Lucia Hendrina Steenkamp

Screening of commercial enzymes for the enantioselective hydrolysis of R,S-naproxen ester

This study focused on the identification of suitable lipase or esterase activity for enantiomeric resolution of ( R,S)-naproxen. For an economically viable reaction the enantiomeric ratio (E) should preferably be >100, while maximising the conversion will reduce the mass of material that requires racemisation and recycling. Hence the aim was to find an enzyme that yields ( S)-naproxen with an enantiomeric excess of more than 98%, a substrate conversion in excess of 40% of the racemate, and an E of >100. (R,S)-Naproxen ethyl ester (NEE) (50 mg) was used as substrate for enzyme hydrolysis reactions at 37 ◦ C for 4 h. Biocatalyst screening was performed in buffered aqueous solvent on a 1 ml scale. The reactions were stopped with 2 ml MeCN, filtered through cotton wool and analysed by HPLC to determine the percentage m/m and R/S ratio. Eight commercially available enzymes were selected for optimisation of enantioselectivity through statistically designed experiments where the reaction conditions were varied. ChiroCLEC-CR from Altus and ESL001-01 from Diversa provided acceptable enantiomeric excess, but only ChiroCLEC-CR met the specification set for the enantiomeric ratio ( E).

Biocatalytic conversion of aloeresin A to aloesin.

Leaf exudates from Aloe species, such as the Southern African Aloe ferox, are used in traditional medicines for both humans and livestock. This includes aloesin, a skin bleaching product that inhibits the synthesis of melanin. Aloesin, (a C-glycoside-5-methylchromone) can be released from aloeresin A, an ester of aloesin, through hydrolysis. The objective of the current study was to identify an enzymatic hydrolysis method for converting aloeresin A to aloesin, resulting in increased concentrations of aloesin in the aloe bitters extract. More than 70 commercially available hydrolytic enzymes were screened for the conversion of aloeresin A. An esterase (ESL001-02) from Diversa, a lipase (Novozym 388) and a protease (Aspergillus oryzae) preparation were identified during screening as being capable of providing conversion of pure aloeresin A, with the protease giving the best conversion (~100%). It was found that a contaminating enzyme in Novo 388 was responsible for the conversion of aloeresin A to aloesin. This contaminating enzyme, possibly a protease, was able to give almost complete conversion using crude aloe bitters extract, doubling the concentration of aloesin in aloe bitters extract via the hydrolysis of aloeresin A.

Profiling of Botanical Extracts for Authentication, Detection of Adulteration and Quality Control Using UPLC-QTOF-MS

Copyright: 2018 Springer. Due to copyright restrictions, the attached PDF file only contains the abstract of the full text item. For access to the full text item, kindly consult the publishers website.