Now showing 1 - 10 of 20
  • Publication
    Open Access
    Absolute stereochemistry of the β-hydroxy acid unit in hantupeptins and trungapeptins
    (2015)
    Gupta, Deepak Kumar
    ;
    Ding, Gary Chi Ying
    ;
    ;
    Theβ-hydroxyl amino acid unit is a common structural feature of many bioactive marine cyanobacterial depsipeptides. In this study, the absolute stereochemistry of the β-hydroxyl acid moieties in hantupeptins and trungapeptins were determined through their synthesis and HPLC analysis of the Mosher ester derivatives. Synthesis of two3-hydroxy-2-methyloctanoic acid (Hmoa) stereoisomers, (2S,3R)-Hmoa and (2S,3S)-Hmoa, were achieved using diastereoselective asymmetric method and the retention times of all four Hmoa isomers were established indirectly by RPLC-MS analysis of their Mosher ester derivative standards. Based on the retention times of the standards, the absolute configuration of the Hmoa unit in hantupeptin C (3) and trungapeptin C (6) was assigned as (2R,3S)- and (2S,3R)-Hmoa, respectively. The use of the Mosher's reagents, coupled with HPLC analysis, provided a viable alternative to the absolute stereochemical determination of -hydroxy acid units in depsipeptides.
      235  207
  • Publication
    Open Access
      147  123
  • Publication
    Open Access
    Project-based learning: Engaging secondary school students in authentic environmental science research
    (2015) ; ;
    Yap, Nicholas Wei Liang
    In the past year (July 2014 to March 2015), 90 secondary school students participated in an Environmental Science themed Project-Based Learning (PBL) program designed by scientists at the National Institute of Education, Singapore. The authenticity of the PBL program was enhanced by partnership with NParks' Coastal Biomonitoring program. A total of 22 school teachers were also involved as facilitators of their students' project work. The strategic partnership of NIE scientists, secondary schools and NParks created a unique experience for students engaging in PBL.
      489  376
  • Publication
    Open Access
    Handbook of marine ecotoxicology techniques
    (National Institute of Education, Nanyang Technological University, 2014) ;
    Lai, Chien Houng
    ;
    ;
    Yap, Nicholas Wei Liang
    ;
    Dissanayake, Awantha
      666  1462
  • Publication
    Open Access
    Draft genome sequence of Bacillus sp. strain 007/aia-02/001, isolated from the marine sponge Coelocarteria singaporensis
    (2019)
    Ong, Marshall Ji Fa
    ;
    Goh, Hui Chin
    ;
    We report the draft genome sequence of a marine bacterium, Bacillus sp. strain 007/AIA-02/001, isolated from the marine sponge Coelocarteria singaporensis, obtained from water off the coast of Singapore. The analysis of the bacterial genome using the bioinformatics tool antiSMASH 4.0.2 showed the presence of a number of unique natural product biosynthetic pathways.
    WOS© Citations 1Scopus© Citations 1  100  74
  • Publication
    Open Access
    Marine cyanobacteria: A source of lead compounds and their clinically-relevant molecular targets
    (2020) ;
    Phyo, Ma Yadanar
    The prokaryotic filamentous marine cyanobacteria are photosynthetic microbes that are found in diverse marine habitats, ranging from epiphytic to endolithic communities. Their successful colonization in nature is largely attributed to genetic diversity as well as the production of ecologically important natural products. These cyanobacterial natural products are also a source of potential drug leads for the development of therapeutic agents used in the treatment of diseases, such as cancer, parasitic infections and inflammation. Major sources of these biomedically important natural compounds are found predominately from marine cyanobacterial orders Oscillatoriales, Nostocales, Chroococcales and Synechococcales. Moreover, technological advances in genomic and metabolomics approaches, such as mass spectrometry and NMR spectroscopy, revealed that marine cyanobacteria are a treasure trove of structurally unique natural products. The high potency of a number of natural products are due to their specific interference with validated drug targets, such as proteasomes, proteases, histone deacetylases, microtubules, actin filaments and membrane receptors/channels. In this review, the chemistry and biology of selected potent cyanobacterial compounds as well as their synthetic analogues are presented based on their molecular targets. These molecules are discussed to reflect current research trends in drug discovery from marine cyanobacterial natural products.
