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Bansal R, Suryan A. A Comprehensive Review on Steroidal Bioconjugates as Promising Leads in Drug Discovery. ACS BIO & MED CHEM AU 2022; 2:340-369. [PMID: 37102169 PMCID: PMC10125316 DOI: 10.1021/acsbiomedchemau.1c00071] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Ever increasing unmet medical requirements of the human race and the continuous fight for survival against variety of diseases give birth to novel molecules through research. As diseases evolve, different strategies are employed to counter the new challenges and to discover safer, more effective, and target-specific therapeutic agents. Among several novel approaches, bioconjugation, in which two chemical moieties are joined together to achieve noticeable results, has emerged as a simple and convenient technique for a medicinal chemist to obtain potent molecules. The steroid system has been extensively used as a privileged scaffold gifted with significantly diversified medicinal properties in the drug discovery and development process. Steroidal molecules are preferred for their rigidness and good ability to penetrate biological membranes. Slight alteration in the basic ring structure results in the formation of steroidal derivatives with a wide range of therapeutic activities. Steroids are not only active as such, conjugating them with various biologically active moieties results in increased lipophilicity, stability, and target specificity with decreased adverse effects. Thus, the steroid nucleus prominently behaves as a biological carrier for small molecules. The steroid bioconjugates offer several advantages such as synergistic activity with fewer side effects due to reduced dose and selective therapy. The steroidal bioconjugates have been widely explored for their usefulness against various disorders and have shown significant utility as anticancer, anti-inflammatory, anticoagulant, antimicrobial, insecticidal/pesticidal, antioxidant, and antiviral agents along with several other miscellaneous activities. This work provides a comprehensive review on the therapeutic progression of steroidal bioconjugates as medicinally active molecules. The review covers potential biological applications of steroidal bioconjugates and would benefit the wider scientific community in their drug discovery endeavors.
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Affiliation(s)
- Ranju Bansal
- University Institute of Pharmaceutical Sciences, Panjab University, Chandigarh 160014, India
| | - Amruta Suryan
- University Institute of Pharmaceutical Sciences, Panjab University, Chandigarh 160014, India
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Duan D, Zheng R, Lin S, Chen Y, Tian H, Zhao J, Tian S, Wei H, Gu X. Modulation of Juvenile Hormone Esterase Gene Expression Against Development of Plutella xylostella (Lepidoptera: Plutellidae). JOURNAL OF ECONOMIC ENTOMOLOGY 2016; 109:865-872. [PMID: 26880398 DOI: 10.1093/jee/tow003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is a widespread and destructive pest of cruciferous crops. Owing to its increasing resistance to conventional pesticides, new strategies need to be developed for diamondback moth control. Here, we investigated factors that modulate juvenile hormone esterase (JHE) activity and jhe (Px004817) transcription, and determined the effects of these factors on subsequent growth and development in diamondback moth. Starvation inhibited JHE activity and jhe transcription, increased mortality, and decreased the rate of molting from the third- to the fourth-instar stages. Larvae kept at 32°C molted earlier and showed increased JHE activity and jhe transcription after 24-h treatment. Exposure to 1,325 mg/liter OTFP (3-octylthio-1,1,1-trifluoro-2-propanone) delayed molting and pupation, increased pupal weight, and decreased JHE activity and jhe transcription at both 24 and 48 h. Treatment with 500 mg/liter pyriproxyfen delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. A combination of OTFP (1,325 mg/liter) and pyriproxyfen (500 mg/liter) induced the highest mortality, delayed molting, completely suppressed pupation, and significantly increased JHE activity at 48 h and jhe transcription at 24 and 48 h. These effects on JHE activity and jhe transcription were similar to those in insects treated only with pyriproxyfen. The results demonstrated that JHE and jhe (Px004817) were involved in the responses of diamondback moth to external modulators and caused changes in growth and development. The combination of OTFP and pyriproxyfen increased the effectiveness of action against diamondback moth.
