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Saha D, Guchhait S, Goswami RK. Total Synthesis and Stereochemical Assignment of Penicitide A. Org Lett 2020; 22:745-749. [DOI: 10.1021/acs.orglett.9b04585] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Dhiman Saha
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India
| | - Sandip Guchhait
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India
| | - Rajib Kumar Goswami
- School of Chemical Sciences, Indian Association for the Cultivation of Science, Jadavpur, Kolkata-700032, India
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2
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Green AP, Hardy S, Thomas EJ. Synthetic approaches to the C11-C27 fragments of bryostatins. Org Biomol Chem 2017; 15:9475-9496. [PMID: 29109991 DOI: 10.1039/c7ob02127e] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The modified Julia reaction and acyl carbanion chemistry, especially reactions of 2-lithiated dithianes, have been investigated for the synthesis of intermediates that are the synthetic equivalents of the C11-C27 fragments of bryostatins. The modified Julia reaction using 2-benzothiazolylsulfones was found to be more useful for the formation of the C16-C17 double-bond than the classical Julia reaction using phenylsulfones, and bulky sulfones gave very good (E)-stereoselectivity. The alkylation of a dithiane monoxide that corresponded to a C19-acyl carbanion using (E)-1-bromobut-2-ene was efficient but the use of a more complex allylic bromide corresponding to the C20-C27 fragment of the bryostatins was unsuccessful, possibly due to competing elimination reactions. This meant that the use of C19 dithianes for the synthesis of 20-deoxybryostatins would have to involve the stepwise assembly of the C20-C27 fragment from simpler precursors. However, lithiated C19 dithianes gave good yields of adducts with aldehydes and conditions were developed for the stereoselective conversion of the major adducts into methoxyacetals that corresponded to the C17-C27 fragment of 20-oxygenated bryostatins. A convergent synthesis of the C11-C27 fragment of a 20-deoxybryostatin was subsequently achieved using a 2-benzothiazolylsulfone corresponding to the intact C17-C27 fragment.
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Affiliation(s)
- Anthony P Green
- The School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
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Green AP, Hardy S, Lee ATL, Thomas EJ. Total synthesis of 7-des-O-pivaloyl-7-O-benzylbryostatin 10. Org Biomol Chem 2017; 15:9497-9526. [PMID: 29109995 DOI: 10.1039/c7ob02129a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The first total synthesis of a derivative of a 20-deoxybryostatin, namely 7-des-O-pivaloyl-7-O-benzylbryostatin 10 is described. Preliminary studies demonstrated that the modified Julia reactions of 2-benzothiazolylsulfones corresponding to the C17-C27 fragment with aldehydes corresponding to the C1-C16 fragment, provided an efficient and stereoselective assembly of advanced intermediates with the (E)-16,17-double-bond. The synthesis of the C1-C16 fragment was then modified so that the C1 acid was present as its allyl ester before the Julia coupling. A more efficient synthesis of the C17-C27 sulfone was developed in which a key step was the bismuth mediated coupling of an allylic bromide with an aldehyde in the presence of an acrylate moiety in the allylic bromide. A scalable synthesis of an advanced macrolide was completed using the modified Julia reaction followed by selective deprotection and macrolactonisation. The final stages of the synthesis required selective hydroxyl deprotection and the introduction of the sensitive C19-C21 unsaturated keto-ester functionality. Unexpected selectivities were observed during studies of the hydroxyl group deprotections. In particular, cleavage of tri-isopropylsilyl ethers of the exocyclic primary allylic alcohols was observed in the presence of the triethylsilyl ether of the secondary alcohol at C19. Model studies helped in the design of the methods used to introduce the C19-C21 keto-ester functionality and led to the completion of a total synthesis of a close analogue of bryostatin 10 in which a benzyloxy group rather than the pivaloyloxy group was present at C7.
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Affiliation(s)
- Anthony P Green
- The School of Chemistry, The University of Manchester, Manchester M13 9PL, UK.
