Medicinal plants: Traditions of yesterday and drugs of tomorrow

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

This review offers a systematic understanding about how polyphenols target multiple inflammatory components and lead to anti-inflammatory mechanisms. It provides a clear understanding of the molecular mechanisms of action of phenolic compounds. Polyphenols regulate immunity by interfering with immune cell regulation, proinflammatory cytokines’ synthesis, and gene expression. They inactivate NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and modulate mitogen-activated protein Kinase (MAPk) and arachidonic acids pathways. Polyphenolic compounds inhibit phosphatidylinositide 3-kinases/protein kinase B (PI3K/AkT), inhibitor of kappa kinase/c-Jun amino-terminal kinases (IKK/JNK), mammalian target of rapamycin complex 1 (mTORC1) which is a protein complex that controls protein synthesis, and JAK/STAT. They can suppress toll-like receptor (TLR) and pro-inflammatory genes’ expression. Their antioxidant activity and ability to inhibit enzymes involved in the production of eicosanoids contribute as well to their anti-inflammation properties. They inhibit certain enzymes involved in reactive oxygen species ROS production like xanthine oxidase and NADPH oxidase (NOX) while they upregulate other endogenous antioxidant enzymes like superoxide dismutase (SOD), catalase, and glutathione (GSH) peroxidase (Px). Furthermore, they inhibit phospholipase A2 (PLA2), cyclooxygenase (COX) and lipoxygenase (LOX) leading to a reduction in the production of prostaglandins (PGs) and leukotrienes (LTs) and inflammation antagonism. The effects of these biologically active compounds on the immune system are associated with extended health benefits for different chronic inflammatory diseases. Studies of plant extracts and compounds show that polyphenols can play a beneficial role in the prevention and the progress of chronic diseases related to inflammation such as diabetes, obesity, neurodegeneration, cancers, and cardiovascular diseases, among other conditions.

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The Immunomodulatory and Anti-Inflammatory Role of Polyphenols.

Pharmacological activities of natural triterpenoids and their therapeutic implications

Tubulin dynamics is a promising target for new chemotherapeutic agents. The colchicine binding site is one of the most important pockets for potential tubulin polymerization destabilizers. Colchicine binding site inhibitors (CBSI) exert their biological effects by inhibiting tubulin assembly and suppressing microtubule formation. A large number of molecules interacting with the colchicine binding site have been designed and synthesized with significant structural diversity. CBSIs have been modified as to chemical structure as well as pharmacokinetic properties, and tested in order to find a highly potent, low toxicity agent for treatment of cancers. CBSIs are believed to act by a common mechanism via binding to the colchicine site on tubulin. The present review is a synopsis of compounds that have been reported in the past decade that have provided an increase in our understanding of the actions of CBSIs.

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An Overview of Tubulin Inhibitors That Interact with the Colchicine Binding Site

NF-kappaB is a ubiquitous and well-characterised protein responsible for the regulation of complex phenomena, with a pivotal role in controlling cell signalling in the body under certain physiological and pathological conditions. Among other functions, NF-kappaB controls the expression of genes encoding the pro-inflammatory cytokines (e. g., IL-1, IL-2, IL-6, TNF-alpha, etc.), chemokines (e. g., IL-8, MIP-1alpha, MCP1, RANTES, eotaxin, etc.), adhesion molecules (e. g., ICAM, VCAM, E-selectin), inducible enzymes (COX-2 and iNOS), growth factors, some of the acute phase proteins, and immune receptors, all of which play critical roles in controlling most inflammatory processes. Since NF-kappaB represents an important and very attractive therapeutic target for drugs to treat many inflammatory diseases, including arthritis, asthma, and the auto-immune diseases, most attention has been paid in the last decade to the identification of compounds that selectively interfere with this pathway. Recently, a great number of plant-derived substances have been evaluated as possible inhibitors of the NF-kappaB pathway. These include a wide range of compound classess, such as lignans (manassantins, (+)-saucernetin, (-)-saucerneol methyl ether), sesquiterpenes (costunolide, parthenolide, celastrol, celaphanol A), diterpenes (excisanin, kamebakaurin), triterpenes (avicin, oleandrin), polyphenols (resveratrol, epigallocatechin gallate, quercetin), etc. In this mini-review we will discuss the medicinal chemistry of these compounds with regards to the NF-kappaB inhibition.

Naturally occurring NF-kappaB inhibitors.

