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- Endoperoxide carbonyl falcipain 2/3 inhibitor hybrids: toward combination chemotherapy of malaria through a single chemical entityPublication . Gibbons, Peter D.; Verissimo, Edite; Araujo, Nuna C. P.; Barton, Victoria; Nixon, Gemma L.; Amewu, Richard K.; Chadwick, J.; Stocks, Paul A.; Biagini, Giancarlo A.; Srivastava, Abhishek; Rosenthal, Philip J.; Gut, Jiri; Guedes, Rita C.; Moreira, Rui; Sharma, Raman; Berry, Neil; Cristiano, Maria Lurdes Santos; Shone, Alison E.; Ward, Stephen A.; O'Neill, Paul M.We extend our approach of combination chemotherapy through a single prodrug entity (O’Neill et al. Angew. Chem., Int. Ed. 2004, 43, 4193) by using a 1,2,4-trioxolane as a protease inhibitor carbonylmasking group. These molecules are designed to target the malaria parasite through two independent mechanisms of action: iron(II) decomposition releases the carbonyl protease inhibitor and potentially cytotoxic C-radical species in tandem. Using a proposed target “heme”, we also demonstrate heme alkylation/carbonyl inhibitor release and quantitatively measure endoperoxide turnover in parasitized red blood cells.
- Diels–alder/thiol–olefin co-oxygenation approach to antimalarials incorporating the 2,3-dioxabicyclo[3.3.1]nonane pharmacophorePublication . O'Neill, Paul M.; Verissimo, Edite; Ward, Stephen A.; Davies, Jill; Korshin, Edward E.; Araujo, Nuna C. P.; Pugh, Matthew D.; Cristiano, Maria Lurdes Santos; Stocks, Paul A.; Bachi, Mario D.Abstract—A Diels–Alder/thiol–olefin co-oxygenation approach to the synthesis of novel bicyclic endoperoxides 17a–22b is reported. Some of these endoperoxides (e.g., 17b, 19b, 22a and 22b) have potent nanomolar in vitro antimalarial activity equivalent to that of the synthetic antimalarial agent arteflene. Iron(II)-mediated degradation of sulfone-endoperoxide 19b and spin-trapping with TEMPO provide a spin-trapped adduct 25 indicative of the formation of a secondary carbon centered radical species 24. Reactive C-radical intermediates of this type may be involved in the expression of the antimalarial effect of these bicyclic endoperoxides.
- Artemisinin-polypyrrole conjugates: synthesis, DNA binding studies and preliminary antiproliferative evaluationPublication . La Pensée, Louise; Sabbani, Sunil; Sharma, Raman; Bhamra, Inder; Shore, Emma; Chadwick, Amy E.; Berry, Neil; Firman, J.; Araujo, Nuna C. P.; Cabral, Lília; Cristiano, Maria Lurdes Santos; Bateman, Cerys; Janneh, Omar; Gavrila, Adelina; Wu, Yi Hang; Hussain, Afthab; Ward, Stephen A.; Stocks, Paul A.; Cosstick, Rick; O'Neill, Paul M.Artemisinin-based combination therapies (ACTs) are currently the recommended treatment for uncomplicated and severe cases of malaria.[1] Additionally, artemisinins, as well as a number of other sesquiterpene lactones (SLs), are currently in phase I–II clinical trials against breast, colorectal and nonsmall-cell lung cancers.[2] As outlined by the iron-dependent activation hypothesis,[3] the activity of artemisinin (ART) is dependent on the endoperoxide bridge.[4] The peroxide is cleaved by endogenous sources of FeII to generate highly reactive carbon-centred radicals (CCRs), which are believed to react with critical cellular targets.[3] ART demonstrates selectivity towards rapidly proliferating cancer cell lines that possess a high intracellular iron content required to sustain their characteristic high rates of multiplication.[5] Iron activation links this particular potency of ART towards rapidly proliferating cancer cell lines; differentiation between healthy and cancerous cells by variation of iron concentration provides a strategy for selective cytotoxicity by ART and its derivatives.[4] The mechanism by which ART exerts its cytotoxic activity still remains elusive. ART acts by disruption of proliferation,[6, 7] oxidative stress,[8] anti-angiogenesis,[9] NF-kB signalling,[10] apoptosis[4] and interfering with iron uptake and metabolism.[6] ART also induces DNA breakage,[11] and it has been reported that artesunate-mediated DNA damage contributes to its therapeutic efficacy.
- Semi-synthetic and synthetic 1,2,4-trioxaquines and 1,2,4-trioxolaquines: synthesis, preliminary SAR and comparison with acridine endoperoxide conjugatesPublication . Araujo, Nuna C. P.; Barton, Victoria; Jones, Michael; Stocks, Paul A.; Ward, Stephen A.; Davies, Jill; Bray, Patrick G.; Shone, Alison E.; Cristiano, Maria Lurdes Santos; O'Neill, Paul M.A novel series of semi-synthetic trioxaquines and synthetic trioxolaquines were prepared, in moderate to good yields. Antimalarial activity was evaluated against both the chloroquine-sensitive 3D7 and resistant K1 strain of Plasmodium falciparum and both series of compounds were shown to be active in the low nanomolar range. For comparison the corresponding 9-amino acridine analogues were also prepared and shown to have low nanomolar activity like their quinoline counterparts.