Roberto R. Gil

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Name: Gil, Roberto R.

Organization: Carnegie Mellon University , USA

Department: Department of Chemistry

Title: Professor(PhD)

TOPICS

Organic Chemistry

Diels Alder Reaction

Chemicals
References

Di(ethylene glycol) methyl ether methacrylate (DEGMEMA)-derived gels align small organic molecules in methanol

Co-reporter:

Magnetic Resonance in Chemistry 2017 Volume 55(Issue 3) pp:206-209

Publication Date(Web):2017/03/01

DOI:10.1002/mrc.4400

Residual dipolar couplings (RDCs) constitute an important NMR parameter for structural elucidation in all areas of chemistry. In this study, di(ethylene glycol) methyl ether methacrylate (DEGMEMA)-based gels are introduced as alignment media for the measurement of RDCs of small organic molecules in polar solvents such as methanol. The low viscosity of methanol permits the execution of J-scaled BIRD HSQC experiments that yield very sharp lines in anisotropic conditions. The gels have excellent mechanical properties, and their compression and expansion in the swollen state can be reversed and performed multiple times. This process enables the easy loading and release of analytes. The excellent performance of these new aligning gels is demonstrated by analyzing the structure of the alkaloid retrorsine. Copyright © 2016 John Wiley & Sons, Ltd.

Collection of NMR Scalar and Residual Dipolar Couplings Using a Single Experiment

Co-reporter:Lero F. Gil-Silva;Raquel Santamaría-Fernández;Dr. Armo Navarro-Vázquez; Roberto R. Gil

Chemistry - A European Journal 2016 Volume 22( Issue 2) pp:472-476

Publication Date(Web):

DOI:10.1002/chem.201503449

Abstract

A new DMSO-compatible aligning gel based on cross-linked poly(2-hydroxylethyl methacrylate) (poly-HEMA) has been developed. Due to a significant difference in bulk magnetic susceptibility between the DMSO inside and outside the gel, it is possible to simultaneously collect isotropic and anisotropic NMR data, such as residual dipolar couplings (RDC), in the same NMR tube. RDC-assisted structural analysis of menthol and the alkaloid retrorsine is reported as proof of concept.

One-Shot Determination of Residual Dipolar Couplings: Application to the Structural Discrimination of Small Molecules Containing Multiple Stereocenters

Co-reporter:Laura Castañar, Manuela Garcia, Erich Hellemann, Pau Nolis, Roberto R. Gil, and Teodor Parella

The Journal of Organic Chemistry 2016 Volume 81(Issue 22) pp:11126-11131

Publication Date(Web):October 6, 2016

DOI:10.1021/acs.joc.6b02103

A novel approach for the fast and efficient structural discrimination of molecules containing multiple stereochemical centers is described. A robust J-resolved HSQC experiment affording highly resolved 1JCH/1TCH splittings along the indirect dimension and homodecoupled 1H signals in the detected dimension is proposed. The experiment enables in situ distinction of both isotropic and anisotropic components of molecules dissolved in compressed PMMA gels, allowing a rapid and direct one-shot determination of accurate residual dipolar coupling constants from a single NMR spectrum.

Frontispiece: Collection of NMR Scalar and Residual Dipolar Couplings Using a Single Experiment

Co-reporter:Lero F. Gil-Silva;Raquel Santamaría-Fernández;Dr. Armo Navarro-Vázquez; Roberto R. Gil

Chemistry - A European Journal 2016 Volume 22( Issue 2) pp:

Publication Date(Web):

DOI:10.1002/chem.201680261

Stability and Reactivity of 1,3-Benzothiaphosphole: Metalation and Diels–Alder Chemistry

Co-reporter:Joshua C. Worch, Erich Hellemann, Gabrielle Pros, Chakicherla Gayathri, Tomislav Pintauer, Roberto R. Gil, and Kevin J. T. Noonan

