Design, synthesis, and validation of rigid linkers for bioactive peptides

Rigid linkers of variable length were synthesized and used to connect two NDP-α-MSH ligands. The linkers were incorporated by solid-phase synthesis. Biological evaluations indicate that there is virtually no effect of these linkers on ligand binding to the human melanocortin 4 receptor.     

Competitive Excimer Formation and Energy Transfer in Zr‐Based Heterolinker Metal–Organic Frameworks

The spectroscopy and dynamics of a series of Zr‐based MOFs in dichloromethane suspension are reported. These Zr‐NADC MOFs were constructed by using different mixtures of 2,6‐naphthalenedicarboxylate (NDC) and 4‐amino‐2,6‐naphthalenedicarboxylate (NADC) as organic linkers. The fraction of NADC relative to NDC in these heterolinker MOFs ranges from 2 to 35 %. The results indicate two competitive photoprocesses: NDC excimer formation and an energy transfer (ET) from excited NDC linkers to NADC linkers. Increasing the fraction of NADC linkers in the Zr‐NADC nanostructure decreases the mean time constant of NDC excimer formation, while the NADC emission intensity experiences a drop at the highest fraction of this linker in the MOF. The first observation is explained by an increase in the energy‐transfer probability between the two linkers, and the second by emission quenching in the NADC linkers due to ultrafast charge transfer assisted by the amino group. Femtosecond time‐resolved emission studies showed that the ET process (recorded as decaying and rising components) from excited NDC to NADC takes place in 1.2 ps. Direct excitation of the NADC linkers (at 410 nm) shows a decaying, but not rising, component of 250–480 fs, which could reflect the formation of a nonemissive charge‐separation state. The results show that by using MOFs having heterolinkers it is possible to trigger and tune excimer formation and ET processes.     

Phosphate-Based Self-Immolative Linkers for the Delivery of Amine-Containing Drugs

Amine-containing drugs often show poor pharmacological properties, but these disadvantages can be overcome by using a prodrug approach involving self-immolative linkers. Accordingly, we designed l-lactate linkers as ideal candidates for amine delivery. Furthermore, we designed linkers bearing two different cargos (aniline and phenol) for preferential amine cargo release within 15 min. Since the linkers carrying secondary amine cargo showed high stability at physiological pH, we used our strategy to prepare phosphate-based prodrugs of the antibiotic Ciprofloxacin. Therefore, our study will facilitate the rational design of new and more effective drug delivery systems for amine-containing drugs.     

Synthetic approaches to a variety of covalently linked porphyrin--fullerene hybrids

There is substantial interest in dyads in which C(60) is covalently linked to electron donors, such as porphyrins, which absorb light strongly in the visible region. We present here the details of the syntheses of such compounds, which can be broadly organized into categories depending upon the nature of the linker joining the two chromophores. The structural aspects of intramolecular electronic interaction that we have sought to explore have dictated the synthetic strategies employed to generate these classes of molecules. Flexible glycol linkers were used to allow close approach between the fullerene and porphyrin, facilitating through-space interactions. These linkers also allowed studies of the effects of metal cation complexation. Naphthalene and alkyne linkers were used to examine the possible effects a conjugated or aromatic linker might have on photophysical properties. Finally, steroids were used as linkers in dyads expected to possess a large distance between the two chromophores, in which only through-bond interactions between the fullerene and porphyrin should be possible.     

Phosphate-Based Self-Immolative Linkers for Tuneable Double Cargo Release

Phosphorus-based self-immolative (SI) linkers offer a wide range of applications, such as smart materials and drug-delivery systems. Phosphorus SI linkers are ideal candidates for double-cargo delivery platforms because they have a higher valency than carbon. A series of substituted phosphate linkers was designed for releasing two phenolic cargos through SI followed by chemical hydrolysis. Suitable modifications of the lactate spacer increased the cargo release rate significantly, from 1 day to 2 hours or 5 minutes, as shown for linkers containing p-fluoro phenol. In turn, double cargo linkers bearing p-methyl phenol released their cargo more slowly (4 days, 4 hours, and 15 minutes) than their p-fluoro analogues. The α-hydroxyisobutyrate linker released both cargos in 25 minutes. Our study expands the current portfolio of SI constructs by providing a double cargo delivery option, which is crucial to develop universal SI platforms.     

