The Experts below are selected from a list of 1662 Experts worldwide ranked by ideXlab platform

Katja Breskvar - One of the best experts on this subject based on the ideXlab platform.

  • Purification and molecular characterization of chitin deacetylase from Rhizopus nigricans
    Enzyme and Microbial Technology, 2006
    Co-Authors: Natasa Jeraj, Helena Lenasi, Barbara Kunič, Katja Breskvar
    Abstract:

    Abstract Chitin deacetylase is an enzyme, which catalyses the hydrolysis of N-acetamido bonds of chitin, converting it to chitosan. In the present report we purified the chitin deacetylase from mycelial extracts of a zygomycete Rhizopus nigricans by sequential ammonium sulfate precipitation, CM Sepharose chromatography and DEAE-cellulose chromatography. The progress of enzyme purification was followed by measurement of enzyme activity using partially O-hydroxyethylated chitin (glycol chitin) radiolabelled in N-acetyl groups as a substrate. The apparent molecular mass of chitin deacetylase obtained by SDS-PAGE was approximately 100 kDa. A cDNA library containing a chitin deacetylase gene from R. nigricans was constructed and the complete gene was sequenced. The complete gene contains an open reading frame of 1341 nucleotides, which encodes a sequence of 447 amino acid residues. The estimated molecular mass is 47 kDa, suggesting that carbohydrate content is 53% by weight of the protein. The gene sequence consists of nucleotides encoding a conserved polysaccharide deacetylase domain located in the middle, covering 34% of the entire sequence. Overall, there were eight possible N-linked glycosylation sites. The deduced amino acid sequence shows the highest identity with chitin deacetylases from other zygomycetes Phycomyces blakesleeanus, Gongronella butleri, Rhizopus oryzae and Mucor rouxii (55%, 48%, 43% and 41% identity, respectively).

  • The involvement of cAMP in the growth inhibition of filamentous fungus Rhizopus nigricans by steroids
    Fems Microbiology Letters, 2004
    Co-Authors: Nataša Jeraj, Helena Lenasi, Katja Breskvar
    Abstract:

    Several steroids, in particular progesterone, are toxic for the filamentous fungus Rhizopus nigricans and, at high concentrations, inhibit its growth. Previous studies on this microorganism revealed progesterone specific receptors coupled to G proteins at the plasma membrane. In this study, the next step of steroid signalling in R. nigricans following G protein activation is investigated, together with the possible impact of this pathway on fungal growth inhibition. The intracellular level of cAMP decreased in the presence of steroids, demonstrating the probable involvement of cAMP signalling in the response of R. nigricans to steroids. Results of the growth analysis in the presence of cAMP increasing agents suggest that the role of cAMP in fungal growth inhibition by steroids cannot be ruled out, but it would appear to be minor and not make a major contribution to growth inhibition.

  • Characterisation and expression of a gene encoding a mutarotase from the fungus Rhizopus nigricans
    FEMS Microbiology Letters, 2004
    Co-Authors: Tanja Vilfan, Bronislava Črešnar, Didier Fournier, Jure Stojan, Katja Breskvar
    Abstract:

    A gene coding for a mutarotase was isolated and characterised from the filamentous fungus Rhizopus nigricans. In order to determine the encoded enzyme's activity a recombinant protein was prepared in the baculovirus expression system and the mutarotase activity was determined. Expression studies showed that the gene is repressed by high as well as low concentrations of glucose and derepressed during deficiency of glucose. Besides the regulation at the level of transcription, an accelerative effect of glucose in growth medium on the mutarotase mRNA decay was also demonstrated. Moreover, a Southern hybridisation performed at lower temperatures suggested that the R. nigricans genome harbours a nucleotide sequence, that is homologous to the isolated gene.

