Daowan Lai

Bis-naphtho-γ-pyrones from Fungi and Their Bioactivities

Bis-naphtho-γ-pyrones are an important group of aromatic polyketides derived from fungi. They have a variety of biological activities including cytotoxic, antitumor, antimicrobial, tyrosine kinase and HIV-1 integrase inhibition properties, demonstrating their potential applications in medicine and agriculture. At least 59 bis-naphtho-γ-pyrones from fungi have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, biosynthesis, and structure, as well as their biological activities. Some considerations regarding to synthesis, production, and medicinal and agricultural applications of bis-naphtho-γ-pyrones are also discussed.

Natural Dibenzo-α-Pyrones and Their Bioactivities

Natural dibenzo-α-pyrones are an important group of metabolites derived from fungi, mycobionts, plants and animal feces. They exhibit a variety of biological activities such as toxicity on human and animals, phytotoxicity as well as cytotoxic, antioxidant, antiallergic, antimicrobial, antinematodal, and acetylcholinesterase inhibitory properties. Dibenzo-α-pyrones are biosynthesized via the polyketide pathway in microorganisms or metabolized from plant-derived ellagitannins and ellagic acid by intestinal bacteria. At least 53 dibenzo-α-pyrones have been reported in the past few decades. This mini-review aims to briefly summarize the occurrence, biosynthesis, biotransformation, as well as their biological activities and functions. Some considerations related to synthesis, production and applications of dibenzo-α-pyrones are also discussed.

Bioactive Spirobisnaphthalenes from the Endophytic Fungus Berkleasmium sp.

Nine new spirobisnaphthalenes, palmarumycins B1-B9 (1-9), along with 13 known compounds (10-22), were isolated from cultures of the fungus Berkleasmium sp., an endophyte isolated from the medicinal plant Dioscorea zingiberensis C. H. Wright. The structures of the new compounds were elucidated by analysis of the 1D and 2D NMR and HRESIMS spectra and by comparison with known compounds. Compounds 7-9 contain an uncommon 2,3-dihydro-1H-inden-1-one unit. All isolated compounds were evaluated for their antibacterial activities against Bacillus subtilis, Staphylococcus hemolyticus, Agrobacterium tumefaciens, Pseudomonas lachrymans, Ralstonia solanacearum, and Xanthomonas vesicatoria and for their antifungal effects against the spore germination of Magnaporthe oryzae. Palmarumycin C8 (22) exhibited the best antibacterial and antifungal effects. In addition, diepoxin δ (11) and palmarumycin C8 (22) showed pronounced cytotoxic activities against five human cancer cell lines (HCT-8, Bel-7402, BGC-823, A 549, A 2780) with IC50 values of 1.28-5.83 μM.

Bioactive Bis-naphtho-γ-pyrones from Rice False Smut Pathogen Ustilaginoidea virens

Ustilaginoidins were bis-naphtho-γ-pyrones mycotoxins possessing an aR configuration of the chiral axis previously reported from the false smut balls of rice infected by the fungal pathogen Ustilaginoidea virens. To investigate the chemical diversity of these metabolites and their bioactivities, we fermented this fungus on solid rice media, which afforded the isolation of 13 ustilaginoidins, including seven new compounds, namely ustilaginoidins K-P, 1-6, and E1, 7, together with the known ustilaginoidins A, 8, D, 9, E, 10, F, 11, and G, 12, and isochaetochromin B2, 13. The structures of the new compounds were elucidated by using (1D, 2D) NMR, high-resolution mass spectrometry, UV, and circular dichroism, as well as by comparison with the literature data. A plausible biosynthesis pathway was proposed for these dimeric polyketides. The isolated compounds were evaluated for their antibacterial, cytotoxic, and radicle elongation inhibitory activities. Ustilaginoidins K, 1 and L, 2 showed cytotoxic activities on the A2780 human ovarian cancer cell line with IC50 values of 4.18 and 7.26 μM, respectively. Ustilaginoidins N, 4, D, 9, E, 10, and G, 12 were active against the tested pathogenic bacteria with MIC values in the range of 16-64 μg/mL. Ustilaginoidins O, 5, E, 10, and F, 11, and isochaetochromin B2, 13 displayed moderate inhibitory activity on the radicle elongation of rice seeds.

