In vitro and in vivo studies of the effects of halogenated histidine analogs on Plasmodium falciparum

Design, synthesis, and applications of ring-functionalized histidines in peptide-based medicinal chemistry and drug discovery

Modified and synthetic α-amino acids are known to show diverse applications. Histidine, which possesses numerous applications when subjected to synthetic modifications, is one such amino acid. The utility of modified histidines varies widely from remarkable biological activities to catalysis, and from nanotechnology to polymer chemistry. This renders histidine residue an important place in scientific research. Histidine is a well-studied scaffold and constitutes the active site of various enzymes catalyzing important reactions in the biological systems. A rational modification in histidine structure with a distinctly developed protocol extensively changes its physical and chemical properties. The utilization of modified histidines in search of potent, target selective and proteostable scaffolds is vital in the development of bioactive peptides with enhanced drug-likeliness. This review is a compilation and analysis of reported side-chain ring modifications at histidine followed by applications of ring-modified histidines in the synthesis of various categories of bioactive peptides and peptidomimetics.

The survival of Plasmodium Under oxidant stress

Oxidant stress is associated with the generation of reactive oxygen-derived species, which are considered as the ultimate agents responsible for the damage of a variety of cellular components. Transition metals such as iron ions serve as catalytic centers for the repeated conversion of superoxide radicals or ascorbate to the highly reactive and deleterious hydroxyl radicals and, indeed, increasing amounts of redox-active iron become available during plasmodial development within the parasitized erythrocytes. Thus, the survival of an intracellular parasite depends on the delicate balance of oxidant stress and defense mechanisms. This balance is continuously changing and the parasite must cope with increasing oxidant stress and the decline of protective capacity.

Antimalarial activities of ring-substituted bioimidazoles

We report in vitro antimalarial activities against chloroquine sensitive and resistant Plasmodium falciparum strains, and in vivo activities against Plasmodium berghei in mice for four series of ring-substituted-L-histidines and histamines.

Antioxidant defense mechanisms in parasitic protozoa

Many of the parasitic protozoa, such as Entamoeba histolytica, Giardia, Trypanosoma, Leishmania, and Plasmodium, are considered to be anaerobes because they can be grown in vitro only under conditions of reduced oxygen tension. However, these parasitic protozoa have been found to be aerotolerant or microaerophilic, and also to consume oxygen to a certain extent. Furthermore, these organisms are highly susceptible to exogenous reactive oxygen species, such as hydrogen peroxide. They must, therefore, detoxify both oxygen and free radical products of enzymatic reactions. However, they lack some or all of the usual antioxidant defense mechanisms present in aerobic or other aerotolerant cells, such as catalase, superoxide dismutase, reduced glutathione, and the glutathione-recycling enzymes glutathione peroxidase and glutathione reductase. Instead, they possess alternative mechanisms for detoxification similar to those known to exist in certain prokaryotes. Although the functional aspects of these alternative mechanisms are yet to be understood completely, they could provide new insights into the biochemical peculiarities of these enigmatic pathogens.