A compound of formula (I) wherein: Ring A is a nitrogen linked mono or bicyclic heterocyclic ring as defined within; R?1 and R2¿ are independently C¿1-3?alkyl optionally substituted by fluoro or chloro; or R?1 and R2¿ together with the carbon atom to which they are attached, form a C¿3-5?cylcoalkyl ring optionally substituted by fluoro; R?3¿ is as defined within; and n is 0-5; wherein the values of R3 may be the same or different; or a pharmaceutically acceptable salt or an in vivo hydrolysable ester thereof is described. The use of compounds of formula (I) in the production of an elevation of PDH activity in a warm-blooded animal such as a human being are also described. Pharmaceutical compositions, methods and processes for preparation of compounds of formula (I) are detailed.