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Advances in the Synthesis of Oligonucleotides by the Phosphoramidite Approach

Biological activities of sesquiterpene lactones

Carbon-13 NMR spectroscopy of steroidal sapogenins and steroidal saponins

The Asteraceae is characterized by structurally diverse sesquiterpene lactones and furanosesquiterpenes. In this review the tribal, subtribal and generic distribution of sesquiterpene lactones is examined and the compounds’ utility as taxonomic characters discussed. Sesquiterpene lactones fulfill the major requirements for good analytic and synthetic characters. Studies of infraspecific sesquiterpene lactone variation indicate that different elements within complex taxa are often defined by distinct chemistries, termed chemotypes. Chemotypes have been identified within many of the thoroughly investigated taxa:Ambrosia camphorata, A. chamissonis, A. confertiflora, theA. cumanensis-A. psilostachya-A. artemisiifolia complex,A. dumosa, Artemisia tridentata, Gaillardia pulchella andMelampodium leucanthum. Such an analytic usage is mostly restricted to the infraspecific level. Synthetic usage at the interspecific level and above profits from the application of a biogenetically based methodology for sorting out the complex molecules’ carbon-skeletal and substitutional features into unit characters. Cladistics or Hennigian phylogenetic systematics provides a useful framework for such an analysis. Preliminary surveys indicate that sesquiterpene lactones are especially good characters for differentiating subtribes within several major tribes: the Vernonieae, Heliantheae and Mutisieae. As yet, too few data are available for other tribes to discern such patterns. Species surveys inVernonia, Ambrosia, Iva, Parthenium,Tetragonotheca andArtemisia demonstrate that sesquiterpene lactones are useful in discerning infrageneric groups. The biogenetic cladistic analysis of the interspecific sesquiterpene lactone variation inIva shows the efficacy of this analytical methodology. At present, such biogenetically based approaches are impeded by limited biosynthetic evidence and the erratic distribution of sesquiterpene lactones within the family. Instances of apparent displacement of sesquiterpene lactones by other terpenoids (i.e. sesquiterpene furans, alcohols and acids, diterpenes, diterpene acids, etc.) at various taxonomic levels suggest that ultimately sesquiterpene lactones must be interpreted as taxonomic characters in the context of the family’s total terpene chemistry. All taxa from which sesquiterpene lactones have been reported are listed together with the compound names, major structural features and the literature cited. A less-complete listing is provided for taxa producing furanosesquiterpenes. Structures for all reported compounds are included. Two appendices listing alphabetically taxa and compounds and relevant text page numbers permit cross-indexing of plants and compounds.

Sesquiterpene lactones as taxonomic characters in the asteraceae

In situ reactions with trichloroacetyl isocyanate and their application to structural assignment of hydroxy compounds by 1 H NMR spectroscopy. A general comment

The structure of exotoxin of Bacillus thuringiensis var. gelechiae . Preliminary communication

Use of structural changes for stereochemical assignments of natural α-exomethylene γ-lactones of the germacra-1(10),4-dienolide type on the basis of allylic and vicinal couplings of bridgehead protons. Hydrogenation of endocyclic double bonds

Zdeněk Samek

Papers

In situ reactions with trichloroacetyl isocyanate and their application to structural assignment of hydroxy compounds by 1 H NMR spectroscopy. A general comment

The structure of exotoxin of Bacillus thuringiensis var. gelechiae . Preliminary communication

Use of structural changes for stereochemical assignments of natural α-exomethylene γ-lactones of the germacra-1(10),4-dienolide type on the basis of allylic and vicinal couplings of bridgehead protons. Hydrogenation of endocyclic double bonds

On terpenes. CXCVIII. Isolation and structure of pinguisone from Aneura pinguis (L.) DUM.

The reaction of 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane with cytosine arabinoside and 1-(6-deoxy-α-L-talofuranosyl)uracil