Isolation, structure, absolute stereochemistry, and HIV-1 integrase inhibitory activity of integrasone, a novel fungal polyketide

HIV-1 integrase is a critical enzyme for replication of HIV, and its inhibition is one of the most promising new drug targets for anti-retroviral therapy with potentially significant advantages over existing therapies. In this Note, the isolation, structure elucidation, and absolute stereochemistry of integrasone, a novel polyketide, derived from an unidentified sterile mycelium have been described. This bicyclic dihydroxy epoxide lactone inhibited the strand transfer reaction of HIV-1 integrase with an IC(50) of 41 microM.     

Structure and absolute stereochemistry of hectochlorin,a potent stimulator of actin assembly

Hectochlorin (1) was isolated from marine isolates of Lyngbya majuscula collected from Hector Bay, Jamaica, and Boca del Drago Beach, Bocas del Toro, Panama. The planar structure was deduced by one- and two-dimensional NMR spectroscopy. X-ray crystallography was used to determine the absolute stereochemistry of hectochlorin as 2S,3S,14S,22S. Hectochlorin is equipotent to jasplakinolide (5) in its ability to promote actin polymerization, but unlike jasplakinolide, is unable to displace a fluorescent phalloidin analogue from polymerized actin. In addition, hectochlorin shows both a unique profile of cytotoxicity by the COMPARE algorithm and potent inhibitory activity toward the fungus Candida albicans. Structurally, hectochlorin resembles dolabellin and the recently reported lyngbyabellin class of compounds.     

Structure and absolute stereochemistry of 21-hydroxyoligomycin A

21-Hydroxyoligomycin A (1) was isolated from Streptomyces cyaneogriseus ssp. noncyanogenus (LL-F28249) and fully characterized by NMR and single-crystal X-ray diffraction methods. The complete 1H and 13C NMR chemical shift assignments for 1 were made using 2D NMR experiments, and the chirality at C-21 was deduced to be R from a J-based configuration analysis. The absolute configuration at C-21 and at the other 18 chiral centers in the molecule were independently confirmed by anomalous dispersion measurements on a crystal of the chloroform methanol solvate of 21-hydroxyoligomycin A (1).     

Coruscol A, a new metabolite from the marine-derived fungus penicillium species

A new metabolite possessing a 1,3-dioxane ring, coruscol A (1), was isolated from the mycelium of the fungus Penicillium sp., which was separated from the Okinawan marine bivalve Mytilus coruscus, and the structure was elucidated by spectroscopic data.     

Acremostrictin, a highly oxygenated metabolite from the marine fungus Acremonium strictum

The novel natural product acremostrictin was isolated from the culture broth of Acremonium strictum, a marine fungus collected from a Choristida sponge off the coast of Korea. Structurally, acremostrictin is a tricyclic lactone of an unprecedented skeletal class based on combined spectroscopic and X-ray crystallographic analyses. The new compound exhibited weak antibacterial and moderate antioxidant activities.     

Structure revision and assignment of absolute stereochemistry of a marine C21 bisfuranoterpene

The C21 bisfuranoterpene (-)-isotetradehydrofurospongin-1 (6), previously isolated from a Western Australian Spongia sp., has been reisolated from a specimen of Spirastrella papilosa collected during scientific trawling operations in the Great Australian Bight. A 2D NMR analysis of 6 has prompted reassignment of the published structure 5, while degradation and chiral HPLC analysis have allowed determination of the absolute stereochemistry.     

Anthraquinones and betaenone derivatives from the sponge-associated fungus Microsphaeropsis species: novel inhibitors of protein kinases

An undescribed fungus of the genus Microsphaeropsis, isolated from the Mediterranean sponge Aplysina aerophoba, produces two new betaenone derivatives (1, 2) and three new 1,3,6, 8-tetrahydroxyanthraquinone congeners (5-7). The structures of the compounds were established on the basis of NMR spectroscopic and mass spectrometric data and by CD spectroscopy. This is the first report wherein the (1)H and (13)C NMR data of the betaenone congeners are fully and unambiguously assigned on the basis of two-dimensional NMR spectroscopy. Furthermore, we describe the first elucidation of the absolute configuration of 1-(2'-anthraquinonyl)ethanols such as 5 and 6, by quantum chemical calculation of their circular dichroism (CD) and comparison with experimentally measured spectra. Moreover, it was shown that compounds 1, 5, 6, and 7 are inhibitors of PKC-epsilon, CDK4, and EGF receptor tyrosine kinases.     

