Ole A. Andersen

Structure-Based Dissection of the Natural Product Cyclopentapeptide Chitinase Inhibitor Argifin

Summary Chitinase inhibitors have chemotherapeutic potential as fungicides, pesticides, and antiasthmatics. Argifin, a natural product cyclopentapeptide, competitively inhibits family 18 chitinases in the nanomolar to micromolar range and shows extensive substrate mimicry. In an attempt to map the active fragments of this large natural product, the cyclopentapeptide was progressively dissected down to four linear peptides and dimethylguanylurea, synthesized using a combination of solution and solid phase peptide synthesis. The peptide fragments inhibit chitinase B1 from Aspergillus fumigatus (AfChiB1), the human chitotriosidase, and chitinase activity in lung homogenates from a murine model of chronic asthma, with potencies ranging from high nanomolar to high micromolar inhibition. X-ray crystallographic analysis of the chitinase-inhibitor complexes revealed that the conformations of the linear peptides were remarkably similar to that of the natural product. Strikingly, the dimethylguanylurea fragment, representing only a quarter of the natural product mass, was found to harbor all significant interactions with the protein and binds with unusually high efficiency. The data provide useful information that could lead to the generation of drug-like, natural product-based chitinase inhibitors.

Natural product family 18 chitinase inhibitors

Covering: 1987 up to May 2005 This review covers the synthesis of natural product chitinase inhibitors, and compares their binding modes with family 18 chitinases from a structural and kinetic viewpoint; 121 references are cited.

Screening-based Discovery and Structural Dissection of a Novel Family 18 Chitinase Inhibitor *

Family 18 chitinases play key roles in the life cycles of a variety of organisms ranging from bacteria to man. Very recently it has been shown that one of the mammalian chitinases is highly overexpressed in the asthmatic lung and contributes to the pathogenic process through recruitment of inflammatory cells. Although several potent natural product chitinase inhibitors have been identified, their chemotherapeutic potential or their use as cell biological tools is limited due to their size, complex chemistry, and limited availability. We describe a virtual screening-based approach to identification of a novel, purine-based, chitinase inhibitor. This inhibitor acts in the low micromolar (Ki = 2.8 ± 0.2 μm) range in a competitive mode. Dissection of the binding mode by x-ray crystallography reveals that the compound, which consists of two linked caffeine moieties, binds in the active site through extensive and not previously observed stacking interactions with conserved, solvent exposed tryptophans. Such exposed aromatics are also present in the structures of many other carbohydrate processing enzymes. The compound exhibits favorable chemical properties and is likely to be useful as a general scaffold for development of pan-family 18 chitinase inhibitors.

Analyzing airway inflammation with chemical biology: dissection of acidic mammalian chitinase function with a selective drug-like inhibitor

Summary Acidic mammalian chitinase (AMCase) is produced in the lung during allergic inflammation and asthma, and inhibition of enzymatic activity has been considered as a therapeutic strategy. However, most chitinase inhibitors are nonselective, additionally inhibiting chitotriosidase activity. Here, we describe bisdionin F, a competitive AMCase inhibitor with 20-fold selectivity for AMCase over chitotriosidase, designed by utilizing the AMCase crystal structure and dicaffeine scaffold. In a murine model of allergic inflammation, bisdionin F-treatment attenuated chitinase activity and alleviated the primary features of allergic inflammation including eosinophilia. However, selective AMCase inhibition by bisdionin F also caused dramatic and unexpected neutrophilia in the lungs. This class of inhibitor will be a powerful tool to dissect the functions of mammalian chitinases in disease and represents a synthetically accessible scaffold to optimize inhibitory properties in terms of airway inflammation.

Solid-phase synthesis of cyclic peptide chitinase inhibitors: SAR of the argifin scaffold

An efficient, all-solid-phase synthesis of argifin, a cyclic peptide chitinase inhibitor with chemotherapeutic potential, is described.

Bisdionin C—A Rationally Designed, Submicromolar Inhibitor of Family 18 Chitinases

Chitinases of the GH18 family play important roles in a variety of pathogenic organisms and have also been shown to be involved in human asthma progression, making these enzymes potential drug targets. While a number of potent GH18 chitinase inhibitors have been described, in general, these compounds suffer from limited synthetic accessibility or unfavorable medicinal-chemical properties, making them poor starting points for the development of chitinase-targeted drugs. Exploiting available structural data, we have rationally designed bisdionin C, a submicromolar inhibitor of GH18 enzymes, that possesses desirable druglike properties and tractable chemical synthesis. A crystallographic structure of a chitinase-bisdionin C complex shows the two aromatic systems of the ligand interacting with two conserved tryptophan residues exposed in the active site cleft of the enzyme, while at the same time forming extensive hydrogen-bonding interactions with the catalytic machinery. The observed mode of binding, together with inhibition data, suggests that bisdionin C presents an attractive starting point for the development of specific inhibitors of bacterial-type, but not plant-type, GH 18 chitinases.

Synthetic approaches to cyclic peptide natural products as chitinase inhibitors

Gonadotropin Releasing Hormone (pGlu-His-Trp-Ser-Tyr-Gly-Leu- Arg-Pro-Gly-NH2, GnRH) plays a signifi cant role in the controlling of gonadotropins and steroids hormones. A large number of linear GnRH analogues has been synthesized and tested for several medical uses. Leuprolide acetate (pGlu-His-Trp-Ser-Tyr-(D)Leu-Leu-Arg-Pro-NHEt, LPA) is a potent GnRH agonist and is used to treat a wide range of sex hormone related disorders, including prostatic cancer, endometriosis and precocious puberty. Despite its widespread use, only limited information based on spectroscopic evidence regarding the solution conformation of Leuprolide are known. Moreover, non crystallographic data is available for the receptor of GnRH (G protein-coupled receptor). The aim of this study was to characterize the conformation of Leuprolide and its modifi ed linear analogue (pGlu-His-Trp-Ser-Tyr(OMe)-(D)Leu-Leu- Arg-Aze-NHEt) in DMSO solution (which simulates better the receptor environment) using Nuclear Magnetic Resonance (NMR) and Molecular Modeling techniques. By using both NMR and Molecular Modeling we have characterized the secondary structural preferences of these GnRH analogues.