ion and allylic carbon radical formation with subsequent triplet ground-state oxygen capture result ultimately in the formation of lipid hydroperoxides. The explicit mechanism depicted in Scheme 1 is supported by the work of Berman and Adams and others, and it was proposed that the damage caused to the parasite’s FV membrane leads to vacuolar rupture and parasite autodigestion.41 This mechanism is consistent with the observed oxygen dependence of antimalarial action of artemisinin and the morphological changes seen following artemisinin administration to parasites in vitro.44 The biological significance of hydroperoxides in relation to biological hydroxylation and autoxidation of, for example, lipids and membrane bilayers is well established. The generation of unsaturated lipid hydroperoxides provides a means of initiation of such processes. In contrast to these proposals, other workers in the field have suggested that membrane-bound heme may have a role to play in reducing the effectiveness of endoperoxides such as dihydroartemisinin. Further work is required to clarify the role of vacuolar membrane bound heme in the mechanism of action of endoperoxide antimalarials.45 An alternative nonlipid “artemisinin derived source of hydroperoxide” is discussed below. Although Scheme 1 would appear chemically plausible, several workers have proposed that the parasite death in the presence of artemisinin is probably not due to nonspecific or random cell damage caused by freely diffusing oxygen radical species but might involve specific radicals and targets, some of which are described later in this review. The following section details the specific “transitory” species that may be responsible for the antimalarial mechanism of action of artemisinin. Targets of these species are discussed and will conclude with the most recent studies by Eckstein-Ludwig who suggest that artemisinin derivatives target the PfATP6, the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) of the parasite.46 Transitory Species Mediating the Antimalarial Activity of Artemisinin: Carbon Radicals, Carbocations, Hydroperoxides, and High-Valent IronOxo Species. On the basis of the seminal work of Posner and co-workers in the early 1990s, the free radical chemistry of artemisinin is now very welldefined and has been shown to involve an initial chemical decomposition induced by heme Fe(II) (reduced hemin) or other sources of ferrous iron within the malaria parasite to produce initially an oxy radical that subsequently rearranges into one or both of two distinctive carbon-centered radical species.47 Scheme 2a summarizes the main radical pathways available for artemisinin following endoperoxide-mediated bioactivation. Since artemisinin is an unsymmetrical endoperoxide, the oxygen atoms of the peroxide linkage can associate with reducing ferrous ions in two ways. Association of Fe(II) with oxygen 1 provides an oxy radical that goes on to produce a primary carbon-centered radical (5a). A surrogate marker for the intermediacy of this radical species is the ring-contracted tetrahydrofuran (RCT) product 5b. Alternatively, association with oxygen 2 provides an oxy radical species that, via a 1,5-H shift, can produce a secondary carbon-centered radical (5c). Again, like the previous route, a stable end-product, hydroxydeoxoartemisinin (HDA) (5d), functions as a surrogate marker for this secondary carbon-centered radical species. It has been proposed that final alkylation by these reactive intermediates of biomacromolecules such as Scheme 1. Proposed Chemical Mechanism for the Observed Artemisinin Mediated Lipid Peroxidation of Cell Membranesa a Carbon radicals, generated from artemisinin, abstract allylic hydrogen atoms from unsaturated lipid bilayers to set in motion the downstream generation of a variety of reactive oxygen species by a classic lipid peroxidation mechanism. Heme or hematin/thiols associated with the lipid bilayer may be the catalysts responsible for initiation of these processes. Perspective Journal of Medicinal Chemistry, 2004, Vol. 47, No. 12 2947

A medicinal chemistry perspective on artemisinin and related endoperoxides.

In the past decade, the encapsulation of enzymes inside inorganic sol-gel matrices has become a generic method to prepare efficient biocatalysts which are easy to recycle. In this review, the sol-gel processes useful for enzyme encapsulation, (mostly sol-gel silica) are outlined. Then, the most recent developments in the applications of such biocatalysts are presented, in particular regarding biosensors and chemical synthesis. Finally, a special attention is addressed to the types of interactions which are considered to prevail between the enzyme or the substrates and products, and the matrix, in these materials.

The sol-gel encapsulation of enzymes

Since ancient times, humankind has had to struggle against the persistent onslaught of pathogenic microorganisms. Nowadays, malaria is still the most important infectious disease worldwide. Considerable success in gaining control over malaria was achieved in the 1950s and 60s through landscaping measures, vector control with the insecticide DDT, and the widespread administration of chloroquine, the most important antimalarial agent ever. In the late 1960s, the final victory over malaria was believed to be within reach. However, the parasites could not be eradicated because they developed resistance against the most widely used and affordable drugs of that time. Today, cases of malaria infections are on the rise and have reached record numbers. This review gives a short description of the malaria disease, briefly addresses the history of antimalarial drug development, and focuses on drugs currently available for malaria therapy. The present knowledge regarding their mode of action and the mechanisms of resistance are explained, as are the attempts made by numerous research groups to overcome the resistance problem within classes of existing drugs and in some novel classes. Finally, this review covers all classes of antimalarials for which at least one drug candidate is in clinical development. Antimalarial agents that are solely in early development stages will be addressed in a separate review.

