Potential inhibitors of collagen biosynthesis. 5,5-Difluoro-DL-lysine and 5,5-dimethyl-DL-lysine and their activation by lysyl-tRNA ligase.

The synthesis of lysine analogues wherein blocking groups are substituted at position 5, the site of hydroxylation by peptidyl lysine hydroxylase, is described. Thus, 5,5-difluorolysine (1) and 5,5-dimethylysine (2) were synthesized via a four- and six-step sequence, respectively, starting from ketone precursors. The propensity for these lysine analogues to be incorporated into procollagen protein in vivo was assessed by their ability to stimulate the lysine-dependent ATP-PPi exchange reaction in the presence of lysyl-tRNA ligase in vitro. The difluoro analogue 1 stimulated exchange, but at a Km (1.3 X 10(-3) M) 1000 times greater than that for lysine itself. The dimethyl analogue 2 did not stimulate exchange, but at high concentrations was a competitive inhibitor of lysine, with an apparent Ki of 1.6 X 10(-2) M. Thus, electronegative and/or bulky substituents at the 5 position of lysine cannot be tolerated by lysyl-tRNA ligase, and this position must be kept free in lysine analogues specifically designed to block collagen biosynthesis.