Research paperNew efficient artemisinin derived agents against human leukemia cells, human cytomegalovirus and Plasmodium falciparum: 2nd generation 1,2,4-trioxane-ferrocene hybrids
Graphical abstract
Introduction
The natural 1,2,4-trioxane sesquiterpene artemisinin (1) (Fig. 1), isolated from the Chinese medicinal plant Artemisia annua L., [1], [2], [3] has proven to be a versatile antimalarial [2], [4], [5], [6], [7], [8], [9], [10], [11], anticancer [6], [8], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24] and antiviral compound [25], [26], [27], [28], [29], [30]. Its mode of action is not yet fully understood, but in the cases of malaria and cancer, the endoperoxide moiety plays a crucial role since it is activated and fragmented by intracellular Fe(II) leading to the formation of reactive oxygen species (ROS) and peroxyl free radicals. These species induce oxidative stress, DNA damage, alkylation of target proteins and apoptosis [7], [11], [19], [31], [32], [33], [34], [35], [36], [37]. Regarding its activity against human cytomegalovirus (HCMV), artemisinin (1) inhibits its replication, most probably on the basis of interfering with virus-supporting cellular signaling pathways including NF-κB-specific signaling [27], [28], [29], [38].
To avoid upcoming drug-resistance [39], [40], [41], [42] against artemisinin (1), more effective drug candidates against malaria, cancer and HCMV can be obtained applying the concept of hybridization: the chemical combination of two or more natural product fragments leads to new structures possessing improved biological activities compared to the natural products itself [43], [44], [45], [46], [47], [48]. Applying this concept, many hybrid molecules based on artemisinin (1) linked to a different subunit/natural product fragment are described in literature [6], [8], [11], [49], [50], [51], [52], [53], [54], [55], [56], [57].
Although ferrocene-derived compounds such as ferroquine (2) (Fig. 1) showed improved antimalarial activity [58], [59], [60], [61] and other derivatives such as ferrocifen possessed anticancer activity [62], [63], [64], [65], [66], [67], [68], hybrids containing a ferrocene and a 1,2,4-trioxane moiety like compound 3 were only reported twice until 2014 [69], [70]. The combination of both entities in one molecule affords hybrids that could produce a greater amount of ROS as they have an interior iron source being able to break the endoperoxide bridge of the 1,2,4-trioxane moiety.
Recently, we reported [71] a study of different 1,2,4-trioxane-ferrocene hybrids and revealed that 1,2,4-trioxane-ferrocene hybrid 4 was the most active compound on wild-type as well as multidrug-resistant leukemia cells. Encouraged by the effective anticancer and antimalarial hybrids of this study [71], we designed four 2nd generation 1,2,4-trioxane-ferrocene hybrids (compounds 5–8, Fig. 2) whose synthesis consist of only a few steps. Their biological activity against drug-sensitive CCRF-CEM leukemia cells, the multidrug-resistant sub-line CEM/ADR5000, Plasmodium falciparum and HCMV are reported here.
Section snippets
Chemistry
All compounds of the present study (Fig. 2) could be regarded as derivatives of dihydroartemisinin (10) and were accessible from this commercially available starting material in only a few steps (Scheme 1).
In addition to dihydroartemisinin (10), its literature known derived alcohols 14 [50], [72], [73], [74], [75], [76], [77] and 11 [78] were chosen as building blocks for the 1,2,4-trioxane-ferrocene hybrids, since both alcohols proved to be versatile precursors for effective anticancer and
Conclusion
This study presents the successful preparation of new 1,2,4-trioxane-ferrocene hybrids 5–8 from ferrocene monocarboxylic acid (9), ferrocene dicarboxylic acid (12), DHA or DHA-derived precursors. Hybrids 5–8 were tested for their activity against two leukemia cells lines (the CCRF-CEM and the multidrug-resistant CEM/ADR5000 cell lines), against HCMV and against P. falciparum 3D7 parasites. All four hybrids 5–8 were more active against CCRF-CEM cells (IC50 ≤ 0.13 μM) than their parent compound
Synthesis of hybrid molecules – general
All reactions were performed in flame-dried glassware under a nitrogen atmosphere. After column chromatography all hybrids, besides 1,2,4-trioxane-ferrocene-hybrid 8, were reprecipitated from DCM in n-hexane to yield a pure compound for elemental analysis and biological tests. Hybrid 8 was reprecipitated from EtOAc in pentane. DCM was dried initially over CaCl2 and then distilled from P2O5. THF was dried initially over KOH. Afterwards, THF was distilled from sodium/benzophenone. All other
Acknowledgment
S.B.T. is grateful to the Deutsche Forschungsgemeinschaft (DFG), the Wilhelm Sander-Stiftung and Interdisciplinary Center for Molecular Materials (ICMM) for generous research support. M.M. greatly acknowledges the experimental support and the scientific contribution in developing strategies of antiviral drug design by Dr. Corina Hutterer (Inst. Virol., Univ. Erlangen-Nuremberg); financial support was provided by the Wilhelm Sander-Stiftung (2011.085.1 and 2011.085.2) and Deutsche
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