Malaria chemotherapeutics part I: History of antimalarial drug development, currently used therapeutics, and drugs in clinical development.

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a leading cause of mortality worldwide into 21st century. The mortality and spread of this disease has further been aggravated because of synergy of this disease with HIV. A number of anti-TB drugs are ineffective against this disease because of development of resistance strains. Internationally efforts are being made to develop new anti-tubercular agents. A number of drug targets from cell wall biosynthesis, nucleic acid biosynthesis, and many other biosynthetic pathways are being unraveled throughout the world and are being utilized for drug development. In this review, socioeconomic problems in developing countries, efforts to control this disease in different individuals, the targets (known already and newly discovered), existing anti-tubercular agents including natural products and lead molecules, and the future prospects to develop new anti-TB agents are described.

Fighting tuberculosis: an old disease with new challenges.

Malaria continues to be a potentially fatal threat to almost half of the world's population. In light of this threat, the armory to fight this disease is rather limited. Resistance against the most common and affordable antimalarials is widespread. Only few new drugs are in clinical development, most of them belong to long used classes of antimalarial drugs. This review will concisely cover the drugs which are currently in use, and describe the drug candidates which are in clinical evaluation.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ardp.200700184

Antimalarial drugs - what is in use and what is in the pipeline.

Antimalarial chemotherapy has become more complex and challenging because of multidrug resistant strains of Plasmodium falciparum. Due to resistance of malarial parasite against well known drugs, the chemotherapy of malaria has become complicated. In this review we have discussed brief introduction followed by life cycle of malaria parasite. The list of commercially available antimalarial drugs along with there action on different stages of parasite have been discussed. A brief description of their mechanism of action and advantages and disadvantages were reported. The natural products as antimalarial have been discussed in the review. On the basis of chemical classes the natural products were divided in the following categories; Quinoline alkaloids, Iso-quinoline alkaloids, Indoloquinoline alkaloids, Carbolines, Bis-isoquinoline, 4-Quinazole derivatives, Trioxanes, Terpenes, Naphthoquinone, Anthraquinones, Chalcones, Hydroxy flavanones, Coumarins and phenolic glycoside. The combination chemotherapy has been highlighted in the review. The Biochemical and Immunological changes in malarial infection are discussed along with complications of malarial chemotherapy due to resistance. In the conclusion section, the future strategies for the chemotherapy of malaria have been discussed.

Perspective in antimalarial chemotherapy.

Syntheses of novel antimycobacterial combinatorial libraries of structurally diverse substituted pyrimidines by three-component solid-phase reactions.

Syntheses of new substituted triazino tetrahydroisoquinolines and β-carbolines as novel antileishmanial agents

This review discusses the commercially available antimalarial drugs that are classified according to their chemical entities and include quinolines, pyrimidines, amidines, guanidines, sulfonamides, sulfones, acridines, antibiotics and sesquiterpene lactones. New anti-malarials reported during 2000 to June 2002 are also classified according to their chemical structures and include trioxanes, tetraoxane derivatives, other peroxides, quinolines and bisquinolines, isoquinolines, pyrimidines, acridine and bisacridine derivatives, bis acyl amino benzophenone, cinnamic acid derivatives, natural products, phenyl β-methoxy acrylates, pyrrolidines, carbolines, imidazoles and tropolones. The complications of malarial chemotherapy are also discussed.

Current trends in antimalarial chemotherapy

Fatty acyl-CoA synthetase (fatty acid: CoA ligase, AMP-forming; (EC 6.2.1.3)) catalyzes the formation of fatty acyl-CoA by a two-step process that proceeds through the hydrolysis of pyrophosphate. Fatty acyl-CoA represents bioactive compounds that are involved in protein transport, enzyme activation, protein acylation, cell signaling, and transcriptional control in addition to serving as substrates for beta oxidation and phospholipid biosynthesis. Fatty acyl-CoA synthetase occupies a pivotal role in cellular homeostasis, particularly in lipid metabolism. Our interest in fatty acyl-CoA synthetase stems from the identification of this enzyme, long-chain fatty acyl-CoA ligase (LCFA) by microarray analysis. We found this enzyme to be differentially expressed by Leishmania donovani amastigotes resistant to antimonial treatment. In the present study, we confirm the presence of long-chain fatty acyl-CoA ligase gene in the genome of clinical isolates of Leishmania donovani collected from the disease endemic area in India. We predict a molecular model for this enzyme for in silico docking studies using chemical library available in our institute. On the basis of the data presented in this work, we propose that long-chain fatty acyl-CoA ligase enzyme serves as an important protein and a potential target candidate for development of selective inhibitors against leishmaniasis.

/pdf/bioinformatic-analysis-of-leishmania-donovani-long-chain-22ovz4moy8.pdf

Arun Kumar

Papers

Perspective in antimalarial chemotherapy.

Syntheses of novel antimycobacterial combinatorial libraries of structurally diverse substituted pyrimidines by three-component solid-phase reactions.

Syntheses of new substituted triazino tetrahydroisoquinolines and β-carbolines as novel antileishmanial agents

Current trends in antimalarial chemotherapy

Bioinformatic Analysis of Leishmania donovani Long-Chain Fatty Acid-CoA Ligase as a Novel Drug Target