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Sexual Assault by NMR

Direct Monitoring of Exogenous γ‑Hydroxybutyric Acid in Body Fluids by NMR Spectroscopy
M. Palomino-Schätzlein, Y. Wang, A. D. Brailsford, T. Parella, D. A. Cowan, C. Legido-Quigley, and M. Pérez-Trujillo

Analytical Chemistry,
89, 8343 (2017). DOI

γ-Hydroxybutyric acid (GHB) is a popular drug increasingly associated with cases of drug-facilitated sexual assault (DFSA). Currently, expanding procedures of analysis
and having forensic evidence of GHB intake in a long term are mandatory. Up to now, most studies have been performed using GC/MS and LC-MS as analytical platforms, which involve significant manipulation of the sample and, often, indirect measurements. In this work, procedures used in NMR-based metabolomics were applied to a GHB clinical trial on urine and serum. Detection, identification, and quantification of the drug by NMR methods were surveyed, as well as the use of NMR-based metabolomics for the search of potential surrogate biomarkers of GHB consumption. Results demonstrated the suitability of NMR spectroscopy, as a robust nondestructive technique, to fast and directly monitor (detect, identify, and quantify) exogenous GHB in almost intact body fluids and its high potential in the search for metabolites associated with GHB intake. 

NMR Profiling
1JCH NMR Profile: Identification of Key Structural Features and Functionalities by Visual Observation and Direct Measurement of One-Bond Proton-Carbon Coupling Constants
N. Marcó, A.A. Souza, P. Nolis, C. Cobas, R.R. Gil and T. Parella

J. Org. Chem, 82, 2040-2044 (2017). DOI
A user-friendly NMR interface for the visual and accurate determination of experimental one-bond proton-carbon coupling constants (1JCH) in small molecules is presented. This intuitive 1JCH profile correlates directly to δ(1H), and 1JCH facilitates the rapid identification and assignment of 1H signals belonging to key structural elements and functional groups. Illustrative examples are provided for some target molecules, including terminal alkynes, strained rings, electronegative substituents, or lone-pair-bearing heteronuclei.

Book Chapter: Small Molecule NMR
Current Pulse Sequence Developments in Small-molecule Nuclear Magnetic Resonance Spectroscopy 
T. Parella

Modern NMR Approaches to the Structure Elucidation of Natural Products : Volume 2: Data Acquisition and Applications to Compound Classes 

Vol. 2, 199-250 (2017). DOI
The current developments in the design and the application of modern nuclear magnetic resonance (NMR) pulse sequences in small molecules are overviewed. The concepts of fast NMR, pure-shift NMR, perfect NMR and ultra-long-range correlation NMR are described and illustrated with examples.

Pure Shift NMR Covariance
Access to experimentally infeasible spectra by pure-shift NMR Covariance
A. Fredi, P. Nolis, C. Cobas and T. Parella

J. Magn. Reson, 270, 161-168 (2016). DOI

Covariance processing is a versatile processing tool to generate synthetic NMR spectral representations without the need to acquire time-consuming experimental datasets. Calculation of experimentally infeasible pure-shift NMR spectra can now be performed using the concept of pure shift NMR covariance.
Challenging Structure Elucidation
Homodecoupled 1,1- and 1,n-ADEQUATE: Pivotal NMR Experiments for the Structure Revision of Cryptospirolepine
J. Saurí., W. Bermel, A.V. Buevich, E.C. Sherer, L.A. Joyce, M.H.M. Sharaf, P.L. Schiff Jr., T. Parella, R.T. Williamson and G.E. Martin

Angew. Chem. Intl. Ed., 54, 10160-10164 (2015). DOI
Cryptospirolepine is the most structurally complex alkaloid discovered and characterized thus far from any Cryptolepis specie. Characterization of several degradants of the original, sealed NMR sample a decade after the initial report called the validity of the originally proposed structure in question. We now report the development of improved, homodecoupled variants of the 1,1- and 1,n-ADEQUATE (HD-ADEQUATE) NMR experiments; utilization of these techniques was critical to successfully resolving long-standing structural questions associated with crytospirolepine.

Pure Shift NMR
Broadband 1H homodecoupled NMR experiments: Recent developments, methods and applications
L. Castañar and T. Parella

Magn. Reson. Chem., 53, 399-426  (2015). DOI
This review aims at presenting the most recent advances in pure shift NMR spectroscopy, with a particular emphasis to the Zangger-Sterk experiment. A detailed discussion about the most relevant practical aspects in terms of pulse sequence design, selectivity, sensitivity, spectral resolution and performance is provided. Finally, the implementation of the different reported strategies into traditional 1D and 2D NMR experiments is described while several practical applications are also reviewed.