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Ermanis K, Hsiao YT, Kaya U, Jeuken A, Clarke PA. The stereodivergent formation of 2,6- cis and 2,6- trans-tetrahydropyrans: experimental and computational investigation of the mechanism of a thioester oxy-Michael cyclization. Chem Sci 2017; 8:482-490. [PMID: 28451195 PMCID: PMC5298201 DOI: 10.1039/c6sc03478k] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2016] [Accepted: 08/26/2016] [Indexed: 11/24/2022] Open
Abstract
Computational and synthetic studies have elucidated the origins of stereodivergence in an oxy-Michael synthesis of 2,6-disubstituted tetrahydropyrans.
The origins of the stereodivergence in the thioester oxy-Michael cyclization for the formation of 4-hydroxy-2,6-cis- or 2,6-trans-substituted tetrahydropyran rings under different conditions was investigated both computationally and experimentally. Synthetic studies showed that the 4-hydroxyl group was essential for stereodivergence. When the 4-hydroxyl group was present, TBAF-mediated conditions gave the 2,6-trans-tetrahydropyran and trifluoroacetic acid-mediated conditions gave the 2,6-cis-tetrahydropyran. This stereodivergence vanished when the hydroxyl group was removed or protected. Computational studies revealed that: (i) the trifluoroacetic acid catalysed formation of 2,6-cis-tetrahydropyrans was mediated by a trifluoroacetate-hydroxonium bridge and proceeded via a chair-like transition state; (ii) the TBAF-mediated formation of 2,6-trans-tetrahydropyrans proceeded via a boat-like transition state, where the 4-hydroxyl group formed a crucial hydrogen bond to the cyclizing alkoxide; (iii) both reactions are under kinetic control. The utility of this stereodivergent approach for the formation of 4-hydroxy-2,6-substituted tetrahydropyran rings has been demonstrated by the total syntheses of the anti-osteoporotic natural products diospongin A and B.
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Affiliation(s)
- Kristaps Ermanis
- Department of Chemistry , University of York , Heslington , York , North Yorkshire YO10 5DD , UK .
| | - Yin-Ting Hsiao
- Department of Chemistry , University of York , Heslington , York , North Yorkshire YO10 5DD , UK .
| | - Uğur Kaya
- Department of Chemistry , University of York , Heslington , York , North Yorkshire YO10 5DD , UK .
| | - Alan Jeuken
- Department of Chemistry , University of York , Heslington , York , North Yorkshire YO10 5DD , UK .
| | - Paul A Clarke
- Department of Chemistry , University of York , Heslington , York , North Yorkshire YO10 5DD , UK .
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Ball M, Gregson T, Omori H, Thomas EJ. Syntheses of C17–C27 fragments of 20-deoxybryostatins for assembly using Julia and metathesis reactions. Org Biomol Chem 2017; 15:2740-2767. [DOI: 10.1039/c7ob00076f] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Two approaches to the synthesis of compounds corresponding to the C17–C27 fragment of the 20-deoxybryostatins are described.
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Affiliation(s)
- Matthew Ball
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Thomas Gregson
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Hiroki Omori
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Eric J. Thomas
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
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Dumeunier R, Gregson T, MacCormick S, Omori H, Thomas EJ. Some limitations of an approach to the assembly of bryostatins by ring-closing metathesis. Org Biomol Chem 2017; 15:2768-2783. [DOI: 10.1039/c7ob00079k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Preliminary studies into the use of ring-closing metathesis (RCM) in a convergent approach for the total synthesis of bryostatins are described.
