Design and development of human neuraminidase inhibitors using amide bioisosteres
Creators: Radwan, Mostafa
Publisher: name: University of Alberta Library
Year: 2023

<p>Human neuraminidases (hNEU, also known as sialidases) are potential targets for the treatment of different pathological conditions. NEU is a class of enzymes that catalyze the hydrolysis of neuraminic acid (Neu, also known as sialic acid) from glycan chains. The 5-Acetamido-3,5-dideoxy-D-glycero-D-galacto-2-nonulopyranosonic acid (Neu5Ac) residue is the most common Neu found in human, and is typically attached at the termini of the glycans. Humans have four isoenzymes; NEU1, NEU2, NEU3, and NEU4. The role of each isoenzyme in different physiological and pathological conditions is not fully investigated. Selective inhibitors will provide essential research tools to study the function of individual enzymes as well as future therapeutics. A commonly used inhibitor of NEU is 2,3-didehydro-5-N-acetyl neuraminic acid (DANA), a non-selective inhibitor that has also been modified to provide enhanced potency and selectivity for hNEU. In this thesis, we hypothesize that tuning chemical structure of DANA-based inhibitors by replacing C5 and C9 linkers with amide bioisosteres will enhance the inhibitory activity for hNEU. As a result, we provide new potent and selective DANA-based hNEU inhibitors and a new synthetic route for easy access to modified DANA. <br>
Chapter 2 describes a synthetic route for 5-azido derivatives of thiosialosides and DANA. The method used a mild deprotection for the 5-acetamido group followed by a diazo transfer step. Two different diazo transfer reagents (trifluoromthanesulfonyl azide and imidazole-1-sulfonyl azide) were used and compared in terms of yields. Acetate protecting groups were also assessed for their effect on the diazo transfer step. C5-azido derivatives of both thiosialosides and DANA were produced in five or six steps with yields up to 76% and 83%, respectively. Results showed that C5-azido derivatives limited observed side reactions due to protecting group migrations as compared to the C5-amide.<br>
Chapter 3 presents the design of hNEU inhibitors by replacing C5-amide of DANA with different amide bioisosteres. Alternative amide bioisosteres were combined with similar substituents were synthesized to test the effect of individual linker on the inhibitory activity. The new inhibitors showed that 1,4-disubstituted-1,2,3-triazole was a suitable linker to target NEU1 and NEU2. Inhibitor 542 that combined a triazole linker with unbranched aliphatic substituent, exhibited high potency for NEU1 (K¬i = 0.4 ± 0.1 μM) and significantly improved the selectivity compared to the reference amide compound 502. In addition, compound 542 had improved hydrophobic characteristics that could offer improved pharmacokinetic properties.<br>
Linkers of C9-modified DANA were studied in Chapter 4 by implementing various amide bioisosteres. A library of C9-modified DANA with either unbranched aliphatic alkyl chain or biphenyl substituent linked through one of six amide bioisosteres (triazole, urea, thiourea, carbamate, thiocarbamate, and sulfonamide) was generated. Derivative 963, which had a biphenyl carbamate group, showed highest potency (K¬i = 0.1 ± 0.01 μM) and selectivity for NEU3.<br>
The work in this thesis expands the structure activity relationship (SAR) of these inhibitors. It provides not only new potent selective inhibitors but also gives an insight of the hNEU binding sites. The synthetic method for 5-azido derivatives offers an easy access for important intermediates for new potent inhibitors. Finally, the work provides new research and therapeutic tools that can target individual hNEU.</p>