CDK inhibitors

A compound of formula:

• or a pharmaceutically acceptable salt thereof, wherein:
• each R1 is independently hydrogen, aryl, alkyl, or haloalkyl, wherein each of said alkyl and haloalkyl groups optionally includes O or N heteroatoms in place of a carbon in the chain and two R1's on adjacent ring atoms can optionally form a 3-8-membered cycle;
• and
• Rx is halo, cyano, nitro, alkyl, haloalkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, heterocyclo, aryl, heteroaryl, arylalkyl, heteroarylalkyl, cycloalkylalkyl, or heterocycloalkyl.