Tryptophan-dehydrobutyrine diketopiperazine, a metabolite of Streptomyces spectabilis.

The biological activities of the streptovaricins, members of the ansamycin1) class of antibiotics, are of continuing interest and we are now investigating the minor components of the streptovaricin complex. In the course of these studies we recently isolated a compound to which we here assign the structure tryptophan-dehydrobutyrine diketopiperazine (TDD, I). Streptovaricin complex, prepared by the fermentation of Streptomyces spectabilis, was chromatographed repeatedly on silica gel to give a fraction containing a mixture of more polar streptovaricins2)and a colorless ultraviolet-absorbing component which was chromatographed repeatedly over silica gel columns to give pale yellow, crystalline needles (TDD) whose high resolution mass spectrum indicated the molecular formula C16H17N3O2. TDD shows weak activity against RNA directed DNA polymerase (reverse transcriptase)-30 % inhibition of RLV reverse transcriptase at 200 ug/ml2)-but it does not have significant in vitro antibacterial activity or inhibitory activity toward Escherichia coli DNA-dependent RNA polymerase. Hydrogenation of TDD over palladium charcoal in ethanol gave dihydro TDD (II), whose molecular formula was assigned as C16H16N3O2 by high resolution mass spectrometry. Hydrolysis of II in 6 N hydrochloric acid at 120°C gave a-aminobutyric acid (Aba), identified by comparison with an authentic sample on thin-layer chromatographs employing a ninhydrin assay. Other products of the hydrolysis were apparently decomposed under these conditions and could not be detected on tlc. The carbon skeleton of Aba can be detected in II from the proton magnetic resonance (pmr) spectrum (C,D,N) of II (Table 1),* which contains a methyl triplet at 0.58 ppm and non-equivalent methylene protons in multiplets at 0.58 and 1.56 ppm, both coupled to a proton at 3.90 ppm in addition to being coupled to the methyl group.