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 ofβ-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 theγ-OH-TPDA residue,displayed significant antiproliferative activity against four(PC9,MKN45,Hep G2,K562)or two(PC9,MKN45)human cancer cell lines.