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

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 IC₅₀ values ranging from 0.16 to 11 μM.