Development of a Monoclonal Antibody-Based icELISA for the Detection of Ustiloxin B in Rice False Smut Balls and Rice Grains

Rice false smut is an emerging and economically-important rice disease caused by infection by the fungal pathogen Villosiclava virens. Ustiloxin B is an antimitotic cyclopeptide mycotoxin isolated from the rice false smut balls that formed in the pathogen-infected rice spikelets. A monoclonal antibody (mAb) designated as mAb 1B5A10 was generated with ustiloxin B—ovalbumin conjugate. A highly-sensitive and specific indirect competitive enzyme-linked immunosorbent assay (icELISA) was then developed. The median inhibitory concentration (IC50) of the icELISA was 18.0 ng/mL for the detection of ustiloxin B; the limit of detection was 0.6 ng/mL, and the calibration range was from 2.5 to 107.4 ng/mL. The LOD/LOQ values of the developed ELISA used for the determination of ustiloxin B in rice false smut balls and rice grains were 12/50 μg/g and 30/125 ng/g, respectively. The mAb 1B5A10 cross-reacted with ustiloxin A at 13.9% relative to ustiloxin B. Average recoveries of ustiloxin B ranged from 91.3% to 105.1% for rice false smut balls at spiking levels of 0.2 to 3.2 mg/g and from 92.6% to 103.5% for rice grains at spiking levels of 100 to 5000 ng/g. Comparison of ustiloxin B content in rice false smut balls and rice grains detected by both icELISA and high performance liquid chromatography (HPLC) demonstrated that the developed icELISA can be employed as an effective and accurate method for the detection of ustiloxin B in rice false smut balls, as well as rice food and feed samples.

Sorbicillinoids from Fungi and Their Bioactivities

Sorbicillinoids are important hexaketide metabolites derived from fungi. They have a variety of biological activities including cytotoxic, antioxidant, antiviral and antimicrobial activity. The unique structural features of the sorbicillinoids make them attractive candidates for developing new pharmaceutical and agrochemical agents. About 90 sorbicillinoids have been reported in the past few decades. This mini-review aims to briefly summarize their occurrence, structures, and biological activities.

Bioactive Dibenzo-α-pyrone Derivatives from the Endophytic Fungus Rhizopycnis vagum Nitaf22

Six new dibenzo-α-pyrones, rhizopycnolides A (1) and B (2) and rhizopycnins A-D (3-6), together with eight known congeners (7-14), were isolated from the endophytic fungus Rhizopycnis vagum Nitaf22 obtained from Nicotiana tabacum. The structures of the new compounds were unambiguously elucidated using NMR, HRESIMS, TDDFT ECD calculation, and X-ray crystallography data. Rhizopycnolides A (1) and B (2) feature an uncommon γ-butyrolactone-fused dibenzo-α-pyrone tetracyclic skeleton (6/6/6/5), while rhizopycnin B (4) was the first amino group containing dibenzo-α-pyrone. Rhizopycnolides A (1) and B (2) are proposed to be biosynthesized from polyketide and tricarboxylic acid cycle pathways. The isolated compounds were tested for their antibacterial, antifungal, and cytotoxic activities. Among them, rhizopycnolide A (1), rhizopycnins C (5) and D (6), TMC-264 (8), penicilliumolide D (11), and alternariol (12) were active against the tested pathogenic bacteria Agrobacterium tumefaciens, Bacillus subtilis, Pseudomonas lachrymans, Ralstonia solanacearum, Staphylococcus hemolyticus, and Xanthomonas vesicatoria with MIC values in the range 25-100 μg/mL. Rhizopycnin D (6) and TMC-264 (8) strongly inhibited the spore germination of Magnaporthe oryzae with IC50 values of 9.9 and 12.0 μg/mL, respectively. TMC-264 (8) showed potent cytotoxicity against five human cancer cell lines (HCT-116, HepG2, BGC-823, NCI-H1650, and A2780) with IC50 values of 3.2-7.8 μM.

