pKa Values of the Opened Form of a Thieno-1,2,4-triazolo-1,4-diazepine in Water

Abstract

The pK _a values of the freely water-soluble opened form of a thieno-1,2,4-triazolo-1,4-diazepine, namely 2-(3-amino- methyl-5-methyl-1,2,4-triazolo)-3-(2-chlorobenzoyl)- [2,3-c]thienopiperidine, were determined. pH measurements were made in the range 1 < pH < 10. Two of the three pK _a values found in this range significantly overlapped; they quantify the ionization of both the aminomethyl residue and the piperidino moiety of the molecule. The third corresponds exclusively to the ionization of the triazolo nucleus. The pK _a value of the thienophenone was obtained by UV spectrophotometry using acidity functions. All results were extracted from experimental data by a curve-fitting method.