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Affiliation(s)
- Raphaël Dumeunier
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Thomas Gregson
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | | | - Hiroki Omori
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Eric J. Thomas
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
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Neumeyer M, Brückner R. Nonracemic γ-Lactones from the Sharpless Asymmetric Dihydroxylation of β,γ-Unsaturated Carboxylic Esters. European J Org Chem 2016. [DOI: 10.1002/ejoc.201600520] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Markus Neumeyer
- Institut für Organische Chemie; Albert-Ludwigs-Universität Freiburg; Albertstraße 21 79104 Freiburg Germany
| | - Reinhard Brückner
- Institut für Organische Chemie; Albert-Ludwigs-Universität Freiburg; Albertstraße 21 79104 Freiburg Germany
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Ball M, Baron A, Bradshaw B, Dumeunier R, O'Brien M, Thomas EJ. The evolution of a stereoselective synthesis of the C1–C16 fragment of bryostatins. Org Biomol Chem 2016; 14:9650-9681. [DOI: 10.1039/c6ob01804a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Scaleable syntheses of the C1–C16 fragment of bryostatins are described.
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Affiliation(s)
- Matthew Ball
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Anne Baron
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Ben Bradshaw
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Raphaël Dumeunier
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Matthew O'Brien
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
| | - Eric J. Thomas
- The School of Chemistry
- The University of Manchester
- Manchester M13 9PL
- UK
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10
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Cossy J, Guérinot A. Natural Products Containing Oxygen Heterocycles—Synthetic Advances Between 1990 and 2015. ADVANCES IN HETEROCYCLIC CHEMISTRY 2016. [DOI: 10.1016/bs.aihch.2016.03.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Mears PR, Thomas EJ. Synthesis of C16–C27-fragments of bryostatins modified by 20,20-difluorination. Tetrahedron Lett 2015. [DOI: 10.1016/j.tetlet.2015.05.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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12
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Wender PA, Donnelly AC, Loy BA, Near KE, Staveness D. Rethinking the Role of Natural Products: Function-Oriented Synthesis, Bryostatin, and Bryologs. METHODS AND PRINCIPLES IN MEDICINAL CHEMISTRY 2014. [DOI: 10.1002/9783527676545.ch14] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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Fletcher CJ, Blair DJ, Wheelhouse KM, Aggarwal VK. The total synthesis of (−)-aplysin via a lithiation–borylation–propenylation sequence. Tetrahedron 2012. [DOI: 10.1016/j.tet.2012.05.095] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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15
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O’Brien M, Thomas EJ. Synthesis of the C(1)–C(16) fragment of bryostatins using an ‘ene’ reaction between an allylsilane and an alkynone. Tetrahedron 2011. [DOI: 10.1016/j.tet.2011.09.064] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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16
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Trost BM, Yang H, Dong G. Total syntheses of bryostatins: synthesis of two ring-expanded bryostatin analogues and the development of a new-generation strategy to access the C7-C27 fragment. Chemistry 2011; 17:9789-805. [PMID: 21780195 PMCID: PMC3517064 DOI: 10.1002/chem.201002932] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 04/26/2011] [Indexed: 11/06/2022]
Abstract
Herein, we report the synthesis of novel ring-expanded bryostatin analogues. By carefully modifying the substrate, a selective and high-yielding Ru-catalyzed tandem enyne coupling/Michael addition was employed to construct the northern fragment. Ring-closing metathesis was utilized to form the 31-membered ring macrocycle of the analogue. These ring-expanded bryostatin analogues possess anticancer activity against several cancer cell lines. Given the difficulty in forming the C16-C17 olefin at a late stage, we also describe our development of a new-generation strategy to access the C7-C27 fragment, containing both the ring B and C subunits.
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Affiliation(s)
- Barry M Trost
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA.
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17
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Trost BM, Yang H, Brindle CS, Dong G. Atom-economic and stereoselective syntheses of the ring a and B subunits of the bryostatins. Chemistry 2011; 17:9777-88. [PMID: 21774000 DOI: 10.1002/chem.201002930] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2010] [Revised: 04/21/2011] [Indexed: 11/06/2022]
Abstract
This article describes chemoselective and atom-economic methods for the stereoselective assembly of the ring A and B subunits of bryostatins. A Ru-catalyzed tandem alkene-alkyne coupling/Michael addition reaction was developed and applied to the synthesis of bryostatin ring B. We explored an acetylide-mediated epoxide-opening/6-exo-dig cyclization route to access the bryostatin ring A, although ring A was eventually furnished through an acid-catalyzed tandem transketalization/ketalization sequence. In addition, a dinuclear zinc-catalyzed methyl vinyl ketone (MVK) aldol strategy was evaluated for the construction of the polyacetate moiety. Utilization of these methods ultimately led to the rapid assembly of the northern bryostatin fragment containing both the ring A and B subunits.