Organometallics 2015 Volume 34(Issue 22) pp:5366-5373

Publication Date(Web):September 8, 2015

DOI:10.1021/acs.organomet.5b00583

The synthesis and functionalization of the parent 1,3-benzothiaphosphole is reported. The phosphole could not be isolated, but the compound could be manipulated in solution to produce several new phosphorus compounds. Metalation of the 2-position using lithium diisopropylamide proceeded smoothly according to 31P NMR spectroscopy, and quenching with trimethylsilyl chloride resulted in the desired 2-(trimethylsilyl)-1,3-benzothiaphosphole. The P═C bond of the thiaphosphole was also explored as a dienophile in Diels–Alder reactions with isoprene, 2,3-dimethylbutadiene, 2,3-dibenzylbutadiene, and cyclopentadiene. The fused-ring structures were fully characterized, and a solid-state molecular structure of the 2,3-dimethylbutadiene cycloadduct was obtained. Residual dipolar coupling (RDC) NMR experiments were used to assign major and minor products for the isoprene and cyclopentadiene adducts.

Self-Sensitized Photooxygenation of 2H-Pyrans: Characterization of Unexpected Products Assisted by Computed Structural Elucidation and Residual Dipolar Couplings

Co-reporter:Martín J. Riveira, Pablo Trigo-Mouriño, Eduardo Troche-Pesqueira, Gary E. Martin, Armando Navarro-Vázquez, Mirta P. Mischne, and Roberto R. Gil

The Journal of Organic Chemistry 2015 Volume 80(Issue 15) pp:7396-7402

Publication Date(Web):June 10, 2015

DOI:10.1021/acs.joc.5b00817

The UVA (350 nm) irradiation of an α-pyran in the presence of oxygen led to the unexpected formation of a tetraoxygenated compound whose structure could not be unambiguously determined on the basis of conventional 1H–13C correlated experiments. 1,1-ADEQUATE (adequate double quantum transfer experiment) and 1,n-ADEQUATE combined with computer-assisted structure elucidation software led to two structural possibilities involving the formation of either an epoxide or an oxetane. Residual dipolar couplings allowed not only the identification of the compound as a spiroepoxide but also the determination of its relative configuration. To account for its formation, we propose a bisepoxide intermediate that, as opposed to most α,β-epoxyketones under irradiation, undergoes O–Cβ cleavage probably due to the presence of an extra oxygen substituent in the β position. 1,2-Acyl migration would then proceed stereoselectively to the final product obtained as a single diastereomer.

Probing Spatial Distribution of Alignment by Deuterium NMR Imaging

Co-reporter:Pablo Trigo-Mouriño;Christian Merle;Martin R. M. Koos; Burkhard Luy; Roberto R. Gil

Chemistry - A European Journal 2013 Volume 19( Issue 22) pp:7013-7019

Publication Date(Web):

DOI:10.1002/chem.201300254

Abstract

Deuterium NMR imaging was used to evaluate the spatial distribution of the degree of alignment in different types of alignment media by monitoring the deuterium quadrupolar splitting using spatially resolved NMR techniques in conventional liquid state NMR instruments. These images allow the unambiguous distinction of magnetic field and alignment inhomogeneities present in partially aligned samples, revealing the underlying reasons for linebroadening within an alignment medium that cannot be explained by the sole analysis of 1D ²H NMR spectra. For example, alignment inhomogeneities due to broken gels or the presence of concentration gradients in liquid crystalline solutions are clearly detected by the imaging methods proposed in this work.