固相有机合成中的连接基团

介绍了固相有机合成中的连接基团,特别是带有隔离单元的连接基团、无痕迹连接基团、安全拉手型连接基团和复合型连接基团的基本概念、发展近况以及它们的应用.     

Single-step affinity purification of toxic and non-toxic proteins on a fluidics platform

Single-step fusion-based affinity purification of proteins with pH-controllable linkers was carried out in a fluidic device. The linkers were previously derived from self-splicing protein elements called inteins. Two different linkers were generated to solve two distinct separation problems: one for rapid single-step affinity purification of a wide range of proteins, and the other specifically for the purification of cytotoxic proteins. Scale-down factors of 185 resulted in separations in a 27 microl bed-volume. A rotating CD format was chosen because of its simplicity in effecting fluid movement through centrifugal force without the complications associated with electro-osmosis and other pumping methods. The design and fabrication of the fluidic device and the protein purification process are described. This work, which demonstrates the purification of active proteins by two distinct fluidic separations, is widely applicable to small-scale massively parallel proteomic separations.     

A Small Change in Central Linker Has a Profound Effect in Inducing Columnar Phases of Triazine‐Based Unconventional Dendrimers

Four unconventional triazine‐based dendrimers have been prepared and characterized by ¹H and ¹³C NMR spectroscopies, mass spectrometry, and elemental analysis. Based on DSC studies, polarizing microscopy, and powder XRD, two of these dendrimers, containing linkers with an odd number of carbon atoms, were observed to display columnar liquid–crystalline phases during thermal treatment. However, the other two dendritic analogues, containing linkers with an even number of carbon atoms, were not observed to behave correspondingly. Based on computer simulation, we reasonably assume that the dendrimers with an odd number of carbon atoms in their linkers distort their molecular shape and adopt two isomeric structures due to asymmetrical congestion. This reduces the molecular π–π face‐to‐face interaction, which in turn causes the dendrimers to form columnar LC phases during thermal treatment. However, the dendrimers with an even number of carbon atoms in their linkers have more symmetrical skeletons and do not display any liquid–crystalline phase upon thermal treatment. This new strategy should be applicable for eliciting the columnar liquid–crystalline properties of other types of unconventional dendrimers with rigid frameworks.     

Can Coordination‐Driven Supramolecular Self‐Assembly Reactions Be Conducted from Fully Aliphatic Linkers?

The reaction between a preassembled Cu^I bimetallic molecular clip with a short intermetallic distance and a series of fully aliphatic cyano‐capped ditopic linkers with increasing lengths was investigated. It is shown that, depending on the length of the ditopic linkers, the rational design of unprecedented supramolecular compact metallacycles containing fully aliphatic walls is possible. The specific preorganized molecular arrangement of the molecular clip used favors stabilizing interlinker London dispersion interactions, which allow, as the length of the linkers increases, the selective formation of discrete compact metallacycles at the expense of 1D coordination polymers. The generalizability of this approach was demonstrated by the reaction of fully aliphatic cyano‐capped linkers with two other types of preassembled Cu^I bimetallic molecular clips that also had short intermetallic distances.     

Double stranded polymeric ladderphanes with 16-π-electron antiaromatic metallocycle linkers

Three double stranded polymeric ladderphanes with 16-π-electron antiaromatic metallocycle linkers are synthesised by ring opening metathesis polymerisation of the corresponding bisnorbornene monomers. Scanning tunnelling microscopic (STM) images indicate that these polymers can assemble nicely on a graphite surface to form a highly ordered pattern which has been observed in other ladderphanes with different kinds of aromatic linkers. Little change in (1)H NMR, absorption spectra and electrochemical oxidation potential between these polymers and the corresponding monomers suggest that there would be no interactions between adjacent antiaromatic linkers in these polymeric ladderphanes. Presumably, the distance between two antiaromatic rings in these ladderphanes (5-6 ?) is far too long in comparison with that between two rings in methylene-bridged antiaromatic superphanes (2.5 ?<), where stabilisation is predicted by theoretical calculations.     

