o or 17 wherein x is a bond or c 1 4 alkylene and r 17 is selected from hydrogen and c 1 6 alkyl r 15 and r 16 are independently selected from u2014 r 18 and u2014 yr 18 wherein y is a selected from c 1 6 alkylene c 2 6 alkenylene u2014 c o nr 17 u2014 and u2014 ox u2014 x is a bond or c 1 4 alkylene r 17 is selected from hydrogen and c 1 6 alkyl and r 18 is selected from c 6 10 aryl c 3 12 cycloalkyl and c 5 13 heteroaryl or r 15 and r 16 together with the atoms to which r 15 and r 16 are attached form fused bicyclic or tricyclic c 5 14 heteroaryl wherein any aryl heteroaryl and cycloalkyl of r 18 or the combination of r 15 and r 16 is optionally substituted with 1 to 3 radicals independently selected from halo nitro cyano c 1 6 alkyl c 1 6 alkoxy c 1 6 alkylthio hydroxy c 1 6 alkyl halo substituted c 1 6 alkyl halo substituted c 1 6 alkoxy c 3 12 cycloalkyl c 3 8 heterocycloalkyl c 6 10 aryl optionally substituted with c 1 6 alkoxy c 5 13 heteroaryl u2014 xs o 0 2 r 17 u2014 xs.