Current Organic Chemistry - Volume 12, Issue 18, 2008

The 2008 Catalysis/Natural Product Chemistry Issue of Current Organic Chemistry contains six contributions from eminent scientists in different field. Professor Adamo summarise the state of art in the synthesis and medicinal properties of 2-deoxyribose- and ribose-Cnucleosides which represent an important class of potential therapeutic agents. Prof. Balme of the University of Lyon provides an article about the preparation of natural lignans and related natural products using transition-metal-catalysed reaction. The review focuses some aspects of the chemistry of transition-metal catalysts applied to the preparation of the title compounds. Palladium-catalysed reactions using ultrasound or microwave irradiaton have been reviewed by Cravotto and coworkers. The non-conventional activation tools in this type of reactions represent an important contribution to the organic synthesis and suggest a reconsideration of some method catalyzed processes. Prof. Enev and coworkers provide an overview of recent results concerning the use of Quinic Acid as chiral pool in organic synthesis. Commercially available Quinic Acid has been used for the preparation of different classes of natural products and represents a versatile starting material for the asymmetric synthesis of chiral compounds. Recent advances in the design and application of ruthenium olefin methathesis catalyst have been reported by Grela and Szadkowska. Some aspects of this type of Chemistry and their application in methathesis reactions including polymerization have been reported. Finally Cosimo Pizza and coworkers provide an overview of secondary metabolites from Solenostemma argel Hayne (Asclepiadonaceae) with antiproliferative activity. This plant contains pregnane and 14,15-secopregnane glycosides with a very unusual structure. I would like to express my sincere thanks to all authors for providing these articles and for the fascinating results reported.

C-nucleosides are important synthetic targets due to their potential as therapeutic agents and as biochemical probes. Nucleosides and nucleoside biochemistry lie at the heart of life and life propagation, and therefore nucleoside analogues have attracted much attention as anti-microbial and anti-cancer agents. In the recent past several groups reported their effort in the preparation of unnatural C-nucleosides based on deoxyribose and ribose. This review summarises the state of the art in the preparation of modified C-nucleosides and their medicinal properties.

The objective of this review is to survey the recent achievements in the preparation of natural lignans and related natural products involving a transition-metal catalyzed reaction as the key step.

Palladium-catalyzed reactions are a cornerstone of modern synthetic chemistry. No other transition metal, has lately displayed a comparable efficiency and versatility in catalysis. Its compounds have revolutionized organic and organometallic synthesis, being systematically employed to catalyze a series of important and elegant carbon-carbon and carbon-heteroatom bond-forming reactions, whose applications range from natural products and pharmaceuticals to polymers and advanced materials. Many of them require prolonged heating and may be plagued by the formation of side- or unwanted products. The current drive toward cleaner chemistry and chemical engineering has spurred a search for more selective and energy-saving protocols, prompting a reconsideration of some metal-catalyzed processes that were once regarded as ideal syntheses. Two non-conventional activation tools, microwaves and ultrasound, have been shown to substantially reduce reaction times, increase product yields and enhance product purity by reducing or even eliminating side reactions. The present article provides an overview of this topic, showing how these energy sources have been successfully applied to some representative Pd-catalyzed reactions. Microwaves and ultrasound can be used alone, as well as combined in either sequential or simultaneous fashion; these variations can lead to significantly different results. These technical aspects are now becoming economically relevant, as Pd-catalyzed reactions are on the verge of being promoted out of the laboratory to the production scale by means of safe and reliable flow systems.

In this review, which covers the literature after 1998 we present new applications of D-(-)-Quinic acid where it has been successfully applied as chiral building block for the effective introduction a new stereogenic centers. Furthermore, examples are presented from complex natural products synthesis which also includes our own work.

This review is devoted to recent advances in the design and application of so-called “dormant” or “latent” ruthenium olefin metathesis catalysts bearing chelating alkylidene ligands. Selected ruthenium complexes of controllable initiation behaviour are presented. Applications of these complexes in various metathesis reactions, including polymerization, are described.

Solenostemma argel Hayne (Asclepiadaceae) is an Egyptian plant whose leaves are commonly used in traditional medicine as a purgative, antipyretic and antispasmodic remedy. From the pericarps, hairy seeds and leaves fifteen new 14,15-secopregnane glycosides, namely argelosides A-J, and nine new 15-ketopregnane glycosides, namely stemmosides C-K, have been isolated. Argelosides A-J show very unusual structures characterized by the opening of ring D between C-14 and C-15, and the occurrence of two ketal functions on C-14 and C-20 generating three five-membered rings with oxygenated functions in positions 16 and 15, respectively. Stemmosides D-J are characterized by the occurrence of an uncommon 14β proton configuration while stemmosides E and F possess in addition a rare enolic function in C-16. Apparently these compounds are the first pregnanes isolated from plants known to have a 15 keto, cis CD ring junction. On the other hand, stemmosides C, D and G-K are the only natural compounds which display an unusual C-17α side chain and no substitution in C-12. On the basis of antitumor and cytotoxic activities reported for pregnane and their glycosides and considering the very unusual structural features of argelosides and stemmosides, the antiproliferative activity of these compounds against Kaposi's sarcoma cells was evaluated. Thus a dose dependence study was performed to test the effects of compounds on the VEGF-induced KS cell proliferation in a concentration range 0.1-20 μM. Results indicated that 15-keto-pregnane glycosides and 14,15-secopregnane glycosides reduced the VEGF-induced KS cell proliferation in a dose-dependent manner and the highest reduction occurred at concentration of 10 μM.