1	The IUPAC International Chemical Identifier Project – InChI. An Open Source/Open Access Project. Stephen Heller, Stephen Stein, & Dmitrii Tchekhovskoi Physical & Chemical Properties Division NIST Gaithersburg, MD srheller@nist.gov
2	The slides from this talk can be found at: http://www.hellers.com/steve/pub-talks/pittcon305/frame.htm
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8	Digital ‘Naming’ of Chemicals Chemical structure is the true ‘identifier’ But, structure representations are not unique or convenient for computers. So, convert structure to a unique ‘name’ by fixed algorithms The IUPAC International Chemical Identifier (InChI)
9	Two Problems Chemicals Fast isomerization (tautomerization) Ill-defined connectivity Chemists Differing conventions Depends on discipline, education and convenience Imprecision/uncertainty
10	3 Steps to InChI Chemistry ‘Normalize’ Input Structure Implement chemical rules Math ‘Canonicalize’ (label the atoms) Equivalent atoms get the same label Format ‘Serialize’ Labeled Structure Output as character string (‘name’)
11	Normalize Simplify Divide structure into ‘layers’ Each layer ‘refines’ structure Ignore ‘Electron Density’ Use simple ‘connectivity’ only Ignore bond type and electron location Stereochemistry sp² and sp³ only Free rotation around single bonds No Z/E stereo for small rings (default)
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19	InChI FAQs How can you represent chemistry without electrons? Chemistry is not represented, just identity Whole molecule properties are easily added. Do big molecules have big InChIs? Yes, just like systematic names How to handle other tautomers, substructures,..? Other software Is InChI reversible? Partly - contains only data needed for ‘naming’ Auxiliary fields can carry other information Is InChI extensible? New layers can add refinement
20	InChI Capabilities Identify compounds at the known level of detail Convention-free (mostly) Generate quickly from structure Contains all essential connectivity information Simple ASCII representation
21	Early InChI Adaptors NIH/NCBI/PubChem project – 700,000+ structures NCI Database – 250,000+ structures EPA –DSSTox database KEGG database – 9584 structures
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23	InChI FAQ’s Available from Nick Day, Cambridge University, UK: ned24@cam.ac.uk
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25	Future Future versions of InChI, for example, could include phase information and crystal structure, conformations, electronic states and additional classes of stereochemistry. First additional project: Investigate adding polymers to InChI
26	Acknowledgements Steve Bachrach, Steve Bryant, Nick Day, Rene Deplanque, Gary Mallard, Alan McNaught, Bill Milne, Peter Murray-Rust, Henry Rzepa, Peter Shepherd, and Bill Town