Bacteria are an impressive source of biologically active secondary metabolites. To date, however, only a relatively small number of bacterial taxa—actinomycetes, bacilli, pseudomonads, and myxobacteria—has entered natural product chemistry studies. Studies on molecular phylogeny have clearly demonstrated that the diversity of microbial populations in natural habitats far exceeds former anticipations. Many of the less well characterized groups evolved independently from other lineages. These taxa show a number of phenotypic idiosyncrasies, and it can be expected that their secondary metabolism differs from that of other bacteria as well. We have directed our interest towards the phylum Chloroflexi which branched off early from the eubacterial stem and is represented by Gram-negative gliding bacteria with an unusual cell-wall composition. Sequence analysis of this phylum shows that the genus Herpetosiphon has noticeable deviations in highly conserved sites in its ribosomal RNA. Thus it appears to be a rather rapidly evolving line that is moving away from its thermophilic ancestors. Although Herpetosiphon strains can be isolated from many habitats, at present little is known about the secondary metabolism of this genus. Screening of ten different Herpetosiphon strains by NMR and LC-MS-based techniques led to the discovery of an unusual metabolite comprising a styrene residue, two oxazole rings connected through a C2 bridge, and an unprecedented amide-bonded N-penta[2,4]diene side chain. Even though some structural elements resemble those of myxobacterial metabolites, the overall composition makes this compound the first member of a new structural class. Here we report the structure elucidation and biosynthesis of the novel compound siphonazole.