Atovaquone-proguanil (Malarone®) is used for malaria prophylaxis and treatment. While the cytochrome bc1-inhibitor atovaquone has potent activity, proguanil’s action is attributed to its cyclization-metabolite, cycloguanil. Evidence suggests that proguanil has limited intrinsic activity, associated with mitochondrial-function. Here we demonstrate that proguanil, and cyclization-blocked analogue tBuPG, have potent, but slow-acting, in vitro anti-plasmodial activity. Activity is folate-metabolism and isoprenoid biosynthesis-independent. In yeast dihydroorotate dehydrogenase-expressing parasites, proguanil and tBuPG slow-action remains, while bc1-inhibitor activity switches from comparatively fast to slow-acting. Like proguanil, tBuPG has activity againstP. bergheiliver-stage parasites. Both analogues act synergistically with bc1-inhibitors against blood-stages in vitro, however cycloguanil antagonizes activity. Together, these data suggest that proguanil is a potent slow-acting anti-plasmodial agent, that bc1 is essential to parasite survival independent of dihydroorotate dehydrogenase-activity, that Malarone® is a triple-drug combination that includes antagonistic partners and that a cyclization-blocked proguanil may be a superior combination partner for bc1-inhibitors in vivo.

Giardia duodenalis is an intestinal parasite that causes giardiasis, a widespread human gastrointestinal disease. Treatment of giardiasis relies on a small arsenal of compounds that can suffer from limitations including side-effects, variable treatment efficacy and parasite drug resistance. Thus new anti-Giardia drug leads are required. The search for new compounds with anti-Giardia activity currently depends on assays that can be labour-intensive, expensive and restricted to measuring activity at a single time-point. Here we describe a new in vitro assay to assess anti-Giardia activity. This image-based assay utilizes the Perkin-Elmer Operetta® and permits automated assessment of parasite growth at multiple time points without cell-staining. Using this new approach, we assessed the "Malaria Box" compound set for anti-Giardia activity. Three compounds with sub-μM activity (IC50 0.6-0.9 μM) were identified as potential starting points for giardiasis drug discovery.

In connection with efforts to develop an efficient total synthesis of the biologically active natural product taxinine 1, the enzymatically-derived and monochiral cis -1,2-dihydrocatechol 7 was converted, over several steps including a Diels–Alder cycloaddition reaction, into the bicyclo[2.2.2]octan-2-one 18. Reaction of the last compound with the organocerium reagent 22 afforded the 1,5-diene 23 which engaged in an anionic oxy-Cope rearrangement reaction to give, after C -methylation of the product enolate 25, bicyclo[5.3.1]undecenone 27 embodying the AB-ring system of target 1. Two methods for allylic oxidation of such products were developed and several unsuccessful attempts to effect a cyclization reaction so as to establish the taxane C-ring are described.

The two isomeric structures (2) and (3) proposed for the photodynamic pigment stentorin have both been synthesized for the first time, thereby allowing unambiguous identification of the natural material as (2). Synthesis of these highly condensed aromatic systems involved controlled oxidative couplings of the new anthrones (7) and (8), each synthesized by regiocontrolled cycloaddition.