Synthesis, structure and in vitro anti-trypanosomal activity of non-toxic Arylpyrrole-Based Chalcone derivatives:
- Zulu, Ayanda I, Oderinlo, Ogunyemi O, Kruger, Cuan, Isaacs, Michelle, Hoppe, Heinrich C, Smith, Vincent J, Veale, Clinton G L, Khanye, Setshaba D
- Authors: Zulu, Ayanda I , Oderinlo, Ogunyemi O , Kruger, Cuan , Isaacs, Michelle , Hoppe, Heinrich C , Smith, Vincent J , Veale, Clinton G L , Khanye, Setshaba D
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/179017 , vital:40096 , https://doi.org/10.3390/molecules25071668
- Description: With an intention of identifying chalcone derivatives exhibiting anti-protozoal activity, a cohort of relatively unexplored arylpyrrole-based chalcone derivatives were synthesized in moderate to good yields. The resultant compounds were evaluated in vitro for their potential activity against a cultured Trypanosoma brucei brucei 427 strain. Several compounds displayed mostly modest in vitro anti-trypanosomal activity with compounds 10e and 10h emerging as active candidates with IC50 values of 4.09 and 5.11 µM, respectively. More importantly, a concomitant assessment of their activity against a human cervix adenocarcinoma (HeLa) cell line revealed that these compounds are non-toxic.
- Full Text:
- Date Issued: 2020
- Authors: Zulu, Ayanda I , Oderinlo, Ogunyemi O , Kruger, Cuan , Isaacs, Michelle , Hoppe, Heinrich C , Smith, Vincent J , Veale, Clinton G L , Khanye, Setshaba D
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/179017 , vital:40096 , https://doi.org/10.3390/molecules25071668
- Description: With an intention of identifying chalcone derivatives exhibiting anti-protozoal activity, a cohort of relatively unexplored arylpyrrole-based chalcone derivatives were synthesized in moderate to good yields. The resultant compounds were evaluated in vitro for their potential activity against a cultured Trypanosoma brucei brucei 427 strain. Several compounds displayed mostly modest in vitro anti-trypanosomal activity with compounds 10e and 10h emerging as active candidates with IC50 values of 4.09 and 5.11 µM, respectively. More importantly, a concomitant assessment of their activity against a human cervix adenocarcinoma (HeLa) cell line revealed that these compounds are non-toxic.
- Full Text:
- Date Issued: 2020
Synthesis, in vitro cytotoxicity and trypanocidal evaluation of novel 1, 3, 6-substituted non-fluoroquinolones
- Beteck, Richard M, Isaacs, Michelle, Khanye, Setshaba D, Hoppe, Heinrich C
- Authors: Beteck, Richard M , Isaacs, Michelle , Khanye, Setshaba D , Hoppe, Heinrich C
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123140 , vital:35409 , https://doi.org/10.17159/0379-4350/2018/v71a25
- Description: Sleeping sickness (trypanosomiasis) is a neglected tropical disease that affects mostly the poorest communities in sub-Saharan Africa. Toxic side effects associated with the use of current anti-trypanosomal drugs, which in some cases kill faster than the disease itself, necessitate the search for new drugs with better safety margins. To this effect, a small library bearing different substituents at position -1, -3, and -6 of the quinolone nucleus were synthesized and evaluated in vitro against HeLa cell lines and Trypanosoma brucei brucei for cytotoxicity and trypanocidal potentials, respectively. While most of these compounds showed no cytotoxic effect, they exhibited moderate to weak anti-trypanosomal activities. The SAR studies of this series provide new information worth considering in future exploration of the quinolone scaffold in search ofmore potent and safe trypanocidal agents.
- Full Text:
- Date Issued: 2018
- Authors: Beteck, Richard M , Isaacs, Michelle , Khanye, Setshaba D , Hoppe, Heinrich C
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123140 , vital:35409 , https://doi.org/10.17159/0379-4350/2018/v71a25
- Description: Sleeping sickness (trypanosomiasis) is a neglected tropical disease that affects mostly the poorest communities in sub-Saharan Africa. Toxic side effects associated with the use of current anti-trypanosomal drugs, which in some cases kill faster than the disease itself, necessitate the search for new drugs with better safety margins. To this effect, a small library bearing different substituents at position -1, -3, and -6 of the quinolone nucleus were synthesized and evaluated in vitro against HeLa cell lines and Trypanosoma brucei brucei for cytotoxicity and trypanocidal potentials, respectively. While most of these compounds showed no cytotoxic effect, they exhibited moderate to weak anti-trypanosomal activities. The SAR studies of this series provide new information worth considering in future exploration of the quinolone scaffold in search ofmore potent and safe trypanocidal agents.
- Full Text:
- Date Issued: 2018
Synthesis, characterization and biological activity of some Dithiourea Derivatives:
- Odame, Felix, Hosten, Eric C, Krause, Jason, Isaacs, Michelle, Hoppe, Heinrich C, Khanye, Setshaba D, Sayed, Yasien, Frost, Carminita L, Lobb, Kevin A, Tshentu, Zenixole R
- Authors: Odame, Felix , Hosten, Eric C , Krause, Jason , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D , Sayed, Yasien , Frost, Carminita L , Lobb, Kevin A , Tshentu, Zenixole R
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/163046 , vital:41007 , DOI: 10.17344/acsi.2019.5689
- Description: Novel dithiourea derivatives have been designed as HIV-1 protease inhibitors using Autodock 4.2, synthesized and characterized by spectroscopic methods and microanalysis.
