Structure determination of a 4-pyrone from the liverwort <i>Plagiochila bifaria</i> (Sw.) Lindenb. (Plagiochilaceae)

The centenary of the presentation in 1907 of the "polyketide" hypothesis by Collie, along with his use of a 4-pyrone as an example, is marked by reporting the discovery and isolation of 2-(3,4-dimethoxyphenethyl)-6-methyl-4-pyrone from &lt;i&gt;Plagiochila bifaria&lt;/i&gt;. This compound dominates the phytochemical profile of the deuteriochloroform extract of a Venezuelan specimen of &lt;i&gt;P. bifaria&lt;/i&gt; and the structure was determined using spectroscopic techniques, especially 2D NMR. This natural product is novel because it contains what appears to be the first example of a monocyclic 4-pyrone that has a polyketide origin. The hypothetical pathway for cyclization of a triketocarboxylic acid to a 4-pyrone was known to be applicable to model systems but no examples of natural products from this route were known. This compound is the same as one of a series of compounds observed previously in an extract of a Brazilian specimen of &lt;i&gt;P. bifaria&lt;/i&gt;; the working structures that were proposed earlier require revision. The mass spectral characteristics are the same as those reported (parent and base peak) in 1987 for the major component observed in the GC-MS profile of an extract of a specimen of &lt;i&gt;P. bifaria&lt;/i&gt; from Peru. The roles played by Birch and Robinson in the renaissance of the polyketide hypothesis almost fifty years after its initial launch are considered. Based on evidence from their publications, they worked independently of each other. It appears Robinson always had knowledge of Collie's hypothesis when developing ideas about structural relations of natural products whereas Birch initially was unaware of both Collie's and Robinson's ideas on the subject

Molecular, morphological, and phytochemical evidence for a broad species concept of Plagiochila bifaria (Hepaticae)

Debate over the synonymy of the European Plagiochila killarniensis and the Neotropical P bifaria of R sect. Arrectae has focused on differences in secondary metabolite composition. The broad morphological species concept of R bifaria proposed in recent papers has now been tested by comparing nrDNA ITS1 and ITS2 sequences of R bifaria populations encompassing several different morpho- and chemotypes from the British Isles, Tenerife, Costa Rica, Brazil, Ecuador, and Bolivia, with sequences of other species of R sects. Arrectae, Rutilantes, and Fuscoluteae. Phylogenetic analyses demonstrate that specimens of P. bifaria form a well supported clade within Plagiochila sect. Arrectae. Sequences of R bifaria from the British Isles, Tenerife, and Ecuador, representing the "methyl everninate" chemotype, form a well supported subclade within the P bifaria clade. Sequences of specimens from Costa Rica, Brazil, and Bolivia are placed in the basal part of the R bifaria clade. The data support a broad species concept of P bifaria. The different chemotypes do not warrant distinct taxonomic ranks. Plagiochila centrifuga and P. compressula are treated as new synonyms of R bifaria

Plagiochila rutilans (Hepaticae): A poorly known species from tropical America

The neotropical liverwort, Plagiochila rutilans Lindenb., is conspecific with P. remotifolia Hampe and Gottsche, P. farlowii Steph., P. harrisana Steph, and P. organensis Herzog. Plagiochila standleyi Carl is reduced to a variety of P. rutilans. Plagiochila gymnocalycina (Lehm. and Lindenb.) Mont. and P. portoricensis Hampe and Gottsche (= P. simplex (Sw.) Lindenb.) are excluded from the synonymy of P. rutilans. Plagiochila rutilans var. liebmanniana Gottsche is a synonym of P. crispabilis Lindenb.; P. rutilans var. laxa Lindenb. and var. angustifolia Herzog are conspecific with P. gymnocalycina. Sporophytes of P. rutilans are described for the first time. Fresh material of P. rutilans exhibits a distinct odor of peppermint caused by the presence of several menthane monoterpenoids, principally pulegone. NMR (nuclear magnetic resonance) fingerprints and GC-MS data indicate that the lipophilic secondary metabolite profiles are distinct for the two varieties accepted in this study

The systematic position of Plagiochila moritziana, P. trichostoma and P. deflexa based on ITS sequence variation of nuclear ribosomal DNA, morphology, and lipophilic secondary metabolites

