Development and Binding Mode Assessment of N-[4-[2-propyn-1-yl[(6S)-4,6,7,8-tetrahydro-2-(hydroxymethyl)-4-oxo-3H-cyclopenta[g]quinazolin-6-yl]amino]benzoyl]-l-γ-glutamyl-D-glutamic Acid (BGC 945), a Novel Thymidylate Synthase Inhibitor That Targets Tumor Cells.