1. The University of Newcastle University Drive Callaghan NSW 2308 Australia
2. Present address: Department of Medicinal Chemistry Uppsala University Box 574 75123 Uppsala Sweden
3. Present address: Chemistry, College of Science & Engineering James Cook University Townsville QLD 4814 Australia
4. Cell Signalling Unit Children's Medical Research Institute The University of Sydney 214 Hawkesbury Road Westmead NSW 2145 Australia