Serendipitous Discovery of a Potent Influenza Virus A Neuraminidase Inhibitor

Abstract

We have previously reported a potent neuraminidase inhibitor that comprises a carbocyclic analogue of zanamivir in which the hydrophilic glycerol side chain is replaced by the hydrophobic 3-pentyloxy group of oseltamivir. This hybrid inhibitor showed excellent inhibitory properties in the neuraminidase inhibition assay (Ki =0.46 nM; Ki (zanamivir) =0.16 nM) and in the viral replication inhibition assay in cell culture at 10(-8) M. As part of this lead optimization, we now report a novel spirolactam that shows comparable inhibitory activity in the cell culture assay to that of our lead compound at 10(-7) M. The compound was discovered serendipitously during the attempted synthesis of the isothiourea derivative of the original candidate. The X-ray crystal structure of the spirolactam in complex with the N8 subtype neuraminidase offers insight into the mode of inhibition.

A new role of neuraminidase (NA) in the influenza virus life cycle: implication for developing NA inhibitors with novel mechanism of action

“…These residues are highly conserved in all NA subtypes . Based on the conserved catalytic site, intensive research has focused on structural modification of existing NAIs, as well as the design of novel NAIs, some of which have been previously reviewed . For example, new derivatives of oseltamivir were prepared by modifying the amino group with glycyl, acetyl, benzyl, and prolyl moieties in order to develop novel influenza virus inhibitors .…”

Exploration of the 150 cavity and the role of serendipity in the discovery of inhibitors of influenza virus A neuraminidase

“…X-ray crystallographic analysis of N8 in complex with 55 and 56 provided better understanding of the molecular basis behind the observed differences in the inhibitory activities. 47 The overall binding mode of both compounds and interactions within the active site were very similar, except for the difference in the orientation of the spirolactam ring. In the case of the N8: 55 complex, the interactions between the spirolactam ring and the enzyme appeared to be influenced by the zwitterionic resonance state (55a) adopted by the thiazolidinone ring.…”

“…We have explained the formation of this spirolactam ring from the coupled product 58 via base-catalyzed double bond migration followed by lactamization, facilitated by the conditions employed in the ester hydrolysis step (Scheme 7). 47 Significantly, the spirolactam 55 was found to be a potent inhibitor of influenza virus replication with an effective concentration as low as 10 -6 -10…”

“…During the course of further optimization of the lead compound 52, we serendipitously discovered a novel spirolactam scaffold with potent neuraminidase inhibitory activity. 47 Our original intention was to synthesize the isothiourea version (53) of the hybrid inhibitor 52. The synthetic approach to this target compound involved nucleophilic ring opening of the N-Acetyl D r a f t aziridine intermediate 54 using Boc-protected thiourea, followed by hydrolysis of the methyl ester and deprotection of the Boc-protecting group, as shown in Scheme 6.…”

Catalytic Enantioselective Reaction of α‐Phenylthioacetonitriles with Imines Using Chiral Bis(imidazoline)–Palladium Catalysts

“…The coordination of palladium to cyanides in α‐phenylthioacetonitriles enhances their acidity of the α‐proton, followed by the reaction of α‐cyano carbanions with imines, giving chiral α‐thio‐β‐aminoacetonitriles, which are precursors for some biologically active compounds, such as influenza neuraminidase inhibitor,8 β‐lactamase inhibitor,9 and botulinum neurotoxin inhibitor (Figure 1). 10…”