Search

BesC catalyzes the iron- and O(2)-dependent cleavage of 4-chloro-l-lysine to form 4-chloro-l-allylglycine, formaldehyde, and ammonia. This process is a critical step for a biosynthetic pathway that generates a terminal alkyne amino acid which can be leveraged as a useful bio-orthogonal handle for protein labeling. As a member of an emerging family of diiron enzymes that are typified by their heme oxygenase-like fold and a very similar set of coordinating ligands, recently termed HDOs, BesC performs an unusual type of carbon–carbon cleavage reaction that is a significant departure from reactions catalyzed by canonical dinuclear-iron enzymes. Here, we show that BesC activates O(2) in a substrate-gated manner to generate a diferric-peroxo intermediate. Examination of the reactivity of the peroxo intermediate with a series of lysine derivatives demonstrates that BesC initiates this unique reaction trajectory via cleavage of the C4–H bond; this process represents the rate-limiting step in a single turnover reaction. The observed reactivity of BesC represents the first example of a dinuclear-iron enzyme that utilizes a diferric-peroxo intermediate to capably cleave a C–H bond as part of its native function, thus circumventing the formation of a high-valent intermediate more commonly associated with substrate monooxygenations.

Fusarium graminearum is a pathogenic fungus causing huge economic losses worldwide via crop infection leading to yield reduction and grain contamination. The process through which the fungal invasion occurs remains poorly understood. We recently characterized fusaoctaxin A in F. graminearum, where this octapeptide virulence factor results from an assembly line encoded in fg3_54, a gene cluster proved to be involved in fungal pathogenicity and host adaptation. Focusing on genes in this cluster that are related to fungal invasiveness but not to the biosynthesis of fusaoctaxin A, we here report the identification and characterization of fusaoctaxin B, a new octapeptide virulence factor with comparable activity in wheat infection. Fusaoctaxin B differs from fusaoctaxin A at the N-terminus by possessing a guanidinoacetic acid (GAA) unit, formation of which depends on the combined activities of the protein products of fgm1-3. Fgm1 is a cytochrome P450 protein that oxygenates l-Arg to 4(R)-hydroxyl-l-Arg in a regio- and stereoselective manner. Then, Cβ-Cγ bond cleavage proceeds in the presence of Fgm3, a pyridoxal-5'-phosphate-dependent lyase, giving guanidinoacetaldehyde and l-Ala. Rather than being directly oxidized to GAA, the guanidine-containing aldehyde undergoes spontaneous cyclization and subsequent enzymatic dehydrogenation to provide glycociamidine, which is linearized by Fgm2, a metallo-dependent amidohydrolase. The GAA path in F. graminearum is distinct from that previously known to involve l-Arg:l-Gly aminidotransferase activity. To provide this nonproteinogenic starter unit that primes nonribosomal octapeptidyl assembly, F. graminearum employs new chemistry to process l-Arg through inert C-H bond activation, selective C-C bond cleavage, cyclization-based alcohol dehydrogenation, and amidohydrolysis-associated linearization.

Nature has developed complexity–generating reactions within natural product biosynthetic pathways. However, direct utilization of these pathways to prepare compound libraries remains challenging due to limited substrate scopes, involvement of multiple-step reactions, and moderate robustness of these sophisticated enzymatic transformations. Synthetic chemistry, on the other hand, offers an alternative approach to prepare natural product analogs. However, owing to complex and diverse functional groups appended on the targeted molecules, dedicated design and development of synthetic strategies are typically required. Herein, by leveraging the power of chemo-enzymatic synthesis, we report an approach to bridge the gap between biological and synthetic strategies in the preparation of quinolone alkaloid analogs. Leading by in silico analysis, the predicted substrate analogs were chemically synthesized. The AsqJ-catalyzed asymmetric epoxidation of these substrate analogues was followed by an Lewis Acid-triggered ring contraction to complete the viridicatin formation. We evaluated the robustness of this method in gram-scale reactions. Lastly, through chemoenzymatic cascades, a library of quinolone alkaloids is effectively prepared.

Aminovinyl-cysteine residues arise from processing the C-terminal l-Cys and an internal l-Ser/l-Thr or l-Cys of a peptide. Formation of these nonproteinogenic amino acids, which occur in a macrocyclic ring of diverse ribosomally synthesized lanthipeptides and non-lanthipeptides, remains poorly understood. Here, we report that LanD-like flavoproteins in the biosynthesis of distinct non-lanthipeptides share an unexpected dual activity for aminovinyl-cysteine formation. Each flavoprotein catalyzes oxidative decarboxylation of the C-terminal l-Cys and couples the resulting enethiol nucleophile with the internal residue to afford a thioether linkage for peptide cyclization. The cyclization step, which largely depends on proximity effect by positioning the enethiol intermediate with a bent conformation at the active site, can be substrate-dependent, proceeding inefficiently through nucleophilic substitution for an unmodified peptide or efficiently through Michael addition for a dehydrated/dethiolated peptide. Uncovering this unusual flavin-dependent paradigm for thioether residue formation advances the understanding in the biosynthesis of aminovinyl-cysteine-containing RiPPs and renews interest in flavoproteins, particularly those involved in non-redox transformations. LanD-like flavoproteins activity, which is flexible in peptide substrate and amenable for evolution by engineering, can be combined with different post-translational modifications for structural diversity, thereby holding promise for peptide macrocyclization/functionalization in drug development by chemoenzymatic or synthetic biology approaches.

