Dr S.Papas (Chemist, PhD) received his PhD in Organic Chemistry and Biochemistry in the Department of Chemistry at University of Ioannina, Greece, in 2007. In his PhD he focuses on peptide synthesis, synthesis of paclitaxel analogues and peptide-paclitaxel conjugates. His scientific areas include synthesis of cell-targeting agents, improvement of the activity of drugs using peptides conjugates and synthesis of macromolecules using chemoselective ligation. During the last three years he worked as an application specialist in the private sector and focused on analytical techniques (LC-MS/MS, GC-MS, HPLC).
Abstract: Paclitaxel (Pac) is the most important anticancer drug used mainly in treatment of breast, lung, and ovarian cancer and is being investigated for use as a single agent for treatment of lung cancer, advanced head and neck cancers, and adenocarcinomas of the upper gastrointestinal tract. In this work, we present the synthesis of five 2'-paclitaxel-substituted analogs in which paclitaxel was covalently bound to peptides or as multiple copies to synthetic carriers. Ac-Cys(CH(2)CO-2'-Pac)-Arg-Gly-Asp-Arg-NH(2), Folyl-Cys(CH(2)CO-2'-Pac)-Arg-Gly-Asp-Ser-NH(2), Ac-[Lys-Aib-Cys(CH(2)CO-2'-Pac)](2)-NH(2), Ac-[Lys-Aib-Cys(CH(2)CO-2'-Pac)](3)-NH(2) and Ac-[Lys-Aib-Cys(CH(2)CO-2'-Pac)](4)-NH(2) were synthesized using 2'-halogeno-acetylated paclitaxel derivatives. Paclitaxel conjugates showed greater solubility in water than paclitaxel and inhibited the proliferation of human breast, prostate, and cervical cancer cell lines. Although all synthesized compounds had an antiproliferative activity, the Ac-[Lys-Aib-Cys(CH(2)CO-2'-Pac)](4)-NH(2) derivative showed improved biological activity in comparison with paclitaxel in cervical and prostate human cancer cells.
Abstract: The progress achieved both in the solid and liquid phase of the synthetic methodologies for peptides, permitted the application of various chemistries for preparing totally synthetic proteins and protein-like macromolecules of branched architecture. Polypeptides with molecular masses in the 10-25 kDa range have been successfully prepared using either the step by step and fragment condensation or the chemoselective ligation methods. Amide, thioether, disulfide, thioester, hydrazone, oxime and thiazolidine linkages have been employed in such syntheses. Fully active proteins or macromolecules mimicking particular protein properties especially in immunology have been synthesized in high purity and large quantities. The branched constructs have found numerous applications in immunology due to their contribution in overcoming the very low ability of short linear peptides to react specifically with antibodies or to induce an immune response. The advantages over almost all the other methods of using synthetic carriers for developing potent antigens and immunogens have placed this approach at the center of extensive research activities. This review focuses on the concept and synthetic strategies suitable for assembling proteins or protein-like macromolecules of branched architecture with application in protein function studies and immunology.
Abstract: Decomposition of the resin linkers during TFA cleavage of the peptides in the Fmoc strategy leads to alkylation of sensitive amino acids. The C-terminal amide alkylation, reported for the first time, is shown to be a major problem in peptide amides synthesized on the Rink amide resin. This side reaction occurs as a result of the Rink amide linker decomposition under TFA treatment of the peptide resin. The use of 1,3-dimethoxybenzene in a cleavage cocktail prevents almost quantitatively formation of C-terminal N-alkylated peptide amides. Oxidized by-product in the tested Cys- and Met-containing peptides were not observed, even if thiols were not used in the cleavage mixture.
Abstract: The undesirable reaction of aspartimide formation has been proved to occur under both acid and base conditions in solid-phase peptide synthesis and is dependent on the beta-carboxyl protecting group, the acid or base used during the synthesis, as well as the peptide sequence. The hydrolysis of aspartimide-containing peptides, especially during HPLC purification, yields a mixture of alpha- and beta-aspartyl peptides that can not be purified easily. A previous study demonstrated that treatment of aspartimide-containing peptides with methanol in the presence of 2% diisopropylethylamine in solution leads to alpha- and beta-aspartyl peptide methyl esters. Taking advantage of these results and aiming at elucidating the optimal conditions for aspartimide ring opening, the effect of different types and concentrations of alcohols (primary and secondary) and bases (diisopropylethylamine, collidine, 4-pyrrolidinopyridine, 1-methyl-2-pyrrolidone, piperidine and KCN) was tested at various temperatures and reaction times. The best results were obtained with a combination of a primary alcohol and diisopropylethylamine, while aspartimide ring opening by secondary alcohols occurred only at high temperatures. The optimal conditions were also applied to solid-phase peptide synthesis.