    WOS© Citations 33Scopus© Citations 39  112  76
  • Publication
    Open Access
    Assessing the diversity and biomedical potential of microbes associated with the Neptune's cup sponge, Cliona patera
    (2021)
    Ho, Xin Yi
    ;
    Nursheena Parveen Katermeran
    ;
    Deignan, Lindsey Kane
    ;
    Phyo, Ma Yadanar
    ;
    Ong, Marshall Ji Fa
    ;
    Goh, Jun Xian
    ;
    Ng, Juat Ying
    ;
    Tun, Karenne
    ;
    Marine sponges are known to host a complex microbial consortium that is essential to the health and resilience of these benthic invertebrates. These sponge-associated microbes are also an important source of therapeutic agents. The Neptune’s Cup sponge, Cliona patera, once believed to be extinct, was rediscovered off the southern coast of Singapore in 2011. The chance discovery of this sponge presented an opportunity to characterize the prokaryotic community of C. patera. Sponge tissue samples were collected from the inner cup, outer cup and stem of C. patera. for 16S rRNA amplicon sequencing. C. patera. hosted 5,222 distinct OTUs, spanning 26 bacterial phyla, and 74 bacterial classes. The bacterial phylum Proteobacteria, particularly classes Gammaproteobacteria and Alphaproteobacteria, dominated the sponge microbiome. Interestingly, the prokaryotic community structure differed significantly between the cup and stem of C. patera., suggesting that within C. patera. there are distinct microenvironments. Moreover, the cup of C. patera. had lower diversity and evenness as compared to the stem. Quorum sensing inhibitory (QSI) activities of selected sponge-associated marine bacteria were evaluated and their organic extracts profiled using the MS-based molecular networking platform. Of the 110 distinct marine bacterial strains isolated from sponge samples using culture-dependent methods, about 30% showed quorum sensing inhibitory activity. Preliminary identification of selected QSI active bacterial strains revealed that they belong mostly to classes Alphaproteobacteria and Bacilli. Annotation of the MS/MS molecular networkings of these QSI active organic extracts revealed diverse classes of natural products, including aromatic polyketides, siderophores, pyrrolidine derivatives, indole alkaloids, diketopiperazines, and pyrone derivatives. Moreover, potential novel compounds were detected in several strains as revealed by unique molecular families present in the molecular networks. Further research is required to determine the temporal stability of the microbiome of the host sponge, as well as mining of associated bacteria for novel QS inhibitors.
    WOS© Citations 3Scopus© Citations 5  61  70
  • Publication
    Open Access
    Trikoramides B-D, bioactive cyanobactins from the marine cyanobacterium Symploca hydnoides
    (2021)
    Phyo, Ma Yadanar
    ;
    Goh, Ben Teo Min
    ;
    Goh, Jun Xian
    ;
    Three new cyanobactins, trikoramides B (1)–D (3), have been isolated from the marine cyanobacterium, Symploca hydnoides, following a preliminary bioassay-guided isolation of the two most active polar fractions based on the brine shrimp toxicity assay. These new cyanobactins are new analogues of the previously reported cytotoxic trikoramide A (4) with differences mainly in the C-prenylated cyclotryptophan unit. Their planar structures were elucidated from their 1D and 2D NMR spectral data in combination with the HRMS/MS data. Marfey’s method, 2D NOESY NMR spectroscopic and ECD spectra analyses were used to determine the absolute stereochemistry of trikoramides B (1)–D (3). Trikoramides B (1) and D (3) exhibited cytotoxicity against MOLT-4 acute lymphoblastic leukemia cell line with IC50 values of 5.2 µM and 4.7 µM, respectively. Compounds 1 and 3 were also evaluated for their quorum-sensing inhibitory assay based on the Pseudomonas aeruginosa PAO1 lasB-gfp and rhlA-gfp bioreporter strains. Although trikoramide B (1) exhibited weak quorum-sensing inhibitory activity, the Br-containing trikoramide D (3) exhibited moderate to significant dose-dependent quorum-sensing inhibitory activities against PAO1 lasB-gpf and rhlA-gfp bioreporter strains with IC50 values of 19.6 µM and 7.3 µM, respectively.
    WOS© Citations 5Scopus© Citations 6  193  79
  • Publication
    Open Access
    Trikoramide A, a prenylated cyanobactin from the marine cyanobacterium symploca hydnoides
    (2019)
    Phyo, Ma Yadanar
    ;
    Ding, Gary Chi Ying
    ;
    Goh, Hui Chin
    ;
    Goh, Jun Xian
    ;
    Ong, Ji Fa Marshall
    ;
    Chan, Siew Herng
    ;
    Yung, Pui Yi Maria
    ;
    Candra, Hartono
    ;
    A new cyclic decapeptide, trikoramide A (1), has been isolated from samples of the marine cyanobacterium Symploca hydnoides, collected from Bintan Island, Indonesia. Trikoramide A (1) is a C-prenylated cyclotryptophan-containing cyanobactin. Its planar structure was deduced by 1D and 2D NMR spectroscopy as well as HR–MS/MS data. In addition, its absolute configuration was determined by Marfey’s method and 2D NOESY NMR spectroscopic analysis. Compound 1 possessed cytotoxicity against the MOLT-4 and AML2 cancer cell lines with IC50 values of 4.8 and 8.2 μM, respectively.
    WOS© Citations 13Scopus© Citations 15  108  80
  • Publication
    Open Access
    Triproamide and pemukainalides, cyclic depsipeptides from the marine cyanobacterium Symploca hydnoides
    (2022)
    Phyo, Ma Yadanar
    ;
    Goh, Jun Xian
    ;
    A new cyclic depsipeptide, triproamide (1), containing the rare 4-phenylvaline (dolaphenvaline, Dpv) and a β-amino acid, dolamethylleucine (Dml), originally found in dolastatin 16, was isolated from the polar VLC-derived fraction of the extracts prepared from the marine cyanobacterium Symploca hydnoides. Triproamide (1) was isolated along with the known molecule kulokainalide-1 (2), as well as its two new analogues, pemukainalides A (3) and B (4). Their planar structures were elucidated based on extensive NMR and mass spectrometric data. The absolute and relative configurations of the compounds were determined utilizing a combination of Marfey’s method, J-based configuration, and chiral-phase HPLC analyses. Kulokainalide-1 (2) and pemukainalide A (3) exhibited cytotoxicity against the MOLT-4 leukemia cell line with IC50 values of 5.9 and 5.6 μM, respectively.
    WOS© Citations 5Scopus© Citations 7  63  69