Fmoc-protected Amino Acids Research Articles

Mitoxantrone release from Fmoc-protected amino acids coated magnetic carbon nanotubes: Computational and experimental study for cancer treatment

Nanoparticles have a high potential for use as drug carrier systems in cancer treatment to reduce severe side effects, as in the treatment of many other diseases. Due to their unique properties, carbon-based nanoparticles such as carbon nanotubes (CNTs) are among the most frequently used nanoparticles in drug carrier systems. In this study, magnetic single-walled CNTs (mCNTs) were synthesized, characterized, coated and their ability to carry the anticancer drug mitoxantrone (MTO) was investigated using computational and experimental methods. First, the mCNT coating capabilities of Fmoc-protected amino acids, Fmoc-Cys(trt)-OH and Fmoc-Trp-OH were demonstrated by Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. Then, full-atom molecular dynamics simulations of MTO-CNT complexes in explicit water were used to understand Fmoc-amino acid and MTO loading experiments at the molecular level. Binding free energies calculated by the Molecular Mechanics/Poisson-Boltzmann Surface Area method suggested MTO-CNT complex stability even at elevated temperatures up to 350 K that can be achieved due to external magnetic stimuli. Drug loading at pH 9 and releases at physiological (pH 7.4) and lysosomal pH (pH 5.5) were carried out for uncoated and coated mCNTs. The drug release and characterization results showed that coated mCNTs have pH-responsive drug release, enhanced dispersibility, and superparamagnetic properties so they promise to be beneficial for MTO delivery in cancer treatment. Cell viability results demonstrated that the mCNT-Fmoc-Cys samples had higher cell viability compared to the mCNT and mCNT-Fmoc-Trp groups.

Application of a new green protocol in solid-phase peptide synthesis: identification of a new green solvent mixture compatible with TBEC/ETT

ABSTRACT Solid Phase Peptide Synthesis (SPPS) is the preferred technique for synthesizing bioactive peptides. However, traditional SPPS generates significant waste and employs hazardous solvents like DMF and DCM. The aim of this research is to investigate solvents and agents of coupling that align with the green chemistry and are suitable for all stages of SPPS. Some solvents, such as p-cymene and anisole, taken into consideration in this work, can be derived from renewable sources like plants and biomass, rendering them environmentally sustainable choices. However, many of these alternative solvents possess different physicochemical properties compared to DMF. To overcome this challenge, solvent mixtures are employed. In this study, we identified a novel green solvent mixture by combining anisole with NOP; its ability to swell different resins and its capability to solubilize all Fmoc protected amino acids was investigated. The same mixture was also assessed with a green coupling agent, TBEC, in combination with ETT as additive. Model peptides Aib-enkephalin and Aib-ACP were synthesized resulting in favorable outcomes in terms of peptide synthesis efficiency, 97.81% and 98.86%, respectively.

Solid Phase Synthesis and TAR RNA-Binding Activity of Nucleopeptides Containing Nucleobases Linked to the Side Chains via 1,4-Linked-1,2,3-triazole.

Nucleopeptides (NPs) represent synthetic polymers created by attaching nucleobases to the side chains of amino acid residues within peptides. These compounds amalgamate the characteristics of peptides and nucleic acids, showcasing a unique ability to recognize RNA structures. In this study, we present the design and synthesis of Fmoc-protected nucleobase amino acids (1,4-TzlNBAs) and a new class of NPs, where canonical nucleobases are affixed to the side chain of L-homoalanine (Hal) through a 1,4-linked-1,2,3-triazole (HalTzl). Fmoc-protected 1,4-TzlNBAs suitable for HalTzl synthesis were obtained via Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) conjugation of Fmoc-L-azidohomoalanine (Fmoc-Aha) and N1- or N9-propargylated nucleobases or their derivatives. Following this, two trinucleopeptides, HalTzlAAA and HalTzlAGA, and the hexanucleopeptide HalTzlTCCCAG, designed to complement bulge and outer loop structures of TAR (trans-activation response element) RNA HIV-1, were synthesized using the classical solid-phase peptide synthesis (SPPS) protocol. The binding between HalTzls and fluorescently labeled 5'-(FAM(6))-TAR UCU and UUU mutant was characterized using circular dichroism (CD) and fluorescence spectroscopy. CD results confirmed the binding of HalTzls to TAR RNA, which was evident by a decrease in ellipticity band intensity around 265 nm during complexation. CD thermal denaturation studies indicated a relatively modest effect of complexation on the stability of TAR RNA structure. The binding of HalTzls at an equimolar ratio only marginally increased the melting temperature (Tm) of the TAR RNA structure, with an increment of less than 2 °C in most cases. Fluorescence spectroscopy revealed that HalTzlAAA and HalTzlAGA, complementary to UUU or UCU bulges, respectively, exhibited disparate affinities for the TAR RNA structure (with Kd ≈ 30 and 256 µM, respectively). Hexamer HalTzlTCCCAG, binding to the outer loop of TARUCU, demonstrated a moderate affinity with Kd ≈ 38 µM. This study demonstrates that newly designed HalTzls effectively bind the TAR RNA structure, presenting a potential new class of RNA binders and may be a promising scaffold for the development of a new class of antiviral drugs.

