Muhammad Abbas - Academia.edu (original) (raw)

Papers by Muhammad Abbas

Research paper thumbnail of Naturally occurring reactive sulfur species, their activity against Caco-2 cells, and possible modes of biochemical action

Journal of Sulfur Chemistry, 2008

Natural sulfur compounds from plants, bacteria, fungi, and animals frequently exhibit interesting... more Natural sulfur compounds from plants, bacteria, fungi, and animals frequently exhibit interesting biological activities, such as antioxidant, antimicrobial, and anticancer activity. Considering the recent developments in medicine (e.g. oxidative stress in aging, antibiotic resistant bacteria, selective anticancer agents) and agriculture (e.g. 'green' pesticides), several of these compounds have become the focus of interdisciplinary research. Among the various sulfur agents isolated to date, polysulfides, such as diallyltrisulfide and diallyltetrasulfide from garlic, are of particular interest, since they combine an unusual chemistry and biochemical mode(s) of action with a distinct biological activity, which includes antimicrobial activity and cytotoxicity against certain cancer cells. In many cases, the biological activity of these compounds is well established, but the underlying causes for this activity are hardly known. As part of our investigations, we have now confirmed the activity of diallyltrisulfide and diallyltetrasulfide against the fairly 'robust' Caco-2 colon cancer cell line. At the concentrations used, the activity observed for tri-and tetrasulfide is considerably higher than that of disulfide, while monosulfide is virtually inactive. Controls with the long chain carbon analog 1,9-decadiene count against solely lipophilic effects of diallyltetrasulfide, and together with the 'ranking' of activity, point toward a 'special' sulfur redox chemistry that emerges when shifting from di-to trisulfide. This special reactivity of polysulfides has previously been associated with certain oxidizing properties of the polysulfides. The electrochemical studies and thiol oxidation assays conducted as part of this study, however, count against the notion of diallyltrisulfide and diallyltetrasulfide as effective oxidants. On the contrary, the rather negative oxidation and reduction potentials associated with these agents point toward a reducing chemistry, which is confirmed in the nitrotetrazolium blue assay: the latter seems to indicate dioxygen reduction to the superoxide radical anion, although other reductive events or H 2 S release cannot be ruled out at this point. It is therefore likely that diallyltrisulfide and diallyltetrasulfide are reduced inside the cancer cells to perthiols and hydropolysulfides, which in turn trigger a lethal oxidative burst, for instance via superoxide radical anion formation. Further interdisciplinary studies are required to investigate in more detail the rather complicated chemical and biochemical processes, which ultimately may explain the biological activity that is clearly associated with many natural polysulfides.

Research paper thumbnail of One pot synthesis of selenocysteine containing peptoid libraries by Ugi multicomponent reactions in water

Chemical Communications, 2006

A variety of selenopeptoids is synthesized for the first time by use of a combinatorial Ugi four-... more A variety of selenopeptoids is synthesized for the first time by use of a combinatorial Ugi four-component reaction in water. -(ABBAS, M.; BETHKE, J.; WESSJOHANN*, L. A.; Chem. Commun. (Cambridge) 2006, 5, 541-543; Inst. Pflanzenbiochem., Leibniz Inst., D-06120 Halle/S., Germany; Eng.) -R. Staver 23-191

Research paper thumbnail of Selenium in chemistry and biochemistry in comparison to sulfur

Biological Chemistry, 2007

What makes selenoenzymes--seen from a chemist&amp... more What makes selenoenzymes--seen from a chemist's view--so special that they cannot be substituted by just more analogous or adapted sulfur proteins? This review compiles and compares physicochemical properties of selenium and sulfur, synthetic routes to selenocysteine (Sec) and its peptides, and comparative studies of relevant thiols and selenols and their (mixed) dichalcogens, required to understand the special role of selenium in selenoproteins on the atomic molecular level. The biochemically most relevant differences are the higher polarizability of Se- and the lower pKa of SeH. The latter has a strikingly different pH-dependence than thiols, with selenols being active at much lower pH. Finally, selected typical enzymatic mechanisms which involve selenocysteine are critically discussed, also in view of the authors' own results.

