A combined experimental and theoretical study of the supramolecular self-assembly of the natural benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-chromane and its isomeric benzofuran 10,11-dihydro-10-hydroxytremetone

Article abstract of DOI:10.1016/j.molstruc.2017.05.137

Epoxidation of 4HMBA, the main metabolite of the medicinal plant Sencecionutans, produces an unstable epoxide eventually giving rise to a mixture of four derivatives, three of them previously reported as natural products. The epoxide product easily undergoes an intra-molecular attack of the phenolic hydroxyl against the epoxide group carbons to produce either a benzofuran or a chromane derivative. When dissolved in methanol-water mixture at room temperature the epoxide is completely solvolyzed to give the corresponding diol (hydrolysis) or vicinal hydroxyl-methoxy (methanolysis) derivative. All the compounds involved in the above reactions were characterized by IR, Raman, H NMR and UV–vis spectroscopies, and by mass spectrometry. Density functional theory (DFT) computations were used to optimize the structure conformations. The optimized structures were further subjected to a Natural Bond Orbital (NBO) and electrostatic potentials analysis. The crystal structures of the title compounds (for short, 3 and 4 respectively) were determined by X-ray diffraction methods. Compound 3 crystallizes in the triclinic P-1 space group with a = 6.4289 (6) ?, b = 8.7120 (6) ?, c = 10.952 (1) ?, α = 92.280 (7)°, β = 95.738 (7)°, γ = 103.973 (7)°, and Z = 2 molecules per unit cell and 4 in the monoclinic P2₁/c space group with a = 11.2891 (6) ?, b = 9.1902 (4) ?, c = 12.4272 (7) ?. Β = 113.689 (7)°, and Z = 4. In 3 neighboring molecules are linked to each other by OH?O (keto) bonds giving rise to a polymeric structure. In 4 the OH group is a bifurcate H-bond donor. It forms a weak intra-molecular OH?O (furan) bond and also a much stronger inter-molecular O[sbnd]H?O (keto) bond giving rise to a zig-zag polymeric structure. A detailed analysis of the solid state molecular interactions of compounds 3 and 4 has been performed using Hirshfeld surface analysis and their associated 2D fingerprint plots.

Full text of DOI:10.1016/j.molstruc.2017.05.137

Accepted Manuscript
A combined experimental and theoretical study of the supramolecular self-assembly
of the natural benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-chromane and its isomeric
benzofuran 10,11-dihydro-10-hydroxytremetone
Diego M. Gil, E. Lizarraga, G.A. Echeverría, O.E. Piro, C.A.N. Catalán, A. Ben Altabef
PII:
S0022-2860(17)30757-3
10.1016/j.molstruc.2017.05.137
MOLSTR 23878
DOI:
Reference:
To appear in: Journal of Molecular Structure
Received Date: 21 April 2017
Revised Date: 29 May 2017
Accepted Date: 30 May 2017
Please cite this article as: D.M. Gil, E. Lizarraga, G.A. Echeverría, O.E. Piro, C.A.N. Catalán,
A. Ben Altabef, A combined experimental and theoretical study of the supramolecular self-
assembly of the natural benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-chromane and its isomeric
benzofuran 10,11-dihydro-10-hydroxytremetone, Journal of Molecular Structure (2017), doi: 10.1016/
j.molstruc.2017.05.137.
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Graphical abstract

ACCEPTED MANUSCRIPT
A combined experimental and theoretical study of the supramolecular
self-assembly of the natural benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-
chromane and its isomeric benzofuran 10,11-dihydro-10-
hydroxytremetone.
Diego M. Gil1,+,*, E. Lizarraga2,3, G. A. Echeverría4,+, O. E. Piro4,+, C. A. N. Catalán1,+, A.
Ben Altabef1,+,
*
1INQUINOA (CONICET-UNT), Facultad de Bioquímica, Química y Farmacia.
Universidad Nacional de Tucumán. San Lorenzo 456. T4000CAN. San Miguel de
Tucumán. R: Argentina.
2Fundación Miguel Lillo, Instituto de Fisiología Animal. Miguel Lillo 251, T4000JFE. San
Miguel de Tucumán, R. Argentina.
3Facultad de Ciencias Naturales e Instituto Miguel Lillo, Universidad Nacional de
Tucumán. Miguel Lillo 205, T4000JFE. San Miguel de Tucumán, R. Argentina.
4Departamento de Física, Facultad de Ciencias Exactas, Universidad Nacional de La Plata y
IFLP (CONICET, CCT-La Plata), C. C. 67, 1900, La Plata, R. Argentina.
+ Members of the Research Career of CONICET.
___________________________________________________________________________
* Corresponding authors address: Instituto de Química Física. Facultad de Bioquímica,
Química y Farmacia. Universidad Nacional de Tucumán. San Lorenzo 456. T4000CAN. San
Miguel de Tucumán. R. Argentina.
e-mail address: altabef@fbqf.unt.edu.ar (Dr. A. Ben Altabef)
dmgil@fbqf.unt.edu.ar (Dr. Diego M. Gil)

