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Yang K, Gallazzi F, Arens C, Glaser R. Importance of Solvent-Bridged Structures of Fluorinated Diphenylalanines: Synthesis, Detailed NMR Analysis, and Rotational Profiles of Phe(2-F)-Phe(2-F), Phe(2-F)-Phe, and Phe-Phe(2-F). ACS OMEGA 2022; 7:42629-42643. [PMID: 36440139 PMCID: PMC9685757 DOI: 10.1021/acsomega.2c06351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Accepted: 11/02/2022] [Indexed: 06/16/2023]
Abstract
The crystal structure of l-phenylalanyl l-phenylalanine (Phe-Phe, FF, a.k.a. diphenylalanine) is not merely noncentrosymmetric, but it is highly dipole parallel aligned. It is for this reason that FF is a nonlinear optical (NLO) material and exhibits strong second harmonic generation (SHG). Enhancement of the SHG response by ortho fluorination was demonstrated. Crystallization is nontrivial, and learning about the zwitterion structures in solution is important for the rational improvement of the crystallization process. Here, we present an NMR study of di-fluorinated FF (Phe(2-F)-Phe(2-F)) and mono-fluorinated FF isomers (Phe(2-F)-Phe and Phe-Phe(2-F)). The dipeptides were prepared by solid-phase synthesis and purified by high-performance liquid chromatography (HPLC). Their 1H and 13C NMR spectra were recorded in partially deuterated water (10% D2O), and two-dimensional (2D) NMR techniques were employed for signal assignments. The unambiguous assignments are reported of all chemical shifts for the aliphatic H and C atoms and of the C atoms of the carboxylate, the amide carbonyl, the CF carbons, and of every arene C atom in each phenyl ring. The dipeptides are trans amides and intramolecular hydrogen bonding between the ammonium group and the amide carbonyl restricts the H3N-CH-C(O) geometry. We explored the rotational profile of the diphenylalanines as a function of the τ = ∠(C-N-C-CO2) dihedral angle at the SMD(B3LYP/6-31G*) level without and with specific hydration and report the associated Karplus curves J(θ) vs θ = ∠(H-N-C-H). The rotational profiles show a maximum of three stationary structures, and relative conformer stabilities of the free diphenylalanines show that the conformation found in the crystal M1 is the least stable among the three, M3 > M2 ≫ M1. Specific water solvation makes all of the difference and adds a large competitive advantage to the water-bridged ion pair M1a. In fact, M1a becomes the most stable and dominant conformation for the parent diphenylalanine and mono1 F-FF and M1a becomes competitive with M3c for mono2 F-FF and di F-FF. Implications are discussed regarding the importance of the conformational preorganization of diphenylalanines in solution and the facility for their crystallization.
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Affiliation(s)
- Kaidi Yang
- Department
of Chemistry, University of Missouri, Columbia, Missouri65211, United States
| | - Fabio Gallazzi
- Department
of Chemistry, University of Missouri, Columbia, Missouri65211, United States
- Molecular
Interactions Core, University of Missouri, Columbia, Missouri65211, United States
| | - Christina Arens
- Department
of Chemistry, Missouri University of Science
and Technology, Rolla, Missouri65409, United States
| | - Rainer Glaser
- Department
of Chemistry, Missouri University of Science
and Technology, Rolla, Missouri65409, United States
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Chourasiya SS, Kathuria D, Nikam SS, Ramakrishnan A, Khullar S, Mandal SK, Chakraborti AK, Bharatam PV. Azine-Hydrazone Tautomerism of Guanylhydrazones: Evidence for the Preference Toward the Azine Tautomer. J Org Chem 2016; 81:7574-7583. [PMID: 27494613 DOI: 10.1021/acs.joc.6b01258] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Guanylhydrazones have been known for a long time and have wide applications in organic synthesis, medicinal chemistry, and material science; however, little attention has been paid toward their electronic and structural properties. Quantum chemical analysis on several therapeutically important guanylhydrazones indicated that all of them prefer the azine tautomeric state (by about 3-12 kcal/mol). A set of simple and conjugated azines were designed using quantum chemical methods, whose tautomeric preference toward the azine tautomer is in the range of 3-8 kcal/mol. Twenty new azines were synthesized and isolated in their neutral state. Variable temperature NMR study suggests existence of the azine tautomer even at higher temperatures with no traces of the hydrazone tautomer. The crystal structures of two representative compounds confirmed that the title compounds prefer to exist in their azine tautomeric form.
