Characterization of novel isobenzofuranones by DFT calculations and 2D NMR analysis

Phthalides are frequently found in naturally occurring substances and exhibit a broad spectrum of biological activities. In the search for compounds with insecticidal activity, phthalides have been used as versatile building blocks for the syntheses of novel potential agrochemicals. In our work, the Diels–Alder reaction between furan‐2(5H)‐one and cyclopentadiene was used successfully to obtain (3aR,4S,7R,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4R,7S,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 2 ) and (3aS,4S,7R,7aR)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4R,7S,7aS)‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 3 ). The endo adduct ( 2 ) was brominated to afford (3aR,4R,5R,7R,7aS,8R)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aS,4S,5S,7S,7aR,8S)‐5,8‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 4 ) and (3aS,4R,5R,6S,7S,7aR)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one and (3aR,4S,5S,6R,7R,7aS)‐5,6‐dibromohexahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one ( 5 ). Following the initial analysis of the NMR spectra and the proposed two novel unforeseen products, we have decided to fully analyze the classical and non‐classical assay structures with the aid of computational calculations. Computation to predict the ¹³C and ¹H chemical shifts for mean absolute error analyses have been carried out by gauge‐including atomic orbital method at M06‐2X/6‐31+G(d,p) and B3LYP/6‐311+G(2d,p) levels of theory for all viable conformers. Characterization of the novel unforeseen compounds ( 4 ) and ( 5 ) were not possible by employing only the experimental NMR data; however, a more conclusive structural identification was performed by comparing the experimental and theoretical ¹H and ¹³C chemical shifts by mean absolute error and DP4 probability analyses. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthetic transformations of methylenelactones of eudesmanic type. Behavior of isoalantolactone under the conitions of heck reaction

By Heck reaction of isoalantolactone with aryl bromides or aryl iodides (3aR,4aS, 8aR,9aR,E)-3-arylmethylidene-8a-methyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-ones and (4aS,8aR,9aS)-3-arylmethyl-8a-methyl-5-methylidene-4a,5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-ones, products of the double bond shift, were synthesized. The yields of the arylation products depend on the nature of the catalytic system and on the structure of the aryl halide. The structures of (3aR,4aS,8aR,9aR,E)-3-(3,4-dimethoxybenzylidene)-8amethyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-one and (4aS,8aR,9aS)-3-(2-methylsulfanylbenzyl)-8amethyl-5-methylidene-4a,5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-one were proved by XRD analysis.     

The conformation of (1R,2S,4R,5S)-2,4-dimethoxybicyclo[3.3.1]nonan-9-one and some related compounds

A mixture of stereoisomers of 2,4-dimethoxybicyclo[3.3.1]nonan-9-one was prepared, separated by column chromatography and characterized by 60 MHz ¹H NMR spectroscopy using Eu(fod)₃. A double chair conformation with axial methoxyl groups is established for (1R,2S,4R,5S)-2,4-dimethoxybicyclo[3.3.1]-nonan-9-one on the basis of the J(12), J(2,H-3 exo) and J(2,3 endo) values and the chemical shifts for H-2(4). The conformation of some related compounds is subsequently inferred.     

The synthesis and conformational analysis of optical isomers of 4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-dione: an example of ‘solid state–frozen’ dynamics in nitrogen-bridged bicyclic 2,6-diketopiperazines

The synthesis, chemical properties, and conformational analysis of enantiopure (4R,9aS)-, (4S,9aR)-, (4S,9aS)-, and (4R,9aR)-4-phenyl-perhydropyrido[1,2-a]pyrazine-1,3-diones having potential biological activity are described. An interesting example of the coexistence of two invertomers of the (4R,9aR)-diastereomer in a single crystal unit cell is reported. The invertomers differ in the cis/trans-relationship between the fused rings and in the absolute configuration at the chiral nitrogen atom. The structure and equilibrium distributions of the respective conformers have been determined by NMR spectroscopy in both polar and non-polar solvents at various temperatures. The NMR spectra show that dynamic processes in the imide parts of the interconverting species are restrained by self-aggregation. The (4S,9aR)-diastereomer exists in a single conformation with insignificant dynamic effects.     

