The chemistry of rubradirin. II. Rubranitrose.

Sir: Rubradirin'-" contains a C8H,5NO5* moiety not found in rubradirin B5). We here report that acid hydrolysis of rubradirin afforded this fragment which was found to be a nitrosugar we have named L-rubranitrose. L-Rubranitrose is shown to have structure la. It is stereoisomeric with evernitrose, 26,1), found in the unrelated antibiotics, everninomicins B and C. Anomeric Ia, b was separated from the second component of the hydrolytic mixture, acidic rubradirin aglycone, by distribution of the former into the chloroform layer of a 2-phase system which also contained a 5 % Na2CO3 solution. The two anomers were distinguished by C-1 proton signals at 8 4.75 and 8 5.28. After chromatography, the latter was crystallized, mp 150-153°, [a]„ + 127° -> + 86° (c 1, ethanol). Acetylation of the mixture in acetic anhydride and pyridine afforded anomeric 1-acetyl rubranitrose, from which we were able to crystallize the opposite anomer, 3a, mp 7476°, [x]„ +36° (c 0.4, ethanol). The 1H NMR signal of its C-1 proton showed that this was the anomeric configuration in the rubradirin glycoside (see Table 1). A further analysis of the proton spectra of 1 and 3 accounted for all of the carbons and hydrogens in three segments,