Structure−Activity Relationship of 3-Substituted N-(Pyridinylacetyl)-4- (8-chloro-5,6-dihydro-11H-benzo5,6cyclohepta1,2-bpyridin-11-ylidene)- piperidine Inhibitors of Farnesyl-Protein Transferase: Design and Synthesis of in Vivo Active Antitumor Compounds