Generic structural formulas

If the enomaticity of the pyridine is ignored, there are 4 = 16 intermediates after the first step, 16 -4 = 256 intermediates after the second step and 256 4 = 4096 products after the third step. Finally, eliminating the aromatic duplicates leads to 2080 members in the virtual library. 

Alternatively, the aromaticity of the central molecule can be considered from the beginning. If this is the case, there are 4 symmetrical intermediates after the first step (containing two identical R ) plus ( ) = 6 asymmetrical intermediates (with two different R ). After the second step, there are 4 4 = 16 symmetrical intermediates and 

In Section 8.3 of [337], Counting and Screening a library , it is shown how such a situation of multiple addition to a central molecule can be formulated as a problem of constructing symmetry classes, and how it may be generalized to arbitrary skeletons. 

Often the search spaces of combinatorial chemistry are described by generic structural formulas [11], and this is true in particular for patent libraries in chemistry [329]. There are only very few structure generators that allow the use of generic structural formulas to their full potential. Moreover, there is not yet a standardized and comprehensive format for the representation of generic structural formulas. 

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Aiming at exhaustive retrieval of relevant and/or similar names to be interpreted as widely as possible from a legal viewpoint, the system adopts two tactics firstly, to describe a specific or generic name with a set of many generic structural formulae which are chosen to be complementary to each other (Figure 1), and secondly, to draw a structural formula by merging more than one usual structural formula (Figure 2). 

The policy of the system would be very reliable for searching of generic representations by means of a set of generic structural formulas which can be built-up without any ad hoc technique. 

Users treating patent documents would demand a large set consisting of many generic structural formulae to completely cover complicated Markush formulae. The... 

The generic structural formula for a l-alkyl-3-methylimida-zolium cation is... 

We present a simple example of a generic structural formula and construct the search space that is obtained by combining the molecular formula and reaction-based struc-... 

In reality, generic structural formulas are often much more complicated. In particular the complexity can increase considerably by combination and recursion of the principles described above. For example, variation of substituents and positions can occur, while the various substituents R can themselves be described by generic structural formulas. Variations resulting from homology especially can result in the possibility of an infinite structure space. In our example, we assume that only alkyl groups with 1 - 6 C atoms are allowed. Such restrictions are certainly both reasonable and necessary. 

Table 5.1. Reactants for generation of the space of structures defined by the generic structural formula of Subsection 5.4.1.

Certainly, complete generation of all structures is not the only way to solve the problem. A review of different methods can be found in [13], where in particular the evaluation of molecular descriptors for large libraries specified by generic structural formulas is described. In any case canonization of data and normal forms play a central role. Hence it is time to consider this problem and to describe a canonizer. 

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