- Full Text:
- Date Issued: 2020
- Authors: Odame, Felix , Hosten, Eric C , Krause, Jason , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D , Sayed, Yasien , Frost, Carminita L , Lobb, Kevin A , Tshentu, Zenixole R
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/163046 , vital:41007 , DOI: 10.17344/acsi.2019.5689
- Description: Novel dithiourea derivatives have been designed as HIV-1 protease inhibitors using Autodock 4.2, synthesized and characterized by spectroscopic methods and microanalysis.
- Full Text:
- Date Issued: 2020
Synthesis, antiplasmodial and antitrypanosomal evaluation of a series of novel 2-oxoquinoline-based thiosemicarbazone derivatives
- Darrell, Oliver T, Hulushe, Siyabonga T, Mtshare, Thanduxolo Elihle, Beteck, Richard M, Isaacs, Michelle, Laming, Dustin, Khanye, Setshaba D, Hoppe, Heinrich C, Krause, Rui W M
- Authors: Darrell, Oliver T , Hulushe, Siyabonga T , Mtshare, Thanduxolo Elihle , Beteck, Richard M , Isaacs, Michelle , Laming, Dustin , Khanye, Setshaba D , Hoppe, Heinrich C , Krause, Rui W M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123117 , vital:35407 , https://doi.org/10.17159/0379-4350/2018/v71a25
- Description: Herein a series of novel thiosemicarbazones (TSCs) derived from 2-oxoquinoline scaffold is reported, and the target compounds have been successfully synthesized and characterized using standard spectroscopic techniques. The in vitro biological activities of synthesized molecules were evaluated against Plasmodium falciparum malaria parasites (strain 3D7), Trypanosoma brucei brucei parasites (strain 427) and HeLa cells. All the compounds displayed modest or no activity at a concentration of 20 μM and percentage viability of >50 % was often observed. Except for compound 9o, none of the final compounds exhibited cytotoxic effects against HeLa cells at 20 μM.
- Full Text:
- Date Issued: 2018
- Authors: Darrell, Oliver T , Hulushe, Siyabonga T , Mtshare, Thanduxolo Elihle , Beteck, Richard M , Isaacs, Michelle , Laming, Dustin , Khanye, Setshaba D , Hoppe, Heinrich C , Krause, Rui W M
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123117 , vital:35407 , https://doi.org/10.17159/0379-4350/2018/v71a25
- Description: Herein a series of novel thiosemicarbazones (TSCs) derived from 2-oxoquinoline scaffold is reported, and the target compounds have been successfully synthesized and characterized using standard spectroscopic techniques. The in vitro biological activities of synthesized molecules were evaluated against Plasmodium falciparum malaria parasites (strain 3D7), Trypanosoma brucei brucei parasites (strain 427) and HeLa cells. All the compounds displayed modest or no activity at a concentration of 20 μM and percentage viability of >50 % was often observed. Except for compound 9o, none of the final compounds exhibited cytotoxic effects against HeLa cells at 20 μM.
- Full Text:
- Date Issued: 2018
Synthesis of N-Substituted phosphoramidic acid esters as “reverse” fosmidomycin analogues
- Adeyemi, Christiana M, Hoppe, Heinrich C, Isaacs, Michelle, Klein, Rosalyn, Lobb, Kevin A, Kaye, Perry T
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Klein, Rosalyn , Lobb, Kevin A , Kaye, Perry T
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443238 , vital:74101 , https://doi.org/10.1016/j.tet.2019.02.003
- Description: An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.
- Full Text:
- Date Issued: 2019
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Klein, Rosalyn , Lobb, Kevin A , Kaye, Perry T
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/443238 , vital:74101 , https://doi.org/10.1016/j.tet.2019.02.003
- Description: An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.
- Full Text:
- Date Issued: 2019
Synthesis of N-Substituted phosphoramidic acid esters as “reverse” fosmidomycin analogues
- Adeyemi, Christiana M, Hoppe, Heinrich C, Isaacs, Michelle, Klein, Rosalyn, Lobb, Kevin A, Kaye, Perry T
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Klein, Rosalyn , Lobb, Kevin A , Kaye, Perry T
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447196 , vital:74591 , xlink:href="https://doi.org/10.1016/j.tet.2019.02.003"
- Description: An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.
- Full Text:
- Date Issued: 2019
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Klein, Rosalyn , Lobb, Kevin A , Kaye, Perry T
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/447196 , vital:74591 , xlink:href="https://doi.org/10.1016/j.tet.2019.02.003"
- Description: An efficient synthetic pathway to a series of novel “reverse” fosmidomycin analogues has been developed, commencing from substituted benzylamines. In these analogues, the fosmidomycin hydroxamate moiety is reversed and the tetrahedral methylene carbon adjacent to the phosphonate moiety is replaced by a nitrogen atom bearing different benzyl groups. The resulting phosphonate esters were designed as potential antimalarial “pro-drugs”.
