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Angucyclines are a family of structurally diverse, aromatic polyketides with some members that exhibit potent bioactivity. Angucyclines have also attracted considerable attention due to the intriguing biosynthetic origins that underlie their structural complexity and diversity. Balmoralmycin (compound 1) represents a unique group of angucyclines that contain an angular benz[α]anthracene tetracyclic system, a characteristic C-glycosidic bond-linked deoxy-sugar (d-olivose), and an unsaturated fatty acid chain. In this study, we identified a Streptomyces strain that produces balmoralmycin and seven biosynthetically related coproducts (compounds 2−8). Four of the coproducts (compounds 5−8) are novel compounds that feature a highly oxygenated or fragmented lactone ring, and three of them (compounds 3−5) exhibited cytotoxicity against the human pancreatic cancer cell line MIA PaCa-2 with IC(50) values ranging from 0.9 to 1.2 μg/mL. Genome sequencing and CRISPR/dCas9-assisted gene knockdown led to the identification of the ~43 kb balmoralmycin biosynthetic gene cluster (bal BGC). The bal BGC encodes a type II polyketide synthase (PKS) system for assembling the angucycline aglycone, six enzymes for generating the deoxysugar d-olivose, and a hybrid type II/III PKS system for synthesizing the 2,4-decadienoic acid chain. Based on the genetic and chemical information, we propose a mechanism for the biosynthesis of balmoralmycin and the shunt products. The chemical and genetic studies yielded insights into the biosynthetic origin of the structural diversity of angucyclines. IMPORTANCE 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. We report a newly isolated Streptomyces strain that produces balmoralmycin in a high fermentation titer as well as several structurally related shunt products. Based on the chemical and genetic information, a biosynthetic pathway that involves a type II polyketide synthase (PKS) system, cyclases/aromatases, oxidoreductases, and other ancillary enzymes was established. The elucidation of the balmoralmycin pathway enriches our understanding of how structural diversity is generated in angucyclines and opens the door for the production of balmoralmycin derivatives via pathway engineering.

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 Ministry of Education (MOE) National Research Foundation (NRF) Submitted/Accepted version We acknowledge the generous funding support from the Ministry of Education of Singapore (ARC Tier 2 grant (T2EP30221-0029) awarded to Z.-X.L.) and National Research Foundation of Singapore (SBP01 grant awarded to Z.-X.L.).

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 (

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. Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version This research was supported by an NIMBEL grant (NIM/03/ 2017, Z.-X.L.) from Nanyang Technological Universty and an NRF-SBP grant (SBP-01 Z.-X.L.) from the National Research Foundation of Singapore.

A joint phytochemical investigation on the MeOH extracts of the twigs and needles of two endangered Pinaceae plants endemic to the Chinese Qinling Mountains, Picea neoveitchii (an evergreen spruce) and Larix potaninii var. chinensis (a deciduous larch), led to the isolation and characterization of 34 and 24 structurally diverse terpenoids, respectively. Among them, seven are previously undescribed, including a picane-type [i.e., 14(13 → 12)abeo-12αH-serratane] (neoveitchin A) and a serratane-type (neoveitchin B) triterpenoids, and an abietane-type (neoveitchin C) as well as four labdane-type (potalarxins A-D) diterpenoids. Their structures and absolute configurations were established by extensive spectroscopic methods and/or X-ray diffraction analyses. All isolates were evaluated for their inhibitory activities against the human protein tyrosine phosphatase 1B (PTP1B). Serrat-14-en-3α,21β-diol, betulinic acid, 3β-hydroxy-11-ursen-13(28)-olide, ursolic acid, and oleanolic acid were found to have considerable inhibitory effects against PTP1B, with IC