Structural Transformation of Coassembled Fmoc-Protected Aromatic Amino Acids to Nanoparticles.

Materials made of assembled biomolecules such as amino acids have drawn much attention during the past decades. Nevertheless, research on the relationship between the chemical structure of building block molecules, supramolecular interactions, and self-assembled structures is still necessary. Herein, the self-assembly and the coassembly of fluorenylmethoxycarbonyl (Fmoc)-protected aromatic amino acids (tyrosine, tryptophan, and phenylalanine) were studied. The individual self-assembly of Fmoc-Tyr-OH and Fmoc-Phe-OH in water formed nanofibers, while Fmoc-Trp-OH self-assembled into nanoparticles. Moreover, when Fmoc-Tyr-OH or Fmoc-Phe-OH was coassembled with Fmoc-Trp-OH, the nanofibers were transformed into nanoparticles. UV-vis spectroscopy, Fourier transform infrared spectroscopy, and fluorescence spectroscopy were used to investigate the supramolecular interactions leading to the self-assembled architectures. π-π stacking and hydrogen bonding were the main driving forces leading to the self-assembly of Fmoc-Tyr-OH and Fmoc-Phe-OH forming nanofibers. Further, a mechanism involving a two-step coassembly process is proposed based on nucleation and elongation/growth to explain the structural transformation. Fmoc-Trp-OH acted as a fiber inhibitor to alter the molecular interactions in the Fmoc-Tyr-OH or Fmoc-Phe-OH self-assembled structures during the coassembly process, locking the coassembly in the nucleation step and preventing the formation of nanofibers. This structural transformation is useful for extending the application of amino acid self- or coassembled materials in different fields. For example, the amino acids forming nanofibers could be applied for tissue engineering, while they could be exploited as drug nanocarriers when they form nanoparticles.

An expedient route for the synthesis of an anti-HIV peptide Kn2-7: A TAG approach

Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS) where the immune system progressively deteriorates and consequently threatens life. The peptide Kn2-7, a modified version of scorpion venom non-disulphide peptide, possesses the highest anti-HIV activity inhibiting antiviral potencies of 13 HIV-1 strains. In the present study, we achieved a new synthesis of Kn2-7 through a commercially viable, scalable, and impurity-free approach using Tagging Technique. We used (2,4-bis(octadecyloxy)phenyl)methanol as the Tag support for the synthesis and couplings were achieved by COMU with Fmoc-protected amino acids. The method is highly advantageous over conventional SPPS or LPPS methods in terms of economy, time, and most importantly purification. The peptide Kn2-7 and the intermediates were isolated as pure solids, the structures of which were unequivocally confirmed by 1H NMR, 13C NMR, and Mass spectroscopy.

Design of Fmoc-Phenylalanine Nanofibrillar Hydrogel and Mechanistic Studies of Its Antimicrobial Action against Both Gram-Positive and Gram-Negative Bacteria.

In pursuit of efficient antimicrobial agents, biomaterials such as hydrogels have drawn a considerable amount of attention due to their numerous advantages such as a high degree of hydration, biocompatibility, stability, and direct application at an infectious site. Particularly, biomaterials such as hydrogels based on Fmoc-protected peptides and amino acids have proven to be immensely advantageous. Such biomaterials can undergo gelation by simple pH modulation and can be used for various biological applications. Keeping this in mind, in this work, we reported the synthesis of Fmoc-phenylalanine (Fmoc-F)-based hydrogels using trisodium citrate as a pH modulator and compared them with the previously reported pH modulator glucono-δ-lactone. The gels were compared using various characterization techniques such as rheometry, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), small angle X-ray scattering (SAXS), FT-IR, thioflavin T (ThT) binding assay, and zeta potential studies. These studies highlighted the role of pH modulators in affecting various parameters such as the ability to alter the zeta potential of the nanofibrils, improve their bactericidal action, reduce the amyloidic characters, shift the lattice packing from amorphous to crystalline, and introduce fluorescence and thermoreversibility. Interestingly, this is the first report where the Fmoc-F-based hydrogel has been shown to be effective against Gram-negative bacteria along with Gram-positive bacteria as well. Additionally, the mechanism of antimicrobial action was investigated using docking and antioxidant studies.

