Solid-phase Synthetic Strategy Research Articles

Synthetic Dual Cysteine-ADP Ribosylated Peptides from the Androgen Receptor are Recognized by the DTX3L/PARP9 Complex.

Androgen signaling in prostate cancer cells involves multisite cysteine ADP-ribosylation of the androgen receptor (AR) by PARP7. The AR modification is read by ADP-ribosyl binding macrodomains in PARP9, but the reason that multiple cysteines are modified is unknown. Here, we use synthetic peptides to show that dual ADP-ribosylation of closely spaced cysteines mediates recognition by the DTX3L/PARP9 complex. Mono and dual ADP-ribosylated cysteine peptides were prepared using a novel solid-phase synthetic strategy utilizing a key, Boc-protected, ribofuranosylcysteine building block. This synthetic strategy allowed us to synthesize fluorescently labeled peptides containing a dual ADP-ribosylation motif. It was found that the DTX3L/PARP9 complex recognizes the dual ADP-ribosylated AR peptide (Kd = 80.5 nM) with significantly higher affinity than peptides with a single ADP-ribose. Moreover, oligomerization of the DTX3L/PARP9 complex proved crucial for ADP-ribosyl-peptide interaction since a deletion mutant of the complex that prevents its oligomer formation dramatically reduced peptide binding. Our data show that features of the substrate modification and the reader contribute to the efficiency of the interaction and imply that multivalent interactions are important for AR-DTX3L/PARP9 assembly.

Solid-Phase Synthesis of the Bicyclic Peptide OL-CTOP Containing Two Disulfide Bridges, and an Assessment of Its In Vivo μ-Opioid Receptor Antagonism after Nasal Administration.

New strategies facilitate the design of cyclic peptides which can penetrate the brain. We have designed a bicyclic peptide, OL-CTOP, composed of the sequences of a selective μ-opioid receptor antagonist, CTOP (f-cyclo(CYwOTX)T) (X = penicillamine, Pen; O = ornithine) and odorranalectin, OL (YASPK-cyclo(CFRYPNGVLAC)T), optimized its solid-phase synthesis and demonstrated its ability for nose-to-brain delivery and in vivo activity. The differences in reactivity of Cys and Pen thiol groups protected with trityl and/or acetamidomethyl protecting groups toward I2 in different solvents were exploited for selective disulfide bond formation on the solid phase. Both the single step and the sequential strategy applied to macrocyclization reactions generated the desired OL-CTOP, with the sequential strategy yielding a large quantity and better purity of crude OL-CTOP. Importantly, intranasally (i.n.s.) administered OL-CTOP dose-dependently antagonized the analgesic effect of morphine administered to mice through the intracerebroventricular route and prevented morphine-induced respiratory depression. In summary, the results demonstrate the feasibility of our solid-phase synthetic strategy for the preparation of the OL-CTOP bicyclic peptide containing two disulfide bonds and reveal the potential of odorranalectin for further modifications and the targeted delivery to the brain.

Developing membrane reactors with suspended polyphthalocyanine nanoplatelets for upscaling syntheses of protein-polymer bioconjugates

The production of polymer bioconjugates at high monomer dilutions and on a large scale suffers a severe limitation as there are typically tedious procedures for prior deoxygenation, catalyst removal and intermittent product purification. In this contribution, the development of suspended-catalysts-based membrane reactors (SCBMR) aims to combine the benefits of heterogeneous catalysis and industrialized membrane technology to streamline the upscaling syntheses of value-added bioactive materials through a robust photopolymerization strategy. The poly(ethylene glycol) methyl ether (MPEG)-linked polyphthalocyanine (PPc-MPEG) nanoplatelets were synthesized using a solid-phase synthetic strategy, followed by exfoliation and post-functionalization with MPEG. Under the catalysis of PPc-MPEG nanoplatelets, well-defined polymers were obtained within a few hours under near-infrared (NIR) light irradiation with excellent control over the molecular weight and polydispersity in batch. The versatility of SCBMR was highlighted through significant simplicity with respect to the elimination of time-consuming prior deoxygenation, catalyst removal and intermittent purification procedures. In addition, SCBMR was expanded as means for designing complex protein-polymer bioconjugates from multiple proteins (e.g., bovine serum albumin, human serum albumin, horseradish peroxidase) and monomer classes. In comparison to dialysis process, SCBMR could afford the bioconjugates with purity exceeding 99% in 4.2 diavolumes. As such, the combination of polyphthalocyanine nanoplatelets and industrialized membrane technology provides a general and highly accessible methodology for the synthetic scaling of bioactive materials with optimized structures for various biomedical applications.

