ethyl tert-butoxycarbonylamino(toluene-4-sulfonyl)acetate

ethyl (4R)-2-(N-tert-butyloxycarbonylamino)-4,5-dihydroxy-2-pentenoa

ethyl (4R)-2-(N-tert-butyloxycarbonylamino)-5-tert-butyldimethylsiloxy-2-pentenoate

ethyl (4R)-N-tert-butyloxycarbonyl-4-tert-butyldiphenylsiloxy-α,β-didehydroprolinate

ethyl (R,Z)-2-((tert-butoxycarbonyl)amino)-4-((tert-butyldiphenylsilyl)oxy)-5-hydroxypent-2-enoate