  • Molecular characterization of a ribosome-associated Hsp70-homologous gene from Rhizopus nigricans.
    Biochimica et biophysica acta, 2003
    Co-Authors: Bostjan Cernila, Bronislava Cresnar, Katja Breskvar
    Abstract:

    A ribosome-associated Hsp70-homologous gene (Rnssb-1) was isolated from the genomic library of the filamentous zygomycete fungus Rhizopus nigricans. The nucleotide sequence of a genomic clone encoded the N-terminal part of a protein with high similarity to the yeast SSB ribosome-associated chaperones. The missing 3' end of the gene was obtained by 3' RACE. The Northern blot analysis showed that the Rnssb-1 gene is constitutively expressed and is not induced upon heat shock at 37 degrees C. The primary structure analyses revealed that the coding region of the Rnssb-1 gene is interrupted by at least four introns. Their splicing was not inhibited by exposure of the organism to heat shock as proven by RT-PCR. A Southern blot analysis of R. nigricans genomic DNA confirmed the presence of two additional gene copies of ribosome-associated Hsp70 genes in the fungal genome.

  • Molecular characterization of a ribosome-associated Hsp70-homologous gene from Rhizopus nigricans.
    Biochimica et Biophysica Acta, 2003
    Co-Authors: Boštjan Černila, Bronislava Črešnar, Katja Breskvar
    Abstract:

    Abstract A ribosome-associated Hsp70-homologous gene ( Rnssb-1 ) was isolated from the genomic library of the filamentous zygomycete fungus Rhizopus nigricans . The nucleotide sequence of a genomic clone encoded the N-terminal part of a protein with high similarity to the yeast SSB ribosome-associated chaperones. The missing 3′ end of the gene was obtained by 3′ RACE. The Northern blot analysis showed that the Rnssb-1 gene is constitutively expressed and is not induced upon heat shock at 37 °C. The primary structure analyses revealed that the coding region of the Rnssb-1 gene is interrupted by at least four introns. Their splicing was not inhibited by exposure of the organism to heat shock as proven by RT-PCR. A Southern blot analysis of R. nigricans genomic DNA confirmed the presence of two additional gene copies of ribosome-associated Hsp70 genes in the fungal genome.

Helena Lenasi - One of the best experts on this subject based on the ideXlab platform.

  • The response of filamentous fungus Rhizopus nigricans to flavonoids
    Journal of basic microbiology, 2017
    Co-Authors: Helena Lenasi, Tomaž Makovec, Dušan Žigon, Marko Slana
    Abstract:

    The saprophytic fungus Rhizopus nigricans constitutes a serious problem when thriving on gathered crops. The identification of any compounds, especially natural ones, that inhibit fungal growth, may therefore be important. During its life cycle, Rhizopus nigricans encounters many compounds, among them the flavonoids, plant secondary metabolites that are involved in plant defense against pathogenic microorganisms. Although not being a plant pathogen, Rhizopus nigricans may interact with these compounds in the same way as plant pathogens - in response to the fungitoxic effect of flavonoids the fungi transform them into less toxic metabolites. We have studied the interaction of R. nigricans with some flavonoids. Inhibition of hyphal spreading (from 3% to 100%) was observed by 300 ?M flavones, flavanones and isoflavones, irrespective of their basic structure, oxidized or reduced C-ring, and orientation of the B-ring. However, a hydrophobic A-ring was important for the toxicity. R. nigricans transformed some of the flavonoids into glucosylated products. Recognition of substrates for glucosylating enzyme(s) did not correlate with their fungitoxic effect but depended exclusively on the presence of a free -OH group in the flavonoid A-ring and of a hydrophobic B-ring. Although the fungus produced glucosyltransferase constitutively, an additional amount of the enzyme was induced by the substrate flavonoid. Moreover, effective detoxification was shown to require the presence of glucose. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • Purification and molecular characterization of chitin deacetylase from Rhizopus nigricans
    Enzyme and Microbial Technology, 2006
    Co-Authors: Natasa Jeraj, Helena Lenasi, Barbara Kunič, Katja Breskvar
    Abstract:

    Abstract Chitin deacetylase is an enzyme, which catalyses the hydrolysis of N-acetamido bonds of chitin, converting it to chitosan. In the present report we purified the chitin deacetylase from mycelial extracts of a zygomycete Rhizopus nigricans by sequential ammonium sulfate precipitation, CM Sepharose chromatography and DEAE-cellulose chromatography. The progress of enzyme purification was followed by measurement of enzyme activity using partially O-hydroxyethylated chitin (glycol chitin) radiolabelled in N-acetyl groups as a substrate. The apparent molecular mass of chitin deacetylase obtained by SDS-PAGE was approximately 100 kDa. A cDNA library containing a chitin deacetylase gene from R. nigricans was constructed and the complete gene was sequenced. The complete gene contains an open reading frame of 1341 nucleotides, which encodes a sequence of 447 amino acid residues. The estimated molecular mass is 47 kDa, suggesting that carbohydrate content is 53% by weight of the protein. The gene sequence consists of nucleotides encoding a conserved polysaccharide deacetylase domain located in the middle, covering 34% of the entire sequence. Overall, there were eight possible N-linked glycosylation sites. The deduced amino acid sequence shows the highest identity with chitin deacetylases from other zygomycetes Phycomyces blakesleeanus, Gongronella butleri, Rhizopus oryzae and Mucor rouxii (55%, 48%, 43% and 41% identity, respectively).

  • The involvement of cAMP in the growth inhibition of filamentous fungus Rhizopus nigricans by steroids
    Fems Microbiology Letters, 2004
    Co-Authors: Nataša Jeraj, Helena Lenasi, Katja Breskvar
    Abstract:

    Several steroids, in particular progesterone, are toxic for the filamentous fungus Rhizopus nigricans and, at high concentrations, inhibit its growth. Previous studies on this microorganism revealed progesterone specific receptors coupled to G proteins at the plasma membrane. In this study, the next step of steroid signalling in R. nigricans following G protein activation is investigated, together with the possible impact of this pathway on fungal growth inhibition. The intracellular level of cAMP decreased in the presence of steroids, demonstrating the probable involvement of cAMP signalling in the response of R. nigricans to steroids. Results of the growth analysis in the presence of cAMP increasing agents suggest that the role of cAMP in fungal growth inhibition by steroids cannot be ruled out, but it would appear to be minor and not make a major contribution to growth inhibition.

  • In situ detection of progesterone binding sites in the plasma membrane of the filamentous fungus Rhizopus nigricans
    Acta Chimica Slovenica, 2003
    Co-Authors: Natasa Jeraj, Helena Lenasi, Rok Romih, Katja Breskvar
    Abstract:

    Steroid hydroxylating enzymes in the fungus Rhizopus nigricans are induced by progesterone and by some other steroids. It is known that in higher organisms steroids exert their nongenomic action via steroid binding proteins located in the plasma membrane of the cells, thus our aim was to detect progesterone binding sites in R. nigricans plasma membrane. In this report membrane receptors were identified by two independent methods, analysis of progesterone binding to plasma membrane fraction by competitive binding assay using [ 3 H]- and [ 1 H] progesterone (EC 5 0 = 55 nM) and in situ binding of fluorescein isothiocyanate-coupled cell impermeant progesterone conjugate to fungal protoplasts, detected by fluorescence microscopy.

  • Membrane-bound progesterone receptors coupled to G proteins in the fungus Rhizopus nigricans.
    FEMS Microbiology Letters, 2002
    Co-Authors: Helena Lenasi, Aljoša Bavec, Matjaž Zorko
    Abstract:

    Steroid binding sites with high affinity for progesterone ( K d= 40±14 nM determined by binding, and K d= 71±22 nM determined by displacement studies) and lower affinity for 21-hydroxyprogesterone and for testosterone, but no affinity for estradiol-17β, onapristone and α-naphthoflavone were detected in the enriched plasma membrane fraction of the fungus Rhizopus nigricans . The amount of steroid binding sites is in accordance with the value of B max= 744±151 fmol (mg protein)−1. In the membrane fraction, progesterone induced about 30% activation of G proteins over basal level, as determined by GTPase activity (EC50= 32±8 nM) and by the guanosine 5′- O -(3-thiotriphosphate) (GTPγS) binding rate (EC50= 61±21 nM). The affinity of receptors for progesterone was substantially decreased in the presence of GTPγS and of cholera toxin. Our results suggest the existence of progesterone receptors in the membrane of Rhizopus nigricans and their coupling to G proteins. * Abbreviation : CTX : cholera toxin EDTA : ethylenediaminetetraacetic acid GTPγS : guanosine 5′- O -(3-thiotriphosphate) PTX : pertussis toxin

Kaoshan Chen - One of the best experts on this subject based on the ideXlab platform.

