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The three reviews cover the advances in the chemistry and biology of withanolides over the last 16 years, review the chemistry and biology of the rocaglamide-type derivatives and related compounds, with emphasis on their structural diversity, biosynthesis, pharmacological significance and total synthesis, and summarize the extensive chemistry and biology studies on a natural product, which have resulted in a novel therapy approved worldwide.

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Resin glycosides are part of a very extensive family of secondary metabolites known as glycolipids or lipo-oligosaccharides and are constituents of complex resins (glycoresins) (1) unique to the morning glory family, Convolvulaceae (2). These active principles are responsible for the drastic purgative action of all the important Convolvulaceous species used in traditional medicine throughout the world since ancient times. Several commercial purgative crude drugs can be prepared from the roots of different species of Mexican morning glories. Their incorporation as therapeutic agents in Europe is an outstanding example of the assimilation of botanical drugs from the Americas as substitutes for traditional Old World remedies (3). Even though phytochemical investigations on the constituents of these drugs were initiated during the second half of the nineteenth century, the structure of their active ingredients still remains poorly known for some examples of these purgative roots. During the last two decades, the higher resolution c- abilities of modern analytical isolation techniques used in conjunction with pow- ful spectroscopic methods have facilitated the elucidation of the active principles of these relevant herbal products. This chapter describes the ethnobotanical information associated with the p- gative morning glory species and how traditional usages were instrumental in plant selection for chemical studies. The advantages and limitations of available analy- cal techniques for the isolation, puri?cation, and structure characterization of the individual constituents of these complex glycoconjugates are also discussed.

Organic chemistry --- Pharmacology. Therapy --- organische chemie --- farmacologie

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Lignans, by convention, are a group of natural products that are formed by linking two phenylpropanoid units (C C units) by oxidative coupling. Most importantly, in 6 3 a lignan, two (C C units) are bound through the central carbon of their side chains, 6 3 0 i. e. the 8 and 8 positions (1, 2). The occurrence of C C -dimers, linked at sites other 6 3 0 than the 8–8 positions, is also known and these compounds have been termed neolignans (3, 4). As these two groups of compounds have close structural as well as biosynthetic relationships, they are often associated together and incorporated under the general term “lignan” (5). The diverse structural categorization of true lignans and of a few neolignans is presented in Fig. 1. Through the years, several review articles or books covering different facets of lignans, including their ch- istry (6, 7), biogenesis (8), synthesis (9), and biological activities (10) have been published. Enduring research for the investigation of secondary metabolites of plants has evidenced some compounds that are biogenetically related to true lignans or neolignans but bear some features not discerned in conventional lignans. These compounds or groups of compounds have been termed as “non-conventional lignans”, and include coumarinolignans, ?avonolignans, and stilbenolignans. The non-conventional lignans, like the conventional ones, have two C C units linked 6 3 together but have additional structural features to place them also under the category of coumarins, ?avonoids, or stilbenes.

Organic chemistry --- organische chemie