- Full Text:
- Date Issued: 2019
Synthesis and trypanocidal activity of substituted 2, 4-diarylquinoline derivatives
- Oluwafemi, Kola A, Phunguphungu, Siyolise, Gqunu, Sinalo, Isaacs, Michelle, Hoppe, Heinrich C, Klein, Rosalyn, Kaye, Perry T
- Authors: Oluwafemi, Kola A , Phunguphungu, Siyolise , Gqunu, Sinalo , Isaacs, Michelle , Hoppe, Heinrich C , Klein, Rosalyn , Kaye, Perry T
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477683 , vital:78111 , xlink:href="https://doi.org/10.24820/ark.5550190.p011.499"
- Description: A small library of nine, novel 2, 4-diarylquinoline derivatives has been prepared in high yield via convenient one-or two-step routes from a series of substituted 2-aminobenzophenones. None of the products exhibited toxicity at 20 μM against human cervix adenocarcinoma (HeLa) cells, while many of them exhibited encouraging trypanocidal activity against T. brucei brucei (a parasite responsible for African cattle trypanosomiasis)-some with IC50 values in the range 2.8–6.2 μM.
- Full Text:
- Date Issued: 2021
- Authors: Oluwafemi, Kola A , Phunguphungu, Siyolise , Gqunu, Sinalo , Isaacs, Michelle , Hoppe, Heinrich C , Klein, Rosalyn , Kaye, Perry T
- Date: 2021
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477683 , vital:78111 , xlink:href="https://doi.org/10.24820/ark.5550190.p011.499"
- Description: A small library of nine, novel 2, 4-diarylquinoline derivatives has been prepared in high yield via convenient one-or two-step routes from a series of substituted 2-aminobenzophenones. None of the products exhibited toxicity at 20 μM against human cervix adenocarcinoma (HeLa) cells, while many of them exhibited encouraging trypanocidal activity against T. brucei brucei (a parasite responsible for African cattle trypanosomiasis)-some with IC50 values in the range 2.8–6.2 μM.
- Full Text:
- Date Issued: 2021
Synthesis and evaluation of substituted 4-(N-benzylamino)cinnamate esters as potential anti-cancer agents and HIV-1 integrase inhibitors
- Faridoon, H, Edkins, Adrienne L, Isaacs, Michelle, Mnkandhla, Dumisani, Hoppe, Heinrich C, Kaye, Perry T
- Authors: Faridoon, H , Edkins, Adrienne L , Isaacs, Michelle , Mnkandhla, Dumisani , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66289 , vital:28929 , https://doi.org/10.1016/j.bmcl.2016.05.023
- Description: publisher version , Encouraging selectivity and low micromolar activity against HeLa cervical carcinoma (IC50 ⩾ 3.0 μM) and the aggressive MDA-MB-231 triple negative breast carcinoma (IC50 ⩾ 9.6 μM) cell lines has been exhibited by a number of readily accessible 4-(N-benzylamino)cinnamate esters. The potential of the ligands as HIV-1 integrase inhibitors has also been examined.
- Full Text: false
- Date Issued: 2016
- Authors: Faridoon, H , Edkins, Adrienne L , Isaacs, Michelle , Mnkandhla, Dumisani , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66289 , vital:28929 , https://doi.org/10.1016/j.bmcl.2016.05.023
- Description: publisher version , Encouraging selectivity and low micromolar activity against HeLa cervical carcinoma (IC50 ⩾ 3.0 μM) and the aggressive MDA-MB-231 triple negative breast carcinoma (IC50 ⩾ 9.6 μM) cell lines has been exhibited by a number of readily accessible 4-(N-benzylamino)cinnamate esters. The potential of the ligands as HIV-1 integrase inhibitors has also been examined.
- Full Text: false
- Date Issued: 2016
Synthesis and conformational studies of 5-bromo-1-[(N-substituted-carbamoyl) methyl]-7-azabenzimidazoles
- Oluwafemi, Kola A, Klein, Rosalyn, Lobb, Kevin A, Tshiwawa, Tendamudzimu, Isaacs, Michelle, Hoppe, Heinrich C, Kaye, Perry T
- Authors: Oluwafemi, Kola A , Klein, Rosalyn , Lobb, Kevin A , Tshiwawa, Tendamudzimu , Isaacs, Michelle , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/452800 , vital:75171 , xlink:href="https://doi.org/10.1016/j.molstruc.2022.133811"
- Description: The Cs2CO3-catalysed condensation of 5-bromo-7-azabenzimidazole with a series of bromomethyl ketones has afforded a small library of ten, novel 5-bromo-1-[(N-substututed-carbamoyl)methyl]-7-azabenzimidazoles. Rotamerism in the products, as evidenced by the splitting of 1H- and 13C-NMR signals, is attributed to hindered internal rotation about the amide N-C(=O) bond, and has been explored using dynamic NMR (DNMR) analysis and computational methods at the GIAO B3LYP/6-311+G(2d,p) level of theory. Coalescence temperatures have been obtained for representative examples and rotational barriers determined experimentally and theoretically. A detailed theoretical analysis has been undertaken to explore conformations which may contribute to the relative populations of the s-cis and s-trans rotamers. The products have also been screened for cytotoxicity and activity against two parasitic protozoan strains (Plasmodium falciparum and Trypanosoma brucei).
- Full Text:
- Date Issued: 2022
- Authors: Oluwafemi, Kola A , Klein, Rosalyn , Lobb, Kevin A , Tshiwawa, Tendamudzimu , Isaacs, Michelle , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/452800 , vital:75171 , xlink:href="https://doi.org/10.1016/j.molstruc.2022.133811"
- Description: The Cs2CO3-catalysed condensation of 5-bromo-7-azabenzimidazole with a series of bromomethyl ketones has afforded a small library of ten, novel 5-bromo-1-[(N-substututed-carbamoyl)methyl]-7-azabenzimidazoles. Rotamerism in the products, as evidenced by the splitting of 1H- and 13C-NMR signals, is attributed to hindered internal rotation about the amide N-C(=O) bond, and has been explored using dynamic NMR (DNMR) analysis and computational methods at the GIAO B3LYP/6-311+G(2d,p) level of theory. Coalescence temperatures have been obtained for representative examples and rotational barriers determined experimentally and theoretically. A detailed theoretical analysis has been undertaken to explore conformations which may contribute to the relative populations of the s-cis and s-trans rotamers. The products have also been screened for cytotoxicity and activity against two parasitic protozoan strains (Plasmodium falciparum and Trypanosoma brucei).
