A compound of Formula I or a pharmaceutically acceptable salt thereof, wherein: X is S, CH 2, or a bond; Y is a bond, an aryl, or a heteroaryl which is unsubstituted or substituted; Z is a bond or selected from the groups consisting of C 1-8 alkylene, NR a, C C 1 - 8 alkylene, C 1-8 alkyleneNRa, C 1-6 alkylenearyleneC 1-6 alkylene, C 2-8 alkenylene, C 1 - 6 alkylenearylene, C 1-6 alkyleneheteroarylene, C 2-6 alkenylenearyleneC 1-6 alkylene; any one of these groups being unsubstituted or substituted with one or more Ra; M is selected from -NHOH, CH 2 SH, or wherein is wherein is selected from the following heterocyclic moieties: R a and R b are independently selected from hydrogen, aliphatic, alicyclic, heteroaliphatic, heterocyclic, aromatic, heteroaromatic, aryl, heteroaryl, alkylaryl, heteroalkylaryl, alkylheteroaryl, heteroalkylheteroaryl, alkoxy, aryloxy, heteroalkoxy, heteroaryloxy, alkylthio, arylthio, heteroalkylthio, heteroarylthio, F, Cl, Br, I, -OH, -NO 2, -CN, -CF 3, -CH 2 CF 3, -CHCl 2, -CH 2 OH, -CH 2 CH 2 OH, - CH 2 NH 2, -CH 2 SO 2 CH 3, -C R x, -CO 2 (R x), -CON(R X) 2,-OC R x, -OCO 2 R x, - OCON(R x) 2, -N(R X) 2, -SF 5, -S R x, -S 2 R x, -NR x R x, wherein each occurrence of R x independently includes aliphatic, alicyclic, heteroaliphatic, heterocyclic, aromatic, heteroaromatic, aryl, heteroaryl, alkylaryl, alkylheteroaryl, heteroalkylaryl or heteroalkylheteroaryl, wherein any one of the aliphatic, alicyclic, heteroaliphatic, heterocyclic, alkylaryl, or alkylheteroaryl substituents are substituted or unsubstituted, branched or unbranched, saturated or unsaturated, and wherein any one of the aromatic, heteroaromatic, aryl, heteroaryl, -(alkyl)aryl or -(alkyl)heteroaryl substituents are substituted or unsubstituted; wherein two adjacent R a or R a and R b can form a 5- to 7-membered carbocyclic ring or a 5- to 7-membered heterocyclic ring in which one or two carbon atoms are replaced by one or two S, O or NR c; wherein R c is selected from hydrogen, C 1 -C 6 alkyl, C 1 -C 6 cycloalkyl, SO 2 R e, C R e; wherein R e is C 1 -C 6 alkyl, C 1 -C 6 cycloalkyl, aryl, heterocycle, heteroaryl. X is S, CH 2, or a bond; Y is a bond, an aryl, or a heteroaryl which is unsubstituted or substituted; Z is a bond or selected from the groups consisting of C 1-8 alkylene, NR a, C C 1 - 8 alkylene, C 1-8 alkyleneNRa, C 1-6 alkylenearyleneC 1-6 alkylene, C 2-8 alkenylene, C 1 - 6 alkylenearylene, C 1-6 alkyleneheteroarylene, C 2-6 alkenylenearyleneC 1-6 alkylene; any one of these groups being unsubstituted or substituted with one or more Ra; M is selected from -NHOH, CH 2 SH, or wherein is wherein is selected from the following heterocyclic moieties: R a and R b are independently selected from hydrogen, aliphatic, alicyclic, heteroaliphatic, heterocyclic, aromatic, heteroaromatic, aryl, heteroaryl, alkylaryl, heteroalkylaryl, alkylheteroaryl, heteroalkylheteroaryl, alkoxy, aryloxy, heteroalkoxy, heteroaryloxy, alkylthio, arylthio, heteroalkylthio, heteroarylthio, F, Cl, Br, I, -OH, -NO 2, -CN, -CF 3, -CH 2 CF 3, -CHCl 2, -CH 2 OH, -CH 2 CH 2 OH, - CH 2 NH 2, -CH 2 SO 2 CH 3, -C R x, -CO 2 (R x), -CON(R X) 2,-OC R x, -OCO 2 R x, - OCON(R x) 2, -N(R X) 2, -SF 5, -S R x, -S 2 R x, -NR x R x, wherein each occurrence of R x independently includes aliphatic, alicyclic, heteroaliphatic, heterocyclic, aromatic, heteroaromatic, aryl, heteroaryl, alkylaryl, alkylheteroaryl, heteroalkylaryl or heteroalkylheteroaryl, wherein any one of the aliphatic, alicyclic, heteroaliphatic, heterocyclic, alkylaryl, or alkylheteroaryl substituents are substituted or unsubstituted, branched or unbranched, saturated or unsaturated, and wherein any one of the aromatic, heteroaromatic, aryl, heteroaryl, -(alkyl)aryl or -(alkyl)heteroaryl substituents are substituted or unsubstituted; wherein two adjacent R a or R a and R b can form a 5- to 7-membered carbocyclic ring or a 5- to 7-membered heterocyclic ring in which one or two carbon atoms are replaced by one or two S, O or NR c; wherein R c is selected from hydrogen, C 1 -C 6 alkyl, C 1 -C 6 cycloalkyl, SO 2 R e, C R e; wherein R e is C 1 -C 6 alkyl, C 1 -C 6 cycloalkyl, aryl, heterocycle, heteroaryl.