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Affiliation(s)
- Barry M Trost
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
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18
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A new strategy for the synthesis of substituted dihydropyrones and tetrahydropyrones via palladium-catalyzed coupling of thioesters. Tetrahedron 2011. [DOI: 10.1016/j.tet.2011.03.114] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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20
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Wender PA, Loy BA, Schrier AJ. Translating Nature's Library: The Bryostatins and Function-Oriented Synthesis. Isr J Chem 2011; 51:453-472. [PMID: 22661768 PMCID: PMC3364006 DOI: 10.1002/ijch.201100020] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
We review in part our computational, design, synthesis, and biological studies on a remarkable class of compounds and their designed analogs that have led to preclinical candidates for the treatment of cancer, a first-in-class approach to Alzheimer's disease, and a promising strategy to eradicate HIV/AIDS. Because these leads target, in part, protein kinase C (PKC) isozymes, they have therapeutic potential even beyond this striking set of therapeutic indications. This program has given rise to new synthetic methodology and represents an increasingly important direction of synthesis focused on achieving function through synthesis-informed design (function-oriented synthesis).
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Affiliation(s)
- Paul A. Wender
- Department of Chemistry Department of Chemical and Systems Biology Stanford University Stanford, CA 94305, USA
| | - Brian A. Loy
- Department of Chemistry Department of Chemical and Systems Biology Stanford University Stanford, CA 94305, USA
| | - Adam J. Schrier
- Department of Chemistry Department of Chemical and Systems Biology Stanford University Stanford, CA 94305, USA
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Qi Y, Ma S. The medicinal potential of promising marine macrolides with anticancer activity. ChemMedChem 2011; 6:399-409. [PMID: 21302362 DOI: 10.1002/cmdc.201000534] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2010] [Revised: 01/08/2011] [Indexed: 12/12/2022]
Abstract
Marine natural products have become a major source of new chemical entities in the discovery of potential anticancer agents that potently suppress various molecular targets. In particular, the marine macrolides, which include an array of novel biomolecules endowed with outstanding cytotoxic and/or antiproliferative activities, are a prominent class of marine natural products that offer continued promise for breakthroughs in anticancer research. Herein we highlight some recent studies of promising marine macrolides, paying particular attention to their discovery, anticancer activities, mechanisms of action, chemical synthesis, and representative analogues.
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Affiliation(s)
- Yunkun Qi
- Department of Medicinal Chemistry, School of Pharmaceutical Sciences, Shandong University, 44, West Culture Road, Jinan 250012, PR China
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Green AP, Lee ATL, Thomas EJ. Total synthesis of a 20-deoxybryostatin. Chem Commun (Camb) 2011; 47:7200-2. [DOI: 10.1039/c1cc12332g] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Trost BM, Dong G. Total synthesis of bryostatin 16 using a Pd-catalyzed diyne coupling as macrocyclization method and synthesis of C20-epi-bryostatin 7 as a potent anticancer agent. J Am Chem Soc 2010; 132:16403-16. [PMID: 21043491 PMCID: PMC2993185 DOI: 10.1021/ja105129p] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Asymmetric total synthesis of bryostatin 16 was achieved in 26 steps in the longest linear sequence and in 39 total steps from aldehyde 10. A Pd-catalyzed alkyne-alkyne coupling was employed for the first time as a macrocyclization method in a natural product synthesis. A route to convert bryostatin 16 to a new family of bryostatin analogues was developed. Toward this end, 20-epi-bryostatin 7 was synthesized from a bryostatin 16-like intermediate; the key step involves a Re-catalyzed epoxidation/ring-opening reaction. Preliminary biological studies indicated that this new analogue exhibits nanomolar anti-cancer activity against several cancer cell lines.
