1. Institute of Pharmaceutical Chemistry, Albert Szent‐Gyögyi Medical University, P.O. Box 121, H‐6701 Szeged, Hungary
2. Chemical Department, Pedagogical Training College, H‐6720 Szeged, Hungary
3. H‐6720 Szeged, Hungary Spectroscopic Department, EGIS Pharmaceuticals, P.O. Box 100, H‐1475 Budapest, Hungary
4. Central Research Institute for Chemistry, Hungarian Academy of Sciences, P.O. Box 17, H‐1525 Budapest, Hungary