Synthesis and Characterisation of Novel Sophorolipids and Their Applications

The present study investigated the structural characterisation of the fermentation products (sophorolipids) produced by Candida. bombicola. The analysis included the use of 1D- and 2D-NMR, FT-IR, HPLC-MS, monomer and linkage analysis employing HPAEC-PAD and GC-MS to fully characterise the main fermentation products: sophorolipids lactone and acid forms. The characterisation also looked at materials present in waste streams. Interestingly, free sophorose was identified in a number of the waste streams. The composition of the lactone waste stream was investigated utilizing HPAEC-PAD and NMR techniques. The results indicated the presence of glucose, sophorose and trace amount of isomaltose; these were separated using a liquid-liquid extraction technique followed by the isolation of each sugar using carbon: celite 535 column chromatography. Attempts were made to determine the origin of sophorose in the waste streams. In aqueous alkali, sophorose was observed to undergo an epimerisation reaction and was converted to 2-O-β-D-glucopyranosyl-D-mannose. Another experiment was performed to investigate if enzyme(s) were present in the spent fermentation liquors, which were capable of hydrolysing sophorolipids to produce sophorose. The result suggested that sophorolipids were being converted into sophorose, glucose, isomaltose, and a glucolipid.
A number of novel sophorolipids were synthesised starting from sophorose and using both enzyme and chemical glycosylation reactions. The lipase Novozyme 435 was used to catalyse the synthesis of the sophorolipid derivatives: 1′,6″-sophorolactone, 1′,6″-sophorolactone-6′-acetate and methyl ester-6′,6″-sophorose dibutyrate. Sophorose was used in the preparation of 2′′,3′,3′′,4′,4″,6′,6″-hepta-O-acetyl-α-D-sophoryl bromide, which was coupled to a range of different fatty alcohols. Finally, the interfacial properties, enzyme inhibition effect and biological activity of a number of novel sophorolipids were explored.