New strategy for RDC-assisted diastereotopic proton assignment using a combination of J-scaled BIRD HSQC and J-scaled BIRD HMQC/HSQC

Co-reporter:Jonathan D. Snider;Eduardo Troche-Pesqueira;Shannon R. Woodruff;Chakicherla Gayathri;Nicolay V. Tsarevsky

Magnetic Resonance in Chemistry 2012 Volume 50( Issue Supplement S1) pp:S86-S91

Publication Date(Web):

DOI:10.1002/mrc.3895

A new strategy to assign diastereotopic protons was developed on the basis of residual dipolar couplings (RDCs) collected in compressed poly(methyl methacrylate) (PMMA) gels. A combination of 2D J-scaled BIRD HSQC and J-scaled BIRD HMQC/HSQC NMR experiments was used to collect the RDC data. In the proposed strategy, the first experiment is used to measure ¹D_CH for methine groups, the sum of ¹D_CHa + ¹D_CHb for methylene groups and the average ¹D_CH3 value for methyl groups. In turn, the small molecule alignment tensor is calculated using these D values without the a priori assignment of CH₂ diastereotopic protons. The D values of each individual CH bond (CHa and CHb) of each methylene group in the molecule are then predicted using the calculated alignment tensor and these values compared with the results from the HMQC/HSQC experiment, leading to their unambiguous assignment. This strategy is demonstrated with the alkaloid strychnine that contains five methylene groups with diastereotopic protons, and our results fully agree with the previously reported assignment using combinations of permutated assignments. Copyright © 2012 John Wiley & Sons, Ltd.

MRC special issue on NMR of small molecules in anisotropic media

Co-reporter:Roberto R. Gil

Magnetic Resonance in Chemistry 2012 Volume 50( Issue Supplement S1) pp:

Publication Date(Web):

DOI:10.1002/mrc.3910

No abstract is available for this article.

Unprecedented stereoselective synthesis of cyclopenta[b]benzofuran derivatives and their characterisation assisted by aligned media NMR and 13C chemical shift ab initio predictions

Co-reporter:Martín J. Riveira, Chakicherla Gayathri, Armando Navarro-Vázquez, Nicolay V. Tsarevsky, Roberto R. Gil and Mirta P. Mischne

Organic & Biomolecular Chemistry 2011 vol. 9(Issue 9) pp:3170-3175

Publication Date(Web):01 Feb 2011

DOI:10.1039/C1OB05109A

A new approach to the synthesis of cyclopenta[b]benzofuran derivatives via reaction of 1,3-dicarbonyl compounds with α,β,γ,δ-unsaturated aldehydes is described. The constitution and configuration of the new products have been firmly established by means of residual dipolar couplings (RDCs) and ab initio13C NMR chemical shift predictions.

Constitutional, Configurational, and Conformational Analysis of Small Organic Molecules on the Basis of NMR Residual Dipolar Couplings

Co-reporter: Roberto R. Gil

Angewandte Chemie International Edition 2011 Volume 50( Issue 32) pp:7222-7224

Publication Date(Web):

DOI:10.1002/anie.201101561

Structural Discrimination in Small Molecules by Accurate Measurement of Long-Range ProtonCarbon NMR Residual Dipolar Couplings

Co-reporter:Pablo Trigo-Mouriño;Armo Navarro-Vázquez;Jinfa Ying;Ad Bax

Angewandte Chemie International Edition 2011 Volume 50( Issue 33) pp:7576-7580

Publication Date(Web):

DOI:10.1002/anie.201101739

Konstitutions-, Konfigurations- und Konformationsanalyse niedermolekularer organischer Verbindungen auf der Grundlage von dipolaren Restkopplungen

Co-reporter: Roberto R. Gil

Angewandte Chemie 2011 Volume 123( Issue 32) pp:7360-7362

Publication Date(Web):

DOI:10.1002/ange.201101561

Structural Discrimination in Small Molecules by Accurate Measurement of Long-Range ProtonCarbon NMR Residual Dipolar Couplings

Co-reporter:Pablo Trigo-Mouriño;Armo Navarro-Vázquez;Jinfa Ying;Ad Bax

Angewandte Chemie 2011 Volume 123( Issue 33) pp:7718-7722

Publication Date(Web):

DOI:10.1002/ange.201101739

Chirality in Gold Nanoclusters Probed by NMR Spectroscopy

Co-reporter:Huifeng Qian, Manzhou Zhu, Chakicherla Gayathri, Roberto R. Gil, and Rongchao Jin

