Hash ring

An alternative methodology based on the ringcontent of a database, using precalculated structure-based hash codes has been proposed (110). The comparison of the hashcode tables can be used to compare two databases and the number of distinct ring-system combinations can be used as an indicator of database diversity. A method for diversity assessment called the saturation diversity approach, based on picking as many mutually dissimilar compounds as possible from a database was also proposed. The methods were used to compare a number of public databases and gave similar results. 

Imagine the ring opening of m-stilbene oxide 37 by an amine in an SN2 reaction. The product is the amino alcohol 38. Redrawing this 38a so that we have the longest chain in a zig-zag is easy by application of a GSR to the right hand portion of the molecule. Note that we have not drawn any structure with a hashed or thick line between two chiral centres. In this sequence the question of absolute stereochemistry does not arise as m-stilbene oxide 37 has a plane of symmetry and is therefore achiral. 

D. F. Ring, W. Hashed, and T. Dow. Microbial polysaccharide articles and methods of production, US Patent 465575S (April 7,1987). 

The creation of a graphical representation of a tetrahedral stereocenter poses a choice as to which substituents should receive the wedge or hash bond. Shelley found that the same atom prioritization used to avert overlap served well. When the stereo bond is assigned to the lowest priority substituent, the stereo bond tends to be directed away from rings and toward hydrogens, as expected. 

To register, look up, or otherwise access a ring template, a canonical (i.e., unique and atom-numbering-independent) description of the RS is first obtained (Figure 54). The hash function reduces this to a short code, which acts as an address in the hash table. The hash table eventually yields the address of a ring data record where the ring is stored. 

Rules are also offered for choosing the substituent of a tetrahedral stereocenter on which it is best to bestow the wedge or hash property (H > 1° > acyclic > ring). (Cf. Shelley s use of atom priority. " )... 

Hash photolysis was extended to study of the ring closure reaction of M(CO)5(l,10-phenanthroline) where M = W, Mo in SCCO2 (64). The reaction proceeds through the following elementary steps ... 

The molecules were analyzed by first identifying features such as rings, chains, and stereocenters. These features were then used to create a hash code which was used to determine if the target or a closely analogous molecule were in the database. If not, then the molecule was broken up into smaller portions, and each of those were treated as a target. If necessary, the dissection could continue down to the level of individual bonds and rings. Eventually AIMB would find one or more database entries which were considered to be analogous to the queries. 

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