2,5-Piperazinedione, 3-(hydroxymethyl)-6-((4-hydroxyphenyl)methyl)-, (3S-cis)- 21754-31-4 Cyclo(D-seryl-L-tyrosyl) Cyclo(L-seryl-L-tyrosyl) Cyclo(ser-tyr) Cyclo(seryltyrosyl)