- Full Text:
- Date Issued: 2022
Synthesis and conformational studies of 5-bromo-1-[(N-substituted-carbamoyl) methyl]-7-azabenzimidazoles
- Oluwafemi, Kola A, Klein, Rosalyn, Lobb, Kevin A, Tshiwawa, Tendamudzimu, Isaacs, Michelle, Hoppe, Heinrich C, Kaye, Perry T
- Authors: Oluwafemi, Kola A , Klein, Rosalyn , Lobb, Kevin A , Tshiwawa, Tendamudzimu , Isaacs, Michelle , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477672 , vital:78110 , xlink:href="https://doi.org/10.1016/j.molstruc.2022.133811"
- Description: The Cs2CO3-catalysed condensation of 5-bromo-7-azabenzimidazole with a series of bromomethyl ketones has afforded a small library of ten, novel 5-bromo-1-[(N-substututed-carbamoyl)methyl]-7-azabenzimidazoles. Rotamerism in the products, as evidenced by the splitting of 1H- and 13C-NMR signals, is attributed to hindered internal rotation about the amide N-C(=O) bond, and has been explored using dynamic NMR (DNMR) analysis and computational methods at the GIAO B3LYP/6-311+G(2d,p) level of theory. Coalescence temperatures have been obtained for representative examples and rotational barriers determined experimentally and theoretically. A detailed theoretical analysis has been undertaken to explore conformations which may contribute to the relative populations of the s-cis and s-trans rotamers. The products have also been screened for cytotoxicity and activity against two parasitic protozoan strains (Plasmodium falciparum and Trypanosoma brucei).
- Full Text:
- Date Issued: 2022
- Authors: Oluwafemi, Kola A , Klein, Rosalyn , Lobb, Kevin A , Tshiwawa, Tendamudzimu , Isaacs, Michelle , Hoppe, Heinrich C , Kaye, Perry T
- Date: 2022
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477672 , vital:78110 , xlink:href="https://doi.org/10.1016/j.molstruc.2022.133811"
- Description: The Cs2CO3-catalysed condensation of 5-bromo-7-azabenzimidazole with a series of bromomethyl ketones has afforded a small library of ten, novel 5-bromo-1-[(N-substututed-carbamoyl)methyl]-7-azabenzimidazoles. Rotamerism in the products, as evidenced by the splitting of 1H- and 13C-NMR signals, is attributed to hindered internal rotation about the amide N-C(=O) bond, and has been explored using dynamic NMR (DNMR) analysis and computational methods at the GIAO B3LYP/6-311+G(2d,p) level of theory. Coalescence temperatures have been obtained for representative examples and rotational barriers determined experimentally and theoretically. A detailed theoretical analysis has been undertaken to explore conformations which may contribute to the relative populations of the s-cis and s-trans rotamers. The products have also been screened for cytotoxicity and activity against two parasitic protozoan strains (Plasmodium falciparum and Trypanosoma brucei).
- Full Text:
- Date Issued: 2022
Synthesis and biological evaluation of bis-N2, N2′-(4-hydroxycoumarin-3-yl) ethylidene]-2, 3-dihydroxysuccinodihydrazides
- Manyeruke, Meloddy H, Tshiwawa, Tendamudzimu, Hoppe, Heinrich C, Isaacs, Michelle, Seldon, Ronnett, Warner, Digby F, Krause, Rui W M, Kaye, Perry T
- Authors: Manyeruke, Meloddy H , Tshiwawa, Tendamudzimu , Hoppe, Heinrich C , Isaacs, Michelle , Seldon, Ronnett , Warner, Digby F , Krause, Rui W M , Kaye, Perry T
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193430 , vital:45331 , xlink:href="https://doi.org/10.1016/j.bmcl.2019.126911"
- Description: A series of N2,N2′-bis[4-hydroxycoumarin-3-yl)ethylidene]-2,3-dihydroxysuccino-hydrazides, containing 4-hydroxycoumarin, hydrazine and tartaric acid moieties, have been prepared and examined for possible biological activity. Several of these compounds exhibit promising HIV-1 integrase inhibition (IC50 = 3.5 μM), and anti-T. brucei (32% viability) and anti-mycobacterial (Visual MIC90 = 15.63 μM) activity.
- Full Text:
- Date Issued: 2020
- Authors: Manyeruke, Meloddy H , Tshiwawa, Tendamudzimu , Hoppe, Heinrich C , Isaacs, Michelle , Seldon, Ronnett , Warner, Digby F , Krause, Rui W M , Kaye, Perry T
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193430 , vital:45331 , xlink:href="https://doi.org/10.1016/j.bmcl.2019.126911"
- Description: A series of N2,N2′-bis[4-hydroxycoumarin-3-yl)ethylidene]-2,3-dihydroxysuccino-hydrazides, containing 4-hydroxycoumarin, hydrazine and tartaric acid moieties, have been prepared and examined for possible biological activity. Several of these compounds exhibit promising HIV-1 integrase inhibition (IC50 = 3.5 μM), and anti-T. brucei (32% viability) and anti-mycobacterial (Visual MIC90 = 15.63 μM) activity.
