1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid (Tic) is a phenylalanine analogue in which the dihedral angle χ is limited to a very small range because of its bicyclic nature. 1 In connection with the design of topographically constrained peptides Tic has been utilized in several instances as a replacement of phenylalanine or tyrosine. 2 Moreover, the tetrahydroisoquinoline unit is an important structural element in several important alkaloids and other medicinally ...