Ascorbigen A—NMR identification

The connectivities of all atoms in ascorbigen A, an important metabolite, were determined unambiguously for the first time. The connectivity between carbon atoms was established by 2D INADEQUATE, and one-bond ¹³C–¹³C coupling constants were determined for all pairs of directly connected carbon atoms except for two strongly coupled carbon pairs. The ¹³C–¹³C coupling in one of the pairs was proved by a modification of standard INADEQUATE; however, the signals from the other pair were too weak to be observed. The connectivity within the two strongly coupled C–C pairs was confirmed by a combination of COSY and gHSQC; the latter experiment also identified all C–H bonds. The proton nuclear magnetic resonance (¹H NMR) spectra in dry dimethyl sulfoxide allowed identification and assignment of the signals due to NH and OH protons. The derived structure, 3-((1H-indol-3-yl)methyl)-3,3a,6-trihydroxytetrahydrofuro[3,2-b]furan-2(5H)-one, agrees with the structure suggested for ascorbigen A in 1966. The density functional theory (DFT) calculations showed that among 16 possible stereoisomers, only two complied with the almost zero value of the measured ³J(H6–H6a). Of the two stereoisomers, 3S,3aS,6S,6aR and 3R,3aR,6R,6aS, the latter was excluded on synthetic grounds. The nuclear Overhauser effect measurements unveiled close proximity between H2′ proton of the indole and the H6a proton of the tetrahydrofuro[3,2-b]furan part. Detailed structural interpretation of the measured NMR parameters by means of DFT NMR was hampered by rotational flexibility of the indole and tetrahydrofuro[3,2-b]furan parts and inadequacy of Polarizable Continuum Model (PCM) solvent model.     

Ajanolide A, a new germacranolide fromAjania fruticulosa

A new germacranolide, ajanolide A, was isolated from aerial parts ofAjania fruticulosa by means of extraction with CHCl₃ and adsorption chromatography. This compound was identified as (1(10)E,3S,4Z,6R,7S,11R)-3-acetoxygermacra-1(10),4-dien-12,6-olide ((1S,7S,10R,13R)-7-acetoxy-4,8,13-trimethyl-11-oxabicyclo[8.3.0]trideca-4(E),8(Z)-dien-12-one) by X-ray diffraction analysis. 2D¹H−¹H (COSY) and¹³C−¹H (COSY) NMR spectroscopy was used for assigning the¹H and¹³C NMR signals in the spectra of ajanolide A. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 167–170, January, 1998.     

Molecular structures of regioisomeric 7‐arylidene hexahydroindazoles from 1H NMR spectra

The structural characterization of two regioisomeric products of the interaction of 2,6‐bis‐(4‐methoxybenzylidene)‐3R‐methylcyclohexanone with methyl hydrazine was achieved using ¹H NMR spectral data, including chemical shifts, coupling constants and results of COSY and nuclear overhauser effect (NOE) experiments. Configurations of the new chiral centers in the (3S,3aR,6R,7E)‐7‐(4‐methoxybenzylidene)‐3,4,5,7‐hexahydro‐3‐(4‐methoxyphenyl)‐2,6‐dimethyl‐ and 2,4‐dimethyl‐2H‐indazoles were assigned on the basis of experimental data combined with molecular modeling by the density functional theory (DFT) method. The distinction in the helical twisting power of studied compounds under addition to a nematic liquid crystal is discussed on the basis of peculiarities of the molecular structures. Copyright © 2009 John Wiley & Sons, Ltd.     

