Bacteria are small, single-celled organisms that vary in shapes and sizes. Their cellular structure includes cytoplasm with organelles, a cytoplasmic membrane, a bacterial wall, and in some cases, a bacterial capsule. There are two main groups of bacteria: gram-negative and gram-positive, distinguished by the thickness and structure of their cell walls. The enzyme MurA is essential in peptidoglycan synthesis in the cell wall, making it an attractive target for antibacterial agents. Due to the excessive and indiscriminate use of antimicrobial agents, bacterial resistance has become one of the major threats to public health in the 21st century. Therefore, the rapid search and development of new antibacterial agents are essential. One of the bacteria posing a significant challenge in hospital-acquired infections is Clostridium difficile. During the synthesis of polysaccharides in C. difficile's cell wall, a new enzyme, mannosyl-1-phosphotransferase (ManPT), was discovered, representing a potential target for the development of new antibacterial drugs. The purpose of this master's thesis was to synthesize derivatives of glucosamine and galactosamine with phosphate groups to mimic the substrate for the ManPT enzyme.
The starting compounds in the synthesis were D-glucosamine hydrochloride and D- galactosamine hydrochloride. A six-step synthesis followed, involving acetylation of the sugar, selective deprotection of anomeric -OH groups, and the introduction of a protected phosphate. After deprotection, the compound was combined with 11-phenoxyundecyl phosphate, resulting in a diphosphate, and then subjected to global deprotection. In the synthesis of α-D-glucosamine-1-phosphate, the amino group was protected in the first step, while the subsequent steps remained the same as with amine-free sugars.
The final compounds were tested for inhibitory activity against the MurA enzyme and minimum inhibitory concentration (MIC) against E. coli and S. aureus bacteria. Compounds 8 (IC50 = 16 μM) and 26 (IC50 = 100 μM) exhibited inhibitory activity against the MurA enzyme. Both compounds showed Hill coefficients of 2 or more, indicating non-specific enzyme inhibition. Compound 26 also demonstrated antibacterial activity against the S. aureus strain with an MIC of 0.625 mg/mL. Successfully synthesized compounds will in the future be used at the Jožef Stefan Institute, where they aim to prepare co-crystals with the enzyme ManPT.
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