Phytochemical studies on Buxus macowanii and microbial transformation of glycyrrhetinic acid

Abstract

This thesis describes phytochemical studies on Buxus macowanii, a medicinal plant collected from South Africa and the fungal transformation of glycyrrhetinic acid (71), a triterpenoid found in Glycyrrhiza plants.

The crude methanolic extract of B. macowanii was active in the acetylcholinesterase inhibition assay (IC50 = 30 μg/mL). Chemical investigation of its alkaline dichloromethane extract afforded five novel triterpenoidal alkaloids, 31-hydroxybuxatrienone (56), macowanioxazine (57), 16α-hydroxyma- cowanitriene (58), macowanitriene (59), and macowamine (60), along with two known Buxus bases, Nb-demethylpapillotrienine (61) and moenjodaramine (62). Compounds 56, 57, and 61 exhibited different level of AChE inhibitory activities with compound 56 being significantly active (IC50 = 8.0 μM).

Glycyrrhetinic acid (71) was incubated with Curvularia lunata (ATCC 12017) for ten days to afford one metabolite which was characterized by NMR spectral data as known biotransformed product, 3-oxo-glycyrrhetinic acid (85). This metabolite was previously obtained through biotransformation of 71 by using other fungi.