Research paper thumbnail of Exploring synthetic avenues for the effective synthesis of selenium- and tellurium-containing multifunctional redox agents

Organic & Biomolecular Chemistry, 2009

Various human illnesses, including several types of cancer and infectious diseases, are related t... more Various human illnesses, including several types of cancer and infectious diseases, are related to changes in the cellular redox homeostasis. During the last decade, several approaches have been explored which employ such disturbed redox balances for the benefit of therapy. Compounds able to modulate the intracellular redox state of cells have been developed, which effectively, yet also selectively, appear to kill cancer cells and a range of pathogenic microorganisms. Among the various agents employed, certain redox catalysts have shown considerable promise since they are non-toxic on their own yet develop an effective, often selective cytotoxicity in the presence of the 'correct' intracellular redox partners. Aminoalkylation, amide coupling and multicomponent reactions are suitable synthetic methods to generate a vast number of such multifunctional catalysts, which are chemically diverse and, depending on their structure, exhibit various interesting biological activities. † Electronic supplementary information (ESI) available: Synthesis of compounds; SK-Mel-5 and HL-60 cell culture studies; activity assays against Plasmodium falciparum and Trichophyton rubrum; 58-cell line screening. See DOI: 10.1039/b907831b ‡ By contrast, cells found in hypoxic regions of tumours are often more reducing than normal cells, which is exploited in bioreductive drug therapy, e.g. by using Mitomycin C (MMC). 6 OS and bioreductive environments are not necessarily mutually exclusive.

Research paper thumbnail of Multicomponent reactions for the synthesis of multifunctional agents with activity against cancer cells

Chemical Communications, 2009

Multicomponent Passerini and Ugi reactions enable the fast and efficient synthesis of redox-activ... more Multicomponent Passerini and Ugi reactions enable the fast and efficient synthesis of redox-active multifunctional selenium and tellurium compounds, of which some show considerable cytotoxicity against specific cancer cells.

Research paper thumbnail of Bucharioside and buchariol from Salvia bucharica

Phytochemistry, 1999

A new monoterpene-glycoside (2-exo-b-D-glucopyranosyl-1,8-cineol) named bucharioside from the met... more A new monoterpene-glycoside (2-exo-b-D-glucopyranosyl-1,8-cineol) named bucharioside from the methanol-soluble part and a new sesquiterpenoid (4,10-epoxy-6a±hydroxyguaiane) named buchariol from the hexane-soluble part of Salvia bucharica were obtained. Their structures were elucidated with the help of NMR spectroscopy including 1D and 2D experiments. #

Research paper thumbnail of Salvadiones-A and B: Two Terpenoids Having Novel Carbon Skeleta from Salvia bucharica

Journal of Organic Chemistry, 1999

... Viqar Uddin Ahmad,* † M. Zahid, M. Shaiq Ali, † Z. Ali, † AR Jassbi, † M. Abbas, † J. Clardy,... more ... Viqar Uddin Ahmad,* † M. Zahid, M. Shaiq Ali, † Z. Ali, † AR Jassbi, † M. Abbas, † J. Clardy, ‡ E. Lobkovsky, ‡ RB Tareen, § and M. Zafar Iqbal. HEJ Research Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan ...

Research paper thumbnail of Eight New Diterpenoids fromEuphorbia decipiens

Helvetica Chimica Acta, 2001

1. Introduction. ± Our group has investigated Euphorbia decipiens Boiss. et Buhse previously, and... more 1. Introduction. ± Our group has investigated Euphorbia decipiens Boiss. et Buhse previously, and eight new diterpene esters were isolated from it [1 ± 3]. To obtain the minor compounds, the plant was again collected and extracted with acetone [4]. The CHCl3-...

Research paper thumbnail of Total synthesis and anti-leishmanial activity of R-(−)-argentilactone

Tetrahedron Letters, 2001

Starting from the commercially available D-glucal (2), the naturally occurring a,b-unsaturated d-... more Starting from the commercially available D-glucal (2), the naturally occurring a,b-unsaturated d-lactone argentilactone (1a) has been synthesized. The important step is the configuration inversion at C-6 by the Mitsunobu reaction following the sugar-non-sugar-sugar strategy. The synthetic argentilactone has been tested against Leishmania mexicana for bioactivity.

