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. S008OEslmR2 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.