  • The anti-gastritis activity of an exopolysaccharide from Rhizopus nigricans
    Food Bioscience, 2019
    Co-Authors: Ge Song, Kaoshan Chen, Nan Zhou, Pengying Zhang
    Abstract:

    Abstract Extracellular polysaccharide (EPS1-1) was obtained from Rhizopus nigricans and its structural features have been measured. The purpose of this study was to investigate the anti-inflammation effect of EPS1-1 on the chronic atrophic gastritis induced by N-methyl-n'-nitro-n-nitrosoguanidine (MNNG). EPS1-1 could decrease the damage of MNNG including the increased hemorrhagic spots, disorganized glands of gastric mucosa and marked inflammatory cell infiltration. Furthermore, compared to the model group, EPS1-1 treatment could down-regulate the level of inflammation-associated genes and up-regulate the expression of immune-related genes with the analysis of a gene expression profile. Besides, EPS1-1 was found to significantly enhance the immunity of mice. The thymus index of the EPS1-1 group increased significantly compared with that of the model group, and the serum creatinine and blood urea nitrogen levels of kidney and liver decreased in the EPS1-1 group. These studies showed that EPS1-1 may be a beneficial ingredient for improving gastrointestinal health.

  • Rhizopus nigricans polysaccharide activated macrophages and suppressed tumor growth in ct26 tumor bearing mice
    Carbohydrate Polymers, 2018
    Co-Authors: Zhihong Wei, Pengying Zhang, Guochuang Chen, Lei Zhu, Linan Zhang, Kaoshan Chen
    Abstract:

    Abstract In this study, a homogeneous polysaccharide (RPS-1) was extracted from liquid-cultured mycelia of Rhizopus nigricans. The weight-average molecular weight of RPS-1 was 1.617 × 107 g/mol and structural characterization indicated that RPS-1 was a non-starch glucan which consisted of a backbone structure of (1→4)-linked α- d -glucopyranosyl residues substituted at the O-6 position with α- d -glucopyranosyl branches. RPS-1 stimulated the production of nitric oxide and tumor necrosis factor-α by triggering phosphorylation of mitogen-activated protein kinases and nuclear translocation of nuclear factor kappa B p65 in RAW 264.7 macrophage cells. Moreover, intragastric administration of RPS-1 improved the immune function of CT26 tumor-bearing mice and significantly inhibited the growth of transplanted tumor. In combination with 5-FU, RPS-1 enhanced antitumor activity of 5-FU and alleviated its toxicity on immune system. These findings suggested that RPS-1 has the potential for the development of functional foods and dietary supplements.

  • Polysaccharide from Rhizopus nigricans inhibits the invasion and metastasis of colorectal cancer.
    Biomedicine & Pharmacotherapy, 2018
    Co-Authors: Qingjie Sun, Pengying Zhang, Ge Song, Jing Liu, Xiujuan Zhang, Guodong Wang, Kaoshan Chen
    Abstract:

    Abstract Polysaccharide (EPS1-1) extracted from fermentation liquor of Rhizopus nigricans possesses antitumor and immune-enhancing activities. The study was the first to investigate the anti-metastasis effects of EPS1-1 in vitro and in vivo. Results suggested that EPS1-1 dose-dependently suppressed the migration, invasion and adhesion abilities of CT26 cells. Furthermore, EPS1-1 dramatically inhibited the enzyme activity and expression levels of matrix metalloproteinases (MMPs) in CT26 cells, as well as the tube formation of HUVECs. Similar results were observed in the lung metastasis mice which were administrated with EPS1-1 for 14 d. EPS1-1 could inhibit angiogenesis by decreasing the expression of vascular endothelial growth factor (VEGF) and microvessel density (MVD) in lung tissue. Moreover, vimentin, as a marker molecule in epithelial-mesenchymal transition (EMT) which is closely related to metastasis, was found to be down expression by EPS1-1 in CT26 cells and lung tissue. These results suggested that EPS1-1 could suppress metastasis in vitro and in vivo by inhibiting invasion and angiogenesis, which provides potential application to against colorectal cancer metastasis.

