(S)-(E)-1-tert-butyl-[bis(2-tert-butoxycarbonyl)amino]-7-oxohept-5-enoate

(S)-(E)-1-tert-butyl-[bis(2-tert-butoxycarbonyl)amino]-7-hydroxyhept-5-eneoate

tert-butyl (2S)-[bis(tert-butoxycarbonyl)amino]-(6R)-[(benzyloxycarbonyl)amino]-7-(methoxycarbonyl)heptanoate

tert-butyl (S)-2-di(tert-butoxycarbonyl)amino-4-(4-hydroxy[1,2,5]thiadiazol-3-yl)butyrate

tert-butyl (2S,5RS)-5-amino-2-di(tert-butoxycarbonyl)amino-5-carbamoylpentanoate