Tunable molecular magnetism in conjugated assembly of functional spin units

Molecular design and photoelectrochemically responsive functions of several redox‐tunable building blocks toward conjugated assembling were described. The viologen dimers and pyridylpyridinium dimers through π‐conjugated linkers showed multi‐step redox processes which were demonstrated electrochemically and photochemically. The 4,6‐pyrimidinylene and 3,6‐pyridazinylene linkers played an important role as effective mediators between two attached electrons in the two viologens or pyridinium groups. The latter pyridylpyridinium dimers and 3‐pyridylviologen have potential to coordinate various metal ions to give conjugated self‐assemblies.     

Linkers for oligonucleotide microarray synthesis

A number of linkers for microchip-based (microarray) synthesis of oligonucleotides were synthesized here using photolabile intermediates. The resulting linkers are designed for covalent immobilization on slides containing both hydroxyl and amino groups.The first series of linkers was intended for the synthesis of oligonucleotide arrays for hybridization analysis. These linkers provide a strong covalent bond with the slide surface when amino groups in oligonucleotide heterocyclic bases are deprotected.The second series of linkers allows to cleave the synthesized oligonucleotides from the support on which they were synthesized. Furthermore, the use of such linkers yields oligonucleotides devoid of the phosphate group at their 3′ end.The obtained linkers were successfully tested in the synthesis of oligonucleotides on a microchip for subsequent hybridization analysis and assembly of a DNA fragment.     

Preparation of fluorinated linkers: use of 19F NMR spectroscopy to establish conditions for solid-phase synthesis of pilicide libraries

Three fluorinated linkers which are analogues of linkers commonly used in solid-phase peptide synthesis have been prepared. One of the linkers was used in combination with gel-phase 19F NMR spectroscopy to develop conditions for solid-phase synthesis of two libraries of pilicides, i.e. compounds designed to inhibit assembly of adhesive pili in uropathogenic Escherichia coli. Attachment to and cleavage from the linker could be monitored based on the chemical shift of the fluorine atom of the linker. In addition, use of the linker as internal standard allowed quantification and optimization of reactions occurring further away from the linker when fluorinated building blocks were employed. Importantly, high-quality 19F NMR spectra were obtained for compounds linked to a TentaGel resin in a standard NMR tube using an ordinary NMR instrument.     

Pore‐Environment Engineering with Multiple Metal Sites in Rare‐Earth Porphyrinic Metal–Organic Frameworks

Multi‐component metal–organic frameworks (MOFs) with precisely controlled pore environments are highly desired owing to their potential applications in gas adsorption, separation, cooperative catalysis, and biomimetics. A series of multi‐component MOFs, namely PCN‐900(RE), were constructed from a combination of tetratopic porphyrinic linkers, linear linkers, and rare‐earth hexanuclear clusters (RE₆) under the guidance of thermodynamics. These MOFs exhibit high surface areas (up to 2523 cm² g^?1) and unlimited tunability by modification of metal nodes and/or linker components. Post‐synthetic exchange of linear linkers and metalation of two organic linkers were realized, allowing the incorporation of a wide range of functional moieties. Two different metal sites were sequentially placed on the linear linker and the tetratopic porphyrinic linker, respectively, giving rise to an ideal platform for heterogeneous catalysis.     

Evidence of a Uranium-Paddlewheel Node in a Catecholate-Based Metal–Organic Framework

The interactions between uranium and non-innocent organic species are an essential component of fundamental uranium redox chemistry. However, they have seldom been explored in the context of multidimensional, porous materials. Uranium-based metal–organic frameworks (MOFs) offer a new angle to study these interactions, as these self-assembled species stabilize uranium species through immobilization by organic linkers within a crystalline framework, while potentially providing a method for adjusting metal oxidation state through coordination of non-innocent linkers. We report the synthesis of the MOF NU-1700 , assembled from U⁴⁺-paddlewheel nodes and catecholate-based linkers. We propose this highly unusual structure, which contains two U⁴⁺ ions in a paddlewheel built from four linkers—a first among uranium materials—as a result of extensive characterization via powder X-ray diffraction (PXRD), sorption, transmission electron microscopy (TEM), and thermogravimetric analysis (TGA), in addition to density functional theory (DFT) calculations.     

