(S)-4-tert-butoxycarbonyl-1-(2,4-dimethoxybenzyl)-5-(2-hydroxyethyl)-2-piperazinone

1(R),5(S)-8-[1-(4-cyano-3-fluorobenzyl)-5-imidazolylmethyl]-3,8-diaza-2-oxobicyclo[3.2.1]octane

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

1(R),5(S)-8-tert-butoxycarbonyl-3-(2,4-dimethoxybenzyl)-3,8-diaza-2-oxobicyclo[3.2.1]octane

6-allyl-2-benzyl-4-(2,4-dimethoxy-benzyl)-3-oxo-piperazine-1-carboxylic acid tert-butyl ester