1
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Mulamreddy R, Hou X, Chemtob S, Lubell WD. Synthesis of 5- and 7-hydroxy indolizidin-2-one prostaglandin-F 2α modulators and activity on myometrial contractility towards development of agents for delaying preterm birth. J Pept Sci 2023; 29:e3455. [PMID: 36184819 DOI: 10.1002/psc.3455] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2022] [Revised: 09/15/2022] [Accepted: 09/28/2022] [Indexed: 11/06/2022]
Abstract
In pursuit of more effective-labor delaying tocolytic agents, the prostaglandin F2α (PGF2α) receptor (FP) modulator PDC113.824 [(6S)-2] represents a potent lead for developing therapy to treat preterm birth. Derivatives of FP modulator (6S)-2 were synthesized, possessing respectively 5- and 7-hydroxyl groups on the indolizidin-2-one amino acid (I2 aa) residue. The effects of the alcohol substituents were examined in a PGF2α-induced myometrial contraction assay. Based on knowledge of dihedral angle values of model I2 aa peptides from X-ray analyses, the results of the study indicate respectively encouraging and limited potential for creating improved tocolytic agents by modifications at the 5- and 7-positions.
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Affiliation(s)
| | - Xin Hou
- Centre Hospitalier Universitaire Sainte-Justine Research Center, Montréal, Québec, Canada
| | - Sylvain Chemtob
- Centre Hospitalier Universitaire Sainte-Justine Research Center, Montréal, Québec, Canada
| | - William D Lubell
- Département de Chimie, Université de Montréal, Montréal, Québec, Canada
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2
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Kazmierski WM, Miriyala N, Johnson DK, Baskaran S. The Discovery of Conformationally Constrained Bicyclic Peptidomimetics as Potent Hepatitis C NS5A Inhibitors. ACS Med Chem Lett 2021; 12:1649-1655. [PMID: 34790290 PMCID: PMC8591741 DOI: 10.1021/acsmedchemlett.1c00391] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2021] [Indexed: 01/03/2023] Open
Abstract
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HCV NS5A inhibitors are the backbone
of directly acting antiviral
treatments against the hepatitis C virus (HCV). While these therapies
are generally highly curative, they are less effective in some specific
HCV patient populations. In the search for broader-acting HCV NS5A
inhibitors that address these needs, we explored conformational restrictions
imposed by the [7,5]-azabicyclic lactam moiety incorporated into daclatasvir
(1) and related HCV NS5A inhibitors. Unexpectedly, compound 5 was identified as a potent HCV genotype 1a and 1b inhibitor.
Molecular modeling of 5 bound to HCV genotype 1a suggested
that the use of the conformationally restricted lactam moiety might
have resulted in reorientation of its N-terminal carbamate to expose
a new interaction with the NS5A pocket located between amino acids
P97 and Y93, which was not easily accessible to 1. The
results also suggest new chemistry directions that exploit the interactions
with the P97–Y93 site toward new and potentially improved HCV
NS5A inhibitors.
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Affiliation(s)
- Wieslaw M. Kazmierski
- GlaxoSmithKline, 5 Moore Drive, Research Triangle Park, North Carolina 27709-3398, United States
| | - Nagaraju Miriyala
- GlaxoSmithKline, 5 Moore Drive, Research Triangle Park, North Carolina 27709-3398, United States
| | - David K. Johnson
- Computational Chemical Biology Core and Molecular Graphics and Modeling Laboratory, University of Kansas, Lawrence, Kansas 66047, United States
| | - Sam Baskaran
- GlaxoSmithKline, 5 Moore Drive, Research Triangle Park, North Carolina 27709-3398, United States
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3
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Mulamreddy R, Lubell WD. Constrained Glu‐Gly and Gln‐Gly dipeptide surrogates from γ‐substituted α‐amino‐δ‐lactam synthesis. Pept Sci (Hoboken) 2020. [DOI: 10.1002/pep2.24149] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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4
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Atmuri NDP, Lubell WD. Stereo- and Regiochemical Transannular Cyclization of a Common Hexahydro-1H-azonine to Afford Three Different Indolizidinone Dipeptide Mimetics. J Org Chem 2019; 85:1340-1351. [DOI: 10.1021/acs.joc.9b01861] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Affiliation(s)
- N. D. Prasad Atmuri
- Département de Chimie, Université de Montréal, P.O. Box 6128, Station Centre-ville, Montréal, Québec H3C 3J7, Canada
| | - William D. Lubell
- Département de Chimie, Université de Montréal, P.O. Box 6128, Station Centre-ville, Montréal, Québec H3C 3J7, Canada
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5
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Kuznetsov NY, Bubnov YN. Ruthenium-catalyzed intramolecular metathesis of dienes and its application in the synthesis of bridged and spiro azabicycles. RUSSIAN CHEMICAL REVIEWS 2015. [DOI: 10.1070/rcr4478] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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6
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Singh P, Samanta K, Das SK, Panda G. Amino acid chirons: a tool for asymmetric synthesis of heterocycles. Org Biomol Chem 2015; 12:6297-339. [PMID: 24989176 DOI: 10.1039/c4ob00943f] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
As a result of their easy availability in enantiomerically enriched form and their possession of synthetically transformable diverse functional groups, amino acids have been extensively used by synthetic organic and medicinal chemists as a chiral pool for access to heterocycles (monocycles, bicycles or polycycles, either bridged or fused). This review describes the syntheses of diverse asymmetric heterocycles with various membered rings (n = 3-9) followed by benzo or heteroannulated ones, for the period from 1996 to Dec. 2013. It details solution phase synthetic methodologies in which the naturally occurring α-amino acid is incorporated, totally or partially, into the final product.
