Halogenated Dipyridine Alkaloids from Actinoalloteichus cyanogriseus and Its Mutant Strain upon Precursor Feeding

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Nineteen uncovered 2,2′-dipyridine alkaloids ( 1 – 19 ), along with six previously reported analogues ( 20 – 25 ), were isolated from the wild strain Actinoalloteichus cyanogriseus OUCMDZ-413 and its mutant strain CRM005. These strains were cultured with the addition of various halogenated pyridine-2-carboxylic acid precursors in a liquid medium. The isolated compounds included nine fluorinated products ( 1 – 4, 9, 11, 14, 17, and 23 ), eight chlorinated products ( 5 – 7, 10, 12, 15, 18, and 19 ), and one brominated product ( 8 ). The molecular structures of these compounds were determined through spectroscopic analysis. Notably, the novel compounds showed cytotoxicity against the HCT-116, B16, and K562 tumor cell lines, with IC 50 values ranging from 0.16 to 11 μM.