- Full Text:
- Date Issued: 2020
Synthesis and anti-parasitic activity of N-benzylated phosphoramidate Mg2+-chelating ligands
- Adeyemi, Christiana M, Hoppe, Heinrich C, Isaacs, Michelle, Mnkandhla, Dumisani, Lobb, Kevin A, Klein, Rosalyn, Kaye, Perry T
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Mnkandhla, Dumisani , Lobb, Kevin A , Klein, Rosalyn , Kaye, Perry T
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451171 , vital:75025 , xlink:href="https://doi.org/10.1016/j.bioorg.2020.104280"
- Description: A series of N-benzylated phosphoramidate esters, containing a 3,4-dihydroxyphenyl Mg2+-chelating group, has been synthesised in five steps as analogues of fosmidomycin, a Plasmodium falciparum 1-deoxy-1-D-xylulose-5- phosphate reductoisomerase (PfDXR) inhibitor. The 3,4-dihydroxyphenyl group effectively replaces the Mg2+- chelating hydroxamic acid group in fosmidomycin. The compounds showed very encouraging anti-parasitic activity with IC50 values of 5.6–16.4 µM against Plasmodium falciparum parasites and IC50 values of 5.2 – 10.2 µM against Trypanosoma brucei brucei (T.b.brucei). Data obtained from in silico docking of the ligands in the PfDXR receptor cavity (3AU9)5 support their potential as PfDXR inhibitors.
- Full Text:
- Date Issued: 2020
- Authors: Adeyemi, Christiana M , Hoppe, Heinrich C , Isaacs, Michelle , Mnkandhla, Dumisani , Lobb, Kevin A , Klein, Rosalyn , Kaye, Perry T
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/451171 , vital:75025 , xlink:href="https://doi.org/10.1016/j.bioorg.2020.104280"
- Description: A series of N-benzylated phosphoramidate esters, containing a 3,4-dihydroxyphenyl Mg2+-chelating group, has been synthesised in five steps as analogues of fosmidomycin, a Plasmodium falciparum 1-deoxy-1-D-xylulose-5- phosphate reductoisomerase (PfDXR) inhibitor. The 3,4-dihydroxyphenyl group effectively replaces the Mg2+- chelating hydroxamic acid group in fosmidomycin. The compounds showed very encouraging anti-parasitic activity with IC50 values of 5.6–16.4 µM against Plasmodium falciparum parasites and IC50 values of 5.2 – 10.2 µM against Trypanosoma brucei brucei (T.b.brucei). Data obtained from in silico docking of the ligands in the PfDXR receptor cavity (3AU9)5 support their potential as PfDXR inhibitors.
- Full Text:
- Date Issued: 2020
Synthesis and anti-parasitic activity of C-benzylated (N-arylcarbamoyl) alkylphosphonate esters
- Adeyemi, Christiana Modupe, Isaacs, Michelle, Mnkandhla, Dumisani, Krause, Rui W M, Klein, Rosalyn, Hoppe, Heinrich C, Lobb, Kevin A, Kaye, Perry T
- Authors: Adeyemi, Christiana Modupe , Isaacs, Michelle , Mnkandhla, Dumisani , Krause, Rui W M , Klein, Rosalyn , Hoppe, Heinrich C , Lobb, Kevin A , Kaye, Perry T
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125641 , vital:35803 , https://doi.org/10.1016/j.tet.2017.01.045
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl)phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
- Authors: Adeyemi, Christiana Modupe , Isaacs, Michelle , Mnkandhla, Dumisani , Krause, Rui W M , Klein, Rosalyn , Hoppe, Heinrich C , Lobb, Kevin A , Kaye, Perry T
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125641 , vital:35803 , https://doi.org/10.1016/j.tet.2017.01.045
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl)phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
Synthesis and anti-parasitic activity of C-benzylated (N-arylcarbamoyl) alkylphosphonate esters
- Adeyemi, Christiana M, Isaacs, Michelle, Mnkandhla, Dumisani, Klein, Rosalyn, Hoppe, Heinrich C, Krause, Rui W M, Lobb, Kevin A, Kaye, Perry T
- Authors: Adeyemi, Christiana M , Isaacs, Michelle , Mnkandhla, Dumisani , Klein, Rosalyn , Hoppe, Heinrich C , Krause, Rui W M , Lobb, Kevin A , Kaye, Perry T
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477661 , vital:78109 , xlink:href="https://doi.org/10.1016/j.tet.2017.01.045"
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl) phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
- Authors: Adeyemi, Christiana M , Isaacs, Michelle , Mnkandhla, Dumisani , Klein, Rosalyn , Hoppe, Heinrich C , Krause, Rui W M , Lobb, Kevin A , Kaye, Perry T
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/477661 , vital:78109 , xlink:href="https://doi.org/10.1016/j.tet.2017.01.045"
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl) phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
Supplementary Material Synthesis and biological evaluation of (E)-cinnamic acid,(E)-2-styrylthiazole and (E)-2-[2-(naphthalen-1-yl) vinyl] thiazole derivatives
- Olawode, Emmanuel O, Tandlich, Roman, Prinsloo, Earl, Isaacs, Michelle, Hoppe, Heinrich C, Seldon, Ronnett, Warner, Digby F, Steenkamp, Vanessa, Kaye, Perry T
- Authors: Olawode, Emmanuel O , Tandlich, Roman , Prinsloo, Earl , Isaacs, Michelle , Hoppe, Heinrich C , Seldon, Ronnett , Warner, Digby F , Steenkamp, Vanessa , Kaye, Perry T
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/431778 , vital:72803 , xlink:href=" https://www.arkat-usa.org/get-file/59868/"
- Description: The screening was conducted using multi-well plates which are suited for HeLa cells in the log phase of growth with final cell density > 10 cells/cm. Each experiment normally includes a blank control, containing medium without the cells.28,45 Non-contaminated HeLa cells (6.57 x 105 cells per well) in media were allowed to grow in the incubator under an atmosphere of 5% CO2 at 37 0C for 24 h. To each well was dispensed 200 µL of HeLa culture, containing 6.57 x 105 cells under LabEAir laminar flow hood (Vivid Air, South Africa); 20 µL of resazurin dye (Sigma TOX-8) and test compound (50 µL) were added, which were then incubated in the presence of 5% CO2 at 37 0C for 24 hours in a shaker, to enhance the distribution of the dye. The absorbance of each well was measured with Bio-tek Power Wave X fluorometer (Beijing, China), and increases in fluorescence was monitored at a wavelength of 590 nm, using an excitation wavelength of 560 nm.
