Scheme 1.

Synthesis of Fmoc-cystathionine isomer 11.^a

^a Reagents and conditions: a) 70% HClO₄, ^tBuOAc; b) Fmoc-OSu, N-methylmorpholine, THF, 62% (two steps); c) PBu₃, H₂O, THF, 86%; d) Alloc-Cl, Na₂CO₃, H₂O, CH₃CN; e) allyl bromide, NaHCO₃, DMF, 77% (two steps); f) PPh₃, CBr₄, CH₂Cl₂, 80%; g) Bu₄NBr, NaHCO₃, H₂O, EtOAc, 84%; h) CF₃CO₂H, PhSiH₃, CH₂Cl₂, 95%.