Pyridapeptides F–I, cyclohexapeptides from marine sponge-derived Streptomyces sp. OUCMDZ-4539

Four new cyclohexapeptides, pyridapeptides F–I(1–4), were isolated from the fermentation broth of marine sponge-derived Streptomyces sp. OUCMDZ-4539. The pyridapeptides F–H(1–3) are composed of β-hydroxyleucine, alanine, O-methylthreonine, hexahydropyridazine-3-carboxylic acid, 5-hydroxytetrahydropyridazine-3-carboxylic acid, and(2S,3R,4E,6E)-2-amino-3–hydroxy-4,6-dienoic acid residues. Pyridapeptide I(4) contains(2S,3R,4E,6E)-2-amino-3–hydroxy-8-methylnona-4,6-dienoic acid residue and a very rare glycose residue, aculose. Their structures were determined based on spectroscopic analysis and chemical methods. Pyridapeptides G–I(2–4) have the 2,3,6-trideoxyhexose units glycosylated at the γ-OH-TPDA residue, displayed significant antiproliferative activity against four(PC9, MKN45, Hep G2, K562) or two(PC9, MKN45) human cancer cell lines.