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Bildziukevich U, Vida N, Rárová L, Kolář M, Šaman D, Havlíček L, Drašar P, Wimmer Z. Polyamine derivatives of betulinic acid and β-sitosterol: A comparative investigation. Steroids 2015; 100:27-35. [PMID: 25963549 DOI: 10.1016/j.steroids.2015.04.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Revised: 04/10/2015] [Accepted: 04/29/2015] [Indexed: 01/29/2023]
Abstract
β-Sitosterol and betulinic acid were used in designing their conjugates with selected polyamines bearing either an amide bond, or an ester and an amide bond simultaneously in the target molecule. The synthesized compounds were subjected to basic cytotoxic and antimicrobial tests. The synthetic protocol is described separately for each of the three series of the target amides, because each series of compounds required a different synthetic approach. The cytotoxicity was tested on cells derived from human T-lymphoblastic leukemia, breast adenocarcinoma and cervical cancer, and compared with the tests on normal human fibroblasts. Most of the target compounds (5a-5c, 11a-11c and 16a-16c) showed medium to high cytotoxicity (0.7-7.8 μM), however, in some cases the compounds showed high cytotoxicity even toward normal human fibroblasts (11a-11c). Two compounds of this series (11c and 16c) also displayed antimicrobial activity with high and selective microbe specificity. The compound 11c was potent against Escherichia coli (minimal inhibition concentration (MIC) 6.25 μg mL(-1), i.e. 9.75 nM mL(-1)) and Staphylococcus aureus (MIC 12.5 μg mL(-1), i.e. 19.5 nM mL(-1)), and showed medium activity against Pseudomonas aeruginosa. The compound 16c was highly active against Enterococcus faecalis and S. aureus (both, MIC 3.125 μg mL(-1), i.e. 4.22 nM mL(-1)), both Gram-positive bacteria, however showed only weak activity against E. coli and no activity against P. aeruginosa, both Gram-negative bacteria, which indicates possible microbe specificity of 16c. Comparing β-sitosterol-based series (5a-5c) and betulinic acid series (11a-11c and 16a-16c) of the target compounds, the latter one gave more promising structures. The compounds 11c and 16c showed effects which may be described as multifarious activity (pleiotropic effects).
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Affiliation(s)
- Uladzimir Bildziukevich
- Institute of Experimental Botany AS CR, v.v.i., Isotope Laboratory, Vídeňská 1083, 14220 Prague 4, Czech Republic; Institute of Chemical Technology, Faculty of Food and Biochemical Technology, Department of Chemistry of Natural Compounds, Technická 5, 16628 Prague 6, Czech Republic
| | - Norbert Vida
- Institute of Chemical Technology, Faculty of Food and Biochemical Technology, Department of Chemistry of Natural Compounds, Technická 5, 16628 Prague 6, Czech Republic
| | - Lucie Rárová
- Institute of Experimental Botany AS CR, v.v.i., Isotope Laboratory, Vídeňská 1083, 14220 Prague 4, Czech Republic; Centre of the Region Haná for Biotechnological and Agricultural Research, Faculty of Science, Palacký University, Šlechtitelů 11, 78371 Olomouc, Czech Republic
| | - Milan Kolář
- Department of Microbiology, Faculty of Medicine and Dentistry, Palacký University, Hněvotinská 3, 77515 Olomouc, Czech Republic
| | - David Šaman
- Institute of Organic Chemistry and Biochemistry AS CR, v.v.i., Flemingovo nám. 2, 16610 Prague 6, Czech Republic
| | - Libor Havlíček
- Institute of Experimental Botany AS CR, v.v.i., Isotope Laboratory, Vídeňská 1083, 14220 Prague 4, Czech Republic
| | - Pavel Drašar
- Institute of Chemical Technology, Faculty of Food and Biochemical Technology, Department of Chemistry of Natural Compounds, Technická 5, 16628 Prague 6, Czech Republic
| | - Zdeněk Wimmer
- Institute of Experimental Botany AS CR, v.v.i., Isotope Laboratory, Vídeňská 1083, 14220 Prague 4, Czech Republic; Institute of Chemical Technology, Faculty of Food and Biochemical Technology, Department of Chemistry of Natural Compounds, Technická 5, 16628 Prague 6, Czech Republic.
