Absolute configuration of the α1B-adrenoceptor antagonist (+)-cyclazosin

Abstract (+)-Cyclazosin is a quinazoline derivative pharmacologically characterized as α 1b -adrenoceptor selective ligand in binding assays and α 1B -selective antagonist in isolated tissues. In this work, we determined the absolute configuration of (+)-cyclazosin by X-ray crystallographic analysis applied to the ( R,R )-(+)-tartrate of (–)- 2 , which is the enantiomer of the specific synthetic precursor of (+)-cyclazosin. Results indicated that (+)-cyclazosin has an R and S configuration at its C4a and C8a atoms, respectively.