Scheme 9.

Synthesis of the Dap units (112 and 123). Reagents and conditions: (a) B₂H₆; (b) SO₃·Py, Et₃N, DMSO; (c) iPr₂NLi, MgBr₂, Et₂O; (d) (CH₃)₃OBF₄, proton sponge; (e) H₂, 10% Pd/C; (f) SmI₂, t-BuOH, THF, −78 °C, 5 h, 75%; (g) TBSOTf, 2,6-lutidine, DCM, 0 °C to r.t., 4 h, 88%; (h) DDQ, DCM/H₂O, 0 °C, 30 min, 68%; (i) (1) MsCl, TEA, DCM, 0 °C, 15 min; (2) t-BuOK, THF, 0 °C, 15 min, for two steps 73%; (j) TBAF, THF, 0 °C to r.t., 4 h, 61%; (k) LiHMDS, HMPA, THF, −78 °C, 30 min, and then MeOTf, −15 °C, 15 min, 95%; (l) (1) HCl/dioxane, MeOH, 0 °C, 30 min; (2) Boc₂O, TEA, DCM, r.t., 12 h, for two steps 79%; (m) Pd/C, H₂, MeOH, 5 h, 72%; (n) (1) DMP, DCM, r.t., 30 min; (2) NaH₂PO₄·2H₂O, NaClO₂, 2-methyl-2-butene/t-BuOH, r.t., 8 h, for two steps 75%.