Double Bond Geometric Isomers of Pentaketide Ansamycins from Streptomyces sp. S008.

Six new pentaketide ansamycins, namely, shengliangmycins A-F ( 1 - 6 , respectively), were obtained from the fermentation products of Streptomyces sp. S008OE slmR2 that was derived by constitutive expression of LAL regulator gene slmR2 . The structures of 1 - 6 were determined through comprehensive spectroscopic analysis and single-crystal X-ray diffraction. Compound 1 has a cis -C6═C7 bond, which is different from that of compounds 2 - 5 . Compounds 3 - 6 feature a morpholinone structural moiety, whereas 5 is characterized by a pyrazoline ring, which is rare in natural products.