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Investigation on how nature produces natural compounds with chemical and biological diversity at the genetic level offers inspiration for the discovery of new natural products and even their biological targets. The polyketide rumbrin (1) is a lipid peroxide production and calcium accumulation inhibitor, which contains a chlorinated pyrrole moiety that is a rare chemical feature in fungal natural products. Here, we identify the biosynthetic gene cluster (BGC) rum of 1 and its isomer 12 E -rumbrin (2) from Auxarthron umbrinum DSM3193, and elucidate their biosynthetic pathway based on heterologous expression, chemical complementation, and isotopic labeling. We show that rumbrins are assembled by a highly reducing polyketide synthase (HRPKS) that uniquely incorporates a proline-derived pyrrolyl-CoA starer unit, and followed by methylation and chlorination. Sequent precursor-directed biosynthesis was able to yield a group of rumbrin analogues. Remarkably, inspired by the presence of a human immunodeficiency virus (HIV)-Nef-associated gene in the rum cluster, we predicted and pharmacologically demonstrated rumbrins as potent inhibitors of HIV at the nanomolar level. This work enriches the recognition of unconventional starter units of fungal PKSs and provides a new strategy for genome mining-guided drug discovery. We reconstituted the biosynthesis of rumbrins, identified a new starter unit of PKS, and obtained nine rumbrin analogues. Guided by rumB , we predicted and pharmacologically demonstrated rumbrins as anti-HIV agents. [Display omitted] [ABSTRACT FROM AUTHOR]

[4 + 2] Cyclases are potent biocatalysts that have been bestowed upon microorganisms and plants by nature, equipping them with the powerful tools to utilize and implement the [4 + 2] cycloaddition reaction for constructing the cyclohexene core in synthesizing valuable molecules. Over the past two years, eleven new enzymes have joined this pericyclase club and undergone extensive investigation. In this review, we present a comprehensive overview of recent advancements in characterizing [4 + 2] cyclases with regard to their catalytic mechanism and stereoselectivity. We particularly focus on insights gained from enzyme co–crystal structures, cofactors, as well as the effects of glycosylation. Advancements in understanding the mechanisms of natural [4 + 2] cyclases offer the potential to mimic evolutionary processes and engineer artificial enzymes for the development of valuable and practical biocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Endophytic fungi are promising producers of bioactive small molecules. Bioinformatic analysis of the genome of an endophytic fungus Penicillium dangeardii revealed 43 biosynthetic gene clusters, exhibited its strong ability to produce numbers of secondary metabolites. However, this strain mainly produce rubratoxins alone with high yield in varied culture conditions, suggested most gene clusters are silent. Efforts for mining the cryptic gene clusters in P. dangeardii , including epigenetic regulation and one-strain-many-compounds (OSMAC) approach were failed probably due to the high yield of rubratoxins. A metabolic shunting strategy by deleting the key gene for rubratoxins biosynthesis combining with optimization of culture condition successfully activated multiple silent genes encoding for other polyketide synthases (PKSs), and led to the trace compounds detectable. As a result, a total of 23 new compounds including azaphilone monomers, dimers, trimers with unprecedented polycyclic bridged heterocycle and spiral structures, as well as siderophores were identified. Some compounds showed significant cytotoxicities, anti-inflammatory or antioxidant activities. The attractive dual PKSs gene clusters for azaphilones biosynthesis were mined by bioinformatic analysis and overexpression of a pathway specific transcription factor. Our work therefor provides an efficient approach to mine the chemical diversity of endophytic fungi. A combinational genome mining strategy based on metabolic shunting and OSMAC by deleting the key gene (rbtJ) for the biosynthesis of main products rubratoxins in fungus Penicillium dangeardii successfully aroused abundant silent gene clusters and led to the production of numerous novel metabolites with unprecedented structures and diverse bioactivities. Image 1 [ABSTRACT FROM AUTHOR]

Epigenetic modifications have been proved to be a powerful way to activate silent gene clusters and lead to diverse secondary metabolites in fungi. Previously, inactivation of a histone H3 deacetylase in Calcarisporium arbuscula had led to pleiotropic activation and overexpression of more than 75% of the biosynthetic genes and isolation of ten compounds. Further investigation of the crude extract of C. arbuscula ΔhdaA strain resulted in the isolation of twelve new diterpenoids including three cassanes ( 1 − 3 ), one cleistanthane ( 4 ), six pimaranes ( 5 − 10 ), and two isopimaranes ( 11 and 12 ) along with two know cleistanthane analogues. Their structures were elucidated by extensive NMR spectroscopic data analysis. Compounds 2 and 4 showed potent inhibitory effects on the expression of MMP1 and MMP2 (matrix metalloproteinases family) in human breast cancer (MCF-7) cells. [ABSTRACT FROM AUTHOR]

