Select a Substituent Set

The concept of plotting parameters and choosing from the plot does go 

In a 1981 QSAR design program aimed at the discovery of new pyreth-roid insecticides, Plummer and Pincus used the cluster sets proposed by 

Hansch and his co-workers to select the initial set of compounds for synthesis. The substituents (see Table 11) were chosen from Hansch s duster set 1 IT, F, R, MW, MR) at the 20-cluster group level The 16 substituents chosen represented what appeared to be synthetically accessible compounds. The set was somewhat biased by induding 4 from duster 18, the cluster containing the most active pyrethroid to date in this chemical dass. Regardless, the set represented a total of 13 of the 20 dusters. 

As indicated by Table 12, two of the major criteria for an ideal substituent set appear to be met by this set the substituents are well spread in parameter space and appear to be orthogonal based on the correlation matrix. 

The only parameters that may be not be orthogonal are Tt and MR. This colinearity is more apparent when the factor loadings are examined (see Table 13). This weakness in design became a problem in the projea when the initial set was finally synthesized. The full duster set was never actually made since synthetic difficulties met in the process were not overcome. Several substitutions were made finally to arrive at a set (see Plummer and Pincus ) that was the same size and suffered the same difficulty of not separating it and MR. This failure to separate these faaors ultimately led to difficulties in developing a model for activity because it was found that tr gave the best model with MR providing the next best. 

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