Research paper thumbnail of Naturally occurring reactive sulfur species, their activity against Caco-2 cells, and possible modes of biochemical action

Journal of Sulfur Chemistry, 2008

Natural sulfur compounds from plants, bacteria, fungi, and animals frequently exhibit interesting... more Natural sulfur compounds from plants, bacteria, fungi, and animals frequently exhibit interesting biological activities, such as antioxidant, antimicrobial, and anticancer activity. Considering the recent developments in medicine (e.g. oxidative stress in aging, antibiotic resistant bacteria, selective anticancer agents) and agriculture (e.g. 'green' pesticides), several of these compounds have become the focus of interdisciplinary research. Among the various sulfur agents isolated to date, polysulfides, such as diallyltrisulfide and diallyltetrasulfide from garlic, are of particular interest, since they combine an unusual chemistry and biochemical mode(s) of action with a distinct biological activity, which includes antimicrobial activity and cytotoxicity against certain cancer cells. In many cases, the biological activity of these compounds is well established, but the underlying causes for this activity are hardly known. As part of our investigations, we have now confirmed the activity of diallyltrisulfide and diallyltetrasulfide against the fairly 'robust' Caco-2 colon cancer cell line. At the concentrations used, the activity observed for tri-and tetrasulfide is considerably higher than that of disulfide, while monosulfide is virtually inactive. Controls with the long chain carbon analog 1,9-decadiene count against solely lipophilic effects of diallyltetrasulfide, and together with the 'ranking' of activity, point toward a 'special' sulfur redox chemistry that emerges when shifting from di-to trisulfide. This special reactivity of polysulfides has previously been associated with certain oxidizing properties of the polysulfides. The electrochemical studies and thiol oxidation assays conducted as part of this study, however, count against the notion of diallyltrisulfide and diallyltetrasulfide as effective oxidants. On the contrary, the rather negative oxidation and reduction potentials associated with these agents point toward a reducing chemistry, which is confirmed in the nitrotetrazolium blue assay: the latter seems to indicate dioxygen reduction to the superoxide radical anion, although other reductive events or H 2 S release cannot be ruled out at this point. It is therefore likely that diallyltrisulfide and diallyltetrasulfide are reduced inside the cancer cells to perthiols and hydropolysulfides, which in turn trigger a lethal oxidative burst, for instance via superoxide radical anion formation. Further interdisciplinary studies are required to investigate in more detail the rather complicated chemical and biochemical processes, which ultimately may explain the biological activity that is clearly associated with many natural polysulfides.

Research paper thumbnail of One pot synthesis of selenocysteine containing peptoid libraries by Ugi multicomponent reactions in water

Chemical Communications, 2006

A variety of selenopeptoids is synthesized for the first time by use of a combinatorial Ugi four-... more A variety of selenopeptoids is synthesized for the first time by use of a combinatorial Ugi four-component reaction in water. -(ABBAS, M.; BETHKE, J.; WESSJOHANN*, L. A.; Chem. Commun. (Cambridge) 2006, 5, 541-543; Inst. Pflanzenbiochem., Leibniz Inst., D-06120 Halle/S., Germany; Eng.) -R. Staver 23-191

Research paper thumbnail of Selenium in chemistry and biochemistry in comparison to sulfur

Biological Chemistry, 2007

What makes selenoenzymes--seen from a chemist&amp... more What makes selenoenzymes--seen from a chemist's view--so special that they cannot be substituted by just more analogous or adapted sulfur proteins? This review compiles and compares physicochemical properties of selenium and sulfur, synthetic routes to selenocysteine (Sec) and its peptides, and comparative studies of relevant thiols and selenols and their (mixed) dichalcogens, required to understand the special role of selenium in selenoproteins on the atomic molecular level. The biochemically most relevant differences are the higher polarizability of Se- and the lower pKa of SeH. The latter has a strikingly different pH-dependence than thiols, with selenols being active at much lower pH. Finally, selected typical enzymatic mechanisms which involve selenocysteine are critically discussed, also in view of the authors' own results.

