(German title: Vom Wertstoff zum Wirkstoff – Konvertierung und Feinreinigung)

Renewable raw materials form the basis for new high-quality products in the pharmaceutical, cosmetics and food industries, etc. One of the greatest added values can be achieved through the cultivation of plants with pharmaceutically active ingredients. These include, for example, the triterpenes ursolic and oleanolic acid, whose pharmacological properties have already been researched in many places. They have antitumor, antiviral and antibacterial properties, among others.

In the project funded by the Rhineland-Palatinate Foundation for Innovation, the triterpenic acid oleanolic acid, which is used as an active component in cosmetics, was to be extracted from sage. During the enzymatic hydrolysis of the plant cell wall to increase the yield during extraction, various enzyme cocktails were tested at different pH values; a significant increase in the triterpene yield through emzymatic pre-treatment was not observed.

Since the two isomeric triterpenes oleanolic and ursolic acid occur together in the sage plant, an efficient separation of the acids is necessary. According to Zhang et al [1], ursolic acid and oleanolic acid are converted to their corresponding methyl esters by Nocardia sp. NRRL 5646; in addition, a methyl group rearrangement from the ursane to the oleane type takes place. Biotransformation could thus degrade unwanted and interfering components or modify the target component for further separation.

The conversion of oleanolic acid and ursolic acid with cell suspensions of Nocardia sp. NRRL 5646 to oleanolic acid methyl ester and to ursolic acid methyl ester was confirmed. The ester compounds are also easier to separate chromatographically, as the retention times are further apart than for the acids. In addition, the experiments showed that Nocardia sp. NRRL 5646 metabolizes ursolic acid to four other ursanic compounds besides ursolic acid methyl ester. The substances could be identified as ursonic acid, ursonic acid methyl ester, 3-oxoursa-1,12-dien-28-oic acid and 3-oxoursa-1,12-dien-28-oic acid methyl ester by HPLC-MS/MS and HPLC-NMR. Based on the results, two new reaction pathways for the conversion of ursane-type triterpenes have been established.

The screening of other Nocardia strains showed that other strains also carry out such biotransformations. Depending on the strain, ursan analogs of the two possible reaction pathways are formed. Ursonic acid and 3-oxoursa-1,12-dien-28-oic acid show pharmacologically interesting properties.

[1] Zhang J, Zhi-Hong Y. Novel biotransformation of pentacyclic triterpenoid acids by Nocardia sp. NRRL 5646. Tetrahedron Lett 2005; 46:2337-2340