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Affiliation(s)
- Priyanka Singh
- Medicinal and Process Chemistry Division, CSIR-Central Drug Research Institute, B.S. 10/1, Jankipuram Extension, Sitapur Road, Lucknow 226031, India.
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7
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Bourguet CB, Claing A, Laporte SA, Hébert TE, Chemtob S, Lubell WD. Synthesis of azabicycloalkanone amino acid and azapeptide mimics and their application as modulators of the prostaglandin F2α receptor for delaying preterm birth. CAN J CHEM 2014. [DOI: 10.1139/cjc-2014-0289] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Premature birth (<37 weeks gestation) is the major cause of perinatal mortality and morbidity and has been steadily increasing worldwide. Towards the rational design of more effective therapeutic agents for inhibiting uterine contractions and prolonging gestation (a so-called tocolytic drug), our team has targeted the prostaglandin F2α receptor (FP) employing a peptidomimetic approach designed to provide modulators of this novel target. We identified first a lead peptide (PDC113) (1) based on the sequence of the second extracellular loop of FP on the basis that the loop itself might modulate receptor activation. Systematic study of the structure−activity relationships of 1 generated hypotheses concerning the conformation and side-chains responsible for activity that led to the synthesis of PDC113.31 (2), a potent all d-amino acid peptide, which has successfully completed Phase 1b clinical trials. Employing indolizidinone amino acids, peptide mimics were developed that served to probe the mechanism of FP modulation. For example, PDC113.824 (9) was shown to allosterically regulate FP activity contingent on the presence of prostaglandin F2α by a mechanism implicating biased signalling. Although attempts to understand the turn geometry responsible for the activity of 9 by replacement of its indolizidin-2-one moiety with other azabicycloalkanones failed to produce biologically active analogs, employment of aza-aminoacyl-proline analogs resulted in a series of FP modulators exhibiting distinct effects on different G protein-mediated signalling pathways. Our program has thus contributed novel probes for understanding the chemical biology of FP as well as new therapeutic agents with promise for inhibiting uterine contractions and preventing preterm birth.
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Affiliation(s)
- Carine B. Bourguet
- Département de Chimie, Université de Montréal, C.P.6128. Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
| | - Audrey Claing
- Département de Pharmacologie, Université de Montréal, C.P.6128. Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
| | - Stéphane A. Laporte
- Department of Medicine, McGill University Health Center Research Institute, Montréal, QC H3A 1A1, Canada
| | - Terence E. Hébert
- Department of Pharmacology and Therapeutics, McGill University, Montréal, QC H3G 1Y6, Canada
| | - Sylvain Chemtob
- Centre Hospitalier Universitaire Sainte-Justine Research Center, Montréal, QC H3T 1C5, Canada
| | - William D. Lubell
- Département de Chimie, Université de Montréal, C.P.6128. Succursale Centre-Ville, Montréal, QC H3C 3J7, Canada
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8
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Khobare SR, Gajare VS, Jammula S, Syam Kumar U, Murthy Y. Diastereoselective total synthesis of 3,6-disubstituted piperidine alkaloids, (3R,6S)-epi-pseudoconhydrine and (3R,6R)-pseudoconhydrine. Tetrahedron Lett 2013. [DOI: 10.1016/j.tetlet.2013.03.051] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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9
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10
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Umezawa T, Seino T, Matsuda F. Novel One-pot Three-component Coupling Reaction with Trimethylsilylmethyl-phosphonate, Acyl Fluoride, and Aldehyde through the Horner–Wadsworth–Emmons Reaction. Org Lett 2012; 14:4206-9. [DOI: 10.1021/ol301879a] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Taiki Umezawa
- Division of Environmental Materials Science, Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Tomoya Seino
- Division of Environmental Materials Science, Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan
| | - Fuyuhiko Matsuda
- Division of Environmental Materials Science, Graduate School of Environmental Science, Hokkaido University, Sapporo 060-0810, Japan
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11
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Bourguet CB, Goupil E, Tassy D, Hou X, Thouin E, Polyak F, Hébert TE, Claing A, Laporte SA, Chemtob S, Lubell WD. Targeting the Prostaglandin F2α Receptor for Preventing Preterm Labor with Azapeptide Tocolytics. J Med Chem 2011; 54:6085-97. [DOI: 10.1021/jm200608k] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Eugénie Goupil
- Department of Medicine, McGill University Health Center Research Institute, Montréal H3A 1A1, Québec, Canada
- Department of Pharmacology and Therapeutics, McGill University, Montréal H3G 1Y6, Québec, Canada
