Scheme 7. Synthesis of Nitrile- and Alkyne-Based Dipeptide Alkynes 56a–f and 62, respectively.

Reagents and conditions: (a) propargylamine or aminoacetonitrile (in THF/H₂O/NaOH), iBCF, NMM, THF, −25 °C, 10 min, rt, 30 min; (b) TFA/CH₂Cl₂ (1:1), 2 h; (c) acidic chloride, TEA, CH₂Cl₂, 2 h, or carboxylic acid, DIPEA, PyBOP, THF, 2 h; procedure following¹⁰² (d) isobutyl bromide, tetrabutylammonium iodide, EtOH/3 M NaOH (1:1), 3 days; (e) Boc₂O, 1 day; (f) KMnO₄, acetic acid, 2.5 h; (g) propargylamine, iBCF, NMM, THF, −25 °C, 10 min, rt, 30 min; (h) 4-fluorobenzoyl chloride, TEA, CH₂Cl₂, 2 h.