Diversity oriented synthesis starting from natural products is a newly coming strategy to build diverse skeletons to meet the demands of high throughput screening in drug development. Caryophyllene was being considered as an ideal starting point to build divers natural-like sesquiterpenes due to its rich sources and build-in reactivity. In this paper, six new natural-like products (2–7) were synthesized form the natural cryophyllene oxide via cascade oxidation and transannular reactions in a one-pot procedure. Their structures were elucidated by exhaustive spectra method including 2D NMR and X-ray diffraction. Of the products, compounds 6 and 7 possess very similar skeleton to natural products. Our findings demonstrated that one-pot cascade reactions on macrocyclic natural products is a concise strategy to create diverse natural-like skeletons.

(-)-β-Caryophyllene was decorated with a privileged β-lactam motif and subsequently converted into highly diverse scaffolds via remodeling of the ring system. The structures were defined by spectroscopic data, X-ray diffraction analysis, and experimental and calculated ECD data. Compound 19 displayed the most potent activity against the rice blast fungus, while 6 had a more potent α-glucosidase inhibition than the drug acarbose. These findings demonstrate a concise protocol to exploit natural product-driven diversity.

Four new highly oxidized caryophyllene-type sesquiterpenes (1–4), one new caryophyllene-type natural product (5), and two new drimane-type sesquiterpenes (6, 7), along with eight known compounds have been isolated from an endophytic fungus Pestalotiopsis adusta. Their structures were elucidated on the basis of HRESIMS, 1D and 2D NMR spectroscopic data analyses. The absolute configurations for 1 and 5 were determined by single-crystal X-ray crystallographic analysis using Cu Kα radiation. The absolute configuration of 6 was determined by CD spectrum associated with TD-DFT calculation of its benzoylated derivative 6a. The in vitro bioassay revealed that 8 and 9 presented cytotoxicity against cancer cell lines A549, HeLa, and SMMC-7721, in which 8 showed comparable activity (IC50 = 28.3 μM) to the positive control etoposide (IC50 = 23.2 μM) against SMMC-7721.

Fifteen aromatic polyketide metabolites, including four new chromones, chaetosemins B–E (2–5), with compound 4 bearing a new skeleton, and two new natural products, chaetosemin A (1) and (+)-(S)-chaetoquadrin J (14), together with nine known ones (6–13, 15), were isolated from the organic extract of a solid fermented culture of an Ascomycete filamentous fungus, Chaetomium seminudum. The structures of 1–5 were determined by spectroscopic analysis, and the absolute configuration of chaetosemin A (1) was confirmed by X-ray crystallography, whereas the stereochemistry of 1–4 and 14 was assigned by comparison of their specific optical rotations with reported data for structurally related compounds. All compounds were isolated for the first time from Chaetomium seminudum. Compounds 1 and 2 consisted of L-cysteine and D-cysteine units, respectively. Most of them were evaluated for in vitro antifungal activities against some phytopathogenic fungi. Among them, chaetosemin B (2) was the most active against Magnaporthe oryzae and Gibberella saubinettii with MICs of 6.25 and 12.5 μM, respectively. In addition, chaetosemin C (3) showed antioxidant activity with 50.7% DPPH free radical scavenging activity at 50 μM, and chaetoquadrin J (14) displayed weak inhibition of soluble epoxide hydrolase (sEH).

The natural product (−)-β-caryophyllene is considered as an ideal initiator to generate diverse scaffolds by transannular cyclization due to its macrocyclic structure and abundant availability in nature. An endophytic strain Aspergillus tubingensis KJ-9 was screened in our lab to catalyse remodeling of the β-caryophyllene skeleton. In the fermentation, macrocyclic β-caryophyllene was remodeled into a series of natural product-like polycyclic compounds with unusual diverse skeletons (1–7). Their structures, including absolute configuration, were elucidated by several spectroscopic methods (1D & 2D NMR, HRMS, ECD and X-ray diffraction). Especially, scaffolds 1 and 3 were not found in acid-catalysed products before. Our findings demonstrated the potential of endophytic fungi for catalyzing macrocyclic compounds into diverse products.

Cultivation of Penicillium minioluteum with azacitidine, a DNA methyltransferase inhibitor, led to the isolation of a novel type of aspertetronin dimer, named miniolins A–C (1–3), along with their precursor aspertetronin A (4). The structures of 1–3 were elucidated by extensive spectroscopic methods, and the absolute configurations were assigned by the chiral HPLC analysis of chemical degradation products and electronic circular dichroism associated with the TDDFT computational method (CAM-B3LYP/TZVP). The miniolins showed moderate cytotoxic activity against Hela cell lines.

