The present invention is directed to novel tricyclic heterocycles of structural formula I which are inhibitors of the dipeptidyl peptidase-IV enzyme and which are useful in the treatment or prevention of diseases in which the dipeptidyl peptidase-IV enzyme is involved, such as diabetes and particularly Type 2 diabetes. The invention is also directed to pharmaceutical compositions comprising these compounds and the use of these compounds and compositions in the prevention or treatment of such diseases in which the dipeptidyl peptidase-IV enzyme is involved. ILa présente invention concerne de nouveaux hétérocycles tricycliques de formule structurale I qui sont des inhibiteurs de l'enzyme dipeptidyl peptidase IV et qui sont utiles dans le traitement ou la prévention de maladies dans lesquelles est impliquée l'enzyme dipeptidyl peptidase IV, telles que le diabète et en particulier le diabète de type 2. L'invention concerne également des compositions pharmaceutiques comprenant ces composés et l'utilisation de ces composés et compositions dans la prévention ou le traitement de telles maladies dans lesquelles est impliquée l'enzyme dipeptidyl peptidase IV. I
