The antitumor antibiotic 'rubiflavin' was investigated. It was shown to be a mixture of several compounds, nine of which -after isolation by HPLC -could be identified by 'H-NMR spectroscopy. The rubiflavins A (4), B (S), C-l(6), C-2 (7), D (8), and E (9) are pluramycin antibiotics differing only in their side chains at C(2). Rubiflavin B (5) was found to be identical with kidamycin, rubiflavin F (10) with isokidamycin. Two unpolar compounds isolated which lack the two sugar rings typical for pluramycin antibiotics were called rubiflavinone C-1 (2) and C-2 (3); they are the 'aglycones' OF the corresponding rubiflavins.
Introduction. -In 1964, Aszalos et al. isolated a new antitumor-active antibiotic from a Streptomyces species [3]. The substance which was called 'rubiflavin'2) was purified by countercurrent distribution and thought to be uniform. The elemental analysis led to the molecular formula C23H,,,,N0,. This was in accord with molecular-weight determinations which yielded 386430 (titration) and 412 (ultracentrifugation). The structure of this 'rubiflavin' was not determined thereafter, but the antibiotic was intensely studied with respect to its biological activities. The most prominent of these werebesides the antitumor activity -the ability to bind to DNA [4] [5] and subsequently inhibit the DNA synthesis [5] [6].
The UV and IR data that Aszalos et al. determined for 'rubiflavin' were very similar to those of hedamycin (l), kidamycin (S), and related compounds [7] and thus indicated that 'rubiflavin' probably belonged to the group of pluramycin antibiotics'). The I3C-NMR spectrum of a sample of crude 'rubiflavin' obtained from Aszalos et a/. corroborated this suggestion; it displayed all the well known resonances of the two 'sugar' rings E and F as in the corresponding spectra of hedamycin (1) and kidamycin (5) [9]. Thus, in 'rubiflavin', these two rings are not acetylated. Accordingly, no ester-carbonyl resonances were detected in the IR spectrum. In the sp2 region of the "C-NMR spectrum of 'rubiflavin', the resonances also corresponded more or less to those commonly observed for pluramycin-like antibiotics [9]. However, signal clusters were detected here as well as in the methyl region of the spectrum, suggesting that 'rubiflavin' was a mixture of several pluramycinlike compounds differing only in their side chains at C(2).
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Taken in part from the dissertation of H. N . [l]; for a preliminary account, see [2]. 'Rubiflavin' -in inverted commas --will be used in this paper to denote the samples described by or obtained from Aszalos et al. [3]. The numbering scheme used in the formulae corresponds to that established for pluramycin-like antibiotics in earlier pdpers [7] [8].