In this paper we describe the syntheses of the tetraoxygenated triarylmethyl (trityl) radical 14 and the tetrathiatriarylmethyl (trityl) radicals 15 and 16. The syntheses include new and improved preparations of the key intermediate compounds 1 and 2. The new route to compound 2 is noteworthy for its efficiency and its avoidance of the highly toxic compound phosgene as well as the isolation of the air-sensitive 1,2,4,5-benzenetetrathiol.

Cathepsin C is a cysteine protease required for the activation of several pro-inflammatory serine proteases and, as such, is of interest as a therapeutic target. In cathepsin C-deficient mice and humans, the N-terminal processing and activation of neutrophil elastase, cathepsin G, and proteinase-3 is abolished and is accompanied by a reduction of protein levels. Pharmacologically, the consequence of cathepsin C inhibition on the activation of these serine proteases has not been described, due to the lack of stable and non-toxic inhibitors and the absence of appropriate experimental cell systems. Using novel reversible peptide nitrile inhibitors of cathepsin C, and cell-based assays with U937 and EcoM-G cells, we determined the effects of pharmacological inhibition of cathepsin C on serine protease activity. We show that indirect and complete inhibition of neutrophil elastase, cathepsin G, and proteinase-3 is achievable in intact cells with selective and non-cytotoxic cathepsin C inhibitors, at concentrations ϳ10-fold higher than those required to inhibit purified cathepsin C. The concentration of inhibitor needed to block processing of these three serine proteases was similar, regardless of the cell system used. Importantly, cathepsin C inhibition must be sustained to maintain serine protease inhibition, because removal of the reversible inhibitors resulted in the activation of pro-enzymes in intact cells. These findings demonstrate that near complete inhibition of multiple serine proteases can be achieved with cathepsin C inhibitors and that cathepsin C inhibition represents a viable but challenging approach for the treatment of neutrophil-based inflammatory diseases.

Inhibition of cathepsin C, a dipeptidyl peptidase that activates many serine proteases, represents an attractive therapeutic strategy for inflammatory diseases with a high neutrophil burden. We recently showed the feasibility of blocking the activation of neutrophil elastase, cathepsin G, and proteinase-3 with a single cathepsin C selective inhibitor in cultured cells. Here we measured the fractional inhibition of cathepsin C that is required for blockade of downstream serine protease processing, in cell-based assays and in vivo. Using a radiolabeled active site probe and U937 cells, a 50% reduction of cathepsin G processing required ϳ50% of cathepsin C active sites to be occupied by an inhibitor. In EcoM-G cells, inhibition of 50% of neutrophil elastase activity required ϳ80% occupancy. Both of these serine proteases were fully inhibited at full cathepsin C active site occupancy, whereas granzyme B processing in TALL-104 cells was partially inhibited, despite complete occupancy. In vivo, leukocytes from cathepsin C ϩ/Ϫ mice exhibited comparable levels of neutrophil elastase activity to wild-type animals, even though their cathepsin C activity was reduced by half. The long-term administration of a cathepsin C inhibitor to rats, at doses that resulted in the nearly complete blockade of cathepsin C active sites in bone marrow, caused significant reductions of neutrophil elastase, cathepsin G and proteinase-3 activities. Our results demonstrate that the inhibition of cathepsin C leads to a decrease of activity of multiple serine proteases involved in inflammation but also suggest that high fractional inhibition is necessary to reach therapeutically significant effects.

The HCV NS5B RNA dependent RNA polymerase plays an essential role in viral replication. The discovery of a novel class of inhibitors based on an N,N-disubstituted phenylalanine scaffold and structure-activity relationships studies to improve potency are described.

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