Mark J. Dixon

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.

Specificity of the Trypanothione-Dependent Leishmania Major Glyoxalase I: Structure and Biochemical Comparison with the Human Enzyme.

Trypanothione replaces glutathione in defence against cellular damage caused by oxidants, xenobiotics and methylglyoxal in the trypanosomatid parasites, which cause trypanosomiasis and leishmaniasis. In Leishmania major, the first step in methylglyoxal detoxification is performed by a trypanothione‐dependent glyoxalase I (GLO1) containing a nickel cofactor; all other characterized eukaryotic glyoxalases use zinc. In kinetic studies L. major and human enzymes were active with methylglyoxal derivatives of several thiols, but showed opposite substrate selectivities: N1‐glutathionylspermidine hemithioacetal is 40‐fold better with L. major GLO1, whereas glutathione hemithioacetal is 300‐fold better with human GLO1. Similarly, S‐4‐bromobenzylglutathionylspermidine is a 24‐fold more potent linear competitive inhibitor of L. major than human GLO1 (Kis of 0.54 µM and 12.6 µM, respectively), whereas S‐4‐bromobenzylglutathione is > 4000‐fold more active against human than L. major GLO1 (Kis of 0.13 µM and > 500 µM respectively). The crystal structure of L. major GLO1 reveals differences in active site architecture to both human GLO1 and the nickel‐dependent Escherichia coli GLO1, including increased negative charge and hydrophobic character and truncation of a loop that may regulate catalysis in the human enzyme. These differences correlate with the differential binding of glutathione and trypanothione‐based substrates, and thus offer a route to the rational design of L. major‐specific GLO1 inhibitors.

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.

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.