N-(1-methyl-1,2,3-trihydroxy-2-cyclopentene-4-ylidene)-2-carboxy-pyrrolidinium betaine

(S)-methyl 2-((S)-1-formylpyrrolidine-2-carbonylamino)-3-phenylpropanoate

(R)-1-(tert-butoxycarbonyl)-2-(hydroxymethyl)pyrrolidine-2-carboxylic acid