4-Hydroxy-2-pyrrolidinone25747-41-5100 % similar 4-Phenyl-2-pyrrolidinone1198-97-641 % similar 2,5-Diketopiperazine106-57-035 % similar Isovalerylglycine16284-60-932 % similar 2-Azetidinone930-21-232 % similar Piperazinone5625-67-231 % similar