Oroxylin A,a methylated metabolite of baicalein,exhibits a stronger inhibitory effect than baicalein on the CYP1B1‐mediated carcinogenic estradiol metabolite formation

Human cytochrome P450 1B1 (CYP1B1)‐mediated formation of 4‐hydroxyestradiol (4‐OHE2) from 17β‐estradiol plays an important role in the progression of human breast cancer, while the biotransformation of 17β‐estradiol to 2‐hydroxyestradiol mediated by cytochrome P450 1A1 (CYP1A1) is considered as a less harmful pathway. In this study, inhibitory effects of flavonoids baicalein and oroxylin A, a metabolite of baicalein in human body, on CYP1A1 and 1B1 activities were investigated in vitro. The inhibition intensities of baicalein and oroxylin A towards CYP1B1 were greater than towards CYP1A1 with a mixed mechanism. In addition, oroxylin A showed a stronger inhibitory effect than baicalein towards the CYP1B1‐mediated 17β‐estradiol 4‐hydroxylation, with the IC₅₀ values of 0.0146 and 2.27 μM, respectively. Docking studies elucidated that oroxylin A had a stronger binding affinity than baicalein for CYP1B1. In MCF‐7 cells, compared with baicalein‐treated groups, oroxylin A with lower doses decreased and increased the formation of 4‐OHE2 and 2‐hydroxyestradiol, respectively, with a preferential induction of mRNA of CYP1A1 over CYP1B1. In conclusion, this study demonstrated that oroxylin A showed a stronger inhibitory effect than baicalein on CYP1B1‐mediated 4‐OHE2 formation in MCF‐7 cells, providing crucial implications for their possibly preventive/therapeutic potential against breast cancer via inhibition of CYP1B1, particularly of oroxylin A.     

Verrucofortine, a major metabolite of Penicillium verrucosum var. cyclopium, the fungus that produces the mycotoxin verrucosidin

Verrucofortine [8], an alkaloid derived from tryptophan and leucine, has been isolated from the fungus Penicillium verrucosum var. cyclopium. The structure and absolute configuration have been established by a combination of spectroscopic and chemical techniques. Its structure is unrelated to that of other major metabolite of the organism, the highly toxic pyrone-type polyketide verrucosidin [1], which was previously reported to be a tremorgen. A second novel metabolite, normethylverrucosidin [3], has also been isolated and identified. Small quantities of several other secondary metabolites, ergosterol, cyclopenin [4], cyclopenol [5], and 3-O-methylviridicatin [6], were isolated. They are known fungal metabolites but had not previously been obtained from this fungus. Studies of verrucofortine toxicity in mice showed no apparent toxic effects at doses as high at 160 mg/kg ip.     

Bromomyrothenone B and botrytinone, cyclopentenone derivatives from a marine isolate of the fungus botrytis

New cyclopentenones, bromomyrothenone B (1) and botrytinone (2), and the known cyclonerodiol (3) were isolated from the marine algicolous fungus of the genus Botrytis. The absolute stereostructures of compounds 1 and 2 were elucidated on the basis of chemical and physicochemical evidence including quantum chemistry calculation, X-ray analysis, and CD exciton chirality method.     

Scopularides A and B, cyclodepsipeptides from a marine sponge-derived fungus, Scopulariopsis brevicaulis

Two novel cyclodepsipeptides, scopularides A and B, were found in the fungus Scopulariopsis brevicaulis, which was isolated from the marine sponge Tethya aurantium. In addition, the known fungal metabolite paxilline was identified. The structures of the scopularides were elucidated by NMR, MS, and chemical derivatization methods as cyclo-(3-hydroxy-4-methyldecanoyl-Gly-L-Val-D-Leu-L-Ala-L-Phe) and cyclo-(3-hydroxy-4-methyloctanoyl-Gly-L-Val-D-Leu-L-Ala-L-Phe) for scopularide A and B, respectively. Antibiotic activity against Gram-negative bacteria was absent and against Gram-positive bacteria was weak, but activity against several tumor cell lines was significant at 10 microg/mL.     

Novel cassane and cleistanthane diterpenes from Myrospermum frutescens: absolute stereochemistry of the cassane diterpene series

Four new diterpenes (1-4) were isolated from the leaves of Myrospermum frutescens as minor constituents. Chagresnol (1), 6beta,18-diacetoxycassan-13,15-diene (2), and chagreslactone (3) possess cassane skeletons, while chagresnone (4) exhibits a cleistanthane skeleton. Molecular structures and their relative stereochemistries were elucidated using NMR spectroscopy in combination with UV, IR, and MS spectral data. Although compound 2 was previously reported as a synthetic product, we report its first isolation as a natural product. Derivative products (10-13) were obtained to test their activities against Chagas's disease. In addition, the absolute stereochemistry of the previously isolated cassane diterpene 5 from M. frutescens is presented.     

