[Show abstract][Hide abstract] ABSTRACT: We report on a novel and user-friendly platform based on a bromomaleimide moiety to obtain branched peptides and stable for all SPPS conditions. The bromomaleimide core was conjugated to n-copies of thiol-peptide in-solution to obtain two/four/eight-armed dendrimers. Using ‘n’ number of bromomaleimide analogues, 2n ligands were incorporated at both bromo and ene-positions via a thioether bond. This method has the advantage of high conversion in a short time, thus enabling effortless purification and characterization processes.
[Show abstract][Hide abstract] ABSTRACT: To date, DMF has been considered the only solvent suitable for peptide synthesis. Here we demonstrate the capacity of THF and ACN, which are friendlier solvents than DMF, to yield the product in higher purity than DMF. Using various peptide models, both THF and ACN reduced racemization in solution-phase and solid-phase synthesis when compared with DMF. Moreover, the use of ACN and THF in the solid-phase peptide synthesis of hindered peptides, such as Aib-enkephaline pentapeptide and Aib-ACP decapeptide, in combination with the totally polyethylene glycol ChemMatrix resin, gave a better coupling efficiency than DMF
[Show abstract][Hide abstract] ABSTRACT: The carbapenem (β-lactam antibiotic) scaffold serves as a useful nucleophile in organocatalytic diarylprolinol trimethylsilyl ether mediated α-heterofunctionalization reactions leading to the formation of diverse products that bear multiple stereocenters in high diastereoselectivity and moderate to good yields.
Annalen der Chemie und Pharmacie 12/2014; · 3.15 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Abstract Context: Granulocyte colony stimulating factor (G-CSF) has been commonly used to treat neutropenia caused by chemotherapy, radiotherapy, and organ transplants. Improved in vitro efficacy of G-CSF has already been observed by conjugating it to polyethylene glycol (PEG). Objective: The in vivo bioassay using tetrazolium dye with the NFS-60 cell line has been recommended for G-CSF but no such monographs are available for PEGylated G-CSF in pharmacopeias. In the present study, the assay recommended for G-CSF was evaluated for its suitability to PEGylated G-CSF. Materials and methods: The generally used MTS [3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium]-based assay was compared with a bioassay employing a water-soluble tetrazolium dye, WST-8 [2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium], using NFS-60 cells at a concentration of 7 × 10(5) cells/ml against 800 IU/ml of PEGylated G-CSF at 24, 48, 72, and 72 h time points to determine the efficacy of PEGylated G-CSF. Further, the optimized WST-8 dye-based assay was used to test the potency of various commercially available PEGylated G-CSF preparations. Results: The results demonstrated enhanced sensitivity of the WST-8-based assay over the conventional MTS-based assay for determining the potency of PEGylated G-CSF using the NFS-60 cell line. Conclusion: Our study demonstrates the potential application of WST-8-based bioassays for other biotherapeutic proteins of human and veterinary interest.
[Show abstract][Hide abstract] ABSTRACT: Here we describe two novel uronium salts, TOMBU and COMBU, derived from the recently described Oxyma-B for use in peptide bond synthesis. These coupling reagents are more stable than COMU in DMF. Furthermore, using various peptide synthetic models in solution and solid-phase synthesis, we reveal that they show better performance than HBTU in terms of preserving chiral integrity and coupling yields, but slightly worse performance than COMU.
[Show abstract][Hide abstract] ABSTRACT: The preliminary idea of using immobilized reagents in organic synthetic chemistry is simplifying the downstream process: product work-up and isolation, and therefore avoiding time consuming and expensive chromatographic separations which are intrinsic to every synthetic process. A numerous polymer-bounded reagents are commercially available and applicable to almost all kinds of synthetic chemistry conversions. Herein, we have covered all known supported-coupling reagents and bases which have had a great impact in amide/peptide bond formation. These coupling reagents have used for the activation of carboxyl moiety; thus generating an active acylating species which are ready to couple with an amine nucleophile liberating the amide/peptide and polymeric support which can be regenerated for reuse. This also addresses about a large variety of anchored coupling reagents, additives and bases which have only been used in amide/peptide syntheses during the last six decades.
[Show abstract][Hide abstract] ABSTRACT: The synthesis of seven novel protected amino acid cavitands is reported. All have four pendantn-undecyl
chains and‘headgroups’ connected by a two-carbon spacer at four positions on the aromatic rings. The
amino acids employed are glycine, alanine, phenylalanine, leucine, proline, tryptophan, serine, glutamine
and lysine. The structures of the compounds were elucidated using one- and two-dimensional NMR
techniques, which verified that all tetra-substituted cavitands have symmetricalC4vconformation. This is
thefirst example of a complete study for amino acid cavitand derivatives.
[Show abstract][Hide abstract] ABSTRACT: Peptide-bond formation is a key process in the synthesis of peptide oligomers. Among the many coupling techniques reported, carbodiimides combine strong acylation potency and smooth reaction conditions and are commonly used in the presence of additives. Recently, ethyl 2-cyano-2-(hydroxyimino)acetate (OxymaPure) has emerged as a highly reactive alternative to the classic and explosion-prone benzotriazolic additives, namely 1-hydroxybenzotriazole (HOBt) and 1-hydroxy-7-azabenzotriazole (HOAt). Here we report on a new oxime additive 5-(hydroxyimino)-1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione (Oxyma-B). This new additive showed satisfactory solubility in various solvents (DMF, ACN, and THF). It was also more effective in the control of optical purity during the synthesis of Z-Phg-Pro-NH2, Z-Phe-Val-Pro-NH2, H-Gly-Ser-Phe-NH2, H-Gly-Cys-Phe-NH2, H-Gly-Cys(Acm)-Phe-NH2 and H-Gly-His-Phe-NH2 than related Oxyma- and benzotriazole-based reagents. Oxyma-B also proved to be advantageous compared to the related HONM, because the latter cannot be used with the carbodiimide. Furthermore, Oxyma-B showed satisfactory performance in assembling demanding sequences such as the Aib-enkephalin pentapeptide (H-Tyr-Aib-Aib-Phe-Leu-NH2).
