Seleno‐Nucleobases and Their Water‐Soluble Ruthenium–Arene Half‐Sandwich Complexes: Chemistry and Biological Activity

Half‐sandwich organometallic ruthenium complexes of seleno‐nucleobases, 3 and 4 , were synthesized and characterized. The structures of both complexes were determined by X‐ray crystallography and are the first crystal structures of ruthenium complexes with seleno‐nucleobases. Interestingly, 3 self‐assembles aided by adventitious water in DMF to give a tetranuclear square 3a· 6H 2 O. Complex 4 is active against Jurkat and Molt‐4 cell lines but inactive against the K562 cell line, whereas 3 is completely inactive against all three cell lines. The free ligand 6‐selenopurine ( 1 ) and 6‐selenoguanine ( 2 ) are highly active against these cell lines. Compound 2 , like its thio analogue, is unstable under UVA light, whereas 4 is stable under similar conditions, which suggests that the ruthenium complex could reduce problems associated with the instability of the free ligand, 2 , under irradiation.