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Affiliation(s)
- Barry M Trost
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, United States.
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Fuwa H, Saito A, Sasaki M. A concise total synthesis of (+)-neopeltolide. Angew Chem Int Ed Engl 2010; 49:3041-4. [PMID: 20309988 DOI: 10.1002/anie.201000624] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Haruhiko Fuwa
- Laboratory of Biostructural Chemistry, Graduate School of Life Sciences, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
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Hale KJ, Manaviazar S. New approaches to the total synthesis of the bryostatin antitumor macrolides. Chem Asian J 2010; 5:704-54. [PMID: 20354984 DOI: 10.1002/asia.200900634] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
In this Focus Review, we give an overview of various bryostatin total syntheses. We also discuss the synthesis of various bryostatin analogues and their biological activity. Work reviewed includes that of Masamune, Evans, Nishiyama and Yamamura, Hale and Manaviazar, Trost, Wender, Keck, Burke, Thomas, and Krische. Our coverage is primarily for the period 2001-2009, since detailed reviews already exist on bryostatin total synthesis work and biology up to this time.
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Affiliation(s)
- Karl J Hale
- School of Chemistry & Chemical Engineering, Queen's Universty Belfast, Stranmillis Road, Belfast BT9 5AG, Northern Ireland, UK.
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Synthetic applications of chiral unsaturated epoxy alcohols prepared by sharpless asymmetric epoxidation. Molecules 2010; 15:1041-73. [PMID: 20335961 PMCID: PMC6263200 DOI: 10.3390/molecules15021041] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2010] [Revised: 02/09/2010] [Accepted: 02/20/2010] [Indexed: 11/16/2022] Open
Abstract
An overview of the synthesis and applications of chiral 2,3-epoxy alcohols containing unsaturated chains is presented. One of the fundamental synthetic routes to these compounds is Sharpless asymmetric epoxidation, which is reliable, highly chemoselective and enables easy prediction of the product enantioselectivity. Thus, unsaturated epoxy alcohols are readily obtained by selective oxidation of the allylic double bond in the presence of other carbon-carbon double or triple bonds. The wide availability of epoxy alcohols with unsaturated chains, the versatility of the epoxy alcohol functionality (e.g. regio- and stereo-selective ring opening; oxidation; and reduction), and the arsenal of established alkene chemistries, make unsaturated epoxy alcohols powerful starting materials for the synthesis of complex targets such as biologically active molecules. The popularization of ring-closing metathesis has further increased their value, making them excellent precursors to cyclic compounds.
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Houghton SR, Furst L, Boddy CN. Biomimetic transannular oxa-conjugate addition approach to the 2,6-disubstituted dihydropyran of laulimalide yields an unprecedented transannular oxetane. J Org Chem 2009; 74:1454-63. [PMID: 19159194 DOI: 10.1021/jo8023494] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
2,6-Disubstituted dihydropyrans are a common feature in many bioactive polyketides, including the anticancer marine polyketide laulimalide. While much of the uncharacterized biosynthetic pathway for laulimalide can be confidently postulated, the biosynthetic origins of the trans 2,6-disubstituted dihydropyran cannot. We hypothesize that a transannular oxa-conjugate addition in a macrocyclic laulimalide precursor could be the origin of the 2,6-dihydropyran. To test this hypothesis, we constructed a model containing the key functional groups for oxa-conjugate addition-mediated dihydropyran formation. Under acid-mediated conditions, the model under went regiospecific oxa-conjugate addition producing a stable trans oxetane as the only regioisomer. The desired, more stable dihydropyran was not detected. This unprecedented regiospecificity is unexpected due to the ring strain of the oxetane and the anticipated facile ring opening retro-oxa-conjugate addition. The oxetane is stable to acid and basic conditions, as are a number of literature acyclic oxetanes that could undergo similar retro-oxa-conjugate addition. While the source of the oxetane kinetic stability is yet to be characterized, it may enable general oxetane construction via oxa-conjugate addition. The more stable dihydropyran regioisomer could not be generated due to poor geometrical orbital alignment and hard-soft incompatibility between the hard oxygen nucleophile and the soft activated polyenoate electrophile. These factors disfavor the breaking of conjugation by oxa-conjugate addition. Based on these results we propose that dihydropyran formation does not occur on completed polyketide macrocycles as we had proposed but rather during polyketide biosynthesis on the growing polyketide chain.