| | | | - Xin Hou
- Centre Hospitalier Universitaire Sainte-Justine Research Center, Montréal H3T 1C5, Québec, Canada
| | | | | | - Terence E. Hébert
- Department of Pharmacology and Therapeutics, McGill University, Montréal H3G 1Y6, Québec, Canada
| | | | - Stéphane A. Laporte
- Department of Medicine, McGill University Health Center Research Institute, Montréal H3A 1A1, Québec, Canada
- Department of Pharmacology and Therapeutics, McGill University, Montréal H3G 1Y6, Québec, Canada
| | - Sylvain Chemtob
- Department of Pharmacology and Therapeutics, McGill University, Montréal H3G 1Y6, Québec, Canada
- Centre Hospitalier Universitaire Sainte-Justine Research Center, Montréal H3T 1C5, Québec, Canada
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12
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Xu HC, Moeller KD. Intramolecular anodic olefin coupling reactions: use of the reaction rate to control substrate/product selectivity. Angew Chem Int Ed Engl 2011; 49:8004-7. [PMID: 20839207 DOI: 10.1002/anie.201003924] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Hai-Chao Xu
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
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13
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Xu HC, Moeller KD. Intramolecular hydroamination of dithioketene acetals: an easy route to cyclic amino acid derivatives. Org Lett 2010; 12:5174-7. [PMID: 20945849 DOI: 10.1021/ol102193x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Catalytic intramolecular hydroamination of dithioketene acetals was developed for the synthesis of cyclic amino acid derivatives. Triggered by the addition of a catalytical amount of n-BuLi, the reaction proceeds to give proline and pipecolic acid derivatives in excellent yields and diastereoselectivity.
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Affiliation(s)
- Hai-Chao Xu
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, United States
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14
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Xu HC, Moeller KD. Intramolecular Anodic Olefin Coupling Reactions: Use of the Reaction Rate To Control Substrate/Product Selectivity. Angew Chem Int Ed Engl 2010. [DOI: 10.1002/ange.201003924] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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15
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Xu HC, Moeller KD. Intramolecular anodic olefin coupling reactions and the synthesis of cyclic amines. J Am Chem Soc 2010; 132:2839-44. [PMID: 20131795 PMCID: PMC3950632 DOI: 10.1021/ja910586v] [Citation(s) in RCA: 98] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Anodic olefin coupling reactions using a tosylamine trapping group have been studied. The cyclizations are favored by the use of a less-polar radical cation and more basic reaction conditions. The most significant factor for obtaining good yields of cyclic product is the use of the more basic reaction conditions. However, a number of factors including the nature of both the solvent and the electrolyte used can influence the yield of the cyclizations. The cyclizations allow for the rapid synthesis of both substituted proline and pipecolic acid type derivatives.
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Affiliation(s)
- Hai-Chao Xu
- Department of Chemistry, Washington University, St. Louis, Missouri 63130
| | - Kevin D. Moeller
- Department of Chemistry, Washington University, St. Louis, Missouri 63130
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16
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Pal U, Ranatunga S, Ariyarathna Y, Del Valle JR. Total Synthesis of the Putative Structure of Lucentamycin A. Org Lett 2009; 11:5298-301. [DOI: 10.1021/ol902251c] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Ujjwal Pal
- Drug Discovery Department, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, and Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
| | - Sujeewa Ranatunga
- Drug Discovery Department, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, and Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
| | - Yamuna Ariyarathna
- Drug Discovery Department, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, and Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
| | - Juan R. Del Valle
- Drug Discovery Department, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida 33612, and Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003
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17
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Abstract
During molecular recognition of proteins in biological systems, helices, reverse turns, and beta-sheets are dominant motifs. Often there are therapeutic reasons for blocking such recognition sites, and significant progress has been made by medicinal chemists in the design and synthesis of semirigid molecular scaffolds on which to display amino acid side chains. The basic premise is that preorganization of the competing ligand enhances the binding affinity and potential selectivity of the inhibitor. In this chapter, current progress in these efforts is reviewed.
