Innovative sophorolipid analogues with tailor-made physico-chemical and biological properties

Sophorolipids are an interesting class of glycolipid biosurfactants. They are produced by different yeast species, mainly Starmerella bombicola, through fermentation. The yeast uses glucose as hydrophilic carbon source and an oil or fatty acid as hydrophobic carbon source. Being amphiphilic compounds, sophorolipids have been commercialized by different companies in their detergent compositions. Nevertheless, their application potential in the detergent sector is limited because they have a competitive disadvantage compared to synthetic surfactants in terms of production cost. Being renewable products with a complex structure and interesting biological properties, sophorolipids can be regarded as excellent building blocks for chemical modification. In the first part, a synthetic pathway was developed to transform the major microbial product, i.e. diacetylated sophorolipid lactone, into a C9 sophorolipid aldehyde intermediate. This pathway constitutes of three consecutive steps, i.e. methanolysis, protection of the sugar head and ozonolysis. The fermentation conditions and concomitant purity of the starting product proved to have an influence on the chemical derivatization. Also the ozonolysis reaction proved to be a key factor in this synthetic pathway. Efforts were made to render this reaction as sustainable as possible while preserving a high product yield and purity. The synthetic pathway was extended to the production of a sophorolipid alcohol intermediate by adjusting the reductive work-up of the ozonolysis reaction and to the production of a C12 sophorolipid aldehyde via the incorporation of petroselinic acid in the sophorolipid structure. In the second part, the sophorolipid aldehyde intermediate was subsequently used as chemical building block for the synthesis of a variety of innovative sophorolipid analogues. The new derivatives comprise sophorolipid amines, sophorolipid quaternary ammonium salts, sophorolipid amine oxides and bolaamphiphilic sophorolipids. Multiple properties were evaluated for these new classes of sophorolipid derivatives. For example, some derivatives showed high antimicrobial activity against Gram-positive bacterial strains such as Staphylococcus aureus and Bacillus subtilis. Also, promising results were obtained for the application of sophorolipid derivatives as vectors for gene delivery. The deprotected quaternary ammonium sophorolipids with an octadecyl chain on the nitrogen atom proved to be the most interesting compounds. The presence of the carbohydrate head proved to have a positive influence on the antimicrobial activity and on the cell viability in the transfection assay

Endocrine disrupting potency and toxicity of novel sophorolipid quaternary ammonium salts

A new class of biosurfactants, namely quaternary ammonium sophorolipids (SQAS), suitable for pharmaceutical applications, was tested for the evaluation of their (anti)estrogenic and (anti)androgenic potency with the help of YES/YAS assays. Also their toxicity towards yeasts (Saccharomyces cerevisiae) and bacteria (Escherichia coli) was checked. The results achieved for SQAS, which can be regarded as potential micropollutants, were compared with those obtained for two well-known micropollutants diclofenac and 17 alpha-ethinylestradiol subjected to the same testing procedures. This work demonstrated that acetylation of the hydroxyl group of the carbohydrate head of SQAS decreased the toxicity of this class of biosurfactants towards Saccharomyces cerevisiae. Furthermore, it contributed to the decrease of their endocrine disrupting potency. None of the SQAS studied showed clear agonist activity for female or male hormones. SQAS1 and SQAS2 revealed weak antiestrogenic and antiandrogenic potency. All of these properties were weaker, not only to the potency of the appropriate positive control in the antagonists bioassays, but also compared to the potency of other tested compounds, i.e. DCF and EE2. SQAS3 possessed most probably inhibitory activity towards male hormones. Moreover, cytotoxicity of two out of four studied SQAS at the highest concentrations towards the strains of Saccharomyces cerevisiae interfered with the endocrine disruption activity. It would be also worth studying it with the use of another endocrine activity test

Self-assembly mechanism of pH-responsive glycolipids : micelles, fibers, vesicles, and bilayers

A set of four structurally related glycolipids are described: two of them have one glucose unit connected to either stearic or oleic acid, and two other ones have a diglucose headgroup (sophorose) similarly connected to either stearic or oleic acid. The self-assembly properties of these compounds, poorly known, are important to know due to their use in various fields of application from cleaning to cosmetics to medical. At basic pH, they all form mainly small micellar aggregates. At acidic pH, the oleic and stearic derivatives of the monoglucose form, respectively, vesicles and bilayer, while the same derivatives of the sophorose headgroup form micelles and twisted ribbons. We use pH-resolved in situ small angle X-ray scattering (SAXS) under synchrotron radiation to characterize the pH-dependent mechanism of evolution from micelles to the more complex aggregates at acidic pH. By pointing out the importance of the COO-/COOH ratio, the melting temperature, T-m, of the lipid moieties, hydration of the glycosidic headgroup, the packing parameter, membrane rigidity, and edge stabilization, we are now able to draw a precise picture of the full self-assembly mechanism. This work is a didactical illustration of the complexity of the self-assembly process of a stimuli-responsive amphiphile during which many concomitant parameters play a key role at different stages of the process

Sophorolipids: Renewable resources for chemical derivatization

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Characterization of french coriander oil as source of petroselinic acid

Coriander vegetable oil was extracted from fruits of French origin in a 23% yield. The oil was of good quality, with a low amount of free fatty acids (1.8%) and a concurrently high amount of triacylglycerols (98%). It is a rich source of petroselinic acid (C18:1n-12), an important renewable building block, making up 73% of all fatty acids, with also significant amounts of linoleic acid (14%), oleic acid (6%), and palmitic acid (3%). The oil was characterized by a high unsaponifiable fraction, comprising a substantial amount of phytosterols (6.70 g/kg). The main sterol markers were β-sitosterol (35% of total sterols), stigmasterol (24%), and Δ7-stigmastenol (18%). Squalene was detected at an amount of 0.2 g/kg. A considerable amount of tocols were identified (500 mg/kg) and consisted mainly of tocotrienols, with γ-tocotrienol as the major compound. The phospholipid content was low at 0.3%, of which the main phospholipid classes were phosphatidic acid (33%), phosphatidylcholine (25%), phosphatidylinositol (17%), and phosphatidylethanolamine (17%). About 50% of all phospholipids were non-hydratable. The β-carotene content was low at 10 mg/kg, while a significant amount of chlorophyll was detected at about 11 mg/kg. An iron content of 1.4 mg/kg was determined through element analysis of the vegetable oil. The influence of fruit origin on the vegetable oil composition was shown to be very important, particularly in terms of the phospholipids, sterols, and tocols composition21

Petroselinic acid purification and its use for the fermentation of new sophorolipids

Petroselinic acid, a positional isomer of oleic acid, was isolated from the vegetable oil of Coriandrum sativum fruits. This uncommon fatty acid was subsequently used as substrate for sophorolipid fermentation with a Starmerella bombicola lactone esterase overexpression (oe sble) strain. A petroselinic acid based diacetylated sophorolipid lactone was obtained in high purity without incorporation of de novo synthesized fatty acids such as oleic acid. A total production of 40 g/L was obtained. The petroselinic acid based sophorolipid lactone was subsequently hydrolyzed towards the petroselinic acid based sophorolipid acid. For both compounds, their critical micelle concentration (CMC) and corresponding surface tension were compared to their oleic acid based counterparts. Both petroselinic acid based sophorolipids displayed a much lower CMC value than their oleic acid based counterparts, although their minimal surface tension was the same. Besides, the sophorolipid fermentation product was chemically modified towards a novel C12 sophorolipid aldehyde. This derivative constitutes an interesting building block for further modification towards new-to-nature sophorolipids with high potential for self-assembly applications