Total Synthesis and Functional Analysis of Complex Peptidic Natural Products and Their Artificial Analogues

This review focuses on a new solid-phase synthetic strategy for an anticancer natural product yaku'amide B (1) and its target identification and structure-function relationship study using synthetic analogues and probes. To realize the Fmoc-based solid-phase synthesis of 1, we developed new synthetic methods for enamide formation. Namely, modified traceless Staudinger ligation using alkenyl azides and newly designed phosphinophenol esters enabled stereoselective construction of the (E)- and (Z)-ΔIle moieties. Furthermore, resin-cleavage and C-terminus modification were simultaneously achieved with an ester-amide exchange reaction using C-terminal amine and AlMe3, which successfully afforded 1 via a full solid-phase route. The developed strategy was applied to the construction of seven E/Z isomers of 1. In the target identification of 1, fluorescent imaging study and affinity pull-down assay using the synthetic probes revealed that 1 exerts potent cytostatic activity by binding to subunits α and β of mitochondrial FoF1-ATP synthase. On the basis of the mode of action of 1, we conducted biological evaluation of the seven E/Z-isomers of 1. Assessment of growth inhibition activity and the effect on FoF1-ATP synthase indicates that the E/Z-stereochemistry of the three ΔIle residues controls the magnitude of biological functions of 1.

Novel Synthetic Strategies Enable the Efficient Development of Folate Conjugates for Cancer Radiotheranostics.

The folate receptor (FR) is an interesting target for radiotheranostics due to its overexpression in several tumor types. The progress in developing novel folate radioconjugates is, however, slow due to the synthetic challenges that folate chemistry presents. The goal of this study was, thus, to establish versatile solid-phase synthetic strategies for a convenient preparation of novel folate conjugates. Two approaches were established based on an orthogonal fluorenylmethyloxycarbonyl (Fmoc)-protection strategy to enable a modular buildup of an albumin-binding DOTA conjugate (known as OxFol-1) using folic acid (oxidized folate version) as a targeting agent. The main difference between the two approaches was the sequence of conjugating the single structural units. The approach that introduced the folate entity as the last unit appeared particularly useful for the preparation of conjugates based on 6R- or 6S-5-methyltetrahydrofolic acid (5-MTHF; a reduced folate version) as targeting entity. Three types of folate conjugates were synthesized either with a p-iodophenyl-based albumin binder (OxFol-1, 6R-RedFol-1, and 6S-RedFol-1) or without an albumin-binding entity (OxFol-14, 6R-RedFol-14, and 6S-RedFol-14). All six conjugates were obtained with high chemical purity (>98%) after 9-13 synthesis steps and a single final HPLC purification. Radiolabeling with lutetium-177 was feasible at high molar activity, and the resulting radioconjugates were stable over at least 24 h. Biodistribution and SPECT/CT imaging studies confirmed the favorable effect of an albumin-binding entity to increase the tumor uptake and reduce kidney retention of folate radioconjugates. The increased tumor-to-kidney ratios obtained with [177Lu]Lu-6R-RedFol-1 and [177Lu]Lu-6S-RedFol-1 as compared to [177Lu]Lu-OxFol-1 indicated that 5-MTHF is the preferred FR-targeting agent for albumin-binding radioconjugates. This was, however, not the case for folate radioconjugates without an albumin binder. Thanks to the established synthesis strategy, the preparation of further folate radioconjugates will be facilitated, potentially enabling the optimization of the tissue distribution characteristics even more.

