Densitometric HPTLC quantification of 2-azaanthraquinone isolated from<i>Mitracarpus scaber</i>and antimicrobial activity against<i>Dermatophilus congolensis</i>

Abstract

2-Azaanthraquinone (benzo[ g ]isoquinoline) isolated from Mitracarpus scaber has been found to have in-vitro antimicrobial activity against Dermatophilus congolensis (MIC 7.5 μg mL −1 ), the causative agent of bovine dermatophilosis. To quantify this compound in Mitracarpus scaber , a new, simple and rapid high-performance thinlayer chromatographic (HPTLC) method was developed and validated for selectivity, recovery, and repeatability. Compounds were separated on silica gel 60F 254 plates with toluene-ethyl acetate-methanol, 80 + 18 + 2, as mobile phase. Detection was performed by densitometric scanning at λ = 310 nm and calibration plots showed the response was linearly dependent on concentration in the range 10–100 μg mL −1 , with good values of R2 . The method was repeatable and precise with relative standard deviations between 0.98 and 1.59% intra-day and between 3.41 and 5.56% inter-day for concentrations from 10 to 100 μg mL −1 . Limits of detection and quantification were 3 and 6 μg mL −1 , respectively (corresponding to 15 and 30 ng, respectively, on the plate). Concentrations of azaanthraquinone were found to be 0.009% in Mitracarpus scaber aerial parts, 0.057% in the alcoholic extract, and 1.95% in the alkaloid extract. Azaanthraquinone may explain the antimicrobial activity of this last extract and part of the effect of the alcoholic extract.