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18
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Bourguet CB, Sabatino D, Lubell WD. Benzophenone semicarbazone protection strategy for synthesis of aza-glycine containing aza-peptides. Biopolymers 2008; 90:824-31. [DOI: 10.1002/bip.21103] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Piras L, Genesio E, Ghiron C, Taddei M. Scaffold Preparation and Parallel Synthesis of Arrays of 5,6,7,8-Tetrahydropyrrolo-azepinones in the Solution Phase. European J Org Chem 2008. [DOI: 10.1002/ejoc.200701024] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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20
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Kesselring D, Maurer K, Moeller KD. Building Addressable Libraries: Site-Selective Formation of an N-Acyliminium Ion Intermediate. Org Lett 2008; 10:2501-4. [DOI: 10.1021/ol8007827] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- David Kesselring
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, and CombiMatrix Corporation, 6500 Harbor Heights Parkway, Suite 301, Mukilteo, Washington 98275
| | - Karl Maurer
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, and CombiMatrix Corporation, 6500 Harbor Heights Parkway, Suite 301, Mukilteo, Washington 98275
| | - Kevin D. Moeller
- Department of Chemistry, Washington University, St. Louis, Missouri 63130, and CombiMatrix Corporation, 6500 Harbor Heights Parkway, Suite 301, Mukilteo, Washington 98275
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21
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Katritzky AR, Angrish P, Todadze E, Ghiviriga I. Expedient synthesis of N-Z-pyroglutamyl-amino acid derivatives. Bioorg Med Chem Lett 2007; 17:6000-2. [PMID: 17845849 DOI: 10.1016/j.bmcl.2007.07.052] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Revised: 07/16/2007] [Accepted: 07/17/2007] [Indexed: 11/19/2022]
Abstract
N-Z-pyroglutamyl pseudopeptides 3a-c are shown to be conveniently prepared from glutamyl-bis-Bt 1a by cyclization of an N-terminal glutamic acid residue. Structures are supported by 2D NMR studies and by comparison with the same products prepared by direct coupling of the C-terminus activated N-pGlu 1b and free amino acids 2a-c.
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Affiliation(s)
- Alan R Katritzky
- Center for Heterocyclic Compounds, Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA.
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22
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Rao MHVR, Pinyol E, Lubell WD. Rigid dipeptide mimics: synthesis of enantiopure C6-functionalized pyrrolizidinone amino acids. J Org Chem 2007; 72:736-43. [PMID: 17253788 DOI: 10.1021/jo0616761] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Enantiopure (3S,5S,6R,8S)- and (3S,5S,6S,8S)-6-hydroxypyrrolizidinone 3-N-(Boc)amino 8-methyl carboxylates (6R)- and (6S)-1 were synthesized in seven steps starting from (2S)-alpha-tert-butyl N-(PhF) aspartate beta-aldehyde (10). Carbene-catalyzed acyloin condensation of beta-aldehyde 10 followed by acetylation provided a separable mixture of diastereomeric (2S,5RS,7S)-diamino-4-oxo-5-acetoxysuberates (13). Reductive amination and lactam annulation of the respective alpha-acetoxy ketones 13 provided hydroxypyrrolizidinones (6R)- and (6S)-1 with retention of the C6-position stereochemistry. The X-ray crystallographic study of (6R)-1 indicated dihedral angles constrained within the heterocycle that were consistent with the ideal values for the i + 1 and i + 2 residues of a type II' beta-turn. Hydrogen-bonding studies on N'-methyl-N-(Boc)aminopyrrolizidin-2-one carboxamides (6R)- and (6S)-21 in DMSO-d6, demonstrated different NH chemical shift displacements and temperature coefficients for the amide and carbamate protons, indicative of solvent shielded and exposed hydrogens in a turn conformation. 6-Hydroxy pyrrolizidinone amino carboxylate 1 may thus find application as a constrained alaninylhydroxyproline dipeptide mimic. In addition, alkylation of the hydroxyl group provided orthogonally protected pyrrolizidinone amino dicarboxylate (6R)-25, demonstrating potential for expanding the diversity of these rigid dipeptide surrogates for the exploration of peptide conformation-activity relationships.
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Affiliation(s)
- Mallem H V Ramana Rao
- Départment de Chimie, Université de Montréal, C. P. 6128, Succursale Centre Ville, Montréal, Québec, Canada H3C 3J7
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23
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Kandula SRV, Kumar P. An asymmetric aminohydroxylation route to cis-2,6-disubstituted piperidine-3-ol: application to the synthesis of (−)-deoxocassine. Tetrahedron 2006. [DOI: 10.1016/j.tet.2006.08.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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24
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Royer J, Halie D, P屍ard-Viret J. Synthesis of Chiral Non Racemic Indolizidin-3-ones as Peptidomimetic Scaffold. HETEROCYCLES 2006. [DOI: 10.3987/com-06-10891] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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25
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26
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Truchot C, Wang Q, Sasaki NA. A New Diastereoselective Synthetic Approach to the Enantiopure Peptidomimetic Scaffold 2-Oxo-1-azabicyclo[4.4.0]decane. European J Org Chem 2005. [DOI: 10.1002/ejoc.200400709] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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27
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Cluzeau J, Lubell WD. Design, synthesis, and application of azabicyclo[X.Y.0]alkanone amino acids as constrained dipeptide surrogates and peptide mimics. Biopolymers 2005; 80:98-150. [PMID: 15795926 DOI: 10.1002/bip.20213] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Azabicyclo[X.Y.0]alkanone amino acids are challenging synthetic targets and useful tools for studying structure-activity relationships of native peptide ligands. They have been employed to increase potency and stability in conformationally rigid enzyme inhibitors and receptor ligands. Since last reviewed in 1997, activity in their synthesis and application has increased significantly and access is now available to a wider diversity of these peptide mimics. This review focuses on recent syntheses of these heterocyclic amino acids and their application in the investigation of biologically active peptides and peptide mimics.