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Abstract
Epoxidation of 4HMBA, the main metabolite of the medicinal plant Sencecionutans,
produces an unstable epoxide eventually giving rise to a mixture of four derivatives, three of
them previously reported as natural products. The epoxide product easily undergoes an intra-
molecular attack of the phenolic hydroxyl against the epoxide group carbons to produce either
a benzofuran or a chromane derivative. When dissolved in methanol-water mixture at room
temperature the epoxide is completely solvolyzed to give the corresponding diol (hydrolysis)
or vicinal hydroxyl-methoxy (methanolysis) derivative. All the compounds involved in the
above reactions were characterized by IR, Raman, H NMR and UV-vis spectroscopies, and by
mass spectrometry. Density functional theory (DFT) computations were used to optimize the
structure conformations. The optimized structures were further subjected to a Natural Bond
Orbital (NBO) and electrostatic potentials analysis. The crystal structures of the title
compounds (for short, 3 and 4 respectively) were determined by X-ray diffraction methods.
Compound 3 crystallizes in the triclinic P-1 space group with a = 6.4289(6) Å, b = 8.7120(6)
Å, c = 10.952(1) Å, α = 92.280(7)°, β = 95.738(7)°, γ = 103.973(7)°, and Z = 2 molecules per
unit cell and 4 in the monoclinic P21/c space group with a = 11.2891(6) Å, b = 9.1902(4) Å, c
= 12.4272(7) Å. Β = 113.689(7)°, and Z = 4. In 3 neighboring molecules are linked to each
other by OH···O(keto) bonds giving rise to a polymeric structure. In 4 the OH group is a
bifurcate H-bond donor. It forms a weak intra-molecular OH···O(furan) bond and also a much
stronger inter-molecular O-H···O(keto) bond giving rise to a zig-zag polymeric structure. A
detailed analysis of the solid state molecular interactions of compounds 3 and 4 has been
performed using Hirshfeld surface analysis and their associated 2D fingerprint plots.
Keywords: Crystal structure; IR and Raman spectroscopy; Hydrogen bonds; Quantum
chemical calculations; Chromane derivative; Benzofuran derivative.

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1. INTRODUCTION
Chromanes and benzofurans are characteristic metabolites of certain tribes of the
Asteraceae family [1]. They are frequently found in several widely distributed American
genera such as Senecio, Ageratina, Liatris, Encelia, Eupatorium, Baccharis, Verbesina and
Flourensia, and have aroused great interest because of their numerous biological activities
such as antimicrobial, allergenic, plant growth inhibitory, pro-apoptotic, and anti-
proliferative against cancer cell lines [2].
Benzopyrans (chromanes) derivatives and, particularly, those with a 2,2-dimethyl-
2H-benzopyran moiety are present in thousands of natural products with a wide range of
biological activities [3]. These plant metabolites generally exhibit low cellular toxicity and
good membrane permeability which makes them ideal as drug template. Thus, several 2,2-
dimethyl-2H-benzopyrans exhibit powerful antitumor activity [4-6] and HIV-1 reverse
transcriptase inhibition [7,8]. Consequently, structural analysis at molecular and supra-
molecular levels of natural chromanes is of great interest because they can be used as
starting compounds to prepare novel drugs with improved pharmaceutical profile. Recently,
we have reported the synthesis and spectroscopic characterization of 6-acetyl-2,2-dimethyl-
chromane; this compound was obtained from 4-hydroxy-3-(3-methyl-2-butenyl)-
acetophenone (4-HMBA) (1), the main secondary metabolite of Senecio nutans
(Asteraceae), a medicinal plant of northwestern Argentina[9].
The molecular design intended to mimic the complex structures and processes found
in nature is known as “bio-inspired chemistry” or “bio-mimetic chemistry”. Several reports
have been published on the biosynthetic origin of benzofurans and chromanes in plants
where p-hydroxyacetophenone derivatives have been proposed as precursors of
benzofurans and chromanes [1, 10-13]. In this sense we have speculated that 4-HMBA
epoxide (2) would be a useful intermediate for synthesizing benzofurans and chromans. In
fact, reaction of 4-HMBA (1) with m-CPBA gave a mixture of epoxide 2 (32.6%) together
with chromane 3 (20.9%) and benzofuran 4 (40.5%). The latter two compounds derive from
an intra-molecular nucleophilic attack of the phenolic hydroxyl at the epoxide carbons.
When this mixture was dissolved in methanol-water solution to be analyzed by preparative
HPLC, a progressive decrease in the peak corresponding to the epoxide 2 until its complete
disappearance and the appearance of two new compounds, later identified as the phenol-