Highly bent crystals formed by restrained π-stacked columns connected via alkylene linkers with variable conformations

A reproducible formation of strongly bent crystals was accomplished by structurally restraining macrocyclic π-conjugated molecules. The model π-units consist of two 9,10-bis(2-thienylethynyl)anthracenes with a strong propensity for stacking, which are connected in a macrocyclic fashion via two alkylene linkers. The correlation between the crystalline morphology and the macrocyclic structures restrained by a variety of flexible alkylene linker combinations was systematically studied. Bent crystals were obtained only with specific alkylene linkers of appropriate chain length. The alkylene linkers can adopt different conformations in the crystal packing, so as to fill voids within the macrocycle. The ability to form several similar molecular structures with different alkylene conformations gives rise to contaminations of different crystalline phases within a single crystal, and it is these phase contaminations which are responsible for the bending of the crystals.     

Synthesis,structure, and photochemistry of exceptionally stable synthetic DNA hairpins with stilbene diether linkers

The structure and properties of 18 hairpin-forming bis(oligonucleotide) conjugates possessing stilbene diether linkers are reported. Conjugates possessing bis(2-hydroxyethyl)stilbene 4,4'-diether linkers form the most stable DNA hairpins reported to date. Hairpins with as few as two T:A base pairs or four noncanonical G:G base pairs are stable at room temperature. Increasing the length of the hydroxyalkyl groups results in a decrease in hairpin thermal stability. On the basis of the investigation of their circular dichroism spectra, all of the hairpins investigated adopt B-DNA structures, except for a hairpin with a short poly(G:C) stem which forms a Z-DNA structure. Both the strong fluorescence of the stilbene diether linkers and their trans-cis photoisomerization are totally quenched in hairpins possessing neighboring T:A and G:C base pairs. Quenching is attributed to an electron-transfer mechanism in which the singlet stilbene serves as an electron donor and T or C serves as an electron acceptor. In contrast, in denatured hairpins and hairpins possessing neighboring G:G base pairs the stilbene diether linkers undergo efficient photoisomerization.     

新型储甲烷金属-有机骨架材料的设计

针对迄今具有最大甲烷存储量的金属-有机骨架(MOF)材料PCN-14, 采用质心分布图研究了甲烷在其中的吸附机理. 结果表明, PCN-14中主要存在两个吸附位, 并且有机配体对材料吸附甲烷有着重要影响. 因此, 通过改变有机配体的类型, 设计了对甲烷具有更高吸附性能的新型MOF材料PCN-M. PCN-M在3.5 MPa下、290 K时对甲烷的吸附量达到了257 V/V, 比PCN-14增加了12%; 298 K时对甲烷的吸附量达到了241 V/V, 超过了DOE标准180 V/V的34%. 此外, 本工作表明了改变有机配体是改善材料存储甲烷能力的一种可行方法, 为合成高甲烷储存量的新MOF材料提供了理论依据.     

Recent Advances and Trends in Chemical CPP–Drug Conjugation Techniques

This review summarizes recent developments in conjugation techniques for the synthesis of cell-penetrating peptide (CPP)–drug conjugates targeting cancer cells. We will focus on small organic molecules as well as metal complexes that were used as cytostatic payloads. Moreover, two principle ways of coupling chemistry will be discussed direct conjugation as well as the use of bifunctional linkers. While direct conjugation of the drug to the CPP is still popular, the use of bifunctional linkers seems to gain increasing attention as it offers more advantages related to the linker chemistry. Thus, three main categories of linkers will be highlighted, forming either disulfide acid-sensitive or stimuli-sensitive bonds. All techniques will be thoroughly discussed by their pros and cons with the aim to help the reader in the choice of the optimal conjugation technique that might be used for the synthesis of a given CPP–drug conjugate     

Synthesis and Characterization of Multithiazoles

Thiazole and its derivatives are of considerable interest because they act as important constituents of many biomolecules, including antibiotics, vitamins, antiarhitritics, sulphatiazoles, etc. [1,2] Thus we were prompted to ex plore new compounds containing two or more thiazole groups using different linkers. The selection of the linkers is crucial, so we consider two aspects: the first is the existing function of linker, and the second is the availability of the starting materials from commercial sources. Herein, seventeen new compounds of thiazole derivatives have been synthesized and determined by IR, 1H NMR, 13C NMR and element analysis.