Treatment of the indolecarboxylic acid (I) with EDC in the presence of DMAP gave rise to the dimeric diketopiperazine (II). Acid cleavage of the Boc protecting group of (II) afforded the free diamine (III), which was then coupled with 4-(dimethylamino)butyric acid (IV) using EDC and DMAP to furnish the title diamide.