(S)-methyl 2-(1-((tert-butoxycarbonyl)amino)ethyl)-5-methyloxazole-4-carboxylate

(S)-ethyl 3-{2-[1-(tert-butoxycarbonyl)aminoethyl]-5-methyloxazol-4-yl}-3-oxopropanoate

(S)-ethyl 3-amino-{2-[1-(tert-butoxycarbonyl)aminoethyl]-5-methyloxazol-4-yl}propenoate