Date: 20 February 2025 | Category: News
Authors: Valentina Marchini, Francesca Paradisi
Valentina Marchini and Francesca Paradisi from The University of Bern have used a packed-bed reactor mounted within the Vapourtec R-Series modular flow chemistry system to synthesise danshensu [1], a pharmacological agent with significant use in traditional Chinese medicine. Starting from L-dopa, preparation of danshensu was achieved with a co-immobilised bioenzymatic system that comprised phenylalanine dehydrogenase from Bacillus sphaericus (BsPheDH) and a novel hydroxyphenylpyruvate reductase from Mentha x piperita (MpHPPR), alongside catalytic NAD+. Conversion of 80% was achieved within 60 minutes to give access to danshensu in 96% purity, with overall preparation rate of 1.84 g L−1 h−1.
Figure 1: Danshensu preparation from L-dopa mediated by Bacillus sphaericus phenylalanine dehydrogenase and Mentha x piperita hydroxyphenylpyruvate reductase in the presence of NAD+.
Danshensu as a pharmaceutical compound
The dried root of Salvia miltiorrhiza, also known as red sage or Danshen, is a major herbal medicine in China. The active ingredient, danshensu (3-(3,4-dihydroxy-phenyl) lactic acid), has numerous listed benefits including therapeutic effect against cardiovascular diseases, cerebral lesions and disorders, and other conditions such as thrombosis, tumorigenesis, pancreatitis and preeclampsia [2].
Approximately 80 million kilograms of the crude drug are consumed per year. However, although several strategies exist for preparation of danshensu, they suffered from low yields and require expensive chiral catalysts that suffer from low enantiopurity. Isolation from natural sources is also difficult due to the chemical instability of the catechol, low content of danshensu in Danshen, and the presence of a variety of structural analogues as impurities.
Immobilisation of biocatalysts for improved catalytic performance
Immobilisation of biocatalysts allows their use within a continuous flow system and also affords the possibility of simplified work-up, avoiding the requirement for centrifugation of samples or complex filtration. In this case, the novel hydroxyphenylpyruvate reductase Mentha x piperita was successfully expressed, characterized, and co-immobilised alongside phenylalanine dehydrogenase from Bacillus sphaericus. The immobilised catalysts were placed in a short glass column, generating a packed-bed reactor, that was then mounted within the R-Series system. While a compromise had to be sought in terms of the required pH of the system, the use of the bioreactor afforded a 58% conversion with a 30-minute residence time, and 80% conversion within 60 minutes, achieving productivity of 1.84 g L−1 h−1, a significant improvement on previous work.
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References:
[1] Self‑sufficient biocatalytic cascade for the continuous synthesis of danshensu in flow (V. Marchini, F. Paradisi, App. Microbiol. Biotechnol. 2025, 109, 13). https://doi.org/10.1007/s00253-025-13407-3
[2] Therapeutic potentials and mechanisms of the Chinese traditional medicine danshensu (J. Zhang, Q. Zhang, G. Liu, N. Zhang, Eur. J. Pharmacol., 2019, 864, 172710). https://doi.org/10.1016/j.ejphar.2019.172710