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Sharma P, Thakur S, Awasthi P. Synthesis, Characterization, Biological Evaluation and Docking Study of Heterocyclic-Based Synthetic Sulfonamides as Potential Pesticide Against G. mellonella. Appl Biochem Biotechnol 2015; 176:125-39. [DOI: 10.1007/s12010-015-1562-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2014] [Accepted: 03/12/2015] [Indexed: 11/28/2022]
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Steroid conjugates: Synthesis and preliminary biological testing of pro-juvenoids. Bioorg Med Chem 2010; 18:8194-203. [DOI: 10.1016/j.bmc.2010.10.013] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2010] [Revised: 09/27/2010] [Accepted: 10/06/2010] [Indexed: 11/22/2022]
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Sub-Lethal Effects of Fenvalerate on the Development, Fecundity, and Juvenile Hormone Esterase Activity of Diamondback Moth, Plutella xylostella (L.). ACTA ACUST UNITED AC 2010. [DOI: 10.1016/s1671-2927(09)60258-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Jurcek O, Wimmer Z, Bennettová B, Moravcová J, Drasar P, Saman D. Novel juvenogens (insect hormonogenic agents): preparation and biological tests on Neobellieria bullata. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2009; 57:10852-10858. [PMID: 19852469 DOI: 10.1021/jf902290s] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
The development of new types of environmentally safe insecticides has been advantageous to replace toxic and persistent insecticides, which have adverse effects on animals and humans. Our effort in this field was aimed at the synthesis of insect juvenile hormone analogues, juvenoids, nontoxic for warm-blooded animals and fish, which can become advanced compounds in regulating many aspects in insect physiology. Structure modification of juvenoids via juvenogen derivatives (hormonogenic substances) plays an important role in controlling the juvenoid liberation rate in the insect digestive system and can also play an important role in the mode of action toward different arthropod groups, with focus on insect pest species. For that reason, juvenoids were esterified with hexadecanoic, butanoic, and 3-methylbut-2-enoic acids. A total of 12 new compounds with potential insecticidal activity were synthesized and characterized, and the results of biological screening tests on blowflies Neobellieria (Sarcophaga) bullata were presented. Results of the inhibitory activity of the tested compounds on the reproduction of the blowflies were also presented.
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Affiliation(s)
- Ondrej Jurcek
- Isotope Laboratory, Institute of Experimental Botany AS CR, Videnska 1083, 14220 Prague 4, Czech Republic
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Jurcek O, Wimmer Z, Svobodová H, Bennettová B, Kolehmainen E, Drasar P. Preparation and preliminary biological screening of cholic acid-juvenoid conjugates. Steroids 2009; 74:779-85. [PMID: 19394354 DOI: 10.1016/j.steroids.2009.04.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Revised: 04/15/2009] [Accepted: 04/16/2009] [Indexed: 11/23/2022]
Abstract
Steroidal compounds have been utilized as carriers and for modification of physico-chemical properties of model biologically active secondary alcohols - juvenoids. Juvenoids are juvenile hormone analogues - environmentally safe insecticides, possessing significant biological activity towards different arthropods groups in focus on insect pest species. Structure modification of juvenoids plays important role to control the rate of liberation and decomposition of juvenoid in digestive system and can also play important role in the mode of action towards selected insect. This study presents an approach to the synthesis of steroidal monomers and dimers carrying one and two molecules of a juvenoid in their structures. The prepared compounds were tested for their inhibition activity on reproduction of the blowfly Neobellieria (Sarcophaga) bullata. These steroid-juvenoid conjugates showed promising possibilities in synthesis of new unique biochemical insecticides. Preliminary biological test results of prepared compounds are presented.
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Affiliation(s)
- Ondrej Jurcek
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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Tykva R, Cerný B, Wimmer Z, Hanus R. Distribution of a juvenogen and its metabolites in a laboratory system during juvenogen-induced caste differentiation in a termite, Reticulitermes santonensis (Isoptera: Rhinotermitidae). PEST MANAGEMENT SCIENCE 2008; 64:654-659. [PMID: 18189273 DOI: 10.1002/ps.1532] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
BACKGROUND Juvenoids and juvenogens have been for many years considered promising candidates for control of pest insect species including termites. Their use as termite pest management agents requires the generation of knowledge concerning their degradation and distribution in time and space. Groups of 40 Reticulitermes santonensis de Feytaud workers were provided with wood impregnated with a juvenogen, ethyl cis-N-{2-[4-(2-butyryloxycyclohexylmethyl)phenoxy]ethyl}carbamate, labelled with tritium in the benzene ring (305 GBq mmol(-1)). After 14 days the radioactivity was determined in all elements of the experimental system. RESULTS The majority of the input activity was detected in the wood, only about 1% in the bodies of surviving termites and 1% in the substrate. A considerable part of the input activity was probably lost as gaseous termite metabolites. The activity in workers was significantly higher than in presoldiers, which had differentiated under the influence of the labelled juvenogen. A stable value of radioactivity was detected on the body surfaces. CONCLUSIONS The results suggest good stability of the compound in the wooden carrier and low contamination of the environment with non-gaseous residuals, together with the desired biological impact on termite caste differentiation.
