The first total synthesis and structural determination of antibiotics K1115 B sub(1)s (alnumycins)

K1115 B sub(1), isolated from the broth of Streptomyces species, was found to be a mixture of stereoisomers. Authors synthesized all stereoisomers of K1115 B sub(1) by convergent synthesis coupling a rhamnose derivative, an isobenzofuranone, and a chiral tetraol. Comparison of super(1)H NMR spectra and optical rotations made it clear that the absolute structures of K1115 B sub(1 alpha ) (the major isomer) and K1115 B sub(1 beta ) (the minor isomer) were (1R, 17S)- and (1R, 17R)-configurations, respectively. The optical rotations of the stereoisomers revealed that alnumycin, reported as the identical structure with K1115 B sub(1), might be another mixture of stereoisomers.