Antimycobacterial agents

Compounds represented by the formula [1] ##STR1## R.sub.1 is H or a substituent; R.sub.2 and R.sub.3 are C.sub.1 -C.sub.3 alkyl; R.sub.4 is siderophore group e.g. CH.sub.3 --(CH.sub.2).sub.n --C(O)--N(OH)--(CH.sub.2).sub.m -- with n=10-22, m=2-6; X is O, S, or NH; X.sub.1 is O or NH; Y is H or alkyl; Z is H or substituted amino, e.g., t-BocNH or CbzNH, and r is 2-4; are useful in the method provided for treating tuberculosis. [1] is prepared by coupling [7], wherein HX.sub.1 is HO-- or H.sub.2 N--, ##STR2## with [4] obtained as the free acid after saponification of the methyl ester.