Protonation Reaction as a Method for Identification of Heptaene Antibiotics of the Candicidin Group

The identification of aromatic heptaene antibiotics of the candicidin group (trichomycin, levorin, candicidin) has been hampered due to the complete coincidence of the usual physicochemical parameters for these antibiotics. They can be distinguished only by extremely complex analysis methods - counterflow distribution, IR and NMR spectra. In seeking a fairly simple method of estabilishing the authenticity of these antibiotics for mass analysis, the authors noticed that all of them form intensively blue solutions in concentrated sulfuric acid. This is evidently explained by their protonation along the haptaene chain with the formation of the carbonic ion II with a positive charge. Preliminary experiments showed that the protonation reaction is suitable for identification of heptaene antibiotics and apparently is characteristic for the majority of polyene antibiotics.
Edited trans. of Nauchno-Issledovatelskii Institut Antibiotikov. Konferentsii Molodykh Uchenykh Leningradskogo Instituta Antibiotikov 2-Y, Leningrad, Jun 64. Materialy, n.p., n.d., p12-13, by Dean F. W. Koolbeck.