Xiang-Hong Liu

Antioxidant activities of extracts and flavonoid compounds from Oxytropis falcate Bunge

The antioxidant properties of the various extracts and flavonoids prepared from Oxytropis falcate Bunge were investigated by 1,1-diphenyl-2-picryldydrazyl (DPPH) radical-scavenging assay. In the chloroform, ethyl acetate and n-butanol extracts, the ethyl acetate extract exhibited the highest antioxidant activity (IC50 = 2.05 mg mL−1). Furthermore, rhamnocitrin, kaempferol, rhamnetin, 2′,4′-dihydroxychalcone and 2′,4′, β-trihydroxy-dihydrochalcone were purified from chloroform and ethyl acetate extracts. The radical-scavenging activities of the five compounds were also measured and the results showed that kaempferol (IC50 = 0.11 mg mL−1), rhamnetin (IC50 = 0.14 mg mL−1) and rhamnocitrin (IC50 = 0.15 mg mL−1) exhibited considerable antioxidant activities, but the antioxidant activities of the two dihydrochalcones were very weak. Although these flavonoids are known, this is the first report of antioxidant activity in this plant.

Aspeverin, a New Alkaloid from an Algicolous Strain of Aspergillus versicolor

A novel carbamate- and cyano-containing alkaloid, aspeverin (1), was isolated from the culture of an algicolous Aspergillus versicolor strain (dl-29). The structure and absolute configuration were unambiguously identified by NMR, IR, ECD, and mass spectrometric methods as well as quantum chemical calculations. 1 exhibited potent bioactivities against some marine-derived organisms.

Terretonin, ophiobolin, and drimane terpenes with absolute configurations from an algicolous Aspergillus ustus

One new meroterpene, 1,2-dihydroterretonin F (2), five new sesterterpenes, (6α)-21-deoxyophiobolin G (3), (6α)-16,17-dihydro-21-deoxyophiobolin G (4), ophiobolin U (5), ophiobolin V (6), and ophiobolin W (7), two new sesquiterpenes, (6-strobilactone-B) esters of (E,E)-6,7-epoxy-2,4-octadienoic acids (13 and 14), and twelve known terpenes (1, 8–12, and 15–20) were isolated from Aspergillus ustus, a fungus from the fresh tissue of marine green alga Codium fragile. Their structures and absolute configurations were identified by NMR and mass spectroscopic methods as well as quantum chemical calculations. Some of the isolates exhibited antibacterial activity and brine shrimp toxicity.

Aspewentins A-C, Norditerpenes from a Cryptic Pathway in an Algicolous Strain of Aspergillus wentii

Through addition of suberoylanilide hydroxamic acid, two new aromatic norditerpenes, aspewentins A (1) and B (2), along with an oxygenated derivative, aspewentin C (3), were obtained from the culture of an Aspergillus wentii strain (na-3) isolated from the tissue of the brown alga Sargassum fusiforme. The structures and absolute configurations were unambiguously elucidated by spectroscopic analyses and quantum chemical calculations. Aspewentins A-C were produced before sporulation and exhibited potent bioactivities against some marine-derived organisms.

Ergosteroid derivatives from an algicolous strain of Aspergillus ustus

One new ergosteroid derivative, isocyathisterol (1), and eight known compounds (2–9) were isolated from the culture of an algicolous strain (cf-42) of Aspergillus ustus obtained from the fresh tissue of marine green alga Codium fragile. The structure and absolute configuration of 1 were unequivocally identified by using NMR and mass spectroscopic methods as well as quantum chemical calculations. Compound 1 exhibited weak antibacterial activity.

Citrinovirin with a new norditerpene skeleton from the marine algicolous fungus Trichoderma citrinoviride

Citrinovirin (1), a novel norditerpene with an unprecedented carbon skeleton along with three known compounds, cyclonerodiol (2), 3-(2-hydroxypropyl)-4-(hexa-2E,4E-dien-6-yl)furan-2(5H)-one (3), and 5-hydroxy-3-hydroxymethyl-2-methyl-7-methoxychromone (4), was isolated from the culture of a marine brown alga-endophytic strain (cf-27) of Trichoderma citrinoviride. The structure and relative configuration of 1 were identified by spectroscopic methods, including 1D/2D NMR and MS. Its absolute configuration was established by analysis of ECD spectrum, aided by quantum chemical calculations. A plausible biogenetic pathway is proposed for 1, and it was evaluated to be active against Staphylococcus aureus.

Sesteralterin and Tricycloalterfurenes A-D: Terpenes with Rarely Occurring Frameworks from the Marine-Alga-Epiphytic Fungus Alternaria alternata k21-1

A new sesterterpene, sesteralterin (1), four new meroterpenes, tricycloalterfurenes A-D (2-5), and a known meroterpene, TCA-F (6), were obtained from the culture extract of an Alternaria alternata strain (k21-1) isolated from the surface of the marine red alga Lomentaria hakodatensis. The structures and relative/absolute configurations of these compounds were identified by spectroscopic analyses, mainly including 1D/2D NMR, ECD, and mass spectra and quantum chemical calculations. Compound 1 represents the first nitidasane sesterterpene naturally produced by fungi, and 2-5 feature a tetrahydrofuran unit rarely occurring in tricycloalternarenes. Compounds 1-6 were assayed for inhibition of the growth of four marine plankton and one marine alga-pathogenic bacterium.

Bisabolane, cyclonerane, and harziane derivatives from the marine-alga-endophytic fungus Trichoderma asperellum cf44-2

Three undescribed bisabolane derivatives, trichaspin, trichaspsides A and B, three undescribed cyclonerane sesquiterpenes, 9-cycloneren-3,7,11-triol, 11-cycloneren-3,7,10-triol, and 7,10-epoxycycloneran-3,11,12-triol, and one undescribed harziane diterpene, 11-hydroxy-9-harzien-3-one, were obtained from the culture of Trichoderma asperellum cf44-2, an endophyte of the marine brown alga Sargassum sp. Their structures and relative configurations were assigned by analysis of 1D/2D NMR and MS data, and their absolute configurations were established by ECD or specific optical rotation data. Trichaspin features an unprecedented ethylated bisabolane skeleton, while trichaspsides A and B represent the first aminoglycosides of bisabolane and norbisabolane sesquiterpenes, respectively. Nine of the compounds were evaluated for inhibition of five marine-derived pathogenic bacteria and toxicity to a marine zooplankton.