MgO-Mediated Synthesis of Fmoc-Protected Amino Acid Hydroxamates

Key words magnesium oxide - amino acids - hydroxamates - hydroxylamine hydrochloride - Fmoc acid chlorides

Structure Revision of Trichomide D by Total Synthesis.

A structure revision of trichomide D has been achieved by its total synthesis. The sterically hindered peptide sequence was successfully prepared using not only a conventional amidation with EDCI but also coupling with an Fmoc-protected amino acid chloride derivative. The cyclization precursor was synthesized by coupling of a tetrapeptide with an acylproline derivative and subsequent removal of silyl groups at the N- and C-termini. Macrolactonization using MNBA/DMAPO followed by preparation of a chlorohydrin moiety furnished the proposed structure of trichomide D, whose spectra were not identical to those of the natural product. Finally, we succeeded in the elucidation of the true structure of trichomide D by its total synthesis, and the absolute configuration of the chlorohydrin moiety was revised to be S. The cytotoxicities of the natural product and its synthetic derivatives against MCF-7 and HeLa S3 cells were evaluated by the MTT method, revealing that the configuration of the chlorohydrin moiety is a pivotal factor for exhibiting potent cytotoxicity against cancer cells.

Minimum ignition energy of amino acids and their Fmocs

Fmoc groups are base labile functional groups attached to amino acids to reduce undesirable reactions in peptide synthesis. As with ordinary amino acids, Fmoc-protected amino acid dusts are combustible, and exhibit the potential for a dust explosion. Dust explosions are a continuing challenge in the process industries and has been the subject of much research. Industrial dusts are usually evaluated for explosion hazard probability on the basis of their minimum ignition energy, the minimum energy an ignition source must supply in order to ignite a dust cloud. Such data is often used in risk assessments and to compare combustible dusts to each other, but there is a lack of data in the literature for minimum ignition energies for both ordinary amino acid dust and Fmoc-protected amino acid dusts. This study experimentally determined minimum ignition energies for the following amino acids and their corresponding Fmoc-protected versions: L-serine, L-proline, glycine, L-glutamic acid, and L-alanine. By comparing the Fmoc-protected amino acid dusts to their ordinary amino acid counterpart, it becomes apparent that the protected variants are much more combustible than the parent molecules. From a perspective of loss prevention, this publication attempts to bring immediate awareness and takes the first step in filling a gap in the published information addressing this topic and contextualize these findings as they pertain to process safety.

Fmoc-protected amino acids as luminescent and circularly polarized luminescence materials based on charge transfer interaction

Fluorenylmethyloxycarbonyl (Fmoc)-protected amino acids are effective building blocks in self-assembled architectures at hierarchical levels, which however show limited luminescent properties and chiroptical activities. Here we introduce a charge-transfer strategy to build two-component luminescent materials with emerged circularly polarized luminescence properties. A library of Fmoc-amino acids was built, which selectively form charge-transfer complexes with the electron-deficient acceptor. Embedding in amorphous polymer matrix or physical grinding could trigger the charge-transfer luminescence with adjusted wavelengths in a general manner. X-ray diffraction results suggest the multiple binding modes between donor and acceptor. And, the solution-processed coassembly could selectively exhibit circularly polarized luminescence with high dissymmetry g-factors. This work illustrates a noncovalent charge-transfer strategy to construct luminescent and chiroptical organic composites based on the easy-accessible and economic chiral N-terminal aromatic amino acids.

Synthesis of N a -Fmoc-Protected Amino Acid Esters and Peptides

Synthesis of N a -Fmoc-Protected Amino Acid Esters and Peptides

On-Resin Ugi Reaction for C-Terminally Modified and Head-to-Tail Cyclized Antibacterial Peptides.

Here we report a method to synthesize C-terminally modified peptides on resin. A four-component Ugi reaction of isocyanide resin, an Fmoc-protected amino acid, an amine, and a 6-nitroveratrylaldehyde gives C-terminal photocaged peptide amides, which can be photolyzed to generate C-terminal peptide amides. Changing the amine component in the Ugi reaction gives peptides with different C-terminal modifications including substituted anilides, alkyne, and azide. By installing an N-terminal azide and C-terminal alkyne, we synthesized a head-to-tail cyclized antibacterial peptide through copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The cyclized peptide exhibited higher proteolytic stability and antibacterial activity than the linear peptide.