Fungal genomes carry many gene clusters seemingly capable of natural products biosynthesis, yet most clusters remain cryptic or down-regulated. Genome mining revealed an unconventional paraherquonin-like meroterpenoid biosynthetic gene cluster in the chromosome of Neosartorya glabra . The cryptic or down-regulated pathway was activated by constitutive expression of pathway-specific regulator gene berA encoded within ber biosynthetic gene cluster. Chemical analysis of mutant Ng -OE: berA extracts enabled the isolation of four berkeleyacetal congeners, in which two of them are new. On the basis of careful bioinformatic analysis of the coding enzymes in the ber gene cluster, the biosynthetic pathway of berkeleyacetals was proposed. These results indicate that this approach would be valuable for discovery of novel natural products and will accelerate the exploitation of prodigious natural products in filamentous fungi. [ABSTRACT FROM AUTHOR]

Abstract: Two chromomycin SA analogs, chromomycin SA3 and chromomycin SA2, along with deacetylchromomycin A3 and five previously reported chromomycin analogs were isolated from a marine-derived Streptomyces sp. The structures of the new compounds were determined by spectroscopic methods including 1D and 2D NMR techniques, HRMS and chemical methods. Chromomycin SA3 and chromomycin SA2 are the first naturally occuring chromomycin analogs with truncated side-chains. Biological evaluation of chromomycin analogs for cytotoxicity against two non-small cell lung cancer (NSCLC) cell-lines, A549 and HCC44, demonstrated a decrease in cytotoxicity for the truncated sides chain chromomycin analogs. [Copyright &y& Elsevier]

Abstract: The mass fragmentation patterns of stilbene glycosides isolated from the genus Lysidice were investigated by negative ion electrospray ionization tandem mass spectrometry, and the influence of collision energy on their fragmentation behavior is discussed. It is found that the presence of the Y0 − and B0 − ions in the MS2 spectra is characteristic for 1→6 linked diglycosyl stilbenes, while the Y0 −, Y1 −, and Z1 − ions are representative ions of 1→2 linked diglycosyl stilbenes. These results indicate that ESI-MS n in the negative ion mode can be used to differentiate 1→6 and 1→2 linked diglycosyl stilbenes. Based on the fragmentation rules, 9 new trace constituents were identified or tentatively characterized in a fraction of Lysidice brevicalyx by using HPLC/HRMS and HPLC-DAD/ESI-MS n . The results of the present study can assist in on-line structural identification of analogous constituents and targeted isolation of novel compounds from crude plant extracts. [Copyright &y& Elsevier]

Abstract: Nine new steroidal glycosides, cynaforrosides B (2), C (3), D (4), E (5), and F (6), based on a 13, 14: 14, 15-disecopregnane-type skeleton, cynaforrosides G (7), H (8), and I (9) with a new aglycone named cynaforrogenin A, and cynaforroside J (10) together with three known C21 steroidal glycosides cynatratoside A (1), hancoside (11) and komaroside C (12) were isolated from the ethanol extract of the roots of Cynanchum forrestii Schlechter. The structures of new compounds were determined on the basis of spectral and chemical evidence. Steroidal glycosides with three kinds of skeletons were isolated from this plant simultaneously. The sugar units of cynaforrosides B-I contained two moieties of glucoses and especially cynaforrosides E-I contained two glucoses with the mode of 1→6 linkage, which were rare among steroidal glycosides of the genus Cynanchum. [Copyright &y& Elsevier]

Abstract: Seven new stigmastane-type steroidal glycosides, vernocuminosides A–G (1–7), have been isolated from the stem barks of Vernonia cumingiana Benth. The structural elucidation and stereochemistry determination were achieved by spectroscopic and chemical methods including 1D and 2D NMR (1H–1H COSY, HSQC, HMBC, and NOE) experiments, especially the employment of Snatzke’s method expressed by the induced circular dichroism spectra. Anti-inflammatory activities and cytotoxicities of compounds 1–7 were evaluated. [Copyright &y& Elsevier]

Abstract: Nine novel steroidal glycosides substituted with the orthoacetate groups, compounds 1–5 based on the aglycon of 12-O-acetyl-20-O-benzoyl-dihydrosarcostin 8,14,18-orthoacetate and compounds 6–9 based on the aglycon of 12-O-acetyl-20-O-benzoyl-dihydrosarcostin 14,17,18-orthoacetate, were isolated from Dregea sinensis var. corrugata. Their structures were deduced on the basis of chemical and spectral evidences. Compound 1 showed moderate anti-inflammatory activity. [Copyright &y& Elsevier]