No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Tam, Yeuk Fei. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 63-74). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese.

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.

Digitized by Kansas Correctional Industries

Trypanosomatid parasites cause a wide range of so-called neglected diseases which affect over 27 million people every year. Current treatments are toxic and prone to resistance; therefore, it is imperative to identify novel protein targets and to develop more efficient treatments. Phosphofructokinase (PFK) is the third enzyme in glycolysis, and its reciprocal enzyme in gluconeogenesis is fructose-1,6-bisphosphatase (FBPase); in trypanosomatid parasites (Trypanosoma brucei [Tb], Trypanosoma cruzi [Tc] and Leishmania [Lm] species), both enzymes are recognised drug targets. This thesis describes biochemical and structural studies on these two allosteric enzymes that have been studied with two main purposes: 1) To understand their intrinsic behaviour. The allosteric mechanism of T. brucei PFK is described with the help of two novel crystal structures: TbPFK with the allosteric activator AMP, and mutant A288D located in the effector site. These studies have provided a better understanding of the effect of evolution on the allostery of PFK; and have introduced the first reproducible crystallisation of TbPFK via its A288D mutant. 2) To find novel inhibitors using in silico and high-throughput methods, and to investigate how the intrinsic behaviour relates to the mechanism of inhibition. Nanomolar selective inhibitors against TbPFK and TcPFK have been obtained and optimised to a novel family with low micromolar inhibitory activity against cultured parasites. Crystal structures with three of these inhibitors on TbPFK have helped us understand the structure-activity relationship. Moreover, novel crystal structures of TcPFK and LmFBPase, as well as reproducible crystallisation conditions for the latter enzyme and a mutant of TbPFK (A288D) will undoubtedly facilitate future drug discovery on these targets. Our long-term aim of finding novel drugs against sleeping sickness has been supported by the Wellcome Trust which has recently granted a Seeding Drug Discovery Award with the name “Optimisation of a trypanosome phosphofructokinase lead series to give candidates for treatment of the trypanosomatid based neglected disease Human African Trypanosomiasis”.