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 <i>Streptomyces olivaceus </i>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 (<b>4</b>) and 8-demethyl-8-d-glucosyltetracenomycin C (<b>7</b>), were elucidated mainly by <sup>1</sup>H and <sup>13</sup>C NMR spectroscopy and by mass spectrometry.