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diol 5 and the methoxy-derivative 6, was evident after a few days. Clearly phenol-diol 5
and methoxyderivative 6 were formed by solvolysis (hydrolysis and methanolysis,
respectively) of epoxide 2. Three of the four compounds obtained in this work were
previously reported as natural products, namely 2,2-dimethyl-3-hydroxy-6-acetylchromane
(3) in the aerial parts of Helicrysumstoechas [14], 10,11-dihydro-10-hydroxytremetone (4)
in the leaves of Fitchiaspeciosa [15], and 3-(2,3-dihydroxysopentyl) 4-hydroxy-
acetophenone (5) in the aerial parts of Werneriaciliolata [16]. It should be noted here that
all the compounds obtained in this work are racemates whereas both the natural benzofuran
4 and the diol 5 are the left-handed enantiomers [15, 16] hence indicating that the reaction
is enzymatically controlled in the plant. The optical rotation of natural chromanol 3 was not
reported [14].
The present work reports a bio-mimetic synthesis of natural chromanes and
benzofurans by epoxidation of the antifungal metabolite 4HMBA (1) [17, 18]. The products
obtained were characterized using different spectroscopic techniques such as infrared
1
absorption, Raman dispersion, UV-visible, H nuclear magnetic resonance (NMR), and
mass spectrometry (MS). In addition, for the structural isomers (RS)-2,2-dimethyl-3-
hydroxy-6-acetylchroman (3), (RS)-10,11-dihydro-10-hydroxytremetone (4) and (RS)-3-
(2,3-dihydroxy-isopentyl)-4-hydroxy-acetophenone (5), the crystal structures have been
determined by single crystal X-ray diffraction methods. The experimental data was
correlated with theoretical calculations using DFT methods and different basis sets. The
intermolecular interactions in the crystal lattice were evaluated through Hirshfeld surface
analysis. The geometry of a Hirshfeld surface reflects the relationship between different
atoms and intermolecular contacts present in the crystal. These surfaces are supported by
2D fingerprint plots which quantify the nature and type of intermolecular interactions in the
solid.
2. EXPERIMENTAL
2.1 Synthesis
To 4-HMBA (1) (1.224 g) in 30 mL of CHCl3 cooled in ice was added in small
portions m-chloroperbenzoic acid (MCPBA) (1.184 g, 77%) with magnetic stirring. The

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progress of the reaction was monitored by TLC. When the reaction was complete
(disappearance of the spot corresponding to 4HMBA) the mixture was filtered out and then
diluted with 50 mL of CHCl3. The organic layer was washed with 10% Na2SO3 (2 x 10
mL), 5% NaHCO3 (2 x 10 mL) and water (1 x 10 mL). After drying with anhydrous
Na2SO4 and solvent evaporation, 768.7 mg of crude residue was obtained. CG-MS analysis
showed a mixture constituted (listed by elution order) by 4 (40.5%), unidentified A (3.6%),
3 (20.9%), 2 (32.6%) and unidentified B (2.5%). The residue was dissolved in a mixture of
methanol-water (55:45) to be processed by semi-preparative HPLC using a C18 column (5
µ; 10 mm x 250 mm) with methanol-water 55:45 as elution solvent (isocratic), flow at 2.0
mL min-1. After a few injections, a progressive decrease in the peak corresponding to the
epoxide 2 and the simultaneous appearance of two new compounds later identified as the
phenol-diol 5 and the methoxy-derivative 6 was evident. The hydro-methanolic solution
was then set aside at room temperature and monitored by HPLC every week. The peak
corresponding to epoxide 2 disappeared completely after four weeks and the chromatogram
showed four major components which were collected separately to yield (by elution order):
5 (73.5 mg), 6 (34 mg), 4 (173 mg) and 3 (122 mg) (Scheme 1). Chromane 3, benzofuran 4
and phenol-diol 5 were re-crystallized from ethanol.

