p. 3281 - 3287
(2007/10/03)(S)-N,N'-bis(p-methoxybenzyl)-3-methylene-6-isopropylpiperazine-2,5-dione
(3S)-N,N'-bis-(p-methoxybenzyl)-3-isopropyl-piperazine-2,5-dione
(3S,6S)-N,N'-bis(4-methoxybenzyl)-3-isopropyl-6-(cyclohexylmethyl)piperazine-2,5-dione