Identification of Highly Selective Lipoprotein-Associated Phospholipase A2 (Lp-PLA2) Inhibitors by a Covalent Fragment-Based Approach

Covalent
ligands are of great interest as therapeutic drugs or
biochemical tools. Here, we reported the discovery of highly selective
and irreversible inhibitors of lipoprotein-associated phospholipase
A2 (Lp-PLA2) using a covalent fragment-based approach. The crystal
structure of Lp-PLA2 in complex with a covalent fragment not only
reveals the covalent reaction mechanism but also provides a good starting
point to design compound 8, which has a more than 130,000-fold
and 3900-fold increase in potency and selectivity, respectively, compared
to those of the covalent fragment. Furthermore, fluorescent probes
with high selectivity and sensitivity are developed to characterize
Lp-PLA2 and its enzymatic activity in vitro or even in living cells
in a way more convenient than immunoblotting tests or immunofluorescence
imaging. Overall, we provide a paradigm for application of the covalent
fragment-based strategy in covalent ligand discovery and the advantage
of enol–cyclocarbamate as a new warhead in designing covalent
inhibitors of serine hydrolases.