Identification of 4,5-Dihydro-4-hydroxygeldanamycins As Shunt Products of Geldanamycin Biosynthesis

Two new geldanamycin (GDM) analogues, (4S)-4,5-dihydro-4-hydroxygeldanamycin (1) and (4R)-4,5-dihydro-4-hydroxygeldanamycin (2), were identified from Streptomyces hygroscopicus 17997. Compounds 1 and 2 were not normal intermediates of GDM biosynthesis but shunt products of C-4,5 oxidation catalyzed by GdmP, a cytochrome P450 oxidase acting as a desaturase in GDM biosynthesis. Preliminary assays implied that, compared with GDM, 1 and 2 exhibited decreased cytotoxicity.