Synthesis of Caffeoyl-Prolyl-Histidyl-Xaa Derivatives and Evaluation of Their Activities and Stability upon Long-Term Storage.

Antioxidants play a critical role in the treatment of degenerative diseases and delaying the aging of dermal tissue. Caffeic acid (CA) is a representative example of the antioxidants found in plants. However, CA is unsuitable for long-term storage because of its poor stability under ambient conditions. Caffeoyl-Pro-His-NH2 (CA-Pro-His-NH2, CA-PH) exhibits the highest antioxidant activity, free radical scavenging and lipid peroxidation inhibition activity among the histidine-containing CA-conjugated dipeptides reported to date. The addition of short peptides to CA, such as Pro-His, is assumed to synergistically enhance its antioxidative activity. In this study, several caffeoyl-prolyl-histidyl-Xaa-NH2 derivatives were synthesized and their antioxidative activities evaluated. CA-Pro-His-Asn-NH2 showed enhanced antioxidative activity and higher structural stability than CA-PH, even after long-term storage. CA-Pro-His-Asn-NH2 was stable for 3 months, its stability being evaluated by observing the changes in its NMR spectra. Moreover, the solid-phase synthetic strategy used to prepare these CA-Pro-His-Xaa-NH2 derivatives was optimized for large-scale production. We envision that CA-Pro-His-Xaa-NH2 derivatives can be used as potent dermal therapeutic agents and useful cosmetic ingredients.

Solid-phase synthesis and evaluation of tumour-targeting phenylboronate-based MRI contrast agents.

Paramagnetic macrocycles functionalized with phenylboronic moieties have proven to be interesting for MRI applications based on their ability to recognize cancer cells and generate local contrast. However, full use of the potential of this class of compounds is hampered by laborious and inefficient synthetic and, especially, purification procedures. The amphiphilic character of water-soluble phenylboronates renders them difficult compounds to be prepared through conventional solution synthesis due to the tendency to aggregate and form adducts with other nucleophiles. The new strategy described herein exploits the advantage of solid-phase synthesis with the application of DEAM-PS resin for anchorage and the subsequent simplified derivatization of boronates. GdDOTA-EN-PBA and its fluorinated analogue GdDOTA-EN-F2PBA were synthesized in a much easier, faster and economically convenient way to achieve good yields and purity. Furthermore, the effect of electron-withdrawing fluorine atoms on the aromatic ring of the latter compound was investigated by comparing the physico-chemical properties of both compounds as well as their binding affinity towards melanoma cancer cells.

Solid-Phase Synthesis of Self-Assembling Multivalent π-Conjugated Peptides.

We present a completely solid-phase synthetic strategy to create three- and four-fold peptide-appended π-electron molecules, where the multivalent oligopeptide presentation is dictated by the symmetries of reactive handles placed on discotic π-conjugated cores. Carboxylic acid and anhydride groups were viable amidation and imidation partners, respectively, and oligomeric π-electron discotic cores were prepared through Pd-catalyzed cross-couplings. Due to intermolecular hydrogen bonding between the three or four peptide axes, these π-peptide hybrids self-assemble into robust one-dimensional nanostructures with high aspect ratios in aqueous solution. The preparation of these systems via solid-phase methods will be detailed along with their self-assembly properties, as revealed by steady-state spectroscopy and transmission electron microscopy and electrical characterization using field-effect transistor measurements.

Solid-Phase Synthetic Strategies for the Preparation of Purine Derivatives.

This Review summarizes all of the currently described strategies applicable for the solid-phase synthesis of purine derivatives. The individual approaches are classified according to the immobilization procedure used resulting in a linkage of the final scaffold at various positions.

Epitope mapping of anti-myelin oligodendrocyte glycoprotein (MOG) antibodies in a mouse model of multiple sclerosis: microwave-assisted synthesis of the peptide antigens and ELISA screening.

