Identification of alkaloids and polyketides in an Actinomycete by high-performance liquid chromatography with mass spectrometric and UV–Visible detection

Abstract

Analytical HPLC with UV–Vis diode array detection and positive electrospray HPLC–MS were employed to characterise the secondary metabolites of Actinomycetes spec. strain BA 909 in crude mycelial extracts and preparative HPLC fractions. It was shown that the strain produced two families of antibiotics previously reported in the literature, namely the polyketides leptomycin A ( 1) and B ( 2), kazusamycins A ( 3) and B ( 4) and the alkaloids nybomycin ( 5) and deoxynybomycin ( 6), respectively. Compounds 1– 4 were identified by comparison of their HPLC–UV and HPLC–MS data with authentic materials obtained from the original producer strain, whereas the identity of the nybomycins 5 and 6 was established by comparison of structural data with those of reference compounds. From HPLC–UV–Vis analyses it was established that both groups of metabolites are produced as complex mixtures of congeners. The employment of a single HPLC–UV–Vis method, aided by HPLC–MS of selected fractions, allowed for simultaneous detection of the main metabolites in the crude extracts during fermentation. Known metabolites could be distinguished from tentatively new congeners. For example, the data available from HPLC–UV–Vis and HPLC–MS analyses point towards the presence of an anguinomycin A ( 7) isomer, two new isomers of kazusamycins A and B ( 8 and 9), and a new nybomycin derivative ( 1 0) in addition to the known compounds 1– 6. The co-occurrence of both leptomycin and nybomycin type metabolites in the same Actinomycete strain was observed for the first time.