Tubulin protein is a major target for anticancer drug discovery. As a result, antimitotic agents constitute an important class of the current anticancer drugs. Hundreds of tubulin inhibitors, naturally occurring, semisynthetic or synthetic, have been reported. Among these, combretastatin A-4 (CA-4), isolated from a South African tree Combretum caffrum, is one of the most potent antimitotic agents. CA-4 shows strong cytotoxicity against a variety of cancer cells, including multi-drug resistant cancer cell lines. It has also been demonstrated to exert highly selective effects in proliferating endothelial cells. CA-4 disodium phosphate (CA4DP), a water-soluble prodrug of CA-4, shows potent antivascular and antitumor effects in a wide variety of preclinical tumor models. Consequently, a number of CA-4 analogues has been synthesized and evaluated. In this paper, the structure-activity relationships and pharmacological properties of the CA-4 derivatives as a class of potent antimitotic anticancer agents are reviewed and discussed.

Combretastatin A-4 analogues as antimitotic antitumor agents.

In the search for antiangiogenic agents from medicinal plants used in Vietnam, a methanol extract of the stem barks of Bombax ceiba was found to exhibit a significant antiangiogenic activity on in vitro tube formation of human umbilical venous endothelial cells (HUVEC). Bioactivity-guided fractionation and isolation carried out on this extract afforded lupeol as an active principle. At 50 and 30 microg/mL lupeol showed a marked inhibitory activity on HUVEC tube formation while it did not affect the growth of tumor cell lines such as SK-MEL-2, A549, and B16-F10 melanoma.

Antiangiogenic activity of lupeol from Bombax ceiba

The call for the discovery of less toxic, more selective, and more effective agents to treat cancer has become more urgent. Inhibition of angiogenesis continues to be one of the main streams in the current cancer drug discovery activity. Insights into tumor angiogenesis biology have led to the identification of a number of molecules, which are important for the progression of these processes. Of particular interest is a group of growth factors including fibroblast growth factor, platelet-derived growth factor, and vascular endothelial growth factor. These growth factors and their corresponding receptor tyrosine kinases have become important targets for inhibition of the proliferation of endothelial cells, the main component of blood vessels. The validated targets for inhibition of angiogenesis also include a family of matrix metalloproteinases and cell adhesion molecules. In the closely related area, protein kinases have emerged as one of the most important targets for drug discovery. Besides growth factor receptor tyrosine kinases, numerous other protein kinases implicated in malignancies have been identified including non-receptor kinases such as Bcl-Abl and Src kinases. In addition, the cell cycle regulators (cyclin-dependent kinases, p21 gene) and apoptosis modulators (Bcl-2 oncoprotein, p53 tumor suppressor gene, survivin protein, etc) have also attracted renewed interest as potential targets for anticancer drug discovery. Other molecular targets include protein farnesyltransferase (FTase), histone deacetylase (HDAC), and telomerase, which have essential roles in cellular signal transduction pathways (FTase, HDAC) and cell life-span (telomerase). This review presents a comprehensive summary and discussion on the most important targets currently attracting a great deal of interest in contemporary anticancer drug design and discovery. Recent advances complementing these targets are also highlighted.

Current Targets for Anticancer Drug Discovery

Protein tyrosine kinases (PTK) are key enzymes of mammalian signal transduction For the fidelity of signal transduction, each PTK phosphorylates only one or a few proteins on specific Tyr residues Substrate specificity is thought to be mediated by PTK–substrate docking interactions and recognition of the phosphorylation site sequence by the kinase active site However, a substrate-docking site has not been determined on any PTK C-terminal Src kinase (Csk) is a PTK that specifically phosphorylates Src family kinases on a C-terminal Tyr In this study, by sequence alignment and site-specific mutagenesis, we located a substrate-docking site on Csk Mutations in the docking site disabled Csk to phosphorylate, regulate, and complex with Src but only moderately affected its general kinase activity A peptide mimicking the docking site potently inhibited (IC50 = 21 μM) Csk phosphorylation of Src but only moderately inhibited (IC50 = 422 μM) its general kinase activity Determination of the substrate-docking site provides the structural basis of substrate specificity in Csk and a model for understanding substrate specificity in other PTKs

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Nguyen Hai Nam

Papers

Naturally occurring NF-kappaB inhibitors.

Combretastatin A-4 analogues as antimitotic antitumor agents.

Antiangiogenic activity of lupeol from Bombax ceiba

Current Targets for Anticancer Drug Discovery

Determination of the substrate-docking site of protein tyrosine kinase C-terminal Src kinase.