Myxobacteria are very remarkable microorganisms which are usually not obtained by standard isolation technique. These organisms form characteristic fruiting bodies which are not produced by other bacteria. Although not much is known about the basic physiology and biochemistry of these bacteria. They have proved to produce a variety of bioactive substances. A great portion of these substances inhibit antifungal or cytotoxic properties.
In the course of screening for new bioactive substances from myxobactera, strain KM593 was found to produce closely related diketopiperazines(cyclic dipeptides). The strain was identified as Archangium gephyra by morphological characteristics and staining with Congo red.
The isolation of diketopiperazines was performed through several steps including silica gel, RP 18, Sephadex LH-20 column chromatography and HPLC. The chemical structures of these compounds were established on basis of their 1-D and 2-D NMR spectroscopic analyses and by comparison with reference data from literature. They were assigned as Cyclo(L-Pro-L-Tyr), Cyclo(L-Pro-L-Phe), Cyclo(D-Pro-L-Tyr), Cyclo(L-Pro-L-Leu), Cyclo(L-Pro-D-Val), respectively.
Antioxidant activities of these compounds were investigated. In particular, Cyclo(L-Pro-L-Tyr) showed higher antioxidant activity than Trolox in terms of ORAC values.
Diketopiperazines are most commonly isolated from terrestrial yeasts, lichens and fungal culture filtrates and are also observed in the culture broth of marine bacteria and marine actinomycetes. This is the first report that diketopiperazines were produced by myxobacteria.