A ready entry to substituted derivatives of pyrido[3″,2″:4′,5′]thieno[2′,3′:5,6]pyrido[2,3-d]-pyrimidines, a new tetraheterocyclic ring system

1. Peinador, C.
2. Veiga, M.C.
3. Ojea, V.
4. Quintela, J.M.