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Affiliation(s)
- Jérôme Cluzeau
- Département de Chimie, Université de Montréal, Montréal H3C 3J7, Québec, Canada
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28
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Kaul R, Brouillette Y, Sajjadi Z, Hansford KA, Lubell WD. Selective tert-Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr2. J Org Chem 2004; 69:6131-3. [PMID: 15373501 DOI: 10.1021/jo0491206] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Chemoselective hydrolysis of tert-butyl esters in the presence of other acid-labile groups has been explored by employing alpha-amino esters and ZnBr(2) in DCM. Although N-Boc and N-trityl groups were found to be labile, PhF protected amines were compatible with these Lewis acid deprotection conditions such that a variety of N-(PhF)amino acids were prepared in good yields from their corresponding tert-butyl esters.
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Affiliation(s)
- Ramesh Kaul
- Département de chimie, Université de Montréal, C.P. 6128, Succursale Centre Ville, Montréal, Québec, Canada H3C 3JC
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29
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Van Cauwenberghe S, Simonin F, Cluzeau J, Becker JAJ, Lubell WD, Tourwé D. Structure-activity study of the ORL1 antagonist Ac-Arg-D-Cha-Qaa-D-Arg-D-p-ClPhe-NH2. J Med Chem 2004; 47:1864-7. [PMID: 15027881 DOI: 10.1021/jm031034v] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The structure-activity requirements of the ORL1 antagonist Ac-Arg-D-Cha-Qaa-D-Arg-D-p-ClPhe-NH(2) 4 were investigated by varying the position, structure, and charge of the Arg residues. Attempts to abridge the peptide by removal of the Arg, D-Cha, and D-p-ClPhe residues abolished affinity for the ORL1 receptor, whereas deletion of the acetamido N-terminus maintained receptor affinity and selectivity. This series of analogues has provided an improved potent and selective ORL1 receptor antagonist, Ac-Cit-D-Cha-Qaa-D-Arg-D-p-ClPhe-NH(2).
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Affiliation(s)
- Sylvia Van Cauwenberghe
- Eenheid Organische Chemie, Vrije Universiteit Brussel, 2, Pleinlaan, B-1050, Brussels, Belgium
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Blomberg D, Hedenström M, Kreye P, Sethson I, Brickmann K, Kihlberg J. Synthesis and Conformational Studies of a β-Turn Mimetic Incorporated in Leu-enkephalin. J Org Chem 2004; 69:3500-8. [PMID: 15132562 DOI: 10.1021/jo0356863] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A beta-turn mimetic in which the four amino acids of a beta-turn have been replaced by a 10-membered ring has been designed, synthesized, and subjected to conformational studies. In the mimetic, the intramolecular CO(i)-HN(i)(+3) hydrogen bond that is often found in beta-turns has been replaced by an ethylene bridge. In addition, the amide bond between residues i and i + 1 was exchanged for a methylene ether isoster. Such a beta-turn mimetic, based on the first four residues of Leu-enkephalin (Tyr-Gly-Gly-Phe-Leu), was prepared in 15 steps. The synthesis relied on a beta-azido alcohol prepared in five steps from Cbz-Tyr(tBu)-OH as a key, i-position building block. tert-Butyl bromoacetate, glycine, and a Phe-Leu dipetide were then used as building blocks for positions i + 1, i + 2, and i + 3, respectively. Conformational studies based on (1)H NMR data showed that the beta-turn mimetic was flexible, but that it resembled a type-II beta-turn at low temperature. This low energy conformer closely resembled the structure determined for crystalline Leu-enkephalin.
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Affiliation(s)
- David Blomberg
- Organic Chemistry, Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden
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Affiliation(s)
- Alessandro Dondoni
- Dipartimento di Chimica, Laboratorio di Chimica Organica,Università di Ferrara, Via L. Borsari 46, 44100 Ferrara, Italy.
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Randl S, Blechert S. Concise Enantioselective Synthesis of 3,5-Dialkyl-Substituted Indolizidine Alkaloids via Sequential Cross-Metathesis−Double-Reductive Cyclization. J Org Chem 2003; 68:8879-82. [PMID: 14604357 DOI: 10.1021/jo0346095] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
An efficient stereoselective synthesis of two 3,5-dialkyl-substituted indolizidine alkaloids is reported. The convergent syntheses are based on a novel sequence of a cross-metathesis (CM) reaction of an alpha,beta-unsaturated ketone and a chiral homoallylic amine followed by a domino reaction involving hydrogenation, N-deprotection, and two diastereoselective reductive aminations. Our concept presents one of a few examples of a highly selective CM reaction in the synthesis of a natural product.
