RESUMO
Feeding experiments with tryptophan samples labeled specifically with radioactive and stable isotopes have shown that Pseudomonas aureofaciens converts this amino acid into pyrrolnitrin in such a way that the indole nitrogen gives rise to the nitro group, the amino group becomes the pyrrole nitrogen, C-3 of the precursor side chain becomes C-3 of the antibiotic, and H-2 of the indole ring and H-alpha of the side chain give rise to H-5 and H-2 of pyrrolnitrin, respectively. Only the L-isomer of tryptophan is incorporated with retention of the alpha-hydrogen and the amino nitrogen. From the D-isomer the labels from these two positions are lost. The obvious conclusion that L-tryptophan is the more immediate precursor is, however, contradicted by the better incorporation of D- than L-tryptophan into the antibiotic. Several potential pathway intermediates were evaluated for incorporation and 4-(0-aminophenyl)-pyrrole was found to be a good precursor. The results area discussed in terms of a plausible pathway for pyrrolnitrin biosynthesis.