  • Immune-enhancing activity of extracellular polysaccharides isolated from Rhizopus nigricans.
    Carbohydrate Polymers, 2016
    Co-Authors: Mengli Kong, Pengying Zhang, Qingjie Sun, Kaoshan Chen
    Abstract:

    Extracellular polysaccharides (EPS1-1) was extracted from fermentation liquor of Rhizopus nigricans and evaluated its immune-enhancing activities in vitro and in vivo. Results suggested that the proliferation of lymphocyte was stimulated after treated with EPS1-1. Moreover, the activities of macrophages were enhanced by increasing the activities of phagocytosis and acid phosphatase, the production of NO and the mRNA levels of IL-2, TNF-α and iNOS. Furthermore, EPS1-1 could significantly boost the immunity of normal and immunosuppressed mice, which included the increase of loaded swimming time, footpad swelling, organ index and the secretion of IL-2 and TNF-α in serum, thus suggesting that EPS1-1 could improve the body immunity through cellular immunity and humoral immunity. These findings provided further insights into the potential use of EPS1-1 as immunopotentiator or new function food.

  • Purification, partial characterization and antitumor effect of an exopolysaccharide from Rhizopus nigricans
    International Journal of Biological Macromolecules, 2016
    Co-Authors: Guochuang Chen, Pengying Zhang, Kaoshan Chen
    Abstract:

    In this study, a homogeneous exopolysaccharide (EPS1-1) was purified from the fermentation broth of Rhizopus nigricans. EPS1-1 was composed of glucose, mannose, galactose and fructose in the molar ratio of 5.89:3.64:3.20:1.00 with weight average molecular weight of 9.7×10(3)g/mol. EPS1-1 could significantly inhibit proliferation of human colorectal carcinoma HCT-116 cells in vitro. EPS1-1 also induced S phase cell cycle arrest and increased sub-G0/G1 population, a hallmark of apoptosis. The results of morphological characterization and flow cytometry showed that EPS1-1 induced apoptotic cell death in HCT-116 cells. EPS1-1 caused dissipation of mitochondrial membrane potential, accumulation of reactive oxygen species, up-regulation of Bax and p53 mRNA expression and down-regulation of Bcl-2 mRNA expression, which suggested that mitochondrial pathway was involved in the EPS1-1-induced apoptosis. These findings bring new insights into the potential use of EPS1-1 as antitumor drug against human colorectal carcinoma.

José María Arias - One of the best experts on this subject based on the ideXlab platform.

  • Chemical Semisynthesis and Biotransformation with Rhizopus nigricans of Several Sesquiterpenes: Obtention of New 1α- and 2α-Hydroxyselinane Derivatives
    Tetrahedron, 2000
    Co-Authors: Andrés García-granados, Andres Parra, Enrique Melguizo, Felipe L. Pérez, Yolanda Simeó, Beatriz Viseras, José María Arias
    Abstract:

    Abstract Starting with the natural product vulgarin, isolated from Artemisia canariensis , several acetylated, acetonated and oxidized polyhydroxylated eudesmanes and eudesmenes were semisynthesized. Some of these derivatives were biotransformed with the fungus Rhizopus nigricans and thus metabolites with new hydroxylation, reduction and/or deacetylation were isolated. Incubation of 1β,6α-diacetoxy-12-hydroxy-5α,11β- H -eudesm-4(15)-ene gave a 2-hydroxyselinane derivative in high yield (60%). Microbiological transformations of 1-oxo- and 6-oxoeudesmanes gave other useful hydroxyselinane derivatives in high proportions as the result of a stereoselective reduction of the carbonyl groups at these positions by the fungus on the β-face. Moreover, R. nigricans gave occasionally, regioselective deacetylated and/or hydrolyzed isopropylidene compounds.

  • Biotransformation of ent-Atisenes and ent-Beyerenes by Rhizopus nigricans and Fusarium moniliforme Cultures
    Journal of Natural Products, 1997
    Co-Authors: Andrés García-granados, And Andrés Parra, José María Arias
    Abstract:

    Microbial transformations of ent-atisene and ent-beyerene compounds were carried out using cultures of R. nigricans and F. moniliforme. Rhizopus nigricans metabolized all of the substrates, at higher yields than F. moniliforme, to give an ent-3β hydroxylation (60-65% for ent-atisenes and 80-85% for ent-beyerenes). Moreover, the double bond of the ent-beyerene skeleton was epoxidized by both fungi at lower yields (3-6%). Fusarium moniliforme produced a number of additional minor products by hydroxylation at other positions.