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Affiliation(s)
- Stefan Randl
- Technische Universität Berlin, Institut für Chemie, Strasse des 17. Juni 135, D-10623 Berlin, Germany
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Abstract
Enantiopure (3S,5R,8S)-3-[N-(Boc)amino]-1-azabicyclo[3.3.0]octan-2-one 8-carboxylic acid (1) was synthesized in nine steps and 16% overall yield from aspartate beta-aldehyde 7. Carbene-catalyzed acyloin condensation of 7, followed by acetylation and samarium iodide reduction, gave linear precursor (2S,7S)-alpha,omega-diamino-4-oxosuberate 11, which was converted to N-(Boc)aminopyrrolizidin-2-one carboxylic acid 1 by a reductive amination/lactam cyclization sequence. X-ray analysis of (3S,5R,8S)-methyl N-(Boc)aminopyrrolizidin-2-one carboxylate 21 showed that its internal backbone dihedral angles (psi = -149 degrees, phi = -49 degrees ) were in good agreement with the ideal values for a type II' beta-turn. Proton NMR experiments on N'-methyl-N-(Boc)aminopyrrolizidin-2-one carboxamide 23 demonstrated significantly different NH chemical displacements and temperature coefficients suggestive of solvent shielded and exposed hydrogens indicative of a turn conformation. Because pyrrolizidinone amino acids can serve as conformationally rigid dipeptide surrogates, this synthesis should facilitate their application in the exploration of conformation-activity relationships of various biologically active peptides.
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Affiliation(s)
- Evelyne Dietrich
- Département de chimie, Université de Montréal, C. P. 6128, Succ. A, Montréal, Québec, Canada H3C 3J7
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36
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Stapon A, Li R, Townsend CA. Carbapenem biosynthesis: confirmation of stereochemical assignments and the role of CarC in the ring stereoinversion process from L-proline. J Am Chem Soc 2003; 125:8486-93. [PMID: 12848554 DOI: 10.1021/ja034248a] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
(5R)-Carbapen-2-em-3-carboxylic acid is the simplest structurally among the naturally occurring carbapenem beta-lactam antibiotics. It co-occurs with two saturated (3S,5S)- and (3S,5R)-carbapenam carboxylic acids. Confusion persists in the literature about the signs of rotation and absolute configurations of these compounds that is resolved in this paper. (3S,5S)-Carbapenam carboxylic acid was prepared from L-pyroglutamic acid to unambiguously establish its absolute configuration as identical to the natural product isolated from Serratia marcescens and from overexpression of the biosynthetic genes carAB in Escherichia coli. L-Proline labeled with deuterium or tritium at the diastereotopic C-5 methylene loci was shown to incorporate one label at the bridgehead of (3S,5S)-carbapenam carboxylic acid, but not into the "inverted" (3S,5R)-carbapenam carboxylic acid or the final carbapenem product. CarC, the third enzyme of the biosynthetic pathway required to synthesize the carbapenem, was demonstrated in cell-free studies to be dependent on alpha-ketoglutarate and ascorbate in keeping with weak sequence identities with other non-heme iron, alpha-ketoglutarate-dependent oxygenases. CarC mediated the stereoinversion of synthetic (3S,5S)-carbapenam carboxylic acid to the (5R)-carbapenem as judged by bioassay. These findings suggest that L-proline is desaturated to pyrroline-5-carboxylic acid prior to uptake into the biosynthetic pathway. The loss of the bridgehead hydrogen from the (3S,5S)-carbapenam during the ring inversion process to form the epimeric (3S,5R)-carbapenam and desaturation to the (5R)-carbapenem are proposed to be coupled by CarC to the reduction of dioxygen to drive the formation of these higher energy products, an unprecedented reaction for this enzyme class.
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Affiliation(s)
- Anthony Stapon
- Department of Chemistry, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA
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Dugave C, Demange L. Cis-trans isomerization of organic molecules and biomolecules: implications and applications. Chem Rev 2003; 103:2475-532. [PMID: 12848578 DOI: 10.1021/cr0104375] [Citation(s) in RCA: 753] [Impact Index Per Article: 35.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Affiliation(s)
- Christophe Dugave
- CEA/Saclay, Département d'Ingénierie et d'Etudes des Protéines (DIEP), Bâtiment 152, 91191 Gif-sur-Yvette, France.
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38
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Luppi G, Lanci D, Trigari V, Garavelli M, Garelli A, Tomasini C. Development and conformational analysis of a pseudoproline-containing turn mimic. J Org Chem 2003; 68:1982-93. [PMID: 12608820 DOI: 10.1021/jo026233l] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The liquid-phase synthesis and the conformational analysis of a small library of fully protected tetramers containing L-pyroglutamic acid (L-pGlu), (4S,5R)-4-methyl-5-carboxybenzyloxazolidin-2-one (L-Oxd), or (4R,5S)-4-methyl-5-carboxybenzyloxazolidin-2-one (D-Oxd) as residue i + 1 are reported to test the tendency of these oligomers to assume a -hairpin conformation. The most promising molecule is Boc-L-Val-D-Oxd-Gly-L-Ala-OBn, which assumes a preferential -turn conformation in CDCl3, as shown by IR and 1H NMR analysis. These findings have been confirmed by DFT calculations, which provide an interpretation for the available experimental data and agree with the reported observations.
