PhD Thesis

Investigation of Anticancer and Antibacterial Metabolites from Seaweeds of the Bay of Bengal and their Associated Endophytic Fungi

2026-03-02T00:00:00Z

Investigation of Anticancer and Antibacterial Metabolites from Seaweeds of the Bay of Bengal and their Associated Endophytic Fungi NOOR, SADIA The relentless pursuit of novel anticancer and antibacterial agents has directed significant research toward marine ecosystems, with seaweeds and their endophytic fungi emerging as exceptionally promising reservoirs of bioactive metabolites. This research aimed to systematically investigate the bioactive potential of marine endophytic fungi derived from seaweeds of the Bay of Bengal, Bangladesh. Three seaweed species—Ulva sp. (Chlorophyta), Gracilaria sp. (Rhodophyta), and Sargassum sp. (Phaeophyta)—were collected, morphologically identified, and served as hosts for the isolation of endophytic fungi on potato dextrose agar (PDA) media. Twelve fungal strains were isolated and identified through a polyphasic approach combining macroscopic/microscopic morphological characterization and molecular phylogenetic analysis of ITS sequences. The fungal strains comprised Chaetomium globosum (UE-1, SE-1), Nigrospora magnoliae (UE-2), Curvularia sp. (UE- 3), Curvularia moringae (UE-4), Aspergillus terreus (UE-5, GE-2, SE-2), Collariella gracilis or C. virescens (UE-6), Aspergillus subversicolor (GE-1), Cladosporium halotolerans (GE-3), and Curvularia perotidis (SE-3). Critically, all twelve endophytic fungal strains were reported for the first time from the Bay of Bengal, Bangladesh, with Nigrospora magnoliae being reported as a fungal endophyte for only the second time worldwide. Preliminary chemical profiling of crude extracts via Thin Layer Chromatography (TLC) and Gas Chromatography-Mass Spectrometry (GC-MS) indicated a rich diversity of secondary metabolites, including steroids, terpenoids, flavonoids, and fatty acid derivatives. Bioassay-guided fractionation led to the isolation of twelve pure compounds using various chromatographic techniques, and their structures were elucidated through 1D and 2D NMR spectroscopy. From C. globosum, six compounds were isolated: the new natural compounds UC-71 [(E)-1-(2′,4′- dihydroxy-3′,5′-dimethylphenyl)-2-buten-1-one] and UC-58 [1-(3′,4′-dihydroxy-2′,5′- dimethylphenyl)-3-hydroxybutan-1-one], alongside known metabolites chaetoviridin E (UC-59), a mixture of chaetoviridin A epimers (UC-60), chaetoglobosin G (UC-62), and chaetoglobosin B (UC-63). Another six compounds were isolated and characterized for the first time from N. magnoliae: ergosta-4,6,8(14),22-tetraene-3-one (UN-172), sterigmatocystin (UN-171), dihydrosterigmatocystin (UN-176), 11-oxo-(9E)- octadecenoic acid (UN-233), ostopanic acid (UN-235), and cerevesterol (UN-411). Bioactivity screening revealed that the crude extracts possessed significant iv antimicrobial activity against Gram-positive (Staphylococcus aureus, Bacillus megaterium) and Gram-negative bacteria (Escherichia coli, Salmonella typhi, Pseudomonas aeruginosa), and antifungal activity against Aspergillus niger and A. flavus in disc diffusion assays, outperforming their host seaweeds which showed no activity. Antioxidant activity, evaluated via DPPH radical scavenging, was particularly potent in extracts of A. terreus strains (IC50 value as low as 7.88 μg/mL). Brine shrimp lethality bioassay indicated strong cytotoxicity (LC50 value less than 30 μg/mL) for numerous extracts. The isolated pure compounds also exhibited notable bioactivities; for instance, UC-60 showed remarkable antifungal activity against Candida albicans (31.3 mm zone at 100 μg/disc), and several compounds demonstrated significant cytotoxicity in subsequent MTT assay on the HeLa cervical cancer cell line. The MTT assay revealed that compound UN-235 exhibited significant dose-dependent cytotoxicity against HeLa cells (IC50 value 243.04 μg/mL), demonstrating potency comparable to doxorubicin, thereby identifying it as a promising cytotoxic candidate worthy of further investigation. These comprehensive findings underscore the immense, largely untapped potential of endophytic fungi from Bangladeshi seaweeds as prolific sources of novel chemotherapeutic agents, with the isolation of new natural compounds and first-reported metabolites highlighting their critical value in anticancer and antibacterial drug discovery pipelines. This thesis is submitted for the degree of Doctor of Philosophy.

