Variable stereochemistry in highly branched isoprenoids from diatoms

Area of Science:

• Geochemistry
• Marine Biology
• Organic Chemistry

Background:

• Highly branched isoprenoid (HBI) alkenes are ubiquitous lipids found globally in geochemical samples.
• Their origin is primarily attributed to a select group of diatoms, including Haslea spp., Rhizosolenia setigera, and Pleurosigma intermedium.
• The structural diversity of HBIs includes variations in unsaturation (2-6 double bonds) and stereogenic centers.

Purpose of the Study:

• To investigate the stereochemical properties of HBI alkenes produced by a novel diatom species.
• To compare the stereochemistry of HBIs from this new species with those from known diatom sources (Haslea spp., P. intermedium, R. setigera).

Main Methods:

• Utilized a combination of Nuclear Magnetic Resonance (NMR) spectroscopy for structural elucidation.
• Employed chiral gas chromatography for determining relative and absolute configurations.
• Cultured diatoms under various growth conditions to analyze HBI production.

Main Results:

• Determined the relative and/or absolute configurations of a range of HBI alkenes.
• Characterized HBIs from Haslea spp. as a specific structural type with configurational diastereoisomerism.
• Identified HBIs from P. intermedium and R. setigera as a different type, typically existing as geometric isomer mixtures.
• Reported HBIs from a new diatom species exhibiting stereochemical properties intermediate between Haslea spp. and P. intermedium.

Conclusions:

• The stereochemical analysis provides insights into the biosynthetic pathways and evolutionary relationships of HBI alkenes in diatoms.
• The discovery of HBIs in a new diatom species expands the known diversity of these important geochemical markers.
• This research contributes to understanding the global distribution and origin of HBI alkenes in the environment.