pKa error??? for sulfamethoxazole

Hello,

I am predicting pka values for several pharmaceutical compounds using MarvinView 5.9.2.  The program predicts that sulfamethoxazole has a pKa around pH 7.7--however, several reports in the literature list its pKa around 5.8.  Can anybody help me reconcile the difference between MarvinView's prediction and literature values?  To be honest, the results from my sorption experiments support the pKa being at 7.7.

Thanks in advance,

Jon Farrell

In case it helps, here is how I am coming sulfamethoxazole pKa 7.7 values in MarvinView:

1.  Open MarvinView 5.9.2

2.  Paste Sulfamethoxazole SMILES into the window (e.g. Nc1ccc(cc1)S(=O)(=O)Nc1noc(C)c1)

3.  Click on Tools/Protonation/pKa

Hi,

Thank you for reporting this bug.

The pKa value of sulfamethoxazole is in the range of [ 5.8 - 6.2]  in the literature. I have modified our pKa calculator accirding to this experimental data.The fixed version will be available asap.

 

Jozsi