Important pathogens such as Mycobacterium tuberculosis and Plasmodium falciparum, the causative agents of tuberculosis and malaria, respectively, and plants, utilize the 2C-methyl-D-erythritol 4-phosphate (MEP, 5) pathway for the biosynthesis of isopentenyl diphosphate (1) and dimethylallyl diphosphate (2), the universal precursors of isoprenoids, while humans exclusively utilize the alternative mevalonate pathway for the synthesis of 1 and 2. This distinct distribution, together with the fact that the MEP pathway is essential in numerous organisms, makes the enzymes of the MEP pathway attractive drug targets for the development of anti-infective agents and herbicides. Herein, we review the inhibitors reported over the past 2 years, in the context of the most important older developments and with a particular focus on the results obtained against enzymes of pathogenic organisms. We will also discuss new discoveries in terms of structural and mechanistic features, which can help to guide a rational development of inhibitors.

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We applied for the first time an innovative ligand-based NMR methodology (STI) to a medicinal-chemistry project aimed at the development of inhibitors for the enzyme 1-deoxy-D-xylulose-5-phosphate synthase (DXS). DXS is the first enzyme of the 2C-methyl-D-erythritol-4-phosphate (MEP) pathway, present in most bacteria (and not in humans) and responsible for the synthesis of the essential isoprenoid precursors. We designed de novo a first generation of fragments, using Deinococcus radiodurans DXS as a model enzyme, targeting the thiamine diphosphate (TDP) pocket of DXS whilst also exploring the putative substrate-binding pocket, where selectivity over other human TDP-dependent enzymes could be gained. The STI methodology -suitable for weak binders -was essential to determine the binding mode in solution of one of the fragments, circumventing the requirement for an X-ray co-crystal structure, which is known to be particularly challenging for this specific enzyme and in general for weak binders. Based on this finding, we carried out fragment growing and optimisation, which led to a threefold more potent fragment, about as potent as the well-established thiamine analogue deazathiamine.The STI methodology proved therefore its strong potential as a tool to support medicinal-chemistry projects in their early stages, especially when dealing with weak binders.

The enzyme DXS catalyzes the first, rate-limiting step of the 2-C-methyl-d-erythritol-4-phosphate (MEP, 1) pathway using thiamine diphosphate (ThDP) as cofactor; the DXS-catalyzed reaction constitutes also the first step in vitamin B1 and B6 metabolism in bacteria. DXS is the least studied among the enzymes of this pathway in terms of crystallographic information, with only one complete crystal structure deposited in the Protein Data Bank (Deinococcus radiodurans DXS, PDB: ). We synthesized a series of thiamine and ThDP derivatives and tested them for their biochemical activity against two DXS orthologues, namely D. radiodurans DXS and Mycobacterium tuberculosis DXS. These experimental results, combined with advanced docking studies, led to the development and validation of a homology model of M. tuberculosis DXS, which, in turn, will guide medicinal chemists in rationally designing potential inhibitors for M. tuberculosis DXS.

The objective of this article is to describe the results of a 2-year pilot programme implementing prevention of mother to child HIV transmission (PMTCT) in a refugee camp setting. Interventions used were: community sensitization, trainings of healthcare workers, voluntary counselling and HIV testing (VCT), infant feeding, counselling, and administration of Nevirapine. Main outcome measures include: HIV testing acceptance rates, percentage of women receiving post test counselling, Nevirapine uptake, and HIV prevalence among pregnant women and their infants. Ninety-two percent of women (n=9,346) attending antenatal clinics accepted VCT. All women who were tested for HIV received their results and posttest counselling. The HIV prevalence rate among the population was 3.2%. The overall Nevirapine uptake in the camp was 97%. Over a third of women were repatriated before receiving Nevirapine. Only 14% of male counterparts accepted VCT. Due to repatriation, parent's refusal, and deaths, HIV results were available for only 15% of infants born to HIV-infected mothers. The PMTCT programme was successfully integrated into existing antenatal care services and was acceptable to the majority of pregnant women. The major challenges encountered during the implementation of this programme were repatriation of refugees before administration of Nevirapine, which made it difficult to measure the impact of the PMTCT programme.