Preclinical Characterization of PC786, an Inhaled Small-Molecule Respiratory Syncytial Virus L Protein Polymerase Inhibitor.

Although respiratory syncytial virus (RSV) is the most common cause of lower respiratory tract infection in infants and young children, attempts to develop an effective therapy have so far proved unsuccessful. Here we report the preclinical profiles of PC786, a potent nonnucleoside RSV L protein polymerase inhibitor, designed for inhalation treatment of RSV infection. PC786 demonstrated a potent and selective antiviral activity against laboratory-adapted or clinical isolates of RSV-A (50% inhibitory concentration [IC50], <0.09 to 0.71 nM) and RSV-B (IC50, 1.3 to 50.6 nM), which were determined by inhibition of cytopathic effects in HEp-2 cells without causing detectable cytotoxicity. The underlying inhibition of virus replication was confirmed by PCR analysis. The effects of PC786 were largely unaffected by the multiplicity of infection (MOI) and were retained in the face of established RSV replication in a time-of-addition study. Persistent anti-RSV effects of PC786 were also demonstrated in human bronchial epithelial cells. In vivo intranasal once daily dosing with PC786 was able to reduce the virus load to undetectable levels in lung homogenates from RSV-infected mice and cotton rats. Treatment with escalating concentrations identified a dominant mutation in the L protein (Y1631H) in vitro In addition, PC786 potently inhibited RSV RNA-dependent RNA polymerase (RdRp) activity in a cell-free enzyme assay and minigenome assay in HEp-2 cells (IC50, 2.1 and 0.5 nM, respectively). Thus, PC786 was shown to be a potent anti-RSV agent via inhibition of RdRp activity, making topical treatment with this compound a novel potential therapy for the treatment of human RSV infections.

Diastereoselective nickel-catalyzed reductive aldol cyclizations using diethylzinc as the stoichiometric reductant: scope and mechanistic insight.

In the presence of diethylzinc as a stoichiometric reductant, Ni(acac) 2 functions as an efficient precatalyst for the reductive aldol cyclization of alpha,beta-unsaturated carbonyl compounds tethered to a ketone electrophile through an amide or an ester linkage. The reactions are tolerant of a wide range of substitution at both alpha,beta-unsaturated carbonyl and ketone components and proceed smoothly to furnish beta-hydroxylactams and beta-hydroxylactones with generally high diastereoselectivities. A series of experiments, including deuterium-labeling studies, was carried out in an attempt to gain some insight into the possible reaction mechanisms that might be operative.