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5'
8
CH3
CH3
7
1'
O
3' CH3
4'
1
3
6
4HMBA (1)
4
MW 204
OH
MCPBA
8
5'
CH3
CH3
4
O
CH3
CH3
H2O
5
CH3
CH3
OH
HO
2'
O
3
2
1
3
O
CH3
CH3
O
CH3
4'
1'
7
7
O
1
OH
OH
6
4
8
OH
(2)
MW 220
(3)
MW 220
(5) MW 238
CH3OH
CH3
CH3
H3C
9
CH3
12
O
OCH3
4
H3C OH
OH
O
8
OH
1
O
2
CH3
6
11
7
MW 252
(6)
(4)
MW 220
Scheme 1: Synthesis of 4HMBA (1) derivatives. *Epoxide 2 is unstable at room temperature: a
nucleophilic attack of the phenolic hydroxyl at the epoxide carbons yields chromane 3 and
benzofuran4 while dissolution in methanol/water 45:55 gives the solvolysis products 5 and 6.
Compound 3: 2,2-dimethyl-3-hydroxy-6-acetyl-chromane (racemic). Needles (122 mg),
mp: 102.4 ºC (from ethanol).1H NMR (200 MHz, CDCl3) δ 7.75 dd (1H, 9.3 and 2.2 Hz,
H-7), 7.73 d (1H, 2.2 Hz, H-5), 6.85 d (9.2 Hz, H-8), 3.86 dd (5.8 and 4.9 Hz, H-3), 3.10dd
(1H, 16.8 and 4.9Hz, H-4a), δ 2.83 dd (1H, 16.8 and 5.8 Hz, H-4b), δ 2.54 s (3H, CH3-
CO), δ 2.18 s (br) (1H, OH), δ 1.38s and 1.35 s (3H each, gem-dimethyl group), in
agreement with published data [14]. EIMS: m/z (rel. int.%) [M]+ 220 (40), 205 (7), 187
(10), 163 (9), 162 (9), 149 (52), 119 (11), 107 (29), 91 (12), 77 (21), 71 (32), 57 (10), 51
(9), 43 (100).
Compound 4: 10,11-Dihydro-10-hydroxytremetone (racemic). Needles (173 mg), mp:
87.1 ºC (from ethanol). EIMS: m/z (rel. int.%) [M]+ 220 (17), 205 (2), 202 (4), 187 (13),