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Affiliation(s)
- Richard Tykva
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic (AS CR), v.v.i., Flemingovo 2, CZ 16610 Prague 6, Czech Republic
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Wimmer Z, Pechová L, Sīle L, Saman D, Jedlicka P, Wimmerová M, Kolehmainen E. Glycosidic juvenogens: Derivatives bearing α,β-unsaturated ester functionalities. Bioorg Med Chem 2007; 15:7126-37. [PMID: 17825568 DOI: 10.1016/j.bmc.2007.07.022] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2007] [Revised: 06/29/2007] [Accepted: 07/10/2007] [Indexed: 11/22/2022]
Abstract
A series of the protected alkyl glycosides 5a/5b-12a/12b was synthesized from the parent isomeric alcohols (insect juvenile hormone bioanalogs; juvenoids), 4-[4'-(2''-hydroxycyclohexyl)methylphenoxy]-3-methyl-but-2-enoic acid ethyl ester (1a/1b-4a/4b; racemic structures) and (1a-4a; enantiopure structures). Cadmium carbonate was used as a promoter of this Koenigs-Knorr reaction, and the products were obtained in 82-92% yields. Deprotection of the carbohydrate functionality of 5a/5b-12a/12b was carefully performed using ethanolysis in the presence of zinc acetate, due to the presence of another ester functionality in the aglycone part of the molecule of protected alkyl glycosides. Resulting alkyl glycosides 13a/13b-20a/20b (diastereoisomeric mixtures) and 13a-20a (enantiopure compounds), biochemically activated hormonogenic compounds (juvenogens), were obtained in 82-93% yields. Finally, chiral HPLC separation of the diastereoisomeric mixtures of alkyl glycosides was applied to get sufficient quantities of the respective enantiomers 13b-20b of the alkyl glycosides for their structure elucidation and (13)C chemical shift assignment by (1)H and (13)C NMR spectroscopy. Partial introductory entomological screening tests of the target alkyl glycosides 13a/13b-20a/20b were performed on the red firebug (Pyrrhocoris apterus). The results of this biological testing clearly demonstrated the time-extended effect of several juvenogens on P. apterus due to their biochemical activation, i.e., hydrolysis of the juvenogen molecule, which results in liberation of the biologically active juvenoid in the insect organism.
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Affiliation(s)
- Zdenek Wimmer
- Institute of Experimental Botany AS CR, Laboratory of Chemistry, Vídenská 1083, CZ-14220 Prague 4, Czech Republic.
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Jedlicka P, Hrdý I, Kuldová J, Wimmer Z. The systemic effects of juvenoids on the red firebug Pyrrhocoris apterus and on the pea aphid Acyrthosiphon pisum with data on life table response. PEST MANAGEMENT SCIENCE 2007; 63:1026-35. [PMID: 17724791 DOI: 10.1002/ps.1435] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
BACKGROUND A series of juvenoid alcohols and their glycosidic derivatives (juvenogens), synthesized at the Institute of Organic Chemistry and Biochemistry in Prague, commercially used juvenoids and the natural derivatives of juvabione were evaluated for their systemic juvenilizing effect on the red firebug, Pyrrhocoris apterus L., and on the pea aphid, Acyrthosiphon pisum Harris. A life table response experiment was designed, and demographic characteristics were computed for a cohort of A. pisum following chronic exposure to a range of concentrations of the selected trans-isomer of carbamate juvenoid 8 applied via the broad bean (Vicia faba L.) root system. RESULTS Using the ratio of topical and per os activities, promising effects were found in two alkyl beta-D-glucopyranosides (3 and 9) and the trans-isomer of carbamate juvenoid 8 in tests on P. apterus. In A. pisum, the highest systemic activity was found in tests with the trans-isomer of carbamate juvenoid 8. The longevity, the number of offspring per female and the number of offspring per reproducing female significantly decreased with concentrations of 0.05 mg mL(-1) and higher. While the net reproductive rate R(0) and the intrinsic rate of natural increase r(m) displayed similar trends, the generation time G varied slightly between 11.6 and 12.8 days. CONCLUSION Expected systemic activity of glycosidic juvenogens in P. apterus was not confirmed by exposure of the pea aphid on broad bean treated with aqueous solutions of the compounds. Nevertheless, the carbamate juvenoid alcohol 8 displayed a considerable juvenilizing effect on A. pisum in screening tests. Furthermore, this compound indicated a sublethal effect as the realized fecundity U(x) decreased disproportionately to the age-specific survival L(x) with increased concentration. The population parameters are compared with the data in similar demographic studies and are discussed together with the possibilities of using the compounds of this structural type in practice.
