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N-linked glycosylation is the most common form of post-translational modification in nature and is essential to almost all enveloped viruses, including members of the Flaviviridae family. The host cell N-linked glycoprotein processing pathway is utilised by these viruses and as such has long been identified as a potential target for the development of antiviral drugs. Here, the antiviral mechanisms of three classes of small molecules targeting the secretory pathway and altering viral envelope glycosylation are investigated, using the HCV surrogate model, BVDV. The antiviral activity of imino sugars, principally through α-glucosidase inhibition, is well-characterised and here, a group of novel adamantyl coupled imino sugars are investigated and demonstrated to inhibit ER α glucosidases, which correlates with their antiviral activity against BVDV. Additionally, BVDV is used to study the antiviral mechanism of action of nitazoxanide. Nitazoxanide, the parent compound of the thiazolide class of structures, is a broadly antimicrobial compound with antiviral activity against HBV, HCV, influenza, JEV and others. Here, nitazoxanide is shown to be antiviral against BVDV by inducing Ca2+ release from ATP-sensitive intracellular calcium stores, disrupting ER-Golgi trafficking and inhibiting complex glycan formation. Finally, the potential of Golgi endo-α-mannosidase as an antiviral target is explored, using the endomannosidase inhibitor glucose-isofagomine in conjunction with the imino sugar α-glucosidase inhibitor NAP-DNJ. Endomannosidase is shown to be a valid antiviral target for BVDV, both alone and in combination with α-glucosidase inhibition, and is utilised by viral glycoproteins to acquire complex glycan structure, even in the absence of α-glucosidase inhibition. Altogether, this work furthers our understanding of the varied antiviral mechanisms of small molecules targeting the secretory pathway, enhancing the search for novel antiviral drugs directed against host cell machinery.

Glycosidases are amongst the most abundant enzymes in nature. This is due to their role in the degradation of carbohydrates which are the major source of carbon or earth. The absence or malfunction of glycosidases is implicated in numerous diseases such as cancers, diabetes, and lysosomal storage disorders, which make them important drug targets for study in medicinal chemistry. The seminal work by Pauling and Wolfenden showed that enzymes bind to their substrate at the transition state with very strong affinity. Wolfenden estimated the dissociation constant to be around 10-22M. This encouraged the design of glycosidase inhibitors which mimicked one or more features of the transition state. The notable features of the transition state of glycosidases include the development of a positive charge on the anomeric carbon atom, and the distortion of the sugar ring into one of a boat, an envelope, or a half-chair conformation to accommodate the formed positive charge. The glyconoamidine family of inhibitors emerged as a class of compounds to mimic both the positive charge and distorted chair conformation of the transition state of glycosidases. Research in the Striegler group identified a library of galactonoamidines as highly potent competitive inhibitors of several β-galactosidases, with inhibition constants in the low nanomolar to picomolar range. The work described here summarizes an effort towards the synthesis of polar and bulky galactonoamidines for the inhibition of the human α-galactosidase. Following a protocol previously established in the group, the precursor galactothionolactam was synthesized and coupled with several amines to yield a library of perbenzylated galactonoamidines. Hydrogenation of the perbenzylated galactonoamidines in the presence of palladium on carbon afforded some of the desired compounds, whereas the others were unsuccessful.