1,3-Dipolar cycloaddition of C-aryl-N-phenylnitrones to (R)-1-(1-phenylethyl)-3-[(E)-arylmethylidene]tetrahydro-4(1H)-pyridinones: synthesis and antimycobacterial evaluation of enantiomerically pure spiroisoxazolidines.

A series of novel enantiomerically pure spiroisoxazolidines were synthesized regioselectively by the 1,3-dipolar cycloaddition of C-aryl-N-phenylnitrones to (R)-1-(1-phenylethyl)-3-[(E)-arylmethylidene]-tetrahydro-4(1H)-pyridinones. These compounds have been screened for their in vitro activity against Mycobacterium tuberculosis H37Rv (MTB) using agar dilution method. Among the twenty two compounds screened, (3S,4S,5R)-3,4-di(4-methylphenyl)-2-phenyl-7-[(R)-1-phenylethyl]-1-oxa-2,7-diazaspiro[4.5]decan-10-one (3e) was found to possess the maximum activity with MIC of 3.02 microM, being 2.5 times more potent than the first-line anti-TB drug ethambutol. For comparison, a series of ten enantiomerically pure spirooxazolines were also screened, among which (4R,5S)-3,4-bis(4-chlorophenyl)-7-[(R)-1-phenylethyl]-1-oxa-2,7-diazaspiro[4.5]dec-2-en-10-one and (4R,5S)-4-(2-chlorophenyl)-3-(4-chlorophenyl)-7-[(R)-1-phenylethyl]-1-oxa-2,7-diazaspiro[4.5]dec-2-en-10-one were found to display maximum activity with MIC of 3.25 microM.