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Affiliation(s)
- Gianluigi Luppi
- Dipartimento di Chimica G. Ciamician, Alma Mater Studiorum, Università di Bologna, Via Selmi 2, I-40126 Bologna, Italy
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Troin Y, Lamazzi C, Carbonnel S, Calinaud P. Synthesis of 4-Substituted Indolizidin-9-one Amino Acid Derivatives. HETEROCYCLES 2003. [DOI: 10.3987/com-03-9757] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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Mizutani N, Chiou WH, Ojima I. New and efficient synthesis of azabicyclo[4.4.0]alkane amino acids by Rh-catalyzed cyclohydrocarbonylation. Org Lett 2002; 4:4575-8. [PMID: 12489933 DOI: 10.1021/ol026782d] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[reaction: see text] Highly efficient syntheses of azabicyclo[4.4.0]alkane amino acids were achieved by Rh-catalyzed cyclohydrocarbonylation of dipeptides bearing a terminal olefin moiety and a heteroatom nucleophile.
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Affiliation(s)
- Nobuhiro Mizutani
- Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA
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Halab L, Becker JAJ, Darula Z, Tourwé D, Kieffer BL, Simonin F, Lubell WD. Probing opioid receptor interactions with azacycloalkane amino acids. Synthesis of a potent and selective ORL1 antagonist. J Med Chem 2002; 45:5353-7. [PMID: 12431062 DOI: 10.1021/jm020078l] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Azacycloalkane turn mimics 6-9 were used to explore the relationship between conformation and biological activity of peptide ligands to the opioid receptor-like (ORL1) receptor. Three azabicyclo[x.y.0]alkane amino acids and a 5-tBuPro type VI beta-turn mimic were introduced into peptides 10-13 by solid-phase synthesis on MBHA resin. Biological examination of peptides 10-13 showed two new antagonists (10 and 12) exhibiting increased selectivity for the ORL1 receptor.
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Affiliation(s)
- Liliane Halab
- Département de Chimie, Université de Montréal, C. P. 6128, Succursale Centre Ville, Montréal, Québec, Canada H3C 3J7
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42
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Simpson JC, Ho C, Shands EFB, Gershengorn MC, Marshall GR, Moeller KD. Conformationally restricted TRH analogues: constraining the pyroglutamate region. Bioorg Med Chem 2002; 10:291-302. [PMID: 11741778 DOI: 10.1016/s0968-0896(01)00287-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
A modified synthetic route has been developed so that the steric size of constraints added to the pyroglutamate region of TRH (pGluHisProNH(2)) can be varied. Both an analogue with a smaller ethylene bridge and a larger, more flexible propane bridge in this region have been synthesized. These analogues were synthesized in order to probe why the initial incorporation of an ethane bridge into this region of the molecule had led to an analogue with a binding constant and potency three times lower than that of an directly analogous unconstrained analogue. The data for both analogues indicated that the fall off in activity caused by the ethane bridge in the initial analogue was not caused by the size of the bridge.
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Affiliation(s)
- Jill C Simpson
- Department of Chemistry, Department of Molecular Biology and Pharmacology, Washington University, St. Louis, MO 63130, USA
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43
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Cluzeau J, Lubell WD. Remarkable asymmetric induction from remote stereocenters in conjugate addition chemistry for the synthesis of alkyl-branched α, ω-diaminoazelates. Isr J Chem 2001. [DOI: 10.1560/e1uk-etwj-wlmf-nha2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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44
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Duan S, Moeller KD. Building constrained peptidomimetics: a convenient approach to 3-phenyl-5-vinyl substituted proline derivatives. Tetrahedron 2001. [DOI: 10.1016/s0040-4020(01)00532-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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46
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Gosselin F, Tourwé D, Ceusters M, Meert T, Heylen L, Jurzak M, Lubell WD. Probing opioid receptor-ligand interactions by employment of indolizidin-9-one amino acid as a constrained Gly(2)-Gly(3) surrogate in a leucine-enkephalin mimic. THE JOURNAL OF PEPTIDE RESEARCH : OFFICIAL JOURNAL OF THE AMERICAN PEPTIDE SOCIETY 2001; 57:337-44. [PMID: 11328491 DOI: 10.1046/j.1397-002x.2000.00812.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The relationship between the conformation and biological activity of Leu-enkephalin was studied using (2S,6R,8S)-9-oxo-8-N-(Boc)amino-1-azabicyclo[4.3.0]nonane-2-carboxylic acid [(2S,6R,8S)-1, I(9)AA] as a constrained Gly(2)-Gly(3) dipeptide surrogate. [I(9)AA](2,3)-Leu-enkephalin 12 was assembled using solid-phase peptide synthesis on Merrifield resin with TBTU as the coupling reagent. The in vitro assays indicated that [I(9)AA](2,3)-Leu-enkephalin 12 exhibited affinities for the mu- and delta-opioid receptors that were three orders of magnitude lower than that of Leu-enkephalin, as well as partial agonist character for both receptors. In in vivo assays for spinal analgesia, the indolizidinone analog 12 showed significantly enhanced duration of action, indicating an increased metabolic stability. Conformational analysis was performed using NMR and CD spectroscopy. The amide temperature coefficients and 3J(NH-CalphaH) coupling constants for 12 could not support a hydrogen-bonded beta-turn structure; however, its CD spectrum indicated a turn conformation. Incorporation of indolizidinone amino acid 1 into Leu-enkephalin thus provided additional support for the importance of a turn conformation for the biological activity of the native peptide.
