Bioisosteres at C9 of 2,3-didehydro-5-N-acetyl neuraminic acid identify selective inhibitors of NEU3

Human neuraminidases play critical roles in many physiological and pathological processes. These enzymes catalyze the hydrolysis of terminal sialic acids (also known as neuraminic acids) from glycan chains. Humans have four isoenzymes of NEU: NEU1, NEU2, NEU3, and NEU4, making selective inhibitors important tools to investigate the function of individual isoenzymes. A typical scaffold used for the development of NEU inhibitors is 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (DANA), which is a general inhibitor of viral, bacterial, and human neuraminidases. Modifications at the C9 position of DANA have been critical for the potency and selectivity of inhibitors that target human NEU. For example, C9-amides bearing alkyl substituents have been used to develop inhibitors with preference for NEU1, while C9-triazoles with aromatic substituents have higher potency for NEU3 and NEU4. To design improved DANA analogs, we generated a library of compounds with either a short alkyl chain or a biphenyl substituent linked to the C9 position through one of six amide bioisosteres. Bioisostere linkers included triazole, urea, thiourea, carbamate, thiocarbamate, and sulfonamide groups. Within this library, we identified a C9-biphenyl carbamate derivative (963) that showed high potency for NEU3 (K¬i = 0.12 ± 0.01 μM). Additionally, the carbamate analog had enhanced selectivity for NEU3 over all other human isoenzymes. In contrast, NEU1 and NEU4 isoenzymes preferred amide and triazole linkers, respectively. Finally, analogs with urea, sulfonamide, and amide linkers showed enhanced inhibitory activity for a bacterial NEU, NanI from Clostridium perfringens.