Mycobacteria are present in a wide range of environments. They contain characteristic complex mixtures of mycolic acids in the cell wall together with other lipids. The high resistance of mycobacteria to the majority of antibiotics, therapeutic agents and disinfectants is thought to be related to the unique structure of the mycobacterial cell wall. Mycolic acids are high molecular weight a-alkyl-branched ß-hydroxy long chain fatty acids (60-90 carbon atoms). Different species of Mycobacteria may produce different classes of mycolic acids including a-, methoxy, keto, and wax ester mycolic acids, each present as mixtures of homologues. These may contain different functional groups such as ester, keto, methoxy, hydroxyl, and alkene.
The most reported lipids present in the cell wall are sugar esters, e.g mycolyl trehalose esters. These mycolic acids and mycolyl trehalose esters show very interesting toxic and immunological properties; these offer considerable potential for application in the detection, control, and treatment of mycobacterial infection, and also in developing sensors for detection of disease. This study will seek to explore these potentials. This project involved the synthesis of several mycolic acids, wax esters and trehalose esters. The biological activities of these synthetic compounds would be studied, particularly their suitability as specific antigens to detect mycobacterial infections in serodiagnostic assays. The objectives of the project are discussed in four parts.
The first part of this project involved the first synthesis of wax ester (A) and its corresponding ω-carboxymycolic acid (B), one component of the complex mixture isolated from Mycobacterium avium. Once the synthesis had been optimised, synthesis of the wax ester (C) and its corresponding ω-carboxymycolic acid (D) were also achieved, the latter compounds being isolated from Mycobacterium gordonae. In addition the wax ester (E) was also prepared introducing longer chain lengths than the natural wax ester. This was to study whether or not the chain length has any effect on the biological activities.
The second part of this project involved the synthesis of novel tehalose esters of the above wax esters. Firstly, the syntheses of trehalose dimycolate (TDM) (F) and trehalose monomycolate (TMM) (G) of the M.avium wax ester were achieved successfully, followed by the synthesis ofTDM (H) and TMM (I) of the M. gordonae wax ester. In addition the syntheses of the trehalose esters of the non-natural wax ester (E) were also attempted, however only the TDM (J) was obtained. These wax esters and their corresponding trehalose esters would be used as a specific antigens to distinguish the M.avium or M.gordonae from M.tuberculosis specifically in serodiagnostic assays (ELISA).
The third part of this study involved the synthesis of diene and alkene mycolic acids (K) and (L), followed by the synthesis of their trehalose esters (M, N, 0, P). These compounds would be tested for their immunological properties (TNF-a cytokine stimulation), as well as the determination of their specificity and sensitivity in ELISA assays to detect mycobacterial infection.
The fourth part entailed the first synthesis of disulfide and thiol modified trehalose esters ( cord factors). This was attempted firstly, by synthesizing the simpler model disulfide trehalose esters (Q) and (R). After the success in making those model compounds, the disulfide trehalose ester of a-mycolic acid (S) and its corresponding thiol (T) were prepared successfully. These compounds were designed to be coated onto a gold surface or gold nanoparticles to form a self-assembled monolayers, and then used as specific antigens to bind with TB-antibodies for the early detection of TB in biosensors.