diketopiperazine

noun

di·​ke·​to·​pi·​per·​a·​zine (ˌ)dī-ˌkēt-ō-pī-ˈper-ə-ˌzēn 

1

: a compound C₄H₆N₂O₂ that is obtainable from two molecules of glycine by dehydration and may be regarded as a cyclic dipeptide

2

: any of various cyclic compounds formed similarly to diketopiperazine from alpha-amino acids other than glycine or obtained by partial hydrolysis of proteins