[Show abstract][Hide abstract] ABSTRACT: The twenty first century has witnessed several advances in synthetic chemistry, among them microreactors. It is expected that these devices will have a considerable impact on synthetic organic chemistry since they offer a wide range of applications in various fields. Perhaps the synthesis of peptides deserves mention in this regard as these molecules are emerging as therapeutics and offer several advantages over the so-called small molecules. This minireview does not aim to address microreactors in detail, but explains various peptide synthesis methods that involve microfluidic techniques, highlighting the need for further improvement and expansion of microdevices/microreactors.
[Show abstract][Hide abstract] ABSTRACT: Small peptides are essential mediators of numerous physiological processes. Consequently, there is huge interest in the de novo design of peptides with a predictable folding and related biological activity. In this study, we investigate the possibility of modulating the secondary structure of tetrapeptides through proline N-oxide moieties and N-methylation of the peptide backbone. A series of tetrapeptides were synthesised to investigate the combined effect of Pro N-oxide and N-methylation of the amide bond on the (n + 1) residue in terms of cis- and trans-isomerization, as well as how these modifications direct potential intramolecular hydrogen bonding interactions. The right combination of both these parameters led to a trans to cis-conformational interconversion and a change in the nature of the hydrogen bonding interactions, as demonstrated by NMR spectroscopic, molecular modeling analysis and thermal coefficient studies. Proline N-oxide residues were proposed to induce turns we named as NO-γ-turns and NO-β-turns based on their similarity to traditional γ- and β-turns.
[Show abstract][Hide abstract] ABSTRACT: Introduction
Human antimicrobial peptides are of interest for the development of positron emission tomography (PET) tracers as they exhibit desirable characteristics that make them good candidates for targeting vectors. Due to their natural role in the innate immune system they selectively bind to pathogenic bacteria and yeast, whilst remaining minimally immunogenic and cytotoxic to humans. Research into ubiquicidin (UBI)-based tracers has focused on 99mTc as a radionuclide, however, the use of bi-functional chelators such as 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), in combination with 68Ga as a radionuclide, allows for a simple radiolabeling procedure which is preferable in a clinical setting using PET/CT.
The peptides fragments UBI29-41, UBI30-41 were synthesized by standard microwave Fmoc/tert-butyl (tBu)-solid phase synthetic protocols. Characterizations were performed using analytical HPLC and LC/MS. Both NOTA-conjugated peptides were exposed to natGa3 +; their complexed form was quantified by direct LC/MS injection. This complexation was utilized to testify bacterial and mammalian cell binding potential of fluorophore-linked NOTA-UBI29-41/30-41. 68Ga labeled NOTA-UBI fragments were also tested for competitive interaction to Staphylococcus aureus to proof the binding target. 68Ga was eluted from SnO2- and TiO2-based 68Ge/68Ga generators using fractionated elution and anion exchanged-based post-procession. NOTA-peptide radiolabeling was carried out including optimization of buffer molarity, NOTA-peptide concentration(s), incubation temperature and –duration as well as considering various SPE purification cartridges.
Pure UBI29-41, UBI30-41 and NOTA-UBI30-41 were successfully characterized. Both, NOTA-UBI fragments exhibited complexation rates to natGa3 + ≥ 99%. The percentage binding was significantly higher to Staphylococcus aureus bacilli over Mt4 human leucocytes (P > 0.05) for NOTA-UBI29-41[Lys(Abz)] < NOTA-UBI30-41[Lys(Abz)]. Significant lower binding was observed for both 68Ga-labeled NOTA-UBI fragments (P > 0.03) after pre-incubation with excess unlabeled NOTA-UBI. Reproducible 68Ga radiolabeling ranged for 51-85% and 46-78% for NOTA-UBI29-41 and NOTA-UBI30-41, respectively.
Aside from successful peptide syntheses the first ever 68Ga-radiolabeling method is reported for NOTA-UBI fragments. The NOTA-conjugation didn’t compromise the selective and specific interaction with bacterial cells in vitro. Both tracers are warranting prospective imaging of infection with PET/CT.
Nuclear Medicine and Biology 05/2014; · 2.41 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Here we review the strategies for the solid-phase synthesis of peptides starting from the side chain of the C-terminal amino acid. Furthermore, we provide experimental data to support that C-terminal and side-chain syntheses give similar results in terms of purity. However, the stability of the two bonds that anchor the peptide to the polymer may determine the overall yield and this should be considered for the large-scale production of peptides. In addition, resins/linkers which do not subject to side reactions can be preferred for some peptides.
[Show abstract][Hide abstract] ABSTRACT: An efficient diastereoselective synthesis of carbapenem Mannich bases was developed using organocatalysis. This method also provides a route to new highly functionalized diazabicyclo[4.2.1]nonanes of proposed biological significance.
Annalen der Chemie und Pharmacie 02/2014; 46(5). · 3.15 Impact Factor