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Matamoros E, Pérez EMS, Light ME, Cintas P, Martínez RF, Palacios JC. A True Reverse Anomeric Effect Does Exist After All: A Hydrogen Bonding Stereocontrolling Effect in 2-Iminoaldoses. J Org Chem 2024; 89:7877-7898. [PMID: 38752850 PMCID: PMC11165589 DOI: 10.1021/acs.joc.4c00562] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2024] [Revised: 04/18/2024] [Accepted: 04/29/2024] [Indexed: 06/13/2024]
Abstract
The reverse anomeric effect is usually associated with the equatorial preference of nitrogen substituents at the anomeric center. Once postulated as another anomeric effect with explanations ranging from electrostatic interactions to delocalization effects, it is now firmly considered to be essentially steric in nature. Through an extensive research on aryl imines from 2-amino-2-deoxyaldoses, spanning nearly two decades, we realized that such substances often show an anomalous anomeric behavior that cannot easily be rationalized on the basis of purely steric grounds. The apparent preference, or stabilization, of the β-anomer takes place to an extent that not only neutralizes but also overcomes the normal anomeric effect. Calculations indicate that there is no stereoelectronic effect opposing the anomeric effect, resulting from the repulsion between electron lone pairs on the imine nitrogen and the endocyclic oxygen. Such data and compelling structural evidence unravel why the exoanomeric effect is largely inhibited. We are now confident, as witnessed by 2-iminoaldoses, that elimination of the exo-anomeric effect in the α-anomer is due to the formation of an intramolecular hydrogen bond between the anomeric hydroxyl and the iminic nitrogen, thereby accounting for a true electronic effect. In addition, discrete solvation may help justify the observed preference for the β-anomer.
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Affiliation(s)
- Esther Matamoros
- Departamento
de Química Orgánica e Inorgánica, Facultad de
Ciencias, and Instituto del Agua, Cambio Climático y Sostenibilidad
(IACYS), Universidad de Extremadura, 06006 Badajoz, Spain
- Departamento
de Química Orgánica, Universidad
de Málaga, Campus
Teatinos s/n, 29071 Málaga, Spain
- Instituto
de Investigación Biomédica de Málaga y Plataforma
en Nanomedicina − IBIMA, Plataforma Bionand, Parque Tecnológico de Andalucía, 29590 Málaga, Spain
| | - Esther M. S. Pérez
- Departamento
de Química Orgánica e Inorgánica, Facultad de
Ciencias, and Instituto del Agua, Cambio Climático y Sostenibilidad
(IACYS), Universidad de Extremadura, 06006 Badajoz, Spain
| | - Mark E. Light
- Department
of Chemistry, Faculty of Natural and Environmental Sciences, University of Southampton, Southampton SO17 1BJ, U.K.
| | - Pedro Cintas
- Departamento
de Química Orgánica e Inorgánica, Facultad de
Ciencias, and Instituto del Agua, Cambio Climático y Sostenibilidad
(IACYS), Universidad de Extremadura, 06006 Badajoz, Spain
| | - R. Fernando Martínez
- Departamento
de Química Orgánica e Inorgánica, Facultad de
Ciencias, and Instituto del Agua, Cambio Climático y Sostenibilidad
(IACYS), Universidad de Extremadura, 06006 Badajoz, Spain
| | - Juan C. Palacios
- Departamento
de Química Orgánica e Inorgánica, Facultad de
Ciencias, and Instituto del Agua, Cambio Climático y Sostenibilidad
(IACYS), Universidad de Extremadura, 06006 Badajoz, Spain
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Matamoros E, Light ME, Cintas P, Palacios JC. Schiff Bases and Stereocontrolled Formation of Fused 1,3-Oxazolidines from 1-Amino-2-Indanol: A Systematic Study on Structure and Mechanism. Molecules 2023; 28:molecules28041670. [PMID: 36838659 PMCID: PMC9961571 DOI: 10.3390/molecules28041670] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/13/2023] [Accepted: 01/31/2023] [Indexed: 02/12/2023] Open
Abstract
This paper thoroughly explores the formation of Schiff bases derived from salicylaldehydes and a conformationally restricted amino alcohol (1-amino-2-indanol), as well as the generation of 1,3-oxazolidines, a key heterocyclic core present in numerous bioactive compounds. We provide enough evidences, both experimental-including crystallographic analyses and DFT-based calculations on imine/enamine tautomerism in the solid state and solution. In the course of imine formation, a pentacyclic oxazolidine-oxazine structure could be isolated with complete stereocontrol, whose configuration has been determined by merging theory and experiment. Mechanistic studies reveal that, although oxazolidines can be obtained under kinetic conditions, the prevalence of imines obeys to thermodynamic control as they are the most stable structures. The stereochemical outcome of imine cyclization under acylating conditions leads to formation of 2,4-trans-oxazolidines.
