The invention relates to a compound of Formula I :or pharmaceutically acceptable enantiomers, or salts thereof. The present invention also relates to the use of compounds of Formula (I) as selective inhibitors of tryptophan 2,3-dioxygenase. The invention also relates to the use of the compounds of Formula (I) for the treatment or prevention of cancer and central nervous system disease or disorder, either as a single agent or in combination with other therapies.