The first organic synthesis was carried out in 1828 with the synthesis of urea, while the first synthetic polymer was produced in 1907 – it was Bakelite. For my thesis, I prepared the monomer β-benzyl-L-aspartate N-carboxyanhydride (BLA NCA) from the α-amino acid β-benzyl-L-aspartate (BLA) using triphosgene. Triphosgene acts as an effective activating and carbamoylating agent in the reaction. The reaction is performed under anhydrous conditions because N-carboxyanhydride (NCA) is highly sensitive to water; contact with water leads to hydrolysis of the NCA, undesirable side reactions, and results in its deactivation. The synthesized monomer, β-benzyl-L-aspartate N-carboxyanhydride, is then polymerized into poly(β-benzyl-L-aspartate) (PBLA). The reaction takes place at the freezing point of water. An initiator for anionic polymerization is also required; in this case, we used hexylamine, which nucleophilically attacks β-benzyl-L-aspartate N-carboxyanhydride and initiates the polymerization. By adjusting the molar ratio between the initiator and the monomer, the polymer chain length can be controlled. The synthesized polymer is then functionalized with two photoresponsive end groups. For my thesis, I selected a maleimide and a tetrazole end group. To functionalize poly(β-benzyl-L-aspartate) with a maleimide group, we added triethylamine and N-succinimidyl 3-maleimidopropionate to a suspension of the polymer in anhydrous dimethylformamide. These reagents react with free amine groups on the poly(β-benzyl-L-aspartate) and contain a reactive maleimide moiety. Triethylamine is used as a basic catalyst to neutralize HCl and other acidic by-products, activate the carboxyl group, and prevent undesired side reactions. The functionalization of poly(β-benzyl-L-aspartate) with a tetrazole group is carried out under the same conditions, but using different reactants: 4-(2-(4-methoxyphenyl)-2H-tetrazol-5-yl)benzoic acid, which is used to functionalize the polymer, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC), and 4-dimethylaminopyridine (DMAP). EDC serves as an activator of the carboxyl group in poly(β-benzyl-L-aspartate), forming a reactive intermediate that allows attachment of the tetrazole group via an amide bond. Because EDC is unstable, it is often used in combination with DMAP, which acts as a catalyst for acyl substitution reactions. After completing the synthesis, all products are isolated from the reaction mixture and characterized using MALDI-TOF and NMR spectroscopy. A photoreaction of PBLA functionalized with maleimide and tetrazole groups is carried out through nitrile imine mediated tetrazole-ene cycloaddition in deuterated DMSO under UVA irradiation; the progress of the reaction is monitored using a TLC lamp. Finally, NMR and MALDI-TOF spectra are recorded. It was found that the photoreaction did not proceed as planned.
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