5(S),3(S)-3-benzyl-4-tert-butoxycarbonyl-1-(2,4-dimethoxybenzyl)-5-[2-(phenylsulfonyloxy)ethyl]-2-piperazinone

tert-butyl (S)-2-allyl-4-benzyl-5-oxopiperazine-1-carboxylate

tert-butyl (2S,6S)-4-benzyl-2-((1S,2S)-2-((tert-butoxycarbonyl)amino)-3-(3,5-difluorophenyl)-1-hydroxypropyl)-6-(2,3-dihydroxypropyl)-3-oxopiperazine-1-carboxylate

tert-butyl (6S)-6-allyl-4-benzyl-2-((1S,2S)-2-(dibenzylamino)-3-(3,5-difluorophenyl)-1-hydroxypropyl)-3-oxopiperazine-1-carboxylate

tert-butyl (2S,6S)-6-allyl-4-benzyl-2-((1S,2S)-2-((tert-butoxycarbonyl)amino)-3-(3,5-difluorophenyl)-1-hydroxypropyl)-3-oxopiperazine-1-carboxylate