Abstract
In the last two decades, large scale axenic cell cultures of the marine species comprising the family Euplotidae have resulted in the isolation of several new classes of terpenoids with unprecedented carbon skeletons including the (i) euplotins, highly strained acetylated sesquiterpene hemiacetals; (ii) raikovenals, built on the bicyclo[3.2.0]heptane ring system; (iii) rarisetenolides and focardins containing an octahydroazulene moiety; and (iv) vannusals, with a unique C30 backbone. Their complex structures have been elucidated through a combination of nuclear magnetic resonance spectroscopy, mass spectrometry, molecular mechanics and quantum chemical calculations. Despite the limited number of biosynthetic experiments having been performed, the large diversity of ciliate terpenoids has facilitated the proposal of biosynthetic pathways whereby they are produced from classical linear precursors. Herein, the similarities and differences emerging from the comparison of the classical chemotaxonomy approach based on secondary metabolites, with species phylogenesis based on genetic descriptors (SSU-rDNA), will be discussed. Results on the interesting ecological and biological properties of ciliate terpenoids are also reported.
Highlights
Ciliate is the common name assigned to a protist taxon comprising the phylum Ciliophora
From the structural chemist’s point of view the most fascinating aspect of this trip into the world of ciliates is represented by the high skeletal chemical diversity found in this phylum
Using sesquiterpenoids as an example, the isolation of four new C15 skeleta was unexpected at the beginning of the study, since more than a century of research had been dedicated to the identification of new metabolites and to explain the mechanism of their biosynthesis
Summary
Ciliate is the common name assigned to a protist taxon comprising the phylum Ciliophora. 7000 ciliate species have been described from marine, freshwater and terrestrial habitats, where they play a key role in microbial food webs These eukaryotic microorganisms are characterized by a nuclear dualism and body-covering cilia used for locomotion and feeding. In the last two decades detailed investigation of ciliate secondary metabolites from the genus Euplotes has added “a new dimension” to the problem of their speciesspecific allocation via a "chemotaxonomic" approach, which is able to define protistan taxonomy to the subspecific level [7]. The first class is represented by pheromone peptides and proteins, of which structural, functional, and evolutionary properties have been described by Luporini and co-workers These cell-specific signal proteins, isolated from ciliated protozoa belonging to the genus Euplotes, constitutively diffuse into the extracellular environment [8]. The evolutionary significance of these metabolites is described in the last section, along with a comparison of the outcomes from the analysis of micromolecular markers (terpenoids) with that of macromolecular descriptors (SSU-rRNA)
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