9-Methyl-6-MP-S35 and 9-ethyl-6-MP-S35 of high specific activity and purity have been synthesized. 6-MP-S35 and these two alkylated S35 derivatives were administered intraperitoneally to rats. The catabolic products of each of these compounds in the 24-hour urine after injection in these rats were determined. 6-MP-S35 was excreted primarily as thiouric acid. 9-Methyl and 9-ethyl-6-MP-S35 were primarily excreted unaltered, and no evidence of dealkylation was obtained. The import of these findings on the possible mechanism of action of 6-MP against neoplastic cells is discussed.

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Aided by grants from the John A. Hartford Foundation and Grant CY5689 from the National Institutes of Health, Bethesda, Md.

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