The role of pathologic auto-antibodies against myelin oligodendrocyte glycoprotein (MOG) in multiple sclerosis is a highly controversial matter. As the use of animal models may enable to unravel the molecular mechanisms of the human disorder, numerous studies on multiple sclerosis are carried out using experimental autoimmune encephalomyelitis (EAE). In particular, the most extensively used EAE model is obtained by immunizing C57BL/6 mice with the immunodominant peptide MOG(35-55). In this scenario, we analyzed the anti-MOG antibody response in this model using the recombinant refolded extracellular domain of the protein, MOG(1-117). To assess the presence of a B-cell intramolecular epitope spreading mechanism, we tested also five synthetic peptides mapping the 1-117 sequence of MOG, including MOG(35-55). For this purpose, we cloned, expressed in Escherichia coli and on-column refolded MOG(1-117), and we applied an optimized microwave-assisted solid-phase synthetic strategy to obtain the designed peptide sequences. Subsequently, we set up a solid-phase immunoenzymatic assay testing both naïve and EAE mice sera and using MOG protein and peptides as antigenic probes. The results obtained disclose an intense IgG antibody response against both the recombinant protein and the immunizing peptide, while no response was observed against the other synthetic fragments, thus excluding the presence of an intramolecular epitope spreading mechanism. Furthermore, as the properly refolded recombinant probe is able to bind antibodies with greater efficiency compared with MOG(35-55), we hypothesize the presence of both linear and conformational epitopes on MOG(35-55) sequence.

Pyrrole-Imidazole Polyamides: Automated Solid-Phase Synthesis.

In this unit, the fully automated solid-phase synthetic strategy of hairpin Py-Im polyamides is described using triphosgene (BTC) as a coupling agent. This automated methodology is compatible with all the typical building blocks, enabling the facile synthesis of polyamide libraries in 9% to 20% yield in 3 days.

Solid-supported cross-metathesis and a formal alkane metathesis for the generation of biologically relevant molecules.

Solid-phase synthetic strategies toward the generation of libraries of biologically relevant molecules were developed using olefin cross-metathesis as a key step. It is remarkably the formal alkane metathesis based on a one-pot, microwave-assisted, ruthenium-catalyzed cross-metathesis and reduction to obtain Csp3-Csp3 linkages.

Fully automated synthesis of DNA-binding Py-Im polyamides using a triphosgene coupling strategy.

The fully automated solid-phase synthetic strategy of hairpin pyrrole-imidazole polyamides is described. A key advance is the development of methodology for the application of triphosgene as a coupling agent in the automated synthesis of hairpin polyamides without racemization. This automated methodology is compatible with all the typical building blocks, enabling the facile synthesis of polyamide libraries in good yield (9-15%) and crude purity.

ChemInform Abstract: Nitrogen‐Containing Privileged Structures and Their Solid‐Phase Combinatorial Synthesis

AbstractReview: 240 refs.

Total Synthesis of Fellutamide B and Deoxy-Fellutamides B, C, and D

The total syntheses of the marine-derived lipopeptide natural product fellutamide B and deoxy-fellutamides B, C, and D are reported. These compounds were accessed through a novel solid-phase synthetic strategy using Weinreb amide-derived resin. As part of the synthesis, a new enantioselective route to (3R)-hydroxy lauric acid was developed utilizing a Brown allylation reaction followed by an oxidative cleavage-oxidation sequence as the key steps. The activity of these natural products, and natural product analogues was also assessed against Mycobacterium tuberculosis in vitro.

Nitrogen Containing Privileged Structures and their Solid Phase Combinatorial Synthesis

The existence of preferred molecular scaffolds that possess inherent biological activity, called privileged structures, is now well recognized. Such privileged structures not only provide enhanced drug-like properties but also give new hits for developing leads. The synthesis of combinatorial libraries, especially with the insertion of privileged substructures into heterocyclic moieties containing nitrogen, provides for a greater probability of the discovery of novel lead compounds using chemical transformation. The review focuses on the progress in the solid-phase synthetic strategies of nitrogen containing privileged structures over the years.

