Antimicrobial and anti tubercular activities of isolates and semi synthetic derivatives of lichen Ramalina leiodea (Nyl.) Nyl.

Abstract

The chemical investigation of lichen Ramalina leiodea (Nyl.) Nyl. yielded five known metabolites, i.e., usnic acid (1), ethyl everninate (2), scro­biculin (3), methyl 2,6-dihydroxy-4-methylbenzoate (4) and 4-[(2-hydroxy-4-methoxy-6-propylbenzoyl)oxy]-2-methoxy-6-propylbenzoic acid (5). To develop compound libraries on 4, a series of semi-synthetic derivatives was prepared (4a–e). All the metabolites and semi-synthetic ana­logues were screened for anti­microbial and anti-tubercular activities. The res­ults showed that compounds 3 and 5 were very active against antibacterial and antifungal strains, while the semi-synthetic analogues 4a–e are moderately active on all tested microbial strains. In addition, compounds 4b and 4d showed better antimycobacterial activity with MIC value of 1.6 µg mL-1, than streptomycin with an MIC of 6.25 µg mL-1 against M. tuberculosis. All the semi-synthetic analogues exhibited better anti-tubercular activity than the isolated metabolites. This is the first report on the synthesis and biological activities of these novel benzohydrazide derivatives.