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Affiliation(s)
- Pavel Jedlicka
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 166 10 Praha 6, Czech Republic.
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Wimmer Z, Jurcek O, Jedlicka P, Hanus R, Kuldová J, Hrdý I, Bennettová B, Saman D. Insect pest management agents: hormonogen esters (juvenogens). JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2007; 55:7387-93. [PMID: 17691805 DOI: 10.1021/jf0710682] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
The chemical part of this investigation focused on designing structures and synthesizing a series of six new esters (juvenogens), derived from biologically active insect juvenile hormone bioanalogues (juvenoids, JHAs) and unsaturated short-chain linear and branched fatty acids for possible application as biochemically targeted insect hormonogen agents. The structures of the new compounds were assigned on the basis of a detailed NMR analysis of their (1)H and (13)C NMR spectra. The biological part of this investigation focused on introductory biological screening tests with these compounds against the red firebug (Pyrrhocoris apterus), termites (Reticulitermes santonensis and Prorhinotermes simplex), and the blowfly (Neobellieria bullata). The biological activity of the juvenogens was studied in relation to the fatty acid functionality in the structures. Notable biological activity in topical tests and medium activity in peroral tests was found for the juvenogens 3 and 7 with P. apterus. The compounds 6 and 8 showed the lowest activity in both topical and oral assays with P. apterus. Considerable effect of all tested juvenogens was observed in P. simplex; however, the juvenogens 5 and 6 (derivatives of the only branched short-chain fatty acid) showed no activity against R. santonensis. The effect of the compounds 3-8 on larval hatching of N. bullata was only moderate (larval hatching 80-90%); however, the proliferation effect caused by 5, 6, and 8 is more pronounced than the effect caused by 3, 4, and 7.
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Affiliation(s)
- Zdenek Wimmer
- Laboratory of Chemistry, Institute of Experimental Botany, Academy of Sciences of the Czech Republic, VídenskA 1083, CZ-14220 Prague 4, Czech Republic.
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Application of ionic liquids in enzymic resolution by hydrolysis of cycloalkyl acetates. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/j.tetasy.2006.10.045] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Šaman D, Kratina P, Moravcová J, Wimmerová M, Wimmer Z. Synthesis and Structure Assignment of 2-(4-Methoxybenzyl)cyclohexyl β-D-Glucopyranoside Enantiomers. ACTA ACUST UNITED AC 2006. [DOI: 10.1135/cccc20061470] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Glucosylation of the cis- and trans-isomers of 2-(4-methoxybenzyl)cyclohexan-1-ol (1a/1b, 2a/2b, 1a or 2a) was performed to prepare the corresponding alkyl β-D-glucopyranosides, mainly to get analytical data of pure enantiomers of the glucosides (3a-6b), required for subsequent investigations of related compounds with biological activity. One of the employed modifications of the Koenigs-Knorr synthesis resulted in achieving 85-95% yields of pure β-anomers 3a/3b, 4a/4b, 3a or 4a of protected intermediates, with several promoters and toluene as solvent, yielding finally the deprotected products 5a/5b, 6a/6b, 5a or 6a as pure β-anomers. To obtain enantiomerically pure β-anomers of the target structure (3a, 4a, 5a and 6a) for unambiguous structure assignment, an enzymic reduction of 2-(4-methoxybenzyl)cyclohexan-1-one by Saccharomyces cerevisiae whole cells was performed to get (1S,2S)- and (1S,2R)-enantiomers (1a and 2a) of 2-(4-methoxybenzyl)cyclohexan-1-ol. The opposite enantiomers of alkyl β-D-glucopyranosides (5b and 6b) were obtained by separation of the diastereoisomeric mixtures 5a/5b and 6a/6b by chiral HPLC. All stereoisomers of the products (3a-6b) were subjected to a detailed 1H NMR and 13C NMR analysis.
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