Synthesis of SARS‐CoV‐2 Transmembrane Domains Using Solid Phase Peptide Chemistry and Analysis of Their Oligomerization for Novel Drug Design

The SARS‐CoV‐2 spike protein transmembrane (TM) domain is an important component of the protein that contributes to its oligomerization for its active configuration. An understanding of this function can yield valuable data to future research on how to inhibit the virus’ infection of a host. The TM region of the protein is not as well studied due to the complication that nonpolar peptides can have in large groups; therefore, an understanding of this region could lead to novel discoveries. A peptide of the TM domain must be synthesized by using Solid Phase Peptide Synthesis, in which a resin is utilized to build a peptide off the c‐terminus using Fmoc‐protected amino acids and a strong base. A fluorescence assay can be performed to determine its oligomerization state by looking at the change of fluorescence that occurs when a quencher is added to the solution. Once the oligomerization state of the spike proteins TM domain is determined, this information will be beneficial the development of drugs against the virus. The set up to run this synthesis was developed in the lab and is causing premature termination of the amino acid chain. Current work involves addressing a potential issue of hydrophobicity due to the volume non‐polar residues, which is currently being address by trying a TGR resin that has a polystyrene core which is suited for long peptides. It is anticipated that addressing this issue will lead to a peptide that can be purified. The future implications of this research is that it has the potential of being useful for drugs that would inhibit the active configuration of SARS‐CoV‐2.

A Scalable Synthesis of the Blue Fluorescent Amino Acid 4-Cyanotryptophan and the Fmoc Derivative: Utility Demonstrated with the Influenza M2 Peptide Tetramer.

A scalable synthesis of the Fmoc-protected blue fluorescent amino acid, l-4-cyanotryptophan (W4CN), that exploits an enantioselective phase transfer-catalyzed alkylation is reported. The red-shifted emission of water-exposed W4CN residues was leveraged to investigate the solvation state of tryptophan (Trp) residues within the influenza M2 proton channel. The correlation of the channel's conformation (i.e., open or closed) with the fluorescence spectrum of a mutated W4CN residue suggests that the channel's conformational state does not impact the hydration status of the Trp residues.

Role of Thermolysin in Catalytic-Controlled Self-Assembly of Fmoc-Dipeptides

In recent years, short peptide self-assembled materials, prepared under the control of the thermolysin catalyst, have been investigated extensively and shown to acquire various morphologies and fun...

Novel chiral stationary phases based on 3,5-dimethyl phenylcarbamoylated β-cyclodextrin combining cinchona alkaloid moiety.

Novel chiral selectors based on 3,5-dimethyl phenylcarbamoylated β-cyclodextrin connecting quinine (QN) or quinidine (QD) moiety were synthesized and immobilized on silica gel. Their chromatographic performances were investigated by comparing to the 3,5-dimethyl phenylcarbamoylated β-cyclodextrin (β-CD) chiral stationary phase (CSP) and 9-O-(tert-butylcarbamoyl)-QN-based CSP (QN-AX). Fmoc-protected amino acids, chiral drug cloprostenol (which has been successfully employed in veterinary medicine), and neutral chiral analytes were evaluated on CSPs, and the results showed that the novel CSPs characterized as both enantioseparation capabilities of CD-based CSP and QN/QD-based CSPs have broader application range than β-CD-based CSP or QN/QD-based CSPs. It was found that QN/QD moieties play a dominant role in the overall enantioseparation process of Fmoc-amino acids accompanied by the synergistic effect of β-CD moiety, which lead to the different enantioseparation of β-CD-QN-based CSP and β-CD-QD-based CSP. Furthermore, new CSPs retain extraordinary enantioseparation of cyclodextrin-based CSP for some neutral analytes on normal phase and even exhibit better enantioseparation than the corresponding β-CD-based CSP for certain samples.

Synthesis, experimental and in silico studies of N-fluorenylmethoxycarbonyl-O-tert-butyl-N-methyltyrosine, coupled with CSD data: a survey of interactions in the crystal structures of Fmoc-amino acids.