Chemical and pharmacological profiling of Jatropha pandurifolia and Syzygium reticulatum

2025-02-19T00:00:00Z

Chemical and pharmacological profiling of Jatropha pandurifolia and Syzygium reticulatum JAHAN, NISRAT Jatropha pandurifolia Andrews (family: Euphorbiaceae) and Syzygium reticulatum (Wight) Walp. (family: Myrtaceae) were studied for their secondary metabolites and their biological activities were evaluated both in vitro and in vivo. Through extensive NMR experiments—including ¹H NMR, ¹³C NMR, and ¹H-¹H COSY, HSQC and mass spectrometry, a total of fifteen compounds were identified from the plant extracts. Thirteen of these chemical compounds were isolated specifically from the stem bark of J. pandurifolia including 2-epi-jatrogrossidione, integerrimene, jatrophatrione, citlalitrione, dotriacontyl trans-ferulate, triacontyl trans-ferulate, octacosyl trans-ferulate, hexacosyl trans-ferulate, octacosyl cis-ferulate, β-sitosterol, stigmasterol, n-dotriacontanol, and 1,2-dioleoyl-3-palmitoyl-glycerol. Dotriacontyl trans-ferulate was isolated and characterized as a previously unreported molecule. Bis(2-ethylhexyl) phthalate and stigmast-4-en-3-one were isolated from the leaves of S. reticulatum, marking the first report of these compounds from this plant species. In vivo investigation was carried out to assess CNS depressant, antidiarrheal, and analgesic activities, while in vitro study was assessed for antioxidant, cytotoxic, and thrombolytic properties. Furthermore, in silico investigation of selected pure compounds were conducted using molecular docking and ADMET (absorption, distribution, metabolism, excretion, and toxicity) profiling. CNS depressant activity was carried out by open field and hole cross methods at 100 mg/kg, 200 mg/kg, and 300 mg/kg, where diazepam was used as standard. In open field and hole cross method, highest inhibition of movements were 87.37% (***P<0.001) and 84.78% (*P<0.05), respectively for methanolic extract of J. pandurifolia leaf at 300 mg/kg. Furthermore, at the same dose highest inhibition of locomotor activity were 73.68% (***P<0.001) and 80.43% (**P<0.01) for ethyl acetate extract of S. reticulatum leaf in aforementioned methods. Diazepam exhibited 91.58% and 95.65% movement inhibition, respectively. The antidiarrheal effect was performed using the castor oil induced diarrheal model at 200, 400, and 600 mg/kg, using loperamide as the standard. The frequency of diarrhea was reduced by 85.95% at 600 mg/kg of Jp-ML, where loperamide showed 98.57% gastric inhibition. At the same dose, Sr-EAL exhibited a delay in diarrheal onset of 87.53% where loperamide showed 94.84% gastric inhibition. The analgesic activity was assessed by acetic acid induced writhing ix method and formalin induced nociception test. Jp-ML showed the highest dosedependent inhibition of writhing by 66.67% (**P<0.01) at 300 mg/kg, whereas indomethacin showed 78.43% pain reduction. In the formalin test, pain inhibition were 63.92% (***P<0.001) in the early phase and 70.35% (***P<0.001) in the late phase at the same dose. On the other hand, Sr-EAL showed the highest inhibition of writhing by 70.59% (***P<0.001) at 300 mg/kg. Inhibition of paw licking were recorded by 54.55% (***P<0.001) and 70.52% (***P<0.001) in the early phase and late phase, respectively. Antioxidant activity was estimated using the DPPH free radical scavenging assay, with BHT as the standard. The lowest IC50 value were 8.11 μg/mL and 10.34 μg/mL for JP-ML and Sr-EAL, respectively. Pure compounds (JP- 10, JP-13, JP-25, and JP-460) exhibited promising antioxidant activity, with highest antioxidant activity of JP-25 (IC50 =13.10 μg/mL). Cytotoxicity was assessed using the brine shrimp lethality assay, with vincristine sulphate as the standard. The LC50 values were 1.60 μg/mL for Jp-EAL and 1.70 μg/mL for Sr-ML. Among the four pure compounds tested, JP-460 exhibited the strongest cytotoxicity, with LC50 value of 1.27 μg/mL. Cytotoxicity test was also carried out on the HeLa cell line both qualitatively and quantitatively. In qualitative test JP-13 and JP-460 showed a cell survival rate of over 95%, whereas JP-200 resulted in a cell survival rate of only 5%, indicating strong cytotoxicity. In quantitative MTT assay, JP-200 exhibited LD50 value of 272.45 μg/mL. Thrombolytic activity was evaluated using streptokinase as standard. The highest clot lysis activity were 63.32% and 67.58% for the Jp-ML and Sr-EAL, respectively. JP-460 demonstrated significant clot lysis activity, with 71.04% clot rupture. Finally, molecular docking studies revealed that compound JP-460 exhibited strong binding affinity (-9.4 kcal/mol) and binding efficacy (0.41 (kcal/mol per non-hydrogen atom) to the human GABA-A receptor. The ADMET assessment confirmed that the isolated compounds have preferable pharmacokinetic and safety profiles, supporting their potential for therapeutic application. This thesis is submitted for the degree of Doctor of Philosophy.

The potentiation and broadening the effect of low molecular hypoglycemic drugs through interaction with some CNS stimulant molecules

2025-03-10T00:00:00Z

The potentiation and broadening the effect of low molecular hypoglycemic drugs through interaction with some CNS stimulant molecules Mohiuddin, Mohammad This thesis is submitted for the degree of Doctor of Philosophy.

Cytotoxic and antimicrobial constituents from some Bangladeshi Bridelia and Erythrina species

2025-03-10T00:00:00Z

Cytotoxic and antimicrobial constituents from some Bangladeshi Bridelia and Erythrina species Anjum, Adeeba This thesis is submitted for the degree of Doctor of Philosophy.