PNA bearing 5-azidomethyluracil: a novel approach for solid and solution phase modification.

Fmoc- and Boc-protected modified monomers bearing 5-azidomethyluracil nucleobase were synthesized. Four different solid-phase synthetic strategies were tested in order to evaluate the application of this series of monomers for the solid-phase synthesis of modified PNA. The azide was used as masked amine for the introduction of amide-linked functional groups, allowing the production of a library of compounds starting from a single modified monomer. The azide function was also exploited as reactive group for the modification of PNA in solution via azide-alkyne click cycloaddition.

Nanoscale Biomolecular Structures on Self-Assembled Monolayers Generated from Modular Pegylated Disulfides

A solid-phase synthetic strategy was developed that uses modular building blocks to prepare symmetric oligo(ethylene glycol)-terminated disulfides with a variety of lengths and terminal functionalities. The modular disulfides, composed of alkyl amino groups linked by an amide group to oligoethylene chains were used to generate self-assembled monolayers (SAMs), which were characterised to determine their applicability for biomolecular applications. X-ray photoelectron spectroscopy (XPS) of the SAMs obtained from these molecules demonstrated improved stability towards displacement by 16-hexadecanethiol, while surface plasmon resonance (SPR) analyses of SAMs prepared with the hydroxy-terminated oligoethylene disulfide showed equal resistance to non-specific protein adsorption in comparison to 11-mercaptoundecyl tri(ethylene glycol). SAMs made from these adsorbates were amenable to nanoscale patterning by scanning near-field photolithography (SNP), facilitating the fabrication of nanopatterned, protein-functionalised surfaces. Such SAMs may be further developed for bionanotechnology applications such as the fabrication of nanoscale biological arrays and sensor devices.

Solid-Phase Synthetic Strategy and Bioevaluation of a Labeled δ-Opioid Receptor Ligand Dmt-Tic-Lys for In Vivo Imaging

A general solid-phase synthetic strategy is developed to prepare fluorescent and/or lanthanide-labeled derivatives of the delta-opioid receptor (deltaOR) ligand H-Dmt-Tic-Lys(R)-OH. The high delta-OR affinity (K(i) = 3 nM) and desirable in vivo characteristics of the Cy5 derivative 1 suggest its usefulness for structure-function studies and receptor localization and as a high-contrast noninvasive molecular marker for live imaging ex vivo or in vivo.

Solid-Phase Synthesis of Amphiphilic Dendron-Surface-Modified Silica Particles and Their Application Toward Water Purification

Surface modification of silica particles by an amphiphilic poly(amido amine) (PAMAM) dendron and investigation of their advanced application toward water purification have been demonstrated. The amphiphilic dendron-surface-modified silica particles (C18GnS, n = 1−3) were prepared by solid-phase synthetic strategy including the propagation of PAMAM dendrons on silica surface through conventional divergent pathway and the end-group functionalization of dendrons by long aliphatic chains. Infrared absorption analyses confirmed the characteristic vibration modes of amide and methylene groups on the dendritic backbone and long alkyl peripherals, respectively. The gradual increasing amount of organic grafts determined by thermogravimetric and elemental analyses also supported the successful modification of amphiphilic dendron on the silica surface. C18GnS effectively adsorbed anionic targets such as organic dyes and surfactants in water, and the adsorption behavior obeyed a Langmuir adsorption isotherm. Moreover, the adsorption isothermal studies indicated that adsorption of surfactants on C18GnS was due to the assistance of hydrophobic interaction between the aliphatic peripherals on the dendron and the alkyl tail on the surfactant, while the electrostatic interaction with C18GnS mainly played a role for the adsorption of dyes. Anionic adsorbates were released from C18GnS in an alkaline environment because of the pH-dependent nature of PAMAM dendron, and thus the surface-modified silica particles were recovered and reused.