Research paper thumbnail of Exploring synthetic avenues for the effective synthesis of selenium- and tellurium-containing multifunctional redox agents

Organic & Biomolecular Chemistry, 2009

Various human illnesses, including several types of cancer and infectious diseases, are related t... more Various human illnesses, including several types of cancer and infectious diseases, are related to changes in the cellular redox homeostasis. During the last decade, several approaches have been explored which employ such disturbed redox balances for the benefit of therapy. Compounds able to modulate the intracellular redox state of cells have been developed, which effectively, yet also selectively, appear to kill cancer cells and a range of pathogenic microorganisms. Among the various agents employed, certain redox catalysts have shown considerable promise since they are non-toxic on their own yet develop an effective, often selective cytotoxicity in the presence of the 'correct' intracellular redox partners. Aminoalkylation, amide coupling and multicomponent reactions are suitable synthetic methods to generate a vast number of such multifunctional catalysts, which are chemically diverse and, depending on their structure, exhibit various interesting biological activities. † Electronic supplementary information (ESI) available: Synthesis of compounds; SK-Mel-5 and HL-60 cell culture studies; activity assays against Plasmodium falciparum and Trichophyton rubrum; 58-cell line screening. See DOI: 10.1039/b907831b ‡ By contrast, cells found in hypoxic regions of tumours are often more reducing than normal cells, which is exploited in bioreductive drug therapy, e.g. by using Mitomycin C (MMC). 6 OS and bioreductive environments are not necessarily mutually exclusive.

Research paper thumbnail of Multicomponent reactions for the synthesis of multifunctional agents with activity against cancer cells

Chemical Communications, 2009

Multicomponent Passerini and Ugi reactions enable the fast and efficient synthesis of redox-activ... more Multicomponent Passerini and Ugi reactions enable the fast and efficient synthesis of redox-active multifunctional selenium and tellurium compounds, of which some show considerable cytotoxicity against specific cancer cells.

Research paper thumbnail of Bucharioside and buchariol from Salvia bucharica

Phytochemistry, 1999

A new monoterpene-glycoside (2-exo-b-D-glucopyranosyl-1,8-cineol) named bucharioside from the met... more A new monoterpene-glycoside (2-exo-b-D-glucopyranosyl-1,8-cineol) named bucharioside from the methanol-soluble part and a new sesquiterpenoid (4,10-epoxy-6a±hydroxyguaiane) named buchariol from the hexane-soluble part of Salvia bucharica were obtained. Their structures were elucidated with the help of NMR spectroscopy including 1D and 2D experiments. #

Research paper thumbnail of Salvadiones-A and B: Two Terpenoids Having Novel Carbon Skeleta from Salvia bucharica

Journal of Organic Chemistry, 1999

... Viqar Uddin Ahmad,* † M. Zahid, M. Shaiq Ali, † Z. Ali, † AR Jassbi, † M. Abbas, † J. Clardy,... more ... Viqar Uddin Ahmad,* † M. Zahid, M. Shaiq Ali, † Z. Ali, † AR Jassbi, † M. Abbas, † J. Clardy, ‡ E. Lobkovsky, ‡ RB Tareen, § and M. Zafar Iqbal. HEJ Research Institute of Chemistry, University of Karachi, Karachi-75270, Pakistan ...

Research paper thumbnail of Eight New Diterpenoids fromEuphorbia decipiens

Helvetica Chimica Acta, 2001

1. Introduction. ± Our group has investigated Euphorbia decipiens Boiss. et Buhse previously, and... more 1. Introduction. ± Our group has investigated Euphorbia decipiens Boiss. et Buhse previously, and eight new diterpene esters were isolated from it [1 ± 3]. To obtain the minor compounds, the plant was again collected and extracted with acetone [4]. The CHCl3-...

Research paper thumbnail of Total synthesis and anti-leishmanial activity of R-(−)-argentilactone

Tetrahedron Letters, 2001

Starting from the commercially available D-glucal (2), the naturally occurring a,b-unsaturated d-... more Starting from the commercially available D-glucal (2), the naturally occurring a,b-unsaturated d-lactone argentilactone (1a) has been synthesized. The important step is the configuration inversion at C-6 by the Mitsunobu reaction following the sugar-non-sugar-sugar strategy. The synthetic argentilactone has been tested against Leishmania mexicana for bioactivity.