Phosphonate as a Stable Zinc-Binding Group for "Pathoblocker" Inhibitors of Clostridial Collagenase H (ColH)

Abstract

Microbial infections are a significant threat to public health, and resistance is on the rise, so new antibiotics with novel modes of action are urgently needed. The extracellular zinc metalloprotease collagenase H (ColH) from Clostridium histolyticum is a virulence factor that catalyses tissue damage, leading to improved host invasion and colonisation. Besides the major role of ColH in pathogenicity, its extracellular localisation makes it a highly attractive target for the development of new antivirulence agents. Previously, we had found that a highly selective and potent thiol prodrug (with a hydrolytically cleavable thiocarbamate unit) provided efficient ColH inhibition. We now report the synthesis and biological evaluation of a range of zinc-binding group (ZBG) variants of this thiol-derived inhibitor, with the mercapto unit being replaced by other zinc ligands. Among these, an analogue with a phosphonate motif as ZBG showed promising activity against ColH, an improved selectivity profile, and significantly higher stability than the thiol reference compound, thus making it an attractive candidate for future drug development.

Keywords: anti-infectives; drug design; medicinal chemistry; metalloenzymes; structure-activity relationships.

Figure 1

Structural diversity of selected previously reported ColH inhibitors with the zinc‐binding groups highlighted in grey. ^[9]

Scheme 1

Structures of the previously identified “hit” ColH inhibitor 5, its active thiol form 5 a (after prodrug cleavage) and previously reported amide analogue 6. General structure 7 of the novel potential collagenase inhibitors reported in this work (ZBG=zinc‐binding group).

Scheme 2

Synthesis of target compounds 8–11.

Scheme 3

Synthesis of azole‐derived target compounds 14–20.

Scheme 4

Synthesis of anionic target compounds 24–26.

Figure 2

Structures and in vitro potencies for collagenase inhibition of compounds 26 and 29. ^[16]

Figure 3

Ex vivo pig skin degradation assay: hydroxyproline release after 24 h upon treatment with 26 and 29 ^[16] (in % relative to the controls).