Scheme 3. Conditions: (a) methyl 4-iodobutyrate, DIPEA, MeCN, 70 °C, 6.5 h, 98%; (b) NaOH, MeOH, 2 d, 57%; c) ethanolamine, PyBOP, DIPEA, DMF, 30 min, 93%; (d) Ms₂O, NEt₃, CH₂Cl₂, 0 °C, 30 min then NaN₃, DMSO, 70 °C, 2 h, 56%; (e), 5 M HCl, 20 min, 94%; (f) 2-((Z)-2-bromocyclooct-2-enyloxy) ethylamine, PyBOP, DIPEA, DMF, 30 min, 80%; (g) 5 M HCl, 6 min, 75%; (h) NaH, 1:1 DMF–THF, 30 min, 95%; (i) MeI, 3:1 MeCN–H₂O, 15: 88%, 16: 86%.