Carbonic anhydrase activators: synthesis of high affinity isozymes I, II and IV activators, derivatives of 4-(arylsulfonylureido-amino acyl)ethyl-1H-imidazole.

Based on the X-ray crystallographic structure of the adduct of human carbonic anhydrase II (hCA II) with the weak activator histamine (Briganti, F., Mangani, S., Orioli, P., Scozzafava, A., Vernaglione, G. and Supuran, C.T. (1997) Biochemistry, 36, 10,384-10,392), a novel class of tight-binding CA activators was designed by using histamine (Hst) as lead molecule. Thus, N-1-tritylsulfenyl Hst was synthesized by reaction of Hst with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aliphatic amino group. Reaction of the key intermediate with 4-fluorophenylsulfonylureido amino acids (fpu-AA) or 2-toluenesulfonylureido amino acids (ots-AA) in the presence of carbodiimides, afforded after deprotection, a series of compounds with the general formula fpu/ots-AA-Hst (fpu = 4-FC6H4SO2NHCO; ots = 2-MeC6H4SO2NHCO). Some structurally related dipeptides with the general formula fpu/ots-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties), were also prepared, by a strategy similar to that used for the simple amino acyl compounds above. The new derivatives proved to be efficient in vitro activators of three CA isozymes. Best activity was shown against hCA I and bCA IV, for which some of the new compounds (such as the Lys, Arg, His or the dipeptide derivatives) showed affinities in the 2-12 nm range (h = human; b = bovine isozymes). hCA II was on the other hand somehow less prone to activation by the new derivatives, which possessed affinities around 30-60 nM for this isozyme. Ex vivo experiments showed some of the new activators to strongly enhance red cell CA activity (180-230%) after incubation with human erythrocytes. This new class of CA activators might lead to the development of drugs/diagnostic tools for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.