Naturally occurring hydrazones are rare despite the ubiquitous usage of synthetic hydrazones in the preparation of organic compounds and functional materials. In this study, we discovered a family of novel microbial metabolites (tasikamides) that share a unique cyclic pentapeptide scaffold. Surprisingly, tasikamides A–C (1–3) contain a hydrazone group (CNN) that joins the cyclic peptide scaffold to an alkyl 5-hydroxylanthranilate (AHA) moiety. We discovered that the biosynthesis of 1–3 requires two discrete gene clusters, with one encoding a nonribosomal peptide synthetase (NRPS) pathway for assembling the cyclic peptide scaffold and another encoding the AHA-synthesizing pathway. The AHA gene cluster encodes three ancillary enzymes that catalyze the diazotization of AHA to yield an aryl diazonium species (diazo-AHA). The electrophilic diazo-AHA undergoes nonenzymatic Japp–Klingemann coupling with a β-keto aldehyde-containing cyclic peptide precursor to furnish the hydrazone group and yield 1–3. The studies together unraveled a novel mechanism whereby specialized metabolites are formed by the coupling of two biosynthetic pathways via an unprecedented in vivo Japp–Klingemann reaction. The findings raise the prospect of exploiting the arylamine-diazotizing enzymes (AAD) for the in vivo synthesis of aryl compounds and modification of biological macromolecules.

Anthraquinone-fused enediynes (AQEs) are renowned for their distinctive molecular architecture, reactive enediyne warhead, and potent anticancer activity. Although the first members of AQEs, i.e., dynemicins, were discovered three decades ago, how their nitrogen-containing carbon skeleton is synthesized by microbial producers remains largely a mystery. In this study, we showed that the recently discovered sungeidine pathway is a “degenerative” AQE pathway that contains upstream enzymes for AQE biosynthesis. Retrofitting the sungeidine pathway with genes from the dynemicin pathway not only restored the biosynthesis of the AQE skeleton but also produced a series of novel compounds likely as the cycloaromatized derivatives of chemically unstable biosynthetic intermediates. The results suggest a cascade of highly surprising biosynthetic steps leading to the formation of the anthraquinone moiety, the hallmark C8–C9 linkage via alkyl–aryl cross-coupling, and the characteristic epoxide functionality. The findings provide unprecedented insights into the biosynthesis of AQEs and pave the way for examining these intriguing biosynthetic enzymes.

A new cyclic decapeptide, trikoramide A (1), has been isolated from samples of the marine cyanobacterium Symploca hydnoides, collected from Bintan Island, Indonesia. Trikoramide A (1) is a C-prenylated cyclotryptophan-containing cyanobactin. Its planar structure was deduced by 1D and 2D NMR spectroscopy as well as HR–MS/MS data. In addition, its absolute configuration was determined by Marfey’s method and 2D NOESY NMR spectroscopic analysis. Compound 1 possessed cytotoxicity against the MOLT-4 and AML2 cancer cell lines with IC50 values of 4.8 and 8.2 μM, respectively.

A family of novel cyclic lipopeptides named tasikamides A−H (Tsk A−H) were discovered recently in Streptomyces tasikensis P46. Aside from the unique cyclic pentapeptide scaffold shared by the tasikamides, Tsk A−C contain a hydrazone bridge that connects the cyclic pentapeptide to the lipophilic alkyl 5‐hydroxylanthranilate (AHA) moiety. Here we report the production of tasikamides I−K (Tsk I−K) by a mutant strain of S. tasikensis P46 that overexpresses two pathway‐specific transcription regulators. Unlike Tsk A−C, Tsk I−K feature a rare enaminone‐bridge that links the cyclic peptide scaffold to the AHA moiety. Our experimental data suggest that Tsk I−K are generated by the coupling of two biosynthetic pathways via a nonenzymatic condensation reaction between an arylamine and a β‐keto aldehyde‐containing precursor. The results underscore the nucleophilic and electrophilic reactivity of the β‐keto aldehyde moiety and its ability to promote fragment coupling reactions in live microbial cells.

Angucyclines are structurally diverse aromatic polyketides that have attracted considerable attention due to their potent bioactivity and intriguing biosynthetic origin. Balmoralmycin is a representative of a small family of angucyclines with unique structural features and an unknown biosynthetic origin.

Transcriptional effects via binding to intragenic regions of many BGCs, observed in S. coelicolor. 60 DasR 61 Activates antibiotic synthesis in S. coelicolor, S. clavuligerus, S. collinus, S. griseus, S. hygroscopicus and S. venezuelae. 61 GlcNAc sensing pleiotropic regulators that activate antibiotic synthesis under nutrient starvation. 61 PhoP-PhoR system 62 Represses the production of: ACT, Red, CDA in S. coelicolor. 62 ACT and Red in S. lividans. 63 avermectin in S. avermitilis. 64 Under phosphate limitation, PhoP upregulates genes for phosphate scavenging and represses nitrogen utilization. It also activates biosynthetic genes, such as Red BGC in S. coelicolor. 65 WblA 66 Represses the production of: daptomycin in S. roseosporus. 67 doxorubicin in S. peucetius. 68 moenomycin in S. ghanaensis. 69 pikromycin in S. venezuelae. 70 tautomycetin in S. sp. CK4412. 71