A chemical view of analogue drug laws in Australia: what is structural similarity?

Abstract

After specific rules establishing whether a molecule is a ‘structural modification’ of a drug molecule, the analogue drug provisions in the various Acts legislated by States and the Commonwealth of Australia rely on rules that determine if a putative drug is ‘structurally similar’ to a dangerous or controlled drug listed by the Act. In some legislation there is a provision for a suitable expert to assert that the two structures are similar. A survey of more than 200 research chemists at UNSW Australia, who are not usually involved in legal matters, asked them to state whether six pairs of molecules were structurally similar or not. There is some correlation with Tanimoto similarity, a measure of similarity often used in pharmaceutical drug discovery, but the use of such an objective measure is not advocated at this time. The concepts of addition of groups, and of replacement of ring structures are discussed in the light of cases and of chemical and general definitions. Regularising the law with chemical understanding and practice is strongly recommended. As similar laws have been enacted in other countries, the conclusions reached here will have interest in jurisdictions outside Australia.