Final Activity Report Summary - NOTB (Novel Therapeutic Agents for the Treatment of Tuberculosis) The overall objective of this project was to synthesise novel therapeutic agents for the treatment of tuberculosis (TB). It is estimated that one third of the global population is infected with mycobacterium TB and 9 million individuals develop the clinical disease each year. At present, TB is increasing again by causing 2 million deaths annually, which is equal to 6 % of the total annual deaths in the world. Until 50 years ago there were no drugs to cure tuberculosis. The currently recommended therapy, known as directly observed therapy, short-course (DOTS), of active infection in patients with drug-susceptible mycobacterium tuberculosis consists of a six month treatment with isoniazid (INH), rifampicin (RIF), pyrazinamide (PZA) and ethambutol (EMB) given for two months, followed by INH and RIF for four months. The spread of TB is a massive global problem and serious measures need to be taken immediately to deal with the disease. Mycobacterium tuberculosis has a unique and strong cell wall structure which is required for the bacterium to survive inside the human body where it can lie dormant for extended periods, from 6 to 9 months. The cell wall is supported by a network of polysaccharides containing uncommon sugars known as L-rhamnose, D-arabinofuranose and D-galactofuranose. As D-galactofuranose or its polymer, known as galactan, are not known to occur in humans, the enzymes involved in its biosynthesis are potentail targets for new anti-TB drugs. Based on Blanchard work on the biosynthesis of the cell wall we designed four molecules as inhibitors of the enzymes UDP-Galp mutase and UDP-Galf transferase that were involved in cell wall biosynthesis. This mode of action was novel in the field of TB research and it was hoped that it would lead to the development of a whole new class of possible therapeutic agents for which multidrug resistance would not be a problem. Our research focussed on converting the well known and readily available sugars glucose and galactose into more complex drug-like structures. The first steps in the synthetic sequence went well and we were able to prepare key intermediates from which to construct the proposed inhibitors. Unfortunately, and despite good supporting literature precedent, one of the key proposed synthetic transformations proved impossible to achieve in the lab. At this point we had to slightly modify our original synthetic route and were able to bypass the failed reaction and utilise another transformation in order to access the key proposed synthetic intermediate which represented one half of the inhibitor molecule, thus achieving one of the milestone points of the project. The next challenge was to couple the newly prepared intermediate to the remaining half of the inhibitor. In order to do so we had to perform a rather challenging metal-catalysed synthetic operation. Our first reagent selection, namely dibenzyl phosphate, failed to couple and none of the desired products could be isolated. We tried a simpler reagent, called dimethyl phosphate, and, although we could isolate some of the desired compound, the whole route proved too inefficient on large scale. As such, we explored an alternative avenue of research. Our modified approach to the treatment of TB was to develop molecules that targeted the genetic information of the TB causing bacterium. As this genetic information was not present in humans it should offer a very safe method of treatment since toxic effects were very unlikely. We therefore started to prepare long polymer-like structures that could bind in a very selective manner, targeting only the disease-causing genetic information in the bacterium. In order to make these molecules compatible with the harsh conditions of the human body we first needed to prepare chemically stable building blocks that could be coupled together to make a metabolically stable drug substance. This chemistry proved to be much more straight-forward than that originally proposed; we were thus able to prepare the desired building block from which to prepare the drug substance. Unfortunately time ran out on the project and we were unable to synthesise the final drug substance.
