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Abstract
Nitroxides, also known as nitroxyl radicals, are long-lived or stable radicals with the general structure R1R2N-O•. The spin distribution over the nitroxide N and O atoms contributes to the thermodynamic stability of these radicals. The presence of bulky N-substituents R1 and R2 prevents nitroxide radical dimerization, ensuring their kinetic stability. Despite their reactivity toward various transient C radicals, some nitroxides can be easily stored under air at room temperature. Furthermore, nitroxides can be oxidized to oxoammonium salts (R1R2N═O+) or reduced to anions (R1R2N-O-), enabling them to act as valuable oxidants or reductants depending on their oxidation state. Therefore, they exhibit interesting reactivity across all three oxidation states. Due to these fascinating properties, nitroxides find extensive applications in diverse fields such as biochemistry, medicinal chemistry, materials science, and organic synthesis. This review focuses on the versatile applications of nitroxides in organic synthesis. For their use in other important fields, we will refer to several review articles. The introductory part provides a brief overview of the history of nitroxide chemistry. Subsequently, the key methods for preparing nitroxides are discussed, followed by an examination of their structural diversity and physical properties. The main portion of this review is dedicated to oxidation reactions, wherein parent nitroxides or their corresponding oxoammonium salts serve as active species. It will be demonstrated that various functional groups (such as alcohols, amines, enolates, and alkanes among others) can be efficiently oxidized. These oxidations can be carried out using nitroxides as catalysts in combination with various stoichiometric terminal oxidants. By reducing nitroxides to their corresponding anions, they become effective reducing reagents with intriguing applications in organic synthesis. Nitroxides possess the ability to selectively react with transient radicals, making them useful for terminating radical cascade reactions by forming alkoxyamines. Depending on their structure, alkoxyamines exhibit weak C-O bonds, allowing for the thermal generation of C radicals through reversible C-O bond cleavage. Such thermally generated C radicals can participate in various radical transformations, as discussed toward the end of this review. Furthermore, the application of this strategy in natural product synthesis will be presented.
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Affiliation(s)
- Dirk Leifert
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
| | - Armido Studer
- Organisch-Chemisches Institut, Westfälische Wilhelms-Universität, Corrensstrasse 40, 48149 Münster, Germany
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Covey DF, Evers AS, Izumi Y, Maguire JL, Mennerick SJ, Zorumski CF. Neurosteroid enantiomers as potentially novel neurotherapeutics. Neurosci Biobehav Rev 2023; 149:105191. [PMID: 37085023 PMCID: PMC10750765 DOI: 10.1016/j.neubiorev.2023.105191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2022] [Revised: 04/17/2023] [Accepted: 04/18/2023] [Indexed: 04/23/2023]
Abstract
Endogenous neurosteroids and synthetic neuroactive steroids (NAS) are important targets for therapeutic development in neuropsychiatric disorders. These steroids modulate major signaling systems in the brain and intracellular processes including inflammation, cellular stress and autophagy. In this review, we describe studies performed using unnatural enantiomers of key neurosteroids, which are physiochemically identical to their natural counterparts except for rotation of polarized light. These studies led to insights in how NAS interact with receptors, ion channels and intracellular sites of action. Certain effects of NAS show high enantioselectivity, consistent with actions in chiral environments and likely direct interactions with signaling proteins. Other effects show no enantioselectivity and even reverse enantioselectivity. The spectrum of effects of NAS enantiomers raises the possibility that these agents, once considered only as tools for preclinical studies, have therapeutic potential that complements and in some cases may exceed their natural counterparts. Here we review studies of NAS enantiomers from the perspective of their potential development as novel neurotherapeutics.
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Affiliation(s)
- Douglas F Covey
- Departments of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA; Developmental Biology, Washington University School of Medicine, St. Louis, MO, USA; Anesthesiology Washington University School of Medicine, St. Louis, MO, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Alex S Evers
- Developmental Biology, Washington University School of Medicine, St. Louis, MO, USA; Anesthesiology Washington University School of Medicine, St. Louis, MO, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Yukitoshi Izumi
- Departments of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Jamie L Maguire
- Department of Neuroscience, Tufts University School of Medicine, Boston, MA, USA
| | - Steven J Mennerick
- Departments of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA
| | - Charles F Zorumski
- Departments of Psychiatry, Washington University School of Medicine, St. Louis, MO, USA; The Taylor Family Institute for Innovative Psychiatric Research, Washington University School of Medicine, St. Louis, MO, USA.
