Scheme 1.

(a) Formamidine acetate, EtOH, reflux, ON, 78%. (b) i. P₂S₅, Pyridine, 110 °C, 2 h; ii. MeI, K₂CO₃, DMF, RT, 1 hr, 65%. (c) DBDMH, DMF, 0 °C, 2.5 h, 45%.(d) i. H₂SO₄, Acetone, RT, 2.5 hr; ii. TBAI, DIPEA, BnBr, 90 °C, 22h, 65%. (e) i. Tf₂O, Pyridine, DCM, 0 °C, 2h; ii. NaN₃, DMF, RT, 48 hr, 53%. (f) i. AcCl, MeOH, RT, ON; ii. NaH, BnBr, TBAI, DMF, 0 °C to RT, ON, 83%. (g) i. HCl, H₂O, Dioxane, 60 °C, ON; ii. PCC, DCM, RT, ON, 78%. (h) n-BuLi, THF,−78°C, 27%. (i) BF₃·OEt₂, Et₃SiH, DCM, −78°C to RT, 55%. (j) RH₂Cl, DBU, DMSO, RT. (k) Fmoc-O-methyl-l-tyrosine, EDC, HOBt, (Me)₃P, THF. (l) i. Piperidine, DMF, RT; ii. BCl₃, DCM, HPLC. Bottom left: Crystal structure of 15.^[30]