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Affiliation(s)
- Esther Matamoros
- Department of Organic and Inorganic Chemistry, Faculty of Sciences and IACYS-Green Chemistry and Sustainable Development Unit, University of Extremadura, 06006 Badajoz, Spain
- Correspondence: (E.M.); (J.C.P.)
| | - Mark E. Light
- Department of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, UK
| | - Pedro Cintas
- Department of Organic and Inorganic Chemistry, Faculty of Sciences and IACYS-Green Chemistry and Sustainable Development Unit, University of Extremadura, 06006 Badajoz, Spain
| | - Juan C. Palacios
- Department of Organic and Inorganic Chemistry, Faculty of Sciences and IACYS-Green Chemistry and Sustainable Development Unit, University of Extremadura, 06006 Badajoz, Spain
- Correspondence: (E.M.); (J.C.P.)
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Matamoros E, Cintas P, Palacios JC. Amphipathic 1,3-oxazolidines from N-alkyl glucamines and benzaldehydes: stereochemical and mechanistic studies. NEW J CHEM 2021. [DOI: 10.1039/d0nj05503d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Chiral N,O-heterocycles appended to a non-reducing carbohydrate chain, which are valuable synthons, reveal further stereodynamic implications.
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Affiliation(s)
- Esther Matamoros
- Departamento de Química Orgánica e Inorgánica
- Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible
- Universidad de Extremadura
- E-06006 Badajoz
- Spain
| | - Pedro Cintas
- Departamento de Química Orgánica e Inorgánica
- Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible
- Universidad de Extremadura
- E-06006 Badajoz
- Spain
| | - Juan C. Palacios
- Departamento de Química Orgánica e Inorgánica
- Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible
- Universidad de Extremadura
- E-06006 Badajoz
- Spain
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Matamoros E, Cintas P, Light ME, Palacios JC. Electronic effects in tautomeric equilibria: the case of chiral imines from d-glucamine and 2-hydroxyacetophenones. Org Biomol Chem 2019; 17:10209-10222. [PMID: 31774417 DOI: 10.1039/c9ob02147g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A one-pot procedure for preparing a series of chiral imines by direct condensation of d-glucamine with 2-hydroxyacetophenones is described. Under conventional acetylation an unexpected mixture of two different peracetylated molecules is obtained, one with an open enamine structure, and the other incorporating an N-acetyl-1,3-oxazolidine into the acyclic skeleton. Surprisingly, both molecules coexist within the crystal's unit cell, as inferred from single-crystal X-ray analysis of a 5-bromo-substituted aryl derivative. Moreover, the 1,3-oxazolidine ring exists as rotational conformers (E,Z) owing to the restricted rotation around the N-acetyl bond. The equilibrium involving imine and enamine structures has been assessed in detail, providing in addition linear free-energy relationships between the tautomerization constants (KT) and the electronic effect of the substituents.
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Affiliation(s)
- Esther Matamoros
- Departamento de Química Orgánica e Inorgánica, Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible, Universidad de Extremadura, E-06006 Badajoz, Spain.
| | - Pedro Cintas
- Departamento de Química Orgánica e Inorgánica, Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible, Universidad de Extremadura, E-06006 Badajoz, Spain.
| | - Mark E Light
- Department of Chemistry, Faculty of Natural and Environmental Sciences, The University of Southampton, Southampton SO17 1BJ, UK
| | - Juan C Palacios
- Departamento de Química Orgánica e Inorgánica, Facultad de Ciencias, and IACYS-Unidad de Química Verde y Desarrollo Sostenible, Universidad de Extremadura, E-06006 Badajoz, Spain.
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Kuznetsov VV. Simulation of Pyramidal Inversion of Nitrogen in Tetrahydro-1,3-Oxazines in Polar Medium. J STRUCT CHEM+ 2018. [DOI: 10.1134/s0022476618060173] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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Akhmetgareev AA, Bochkor SA, Kuznetsov VV. Conformational analysis of 3-methyltetrahydro-1,3-oxazine. RUSS J GEN CHEM+ 2014. [DOI: 10.1134/s1070363214100107] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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