Hanjo Kim

Recent advances in artemisinin and its derivatives as antimalarial and antitumor agents.

Artemisinin, the first and last naturally occurring 1, 2, 4-trioxane originated from Artemisia annua, L. and its derivatives are a potent class of antimalarial drugs. The clinical efficacy of these drugs is characterized by an almost immediate onset and rapid reduction of parasitemia, and it is high in such areas as well where multidrug-resistance is rampant. Furthermore, artemisinin and many of its analog possess not only antiparasitic effect against Plasmodium falciparum, Schistosoma japonicum and Clonorchis sinensi but also immuno-modulation effects, and antitumor activities. This review covers the chemistry of artemisinin including synthesis of acetal-, non acetal-type C-12 analogs, C-11- and C-13 derivatives from artemisitene, ring-contracted derivatives, dimers, and trimers. Modes of biological action of artemisinin - derived analogs are also reviewed. The main objective of this article is to review the literatures of recent progress taken place in chemistry, mode of biological actions of artemisinin, and its derivatives as antimalarial and antitumor agents during the last three years (1999-2001).

Naturally Occurring Peroxides with Biological Activities

New natural peroxides that have potent biological activities with novel diverse structures are reviewed with classification as secondary metabolites such as terpenes, polyketides, phenolics, and hydroperoxides. These compounds, isolated mainly from medicinal plants and marine sponges, are valuable sources in the drug discovery for particularly antitumor and antimalarial agents.

Recent Studies on Natural Products as Anti-HIV Agents

The discovery of medicinal agents capable of specifically inhibiting human immunodeficiency virus (HIV) is urgently needed due to its globally widespread infection. Most of clinically useful anti-HIV agents are nucleosides but their use is limited due to their severe toxicity and emerging drug resistance. More than 50% of world marketed drugs have their origin of the nature. Natural products, of which structural diversity is so broad, are good sources for the effective discovery of anti-HIV agents with decreased toxicity. Over the past decade, substantial progress has been made in research on the natural products for the anti-HIV agents. New natural products that have potent anti-HIV activities with novel structures were reviewed in this article. These compounds, isolated mainly from medicinal plants, in this review have been classified as secondary metabolites such as terpenes, phenolics, and naturally scarce peptides and sugars. Especially, terpenes and phenol substances have gained much interest due to their significant anti-HIV activities along with their structural diversity. Recent studies also showed that several polysaccharides are effective inhibitors of HIV replication. Most of chemotherapeutic targets reviewed in this article are found to be HIV reverse transcriptase (RT).

Synthesis of C-4-modified zanamivir analogs as neuraminidase inhibitors and their anti-AIV activities

With the introduction of bioisosteres of the guanidinium group together with scaffold hopping, 35 zanamivir analogs with C-4-modification were synthesized, and their inhibitory activities against both group-1 and group-2 neuraminidase (H5N1 and H3N2) were determined. Compound D26 exerts the most potency, with IC(50) values of 0.58 and 2.72 μM against N2 and N1, respectively. Further preliminary anti-avian influenza virus (AIV, H5N1) activities against infected MDCK cells were evaluated, and D5 exerts ∼58% protective against AIV infection, which was comparable to zanamivir (∼67%). In a rat pharmacokinetic study, compound D5 showed an increased plasma half-life (t(1/2)) compared to zanamivir following either intravenous or oral administration. This study may represent a new start point for the future development of improved anti-AIV agents.

Classification models for CYP450 3A4 inhibitors and non-inhibitors.

Cytochrome P450 3A4 (CYP3A4) is the predominant enzyme involved in the oxidative metabolic pathways of many drugs. The inhibition of this enzyme in many cases leads to an undesired accumulation of the administered therapeutic agent. The purpose of this study is to develop in silico model that can effectively distinguish human CYP3A4 inhibitors from non-inhibitors. Structural diversity of the drug-like compounds CYP3A4 inhibitors and non-inhibitors was obtained from Fujitsu Database and Korea Research Institute of Chemical Technology (KRICT) as training and test sets, respectively. Recursive Partitioning (RP) method was introduced for the classification of inhibitor and non-inhibitor of CYP3A4 because it is an easy and quick classification method to implement. The 2D molecular descriptors were used to classify the compounds into respective inhibitors and non-inhibitors by calculation of the physicochemical properties of CYP3A4 inhibitors such as molecular weights and fractions of 2D VSA chargeable groups. The RP tree model reached 72.33% of accuracy and exceeded this percentage for the sensitivity (75.82%) parameter. This model is further validated by the test set where both accuracy and sensitivity were 72.58% and 82.64%, respectively. The accuracy of the random forest model was increased to 73.8%. The 2D descriptors sufficiently represented the molecular features of CYP3A4 inhibitors. Our model can be used for the prediction of either CYP3A4 inhibitors or non-inhibitors in the early stages of the drug discovery process.

CoMFA of Artemisinin derivatives: effect of location and size of lattice

A CoMFA study of artemisinin derivatives with changes of the location and the number of lattice points was performed. The location of probe atoms in a large lattice has practically no effect on the cross-validated r(2) value (r(2)(cv)). The selection of only 18 probe atoms around the peroxide bond, considering the action mechanism of artemisinin, provided a less time-demanding and more reliable CoMFA model, which forecasts better than the large lattice model despite the lower r(2)(cv) value. Only 1 A displacement of the small lattice caused a reduction of cross-validated r(2) value of more than 50%, which indicates the lattice location played an important role in this small lattice model.

Chemical Genomics Strategy for the Discovery of New Anticancer Agents

Chemical genomics represents a cooperation of biology and chemistry to identify and intervene the biological targets. Small molecules with diverse structural characteristics should be used to validate the target through interfering with the biological processes. Because of the limitation of existing chemical libraries, the diversity can be exploited using both the molecular design techniques; structure-based design and ligand-based design. These methods can guide the selection of small molecules with optimal binding properties to desired biological targets. Studies of potential molecular targets for novel anticancer drug discovery including in silico screening, QSAR, and de novo design demonstrated the importance of chemical genomics strategy to find the chemical probes and drug lead compounds.