QSAR Study of the Fungicidal Activity of Thiophosphorylglycinamide Derivatives. Comparison of Principal Component Analysis and Spectral Mapping Technique

The growth inhibitory effect of 38 thiophosphorylglycinamide (TPGA) derivatives against 25 fungal species (test organisms) belonging to various taxonomic groups was determined. Principal component analysis (PCA) was used for the elucidation of similarities and dissimilarities between TPGAs and between fungi. The strength (potency) and selectivity of the fungicidal effect were separated by the spectral mapping technique (SPM). The dimensionality of the matrices of PC loadings and variables and the selectivity maps were reduced to two by the nonlinear mapping technique. PCA and SPM were compared by calculating linear relationships between the potency values and the corresponding coordinates of maps calculated by PCA and SPM. The relationship between fungicidal effect and molecular structure was elucidated by stepwise regression analysis. It was established that the coordinates of maps are orthogonal and the results of PCA and SPM are similar but not identical. The advantage of SPM is the separation of the strength and selectivity of fungicidal effect facilitating the rational design of new TPGA derivatives. Stepwise regression analysis indicated that the position of substituents in the TPGA molecule, its bulkiness and hydrophobicity exert the highest impact on both the strength and selectivity of fungicidal effect. No relationship was found between sensitivity of fungal species towards TPGAs and their taxonomic position.