title: Variable stereochemistry in highly branched isoprenoids from diatoms.
abstract: C(25) highly branched isoprenoid (HBI) alkenes are ubiquitous lipids found in geochemical samples around the globe. The origins of these widespread geochemicals are believed to be restricted to a limited number of diatoms, including Haslea ostrearia (and related species), Rhizosolenia setigera, and Pleurosigma intermedium. The unsaturation of the HBI alkenes ranges from 2-6 in different species and cultures. The number of stereogenic centres is usually limited to two in the HBI alkenes due to double bond positions. The relative and/or absolute configurations for these have been determined for a range of HBI alkenes produced from different diatoms cultured under a number of growth conditions. These determinations have involved a combined spectroscopic and chromatographic analysis using NMR spectroscopy and chiral gas chromatography, respectively. HBIs isolated from Haslea spp. belong to a specific structural type which exhibit configurational diastereoisomerism, while those isolated from P. intermedium and R. setigera represent a different structural type and usually exist as mixtures of geometric isomers only. HBIs are reported from a new species of diatom whose stereochemical properties lie between those found for Haslea spp. and P. intermedium.
authors.affiliation: Department of Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, PL4 8AA, Devon, UK. sbelt@plymouth.ac.uk
authors.forename: S T
authors.initials: ST
authors.lastname: Belt
authors.forename: W G
authors.initials: WG
authors.lastname: Allard
authors.forename: L
authors.initials: L
authors.lastname: Johns
authors.forename: W A
authors.initials: WA
authors.lastname: König
authors.forename: G
authors.initials: G
authors.lastname: Massé
authors.forename: J M
authors.initials: JM
authors.lastname: Robert
authors.forename: S
authors.initials: S
authors.lastname: Rowland
mesh_terms: D000475:Alkenes / Q000737:chemistry* / Q000378:metabolism; D002849:Chromatography, Gas / Q000379:methods; D017377:Diatoms / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D013045:Species Specificity; D013237:Stereoisomerism; D013729:Terpenes / Q000737:chemistry*
chemical_list: D000475:Alkenes; D013729:Terpenes