  • Biotransformation of ent-Atisenes and ent-Beyerenes by Rhizopus nigricans and Fusarium moniliforme Cultures
    1996
    Co-Authors: Andrés García-granados, Andres Parra, José María Arias
    Abstract:

    Microbial transformations of ent-atisene and ent-beyerene compounds were carried out using cultures of R. nigricans and F. moniliforme. Rhizopus nigricans metabolized all of the substrates, at higher yields than F. moniliforme, to give an ent-3β hydroxylation (60-65 % for ent-atisenes and 80-85 % for ent-beyerenes). Moreover, the double bond of the ent-beyerene skeleton was epoxidized by both fungi at lower yields (3-6%). Fusarium moniliforme produced a number of additional minor products by hydroxylation at other positions. Numerous papers have been published on the microbial transformations of diterpene compounds, 1 although those devoted to the biotransformation of ent-beyerene2-7 and ent-atisene8,9 diterpenes are scarce. In previous papers we reported the bioconversion of some entbeyerenes by Rhizopus nigricans and Curvularia lunata

  • Microbial Transformations of 6α- and 6β-Eudesmanolides by Rhizopus nigricans Cultures
    Journal of Natural Products, 1995
    Co-Authors: Yolanda García, Andres Parra, Andrés García-granados, Antonio Martínez, Fatima Rivas, José María Arias
    Abstract:

    Microbial transformations of 6α-eudesmanolides and 6β-eudesmanolides were accomplished using the hydroxylating fungus Rhizopus nigricans. The eudesmane skeleton was functionalized principally at positions C-1, C-4, and C-8. Hydroxylation yields depended on the configuration of the hydroxyl group at C-3, the methyl group at C-4, and the lactone ring in the substrates. Several metabolites with hydroxylation at C-9 and C-11 were also obtained with 6α-eudesmanolide substrates. An inversion of configuration at C-3 may occur when the substrates have an axial hydroxyl group at this carbon. Hydroxylation at C-4 was observed only when the substrate had a 4β-methyl group.

  • BIOTRANSFORMATION OF ENT-BEYERENONES BY Rhizopus nigricans AND CURVULARIA LUNATA CULTURES
    Phytochemistry, 1994
    Co-Authors: Andrés García-granados, Andres Parra, Antonio José Moreno Guerrero, Antonio Martínez, José María Arias
    Abstract:

    Abstract We have demonstrated the biotransformation of ent -7α,18-diacetoxybeyer-15-en-14-one, ent -14β,18-diacetoxybeyer-15-en-7-one and ent - 1β-acetoxy-17-hydroxybeyer-15-en-12-one by Rhizopus nigricans and Curvularia lunata cultures. Rhizopus nigricans metabolized the indicated substrates at higher yields than C. lunata to give hydroxylations at C-3, C-1 and C-12, if the substrates were functionalized at C-7, C- 14 and C-18. However, when the substrates were functionalized at C-1, C-12 and C-17, R. nigricans hydroxylated at C-19 and C. lunata at C-18.

Antonio Martínez - One of the best experts on this subject based on the ideXlab platform.

  • Biotransformation of shiromool derivatives by Rhizopus nigricans cultures: Chemical-microbiological synthesis of michelenolide analogues
    Tetrahedron, 1998
    Co-Authors: Andrés García-granados, Antonio Martínez, Francisco Rivas, María C. Gutiérrez, J. M. Arias
    Abstract:

    Abstract The biotransformation of two derivatives of shiromool was carried out with Rhizopus nigricans cultures to obtain 11- and 12- hydroxylated metabolites. The 11-hydroxyl germacrane compound was transformed to 11-R and 11-S 12-hydroxyl derivatives which were oxidised with TPAP to give michelenolide analogues. In the biotransformation processes, 2β- 3α- and 9β-hydroxyl derivatives were also obtained, as well as a 2β, 11-dihydroxylated metabolite.