ACS Nano 2011 Volume 5(Issue 11) pp:8935

Publication Date(Web):October 7, 2011

DOI:10.1021/nn203113j

We report the analysis of chirality in atomically precise gold nanoclusters by nuclear magnetic resonance (NMR) spectroscopic probing of the surface ligands. The Au38(SR)24 and Au25(SR)18 (where, R = CH2CH2Ph) are used as representative models for chiral and nonchiral nanoclusters, respectively. Interestingly, different 1H signals for the two germinal protons in each CH2 of the ligands on the chiral Au38(SR)24 nanocluster were observed, so-called diastereotopicity. For α-CH2 (closest to the chiral metal core), a chemical shift difference of up to ∼0.8 ppm was observed. As for the nonchiral Au25(SCH2CH2Ph)18–TOA+ nanocluster, no diastereotopicity was detected (i.e., no chemical shift difference for the two protons in the CH2), confirming the Au25 core being nonchiral. These two typical examples demonstrate that NMR spectroscopy can be a useful tool for investigating chirality in Au nanoclusters. Since the diastereotopicity induced on the methylene protons by chiral nanoclusters is independent of the enantiomeric composition of the chiral particles, NMR can probe the chirality of the nanoclusters even in the case of a racemic mixture, while circular dichroism spectroscopy is not useful for racemic mixtures.Keywords: chirality; diastereotopicity; gold nanoclusters; NMR

Probing heterocycle conformation with residual dipolar couplings

Co-reporter:Chakicherla Gayathri, M. Carmen de la Fuente, Burkhard Luy, Roberto R. Gil and Armando Navarro-Vázquez

Chemical Communications 2010 vol. 46(Issue 32) pp:5879-5881

Publication Date(Web):13 Jul 2010

DOI:10.1039/C0CC01271H

Residual dipolar couplings (RDCs) obtained in a stretched polydimethylsiloxane gel are applied to determine the 7-membered ring conformation in a 2-phenyl-3-benzazepine derivative, and to simultaneously assign all methylene proton pairs using only 1DCH RDCs and DFT molecular modelling data.

The structure of a γ-modified peptide nucleic acid duplex

Co-reporter:Wei He, Matthew J. Crawford, Srinivas Rapireddy, Marcela Madrid, Roberto R. Gil, Danith H. Ly and Catalina Achim

Molecular BioSystems 2010 vol. 6(Issue 9) pp:1619-1629

Publication Date(Web):13 Apr 2010

DOI:10.1039/C002254C

This paper presents the results of an NMR spectroscopy and distance-restrained molecular dynamics (MD) study of a γ-methylated, palindromic, 8-base pair peptide nucleic acid (γ-PNA) duplex. The goal of this study was to examine the impact of the γ-backbone modification on the structure of the PNA duplex. The 2D NMR information involving the backbone methyl group, especially the NOEs between the methyl protons and those of the amide and methylene groups of the backbone, led to distance restraints useful in the elucidation of the structure of the backbone of γ-PNA. Integration of the NOE peaks resulted in 138 inter-proton distance restraints, which were used in ten independent simulated annealing followed by 2 ns restrained MD runs. These simulations led to the conclusion that the γ-PNA duplex adopts a general P-form helical structure similar to that observed for non-modified PNA but with a smaller base pair rise, which is an A-like helical feature, and a slight helical bending towards the major groove (PDB ID 2KVJ). These properties of the γ-PNA duplex may be induced by the γ-methyl group. A similar effect of the methyl group was revealed by a previous NMR study of single stranded γ-PNA [A. Dragulescu-Andrasi, S. Rapireddy, B. M. Frezza, C. Gayathri, R. R. Gil and D. H. Ly, J. Am. Chem. Soc., 2006, 128, 10258–10267]. It appears that the steric constraint exerted by the γ-methyl on the backbone orientation is relatively independent of the base pairing and stacking and thus is likely to manifest when other substituents are introduced at the γ-position of the PNA.

