cyclo[-Val(1)-Pro(2)-Pro(3)-Ala(4)-Phe(5)-Phe(6)-Pro(7)-Pro(8)-Phe(9)-Phe(10)-], (3s)-3-isopropylpiperazine-2,5-dione, (S)-3-isopropylpiperazine-2,5-dione, (3S)-isopropylpiperazine-2,5-dione, cyclo-(Val-Pro-Pro-Ala-Phe-Phe-Phr-Pro-Phe-Phe), cyclo(Val-Gly), (2S)-isopropyl-2,5-diketopiperazine, cyclo-(L-alanyl->-L-phenylalanyl->-L-phenylalanyl->-L-prolyl->-L-prolyl->-L-phenylalanyl->-L-phenylalanyl->-L-valyl->-L-prolyl->-L-prolyl), cyclo[Val-Pro-Pro-Ala-Phe-Phe-Pro-Pro-Phe-Phe], [U-13C]antamanide, (2S)-isopropylpiperazine-3,6-dione, (S)-3-(1-methylethyl)piperazine-2,5-dione, (S)-3-Isopropyl-2,5-piperazinedione, cyclo-[Gly-(L)-Val]