The objectives of this thesis may be divided into four parts:
[1] Preparation of Methyl Arabino-Mycolates (MAM) (I) via the esterification of methyl-a-D-arabinofuranoside with seven classes of synthetic mycolic acids, and also esterifying with four fatty acids as model systems: The initial biological and statistical analysis studies carried out on these compounds afforded promising results in ELISA assays for detection of TB. Also, most of these compounds showed a good response in the stimulation of the bone marrow-derived dendritic cells derived from mice.
[2] Preparation of Glycerol-Arabino-Mycolates (GAM). In this part, the synthesis of both D- and L-Glycerol-a-D-arabinofuranoside was undertaken, and subsequent esterification of each glycan with three different synthetic mycolic acids (II) was carried out. Also, two models were prepared from the D-glycan, derived from simple fatty acids. The main aim of this part was to prove the stereochemistry of the GAM (i.e. whether the desymmetrised glycerol unit resides in either the D or L configuration), and this was achieved by comparing the NMR data for both synthetic isomers (L and D-GAM) with those reported for the natural extract. This exercise confirmed the natural stereochemistry to be L-GAM. Some of the compounds produced in this part of the project were shown, via biological testing, to possess a good capacity for the induction of Bone marrow-derived dendritic cells (BMDCs) to stimulate a variety of proinflammatory cytokines (e.g., TNF-a, IL-β, IL-6), the latter being essential to control TB disease.
[3] The third part entailed preparation of Methyl Tri-Arabino-Di-Mycolates (MTADM) (III), which involved synthesis of both the donor and the acceptor according to literature methods with slight modifications. The coupling of the donor and the acceptor to prepare the desired glycan was carried out using known coupling conditions. A model of this glycan was prepared through esterification with a normal fatty acid. A series of five compounds from MTADM was prepared, based on the three common classes of MAs. The ELISA assay for detection of TB employing these as the antigenic compounds is in progress. This series of compounds was subjected to stimulation assays, however, the compounds were found to engender low responses compared with the members of the other two series.
[ 4] The final part of this project involved synthesis of Di-Mycolyl-Di-Araf-Glycerol (DMAD) (IV). The glycan moiety of DMAG was successfully prepared for both stereochemistries of the glycerol component. A study to explore the effect of the
protecting group on the yield and the β-selectivity of the glycosylation was carried out, and we were successful in the development of efficient route to prepare the DMAG glycan with an excellent β-selectivity and in excellent yield. The attempted esterification of this glycan with MAs was found, however, to be unsuccessful. The testing and assay of the effects of the DMAG glycan on a range of cytokines involved in the immune system, in addition to an assessment of their antigenic capacity,are expected to be carried out in the near future.