1. Department of Microbiology, Fukushima Medical College, Hikarigaoka 1, Fukushima 960-12, Japan
2. Rega Institute for Medical Research, Katholieke Universiteit Leuven, Minderbroedersstraat 10, B-3000 Leuven, Belgium
3. Department of Medicinal Chemistry and Pharmacognosy (M/C 781), College of Pharmacy, University of Illinois at Chicago, Box 6998, Chicago, IL, 60680, USA