A compound of the Formula I and optionally a pharmaceutically acceptable salt thereof is provided: Formula I, wherein, R is one selected from the group consisting of H and CH3; n is an integer ranging from 1 to 4; X is one selected from the group consisting of —CH2—, O, S, —NH—, —NHCHO—, —NHCOCH3—, and —NHCOCF3—; and Ar is one selected from the group consisting of (a) 1,4-phenyl, (b) 2′-fluoro-1,4-phenyl, and (c) 2,5-thienyl. Methods of treating a patient having cancer, targeting mitochondrial metabolism, and targeting SHMT2 and MTHFD2 using the compounds of this invention are disclosed.