(1'R,6R,6aR,7R,13S,14S,16R)-3',4',6,6a,7,13,14,16-octahydro-5,6',8,14-tetrahydroxy-7',9-dimethoxy-4,10,23-trimethyl-Spiro[6,16-(epithiopropanoxymethano)-7,13-imino-12H-1,3-dioxolo[7,8]isoquino[3,2-b][3]benzazocine-20,1'(2'H)-isoquinolin]-19-one,Trabectedin Impurity