- Full Text:
- Date Issued: 2016
- Authors: Olawode, Emmanuel O , Tandlich, Roman , Prinsloo, Earl , Isaacs, Michelle , Hoppe, Heinrich C , Seldon, Ronnett , Warner, Digby F , Steenkamp, Vanessa , Kaye, Perry T
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/431778 , vital:72803 , xlink:href=" https://www.arkat-usa.org/get-file/59868/"
- Description: The screening was conducted using multi-well plates which are suited for HeLa cells in the log phase of growth with final cell density > 10 cells/cm. Each experiment normally includes a blank control, containing medium without the cells.28,45 Non-contaminated HeLa cells (6.57 x 105 cells per well) in media were allowed to grow in the incubator under an atmosphere of 5% CO2 at 37 0C for 24 h. To each well was dispensed 200 µL of HeLa culture, containing 6.57 x 105 cells under LabEAir laminar flow hood (Vivid Air, South Africa); 20 µL of resazurin dye (Sigma TOX-8) and test compound (50 µL) were added, which were then incubated in the presence of 5% CO2 at 37 0C for 24 hours in a shaker, to enhance the distribution of the dye. The absorbance of each well was measured with Bio-tek Power Wave X fluorometer (Beijing, China), and increases in fluorescence was monitored at a wavelength of 590 nm, using an excitation wavelength of 560 nm.
- Full Text:
- Date Issued: 2016
Preparation and characterization of isoniazid-loaded crude soybean lecithin liposomes
- Nkanga, Christian I, Isaacs, Michelle, Noundou, Xavier S, Krause, Rui W M, Walker, Roderick B
- Authors: Nkanga, Christian I , Isaacs, Michelle , Noundou, Xavier S , Krause, Rui W M , Walker, Roderick B
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125654 , vital:35804 , https://doi.org/10.1016/j.ijpharm.2017.04.074
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl)phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
- Authors: Nkanga, Christian I , Isaacs, Michelle , Noundou, Xavier S , Krause, Rui W M , Walker, Roderick B
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/125654 , vital:35804 , https://doi.org/10.1016/j.ijpharm.2017.04.074
- Description: Unexpected substituent-dependent regioselectivty challenges in the synthesis of C-benzylated (N-arylcarbamoyl)phosphonate esters have been resolved. The C-benzylated N-furfurylcarbamoyl derivative showed low micromolar PfLDH inhibition, while one of the C-benzylated N-arylcarbamoyl analogues was active against Nagana Trypanosoma brucei parasites which are responsible for African trypanosomiasis in cattle.
- Full Text:
- Date Issued: 2017
Novobiocin–ferrocene conjugates possessing anticancer and antiplasmodial activity independent of HSP90 inhibition.
- Mbaba, Mziyanda, de la Mare, Jo-Anne, Sterrenberg, Jason N, Kajewole, Deborah, Maharaj, Shantal, Edkins, Adrienne L, Isaacs, Michelle, Hoppe, Heinrich C, Khanye, Setshaba D
- Authors: Mbaba, Mziyanda , de la Mare, Jo-Anne , Sterrenberg, Jason N , Kajewole, Deborah , Maharaj, Shantal , Edkins, Adrienne L , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/122858 , vital:35359 , https://doi.org/10.1007/s00775-018-1634-9
- Description: A series of tailored novobiocin–ferrocene conjugates was prepared in moderate yields and investigated for in vitro anticancer and antiplasmodial activity against the MDA-MB-231 breast cancer line and Plasmodium falciparum 3D7 strain, respectively. While the target compounds displayed moderate anticancer activity against the breast cancer cell line with IC50 values in the mid-micromolar range, compounds 10a–c displayed promising antiplasmodial activity as low as 0.889 µM. Furthermore, the most promising compounds were tested for inhibitory effects against a postulated target, heat shock protein 90 (Hsp90).
