1. School of Pharmacy and Molecular Sciences, James Cook University, Townsville, Queensland 4811, Australia, Fax: +61‐7‐4781‐6078
2. Department of Chemistry, Northwestern University, 211 Sheridan Road, Evanston, IL 60208‐3113, USA
3. School of Pharmacy and Molecular Sciences, James Cook University, Townsville, Queensland 4811, Australia
4. Present address: Department of Chemistry, Monash University, Clayton, Victoria 3800, Australia