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Organocatalyst Design for the Stereoselective Annulation towards Bicyclic Diketones and Analogues. Symmetry (Basel) 2022. [DOI: 10.3390/sym14020355] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The Wieland–Miescher ketone, Hajos–Parrish–Eder–Sauer–Wiechert ketone, and their analogues are bicyclic diketones essential as building blocks for the synthesis of several natural and bioactive molecules. For this reason, since 1971, when Hajos and Parrish and Eder, Sauer, and Wiechert reported the stereoselective synthesis of these compounds promoted by L-proline, numerous methodologies and organocatalysts have been studied over the years with the aim of identifying increasingly efficient asymmetrical syntheses of these bicyclic ketones. This review will outline the methodological and stereochemical features of the organocatalytic stereoselective synthesis of these bicyclic scaffolds based on the different organocatalysts employed from 1971 until today. Particular emphasis will be given to the structural features of the catalysts and to the reaction conditions.
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Han B, He XH, Liu YQ, He G, Peng C, Li JL. Asymmetric organocatalysis: an enabling technology for medicinal chemistry. Chem Soc Rev 2021; 50:1522-1586. [PMID: 33496291 DOI: 10.1039/d0cs00196a] [Citation(s) in RCA: 150] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The efficacy and synthetic versatility of asymmetric organocatalysis have contributed enormously to the field of organic synthesis since the early 2000s. As asymmetric organocatalytic methods mature, they have extended beyond the academia and undergone scale-up for the production of chiral drugs, natural products, and enantiomerically enriched bioactive molecules. This review provides a comprehensive overview of the applications of asymmetric organocatalysis in medicinal chemistry. A general picture of asymmetric organocatalytic strategies in medicinal chemistry is firstly presented, and the specific applications of these strategies in pharmaceutical synthesis are systematically described, with a focus on the preparation of antiviral, anticancer, neuroprotective, cardiovascular, antibacterial, and antiparasitic agents, as well as several miscellaneous bioactive agents. The review concludes with a discussion of the challenges, limitations and future prospects for organocatalytic asymmetric synthesis of medicinally valuable compounds.
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Affiliation(s)
- Bo Han
- State Key Laboratory of Southwestern Chinese Medicine Resources, Chengdu University of Traditional Chinese Medicine, Chengdu 611137, China.
| | - Xiang-Hong He
- State Key Laboratory of Southwestern Chinese Medicine Resources, Chengdu University of Traditional Chinese Medicine, Chengdu 611137, China.
| | - Yan-Qing Liu
- State Key Laboratory of Southwestern Chinese Medicine Resources, Chengdu University of Traditional Chinese Medicine, Chengdu 611137, China.
| | - Gu He
- State Key Laboratory of Biotherapy and Cancer Centre, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Cheng Peng
- State Key Laboratory of Southwestern Chinese Medicine Resources, Chengdu University of Traditional Chinese Medicine, Chengdu 611137, China.
| | - Jun-Long Li
- State Key Laboratory of Southwestern Chinese Medicine Resources, Chengdu University of Traditional Chinese Medicine, Chengdu 611137, China. and Antibiotics Research and Re-evaluation Key Laboratory of Sichuan Province, Sichuan Industrial Institute of Antibiotics, School of Pharmacy, Chengdu University, Chengdu 610106, China.
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Hagiwara H. Aspects in the Total Syntheses of Higher Terpenoids Starting From Wieland–Miescher Ketone and Its Derivative: A Review. Nat Prod Commun 2020. [DOI: 10.1177/1934578x20925340] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Synthetic studies of higher terpenoids starting from Wieland–Miescher ketone since 2012 have been compiled.
