Antibiotics from Gliding Bacteria, LXXV. Absolute Configuration and Biosynthesis of Tartrolon B, a Boron‐Containing Macrodiolide from Sorangium cellulosum

The absolute configuration of tartrolon B (1), a boron‐containing macrodiolide from Sorangium cellulosum, was established by X‐ray structure analysis as (2R,3R,4R,7S,8S,11S). Compared to the related boron‐containing macrodiolides boromycin (2), aplasmomycin (3), and borophycin (4), and identical substructure and configuration of the boron‐binding site was found for all four compounds. The biosynthesis of 1 was investigated by feeding experiments with 13C‐labeled precursors. According to NMR analyses, the carbon atoms from C‐1 to C‐18 are derived from acetate units, the two methyl groups at C‐22 and C‐23 are derived from methionine, and a three‐carbon starter unit C‐19 to C‐21 is derived from glycerol. The biosynthesis of 1 is closely related to those of 2 and 3 but with respect to the origin of the starter unit it is more distant to that of 4.