The first total synthesis and structural determination of antibiotics K1115 B1s (alnumycins)

K1115 B-1, isolated from the broth of Streptomyces species, was found to be a mixture of stereoisomers. Authors synthesized all stereoisomers of K1115 B-1 by convergent synthesis coupling a rhamnose derivative, an isobenzofuranone, and a chiral tetraol. Comparison of H-1 NMR spectra and optical rotations made it clear that the absolute structures of K1115 B-1 alpha (the major isomer) and K1115 B-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-1, might be another mixture of stereoisomers. (C) 2010 Elsevier Ltd. All rights reserved.