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Affiliation(s)
- Sumit S Chourasiya
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
| | - Deepika Kathuria
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
| | - Sampada S Nikam
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
| | - Ashok Ramakrishnan
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
| | - Sadhika Khullar
- Department of Chemical Sciences, Indian Institute of Science Education and Research , Mohali Sector 81, S.A.S. Nagar 140 306, Punjab, India
| | - Sanjay K Mandal
- Department of Chemical Sciences, Indian Institute of Science Education and Research , Mohali Sector 81, S.A.S. Nagar 140 306, Punjab, India
| | - Asit K Chakraborti
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
| | - Prasad V Bharatam
- Department of Medicinal Chemistry, National Institute of Pharmaceutical Education and Research (NIPER) , Sector 67, S.A.S. Nagar 160 062, Punjab, India
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Affiliation(s)
- Kenneth M. Merz
- Quantum
Theory Project, University of Florida, 2234 New Physics Building, Gainesville, 32611 Florida, United States
- Institute for Cyber Enabled Research, Department of Chemistry,
and Department of Biochemistry and Molecular Biology, Michigan State University, 578 South Shaw Lane, East Lansing, Michigan 48824, United States
| | - Eduardo C. Aguiar
- Departamento
de Química Fundamental, Universidade Federal de Pernambuco, Recife, 54740-540 Pernambuco, Brazil
| | - Joao Bosco P. da Silva
- Departamento
de Química Fundamental, Universidade Federal de Pernambuco, Recife, 54740-540 Pernambuco, Brazil
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Kurteva VB, Lubenov LA, Antonova DV. On the mechanism of the direct acid catalyzed formation of 2,3-disubstituted imidazo[1,2-a]pyridines from 2-aminopyridines and acetophenones. Concurrence between ketimine and Ortoleva–King type reaction intermediated transformations. RSC Adv 2014. [DOI: 10.1039/c3ra45005h] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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5
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Glaser R, Ulmer L, Coyle S. Mechanistic models for LAH reductions of acetonitrile and malononitrile. Aggregation effects of Li+ and AlH3 on imide-enamide equilibria. J Org Chem 2013; 78:1113-26. [PMID: 23327108 DOI: 10.1021/jo302527k] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The results are reported of an ab initio study of the addition of LiAlH(4) to acetonitrile and malononitrile at the MP2(full)/6-311+G* level considering the effects of electron correlation at higher levels up to QCISD(T)/6-311++G(2df,2pd) and including ether solvation. All imide (RCH(2)CH═N(-)) and enamide (RCH(-)CH═NH ↔ RCH═CHN(-)H) adducts feature strong interactions between the organic anion and both Li(+) and AlH(3). The relative stabilities of the tautomeric LAH adducts are compared to the tautomer preference energies of the LiH adducts and of the hydride adducts of the nitriles. Alane affinities were determined for the lithium ion pairs formed by LiH addition to the nitriles. The results show that alane binding greatly affects the imide-enamide equilibria and that alane complexation might even provide a thermodynamic preference for the imide intermediate. While lithium enamides of malononitrile are much more stable than lithium imides, alane binding dramatically reduces the enamide preference so that both tautomers are present at equilibrium. Implications are discussed regarding to the propensity for multiple hydride reductions and with regard to the mechanism of reductive nitrile dimerization. A detailed mechanism is proposed for the formation of 2-aminonicotinonitrile (2ANN) in the LAH reduction of malononitrile.
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Affiliation(s)
- Rainer Glaser
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, USA.
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Coyle S, Glaser R. Asymmetric Imine N-Inversion in 3-Methyl-4-pyrimidinimine. Molecular Dipole Analysis of Solvation Effects. J Org Chem 2011; 76:3987-96. [DOI: 10.1021/jo200411f] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Affiliation(s)
- Stephanie Coyle
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
| | - Rainer Glaser
- Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
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Huang C, Yan SJ, Zeng XH, Dai XY, Zhang Y, Qing C, Lin J. Biological evaluation of polyhalo 1,3-diazaheterocycle fused isoquinolin-1(2H)-imine derivatives. Eur J Med Chem 2011; 46:1172-80. [DOI: 10.1016/j.ejmech.2011.01.036] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2010] [Revised: 10/07/2010] [Accepted: 01/24/2011] [Indexed: 10/18/2022]
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