Quantitative structure-activity relationships (QSAR) have been formulated for a set of 15 2, 4- diamino-5-(2-X-benzyl) pyrimidines versus dihydrofolate reductase from Lactobacillus casei and chicken liver. QSARs were also developed for comprehensive data sets containing mono-, di-, and trisubstituted benzyl derivatives. Particular emphasis was placed on the role played by ortho substituents in the overall binding process and subsequent inhibition of ...