The present invention relates to compounds of Formula (I)or salts thereof wherein R1, R2, R3, R4, R5, R6, and other variables enumerated under one or more of same are as defined herein. Compounds of Formula I have activity as antimicrobial agents. Also disclosed are pharmaceutical compositions and methods of treating and preventing microbial infections in mammals, for example, a tuberculosis or leprosy infection, which employ compounds of Formula (I) or salts thereof.