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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.

Fortschritte der Chemie organischer Naturstoffe / Progress in the Chemistry of Organic Natural Products, Vol. 93. Vol.93

List of Contributors

Nonconventional Lignans: Coumarinolignans, Flavonolignans, and Stilbenolignans

by Sajeli A. Begum, Mahendra Sahai, and Anil B. Ray

1. Introduction

2. Coumarinolignans

3. Flavonolignans

4. Stilbenolignans

References

Picrotoxanes

by Edda Gössinger

1. Introduction

2. Tabular Overview of the Picrotoxanes

3. Occurrence

4. Isolation of Picrotoxanes

5. Structure Determination of Picrotoxanes

6. Total Syntheses of Picrotoxanes

7. Biosynthesis of Picrotoxanes

8. Physiological Activity of Picrotoxanes

Abbreviations

References

Combinatorial and Synthetic Biosynthesis in Actinomycetes

by Marta Luzhetska, Johannes Härle, and Andreas Bechthold

1. Introduction

2. Combinatorial Biosynthesis and Synthetic Biosynthesis

References

Author Index

Subject Index