Lycopodium alkaloids (LAs) are the characteristic metabolites of club mosses. Chemical differences often exist in different specimens of a single plant species collected from different geographic origins. In this study, a preliminary LC-MS detection and dereplication analyses of alkaloidal constituents of Lycopodium cernuum var. sikkimense (Mull. Hal.) C.B. Clarke (LCVS2) collected from Fujian province led to the isolation and characterization of three undescribed LAs, lycocernuskines A-C, and six known cernuane-type LAs. The known compounds were previously isolated from the same plant species (LCVS1) collected from Chongqing, and so their dereplication in LCVS2 was accomplished based on their retention times (tR) and the quasi-molecular ion peaks in the LC-MS fingerprint. Chemical structures were identified by spectroscopic methods, single-crystal X-ray diffraction analysis, and electronic circular dichroism calculations. Lycocernuskines A and B are the first two examples of C-12 hydroxylated phlegmarane-type LAs bearing a nitrone residue at the quinoline ring. The isolates were evaluated for their anti-AChE and neuroprotective effects.

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. Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version This research was supported by a NIMBEL grant (Z.-X.L. NIM/03/2017) and an NRF grant (Z.-X.L., NRF-SBP-01).

The ethanolic extracts of the dried flower buds of two Caprifoliaceae plants, Lonicera japonica and Abelia × grandiflora, showed considerable inhibitory activities against adenosine triphosphate (ATP)-citrate lyase (ACL), a new promising drug target for the treatment of metabolic disorders. Bioassay-guided purification in conjunction with HPLC-PDA profiling led to the isolation and characterization of thirty-five (1-35) and fourteen (1'-14') structurally diverse compounds from the above two plant extracts, respectively. Compounds 1-9 and 1'-6' are previously undescribed glycosides. Their structures were elucidated on the basis of spectroscopic data, electronic circular dichroism (ECD), and single crystal X-ray diffraction analyses. In particular, lonicejaposide A (1) has an unprecedented skeleton generated through the coupling of C-7 in secologanin with C-2'' in phenylacetaldehyde via an aldol condensation. Abeliflorosides A (1') and B (2') are hitherto unknown glycosides of triterpene and bisiridoid conjugates constructed through the formation of a 1,3-dioxane moiety. All the isolates were evaluated for their inhibitory activities against ACL. Compounds 9, 25-28, 31, 1', 2', and 14' displayed significant inhibitory effects, with IC

Rare and endangered plants (REPs) and their associated endophytes survived in unique habitats are promising sources for natural product-derived drug discovery. In this study, six new (cephaloverines A–F, 1–6, resp.) and 16 known (11–26) cephalotaxine-type alkaloids, together with three new (oliverbiflavones A–C, 7–9, resp.) and 11 known (27–37) biflavonoids were isolated and characterized from the twigs and leaves of Cephalotaxus oliveri, an endangered plant endemic to China. Meanwhile, a preliminary investigation on the secondary metabolites from a selected fungal endophyte (i.e., Alternaria alternate Y-4–2) associated with the title plant led to the isolation of 21 structurally distinct polyketides including one new dimeric xanthone (10). The new structures (1–10) with the absolute configurations were determined by detailed spectroscopic analyses, electronic circular dichroism (ECD) or Na2MoO4-induced ECD, the modified Mosher’s method, and some chemical transformations. Compounds 1–4 are the first representatives of naturally occurring N-oxides of cephalotaxine esters, while compounds 7–9 have a special structural feature of having a C-methylated biflavonoid skeleton. The Cephalotaxus alkaloids with ester side-chains at C-3 (1–6, 13–22, and 26) and four biflavonoids (27–29 and 34) were found to show pronounced cytotoxicities against a small panel of human cancer cell lines (A549, NCI-H460, HL60, NCI-H929, and RPMI-8226), with IC50 values mainly ranging from 0.003 to 9.34 μM. The most potent compound, deoxyharringtonine (16), generally exhibited IC50 values less than 10 nM. The structure–activity relationship (SAR) of the aforementioned Cephalotaxus alkaloids was briefly discussed.