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Affiliation(s)
- Hisahiro Hagiwara
- Graduate School of Science and Technology, Niigata University, Nishi-Ku, Niigata, Japan
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Šimek M, Bártová K, Pohl R, Císařová I, Jahn U. Tandemreaktionen aus anionischer Oxy‐Cope‐Umlagerung und Oxygenierung als vielseitiger Zugang zu verschiedenartigen Gerüsten. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201916188] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Michal Šimek
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Kateřina Bártová
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Radek Pohl
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
| | - Ivana Císařová
- Institut für Anorganische ChemieNaturwissenschaftliche FakultätKarls-Universität Prag Hlavova 2030/8 12843 Prag 2 Czech republic
| | - Ullrich Jahn
- Institut für Organische Chemie und BiochemieTschechische Akademie der Wissenschaften Flemingovo náměstí 2 16610 Prag 6 Czech republic
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Šimek M, Bártová K, Pohl R, Císařová I, Jahn U. Tandem Anionic oxy-Cope Rearrangement/Oxygenation Reactions as a Versatile Method for Approaching Diverse Scaffolds. Angew Chem Int Ed Engl 2020; 59:6160-6165. [PMID: 31994304 DOI: 10.1002/anie.201916188] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Indexed: 12/29/2022]
Abstract
Tandem anionic oxy-Cope rearrangement/radical oxygenation reactions provide δ,ϵ-unsaturated α-(aminoxy) carbonyl compounds, which serve as convenient precursors to diverse compound classes. Functionalized carbocycles are accessible by very rare all-carbon 5-endo-trig cyclizations, but also common 5-exo-trig radical cyclizations, based on the persistent radical effect. The tandem reactions can be further extended by highly diastereoselective allylation or reduction steps to give complex scaffolds.
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Affiliation(s)
- Michal Šimek
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Kateřina Bártová
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
| | - Ivana Císařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843, Prague 2, Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo náměstí 2, 16610, Prague 6, Czech Republic
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Klychnikov MK, Pohl R, Císařová I, Jahn U. Application of the Brook Rearrangement in Tandem with Single Electron Transfer Oxidative and Radical Processes. European J Org Chem 2020. [DOI: 10.1002/ejoc.202000126] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Mikhail K. Klychnikov
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
| | - Ivana Císařová
- Department of Inorganic Chemistry; Faculty of Science; Charles University in Prague; Hlavova 2030/8 12843 Prague 2 Czech Republic
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry; Czech Academy of Sciences; Flemingovo náměstí 2 16610 Prague 6 Czech Republic
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Shiina I, Miesch M, Peter C, Geoffroy P, Murata T, Tonoi T. Diastereo–/Enantioselective Diels–Alder Synthesis of 14β-Hydroxysteroid Scaffolds: A Combined Experimental and DFT Study. HETEROCYCLES 2019. [DOI: 10.3987/com-18-s(f)99] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Offei SD, Arman HD, Baig MO, Chavez LS, Paladini CA, Yoshimoto FK. Chemical synthesis of 7-oxygenated 12α-hydroxy steroid derivatives to enable the biochemical characterization of cytochrome P450 8B1, the oxysterol 12α-hydroxylase enzyme implicated in cardiovascular health and obesity. Steroids 2018; 140:185-195. [PMID: 30399365 PMCID: PMC6249089 DOI: 10.1016/j.steroids.2018.10.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Revised: 10/10/2018] [Accepted: 10/19/2018] [Indexed: 10/27/2022]
Abstract
Cholic acid is the endogenous 12α-hydroxylated bile acid, which possesses enhanced cholesterol absorption properties compared to its 12-desoxy counterpart, chenodeoxycholic acid. The oxysterol 12α-hydroxylase enzyme is cytochrome P450 8B1 (P450 8B1), which regioselectively and stereoselectively incorporates the 12α-hydroxy group in 7α-hydroxycholest-4-en-3-one, the biosynthetic precursor of cholic acid. Despite the vital role of P450 8B1 activity in cardiovascular health, research studies of other 12α-hydroxy steroid derivatives are rare. A synthetic route to incorporate a C12α-hydroxy group into the C12-methylene (-CH2-) in dehydroepiandrosterone derivatives is disclosed. The incorporation of the C12-oxygen was accomplished through a copper mediated Schönecker oxidation of an imino-pyridine intermediate, introducing the 12β-hydroxy group. The resulting 12β-hydroxy steroid derivative was oxidized to the C12-ketone, which was stereoselectively reduced with lithium tri-sec-butylborohydride to afford the 12α-hydroxy stereochemistry. The C7-position was oxidized to yield the various 7-keto, 7β-hydroxy, and 7α-hydroxy derivatives. Furthermore, 7-ketodehydroepiandrosterone and 12 α-hydroxy-7-ketodehydroepiandrosterone both displayed NMDA receptor antagonistic activities at 10 μM concentrations. These C12α-hydroxy steroids will be used as tools to identify new biochemical properties of the enzymatic products of P450 8B1, the oxysterol 12α-hydroxylase.
