Elimination or Stabilization of Vulnerable Moieties

The effects of the 15-methyl-substituted prostaglandins might be partially based on such an enzyme inhibition. 

PG 15(S) 15-me-E2me ester inhibitor gastric secretion prolonged action active at oral administration 

The reverse situation - selective bioactivation in the uneconomic species — is realized in the selectively acting weedkillers of the phenoxybutyric acid type (Fig. 8). The butyric acid derivatives, as such, are inactive they have to be converted by 0-oxidation to the corresponding phenoxyacetic acid derivatives, which have the required auxin and hence weedkiller action. Since plant species 

Efforts to obtain tumor-selective cytostatic agents, based on a selective bioactivation in the malignant tissues, have not been very successful up to now. This is mainly due to a lack of enzyme specificity in malignant tissues as compared to healthy vital tissues. Diethylstilbestrol, an estrogen, is active against tumors of the prostate. The phosphate ester of diethylstilbestrol, Honvan, is inactive but is converted to the active product by the acidic phosphatase that is abundant in the prostate tissue. The enzyme concerned, however, is not restricted to the prostate kidney and bone tissues are also rich in acidic phosphatase, so that the bioactivation is not restricted to the target tissue. 

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