Consistent with the agar diffusion method, the results from BDS showed that fatty alcohols with carbon number

7–10 possess considerable antimycobacterial activity, and among which decanol is the most potent candidate with an MIC of 0.4 mM (Table 1). In addition, results from BDS also showed GSK126 no or very little antimycobacterial activity for long-chain fatty alcohols with an aliphatic carbon chain containing fewer than seven and more than 11 carbon atoms. To establish the relationship between the lipophilicity of the alkanols and their antimycobacterial activity we plotted MIC values against the corresponding log P (water/octanol partition coefficient) value (Table 1). The result revealed a marked reduction of MIC for alkanols with an increase in lipophilicity up to decanol. A further increase in carbon number resulted in a very sharp increase in MIC (Fig. 1b), with no toxicity with 1-dodecanol and 1-tridecanol. It appears that these alcohols with high lipophilicity should be taken up preferentially by the membrane, but possibly due to their poor partition coefficient from water to the membrane (PM/W) (De Bont Jan, 1998) they failed to reach higher membrane concentration, thereby resulting

in low toxicity. On the other hand, smaller alkanols did not show higher toxicity as expected from their high PM/W. The reason of this disparity may lie in the fact that partitioning into the membrane does not depend solely on the value of the PM/W coefficient, but also on the cell-wall composition of the organism. In our case it could be the unique cell-wall composition of the mycobacteria that did not allow smaller GSK-3 inhibitor alkanols to accumulate in the membrane at a toxic concentration. Therefore, Avelestat (AZD9668) both the partition coefficient of the alkanol between water and membrane and the cell-wall composition of a particular organism will determine the extent of accumulation of the agent in the membrane and thus determine toxicity. Naturally available alcohols often occur with unsaturations at different positions of the alkanol chains. To verify if

unsaturation has any influence on antimycobacterial activity, we used decanol as it showed maximum activity against mycobacteria and compared its activity with its alkene and alkene-1-ol counterparts, i.e. 1-decene and 9-decene-1-ol. The results showed that 9-decene-1-ol has greater activity than decanol and 1-decene has no activity against both M. smegmatis and M. tuberculosis (Table 2). These data are also true for other alcohols with moderate antimycobacterial activity; for example, hexene-1-ol exhibits greater activity than hexanol and hexene shows no activity (Table 2). These results suggest that a long-chain aliphatic hydrocarbon and a hydrocarbon with only a terminal double bond were completely inactive against mycobacteria. However, the presence of a terminal double bond along with a hydroxyl group provided greater activity against mycobacteria.