Residual Dipolar Couplings (RDCs) Analysis of Small Molecules Made Easy: Fast and Tuneable Alignment by Reversible Compression/Relaxation of Reusable PMMA Gels

Co-reporter:Chakicherla Gayathri Dr.;NicolayV. Tsarevsky Dr.;RobertoR. Gil

Chemistry - A European Journal 2010 Volume 16( Issue 12) pp:3622-3626

Publication Date(Web):

DOI:10.1002/chem.200903378

Stereochemistry Determination by Powder X-Ray Diffraction Analysis and NMR Spectroscopy Residual Dipolar Couplings

Co-reporter:ManuelaE. García;Silvina Pagola Dr.;Armo Navarro-Vázquez Dr.;DamilolaD. Phillips;Chakicherla Gayathri Dr.;Henry Krakauer ;PeterW. Stephens ;VivianaE. Nicotra Dr.;RobertoR. Gil

Angewandte Chemie International Edition 2009 Volume 48( Issue 31) pp:5670-5674

Publication Date(Web):

DOI:10.1002/anie.200900760

Modified secoiridoid from Acicarpha tribuloides and inhibition of nitric oxide production in LPS-activated macrophages

Co-reporter:Tamara L. Meragelman, Beatriz Salido Renteria, Gloria L. Silva, Claudia Sotomayor, Roberto R. Gil

Phytochemistry 2006 Volume 67(Issue 14) pp:1534-1538

Publication Date(Web):July 2006

DOI:10.1016/j.phytochem.2006.05.014

Bioassay-guided fractionation of Acicarpha tribuloides Juss. resulted in the isolation of an uncommon non-glycosylated secoiridoid, tribulolide (1), two known secoiridoid glycosides named secologanic acid (2) and vogeloside (3) as well as two natural chromones, 6,7-dimethoxychromone (4) and 7-hydroxy-6-methoxy-chromone (5). Compounds 1–3 showed inhibition of nitric oxide production in lipopolysaccharide-activated macrophages; their activity is comparable to that of aminoguanidine, a classic inhibitor.The search for nitric oxide inhibitors from Acicarpha tribuloides Juss. resulted in the isolation of an uncommon non-glycosylated secoiridoid, tribulolide (1), as well as two natural chromones together with two known secoiridoid glycosides. The secoiridoids showed inhibition of NO production in lipopolysaccharide-activated macrophages with activity comparable to aminoguanidine, a classic inhibitor.

Diterpenes from Stevia gilliesii

Co-reporter:Tamara L. Meragelman, Diego S. Pedrosa, Roberto R. Gil

Biochemical Systematics and Ecology 2004 Volume 32(Issue 1) pp:45-53

Publication Date(Web):January 2004

DOI:10.1016/S0305-1978(03)00178-9

Three new and one known diterpenes were isolated from a chloroform extract of Stevia gilliesii Hook and Arn. One of them possesses the rare halimane skeleton. The structure of the new compounds was determined using a combination of modern spectroscopic techniques, including 2D NMR experiments and molecular modeling.

Probing heterocycle conformation with residual dipolar couplings

Co-reporter:Chakicherla Gayathri, M. Carmen de la Fuente, Burkhard Luy, Roberto R. Gil and Armando Navarro-Vázquez

Chemical Communications 2010 - vol. 46(Issue 32) pp:NaN5881-5881

Publication Date(Web):2010/07/13

DOI:10.1039/C0CC01271H

Unprecedented stereoselective synthesis of cyclopenta[b]benzofuran derivatives and their characterisation assisted by aligned media NMR and 13C chemical shift ab initio predictions

Co-reporter:Martín J. Riveira, Chakicherla Gayathri, Armando Navarro-Vázquez, Nicolay V. Tsarevsky, Roberto R. Gil and Mirta P. Mischne

Organic & Biomolecular Chemistry 2011 - vol. 9(Issue 9) pp:NaN3175-3175

Publication Date(Web):2011/02/01

DOI:10.1039/C1OB05109A