NMR structure determination of (11E)-trinervita-1(14),2,11-triene, a new diterpene from sexual glands of termites

Female alates of Nasutitermes ephratae termites from Guadeloupe and Nasutitermes sp. from Brazil produce a diterpene hydrocarbon of the molecular formula C₂₀H₃₀ as the main component of their tergal gland secretion. Analysis of NMR, IR, and mass spectra of the diterpene led to a structure of (11E)-trinervita-1(14),2,11-triene. Based on a comparison with the published oxygenated trinervitane skeleton from termites we prefer the enantiomer with absolute configurations (4R,7S,8R,15S,16S). The suggested structure is supported by ab initio quantum chemical calculation of ¹H and ¹³C chemical shifts for the optimized geometry of the molecule.     

Electron density distributions in substituted 2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-dienes studied by NMR spectroscopy

The signals in the¹³C NMR spectra of 2,3,4,5-tetraphenyl-1-germacyclopenta-2,4-dienes (R¹=R²=H, Me,cyclo-C₃H₅, SiMe₃, SnMe₃, R¹=Me, R²=H, Cl) were completely assigned using 2D NMR spectroscopy. The pattern of the variation of the chemical shifts in the¹³C NMR spectra indicates that the effects of substituents R¹ and R² on the heterocycle and on the phenyl groups are of inductive rather than mesomeric origin and include the direct through-space polarization of bonds (field effect). Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1962–1965, November, 1997.     

QSAR studies of phenylhydrazine-substituted tetronic acid derivatives based on the 1H NMR and 13C NMR chemical shifts

The quantitative structure–activity relationship models of 40 phenylhydrazine-substituted tetronic acid derivatives were established between the ¹H nuclear magnetic resonance (NMR) and ¹³C NMR chemical shifts and the antifungal activity against Fusarium graminearum, Botrytis cinerea, Rhizoctonia cerealis, and Colletotrichum capsici. The models were validated by R, R², R_A², variance inflation factor, F, and P values testing and residual analysis. It was concluded from the models that the ¹³C NMR chemical shifts of C8, C10, C7, and the ¹H NMR chemical shifts of Ha contributed positively to the activity against Fusarium graminearum, Botrytis cinerea, Colletotrichum capsici, and Rhizoctonia cerealis, respectively. The models indicated that decreasing the election cloud density of specific nucleuses in compounds, for example, by the substituting of electron withdrawing groups, would improve the antifungal activity. These models demonstrated the practical application meaning of chemical shifts in the quantitative structure–activity relationship study. Furthermore, a practical guide was provided for further structural optimization of the antifungal phenylhydrazine-substituted tetronic acid derivatives based on the ¹H NMR and ¹³C NMR chemical shifts.     

Asymmetric Synthesis of Complicated Bicyclic and Tricyclic Polypropanoates via the Double Diels‐Alder Addition of 2,2′‐Ethylidenebis[3,5‐dimethylfuran]

