Publications
In situ Generation of Aldehydes for Subsequent Biocatalytic Cascade Reactions in Whole Cells
Abstract
Aldehydes are highly reactive compounds. Byproduct formation to the corresponding alcohol or carboxylic acid in E. coli can be avoided by enzymes with reversing activity (alcohol dehydrogenase ADH and carboxylic acid reductase CAR). This concept was expanded by three new enzymes: pyruvate decarboxylase PDC, ω-transaminase ω-TA and imine reductase IRED. That enabled the synthesis of α-hydroxy ketones, primary and secondary amines in E. coli.
Surveying the mugineic acid family: Ion mobility – quadrupole time-of-flight mass spectrometry (IM-QTOFMS) characterization and tandem mass spectrometry (LC-ESI-MS/MS) quantification of all eight naturally occurring phytosiderophores
Abstract
Phytosiderophores (PS) are root exudates released by grass species (Poaceae) that play a pivotal role in iron (Fe) plant nutrition. A direct determination of PS in biological samples is of paramount importance in understanding micronutrient acquisition mediated by PS. To date, eight plant-born PS have been identified; however, no analytical procedure is currently available to quantify all eight PS simultaneously with high analytical confidence. With access to the full set of PS standards for the first time, we report comprehensive methods to both fully characterize (IM-QTOFMS) and quantify (LC-ESI-MS/MS) all eight naturally occurring PS belonging to the mugineic acid family. The quantitative method was fully validated, yielding linear results for all eight analytes, and no unwanted interferences with soil and plant matrices were observed. LOD and LOQ values determined for each PS were below 11 and 35 nmol L−1, respectively. The method’s precision under reproducibility conditions (intra- and inter-day) of measurement was less than 2.5% RSD for all analytes. Additionally, all PS were annotated with high-resolution mass spectrometric fragment spectra and further characterized via drift tube ion mobility-mass spectrometry. The collision cross-sections obtained for primary ion species yielded a valuable database for future research focused on in-depth PS studies. The new quantitative method was applied to analyse root exudates from Fe-controlled and deficient barley, oat, rye, and sorghum plants. All eight PS, including mugineic acid (MA), 3″-hydroxymugineic acid (HMA), 3″-epi-hydroxymugineic acid (epi-HMA), hydroxyavenic acid (HAVA), deoxymugineic acid (DMA), 3″-hydroxydeoxymugineic acid (HDMA), 3″-epi-hydroxydeoxymugineic acid (epi-HDMA) and avenic acid (AVA) were for the first time successfully identified and quantified in root exudates of various graminaceous plants using a single analytical procedure. These newly developed methods can be applied to studies aimed at improving crop yield and micronutrient grain content for food consumption via plant-based biofortification.
Identification of a novel PDE4 inhibitor inspired by leoligin-derived lignans
Abstract
The phosphodiesterase 4 (PDE4) family comprises isoenzymes that selectively hydrolyse the second messenger cyclic adenosine monophosphate (cAMP). PDE4s are widely expressed and play key roles in various physiologic paradigms, including immune responses, memory, cognition, and metabolism. Marketed PDE4 inhibitors, such as roflumilast and apremilast, treat chronic obstructive pulmonary disease and psoriasis. Identification and characterisation of PDE4 inhibitors offer a promising strategy for targeting diverse pathological processes. In this study, leoligin, a natural lignan found in the roots of Edelweiss (Leontopodium nivale subsp. alpinum (Cass.) Greuter (Asteraceae)) and 165 analogues were screened for their PDE inhibitory activity using a cAMP accumulation assay employing an exchange protein activated by cAMP-based biosensor. Six compounds, including leoligin itself, were identified to cause a significant accumulation of cAMP, and structure-activity relationships were deduced. One analogue, designated LT-104A, showed a concentration-dependent activity with the highest determined potency (EC50 = 1.9 μM) in the cAMP accumulation assay. LT-104A was further characterised using a CRE-Luciferase assay, showing comparable activity to known PDE4 inhibitors in inducing the anti-inflammatory cAMP-PKA-CREB pathway. The inhibitory activity of LT-104A was also confirmed against recombinant PDE4D3 in a cell-free cAMP hydrolysis assay (IC50 = 9.3 μM). The potential binding mode of LT-104A with the catalytic domain of PDE4D was predicted using induced-fit docking. Lastly, a functional study was conducted in LPS-activated macrophages, where LT-104A reduced nitric oxide release and decreased mRNA expression of Il1b and Nos2. In conclusion, extensive in vitro screening of leoligin analogues led to the identification and characterisation of a novel PDE4 inhibitor, LT-104A, with potential in vitro anti-inflammatory properties.
Mechanically induced sequential one-pot Wittig olefination–Diels–Alder reaction: a solvent-free approach to complex bicyclic scaffolds
Abstract
Herein we present a mechanically induced, solvent-free protocol that sequentially combines the Wittig olefination and Diels–Alder cycloaddition in one-pot and enables the synthesis of structurally complex bicyclic compounds. This method proceeds entirely under ball milling conditions without the requirement of any solvent while eliminating the need for intermediate purification. Careful optimization of the milling parameters and reagent addition enables efficient conversion of various α,β-unsaturated aldehydes and ketones with electron-deficient dienophiles to the corresponding cycloadducts via diene intermediates, demonstrating high stereoselectivity and yielding exclusively endo Diels–Alder adducts. Furthermore, the extension of the sequence by a solvent-free one-pot oxidation is exemplified, achieving a three-step synthesis in a single milling vessel without intermediate workup and purification, which exhibits excellent green metrics in comparison with solution-based methods. This operationally simple and sustainable approach demonstrates the potential of mechanochemistry to streamline multistep organic synthesis, while reducing solvent use and energy demand.