Both transport and biotransformation processes for a series of pyrimidine nucleobases, ribonucleosides, 2'-deoxyribonucleosides, and acetyl and 5'-substituted derivatives of the cancerostatic agent araC were studied in the isolated everted rat jejunum with a continuous perfusion technique. Metabolic alterations during penetration were assessed by HPLC. 5'-Halogeno and 5'-deoxy derivatives of cytosine nucleosides exhibited higher transport rates and higher stability towards the deamination reaction than did unsubstituted derivatives. Octanol-buffer partition coefficients were estimated for the study compounds, and fragmental constants for the sugar moieties of nucleosides were assessed. With the present study compounds there was no correlation between lipophilicity and transport rate, as previously reported, but there was a correlation between lipophilicity and metabolic alteration of araC derivatives (r = 0.99, n = 5).
The inhibition of growth of Escherichia coli B by series of 6-azaanalogs of pyrimidine nucleosides, their precursors, and analogs of cancerostatic agents 5-fluorouracil and arabinosylcytosine is reported. A very high antibacterial activity is observed with most of the 5-fluorouracil nucleosides where a cleavage (30%) to 5-fluorouracil is observed at the most active compounds (5-fluorouridine, 5-fluoro-2'-deoxyuridine). Arabinosylcytosine and its derivatives express very low activity.
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