Benzofuro[3,2-f]benzopyrans: a new class of antitubercular agents.
Alkylation of 2-hydroxydibenzofuran with 3-chloro-3-methyl-1-butyne, followed by Claisen rearrangement, gave access to 3,3-dimethyl-3Hbenzofuro[3,2-f]-benzopyran. Several derivatives modified at the pyran 1,2-double bond were prepared, including the corresponding dihydro compound and (+/-)-cis-diol, which was converted into diacetate and cyclic carbonate upon acylation. Both 3,3-dimethyl-3Hbenzofuro[3,2-f]benzopyran and 1,2-dihydro-3,3-dimethyl-3Hbenzofuro[3,2-f]benzopyran displayed significant activities when tested against Mycobacterium tuberculosis H37Rv and Beijing strains, with MIC99 in the range of 1-10 microg/ml. Further biological studies demonstrated good activities against drug-resistant mycobacterial strains. These compounds appear as promising specific antitubercular agents, since they exhibited neither significant cytotoxicity against mammal cells, nor effect on the growth of various bacteria and fungi.