TOCSY on quaternary carbons
Extending long-range heteronuclear NMR connectivities by HSQMBC-COSY and HSQMBC-TOCSY experiments

J. Saurí, N. Marcó, R.T Williamson, G.E Martin and T. Parella

J. Magn. Reson., 258, 25-32 (2015).DOI

The detection of long-range heteronuclear correlations presenting J(CH) coupling values smaller than 1–2 Hz is a challenge in the structural analysis of small molecules and natural products. HSQMBC-COSY and HSQMBC-TOCSY pulse schemes are evaluated as complementary NMR methods to standard HMBC/HSQMBC experiments. Incorporation of an additional J(HH) transfer step in the basic HSQMBC pulse scheme can favor the sensitive observation of traditionally missing or very weak correlations and, in addition, facilitates the detection of a significant number of still longer-range connectivities to both protonated and non-protonated carbons under optimum sensitivity conditions..

Implementing multiplicity editing in selective HSQMBC experiments
J. Saurí, E. Sistaré, R.T Williamson, G.E Martin and T. Parella

J. Magn. Reson., 252, 170-175 (2015). DOI

Even C/CH2 and odd CH/CH3 carbon-multiplicity information can be directly distinguished from the relative positive/negative phase of cross-peaks in a novel ME(Multiplicity-Edited)-selHSQMBC experiment. The method can be extended by a TOCSY propagation step, and it is fully compatible for the simultaneous and precise determination of long-range heteronuclear coupling constants. Broadband homonuclear decoupling techniques can also be incorporated to enhance sensitivity and signal resolution by effective collapse of J(HH) multiplets.

Optimized polarization build-up times in dissolution DNP-NMR using a benzyl amino derivative of BDPA

J. L. Muñoz-Gómez, E. Monteagudo, V. Lloveras, T. Parella, J. Veciana and J. Vidal-Gancedo

RSC Advances,
6, 27077-27082 (2016).

The synthesis of two novel BDPA-like radicals, a benzyl amino (BAm-BDPA, 7) and a cyano (CN-BDPA, 5) derivative, is reported and their behaviour as polarizing agents for fast dissolution Dynamic Nuclear Polarization (DNP) is evaluated. The radical 7 is a promising candidate for DNP studies since it is soluble in neat [1-13C]pyruvic acid (PA), and therefore the use of an additional glassing agent for sample homogeneity is avoided. In addition, a 60 mM sample of 7 offers optimum 13C NMR signal enhancements using fairly short polarization times (about 1800 s). It is shown that DNP-NMR measurements using 7 can be performed much more efficiently in terms of the signal enhancement per polarization build-up time unit than when using the reference OX63 or BDPA radicals. These enhanced features are translated to a substantial reduction of polarization times that represents an optimum temporary use of the DNP polarizer and allow economized liquid helium consumption.

Perfect NMR
Suppression of phase and amplitude J(HH) modulations in HSQC experiments
L. Castañar, E. Sistaré, A. Virgili, R.T. Williamson and T. Parella

Magn. Reson. Chem,, 53, 115 (2015). DOI

The amplitude and the phase of cross peaks in conventional 2D HSQC experiments are modulated by both proton–proton, J(HH), and proton–carbon, 1J(CH), coupling constants. It is shown by spectral simulation and experimentally that J(HH) interferences are suppressed in a novel perfect-HSQC pulse scheme that incorporates perfect-echo INEPT periods. The improved 2D spectra afford pure in-phase cross peaks with respect to 1J(CH) and J(HH), irrespective of the experiment delay optimization. In addition, peak volumes are not attenuated by the influence of J(HH), rendering practical issues such as phase correction, multiplet analysis, and signal integration more appropriate.

Three catalan guys from Santa Coloma de Farners (Girona) publishing together in Chemical Science and drinking ratafia...
Cross-Coupling using Gold
Au(III)-aryl intermediates in oxidant-free C-N and C-O cross-coupling catalysis
J. Serra, T. Parella and X. Ribas

Chemical Science,
 8, 946-952 (2017). DOI

Au(III)-aryl species have been unequivocally identified as reactive intermediates in oxidant-free C–O and C–N cross coupling catalysis. The structures of cyclometalated neutral and cationic Au(III) species are described and their key role in 2 electron-redox Au(I)/Au(III) catalysis in C–O and C–N cross couplings is shown. Nucleophiles compatible with Au-catalyzed cross couplings include aromatic and aliphatic alcohols and amines, as well as water and amides. More info here...

