New N.alpha.-Guanidinobenzoyl Derivatives of Hirudin-54-65 Containing Stabilized Carboxyl or Phosphoryl Groups on the Side Chain of Phenylalanine-63

We report on the synthesis and pharmacological properties of a new series of thrombin inhibitors derived from hirudin carboxyl-terminal fragments. Two (arylphosphono)phenylalanines, p-PO 3 H 2 -L-Phe 1 and m-PO 3 H 2 -L-Tyr, and one (carboxymethyl)phenylalanine, p-CH 2 COOH-L-Phe, were prepared and incorporated into position 63 of the modified hirudin's C-terminal dodecapeptide using the Fmoc solid-phase synthesis strategy. Substitution by any one of the residues led to very active analogs which doubled the thrombin time at low micromolar concentration (C tt2 ) in vitro (1μM< C tt2 <3μM) and potently increased the activated partial thromboplastin time (APTT) ex vivo. These compounds displayed a higher potency in vitro and a longer duration of action in vivo than both the corresponding sulfated or phosphorylated tyrosine counterparts