Recently, fluorenylmethoxycarbonyl (Fmoc) amino acids (e.g. Fmoc-tyrosine or Fmoc-phenylalanine) have attracted growing interest in biomedical research and industry, with special emphasis directed towards the design and development of novel effective hydrogelators, biomaterials or therapeutics. With this in mind, a systematic knowledge of the structural and supramolecular features in recognition of those properties is essential. This work is the first comprehensive summary of noncovalent interactions combined with a library of supramolecular synthon patterns in all crystal structures of amino acids with the Fmoc moiety reported so far. Moreover, a new Fmoc-protected amino acid, namely, 2-{[(9H-fluoren-9-ylmethoxy)carbonyl](methyl)amino}-3-{4-[(2-hydroxypropan-2-yl)oxy]phenyl}propanoic acid or N-fluorenylmethoxycarbonyl-O-tert-butyl-N-methyltyrosine, Fmoc-N-Me-Tyr(t-Bu)-OH, C29H31NO5, was successfully synthesized and the structure of its unsolvated form was determined by single-crystal X-ray diffraction. The structural, conformational and energy landscape was investigated in detail by combined experimental and in silico approaches, and further compared to N-Fmoc-phenylalanine [Draper et al. (2015). CrystEngComm, 42, 8047-8057]. Geometries were optimized by the density functional theory (DFT) method either in vacuo or in solutio. The polarizable conductor calculation model was exploited for the evaluation of the hydration effect. Hirshfeld surface analysis revealed that H...H, C...H/H...C and O...H/H...O interactions constitute the major contributions to the total Hirshfeld surface area in all the investigated systems. The molecular electrostatic potentials mapped over the surfaces identified the electrostatic complementarities in the crystal packing. The prediction of weak hydrogen-bonded patterns via Full Interaction Maps was computed. Supramolecular motifs formed via C-H...O, C-H...π, (fluorenyl)C-H...Cl(I), C-Br...π(fluorenyl) and C-I...π(fluorenyl) interactions are observed. Basic synthons, in combination with the Long-Range Synthon Aufbau Modules, further supported by energy-framework calculations, are discussed. Furthermore, the relevance of Fmoc-based supramolecular hydrogen-bonding patterns in biocomplexes are emphasized, for the first time.

Diversity-oriented synthesis of peptide-boronic acids by a versatile building-block approach.

A new strategy for the synthesis of peptide-boronic acids (PBAs) is presented. 20 Fmoc-protected natural amino acids with orthogonal side-chain protection were straightforwardly converted into their corresponding boron analogues in three simple steps. Subsequent immobilisation on commercially available 1-glycerol polystyrene resin and on-resin transformations yielded a diversity of sequences in high purity. The strategy eliminates various synthetic obstacles such as multi-step routes, low yields, and inseparable impurities. The described method comprises great potential to be implemented in automated combinatorial approaches by markedly facilitating the access to a variety of PBAs. The coupling of amino acids or other building blocks with α-aminoboronates allows the creation of hybrid molecules with significant potential in various scientific disciplines, such as medicinal chemistry, structural biology, and materials science.

Recovery, Purification, and Reusability of Building Blocks for Solid Phase Synthesis.

Solid phase synthesis (SPS) is well established for the synthesis of biomacromolecules such as peptides, oligonucelotides, and oligosaccharides, and today is also used for the synthesis of synthetic macromolecules and polymers. The key feature of this approach is the stepwise assembly of building blocks on solid support, enabling monodispersity and monomer sequence control. However, in order to achieve such control, a high excess of building blocks is required during the reaction. Herein, the recovery, purification, and reusability of building blocks used in SPS, including representative examples of tailor-made building blocks, Fmoc-protected amino acids, and functionalized carbohydrate ligands, are reported for the first time. Results demonstrate the general applicability with recovery in high yields and high purity. Furthermore, the described recovery process can be applied in both manual and automated synthesis using a standard peptide synthesizer. Overall, this process is envisioned to be applicable for a large variety of building blocks used in the SPS of different types of molecules, and to contribute to more resourceful SPS syntheses.

Directed C(sp3)-H arylation of tryptophan: transformation of the directing group into an activated amide.

The 8-aminoquinoline (8AQ) directed C(sp3)-H functionalization was applied in the synthesis of β-arylated tryptophan derivatives. The laborious protecting group reorganization towards α-amino acids compatible for solid phase peptide synthesis (SPPS) was cut short by the transformation of the directing group into an activated amide, which was either used directly in peptide coupling or in the gram scale synthesis of storable Fmoc-protected amino acids for SPPS. In this work, directed C-H activation and nonplanar amide chemistry complement each other for the synthesis of hybrids between phenylalanine and tryptophan with restricted side chain mobility.