Hyperpolarized Chiral Recognition
Chiral Recognition by Dissolution DNP NMR Spectroscopy of 13C-Labeled dl-Methionine

E. Monteagudo, A. Virgili,
T. Parella and M. Pérez-Trujillo

Analytical Chemistry,
89, 4939-4944 (2017).

A method based on d-DNP NMR spectroscopy to study chiral recognition is described for the first time. The enantiodifferentiation of a racemic metabolite in a millimolar aqueous solution using a chiral solvating agent was performed. Hyperpolarized 13C-labeled dl-methionine enantiomers were differently observed with a single-scan 13C NMR experiment, while the chiral auxiliary at thermal equilibrium remained unobserved. The method developed entails a step forward in the chiral recognition of small molecules by NMR spectroscopy, opening new possibilities in situations where the sensitivity is limited, for example, when a low concentration of analyte is available or when the measurement of an insensitive nucleus, like 13C, is required. The advantages and current limitations of the method, as well as future perspectives, are discussed. 

Cobalt-catalyzed annulation 
Isolation of Key Organometallic Aryl-Co(III) Intermediates in Cobalt- Catalyzed C(sp2)−H Functionalizations and New Insights into Alkyne Annulation Reaction Mechanismse
O. Planas, C. J. Whiteoak, V. Martin-Diaconescu, I. Gamba, J. M. Luis, T. Parella, A. Company and X. Ribas

J. Am. Chem. Soc. 138, 14388-14397 (2016). DOI,
The selective annulation reaction of alkynes with substrates containing inert C−H bonds using cobalt as catalyst is currently a topic attracting significant interest. Herein, we describe a rare example of the preparation and characterization of benchtop-stable organometallic aryl-Co(III) compounds (NMR, HRMS, XAS, and XRD) prepared through a C(sp2)−H activation, using a model macrocyclic arene substrate. Subsequent insights obtained from the application of our new organometallic aryl-Co(III) compounds in alkyne annulation reactions are also disclosed. Evidence obtained from the resulting regioselectivity of the annulation reactions and DFT studies indicates that a mechanism involving an organometallic aryl-Co(III)-alkynyl intermediate species is preferred for terminal alkynes, in contrast to the generally accepted migratory insertion pathway.

Engineered biocatalysis
Asymmetric assembly of formaldehyde and glycolaldehyde into aldose carbohydrates by tandem biocatalytic aldol reactions
A. Szekrenyi, X. Garrabou, T. Parella, J. Joglar, J. Bujons and P. Clapés

Nature Chemistry,
7, 724-729 (2015). DOI
The preparation of multifunctional chiral molecules can be largely simplified by a sequential catalytic assembly of achiral building blocks. In the bottom-up synthesis of aldose sugars, biomimetic routes starting from simple substrates result inconveniently complex, requiring multiple enzymes and cofactors that hamper the efficiency of the process. Pursuing a simpler and more expedient enzymatic approach, we used engineered variants of the D-fructose-6-phosphate aldolase from E. coli (FSA) to prepare a stereochemically consistent series of three to six-carbon aldoses by sequential addition of formaldehyde and glycolaldehyde. The stereochemical outcome of the addition was also altered to allow the one-pot synthesis of L-glucose and derivatives.

Supramolecular Metallocage
Enantioselective hydroformylation by a Rh catalyst entrapped in a supramolecular metallocage
C. García-Simón, R. Gramage-Doria, S. Raoufmoghaddam, T. Parella, M. Costas, X. Ribas and J N. H. Reek

J. Am. Chem. Soc.,
137, 2680-2687 (2015). DOI
Regio and enantioselective hydroformylation of styrenes is described upon embedding a chiral Rh complex in a non-chiral supramolecular cage formed from coordination-driven self assembly of macrocyclic dipalladium complexes and tetracarboxylate zinc porphyrins. The supramolecular catalyst that results converts styrene derivatives into aldehyde products with much higher chiral induction in comparison to the non-encapsulated Rh catalyst. These results are a showcase for the future development of asymmetric catalysis by using size-tunable supramolecular capsules.

Stereoselective Hydrosilylation
Rhodium Nanoflowers Stabilized by a Nitrogen-Rich PEG- Tagged Substrate as Recyclable Catalyst for the Stereoselective Hydrosilylation of Internal Alkynes
W. Guo, R. Pleixats, A. Shafir and T. Parella

Adv. Synth. Cat., 357, 89-99 (2015). DOI

Morphology and size controllable rhodium nanoparticles stabilized by a nitrogen-rich polyoxyethylenated derivative have been prepared and fully characterized. The flower-like Rh NPs are effective and recyclable catalysts for the stereoselective hydrosilylation of challenging internal alkynes and diynes, affording the ( E )-vinylsilanes in quantitative yields for a wide range of substrates. The insolubility of the nanocatalyst in diethyl ether allows its easy separation and recycling.