We report the genome-guided discovery of sungeidines, a class of microbial secondary metabolites with unique structural features. Despite evolutionary relationships with dynemicin-type enediynes, the sungeidines are produced by a biosynthetic gene cluster (BGC) that exhibits distinct differences from known enediyne BGCs. Our studies suggest that the sungeidines are assembled from two octaketide chains that are processed differently than those of the dynemicin-type enediynes. The biosynthesis also involves a unique activating sulfotransferase that promotes a dehydration reaction. The loss of genes, including a putative epoxidase gene, is likely to be the main cause of the divergence of the sungeidine pathway from other canonical enediyne pathways. The findings disclose the surprising evolvability of enediyne pathways and set the stage for characterizing the intriguing enzymatic steps in sungeidine biosynthesis. Submitted/Accepted version

Correction for ‘Discovery, biosynthesis and antifungal mechanism of the polyene-polyol meijiemycin’ by Zhen Jie Low et al., Chem. Commun., 2020, DOI: 10.1039/c9cc08908j.

Pseudomonads rely on the flagellar motor to rotate a polar flagellum for swimming and swarming, and to sense surfaces for initiating the motile‐to‐sessile transition to adopt a surface‐dwelling lifestyle. Deciphering the function and regulation of the flagellar motor is of paramount importance for understanding the behaviours of environmental and pathogenic pseudomonads. Recent studies disclosed the preeminent role played by the messenger c‐di‐GMP in controlling the real‐time performance of the flagellar motor in pseudomonads. The studies revealed that c‐di‐GMP controls the dynamic exchange of flagellar stator units to regulate motor torque/speed and modulates the frequency of flagellar motor switching via the chemosensory signalling pathways. Apart from being a rotary motor, the flagellar motor is emerging as a mechanosensor that transduces surface‐induced mechanical signals into an increase of cellular c‐di‐GMP concentration to initiate the cellular programs required for long‐term colonization. Collectively, the studies generate long‐awaited mechanistic insights into how c‐di‐GMP regulates bacterial motility and the motile‐to‐sessile transition. The new findings also raise the fundamental questions of how cellular c‐di‐GMP concentrations are dynamically coupled to flagellar output and the proton‐motive force, and how c‐di‐GMP signalling is coordinated spatiotemporally to fine‐tune flagellar response and the behaviour of pseudomonads in solutions and on surfaces. Nanyang Technological University National Research Foundation (NRF) Submitted/Accepted version The authors are grateful for the generous financial support from the Nanyang Technological University (NTU) (NIMBEL grant NIM/03/2017) and National Research Foundation of Singapore (SBP‐01).

A preliminary phytochemical investigation on the MeOH extract of the leaves and twigs of the endangered ornamental plant Michelia shiluensis led to the isolation of 16 sesquiterpenoids. The isolated compounds comprised germacrane- (1-4, 13, 14), guaiane- (5-9, 15), amorphane- (10), and eudesmane-type (11, 12, 16) sesquiterpenoids. The new structures (1-12) were elucidated by spectroscopic and computational methods, and their absolute configurations (except for 9) were assigned by single-crystal X-ray diffraction crystallographic data and/or electronic circular dichroism spectra. Shiluolides (A-D, 1-4) are unprecedented C16 or C17 homogermacranolides, and their putative biosynthetic pathways are briefly discussed. Shiluone D (8) is a rare 1,10- seco-guaiane sesquiterpenoid featuring a new ether-containing spirocyclic ring, whereas shiluone E (9) represents the first example of a 1,5-4,5-di- seco-guaiane with a rare 5,11 -lactone moiety. Shiluone F (10) is the first amorphane-type sesquiterpenoid possessing an oxetane ring bridging C-1 and C-7. Bioassay evaluations indicated that lipiferolide (13) showed noteworthy cytotoxicities toward human cancer cell lines MCF-7 and A-549, with IC50 values of 1.5 and 7.3 μM, respectively. Shiluone D (8) exerted inhibition against protein tyrosine phosphatase 1B (IC50: 46.3 μM).

Two previously undescribed chimonanthine-type [sinodamines A and B] and five related known dimeric tryptamine-derived alkaloids were isolated and characterized from the leaves of the endangered ornamental plant Sinocalycanthus chinensis under the guidance of LC-MS detection and dereplication analyses, along with conventional isolation procedures. Their structures were established on the basis of spectroscopic methods and chemical transformations. Sinodamine A can be regarded as the naturally occurring N-oxide derivative of its pseudo-mesomer sinodamine B. An acid-catalyzed Meisenheimer rearrangement from sinodamine A to its oxazine-form with a final equilibrium of 1:2 was observed by monitoring their NMR spectra. (−)-Folicanthine showed significant cytotoxicity against human lung carcinoma A549 and colorectal carcinoma HT29 cells, with IC50 values of 7.76 and 6.16 μM, respectively.