A new, non‐iterative method for the asymmetric synthesis of long‐chain and polycyclic polypropanoate fragments starting from 2,2′‐ethylidenebis[3,5‐dimethylfuran] ( 2 ) has been developed. Diethyl (2E,5E)‐4‐oxohepta‐2,5‐dienoate ( 6 ) added to 2 to give a single meso‐adduct 7 containing nine stereogenic centers. Its desymmetrization was realized by hydroboration with (+)‐IpcBH₂ (isopinocampheylborane), leading to diethyl (1S,2R,3S,4S,4aS,7R,8R,8aR,9aS,10R,10aR)‐1,3,4,7,8,8a,9,9a‐octahydro‐3‐hydroxy‐2,4,5,7,10‐pentamethyl‐9‐oxo‐2H,10H‐2,4a : 7,10a‐diepoxyanthracene‐1,8‐dicarboxylate ((+)‐ 8 ; 78% e.e.). Alternatively, 7 was converted to meso‐(1R,2R,4R,4aR,5S,7S,8S,8aR,9aS,10s,10aS)‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐2,4,5,7,10‐pentamethyl‐2H‐10H‐2,4a : 7,10a‐diepoxyanthracene‐3,6,9(4H,5H,7H)‐trione ( 32 ) that was reduced enantioselectively by BH₃ catalyzed by methyloxazaborolidine 19 derived from L ‐diphenylprolinol giving (1S,2S,4S,4aS,5S,6R,7R,8R,8aS,9aR,10R,10aS)‐1,8‐bis(acetoxymethyl)‐1,8,8a,9a‐tetrahydro‐6‐hydroxy‐2,4,5,7,10‐pentamethyl‐2H,10H‐2,4a : 7,10a‐diepoxyanthracene‐3,9(4H,7H)‐dione ((−)‐ 33 ; 90% e.e.). Chemistry was explored to carry out chemoselective 7‐oxabicyclo[2.2.1]heptanone oxa‐ring openings and intra‐ring C−C bond cleavage. Polycyclic polypropanoates such as (1R,2S,3R,4R,4aR,5S,6R,7S,8R,9R,10R,11S,12aR)‐1‐(ethoxycarbonyl)‐1,3,4,7,8,9,10,11,12,12a‐decahydro‐3,11‐dihydroxy‐2,4,5,7,9‐pentamethyl‐12‐oxo‐2H,5H‐2,4a : 6,9 : 6,11‐triepoxybenzocyclodecene‐10,8‐carbolactone ( 51 ), (1S,2R,3R,4R,4aS,5S,7S,8R,9R,10R,12S,12aS)‐1,10‐bis(acetoxymethyl)tetradecahydro‐8‐(methoxymethoxy)‐2,4,5,7,9‐pentamethyl‐3,9‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}‐6,11‐epoxycyclodecene‐4a,6,11,12‐tetrol ((+)‐ 83 ), and (1R,2R,3R,4aR,4bR,5S,6R, 7R,8R,8aS,9S,10aR)‐3,5‐bis(acetoxymethyl)‐4a,8a‐dihydroxy‐1‐(methoxymethoxy)‐2,6,8,9,10a‐pentamethyl‐2,7‐bis{[2‐(trimethylsilyl)ethoxy]methoxy}dodecahydrophenanthrene‐4,10‐dione ( 85 ) were obtained in few synthetic steps.     

Computation and structural elucidation of compounds formed via epoxide alcoholysis

Isobenzofuranones are known for their wide range of biological activities such as fungicide, insecticide, and anticancer. The search for novel bioactive compounds was performed by reaction of epoxide 2 with methanol, ethanol, propan-1-ol, propan-2-ol, and butan-1-ol. The mechanism for the stereoselective and stereospecific epoxide opening with methanol was reasoned by calculating the transition states for the two putative structures (rac)-3a and (rac)-3b. The compound (rac)-3a is the kinetic product as inferred from the lower energies of its transition state (TS1). The ¹H and ¹³C nuclear magnetic resonance (NMR) chemical shifts for these two candidate structures were calculated and compared with the experimental data using mean absolute error (MAE) and DP4 analyses. Therefore, the relative stereochemistry of (rac)-3a was established by the mechanism, MAE, and DP4 approaches. The hydroxyl group was acetylated to surpass the problem of signal overlapping of H5 and H6 in the ¹H NMR. The relative stereochemistry of the corresponding ester determined by NMR interpretation was in agreement with the structure of (rac)-3a.     

Three ginkgolide hydrates from Ginkgo biloba L.: ginkgolide A monohydrate,ginkgolide C sesquihydrate and ginkgolide J dihydrate,all determined at 120 K