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Affiliation(s)
- F Gosselin
- Département de chimie, Université de Montréal, C. P. 6128, Succursale Center Ville, Montréal, Québec, Canada
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47
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Halab L, Gosselin F, Lubell WD. Design, synthesis, and conformational analysis of azacycloalkane amino acids as conformationally constrained probes for mimicry of peptide secondary structures. Biopolymers 2001; 55:101-22. [PMID: 11074409 DOI: 10.1002/1097-0282(2000)55:2<101::aid-bip20>3.0.co;2-o] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Conformationally constrained amino acid and dipeptide units can serve in mimics of specific secondary structures for studying relationships between peptide conformation and biological activity. A variety of mimics are required to study systematically the structure-activity relationships in biologically relevant peptides. We present our efforts on the design, synthesis, and conformational analysis of a series of rigid surrogates of amino acid and dipeptide units for application within constrained peptide analogues, and for employment as inputs for combinatorial science. Conceived to be general and versatile, our methodology has delivered a variety of azacycloalkane and azabicycloalkane amino acids in enantiomerically pure form, via practical methods, from readily available and inexpensive starting materials.
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Affiliation(s)
- L Halab
- Département de chimie, Université de Montréal, C. P. 6128, Succursale Centre Ville, Montréal, Québec, Canada H3C 3J7
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Polyak F, Lubell WD. Mimicry of peptide backbone geometry and heteroatomic side-chain functionality: synthesis of enantiopure indolizidin-2-one amino acids possessing alcohol, acid, and azide functional groups. J Org Chem 2001; 66:1171-80. [PMID: 11312944 DOI: 10.1021/jo001251t] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Indolizidinone amino acids possessing various heteroatomic side chains at their 5- and 7-positions have been synthesized through modification of hydroxymethyl indolizidinone amino acids 5 and 6. Displacements of the methanesulfonates from alcohols 5 and 6 with sodium azide, as well as oxidation of alcohol 5, have been used to furnish orthogonally protected indolizidin-2-one diamino carboxylates 7 and 8, and indolizidin-2-one amino dicarboxylate 9. Both 5- and 7-hydroxymethylindolizidinone amino acids 5 and 6 were obtained from sequences commencing with the Claisen condensation of alpha-tert-butyl gamma-methyl l-N-(PhF)-L-glutamate to furnish di-tert-butyl 4-carbomethoxy-5-oxo-2,8-di-[N-(PhF)amino]azelate 10 (PhF = 9-(9-phenylfluorenyl)). Subsequent hydride reduction of 10 to an isomeric mixture of diols 12, selective protection of the primary alcohol as tert-butyldimethylsilyl ether 14 and oxidation of the secondary alcohol gave di-tert-butyl 4-tert-butyldimethylsilyloxymethyl-5-oxo-2,8-di-[N-(PhF)amino]azelate 15 as a separable diastereomeric mixture. Linear ketone 15 and alcohol 14 were then converted to the indolizidinone heterocycles by routes featuring reductive aminations, methanesulfonate displacements, and lactam cyclizations. A series of rigid scaffolds designed to mimic the conformations of dipeptides possessing serine, lysine, and glutamate residues has thus been synthesized by this new route for installing heteroatomic side-chain functional groups onto the indolizidin-2-one system.
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Affiliation(s)
- F Polyak
- Département de Chimie, Université de Montréal, C. P. 6128, Succursale Centre Ville, Montréal, Québec, Canada H3C 3J7
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Alcaide B, Almendros P, Alonso JM, Aly MF. Rapid and stereocontrolled synthesis of racemic and optically pure highly functionalized pyrrolizidine systems via rearrangement of 1,3-dipolar cycloadducts derived from 2-azetidinone-tethered azomethine ylides. J Org Chem 2001; 66:1351-8. [PMID: 11312966 DOI: 10.1021/jo005686s] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
This work describes a convenient procedure for the straightforward preparation of polyfunctionalized enantiopure pyrrolizidine systems. The methodology capitalizes on a HCl(g)-promoted reaction of the 1,3-dipolar cycloadducts derived from 2-azetidinone-tethered azomethine ylides, smoothly affording different types of highly functionalized bi- and tricyclic systems in racemic and optically pure forms. This process involves a selective bond cleavage of the four-membered ring, followed by a rearrangement under the reaction conditions. The synthetic route employed was shown to be compatible with a variety of 4-oxoazetidine-2-carbaldehydes, alpha-amino esters, or dipolarophiles, offering a versatile entry to pyrrolizidine systems.
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Affiliation(s)
- B Alcaide
- Departamento de Química Orgánica I, Facultad de Química, Universidad Complutense, 28040 Madrid, Spain.
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