Scheme 1.

Preparation of TC-1-2, FTC-1-2 and TD-1a-1m. Reagents and conditions: (i) Boc-L-phenylalanine or Boc-3,5-difluoro-L-phenylalanine, HATU, DIEA, dichloromethane, 0 °C to r.t.; (ii) trifluoroacetic acid, dichloromethane, r.t.; (iii) bromoacetic acid, HATU, DIEA, dichloromethane, 0 °C to r.t.; (iv) tert-butyl (2-oxo-1,2-dihydropyridin-4-yl)carbamate, NaH, THF, 0 °C to r.t.; (v) trifluoroacetic acid, dichloromethane, r.t.; (vi) substituted benzoyl chloride, TEA, DCM, 0 °C to r.t.: (vii) H₂, Pd/C, DCM.