The Chemical Abstracts Service Chemical Registry System. III. Stereochemistry

GMA: A Generic Match Algorithm for Structural Homomorphism, Isomorphism, and Maximal Common Substructure Match and Its Applications

“…The structural match problem is a well-known example of an NP-complete problem. , Since the 1970s, a number of algorithms have been proposed and implemented. These algorithms have been reviewed by monographs and papers. − Traditionally, MCSSM − and other structure perception algorithms, such as smallest set of the smallest rings algorithm (SSSRA), − Cahn−Ingold−Prelog priority detection algorithm (CIP algorithm), chiral center detection algorithm (CCDA), Z−E configuration identification algorithm (ZECIA), and tautomer detection algorithm (TDA) − are studied separately and cost many man-years of effort. The structural match algorithms can be classified into three types: 7…”

The InChI Code

“…Not included are polymers, molecular class representations (Markush structures), electronic states and conformations. Also, the present version only considers traditional organic stereochemistry (double bond -sp 2 and tetrahedral -sp 3 ) and the most common forms of H-migration (tautomerism). However, the layered structure of the InChI allows future refinements with little or no change to the layers described here.…”

“…Search for "/r" in S. If "/r" is found then copy preceding "/r" substring to P [1] and the following "/r" string to P [2] else copy S to P[1] (P [1] represents the whole identifier or an identifier of a disconnected structure; P [2] if not empty represents an identifier of a "reconnected" structure". )…”

“…The Identifier is created from the input structure in three steps: 1) normalization (removing information not needed for layer construction and separating information into layers); 2 2) canonicalization (generating a set of atom labels that do not depend on how the structure was initially drawn);…”

Tautomerism in chemical information management systems

“…Common ones are the Chemical Abstracts Service (CAS) connection table used in the REGISTRY system [3][4][5][6][7][8][9][10][11][12][13][14][15]; molfile, SDfile and other file standards developed by MDL, now Symyx [16,17]; the International Union of Pure and Applied Chemistry (IU-PAC) International Chemical Identifier, InChI [18]; and SMILES, developed by Daylight Chemical Information Systems [19,20].…”