Discovery and Optimization of a Novel Macrocyclic Amidinourea Series Active as Acidic Mammalian Chitinase Inhibitors

Abstract

Our research group has been involved for a long time in the development of macrocyclic amidinoureas (MCAs) as antifungal agents. The mechanistic investigation drove us to perform an in silico target fishing study, which allowed the identification of chitinases as one of their putative targets, with 1a showing a submicromolar inhibition of Trichoderma viride chitinase. In this work, we investigated the possibility to further inhibit the corresponding human enzymes, acidic mammalian chitinase (AMCase) and chitotriosidase (CHIT1), involved in several chronic inflammatory lung diseases. Thus, we first validated the inhibitory activity of 1a against AMCase and CHIT1 and then designed and synthesized new derivatives aimed at improving the potency and selectivity against AMCase. Among them, compound 3f emerged for its activity profile along with its promising in vitro ADME properties. We also gained a good understanding of the key interactions with the target enzyme through in silico studies.

Figure 1

Structure of representative antifungal macrocycles, argifin, and hybrid compound 1a, previously described as a submicromolar inhibitor of T. viride chitinase.

Figure 2

General structure of the three series of derivatives.

Figure 3

Binding mode of 1a in AMCase (a, cyan) and in CHIT1 (b, magenta and c pale green) binding sites. Protein backbones are presented in cartoon and interacting residues in thin sticks and labeled. Compound 1a is presented as salmon (a), yellow (b), or orange (c) sticks. Hydrogen bonds are shown as yellow dotted lines. (d) Superimposition of 1a in AMCase (cyan) and in CHIT1 (magenta, pale green) binding sites. The figure highlights that the previously described differences in the binding sites of AMCase and CHIT1 lead to a strong displacement of 1a from the binding site with a consequent loss of interactions between the compound and the catalytic residues in CHIT1.