  • biotransformation of ent 6α acetoxy and ent 6 ketomanoyl oxides with Rhizopus nigricans and curvularia lunata cultures
    Phytochemistry, 1997
    Co-Authors: Andres Garciagranados, Antonio Martínez, Francisco Rivas, Juan J Gutierrez, J. M. Arias
    Abstract:

    Abstract Microbial transformation of ent -16,18-dihydroxy-6-oxo-13- epi -manoyl oxide by Rhizopus nigricans produced ent -11 β -hydroxy, ent -20-hydroxy and ent -3 β -hydroxy derivatives. Biotransformation of ent -16,18-dihydroxy-6-oxomanoyl oxide gave ent -11 β -hydroxy and ent -3 β -hydroxy derivatives. However, biotransformations of these substrates with Curvularia lunata produced only ent -11 β -hydroxy derivatives. Incubation of ent -18-hydroxy-6-oxo-13- epi -manoyl oxide with R. nigricans produced 14,15-epoxy derivatives with and without hydroxylation at C-3, whereas microbial transformation of its epimer at C-13 gave ent -11 β -hydroxylated derivatives.

  • Microbial Transformations of 6α- and 6β-Eudesmanolides by Rhizopus nigricans Cultures
    Journal of Natural Products, 1995
    Co-Authors: Yolanda García, Andres Parra, Andrés García-granados, Antonio Martínez, Fatima Rivas, José María Arias
    Abstract:

    Microbial transformations of 6α-eudesmanolides and 6β-eudesmanolides were accomplished using the hydroxylating fungus Rhizopus nigricans. The eudesmane skeleton was functionalized principally at positions C-1, C-4, and C-8. Hydroxylation yields depended on the configuration of the hydroxyl group at C-3, the methyl group at C-4, and the lactone ring in the substrates. Several metabolites with hydroxylation at C-9 and C-11 were also obtained with 6α-eudesmanolide substrates. An inversion of configuration at C-3 may occur when the substrates have an axial hydroxyl group at this carbon. Hydroxylation at C-4 was observed only when the substrate had a 4β-methyl group.

  • BIOTRANSFORMATION OF ENT-BEYERENONES BY Rhizopus nigricans AND CURVULARIA LUNATA CULTURES
    Phytochemistry, 1994
    Co-Authors: Andrés García-granados, Andres Parra, Antonio José Moreno Guerrero, Antonio Martínez, José María Arias
    Abstract:

    Abstract We have demonstrated the biotransformation of ent -7α,18-diacetoxybeyer-15-en-14-one, ent -14β,18-diacetoxybeyer-15-en-7-one and ent - 1β-acetoxy-17-hydroxybeyer-15-en-12-one by Rhizopus nigricans and Curvularia lunata cultures. Rhizopus nigricans metabolized the indicated substrates at higher yields than C. lunata to give hydroxylations at C-3, C-1 and C-12, if the substrates were functionalized at C-7, C- 14 and C-18. However, when the substrates were functionalized at C-1, C-12 and C-17, R. nigricans hydroxylated at C-19 and C. lunata at C-18.

  • Chemical-microbiological synthesis of 6β-eudesmanolides from 11-hydroxyl derivatives obtained by Rhizopus nigricans cultures: Synthesis of 6β-dendroserins
    Tetrahedron, 1993
    Co-Authors: Andrés García-granados, Andres Parra, Antonio Martínez, Francisco Rivas, M. Esther Onorato, José M. Arias
    Abstract:

    Abstract The relationship between the structure of the substrates and the action of the fungus Rhizopus nigricans has been studied in order to obtain, in the highest possible yield, 11-hydroxyl derivatives which were dehydrated to the “exo” position, hydroborated with 9-BBN and oxidized with RuH2(Ph3P)4 to give 11-R and 11-S-6-epi-dendroserin. In the course of the biotransformation processes, 8α-hydroxyl and 7α-hydroxyl derivatives were also obtained, as well as the oxidation of the hydroxyl groups at C-1, an unusual process with Rhizopus nigricans. We have proved that the eudesmanones are more easily hydroxylated at C-11 than the hydroxyeudesmane compounds.