- Full Text:
- Authors: Mbaba, Mziyanda , de la Mare, Jo-Anne , Sterrenberg, Jason N , Kajewole, Deborah , Maharaj, Shantal , Edkins, Adrienne L , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/122858 , vital:35359 , https://doi.org/10.1007/s00775-018-1634-9
- Description: A series of tailored novobiocin–ferrocene conjugates was prepared in moderate yields and investigated for in vitro anticancer and antiplasmodial activity against the MDA-MB-231 breast cancer line and Plasmodium falciparum 3D7 strain, respectively. While the target compounds displayed moderate anticancer activity against the breast cancer cell line with IC50 values in the mid-micromolar range, compounds 10a–c displayed promising antiplasmodial activity as low as 0.889 µM. Furthermore, the most promising compounds were tested for inhibitory effects against a postulated target, heat shock protein 90 (Hsp90).
- Full Text:
NMR structural elucidation of channaine, an unusual alkaloid from Sceletium tortuosum:
- Veale, Clinton G L, Chen, Weiyang, Chaudhary, Sushil, Kituyi, Sarah N, Isaacs, Michelle, Hoppe, Heinrich C, Edkins, Adrienne L, Combrinck, Sandra, Mehari, Bewketu, Viljoen, Alvaro
- Authors: Veale, Clinton G L , Chen, Weiyang , Chaudhary, Sushil , Kituyi, Sarah N , Isaacs, Michelle , Hoppe, Heinrich C , Edkins, Adrienne L , Combrinck, Sandra , Mehari, Bewketu , Viljoen, Alvaro
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/164345 , vital:41110 , DOI: 10.1016/j.phytol.2017.11.018
- Description: Chemical interrogation of the Sceletium genus and Amaryllidaceae family of plants has yielded a diverse array of aryl-hydroindole containing alkaloids. Included in this class is channaine, which was tentatively identified, without comprehensive structural elucidation from Sceletium tortuosum in 1957. Following its isolation from S. strictum, the structure of channaine was eventually resolved by X-ray crystallographic analysis, which revealed an unusual cage-like ring structure at the interface of two aryl-hydroindole subunits. However, since this report in 1978, channaine has not re-appeared in the literature. In this letter, the full NMR characterisation of channaine, isolated from S. tortuosum collected from St Helena in the Western Cape Province of South Africa, is reported for the first time.
- Full Text:
- Date Issued: 2018
- Authors: Veale, Clinton G L , Chen, Weiyang , Chaudhary, Sushil , Kituyi, Sarah N , Isaacs, Michelle , Hoppe, Heinrich C , Edkins, Adrienne L , Combrinck, Sandra , Mehari, Bewketu , Viljoen, Alvaro
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/164345 , vital:41110 , DOI: 10.1016/j.phytol.2017.11.018
- Description: Chemical interrogation of the Sceletium genus and Amaryllidaceae family of plants has yielded a diverse array of aryl-hydroindole containing alkaloids. Included in this class is channaine, which was tentatively identified, without comprehensive structural elucidation from Sceletium tortuosum in 1957. Following its isolation from S. strictum, the structure of channaine was eventually resolved by X-ray crystallographic analysis, which revealed an unusual cage-like ring structure at the interface of two aryl-hydroindole subunits. However, since this report in 1978, channaine has not re-appeared in the literature. In this letter, the full NMR characterisation of channaine, isolated from S. tortuosum collected from St Helena in the Western Cape Province of South Africa, is reported for the first time.
- Full Text:
- Date Issued: 2018
New thiazolidine-2,4-dione derivatives combined with organometallic ferrocene: Synthesis, structure and antiparasitic activity
- Oderinlo, Ogunyemi O, Tukulula, Matshawandile, Isaacs, Michelle, Taylor, Dale, Smith, Vincent J, Khanye, Setshaba D, Hoppe, Heinrich C
- Authors: Oderinlo, Ogunyemi O , Tukulula, Matshawandile , Isaacs, Michelle , Taylor, Dale , Smith, Vincent J , Khanye, Setshaba D , Hoppe, Heinrich C
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/122978 , vital:35382 , https://doi.org/10.1002/aoc.4385
- Description: Favourable physicochemical properties of an organometallic ferrocene and antiplasmodial potency of compounds containing the thiazolidine‐2,4‐dione framework (TZD‐4) prompted us to explore compounds containing both the thiazolidine‐2,4‐dione core and the ferrocenyl unit with the primary aim of identifying compounds with promising antiprotozoal activities. Thus, a new series of rationally designed ferrocene‐based thiazolidine‐2,4‐dione derivatives, containing a selection of secondary cyclic amines, was synthesised and fully characterised using standard spectroscopic techniques. The resulting compounds were screened for their antiplasmodial and antitrypanosomal activities against both the chloroquine‐resistant (Dd2) strain of Plasmodium falciparum and the Nagana Trypanosoma brucei brucei 427. The general trend that emerged indicated that the target compounds were more selective towards T. b. brucei compared to the P. falciparum parasite. Moreover, the analogues bearing methylpiperazine (8a) and piperidine (8b) rings were more active against T. b. brucei compared to hit compound TZD‐4. Except compound 8b, which appeared promising, none of the synthesised compounds showed better activity than TZD‐4 against the P. falciparum parasite. All the synthesised compounds were non‐toxic and often showed >90% viability of the HeLa cell line screened.
