"Simulating molecular complexity of dissolved organic matter by chemical synthesis"
Broader background of the proposed research project
The extraordinary molecular complexity of DOM combined with its almost infinite dilution of each single species suggests that this material could be chemical waste resulting from erroneous metabolic transformations (Wortmann et al. 2015). The synthesis of fatty acids from acetyl-CoA via malonyl-CoA (Bae 2015) is a metabolic pathway commonly used by all marine organisms (Finzel et al. 2015, Dibrova et al. 2014, Li et al. 2014). We propose the hypothesis that synthetic mistakes in the five step elongation by two carbon atoms (Claisen condensation, decarboxylation, carbonyl reduction, water elimination, C-C double bond reduction) could lead to such complex mixtures of useless "waste" byproducts without biological function, which are secreted into the marine environment. Actually, further postbiosynthetic intra- or extracellular processing by aldol condensation could be assumed leading to polyketide type constitutions. Furthermore, by incorporation of propionyl instead of acetyl-CoA building blocks, also species with odd carbon numbers could be generated.
Outline for the proposed PhD research project
Aim of the PhD thesis is to simulate the molecular complexity of DOM by chemical synthesis. The molecular complexity of DOM should be synthetically modelled by the product distribution obtained by Claisen condensations from beta-dicarbonyl compounds (as a mimic of malonyl-CoA). Products of these transformations are prone for subsequent aldol (in particular Knoevenagel) processes under suitable basic or acidic reaction conditions, thus, leading to polyketide type products including hydroxylated and annulated aromatic rings. Of course, not the physiological reaction conditions shall be mimicked, but the products distribution patterns. Thus, reaction conditions will preferably be elevated temperatures, high concentrations and strongly acidic or basic heterogeneous catalysts, such as aluminum silicates ("zeolites"). Product distributions will be analyzed by GC, GC-MS-coupling techniques (for higher molecular weights LC, LC-MS) and ultrahigh-resolution MS (FT-ICR-MS) and compared with data obtained from natural DOM. Furthermore, selected unique species with be isolated by preparative LC, and their constitution elucidated by NMR-spectroscopic methods. If required, independent synthetic routes to selected species will be developed. Molecular analyses will be performed in the central analytical facility of IfC, and in cooperation with WPs 3 and 4. The synthetic diverse mixtures will used as substrates for microbiological incubations in WP 2.