A low‐temperature structure of ginkgolide A monohydrate, (1R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐dimethylethyl)‐hexa­hydro‐4,7b‐di­hydroxy‐8‐methyl‐9H‐1,7a‐epoxymethano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclopenta­[1,2‐d]­furan‐5,9,12(4H)‐trione monohydrate, C₂₀H₂₄O₉·H₂O, obtained from Mo Kα data, is a factor of three more precise than the previous room‐temperature determination. A refinement of the ginkgolide A monohydrate structure with Cu Kα data has allowed the assignment of the absolute configuration of the series of compounds. Ginkgolide C sesquihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11S,11aR)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b,11‐tetrahydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclopenta­[c]­furo­[2,3‐b]­furo­[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione sesquihydrate, C₂₀H₂₄O₁₁·1.5H₂O, has two independent diterpene mol­ecules, both of which exhibit intramolecular hydrogen bonding between OH groups. Ginkgolide J dihydrate, (1S,2R,3S,3aS,4R,6aR,7aR,7bR,8S,10aS,11aS)‐3‐(1,1‐di­methyl­ethyl)‐hexa­hydro‐2,4,7b‐tri­hydroxy‐8‐methyl‐9H‐1,7a‐epoxy­methano‐1H,6aH‐cyclo­penta­[c]­furo­[2,3‐b]furo[3′,2′:3,4]­cyclo­penta­[1,2‐d]­furan‐5,9,12(4H)‐trione dihydrate, C₂₀H₂₄O₁₀·2H₂O, has the same basic skeleton as the other ginkgolides, with its three OH groups having the same configurations as those in ginkgolide C. The conformations of the six five‐membered rings are quite similar across ­ginkgolides A–C and J, except for the A and F rings of ginkgolide A.     

A New Alkaloid from the Seeds of Sophora alopecuroides L.

Alopecurin A, an alkaloid with an unprecedented skeleton, was isolated from the seeds of Sophora alopecuroides L. The absolute configuration and structure of this compound was identified as (3S,12R)‐3‐hydroxy‐1,7‐diazatricyclo[10.4.0.1^3,7]heptadecane‐11,16,17‐trione (=(7S,15aR)‐decahydro‐7‐hydroxy‐6H‐7,11‐methano‐4H‐pyrido[1,2‐a][1,7]diazacyclododecine‐4,15,16(12H)‐trione). The structure and absolute configuration was elucidated by spectroscopic methods, mainly HR‐ESI‐TOF‐MS, IR, 1D‐NMR (¹H‐ and ¹³C‐NMR), 2D‐NMR (COSY, NOESY, HSQC, HMBC), and particularly X‐ray crystal‐diffraction and CD spectral analysis.     

The Stereochemistry of 1,2,3‐Triols Revealed by 1H NMR Spectroscopy: Principles and Applications

The conformational compositions of the tris(α‐methoxy‐α‐phenylacetic acid) ester derivatives of 1,2,3‐prim,sec,sec‐triols are presented. These conformations have been determined by theoretical and experimental data (i.e., energy‐ and chemical‐shift calculations, circular dichroism (CD) experiments, coupling‐constant analysis, enantioselective deuteration experiments, and low‐temperature NMR spectroscopic studies). A detailed analysis of the anisotropic effects due to the most significant conformers in the ¹H NMR spectra supported the correlation between the ¹H NMR spectra (Δδ^RS value of H(3′) and |Δ(Δδ^RS)| parameters) and the absolute configuration of the substrate. The study also allows the identification of the pro‐R and pro‐S methylene protons from their vicinal coupling constants and relative chemical shifts.     

Cadinene Derivatives from Eupatorium adenophorum

A new norsesquiterpene named eupatorone (= (4S,4aR,6R)‐1‐acetyl‐6‐(acetyloxy)‐4,4a,5,6‐tetrahydro‐4,7‐dimethylnaphthalen‐2(3H)‐one; 1 ) and a new sesquiterpene derivative named 2‐deoxo‐2‐(acetyloxy)‐9‐oxoageraphorone (= (1R,4S,4aR,6R,8aS)‐6‐(acetyloxy)‐3,4,4a,5,6,8a‐hexahydro‐4,7‐dimethyl‐1‐(1‐methylethyl)naphthalen‐2(1H)‐one; 2 ), together with the five known cadinene derivatives 3 – 7 were isolated from the flower of Eupatorium adenophorum (Spreng. ). Their structures were established by extensive NMR experiments, including 1D and 2D NMR.     