Enzymatic Aldol Catalysis
Engineered L-serine hydroxymethyltransferase from Streptococcus thermophilus for the synthesis of a,a-dialkyl-a-amino acids
K. Hernández, I. Zelen, G. Petrillo, I. Usón, C.M. Wandtke, J. Bujons, J. Joglar, T. Parella and P. Clapés

Angew. Chem. Intl. Ed.54, 3013-3017 (2015). DOI
A SHMT(sth) Y55T biocatalyst was designed from the native enzyme, achieving efficient and highly stereoselective catalysis in aldol addition reactions of D-ser and D-ala to a structural variety of aldehydes. The reaction rendered a-substituted b-hydroxy-a-amino acids with high to full diastereomeric ratio.

Biocatalytic Carbohydrate Analogues
Expedient Synthesis of C-Aryl Carbohydrates by Consecutive Biocatalytic Benzoin and Aldol Reactions
K. Hernández, T. Parella, J. Joglar, J. Bujons, M. Pohl and P. Clapés

Chem. Eur. J., 21, 3335-3346, (2015).DOI

An expedient asymmetric “de novo” synthetic route to new aryl carbohydrate (6-C-aryl-l-sorbose, 6-C-aryl–l-fructose, 6-C-aryl–l-tagatose, and 5-C-aryl-l-xylose) derivatives based on two sequential stereoselectively biocatalytic carboligation reactions is presented.

Recent Advances in Small Molecule NMR: Improved HSQC and HSQMBC Experiments
L. Castañar and T. Parella

Annual Reports on NMR spectroscopy, 84, 163-232 (2015).DOI

A general description of the latest developments in HSQC and HSQMBC experiments designed for small molecules at the natural isotopic abundance is reported. A discussion is made on the details introduced into novel NMR pulse sequences with special emphasis on modern concepts such as fast NMR or pure-shift NMR and also on robust techniques affording pure in-phase multiplet patterns, which are amenable for a simpler and a more accurate analysis. The suitability of some of these methods for the quantitative measurement of one-bond and long-range proton–carbon coupling values in molecules in isotropic and weakly aligned anisotropic conditions is also reviewed.
Enjoying NMR with Gary Martin, Armando Vázquez and Roberto Gil in the SMASH-2016 conference (La Jolla, USA)

Residual Dipolar Couplings
2J(HH)-resolved HSQC: Exclusive determination of geminal proton-proton coupling constants
N. Marcó, P. Nolis, R.R. Gil and T. Parella

J. Magn. Reson., 282,18-26  (2017). DOI
Perfect 1JCH-resolved HSQC: Efficient measurement of one-bond proton-carbon coupling constants along the indirect dimension
N. Marcó, A.A. Souza, P. Nolis, R.R. Gil and T. Parella

J. Magn. Reson, 276, 37-42 (2017). DOI
Structural discrimination from in-situ measurement of 1DCH and 2DHH residual dipolar coupling constants
N. Marcó, R. R. Gil and T. Parella

Magn. Reson. Chem, 55, 540-545 (2017). DOI

One-Shot Determination of Residual Dipolar Couplings: Application to the Structural Discrimination of Small Molecules Containing Multiple Stereocenters
L. Castañar, M. Garcia, E. Hellemann, P. Nolis, R. R. Gil and T. Parella

J. Org. Chem, 81, 11126-11131 (2016). DOI

Ultra high-resolved NMR
Ultra high-resolution HSQC: Application to the efficient and accurate measurement of heteronuclear coupling constants
N. Marcó, A. Fredi and T. Parella

Chem. Comm., 51, 3262-3265 (2015).DOI

A rapid NMR data acquisition strategy in terms of enhanced resolution per time unit for the simple and efficient determination of multiple coupling constants is described. The use of 13C spectral aliasing combined by broadband 1H homodecoupling allows accurate measurements from ultra high resolved 2D HSQC cross-peaks.

Near-Identical NMR spectra
Disentangling Complex Mixtures of Compounds with Near-Identical 1H and 13C NMR Spectra using Pure Shift NMR Spectroscopy

L. Castañar, R. Roldán, P. Clapés, A. Virgili and T. Parella

Chem. Eur. J., 21, 7682-7685 (2015). DOI

The thorough analysis of highly complex NMR spectra using pure shift NMR experiments is described. The enhanced spectral resolution obtained from modern 2D HOBS experiments incorporating spectral aliasing in the 13C indirect dimension enables the distinction of similar compounds exhibiting near-identical 1H and 13C NMR spectra. It is shown that a complete set of extremely small Δδ(1H) and Δδ(13C) values, even below the natural line width (1 and 5 ppb, respectively), can be simultaneously determined and assigned.

