Anti microbial activity of Murraya koenigii alkaloids

Primary screening of a methylene chloride extract of Murraya koenigii twigs showed good activity against both methicillin-resistant Staphylococcus aureus (MRSA), and methicillin-sensitive S. aureus (MSSA), and Cryptococcus neoformans. Activity-guided fractionation of this extract led to the identification of two closely related carbazol alkaloids, mahanine (1) and isomahanine (2), which had previously been isolated from the same source. The major compound, mahanine, showed potent antibacterial activity against MRSA and MSSA (IC₅₀ 0.69 and 0.78 µg/mL, respectively) and antifungal activity (IC₅₀ 0.46 µg/mL) against Cryptococcus neoformans. The minor compound, isomahanine, also showed comparable activities against the above strains. Several analogs of mahanine were prepared and tested for their activities. Structure activity relationships showed that the free -NH and -OH groups, and the unsaturation sites in the pyran ring and the side chain were required for the antimicrobial activities.

Fig. 1