New Antifungal `Quinone Methide' Diterpenes from Bobgunnia madagascariensis and Study of Their Interconversion by LC/NMR

Two new `quinone methide' diterpenes with a cassane skeleton were isolated from the root bark of Bobgunnia madagascariensis (Desv. ) J. H. Kirkbr. & Wiersema (Leguminosae). The two compounds occurred as a diastereoisomer mixture 1 / 2 . Their structure was established as (4R,6aS,10aS)‐ and (4S,6aS,10aS)‐ 1,4,6a,7,8,9,10,10a‐octahydro‐4,11‐dihydroxy‐7,7,10a‐trimethyl‐2H‐phenanthro[1,2‐c]pyran‐6,12‐dione by spectroscopic methods and by comparison with the data obtained for another `quinone methide' diterpene isolated previously from the same plant and identified by single‐crystal X‐ray analysis. ¹H‐ and ¹³C‐NMR signals were assigned by extensive in‐mixture 2D correlation experiments, and ¹H‐NMR spectra of the separated diastereoisomers 1 and 2 were recorded by on‐flow LC/NMR. The interconversion of 1 and 2 was followed by repeated stop‐flow LC/NMR experiments over a two‐hour period. Compounds 1 and 2 showed moderate antifungal properties towards human pathogenic fungi, in particular the yeast Candida albicans.     

NMR- und schwingungsSpektroskopische Untersuchungen höherer Indiumtrialkyle

NMR and Vibrational Spectroscopic Investigations on Higher Indium Trialkyls Several isomeric indium tripentyles and trihexyles are synthesized by known methods. The chemical shifts δ of the ¹³C NMR spectra are used together with those of the corresponding alkanes for determining the increments Δδ(¹³C) = δ(InR₃)–δ(RH). By means of these increments and the Grant/Paul-method the chemical shifts δ(¹³C) of any indium trialkyl can be calculated. The vibrational spectra (IR and Raman) of most liquid trialkyls show very obvious rotameric splittings of the InC vibrations between 450–600 cm^?1. Both frequent conformations of the alkyl ligands with three and more C atoms consist of either a βH atom (notations P_H, S_HH, and T_HHH with vInC between 450–500 cm^?1) or a γC atom (P_C, S_CH, T_CHH with vInC between 550–600 cm^?1) in the transposition to indium. The InC stretching modes of all other more rare configurations can be observed between 500 to 550 cm^?1.     

25R/25S stereochemistry of spirostane‐type steroidal sapogenins and steroidal saponins via chemical shift of geminal protons of ring‐F

A method based on the differences among the ¹H NMR chemical shifts of geminal protons of ring‐F methylene resonances (H₂‐23, H₂‐24 and H₂‐26) is proposed for ascertaining the 25R/25S stereochemistry of ring‐F unsubstituted spirostane‐type steroidal sapogenins and steroidal saponins. Copyright © 2003 John Wiley & Sons, Ltd.     

Structural elucidation of dioxa‐cage compounds from tetrahydroisobenzofuran‐1(3H)‐one: analysis of NMR data and GIAO chemical shifts calculations

The polycyclic compounds, especially the dioxa‐cages, have attracted considerable attention in recent years. In our work, a series of 9β‐substituted 3‐oxo‐4,11‐dioxatetracyclo[5.2.1.1^5,8.0^2,6]undecane compounds were unexpectedly isolated during bromination, chlorination and epoxidation reactions of the 3‐hydroxy‐3a,4,7,7a‐tetrahydro‐4,7‐methanoisobenzofuran‐1(3H)‐one. After careful analysis of the NMR data, the chemical shifts of the isolated and the expected products were predicted by theoretical calculations using density functional theory and gauge including atomic orbitals. The best correlation between calculated and experimental data was evaluated by comparing mean absolute errors and applying DP4 probability methodology. Results from both approaches indicated a correct structural elucidation. Copyright © 2016 John Wiley & Sons, Ltd.