The structure of the chromophore chromomyclnone was deduced as Indicated in the following scheme. Chromomrcin A3 1 CH3COOH, boil 2 hrs Chromomvcinone (CHR) UV same as chromomycin A5 :. Chromophore still intact. Chromomycinone No.34 m.p. 183-135', having a typical naphthoquinone UV spectrum, A",izH 259 np(4.33*), 276 mP(4.04), 355 mp(3.56); whereas with zinc dust, sodium acetate and acetic anhydrlde it afforded a reductive octaacetate , C3$44017, m.p. 130Β°, having a naphthalenoid W spectrum, h,,, EtoH 235 mp(4.80), 285 mu(3.27). CHQ with acetone and a trace of cont. sulfuric acid yielded an acetonlde, C24H300g, 1o.p. 130Β°, which could be converted into CHQ acetonide tetraacetate, C H 0 32 38 13' m'p' 176' (FIG.la and lb). This acetonlde tetraacetate was hydrolyzed by acetic acid to the dlol tetraacetate, C2gH34013, m.p. 206" (FIG.lc). The szucture of CHQ was deduced by examining the 100 mc spectra ** of CHQ acetonide tetraacetate in CDC13 (FIG.la) and In C6R6 (FIG.lb) and of CHQ dial tetraacetate In CDC13 (FIG.lc), together w:ith UV and IR spectra and chemical evidence. In FIG.la the tall peak at 1.36 is due to the lsopropylidene group protons while the two strong signals at 1.28 correspond to a secondary methyl group. The absorption due to the latter group appears as a single peak when proton (A) whose resonance occurs at 4.08 is irradiated. Conversely the multiplet (A) a-z 4.08 changes Into a doublet when the secondary methyl signals are irradiated. Furthermore, the triplet at 3.70 arising from proton (B) also becomes a doublet when the resonance :lattern around 5.15 is Irradiated. The last two decoupled patterns due to protons (A) and (B) appear to be mirror images of each other, indicating that the two protons * Log E values enclosed in parenthesis.
** The spectra where obtained on a Varlan HR-100 spectrometer equipped to accomplish proton-proton spin-decoupling. TMS was used as internal reference, the chemical shifts being given in ppm.