According to phylogenetic analyses of nrDNA ITS1 and ITS2 sequences (including the 5.8S unit) the Neotropical Plagiochila moritziana, P. rutilans var. rutilans, P. rutilans var. standleyi, P. trichostoma (= P. permista, syn. nov.), and P. subtrinitensis form a monophyletic lineage and are placed in P. sect. Rutilantes; all five taxa lack a ca 20 base pair sequence that is present in all the taxa of the other Plagiochila sections investigated. The Central American P. subtrinitensis is treated as a synonym of the Hawaiian endemic P. deflexa. Plagiochila moritziana is excluded from sect. Fuscoluteae and reduced to a variety of P. rutilans; P. sect. Permistae is treated as a synonym of P. sect. Rutilantes. The sporophytes of P. trichostoma and P. deflexa are described for the first time. Fresh material of P. rutilans var. moritziana exhibits a distinct odor of peppermint caused by the presence of several menthane monoterpenoids, principally pulegone. The Central American P. rutilans var. standleyi is reported from Ecuador, new to South America. Lectotypes are designated for P. rutilans var. moritziana, P. subtrinitensis, and P. trichostoma

Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

A chemist's view of liverworts: NMR fingerprinting and chemotype classification of British Plagiochilae

This work has evolved out of the chemical studies of the secondary metabolites of liverworts that have been going on at Glasgow for over 25 years. In considering both our and other people's work in this area, a recurring question was: are the secondary metabolites characteristic of the species or just of the particular specimen? Our efforts to answer this question for particular liverworts have involved using NMR spectroscopy to develop NMR fingerprinting (Rycroft, 1996). The novel aspect of this technique is to extract the plant material with deuterochloroform, the deuterated solvent that is normally used to measure NMR spectra; many benefits arise from the simplicity and directness of the procedure compared to more conventional methods (Rycroft, 1998a). In favourable circumstances, the amount of plant material required is only a fraction of many herbarium specimens, and the method opens up the possibility of undertaking comparative chemical studies using a wide range of fresh and/or herbarium material

Plagiochila in Europe (and beyond)

This paper reports progress in the three years since the 1998 BBS Loughborough meeting. It looks at aspects of Plagiochila in Britain, Europe and Macaronesia, but, as the title implies, it is also necessary to take account of the situation further afield. The topics covered include evidence relating to the presence in Macaronesia of P. bifaria (Sw.) Lindenb., P. dubia Lindenb. and Gottsche and P. spinulosa (Dicks.) Dumort., to the synonymy of P. killarniensis Pearson and P. bifaria, and to the systematic position of P. atlantica F. Rose. Much of the work has involved others (who are cited along the way) and I wish to acknowledge particularly close collaboration with Jochen Heinrichs (Gottingen), much facilitated by the tremendous benefits of electronic mail

Chemosystematics and the liverwort genus Plagiochila

Recent discoveries that have been facilitated by phytochemical studies based on NMR and GC-MS profiling include: (1) Plagiochila atlantica of Europe belongs to the Neotropical P sect. Fuscoluteae; (2) the Central American P. retrorsa occurs in North America as well as Madeira and the Azores; (3) the Neotropical P. stricta occurs in the Canary Islands; (4) the South American P papillifolia Steph. occurs in the Azores. Phytochemical data support taxonomic changes involving varieties of the Neotropical P. rutilans. Plagiochila species in Europe (including Macaronesia) may be classified into two chemotypes, characterised by 2,3-secoaromadendranes on the one hand and aromatic compounds on the other

Phytochemical variations on a biosynthetic theme

Biosynthetic pathways that may lead to the diverse secondary metabolites occurring in liverwort oil bodies are considered in relation to the apparently disparate products that can be found in closely related taxa. Discussion centres on recent work with Plagiochila bifaria (Sw.) Lindenb., a broadly defined species where different chemotypes are characterized by either 9,10-dihydrophenanthrenes, methyl orsellinates, or 9-arylnon-6-en-2-ones. A scenario is presented to illustrate the possibility that a biosynthetic theme common to all examples of the taxon studied could account for the phytochemical variations observed. A complementary study of members of Plagiochila sect. Rutilantes Carl illustrates that taxa maintained at specific rank may nevertheless contain several secondary metabolites in common

A phytochemical and morphological study of the liverwort Plagiochila retrorsa Gottsche, new to Europe

The Neotropical liverwort Plagiochila retrorsa Gottsche is conspecific with P. sharpii H.L.Blomq., known previously as a Southern Appalachian endemic, as well as P. tricarinata Carl and P. permista Spruce var, subintegerrima Herzog from Costa Rica. It has been discovered recently in the Azores and Madeira, new to Europe. Illustrations, SEM micrographs of spores and elaters, nuclear magnetic resonance (NMR) fingerprints and gas chromatography-mass spectrometry (GC-MS) data are presented, based on American and European material. Costa Rican material used for an earlier phytochemical study has now also been identified as P. retrorsa. Although NMR fingerprinting initiated the present discoveries, the NMR fingerprint of P. retrorsa is not unique and NMR fingerprinting alone is not sufficient to identify the species. P. retrorsa belongs to the 9,10-dihydrophenanthrene chemotype group and the two principal secondary metabolites are 3,5-dimethoxy-9,10- dihydrophenanthren-2-ol and methyl 4-hydroxy-4'-O- methyllunularate