pK(a) determination of angiotensin II receptor antagonists (ARA II) by spectrofluorimetry

The acid-base equilibrium constants of a new family of antihypertensive dru gs, the angiotensin II receptor antagonists (ARA II), Losartan, Irbesartan, Valsartan, Candesartan cilexetil, its metabolite Candesartan M1 and Telmis artan were determined by spectrofluorimetry. Relative fluorescent intensity (I-F,I-rel)-pH data were treated by graphical (derivatives and curve-fitti ng) and numerical methods (LETAGROP SPEFO). The resultant pk,, values at an ionic strength of 0.5 M were (3.15 +/- 0.07) for Losartan, (4.70 +/- 0.06) for Irbesartan, (4.90 +/- 0.09) for Valsartan, (6.0 +/- 0.1) for Candesart an cilexetil, (3.9 +/- 0.1) for Candesartan M1, and (4.45 +/- 0.09) for Tel misartan. (C) 2001 Elsevier Science B.V. All rights reserved.