Pharmaceutical Sciences

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New disulfide reducing reagent for solid phase peptide synthesis.
(2019) Mthembu, Sinenhlanhla Nonhlanzeko.; Albericio, Fernando.
The special physical and chemical properties of sulfur atom make thiols and disulphide bonds of vital importance in many biological processes. For instance, it is well known, the role of cysteine residues in proteins, acting as key in the catalytic site of enzymes or stabilizing the tertiary structure of proteins through disulfide bonds. In nature, glutathione is responsible for reducing disulphide bonds formed within the cytoplasmic proteins to cysteines. To mimic this function on the bench, many disulfide reducing agents have been developed. β-mercaptoethanol (β-ME) and dithiothreitol (DTT) work in a similar manner as GSH except that DTT forms intramolecular disulphide bond yielding a very stable six-membered ring, making DTT a more effective reducing agent. Recently, a new reducing agent inspired in DTT was developed from aspartic acid, Dithiobutylamine (DTBA), which work faster and because its lower thiol pKa value, showed a good reactivity at physiological pH. Due to the high polarity of DTBA, it is only soluble in aqueous solution, thus in this work, a non-polar analogue 2-(dibenzylamino)butane-1,4-dithiol (DABDT) has been developed. The molecule has been successfully obtained in good yield by a five-step process as an almost odorless solid. In solution, DABDT has good stability and its performance as reducing agent is comparable to DTT. Moreover, its efficacy has been probed as reducing agent of disulfide protected Cys and thiol derivatized peptide on solid phase.
Solid phase peptide synthesis: new resin and new protecting group.
(2018) Ramkisson, Shaveer.; Albericio, Fernando.; Garcia-de-la-Torre, Beatriz.
Solid phase peptide synthesis is the common approach used today in synthesizing peptides in a research scale and production. Success in this approach are governed by several factors. These are; (1) the solid support on which synthesis is to be carried out, (2) linker/spacer on which the first amino acid is linked to the support to allow stepwise growth of the peptide chain, (3) protecting groups of amino acids to allow a clean synthesis without disruption of the growing peptide chain and (4) coupling reagents for improved amide bond formation yielding peptides in the shortest amount of time and with the highest quality. The following thesis shows work conducted on some of these aspects. Chapter two is based on the application of a novel resin Fmoc-Rink-Amide PEG Octagel surface resin. Chapter three describes the development of a novel protecting group for histidine amino acid. A new PEG-PS based resin called Octagel has been developed by Aapptec. Fmoc-Rink-Amide Octagel PEG surface resin is a unique highly uniform surface-active resin. To study the resin’s performance, two peptides Aib-enkephalin pentapeptide and Aib-ACP decapeptide were synthesized and results were compared to Polystyrene and ChemMatrix resins. Swelling and microscope imaging studies were also conducted on each of the resins to highlight their performance associated with Solid Phase Peptide Synthesis. Results have demonstrated that Octagel resin has the potential to synthesize peptide sequences with high purity and therefore to be a good alternative to those currently in the market. Histidine is an important amino acid used in SPPS. It contains a reactive imidazole side group that can cause side reactions in SPPS if left unprotected. Fmoc-based SPPS is the most commonly used strategy in synthesizing peptides today. A protecting group was created for Fmoc-Histidine. SPPS was carried out on the protected histidine and results show that the group is stable in acidic conditions.
Synthesis and physiochemical characterization of new siderophore-inspired peptide-chelators with 1-hydroxypridine-2-one (1,2-HOPO).
