- Structural studies on bioactive compounds. 28. Selective activity of triazenyl-substituted pyrimethamine derivatives against Pneumocystis carinii dihydrofolate reductase. Stevens, M.F., Phillip, K.S., Rathbone, D.L., O'Shea, D.M., Queener, S.F., Schwalbe, C.H., Lambert, P.A. J. Med. Chem. (1997)