Chitin, a linear polymer of N-acetylglucosamine, is an essential structural component of fungal, nematode and insect pathogens but is not found in human physiology. Chitinases, which hydrolyze this polymer, play a key role in life cycle of these pathogens and associated pathogenesis. Consequently chitinase inhibitors have generated a lot of interest given their potential as insectides, fungicides and antimalarials. Herein, approaches are reported to the synthesis of some non-sugar based chitinase inhibitors: the cyclic pentapeptide natural products argifin, banyasin A and diketopiperazines related to the natural product CI-4. In order to improve the efficiency of production of argifin and facilitate SAR on analogues of the natural product, a revised synthesis of argifin has been developed. The synthesis of argifin was carried out by a combination of solid-phase and solution chemistry. The assembly of the linear peptide was carried out by SPPS and the cyclisation was performed in solution. The protecting groups chosen for the Asp and Arg residues were removable by hydrogenolysis, as this allowed aspartimide formation under acidic conditions to be avoided. Only one HPLC purification was required at the final step; argifin was isolated in 19% yield, compared to 18% yield for the first synthesis by Dixon et al. Banyasin A contains the same essential Arg(MC)-MePhe dipeptide motif as argifin and so it is of considerable interest as a potential Family 18 chitinase inhibitor. The synthesis of Amoa (3-amino-2-methyl-5E-octenoic acid) a rare amino-acid present in banyasin A was investigated. An advanced intermediate for the synthesis of Amoa was successfully obtained via chiral pool chemistry in an 8 step sequence from L-Asp. This involved preparation of a selectively protected β-methyl-substituted Asp derivative, which was then homologated to the β-amino-acid via Arndt-Eistert chemistry to give (3R,4R)-3-(((benzyloxy)carbonyl)amino)-4-methyl-5-oxo-5-allyloxypentanoic acid in 27% yield for the final step. The cyclic dipeptide CI-4, cyclo (L-Arg-D-Pro) is a weak inhibitor (IC50 = 1.2 mM) of Family 18 chitinases, however its binding efficiency index (BEI) is comparable to more potent inhibitors such as argifin. Some analogues of CI-4 show promising activity against a typical bacterial type Family 18 chitinase, SmChiB1 from Serratia marcescens. The cyclic dipeptide should therefore be a useful starting point for the development of more effective and selective inhibitors of this enzyme class. A series of cyclo (Xaa-Pro)-based dipeptides were synthesized, with different Xaa such as L/D-Pro, Gly, L-Ser, L/D-Arg, D-His, D-Phe, with yields ranging from 12 to 84%. Preliminary biological data confirm that cyclo(D-Xaa-D-Pro) may be a novel template for the development of new drug-like inhibitors of Family 18 chitinases.

Chitin ist ein Polysaccharid, welches aus N-Acetylglucosamin (GlcNAc) aufgebaut ist. Das Biopolymer kommt in der Natur in Invertebraten, Algen, Pilzen und Einzellern vor. Chitinasen hydrolysieren Chitin. Diese Enzyme sind essentiell für die Regulierung und Entwicklung von Arthropoden und Mikroorganismen. Sie fungieren in Pflanzen als Phytoalexine. <br> Das verstärkt das Interesse am Design neuer natürlicher und synthetischer Chitinase-inhibitoren, die als potentielle Insektizide, Fungizide, Antimalaria bzw. Antiasthmatika eingesetzt werden können. <br><br> Ziel dieser Arbeit war die Synthese von neuen Thioglycosidanaloga von N-Acetyl-chitooligosacchariden und deren Untersuchung als Enzyminhibitoren. <br><br> Die geschützten 4-O-Tf-galactopyranosylthioglycoside wurden aus den korrespondierenden p-Methoxyphenylglycosiden von GlcNAc nach einer neuen Methode in einer Stufe hergestellt. Die Reaktion der galacto-Triflate mit 2-Acetamido-3,4,6-tri-O-acetyl-2-desoxy-1-thio-ß-D-glucopyranose in Gegenwart von Natriumhydrid und 15-Krone-5 in THF lieferte die Pseudo-Trisaccharide.<br><br> Die Herstellung der Glycosyl-Thiazoline aus den entsprechenden p-Methoxyphenyl-glycosiden mit Lawesson's Reagenz ist nach einem neuen Reaktionsweg beschrieben wie auch die Synthese der Thioacetamide von GlcNAc-Oligomeren.<br><br> Die Pseudo-Oligosaccharide wurden als Inhibitoren der Chitinasen von Serratia marcescens, Chironomus tentans, Acanthocheilonema viteae und Hevaea brasiliensis sowie der N-Acetyl-glucosaminidase von Chironomus tentans getestet. In einigen Fällen ergab sich eine Hemmung (IC50) im µM-Bereich. / Chitin is a polysaccharide composed of N-acetylglucosamine (GlcNAc). The biopolymer is distributed in Invertebrates, algae, fungi and Protozoa. Chitinases hydrolyse chitin. These enzymes are essential for the regulation and development of Arthropoda and micro organisms. In bacteria chitinase degrade chitin as source of carbon and act in plants as phytoalexins. Currently, there is a great interest in the design of novel natural and synthetic chitinase inhibitors, which may act as potential insecticides, fungicides, antimalaria or antiasthmatics.<br><br> Thio-oligosaccharides and related thio-glycosides are rarely described in the literature. Thio-analogues of oligosaccharides derived from N-acetylglucosamine are of interest as potential enzyme inhibitors. The synthesis and enzymatic investigations of thio-glycoside analogues of N-acetyl-chitooligosaccharides are described in this thesis.<br><br> The protected 4-O-Tf-galactopyranosyl thioglycosides were prepared by a new method in one step from the corresponding p-methoxyphenyl glycosides of N-acetylglucosamine. Coupling of galacto-triflates with 2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-1-thio-ß-D-glucopyranose in the presence of sodium hydride and 15-crown-5 in THF, followed by deprotection, afforded the pseudo-trisaccharides. <br><br> The preparation of glycosyl thiazolines by a new manner from the analogues p-methoxyphenyl glycosides with Lawesson's reagent is also described however the synthesis of thioacetamides of N-acetylglucosamine.<br><br> The pseudo-oligosaccharides were tested for inhibition of chitinases from Serratia marcescens, Chironomus tentans, Acanthocheilonema viteae, and Hevaea brasiliensis, and also with N-acetyl-glucosaminidase from Chironomus tentans. Inhibition with IC50 values in the µM range was found in a few cases.