(2020) Alshaer, Danah Mahdi Mohammad.; Garcia de la Torre, Beatriz.; Albericio, Fernando.;
Compounds containing hydroxamate moieties (N-hydroxyl amides) in their structure have found a vast range of therapeutic applications such as antibacterial, anti-tumour, anti-immune suppressor, and for iron overloading treatment. Hydroxamate chelators binds to Fe (III) tightly through its electron donating oxygens. The binding strength is maximized in compounds containing three hydroxamic moieties due to the so called “chelate effect”. As all microorganisms require iron for surviving, they develop endogenous siderophores to acquire iron from the surroundings. Siderophores contain hydroxamate, catecholates, α-hydroxy carboxylates groups, among others, in their structures. The acquisition of iron by siderophores in microorganisms goes through specific cycles that includes sequestration of Fe(III), recognition and uptake of the ferrisiderophore through the cell membrane, and then release of the iron in the cytoplasm. Many natural hydroxamate siderophores contain a peptidyl backbone. In this work, peptides containing one or more units of 1,2-hydroxypyridine-N-oxide (1,2-HOPO) have been synthesized. The introduction of these units on the peptides has been done by means of 4- carboxy-1-hydroxypyridil-2-one (1,2-HOPO-4-COOH) using solid-phase peptides synthesis (SPPS) protocols. The obtention of the new “siderophores” containing three 1,2-HOPO units have been done by two different approaches, sequential and convergent. The compounds have been evaluated as potential iron chelators. Thus, the pKa values and the thermodynamic constants of all ligands have been spectrophotometrically determined. The Fe(III) affinities of the two hexadentate ligands (ligand B and ligand C) have been determined by competition experiments against EDTA. The results showed that the iron complex ligand B is stronger that the iron complex EDTA since the last is not be able to replace it. Hence, this new siderophore could be a promising candidate to be used in further therapeutic applications.
Thiobarbituric acid a useful scaffold for medicinal chemistry.
(2018) Noki, Sikabwe.; Albericio, Fernando.; Garcia-de-la-Torre, Beatriz.
Due to the growth number of infectious diseases, a huge demand of new antimicrobial agents are required. In this regard, Thiobarbituric acid (TBA) moieties were explored. As its name indicates, TBA is the sulfur version of the barbituric acid. The work in barbituric moieties dated long ago in 1864 by Baeyer, when it was reported that these barbituric derivatives can be used as anesthetics, sedative or anticonvulsive agents. In the present work and taking advantage that TBA structure shows several points where diversity can be introduced, therefore several functionalities were introduced in the TBA analogues and their antimicrobial properties were studied in Gram-positive and Gram-negative bacteria. (Chapter 1) These are the chemical modifications explored: i) N- substitution, where this site can be substituted with a symmetrical substituents; ii) reaction at C-5 position owing to the high acidity of the protons which includes acylation, acetylation, Schiff bases, Knoevenagel condensation thioamide and enamine formation. The antimicrobial activity screening for the synthesized compounds were against Gram-positive (S. aureus and B. subtilus) and Gram negative (E. coli and P. aeruginosa) bacteria. Among all thiobabituric derivatives synthesized, Boc-Phe-TBA showed a promising activity, which confirms that TBA could be an excellent scaffold when combined with N-protected amino acids for developing antimicrobial compounds. (Chapter 2) The characterization of 20 thiobarbituric derivatives was carried out in different spectroscopy techniques such as: Nuclear Magnetic Resonance (NMR), Ultra violet spectroscopy, Infra-Red spectroscopy and single X-ray crystallography. In NMR characterization the acetylation of TBA was the most interesting due to the fact that this type of compound have the tendency of forming Enol and Keto tautomerism. This was proved by NMR and also by theoretical calculation, and the results confirm that the 1H NMR for this compound (A01)showed resonance at 17.72 ppm (singlet) for OH. This indicate that the enol form is more stable than the keto form. In UV characterization due to the fact TBA derivatives are not known aromatic and yet they are UV active. Therefore the absorption of few TBA derivatives were study in different solvents hence these showed absorption iv at maximum wavelength (max) in the range of 322 – 285 nm respectively. For IR characterization, these derivatives (A01, A02, A03, A04, A06, A10, A12, A13, A14 and A17) were evaluated, and showed absorption stretching frequency of thiocarbonyl (C=S) in three different ranges, 1395– 1570 cm-1 , 1260– 11420 cm-1 and 940 – 1140 cm-1 . For X- ray crystallography, crystals of A01, A02, A06, A13, A17 and A18 were obtained by hot recrystallization from ethanol and the intramolecular H-Bonding formation was observed in all cases, intermolecular H-bonding was observed for A17. (Chapter 3)

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Browsing Pharmaceutical Sciences by Author "Albericio, Fernando."