(-)-(3R,4R)-5-benzyloxycarbonyl-3-(1,2-dihydroxy)-2-(4-methoxyphenyl)-2,5-diazaspiro[3.4]octan-1-one

(+)-(3R,4S)-5-benzyloxycarbonyl-3-[(R)-3-tert-butoxycarbonyl-2,2-dimethyl-1,3-oxazolidin-4-yl]-2,5-diazaspiro[3.4]octan-1-one

(2S)-2-((4R)-4-phenyl-4,5-dihydro-oxazol-2-yl)-pyrrolidine-1-carboxylic acid benzyl ester

(4R)-4-isopropyl-2-pyrrolidine-(2S)-2-yl-4,5-dihydro-oxazole

benzyl (S)-2-(4-methyl-1,4-diazepane-1-carbonothioyl)pyrrolidine-1-carboxylate