Lyngbyastatin 1 and Ibu-epilyngbyastatin 1: synthesis,stereochemistry, and NMR line broadening

The synthesis of a lyngbyastatin 1-Ibu-epilyngbyastatin 1 mixture combined with NMR and molecular modeling studies proved that natural lyngbyastatin 1 was only one Ibu epimer rather than a mixture of both and that the configuration of this epimer in the Ibu unit was R. The substance isolated with lyngbyastatin 1 was Ibu-epidolastatin 12. The extreme broadness in the proton NMR spectra of lyngbyastatin 1 and Ibu-epidolastatin 12 was exchange broadening due to rotation about the Ibu-Ala amide bond. It was a consequence of (1) a small energy difference between the cis and trans forms of this bond, (2) a substantial difference in conformation between these forms, and (3) a lowered barrier between them compared to most amide bonds (due to steric hindrance). The synthetic lyngbyastatin 1-Ibu-epilyngbyastatin 1 mixture had significant activities against cancer cells and in stimulating actin polymerization, but was less active than dolastatin 11 in all assays.     

Lyngbyabellin B, a toxic and antifungal secondary metabolite from the marine cyanobacterium Lyngbya majuscula

Lyngbyabellin B (1) was isolated from a marine cyanobacterium, Lyngbya majuscula, collected near the Dry Tortugas National Park, Florida. This new cyclic depsipeptide displayed potent toxicity toward brine shrimp and the fungus Candida albicans. The planar structure was deduced using 1D and 2D NMR spectroscopic methods, and the stereochemistry is proposed through a combination of NMR and chiral GC/MS analysis.     

Determination of the stereochemistry of the tetrahydropyran sesquineolignans morinols A and B

The 7',8'-stereochemistry of the tetrahydropyran sesquineolignans morinols A and B was determined as threo via synthetic studies and by comparison of NMR data of 7',8'-threo-morinol and 7',8'-erythro-morinol. This study also confirmed that the biosynthetic process produces enantiomeric mixtures of morinols A and B. This was ascertained by comparing the specific rotations of synthesized morinols A and B with those of naturally occurring morinols A and B.     

Modiolides A and B,two new 10-membered macrolides from a marine-derived fungus

Two new 10-membered macrolides, modiolides A (1) and B (2), and a new linear pentaketide, modiolin (3), were isolated from the cultured broth of a fungus Paraphaeosphaeria sp. (N-119), which was separated from a marine horse mussel, and the structures were elucidated by spectroscopic data.     

Pibocin B, the first N-O-methylindole marine alkaloid, a metabolite from the Far-Eastern ascidian Eudistoma species.

Pibocin B (2), the first representative of marine alkaloids with a unique structural feature, an N-O-methylindole group, was isolated from the Far-Eastern ascidian Eudistoma sp. Its structure has been established as (8 beta)-2-bromo-N-O-methyl-6,8-dimethylergoline on the basis of NMR data, FAB and MALDI-TOF MS, and chemical correlations. Pibocin B showed moderate cytotoxic activity against mouse Ehrlich carcinoma cells.     

Gliotoxin analogues from a marine-derived fungus, Penicillium sp., and their cytotoxic and histone methyltransferase inhibitory activities

Seven gliotoxin-related compounds were isolated from the fungus Penicillium sp. strain JMF034, obtained from deep sea sediments of Suruga Bay, Japan. These included two new metabolites, bis(dethio)-10a-methylthio-3a-deoxy-3,3a-didehydrogliotoxin (1) and 6-deoxy-5a,6-didehydrogliotoxin (2), and five known metabolites (3-7). The structures of the new compounds were elucidated by analysis of spectroscopic data and the application of the modified Mosher's analysis. All of the compounds exhibited cytotoxic activity, whereas compounds containing a disulfide bond showed potent inhibitory activity against histone methyltransferase (HMT) G9a. None of them inhibited HMT SET7/9.     

Metacridamides A and B, macrocycles from conidia of the entomopathogenic fungus Metarhizium acridum

Metarhizium acridum, an entomopathogenic fungus, has been commercialized and used successfully for biocontrol of grasshopper pests in Africa and Australia. Its conidia produce two novel 17-membered macrocycles, metacridamides A and B, which consist of a Phe unit condensed with a nonaketide. Planar structures were elucidated by a combination of mass spectrometric and NMR techniques. Following hydrolysis of 1, chiral amino acid analysis assigned the L-configuration to the Phe unit. A crystal structure established the absolute configuration of the eight remaining stereogenic centers in 1. Metacridamide A showed cytotoxicity to three cancer lines with IC??'s of 6.2, 11.0, and 10.8 μM against Caco-2 (epithelial colorectal adenocarcinoma), MCF-7 (breast cancer), and HepG2/C3A (hepatoma) cell lines, respectively. In addition, metacridamide B had an IC?? of 18.2 μM against HepG2/C3A, although it was inactive at 100 μM against Caco-2 and MCF-7. Neither analogue showed antimicrobial, phytotoxic, or insecticidal activity.     

Sculezonones A and B, two metabolites possessing a phenalenone skeleton from a marine-derived fungus Penicillium species

Two new metabolites possessing a phenalenone skeleton, sculezonones A (1) and B (2), were isolated from cultured broth of the fungus Penicillium sp., which was separated from the Okinawan marine bivalve Mytilus coruscus, and the structures were elucidated by spectroscopic data.