Reactivity of N-(3-hydroxyacyl)amino acids and influence of their corresponding homoserine lactones on cyclic lipopeptide production

In this PhD thesis isotope-labelled AHLs were synthesized which can be used as a tool to study the metabolization of AHLs. Secondly, the possible rearrangement of N-(3-hydroxyacyl)- L-homoserine lactones was investigated and proven to be very unlikely. This investigation resulted in the successful development of a synthetic entry toward 1,4-oxazepane-2,5-diones, which are extremely difficult to synthesize due to the presence of a lactam with a preference for the trans-conformation and a labile lactone moiety in one ring structure. By applying the disclosed methodology on the synthesis of the natural product serratin, the incorrect structural assignment of this compound was identified. Thirdly, the profound effect of a QS signal molecule, HO8, on the swarming behavior of Pseudomonas species CMR12a, was demonstrated. This influence goes presumably via an elegant fine-tuning of the ratio of the two produced CLPs, orfamide and sessilin via the control of orfamide production

Synthesis and analysis of stable isotope-labelled N-acyl homoserine lactones

Aliphatic aldehydes were deuterated at the alpha-position via a base-catalyzed exchange reaction with D2O. These deuterated building blocks were used for the synthesis of labelled analogues of quorum sensing signal molecules belonging to the three major classes of naturally occurring N-acylated homoserine lactones (AHLs), with the label on a non-enolizable and therefore stable position. Besides the application of these stable isotope-labelled AHLs as a labelled standard for analysis via isotope dilution mass spectrometry, these compounds can be used to study the metabolic fate of the fatty acid tail of the AHL-molecule. These isotope-labelled compounds were fully characterized and used to synthesize the deuterated analogues of two commonly occurring AHL-degradation products, a tetramic acid and a ring opened N-acyl homoserine

Synthesis and biological evaluation of novel N-α-haloacylated homoserine lactones as quorum sensing modulators

Novel N-α-haloacylated homoserine lactones, in which a halogen atom was introduced at the α-position of the carbonyl function of the N-acyl chain, have been studied as quorum sensing (QS) modulators and compared with a library of natural N-acylated homoserine lactones (AHLs). The series of novel analogues consists of α-chloro, α-bromo and α-iodo AHL analogues. Furthermore, the biological QS activity of the synthetic AHL analogues compared to the natural AHLs was evaluated. Halogenated analogues demonstrated a reduced activity in the Escherichia coli JB523 bioassay, with the α-iodo lactones being the less active ones and the α-chloro AHLs the most potent QS agonists. Most of the α-haloacylated analogues did not exhibit a significant reduction when tested in the QS inhibition test. Therefore, these novel analogues could be utilized as chemical probes for QS structure–activity studies

Haloperoxidase mediated quorum quenching by Nitzschia cf pellucida: study of the metabolization of N-acyl homoserine lactones by a benthic diatom

Diatoms are known to produce a variety of halogenated compounds, which were recently shown to have a role in allelopathic interactions between competing species. The production of these compounds is linked to haloperoxidase activity. This research, has shown that this system may also be involved in diatom-bacteria interactions via the H2O2 dependent inactivation of a type of quorum sensing (QS) molecule, i.e., N-beta-ketoacylated homoserine lactones (AHLs), by a natural haloperoxidase system from the benthic diatom Nitzschia cf pellucida. The AHL degradation pathway towards corresponding halogenated derivatives was elucidated via HPLC-MS analysis and the synthesis of a broad series of novel halogenated AHL analogues as reference compounds. Furthermore, their biological activity as quorum sensing modulators was directly compared and evaluated against a series of naturally occurring beta-keto-AHLs. It has been demonstrated that the loss of the QS activity results from the final cleavage of the halogenated N-acyl chain of the signal molecules

N-acylated homoserine lactone-derived tetramic acids as algicidal compounds

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Synthesis of 1,4-oxazepane-2,5-diones via cyclization of rotationally restricted amino acid precursors and structural reassignment of serratin

Several natural products containing a 1,4-oxazepane-2,5-dione-core are known. One example is serratin, isolated from Serratia marcescens. Because of the presence of a carboxylic amide, which has a preference for a trans conformation, and the presence of a labile lactone in this core, many synthetic methodologies commonly used for the cyclization toward medium-sized heterocycles cannot be applied. As N-acyl amino acids lacking a third substituent at nitrogen failed to undergo ring-closure, several N-protecting groups were evaluated. With the use of the removable PMB-group, an N-unsubstituted 1,4-oxazepane-2,5-dione was synthesized. Via the application of pseudoprolines (i.e. serine-derived oxazolidines as another type of protecting group), a compound with the presumed structure of the natural product serratin was obtained. As a result of the differences in spectral data, the incorrect structural assignment of the natural product serratin was identified. Instead of the predicted seven-membered heterocycle, a symmetrical serratamolide analogue is proposed to be the correct structure of serratin

Mechanistic modelling of reactive liquid-liquid extraction towers using polar PC-SAFT : industrial validation and optimization of fat/oil hydrolysis

Biorefineries provide an important alternative for petroleum-based refineries to reduce CO2 emissions and increase the share of renewable feedstocks for the production of chemicals and fuels. Vegetable oils and animal fats are used as renewable raw materials for the production of oleochemicals. Never before in the history of the oleochemical industry have the changes been more dramatic than in the last decades. The rapid growth of palm oil, the rise of oleochemicals production in Southeast Asian Nations and an increased competition with the biofuel industry for feedstocks form a challenge for the traditional oleochemical players in Europe and North America. This increased competition forces European oleochemical companies such as Oleon NV to diversify the feedstocks they process, ranging from low quality animal fat to higher quality vegetable oils. Operating a continuous installation with a variable feed composition poses significant challenges for process operation and control to ensure resource efficiency, high product yields and excellent product quality. Petroleum refineries regularly use mechanistic and statistical modelling to tackle this challenge of feedstock diversity and adapt process conditions for compositional variability of the incoming crude oil. Applying these techniques to biorefineries, such as for the production of oleochemicals, could aid in utilizing variable bio-based feedstock streams more efficiently, enable the use of lower quality-grade feedstocks and improve adaptability toward future changes in demand and supply

Simulation of an Industrial-Scale Reactive Liquid–Liquid Extraction Tower Using Polar PC-SAFT Toward Understanding and Improving the Hydrolysis of Triglycerides

A comprehensive model for simulation and optimization of industrial-scale splitting towers that is able to predict the yield for the hydrolysis of bio-based triglyceride feedstocks is presented in this work. This model includes a variable glycerol equilibrium ratio, which is a function of the composition and temperature and is calculated using the polar version of the perturbed chain statistical association fluid theory (PC-SAFT), the autocatalytic effect of fatty acids in hydrolysis, and isomerization of poly-unsaturated fatty acids. Model validation is performed using process data from three real-life splitting towers covering four feedstock types, i.e., tallow, rapeseed oil, palm oil, and palm fatty acid distillate. Due to the composition gradients of the organic phase throughout the tower, it is crucial to properly account for the changes in the glycerol equilibrium ratio. The importance of feedstock flow rate, water/oil ratio, and temperature profile throughout the tower is analyzed and confirmed by sensitivity analysis. Our results show that modifying the temperature profile may shift the reaction equilibrium toward the fatty acid product. This knowledge is crucial for improving the energy and resource efficiency of fatty acid production, thereby improving its economic and environmental sustainability