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Affiliation(s)
- Stephen R Houghton
- Department of Chemistry, Syracuse University, Syracuse, New York 13244, USA
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Trost BM, Dong G. Total synthesis of bryostatin 16 using atom-economical and chemoselective approaches. Nature 2008; 456:485-8. [PMID: 19037312 DOI: 10.1038/nature07543] [Citation(s) in RCA: 213] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2008] [Accepted: 10/10/2008] [Indexed: 11/09/2022]
Abstract
Of the concepts used to improve the efficiency of organic syntheses, two have been especially effective: atom economy (the use of routes in which most of the atoms present in the reactants also end up in the product) and chemoselectivity (the use of reactions that take place only at desired positions in a molecule). Synthesis of complex natural products is the most demanding arena in which to explore such principles. The bryostatin family of compounds are especially interesting targets, because they combine structural complexity with promising biological activity. Furthermore, synthetic routes to some bryostatins have already been reported, providing a benchmark against which new syntheses can be measured. Here we report a concise total synthesis of bryostatin 16 (1), a parent structure from which almost all other bryostatins could in principle be accessed. Application of atom-economical and chemoselective reactions currently under development provides ready access to polyhydropyran motifs in the molecule, which are common structural features of many other natural products. The most notable transformations are two transition-metal-catalysed reactions. The first is a palladium-catalysed reaction of two different alkynes to form a large ring. The product of this step is then converted into a dihydropyran (the 'C ring' of bryostatins) in the second key reaction, which is catalysed by a gold compound. Analogues of bryostatin that do not exist in nature could be readily made by following this route, which might allow the biological activity of bryostatins to be fine-tuned.
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Affiliation(s)
- Barry M Trost
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
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Allen JV, Green AP, Hardy S, Heron NM, Lee AT, Thomas EJ. On the use of the modified Julia olefination for bryostatin synthesis. Tetrahedron Lett 2008. [DOI: 10.1016/j.tetlet.2008.08.075] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Fürstner A, Fasching B, O'Neil GW, Fenster MDB, Godbout C, Ceccon J. Toward the total synthesis of spirastrellolide A. Part 3: Intelligence gathering and preparation of a ring-expanded analogue. Chem Commun (Camb) 2007:3045-7. [PMID: 17639136 DOI: 10.1039/b707835h] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Different methods for the formation of the C.25-C.26 bond of spirastrellolide A () are evaluated that might qualify for the end game of the projected total synthesis, with emphasis on metathetic ways to forge the macrocyclic frame.
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Affiliation(s)
- Alois Fürstner
- Max-Planck-Institut für Kohlenforschung, D-45470, Mülheim/Ruhr, Germany.
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Kotha S, Mandal K. Suzuki–Miyaura Cross-Coupling and Ring-Closing Metathesis: A Strategic Combination for the Synthesis of Cyclophane Derivatives. European J Org Chem 2006. [DOI: 10.1002/ejoc.200600549] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Spino C, Boisvert L, Douville J, Roy S, Lauzon S, Minville J, Gagnon D, Beaumier F, Chabot C. Cleavage of a chiral auxiliary using RCM on an especially sterically crowded alkene: Syntheses of chiral carbo- and heterocycles. J Organomet Chem 2006. [DOI: 10.1016/j.jorganchem.2006.07.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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