Dimeric 3-Vinylindoles as Potential Antitumor Active Compounds: 1,1,3,4-Tetramethyl-3-(1-methyl-1H-indol-3-yl)-1,2,3,4-tetrahydrocyclopenta[b]indole and 1,1,3-Trimethyl-4-phenylsulfonyl-3-(1-phenylsulfonyl-1H-indol-3-yl)-1,2,3,4-tetrahydrocyclopenta[b]indole |