low catalyst loading required (0.025 mol%), as well as the absence of contamination of the product by palladium residues (<4 ppb), make this a sustainable, useful process for organic chemists. Alternatively, the protocol can be carried out under microwave activation, to shorten the reaction times, with cyclohexene as the hydrogen source.

NMR and molecular modeling of wine tannins binding to saliva proteins: revisiting astringency from molecular and colloidal prospects

In organoleptic science, the association of tannins to saliva proteins leads to the poorly understood phenomenon of astringency. To decipher this interaction at molecular and colloidal levels, the binding of 4 procyanidin dimers (B1-4) and 1 trimer (C2) to a human saliva proline-rich peptide, IB7(14), was studied. Interactions have been characterized by measuring dissociation constants, sizes of complexes, number, and nature of binding sites using NMR (chemical shift variations, diffusion-ordered spectroscopy, and saturation transfer diffusion). The binding sites were identified using molecular mechanics, and the hydrophilic/hydrophobic nature of the interactions was resolved by calculating the molecular lipophilicity potential within the complexes. The following comprehensive scheme can be proposed: 1) below the tannin critical micelle concentration (CMC), interaction is specific, and the procyanidin anchorage always occurs on the same three IB7(14) sites. The tannin 3-dimensional structure plays a key role in the binding force and in the tannin's ability to act as a bidentate ligand: tannins adopting an extended conformation exhibit higher affinity toward protein and initiate the formation of a network. 2) Above the CMC, after the first specific hydrophilic interaction has taken place, a random hydrophobic stacking occurs between tannins and proteins. The whole process is discussed in the general frame of wine tannins eliciting astringency.

Room-temperature, ligand- and base-free Heck reactions of aryl diazonium salts at low palladium loading: sustainable preparation of substituted stilbene derivatives

The Pd(OAc)(2)-catalyzed Heck reaction of aryl diazonium salts with 2-arylacrylates led to cis-stilbenes with good to excellent stereoselectivity. The environmentally friendly protocol developed in this work features low palladium loading in technical-grade methanol at room temperature under base-, additive-, and ligand-free conditions. The same protocol applied to simple Heck coupling of aryl diazonium salts with methyl acrylate allows astonishingly low palladium loading, down to 0.005 mol%. The stereoselectivity experimentally observed for the synthesis of cis-stilbenes has been rationalized by DFT calculations. Moreover, the role of methanol in promoting the reaction has been clarified by a computational study.