Search results for "combinatorial"

Coordination complexes incorporating pyrophosphate: Structural overview and exploration of their diverse magnetic, catalytic and biological properties

2010

Abstract Current attention continues to revolve around the chemistry and biochemistry associated with polyphosphate anions because of their importance in biology. A pivotal intermediate within this family is the pyrophosphate tetraanion, P2O74−. Considering its biological relevance and the multidentate nature that makes it an ideal ligand in the field of the coordination chemistry, there is a growing interest in the use of this anion in building new class of molecules/compounds for different purposes. While the total number of characterized structures still remains modest, several new pyrophosphate-containing coordination complexes have been reported in the last decade, as well as different…

Functionalized Tri‐ and Tetraphosphine Ligands as a General Approach for Controlled Implantation of Phosphorus Donors with a High Local Density in Im…

2014

Supported phosphine ligands are auxiliaries of topical academic and industrial interest in catalysis promoted by transition metals. However, both controlled implantation and controlled conformation of ligands should be achieved to produce immobilized catalysts that are able to structurally “copy” efficient homogeneous systems. We provide herein a general synthetic strategy for assembling a new class of branched tetra- and triphosphine ligands with a unique controlled rigid conformation, and thus providing a high local density of phosphorus atoms for extended coordination to the metal center. We prepared new functionalized cyclopentadienyl (Cp) salts to design polyphosphines that were “ready…

Modular Hemisyntheses of Boronato- and Trifluoroborato-SubstitutedL-NHBoc Amino Acid and Peptide Derivatives

2013

Modular hemisyntheses of boronato- and trifluoroborato-substituted amino acid and peptide derivatives by using Wittig and C–H iridium-catalyzed borylation as key reactions, are described. Amino ester precursors bearing an aromatic moiety on a lateral chain were prepared by reaction of a new L-NHBoc-amino acid Wittig reagent with the corresponding aromatic aldehydes. After esterification and hydrogenation, the borylation of amino esters was achieved with yields up to 82 % by using the catalysed reaction of bis(pinacolato) diborane reagent (B2Pin2) in the presence of an iridium complex. Interestingly, this iridium-catalyzed borylation was also performed with a dipeptide in 78 % yield. Finally…

Synthesis of cyclic dipeptide templates, their incorporation into peptides and studies on their conformational and biological properties.

2009

This study investigated the diastereoselective synthesis of three dipeptide templates 1, 2 and 3, which may be regarded as conformationally restricted analogs of H-Gly-Xaa-OH, in which Xaa constitutes an aromatic amino acid. Bond formation between α-C of Gly and the aromatic moiety was achieved by proton-catalyzed intramolecular electrophilic aromatic substitution. The absolute configuration of the dipeptide templates was determined by single-crystal X-ray crystallography or by nuclear Overhauser enhancement measurements. A protective group strategy was elaborated to allow their incorporation into peptide sequences by liquid phase as well as by solid-phase peptide synthesis. The templates w…

Conjugate Alkynylation of Electrophilic Double Bonds. From Regioselectivity to Enantioselectivity

2018

This review surveys the historical efforts addressed toward the development of the conjugate alkynylation reaction. The regio- and enantioselective conjugate alkynylation of electron-deficient double bonds, most commonly unsaturated carbonyl compounds, has been an elusive reaction for a long time. Intensive research during the last decades has resulted in the identification of a number of effective reagents and catalysts to perform this reaction. Non-stereoselective conjugate alkynylation of unsaturated carbonyl compounds was first achieved by using preformed alkynyl organometallics and later with terminal alkynes under catalytic conditions. These methods paved the way for the development o…

Chemical conjugation of dexamethasone to a polyaspartamide and in vitro evaluation studies

2004

Two macromolecular conjugates of dexamethasone containing different drug amounts were synthesized using PHEA as the polymeric carrier and a succinic group as spacer. The content of linked drug was equal to 25.3% w/w (conjugate A) and 12.7% w/w (conjugate B). Both polymeric conjugates, unlike the free drug, were water-soluble and the amount of unlinked drug was evaluated to be approximately about 0.01% w/w. Both conjugates were relatively stable in vitro at pH 7.4 whereas in the presence of esterase only the conjugate B was able to release drug under the used experimental conditions. This dissimilar behavior has been attributed to the distinct macromolecular conformations assumed in aqueous …

Merging shuttle reactions and paired electrolysis for reversible vicinal dihalogenations

2021

Vicinal dibromides and dichlorides are important commodity chemicals and indispensable synthetic intermediates in modern chemistry that are traditionally synthesized using hazardous elemental chlorine and bromine. Meanwhile, the environmental persistence of halogenated pollutants necessitates improved approaches to accelerate their remediation. Here, we introduce an electrochemically assisted shuttle (e-shuttle) paradigm for the facile and scalable interconversion of alkenes and vicinal dihalides, a class of reactions that can be used both to synthesize useful dihalogenated molecules from simple alkenes and to recycle waste material through retro-dihalogenation. The reaction is demonstrated…

A l-glutamate-responsive delivery system based on enzyme-controlled self-immolative arylboronate-gated nanoparticles

2019

We report herein a L-glutamate (L-Glu)-responsive delivery system. It consists of Janus Au–mesoporous silica (MS) nanoparticles functionalized with L-glutamate oxidase on the Au face and with self-immolative arylboronate derivatives as caps on the MS face. The MS face is additionally loaded with a cargo. The delivery paradigm is based on the recognition of L-Glu by the enzyme and the subsequent formation of H2O2, which induces the cleavage of the self-immolative gate and the uncapping of the pores. Given the importance of L-Glu as a key neurotransmitter, we hope that these findings will help in designing new therapeutic strategies for nervous system diseases.

Nanoparticles as Enzyme Mimics

2013

Photoredox-Catalyzed Four-Component Reaction for the Synthesis of Complex Secondary Amines.

2020

The one-pot sulfonylation/aminoalkylation of styrene derivatives furnishing substituted γ-sulfonylamines was accomplished through a photoredox-catalyzed four-component reaction. Besides one molecule of water and the sodium counterion of the sulfinate, all atoms of the starting materials are transferred to the final product, rendering this process highly atom-efficient. The operationally simple protocol allows for the simultaneous formation of three new single bonds (C-S, C-N, and C-C) and therefore grants rapid access to structurally diverse products.