Antibacterial activity of diospyrin, isodiospyrin and bisisodiospyrin from the root of Diospyros piscatoria (Gurke) (Ebenaceae)

Two dimeric naphthoquinones, diospyrin and isodiospyrin, isolated from the root of Diospyros piscatoria (Gurke), a common ingredient in several folk medicines, have been shown to have a broad spectrum of Antibacterial activity. The minimum inhibitory concentrations (MICs) of diospyrin against Streptococcus pyogenes ATCC 12344 and Streptococcus pneumoniae ATCC 33400 ranged from 1.56 to 50 microg/mL. While those against Salmonella choleraesuis serotype typhi (S. typhi), ATCC 6539 and Mycobacterium chelonae ATCC 19977 were between 25 and 100 microg/mL. Isodiospyrin was more active than its racemic isomer diospyrin. The MICs against Gram-positive bacteria ranged from 0.78 to 50 microg/mL. While those against Pseudomonas aeruginosa ATCC 15443 and S. typhi ranged from 50 to 100 microg/mL. The MIC for M. chelonae was between 6.25 and 25 microg/mL. MICs were found to increase with the concentration of cells used for the inoculum. The MICs for Bacillus subtilis ATCC 6633 increased up to the highest concentration of cells tested. The same phenomenon was observed on M. chelonae, but with better effect in the latter. The kinetics of bacteria studies against both B. subtilis and M. chelonae increases with increasing concentration of isodiospyrin tested. Two tetrameric forms of plumbagin were isolated. The naphthoquinone bisisodiospyrin, gave MIC values between 300 and 400 micro g/mL. The second, as yet unidentified tetramer, was not active at 500 micro g/mL.