Krasilnikolides A and B and Detalosylkrasilnikolide A, Cytotoxic 20-Membered Macrolides from the Genus : Assignment of Anomeric Configuration by -Based Configuration Analysis.

A chemical investigation of strain RD003821, belonging to the underexplored actinomycetes genus , led to the discovery of three novel polyketides: two 20-membered glycomacrolides, krasilnikolides A () and B (), and an aglycone of , detalosylkrasilnikolide A (). A major challenge in the structure elucidation of was to determine the anomeric configuration of the α-l-6-deoxytalose (6dTal) unit, which was achieved by -based configuration analysis (JBCA) that incorporated anomeric carbon- and proton-specific two-bond C-H spin-spin coupling constants as diagnostic parameters. The updated criteria for the conformation/configuration assignment facilitated discrimination of three out of four stereochemical variants at the anomeric and the adjacent C2 positions, which expanded the scope of the JBCA method to determination of the anomeric configuration of aldohexopyranoses. Compounds and are the first macrolides decorated by 6dTal. Compounds - exhibited cytotoxicity against P388 murine leukemia cells with IC values of 14, 8.4, and 3.9 μM, respectively. In addition, - were antibacterial against the Gram-positive bacterium with MIC values of 25, 50, and 100 μg/mL. was inhibitory against with an MIC of 50 μg/mL.