Twelve new quaternary ammonium sophorolipids with long alkyl chains on the nitrogen atom were synthesized starting from oleic and petroselinic acid‐based sophorolipids. These novel derivatives were evaluated for their antimicrobial activity against selected Gram‐negative and Gram‐positive bacteria and their transfection efficacies on three different eukaryotic cell lines in vitro as good activities were demonstrated for previously synthesized derivatives. Self‐assembly properties were also evaluated. All compounds proved to possess antimicrobial and transfection properties, and trends could be observed based on the length of the nitrogen substituent and the total length of the sophorolipid tail. Moreover, all long‐chain quaternary ammonium sophorolipids form micelles, which proved to be a prerequisite to induce antimicrobial activity and transfection capacity. These results are promising for future healthcare applications of long‐chained quaternary ammonium 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0199-7) contains supplementary material, which is available to authorized users.
New
synthetic pathways are proposed for the synthesis of a new
set of bolaamphiphilic derivatives starting from microbiologically
produced sophorolipids. A total set of 43 new derivatives was synthesized
via reductive amination of a previously synthesized sophorolipid aldehyde
with diamines and primary amines. The new derivatives were evaluated
for their antimicrobial activity against Gram-negative and Gram-positive
bacteria. Minimum inhibitory concentration (MIC) and minimum bactericidal
concentration (MBC) values were determined for the active compounds.
Transfection efficiencies were also evaluated for some of the deprotected
derivatives via the assessment of their capacity to transfect three
different eukaryotic cell lines in vitro. Finally,
the self-assembly properties were evaluated for the deprotected derivatives.
Antimicrobial activities were mostly observed for the peracetylated
mono- or dicationic bolaamphiphiles, and only the deprotected monocationic
bolaamphiphile with an octadecyl chain on the nitrogen atom was eligible
for the evaluation of its transfection properties. Evaluation of the
self-assembly properties indicated that the presence of an octadecyl
chain was necessary for micelle formation. Both micelle formation
and the net charge of the compounds seem to have an influence on the
antimicrobial activity and transfection efficiency. These results
are promising for use of bolaamphiphilic sophorolipids in medical
and self-assembly applications.
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