Abstract: Compounds of formula (I), pharmaceutically acceptable salts or in vivo hydrolysable esters thereof, wherein: Ring X is phenyl or a six membered heteroaryl ring containing one or two ring nitrogens where said nitrogens are optionally oxidised to form the N-oxide; R1 and R2 are substituents as defined within; R3 and R4 are defined within and are alkyl or halo alkyl or together form a halocycloalkyl ring; R5 is a substituent as defined within; Y—Z is a linking group as defined within; are useful in the production of a elevation of PDH activity in a warm-blooded animal such as a human being. Pharmaceutical compositions, methods and processes for preparation of compounds of formula (I) are described.