Potential causes for the formation of synthetic impurities that are present in solithromycin (1) during laboratory development are studied in the article. These impurities were monitored by HPLC, and their structures are identified on the basis of MS and NMR spectroscopy. In addition to the synthesis and characterization of these seven impurities, strategies for minimizing them to the level accepted by the International Conference on Harmonization (ICH) are also described.

ABSTRACT. With −OCH2CO− as a linker, a non β-substituted cationic bisporphyrin (4a) and a β-substituted cationic bisporphyrin (4b) were prepared through methylation of the intermediate which was obtained from β-amino-5,10,15,20-tetra (4-cyanophenyl) porphyrin or 5-hydroxylphenyl-10,15,20-tris(4-cyanophenyl) reacting with 5-hydroxy-10,15,20-trispyridinylporphyrin. Their structures were confirmed by 1 H NMR, IR, UV-vis, MS and elemental analysis. DNA photocleavage ability and the singlet oxygen ability of those cationic bisporphyrins were investigated. DNA photocleavage activity of β-substituted cationic bisporphyrin was significantly weaker than that of H2TMPyP, but similar to that of non β-substituted cationic bisporphyrin. While 4a and 4b showed substantial photocleavage activities toward DNA, with 68% and 66% observed at 10 µM. The assessment of indirectly measured 1 O2 production rates against H2TMPyP were described and the relative singlet oxygen production yields were: free cationic bisporphyrins > H2TMPyP. The results showed the cationic bisporphyrins with β-substitution and non β-substitution could be developed as potential photodynamic agents.

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