Preparation of oligodeoxynucleotides containing a diastereoisomer of alpha-(N(2)-2'-deoxyguanosinyl)tamoxifen by phosphoramidite chemical synthesis.

Women treated with an antiestrogen tamoxifen (TAM) for endocrine therapy or prevention of breast cancer show an increased risk of developing endometrial cancer. TAM-DNA adducts have been detected in the liver of rodents treated with TAM and in the endometrium of women taking TAM. The major TAM adducts have been identified as diastereoisomers of trans- and cis-forms of alpha-(N(2)-deoxyguanosinyl)tamoxifen (dG-N(2)-TAM) and alpha-(N(2)-deoxyguanosinyl)-N-desmethyltamoxifen. In the study presented here, we prepared oligodeoxynucleotides containing a diastereoisomer of dG-N(2)-TAM by phosphoramidite chemical synthesis. Initially, the trans- and cis-forms of alpha-aminotamoxifen (alpha-NH(2)-TAM) were synthesized from alpha-hydroxytamoxifen using the Mitsunobu reaction followed by hydrolysis. Thereafter by coupling the trans- and cis-form of alpha-NH(2)-TAM with the DMT-derivative of 2-fluoro-(O(6)-2-(trimethylsilyl)ethyl)-2'-deoxyinosine, the trans- and cis-forms of DMT-dG-N(2)-TAM, respectively, were prepared in high yield and used in the preparation of the phosphoramidite precursors. Large quantities of oligodeoxynucleotides containing a trans- or a cis-form of dG-N(2)-TAM were prepared efficiently by automated DNA synthesizer. The incorporation of dG-N(2)-TAM adduct into the oligodeoxynucleotides was confirmed using (32)P-postlabeling/polyacrylamide gel electrophoresis analysis. These site-specifically modified oligodeoxynucleotides will be used for exploring biological properties and three-dimensional structure of TAM-DNA adducts.

Biosynthesis of fluorinated secondary metabolites by Streptomyces cattleya.

The biosynthesis of organofluorine compounds by Streptomyces cattleya NRRL 8057 was examined using 19F NMR spectroscopy. The organism produced 1.2 mM fluoroacetate and 0.5 mM 4-fluorothreonine as secondary metabolites when cultured for 28 d on a chemically defined medium containing 2 mM fluoride. Cell suspensions from batch cultures harvested at the growth maximum of 4 d were not capable of fluoride uptake or fluorometabolite biosynthesis, but by 6 d had developed an efficient fluoride-uptake system and biosynthesized the two fluorometabolites in almost equal proportions. As the harvest age increased, the proportion of fluoroacetate to 4-fluorothreonine formed by cell suspensions rose progressively so that 16-d-old cells showed a ratio of 76:26 for the two compounds. Fluoride uptake and fluorometabolite production by cell suspensions were highly dependent on pH, with both processes showing a maximum rate at pH 6.0 but declining rapidly at higher pH values. This decrease was particularly marked in the case of fluoroacetate biosynthesis which was barely detectable at pH 7.5. Fluoroacetate and 4-fluorothreonine showed only low levels of interconversion by cell suspensions, suggesting that the carbon skeleton of neither was derived by metabolism of the other. The limited interconversion observed is explicable in terms of a small degree of biological defluorination occurring with each compound, followed by reincorporation of the resulting fluoride ion into the organic form by the active fluorinating system, a phenomenon also noted on incubation of cell suspensions with a number of other fluorinated biochemical intermediates.(ABSTRACT TRUNCATED AT 250 WORDS)