Two new (1 and 2) and 10 known (3−12) acylated iridoid diglycosides were isolated from the twigs and leaves of the cultivated endangered ornamental plant Gmelina hainanensis. Based on spectroscopic data interpretation and chemical transformation, the new triacyl and the new diacyl iridoid diglycosides were established to be 6-O-α-L-(2″,3″-di-O-acetyl-4″-O-cis-cinnamoyl)rhamnopyranosylcatalpol (1) and 6-O-α- l -(2″,4″-di-O-trans-cinnamoyl)rhamnopyranosylcatalpol (2), respectively. All the isolates were evaluated for their inhibitory effects against the protein tyrosine phosphatase 1 B (PTP1B) enzyme.

Pinus kwangtungensis is an endangered pine species native to China. In the present study, 15 diterpenoids including three new labdane-type analogs were isolated and characterized during a pioneer phytochemical investigation on a mass-limited sample of the needles and twigs of this plant, which is growing in a Cantonese garden. The new structures, (4S,5R,9S,10R)-6-oxo-labd-7,13-dien-16,15- olid-19-oic acid (1), 15(S)-n-butoxypinusolidic acid (2), and β- d -glucopyranosyl- (4S,5R,9S,10R)-labda-8(17),13-dien-15,16-olid-19-oate (3), were established by extensive spectroscopic methods and some chemical transformations. Among the isolates, lambertianic acid (10) and cassipourol (15) showed inhibitory activities against human protein tyrosine phosphatase 1 B (PTP1B), a target for the treatment of type-II diabetes and obesity, with IC50 values of 25.5 and 11.2 μM, respectively.

Supplemental material, Supplementary Data, for Simultaneous Identification of Characteristic Components in HPLC-PDA-ELSD Fingerprint Profile of Ginkgo biloba Leaves Extract by Guang-Lei Ma, Jiang Wan, Juan Xiong, Guo-Xun Yang, and Jin-Feng Hu in Natural Product Communications

Produced by a newly isolated Streptomycetes strain, meijiemycin is a gigantic linear polyene-polyol that exhibits structural features not seen in other members of the polyene-polyol family. We propose a biosynthetic mechanism and demonstrate that meijiemycin inhibits hyphal growth by inducing the aggregation of ergosterol and restructuring of the fungal plasma membrane. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

In this review, we intensively focus on the advances in research of natural products (NPs) discovery carried out by domestic scholars in China from 2015 through 2017. In general, a total of 1811 publications (1479 in English and 332 in Chinese) were accumulated regarding newly isolated NPs from plants, microorganisms, and marine sources. As a result, 277 selected papers concerning naturally occurring compounds with extraordinary frameworks, origins, and promising activities were discussed in this review article, mainly organized according to their structural classes and novelties.

Two new [named salicifoxazines A (1) and B (2)] and six known dimeric tryptamine-derived alkaloids (3–8) were isolated from the leaves of Chimonanthus salicifolius. The new structures were established on the basis of extensive spectroscopic methods and chemical transformations. The absolute configuration of 1 was determined by the observed Cotton effects in its circular dichroism (CD) spectrum, whereas 2 is a pseudo-mesomer of 1. In fact, the first two naturally occurring asymmetric tetrahydro-1,2-oxazine-containing tryptamine-derived alkaloids 1 and 2 are diastereoisomers at C-3a/C-8a or at C-3a′/C-8a′. Compounds 1, 2, (−)-chimonanthine (3), and meso-chimonanthine (4) were found to show moderate cytotoxic effects against human colorectal carcinoma cells (SW-1116 and HCT-116) and/or gastric carcinoma cells (SGC-7901).

