A compound, or a pharmaceutically acceptable salt thereof, having a structure of: ##STR00001##
wherein L is a cleavable linker group;
X is a cargo moiety-containing group; and
R.sup.1 and R.sup.2 are each independently hydrogen, alkyl, or substituted alkyl; or R.sup.1 and R.sup.2 together form a boronic ester ring or a substituted boronic ester group.

A compound is provided, comprising: an Fe(III)-binding or an Fe(III)-bound siderophore; one or more optional linker covalently bound to the siderophore; a drug; and an Fe(III) to Fe(II) reduction triggered linker bound to the drug and the linker or, if no linker is present, then bound to the drug and the siderophore. Compositions and methods including the compound are also provided.

A compound, or a pharmaceutically acceptable salt thereof, having a structure of:

##STR00001##

wherein L is a cleavable linker group;
X is a cargo moiety-containing group; and
R.sup.1 and R.sup.2 are each independently hydrogen, alkyl, or substituted alkyl; or R.sup.1 and R.sup.2 together form a boronic ester ring or a substituted boronic ester group.