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Affiliation(s)
- Samuel D Offei
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States
| | - Hadi D Arman
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States
| | - Mirza Oais Baig
- Department of Biology, UTSA Neurosciences Institute, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States
| | - Lazaro S Chavez
- Department of Biology, UTSA Neurosciences Institute, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States
| | - Carlos A Paladini
- Department of Biology, UTSA Neurosciences Institute, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States
| | - Francis K Yoshimoto
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX 78249-0698, United States.
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Romero KJ, Galliher MS, Pratt DA, Stephenson CRJ. Radicals in natural product synthesis. Chem Soc Rev 2018; 47:7851-7866. [PMID: 30101272 PMCID: PMC6205920 DOI: 10.1039/c8cs00379c] [Citation(s) in RCA: 164] [Impact Index Per Article: 27.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Free radical intermediates have intrigued chemists since their discovery, and an ever-increasing appreciation for their unique reactivity has resulted in the widespread utilization of these species throughout the field of chemical synthesis. This is most evident from the recent surge in the application of intermolecular radical reactions that feature in complex molecule syntheses. This tutorial review will discuss the diverse methods utilized for radical generation and reactivity to form critical bonds in natural product total synthesis. In particular, stabilized (e.g. benzyl) and persistent (e.g. TEMPO) radicals will be the primary focus.
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Affiliation(s)
- Kevin J Romero
- Department of Chemistry, University of Michigan, 930 N. University Ave, Ann Arbor, MI 48109, USA.
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Amatov T, Jangra H, Pohl R, Cisařová I, Zipse H, Jahn U. Unique Stereoselective Homolytic C-O Bond Activation in Diketopiperazine-Derived Alkoxyamines by Adjacent Amide Pyramidalization. Chemistry 2018; 24:15336-15345. [PMID: 30092124 DOI: 10.1002/chem.201803284] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 08/02/2018] [Indexed: 12/12/2022]
Abstract
Simple monocyclic diketopiperazine (DKP)-derived alkoxyamines exhibit unprecedented activation of a remote C-O bond for homolysis by amide distortion. The combination of strain-release-driven amide planarization and the persistent radical effect (PRE) enables a unique, irreversible, and quantitative trans→cis isomerization under much milder conditions than typically observed for such homolysis-limited reactions. This isomerization is shown to be general and independent of the steric and electronic nature of both the amino acid side chains and the substituents at the DKP nitrogen atoms. Homolysis rate constants are determined, and they significantly differ for both the labile trans diastereomers and the stable cis diastereomers. To reveal the factors influencing this unusual process, structural features of the kinetic trans diastereomers and thermodynamic cis diastereomers are investigated in the solid state and in solution. X-ray crystallographic analysis and computational studies indicate substantial distortion of the amide bond from planarity in the trans-alkoxyamines, and this is believed to be the cause for the facile and quantitative isomerization. Thus, these amino-acid-derived alkoxyamines are the first examples that exhibit a large thermodynamic preference for one diastereomer over the other upon thermal homolysis, and this allows controlled switching of configurations and configurational cycling.
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Affiliation(s)
- Tynchtyk Amatov
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic.,Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Harish Jangra
- Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Radek Pohl
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic
| | - Ivana Cisařová
- Department of Inorganic Chemistry, Faculty of Science, Charles University in Prague, Hlavova 2030/8, 12843, Prague, Czech Republic
| | - Hendrik Zipse
- Ludwig Maximilian University, Department of Chemistry, Butenandstrasse 5-13, 81377, München, Germany
| | - Ullrich Jahn
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo náměstí 2, 16610, Prague, Czech Republic
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Jones KD, Stewart SG. Recent Advances in Steroid Synthesis: A Tribute to Sir Derek Barton. Aust J Chem 2018. [DOI: 10.1071/ch18256] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The synthesis of steroids and gaining an ultimate understanding of their reactivity was one of Sir Derek Barton’s most notable research areas. This highlight will focus on the construction of the steroid ring system from 2016 to 2018, and will include pathways that eventually led to natural product synthesis. For example, efficient syntheses of ent-pregnanolone sulfate and oestradiol methyl ether will be explained along with the total synthesis of cannogenol-3-O-α-l-rhamnoside.
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