Main Ustilaginoidins and Their Distribution in Rice False Smut Balls

Rice false smut has become an increasingly serious fungal disease in rice (Oryza sativa L.) production worldwide. Ustilaginoidins are bis-naphtho-γ-pyrone mycotoxins previously isolated from the rice false smut balls (FSBs) infected by the pathogen Villosiclava virens in rice spikelets on panicles. To investigate the main ustilaginoidins and their distribution in rice FSBs, five main bis-naphtho-γ-pyrones, namely ustilaginoidins A (1), G (2), B (3), I (4) and C (5), were isolated and identified by NMR and high-resolution mass spectrometry as well as by comparison with the data in the literature. The rice FSBs at early, middle and late maturity stages were divided into their different parts and the contents of five main ustilaginoidins for each part were determined by HPLC analysis. The results revealed that the highest levels of ustilaginoidins were in late stage rice FSBs, followed by those at middle stage. Most ustilaginoidins, 96.4% of the total quantity, were distributed in the middle layer at early stage. However, ustilaginoidins were mainly distributed in the outer and middle layers at middle and late stages. Small amounts of ustilaginoidins A (1) and G (2) were found in the inner part of rice FSBs at each maturity stage. The contents of ustilaginoidins A (1) and G (2) without hydroxymethyl groups at C-2 and C-2’ of the γ-pyrone rings in rice FSBs were relatively high at early stage, while the contents of ustilaginoidins B (3), I (4), and C (5) with hydroxymethyl groups at C-2 or C-2’ were relatively high at late stage.

A monoclonal antibody-based enzyme-linked immunosorbent assay for detection of ustiloxin A in rice false smut balls and rice samples.

Ustiloxin A, a cyclopeptide mycotoxin, was isolated from the pathogenic fungus Villosiclava virens that causes rice false smut, a worldwide devastating rice disease. A monoclonal antibody (mAb) 2D3G5 was generated with ustiloxin A-bovine serum albumin conjugate. A highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (icELISA) was then developed. It possessed a median inhibition concentration (IC50) of 13.8 ng/mL and a working range of 2.8-72 ng/mL. The mAb 2D3G5 recognized ustiloxin B with the cross-reactivity as 4%. The average recoveries of ustiloxin A from rice false smut balls and peeled rice samples ranged from 92% to 117% and from 92% to 107%, respectively. Comparison of the concentrations of ustiloxin A in rice false smut balls detected by both icELISA and high performance liquid chromatography-photodiode array detection indicated that the developed icELISA was suitable for detection of ustiloxin A in rice food and feed samples.

Enhanced Production of Botrallin and TMC-264 with in Situ Macroporous Resin Adsorption in Mycelial Liquid Culture of the Endophytic Fungus Hyalodendriella sp. Ponipodef12

Hyalodendriella sp. Ponipodef12, an endophytic fungus from the hybrid “Neva” of Populus deltoides × P. nigra, is a high producer of the bioactive dibenzo-α-pyrones botrallin and TMC-264. However, both the botrallin and TMC-264 produced by Hyalodendriella sp. Ponipodef12 were retained as both intracellular and extracellular products. The aim of this study was to evaluate an in situ macroporous resin adsorption for enhancement of botrallin and TMC-264 production in mycelial liquid culture of Hyalodendriella sp. Ponipodef12. Production of botrallin and TMC-264 was most effectively enhanced by macroporous resin DM-301 among the thirteen nonionic macroporous resins tested. The highest botrallin yield (51.47 mg/L, which was 2.29-fold higher than the control at 22.49 mg/L) was obtained by adding resin DM-301 at 4.38% (g/mL) to the culture broth on day 24 and allowing a period of 4 days for adsorption. The highest TMC-264 yield reached 47.74 mg/L, which was 11.76-fold higher than that of the control (4.06 mg/L), and was achieved by adding DM-301 resin at 4.38% (w/v) in the culture broth on day 24 and allowing a period of 6 days for adsorption. The results show that in situ resin adsorption is an effective strategy for enhancing production of botrallin and TMC-264, and also for facilitating their recovery from mycelial liquid culture of Hyalodendriella sp. Ponipodef12.