Digitoxosyltetracenomycin C and Glucosyltetracenomycin C, Two Novel Elloramycin Analogues Obtained by Exploring the Sugar Donor Substrate Specificity of Glycosyltransferase ElmGT

Our explorations of glycosyltransferase ElmGT from Streptomyces olivaceus Tü 2353, which shows an interesting flexibility regarding its sugar donor substrate, were extended toward various previously unexplored sugar co-substrates. The studies revealed that ElmGT, which normally transfers l-rhamnose to 8-demethyltetracenomycin C as a crucial biosynthetic step in elloramycin biosynthesis, is also able to process an activated non-deoxygenated sugar, NDP-d-glucose, as well as NDP-l-digitoxose, which is the first example of an NDP-l-sugar co-substrate of ElmGT possessing an axial 3-OH group. The structures of the resulting novel elloramycin analogues of these experiments, 8-demethyl-8-l-digitoxosyltetracenomycin C (4) and 8-demethyl-8-d-glucosyltetracenomycin C (7), were elucidated mainly by 1H and 13C NMR spectroscopy and by mass spectrometry.