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One of the preprocessing methods used in pattern recognition-factor analysis-is shown to be well suited to the derivation of structure-activity relationships. Applications of the procedure developed are illustrated using sets of compounds which are of accepted therapeutic utility.

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CHLORAMPHENICOL ACTIVITP AND POLARIZABILITY 525 (I) The prodiict (IT, R = OH) was suspended in H20 and acidified with dilute acetic acid; the solid was washed with hot R20, boiled with CHIOH, dissolved in 2% aqueous-alcoholic XaOH, and precipitated on cooling as the sodium salt'; after crystallization from CH30H, the prodiict was acidified with dilute acetic acid and boiled with H20.( b ) The crude product (T, R = OH) was suspended in H20, neutralized with dilute acetic acid, and recrystallized from pyridine or N-methylformamide.Sodium salts of 11. were obtained in 2Yc HYO-alcohol solution of S a O H arid recrystallized from alcohol; they crystallize with 1 mole of alcohol.Hydrochlorides of IT were prepared in hot Concentrated HC1, washed with absolute ether and dried in vacuo; they lose HCl on heating.l-Aryl-3-(4,6-dimethyl-2-pyrimidyl)ureas (IV, Y = 0 ; R = CH,) and l-Aryl-3-(4,6-dimethyl-2-pyrimidyl)guanidines (V, Y = N H ; R : CH1).-Both compounds of type IV and V neie prepared according to methods A arid B using acetylacetone instead of ethyl acetoacetate and recrystallized from acetoneethanol solution, 1-butanol, or pyridine.An apparent correlation between the activity of chloramphenicol analogs, as determined by microbial kinetics, and the electronic polarizability of their aromatic substituents has been found which suggests the activity of chloramphenicol and its thiomethyl analog may arise, in part, by intramolecular charge transfer.