- Full Text:
- Date Issued: 2018
- Authors: Oderinlo, Ogunyemi O , Tukulula, Matshawandile , Isaacs, Michelle , Taylor, Dale , Smith, Vincent J , Khanye, Setshaba D , Hoppe, Heinrich C
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/122978 , vital:35382 , https://doi.org/10.1002/aoc.4385
- Description: Favourable physicochemical properties of an organometallic ferrocene and antiplasmodial potency of compounds containing the thiazolidine‐2,4‐dione framework (TZD‐4) prompted us to explore compounds containing both the thiazolidine‐2,4‐dione core and the ferrocenyl unit with the primary aim of identifying compounds with promising antiprotozoal activities. Thus, a new series of rationally designed ferrocene‐based thiazolidine‐2,4‐dione derivatives, containing a selection of secondary cyclic amines, was synthesised and fully characterised using standard spectroscopic techniques. The resulting compounds were screened for their antiplasmodial and antitrypanosomal activities against both the chloroquine‐resistant (Dd2) strain of Plasmodium falciparum and the Nagana Trypanosoma brucei brucei 427. The general trend that emerged indicated that the target compounds were more selective towards T. b. brucei compared to the P. falciparum parasite. Moreover, the analogues bearing methylpiperazine (8a) and piperidine (8b) rings were more active against T. b. brucei compared to hit compound TZD‐4. Except compound 8b, which appeared promising, none of the synthesised compounds showed better activity than TZD‐4 against the P. falciparum parasite. All the synthesised compounds were non‐toxic and often showed >90% viability of the HeLa cell line screened.
- Full Text:
- Date Issued: 2018
Living phosphatic stromatolites in a low-phosphorus environment: Implications for the use of phosphorus as a proxy for phosphate levels in paleosystems
- Buttner, Steffen H, Isemonger, Eric W, Isaacs, Michelle, van Niekerk, Deon, Sipler, Rachel E, Dorrington, Rosemary A
- Authors: Buttner, Steffen H , Isemonger, Eric W , Isaacs, Michelle , van Niekerk, Deon , Sipler, Rachel E , Dorrington, Rosemary A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429450 , vital:72611 , xlink:href="https://doi.org/10.1111/gbi.12415"
- Description: In the geological record, fossil phosphatic stromatolites date back to the Great Oxidation Event in the Paleoproterozoic, but living phosphatic stromatolites have not been described previously. Here, we report on cyanobacterial stromatolites in a supratidal freshwater environment at Cape Recife, South African southern coast, precipitating Ca carbonate alternating with episodes of Ca phosphate deposition. In their structure and composition, the living stromatolites from Cape Recife closely resemble their fossilized analogues, showing phosphatic zonation, microbial casts, tunnel structures and phosphatic crusts of biogenic origin. The microbial communities appear to be also similar to those proposed to have formed fossil phosphatic stromatolites. Phosphatic domains in the material from Cape Recife are spatially and texturally associated with carbonate precipitates, but form distinct entities separated by sharp boundaries. Electron Probe Micro-Analysis shows that Ca/P ratios and the overall chemical compositions of phosphatic precipitates are in the range of octacalcium phosphate, amorphous tricalcium phosphate and apatite. The coincidence in time of the emergence of phosphatic stromatolites in the fossil record with a major episode of atmospheric oxidation led to the assumption that at times of increased oxygen release the underlying increased biological production may have been linked to elevated phosphorus availability. The stromatolites at Cape Recife, however, form in an environment where ambient phosphorus concentrations do not exceed 0.28μM, one to two orders of magnitude below the previously predicted minimum thresh-old of >5 μM for biogenic phosphate precipitation in paleo-systems. Accordingly, we contest the previously proposed suitability of phosphatic stromatolites as a proxy for high ambient phosphate concentrations in supratidal to shallow ocean settings in earth history.
- Full Text:
- Date Issued: 2020
- Authors: Buttner, Steffen H , Isemonger, Eric W , Isaacs, Michelle , van Niekerk, Deon , Sipler, Rachel E , Dorrington, Rosemary A
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/429450 , vital:72611 , xlink:href="https://doi.org/10.1111/gbi.12415"
- Description: In the geological record, fossil phosphatic stromatolites date back to the Great Oxidation Event in the Paleoproterozoic, but living phosphatic stromatolites have not been described previously. Here, we report on cyanobacterial stromatolites in a supratidal freshwater environment at Cape Recife, South African southern coast, precipitating Ca carbonate alternating with episodes of Ca phosphate deposition. In their structure and composition, the living stromatolites from Cape Recife closely resemble their fossilized analogues, showing phosphatic zonation, microbial casts, tunnel structures and phosphatic crusts of biogenic origin. The microbial communities appear to be also similar to those proposed to have formed fossil phosphatic stromatolites. Phosphatic domains in the material from Cape Recife are spatially and texturally associated with carbonate precipitates, but form distinct entities separated by sharp boundaries. Electron Probe Micro-Analysis shows that Ca/P ratios and the overall chemical compositions of phosphatic precipitates are in the range of octacalcium phosphate, amorphous tricalcium phosphate and apatite. The coincidence in time of the emergence of phosphatic stromatolites in the fossil record with a major episode of atmospheric oxidation led to the assumption that at times of increased oxygen release the underlying increased biological production may have been linked to elevated phosphorus availability. The stromatolites at Cape Recife, however, form in an environment where ambient phosphorus concentrations do not exceed 0.28μM, one to two orders of magnitude below the previously predicted minimum thresh-old of >5 μM for biogenic phosphate precipitation in paleo-systems. Accordingly, we contest the previously proposed suitability of phosphatic stromatolites as a proxy for high ambient phosphate concentrations in supratidal to shallow ocean settings in earth history.
- Full Text:
- Date Issued: 2020