Drought and Plant Metabolism
Warming differentially influences the effects of drought on stoichiometry in metabolomics in shoots and roots
A. Gargallo-Garriga, J. Sardans, M. Pérez-Trujillo, M. Oravec, O. Urban, A. Jentsch, J. Kreyling, C. Beierkuhnlein,  T. Parella, and J. Peñuelas

New Phytologist, 207, 591-603 (2015). DOI

The stoichiometric and metabolomic responses of plants to warming strongly depend on water availability, and the response differs in shoots and roots. Warming under drought conditions stimulates root primary metabolic activity more strongly than under drought alone. Compared with drought alone, shoots under simultaneous warming and drought shifted their osmoprotective and antistress strategies by the down- and upregulation of the synthesis of various secondary metabolites and by the activation of some primary metabolic pathways. Our results thus demonstrated different metabolomic expressions in different parts of the plant and a large plasticity in the responses to environmental changes. 

Enantioresolution NMR
NMR-aided differentiation of enantiomers: Signal enantioresolution

M. Pérez-Trujillo, T. Parella and L. T. Kuhn

Analytica Chimica Acta,
876, 63-70  (2015). DOI
NMR-aided enantiodiscrimination using chiral auxiliaries (CAs) is a recognized method for differentiating enantiomers and for measuring enantiomeric ratios (er). Up to the present, the study, optimization, and comparison of such methods have been performed based on the enantiodifferentiation of NMR signals via analyzing non-equivalent chemical-shift values (ΔΔδ) of the diastereoisomeric species formed. However, a poor and non-reliable comparison of results is often obtained via the analysis of ΔΔδ exclusively. In here, the concept of enantioresolution of an individual NMR signal and its importance for NMR-aided enantiodifferentiation studies is introduced and discussed. In addition, the enantioresolution quotient, E, is proposed as the parameter to describe its quantification. 

NMR Diffusion of dendrimers
High-Boron-Content Porphyrin-Cored Aryl Ether Dendrimers: Controlled Synthesis, Characterization, and Photophysical Properties
J. Cabrera-González, E. Xochitiotzi-Flores, C. Viñas, F. Teixidor, H. García-Ortega, N Farfán, R. Santillan, T. Parella and R. Núñez

Inorganic Chemistry, 54, 5021-5031 (2015). DOI
The synthesis and characterization of a set of poly(aryl ether) dendrimers with tetraphenylporphyrin as the core and 4, 8, 16, or 32 closo-carborane clusters are described. A regioselective hydrosilylation reaction on the allyl-terminated functions with carboranylsilanes in the presence of Karstedt’s catalyst leads to different generations of boronenriched dendrimers. This versatile approach allows the incorporation of a large number of boron atoms in the dendrimers’ periphery. Translational diffusion coefficients (D) determined by DOSY NMR experiments permit estimation of the hydrodynamic radius (RH) and molecular size for each dendrimer. Furthermore, a notable correlation between D and the molecular weight (MW) is found and can be used to predict their overall size and folding properties. The UV−vis and emission behavior are not largely affected by the functionalization, therefore implying that the presence of carboranes does not alter their photoluminescence properties.

Structure-Guided Engineering of d-Fructose-6-Phosphate Aldolase for Improved Acceptor Tolerance in Biocatalytic Aldol Additions
A. Soler, M.L. Gutiérrez, J. Bujons, T. Parella,C. Minguillon,  J. Joglar and P. Clapés

Adv. Synth. Catalysis, 357, 1787-1807 (2015). DOI

A structure-guided redesign of d-fructose-
6-phosphate aldolase from Escherichia coli (FSA) was devised for improving the acceptor tolerance towards a-substituted and conformationally constrained aldehydes. Two FSA variants, were the most suited biocatalysts for dihydroxyacetone, hydroxyacetone and glycolaldehyde additions to 20 a-substituted N-Cbz-aminoaldehydes (Cbz=benzyloxycarbonyl) including pyrrolidine and piperidine derivatives. Full kinetic stereocontrol for si-si face addition of the aldolase-bound nucleophile to the N-Cbz-aminoaldehyde carbonyl was observed, furnishing the corresponding d-threo configured aldol adduct in >95:5 dr as assessed by NMR. After reductive amination, 47 different iminocyclitols were identified and characterized. In some examples partial racemization of the corresponding aldehyde was observed, which appears to be produced mostly during the aldol addition reactions.