Smith degradation, an efficient method for the preparation of cycloastragenol from astragaloside IV.

Cycloastragenol (CA) is the genuine sapogenin of astragaloside IV (ASI). This study focuses on the preparation of CA from ASI. Five hydrolysis methods were compared including H2SO4 hydrolysis, HCl hydrolysis, two-phase acid hydrolysis, mild acid hydrolysis, and Smith degradation. Seven hydrolysis products were purified, and five of them were identified as new compounds. The results indicated that Smith degradation was the most effective approach to prepare CA. In contrast, mild acid hydrolysis produced CA at a low yield, accompanied with the artificial sapogenin astragenol. The other three acid hydrolysis methods mainly produced astragenol. Furthermore, the reaction conditions for Smith degradation were optimized as follows: ASI was dissolved in 60% MeOH-H2O solution, oxidized with 5 equiv. NaIO4 for 12h, followed by reduction with 3 equiv. NaBH4 for 4h, and finally acidified with 1M H2SO4 at pH2 for 24h. Under the optimal conditions, CA could be prepared from ASI at a yield of 84.4%.

Two new oxidation products obtained from the biotransformation of asiatic acid by the fungus Fusarium avenaceum AS 3.4594.

Asiatic acid (AA) is a natural triterpenoid possessing anti-inflammatory, anticancer, neuroprotective, and hepatoprotective activities. Structural modification of AA may provide valuable information for further structure-activity relationship analysis. Biotransformation is an efficient, specific, and environment friendly technology for structural modification of complicated natural products. In this study, the capabilities of twenty-five strains of filamentous fungi to transform AA were screened. Two new and one known oxidation products metabolized by Fusarium avenaceum AS 3.4594 were isolated. Their chemical structures were characterized as 2-oxo-3ß,15α,23-trihydroxyurs-12-en-28-oic acid (1), 3-oxo-2,15α,23-trihydroxyurs-1,12-dien-28-oic acid (2), and 2-oxo-3ß,23-dihydroxyurs-12-en-28-oic-acid (3) by extensive analysis of spectroscopic data.

Microbial transformation of ursolic acid by Syncephalastrum racemosum (Cohn) Schroter AS 3.264.

Biotransformation of ursolic acid by the filamentous fungus Syncephalastrum racemosum (Cohn) Schroter AS 3.264 yielded five metabolites. Their structures were identified as 3ß,21ß-dihydroxy-urs-11-en-28-oic acid-13-lactone, 3ß,7ß,21ß-trihydroxy-urs-11-en-28-oic acid-13-lactone, 1ß,3ß-dihydroxy-urs-12-en-21-one-28-oic acid, 1ß,3ß,21ß-trihydroxy-urs-12-en-28-oic acid and 11,26-epoxy-3ß,21ß-dihydroxy-urs-12-en-28-oic acid based on NMR and MS spectroscopic analyses. The condensation reactions to form 28-oic acid-13-lactone ring and 11,26-epoxy ring are not frequently seen for the biotransformation of triterpenoids. One compound showed moderate inhibitory activity against protein tyrosine phosphatase 1B (PTP1B).