Four new naturally occurring steroidal glycosides (leonurosides A–D, 1 – 4 ) were isolated from the dried fruits of Leonurus japonicus (motherwort fruit). Their structures were established by spectroscopic and chemical methods. The monosaccharide unit was identified to be a 2-acetamido-2-deoxy-β- d- glucose and the aglycone is either a common 3β-stigmasterol or 3β-ergosterol derivative. These compounds are the first representatives of steroid N -acetylglucosaminides from vascular plants.

Ten diterpenoids including three new abietanes (1–3) were isolated from the twigs and needles of Podocarpus imbricatus, an endangered conifer growing in a Cantonese garden. The new structures were established by means of spectroscopic methods. Among the isolates, 3β-hydroxy-abieta-8,11,13-trien-7-one (5), decandrin G (6), and 7,15-pimaradien-18-oic acid (8) showed significant anti-neuroinflammatory activities by inhibiting the overproduction of nitric oxide (NO) in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells, with IC50 values of 3.7, 11.1, and 4.5 μM, respectively.

Four novel naturally occurring diastereoisomers of dinor-eudesmenes, named chloranthones A-D (1-4, resp.), were isolated as minor components from the EtOH extract of the aerial parts of Chloranthus elatior. The unprecedented framework was established using extensive 2D-NMR techniques. Their absolute configurations were deduced from the observed Cotton effects in their circular dichroism (CD) spectra. A plausible biosynthetic pathway to the dinor-eudesmenes is proposed.

This is an updated fingerprint profile for the simultaneous identification of 29 compounds, mainly including characteristic -terpene trilactones and flavonoid glycosides from Ginkgo biloba leaves (EGb) by employing a high-performance liquid chromatography-photodiode array-evaporative light scattering detector method. Compounds 1 and 6 had not been previously either detected or described in any EGb samples. In general, these 29 compounds were distributed into 5 regions in the fingerprint according to their different structural properties. This efficient analytical method could be generally applied to the quality control of EGb761 and other commercially available EGb products in the Chinese active pharmaceutical ingredients market.

Nine unexpected new flavonol glycoside cyclodimers in the truxinate (1–7, biginkgosides A–G, respectively) or truxillate [biginkgosides H (8) and I (9)] forms were isolated as minor components from the extract of Ginkgo biloba leaves. The new dimers possess an unusual cyclobutane ring formed by a [2+2]-cycloaddition between two symmetric (for compounds 1–5 and 7–9) or nonsymmetric (for 6) flavonol coumaroyl glucorhamnosides. A plausible biosynthetic pathway for these new compounds based on the frontier molecular orbital theory of cycloaddition reactions is briefly discussed. An antineuroinflammatory screening revealed that biginkgosides E (5) and H (8) inhibited nitric oxide production in lipopolysaccharide-activated BV-2 microglial cells, with IC50 values of 2.91 and 17.23 μM, respectively. Additionally, biginkgoside F (6) showed a significant neuroprotective effect (34.3% increase in cell viability at 1 μM) against Aβ25–35-induced cell viability decrease in SH-SY5Y neuroblastoma cells.

Four new diastereomers of dinor-eudesmenes, named chloranthones A-D (Ia)-(Id), are isolated as minor components from the EtOH extract of the aerial parts of Chloranthus elatior.

Ten new lycodine-type alkaloids, named casuarinines A-J (1-10), along with eight known analogues (11-18), were isolated from the whole plant of Lycopodiastrum casuarinoides . The new structures were established by spectroscopic methods and chemical transformations. Casuarinines A-D (1-4) and J (10) are common lycodine alkaloids possessing four connected six-membered rings, while tricyclic casuarinines E-H (5-8) are the piperidine ring cleavage products. In particular, casuarinine I (9) has an unprecedented five-membered tetrahydropyrrole ring instead of the piperidine ring. A plausible biosynthetic pathway to 9 is proposed. Among the compounds reported, casuarinine H (8) exhibited significant neuroprotective effect against hydrogen peroxide (H₂O₂)-induced neuronal cell damage in human neuroblastoma SH-SY5Y cells, while casuarinines C (3) and I (9) showed moderate inhibitory activity against acetylcholinesterase (AChE).