The invention relates to compounds of formula (I): wherein R1, R2, R3, R4, L and A are as defined in the description and claims, or pharmaceutically acceptable salts thereof having mTOR kinase inhibitor activity. The invention also relates to pharmaceutical compositions including a compound of formula (I) or a pharmaceutically acceptable salt thereof, and to the use of a compound of formula (I) or a pharmaceutically acceptable salt thereof in therapy, including in the treatment of a disease or condition for which an mTOR kinase inhibitor activity is indicated, and in particular the treatment of idiopathic pulmonary fibrosis.