A Primary Evaluation of Potential Small‐Molecule Inhibitors of the Astacin Metalloproteinase Ovastacin, a Novel Drug Target in Female Infertility Treatment

Abstract

Despite huge progress in hormonal therapy and improved in vitro fertilization methods, the success rates in infertility treatment are still limited. A recently discovered mechanism revealed the interplay between the plasma protein fetuin‐B and the cortical granule‐based proteinase ovastacin to be a novel key mechanism in the regulation of fertilization. Upon sperm–egg fusion, cleavage of a distinct zona pellucida component by ovastacin destroys the sperm receptor, enhances zona robustness, and eventually provides a definitive block against polyspermy. An untimely onset of this zona hardening prior to fertilization would consequently result in infertility. Physiologically, this process is controlled by fetuin‐B, an endogenous ovastacin inhibitor. Here we aimed to discover small‐molecule inhibitors of ovastacin that could mimic the effect of fetuin‐B. These compounds could be useful lead structures for the development of specific ovastacin inhibitors that can be used in infertility treatment or in vitro fertilization

Heteroaromatic Inhibitors of the Astacin Proteinases Meprin α, Meprin β and Ovastacin Discovered by a Scaffold‐Hopping Approach

“…For dockings only chain A and the corresponding zinc ion were used (monomer). For the targets meprin α and ovastacin the recently reported homology models were employed [13,14] . Compounds 2 a , 2 b , 3 a , 3 b , 4 a and 4 b were docked to a 20 Å radius around the catalytic zinc ion.…”

“…We formally assumed three possible heteroaromatic cyclizations for the rigidification of the tertiary amine, a "1,2,3" and "1,2,4" cyclization yielding scaffolds 2 and 3, or a ring fusion yielding scaffold 4, respectively. As either glycine and β-alanine derivatives were found to be suitable spacers between the tertiary amine and the hydroxamic acid and could affect the inhibitor activity against meprin α or β and ovastacin, [12][13][14] both spacers between hydroxamic acid and the heteroaromatic cores were investigated, as well. Prototypic, synthetically tractable inhibitors of these three scaffolds are represented by 2,5diphenyl-1-yl-pyrroles 2 a, b, 3,5-diphenyl-1-yl-pyrazoles 3 a, b and 2-phenyl-1-yl-indoles 4 a, b.…”

“…Of note, isoxazole 2 c, pyrazole 2 e and indole 4 a exhibit even higher activities without any scaffold decoration as the recently reported tertiary amine based ovastacin inhibitors. [14] Thus, these compounds are the most potent small molecule ovastacin inhibitors reported to date.…”

“…For the targets meprin α and ovastacin the recently reported homology models were employed. [13,14] Compounds 2 a, 2 b, 3 a, 3 b, 4 a and 4 b were docked to a 20 Å radius around the catalytic zinc ion. The hydroxamic acid was substructure constrained, based on the orientation of the co-crystalized hydroxamate of compound 1a.…”

“…[12,13] More recently, selected compounds of this chemotype were also found to be potent inhibitors of ovastacin ( Figure 1), rendering them as pan-selective astacin inhibitors. [14] Nevertheless, the tertiary amine motif exhibits a high conformational freedom, potentially leading to entropic penalty upon binding to the active site of the enzyme. Furthermore, the benzylic CH 2 -N bonds represent hotspots that might lead to reduced metabolic stability due to oxidative dealkylation, albeit the compounds exhibited acceptable plasma half-lives in rats.…”