Eleven compounds were isolated from the culture of an endophytic bacterium Pseudomonas brassicacearum subsp. Neoaurantiaca in Salvia miltiorrhiza Bunge. Their structures were elucidated by spectroscopic methods as cyclo-(Gly-L-Ala) (1), cyclo-(L-Ala-L-Ala) (2), cyclo-(L-Pro-Gly) (3), cyclo-(L-Pro-L-Ser) (4), cyclo-(L-Ala-trans-4-hydroxy-L-Pro) (5), cyclo-(L-Val-L-Pro) (6), cyclo-(Gly-L-Tyr) (7), cyclo-(L-Ala-L-Tyr) (8), cyclo-(L-Tyr-trans-4-hydroxy-L-Pro) (9), 3-methylhydantoin (10) and 2-piperidinone (11). All these compounds were isolated from this bacterium for the first time. The brine shrimp lethality, antifungal and antibacterial activities of these compounds were evaluated. The results indicated that some cyclodipeptides may play an important role in plant-bacteria interactions.

Cyathane diterpenoids, occurring exclusively in higher basidiomycete (mushrooms), represent a structurally diverse class of natural products based on a characteristic 5-6-7 tricyclic carbon scaffold, including 105 members reported to date. These compounds show a diverse range of biological activities, such as antimicrobial, anti-MRSA, agonistic toward the kappa-opioid receptor, antiinflammatory, anti-proliferative and nerve growth factor (NGF)-like properties. The present review focuses on the structure diversity, structure elucidation and biological studies of these compounds, including mechanisms of actions and structure-activity relationships (SARs). In addition, new progress in chemical synthesis of cyathane diterpenoids is discussed.

Six known compounds, isoroquefortine C (1), griseofulvin (2), ergosterol peroxide (3), 3β-hydroxy-(22E,24R)-ergosta-5,8,22-trien-7-one (4), cerevisterol (5) and (22E,24R)-6β-methoxyergosta-7,22-diene-3β,5α-diol (6), were produced by the fungus Penicillium brasilianum, and their structures were elucidated by spectroscopic methods. This is the first report on isoroquefortine C as naturally occurring compound. Their bioactivities against five phytopathogenic fungi (Gibeberalla saubinetti, Fusarium solani, Botrytis cinerea, Colletotrichum gloeosporioides and Alternaria solani) and four pathogenic bacteria (Escherichia coli, Bacillus subtilis, Staphyloccocus aureus and Bacillus cereus), as well as allelopathic activities on Raphanus sativus were tested. Compound 1 exhibited a remarkable antifungal activity with minimum inhibitory concentration (MIC) of 12.5 μM against C. gloeosporioides, in comparison with positive control hymexazol (MIC 25 μM). Compound 2 displayed strong inhibitory effects on the growth of A. solani and S. aureus with MIC of 3.13 μM for each. Compounds 2 and 3 displayed a significant growth-inhibition activity on R. sativus.

On the basis of the OSMAC (one strain-many compounds) strategy, 14 indole diketopiperazine (DKP) alkaloids, including spirotryprostatins (1-3), tryprostatins (4-6), and cyclotryprostatins (7-14), were isolated from the endophyte Aspergillus fumigatus associated with Melia azedarach L. Their structures were identified by nuclear magnetic resonance and electrospray ionization mass spectrometry data. All the indole DKPs were evaluated for plant growth regulation using the lettuce (Lactuca sativa) seedling growth bioassay, which showed the plant growth influence of the seedling. Among these compounds tested, a tryprostatin-type compound, brevianamide F (6), was identified as a new type of natural potential plant growth inhibitor with a response index (RI) higher than that of the positive control glyphosate, a broad-spectrum systemic herbicide. 6 can also inhibit turnip (Raphanus sativus) shoot and root elongation with RIs of -0.76 and -0.70, respectively, at 120 ppm, and it strongly inhibits amaranth (Amaranthus mangostanus) seedling growth with a high RI of -0.9 at 40 ppm. The structure-allelopathic activity relationship analysis of these isolated alkaloids indicates that tryprostatin-type alkaloids without the C5 prenyl and methoxy group give the most potent inhibition of seedling growth. Brevianamide F (6) could be used to develop a natural eco-friendly herbicide.

To observe the clinical effects of using the Chinese Shang Ring in circumcision children with either phimosis or redundant prepuce, and to investigate its superiority over the similar devices available.A total of 824 children with phimosis or redundant prepuce underwent circumcision with the Shang Ring. The clinical data were assessed concerning the duration of the procedure, incidence of post-operative complications, time of recovery and appearance of the penis.The procedure duration was (2.6 +/-1.2) min, and the complications included infection in 4 (0.6%), edema in 21 (3.2%), delayed removal of the ring in 10 (1.5%), redundant and asymmetric mucosa attributable to performance in 6 (0.9%) of the cases. The wounds healed and the rings were removed at 13.4 +/- 5.8 days after circumcision, with well-smoothed incision and good cosmetic results.Child circumcision with the Chinese Shang Ring is easy and simple in performance, with less operative time, fewer complications and better cosmetic results.