1,2,4-Benzothiadiazine derivatives as alpha(1) and 5-HT1A receptor ligands

A series of new 1,2,4-benzothiadiazine derivatives with an arylpiperazine mojety linked at position 3 of the heterocyclic ring were synthesized and assessed for their pharmacological profiles at alpha(1)-adrenoceptor subtypes (alpha(1A), alpha(1B) and alpha(1D)) by functional experiments and by in vitro binding studies at human cloned 5-HT1A receptor. Compound I was identified as a novel (alpha(1D) antagonist (pK(b)alpha(1D) = 7.59; alpha(1D)/alpha(1A) > 389; alpha(1D)/alpha(1B) = 135) with high selectivity over 5-HT1A receptor (5-HT1A/alpha(1D) < 0.01), while compound 6, a 3,4-dihydro-derivative, was characterized as a novel 5-HT1A receptor ligand, highly selective over alpha(1D)-adrenoceptor subtype (pK(i)5-HT1A = 8.04; 5-HT1A/alpha(1D) = 1096). Further pharmacological studies demonstrated that 6 is a partial agonist at 5-HT1A receptor (E-max = 23, pD(2) = 6.92).