Text this: Synthesis and Biological Evaluation of (<i>S</i>)-2-(Substituted arylmethyl)-1-oxo-1,2,3,4-tetrahydropyrazino[1,2-<i>a</i>]indole-3-carboxamide Analogs and Their Synergistic Effect against PTEN-Deficient MDA-MB-468 Cells