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Zika virus belongs to the Flavivirus family of RNA viruses, which include other important human pathogens such as dengue and West Nile virus. There are no approved antiviral drugs for these viruses. The highly conserved NS2B-NS3 protease of Flavivirus is essential for the replication of these viruses and it is therefore a drug target. Compound screen followed by medicinal chemistry optimization yielded a novel series of 2,6-disubstituted indole compounds that are potent inhibitors of Zika virus protease (ZVpro) with IC50 values as low as 320 nM. The structure-activity relationships of these and related compounds are discussed. Enzyme kinetics studies show the inhibitor 66 most likely exhibited a non-competitive mode of inhibition. In addition, this series of ZVpro inhibitors also inhibit the NS2B-NS3 protease of dengue and West Nile virus with reduced potencies. The most potent compounds 66 and 67 strongly inhibited Zika virus replication in cells with EC68 values of 1–3 μM. These compounds are novel pharmacological leads for further drug development targeting Zika virus.

The spike protein N-terminal domains (NTDs) of bovine coronavirus (BCoV) and mouse hepatitis coronavirus (MHV) recognize sugar and protein receptors, respectively, despite their significant sequence homology. We recently determined the crystal structure of MHV NTD complexed with its protein receptor murine carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1), which surprisingly revealed a human galectin (galactose-binding lectin) fold in MHV NTD. Here, we have determined at 1.55 Å resolution the crystal structure of BCoV NTD, which also has the human galectin fold. Using mutagenesis, we have located the sugar-binding site in BCoV NTD, which overlaps with the galactose-binding site in human galectins. Using a glycan array screen, we have identified 5-N-acetyl-9-O-acetylneuraminic acid as the preferred sugar substrate for BCoV NTD. Subtle structural differences between BCoV and MHV NTDs, primarily involving different conformations of receptor-binding loops, explain why BCoV NTD does not bind CEACAM1 and why MHV NTD does not bind sugar. These results suggest a successful viral evolution strategy in which coronaviruses stole a galectin from hosts, incorporated it into their spike protein, and evolved it into viral receptor-binding domains with altered sugar specificity in contemporary BCoV or novel protein specificity in contemporary MHV.

The stereochemistry of cyclopropanation reactions between allylsilanes and allylstannanes 6 with four representative diazoalkanes in the presence of rhodium acetate has been studied. Cyclopropanations with ethyl diazoacetate show a preference for the formation of the trans cyclopropane esters 7 , whereas the corresponding reactions with (trimethylsilyl)diazomethane favor the cis stereoisomers. In both cases, overall stereoselection is low, ranging from 1.3:1 to 2.4:1. The product ratios show a small dependence on the nature of the silyl or stannyl groups, with silyl substituents giving better stereoselection than stannyl, and larger ligands on the metal center leading to lower selectivity. On the other hand, rhodium-catalyzed cyclopropanations using methyl 2-diazo-4-phenyl-3-butenoate or 1-aryldiazoacetates occur with excellent stereocontrol. The stereochemical patterns found in these reactions are in accord with an open transition state model wherein the rhodium carbenoid approaches the allylmetal π-bond from an antiperiplanar orientation with respect to the allylic carbonML 3 bond. While the metal center may help stabilize developing β-cationic charge in the transition states, hyperconjugation effects appear to play a minor role, if any, in directing the stereochemical course of cyclopropanation.