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1
162 (63), 147 (71), 133 (6), 119 (85), 91 (23), 77 (9), 65 (6), 59 (74), 51 (7), 43 (100). H
NMR (200 MHz, CDCl3): δ 7.83 s (br) (1H, H-4), 7.81 dd (1H, 8 and 1.5 Hz, H-6), 6.82 d
(1H, 8 Hz, H-7), 4.72 t (1H, 9 Hz, H-2), 3.22 d (2H, 9 Hz, H-3a,b), 2.54 s (3H, H-9), 1.25
s and 1.23 s (3H each, H-4’ and H-5) in agreement with published data [15].
Compound 5: 3-(2,3-dihydroxy-isopentyl)-4-hydroxy-acetophenone (racemic). Crystals
(73 mg), mp: 135 °C (from ethanol) . EIMS: m/z (rel. int.%) [M]+ 238 (4), 220 (5), 205 (2),
187 (2), 180 (18), 165 (6), 163 (7), 150 (25), 149 (29), 137 (52), 119 (12), 107 (21), 91
1
(11), 77 (16), 71 (17), 59 (39), 43 (100). H NMR (200 MHz, CDCl3):δ 7.79 d (1H, H-2),
7.70dd (1H, 8.3 and 2.1 Hz, H-6), 6.88 d (1H, 8.3 Hz, H-5), 3.60 dd (1H, 10.3 and 1.4 Hz,
H-2’), 2.91 dd (1H, 14 and 1.4 Hz, H-1’a), 2.66 dd (1H, 14 and 10.3 Hz, H-1’b), 2.52 s
1
(3H, H-8), 2.06 br s (1H, OH), 1.37 s and 1.24 s (3H each, H-11 and H-12) (for H NMR
in CD3OD see [16].
Compound 6: 3-(2-hydroxy-3-methoxy-isopentyl)-4-hydroxy-acetophenone (racemic).
White solid (34 mg). EIMS: m/z (rel. int.%) [M]+ 252 (2), 220 (2), 205 (1), 187 (1.5), 180
(8), 150 (14), 149 (21), 107 (7), 73 (100), 43 (42).1H NMR (200 MHz, CDCl3):δ 7.76dd
(1H, 8.2 and 2.1 Hz, H-6), 7.73 d (1H, 2.1Hz, H-2), 6.94 d (1H, 8.2 Hz, H-5), 3.74 dd (1H,
9.6 and 1.5 Hz, H-2’), 3.24 s (3H, OCH3),2.83dd (1H, 14.5 and 9.6 Hz, H-1’a), 2.68dd
(1H, 14.5 and 1.5 Hz, H-1’b), 2.54 s (3H, H-8), 1.25 s and 1.20 s (3H each, H-4’ and H-
5’); 13C NMR (CDCl3):δ 197.2 s (C-7), 160.9 s (C-4), 131.7 d (C-2), 129.9 d (C-6), 129.7
s (C-1), 126.2 s (C-3), 117.2 d (C-5), 79.2 d (C-2’), 77.1 s (C-3’), 49.1 q (OCH3), 34.6 t (C-
1’), 26.2 q (C-8), 20.4 q and 18.2 q (C-4’ and C-5’).
2.2 Characterization techniques
The crystal melting points were determined using Differential Scanning Calorimetry
(DSC) technique. The measurement was performed with a differential scanning calorimeter
Perkin Elmer Pyris DSC 6 using 1.150 mg of powdered sample sealed in aluminum pans
with a mechanical crimp. Temperature and heat flow calibrations were made with standard
samples of indium at its melting transition. Enthalpy changes associated with the melting
point of the sample in study (ꢀH) were directly obtained from the DSC data by integrating

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the anomalous peak in the baseline subtracted curve. The entropy change relative to the
phase transition was finally determined using the relationship ꢀS = ꢀH/T.
1H NMR spectra were recorded on a Bruker AC (200 MHz) spectrometer. Sample
was dissolved in CDCl3 and tetramethylsilane (TMS) was used as internal standard.
Chemical shifts were recorded in δ (ppm) values relative to TMS and J values are
expressed in Hertz.
The GC-MS analysis was carried out with a 5973 Hewlett Packard selective mass
detector (quadrupole), source 70 eV, coupled to a HP 6890 GC fitted with a HP-5MS
column (5% phenylmethylsiloxane, 30 m x 0.25 mm; film thickness 0.25 ꢁm) with helium
as carrier gas (1.0 mL/min; constant flow). The oven was programmed for 150ºC (0 min),
150º-180º (3ºC/min) and 234º (3 min). The sample was dissolved in CHCl2 and the
injection volume was 0.1 ꢁL. Injector and detector temperatures were kept at 250ºC and
270ºC, respectively. Injection port was kept at 250ºC, GC-MS interphase at 275ºC, ion
source 230ºC, and MS Quad at 150ºC.
The FTIR absorption spectra of the solid state compounds (in KBr pellets) were
recorded in the 4000-400 cm-1 region at room temperature on a Perkin-Elmer GX1 Fourier
Transform infrared spectrometer with 2 cm-1 of spectral resolution. The Raman dispersion
spectra of the solids were recorded at room temperature in the 3500-50 cm-1 range with a
Thermoscientific DXR Raman microscope.
UV- visible spectra were obtained on a Shimadzu 160A spectrophotometer. For this
purpose, 6.1 mg of compound 3 and 6.5 mg of compound 4 were dissolved in 10 mL
ethanol 96° and from this mother solution appropriate dilutions were obtained with the
same solvent. The spectra were recorded between 800 and 200 nm.
2.3 X-ray diffraction data and structure refinement of compounds 3 and 4
The measurements were performed on an Oxford Xcalibur Gemini, Eos CCD
diffractometer with graphite-monochromated CuKα (λ=1.54184 Å) radiation. X-ray
diffraction intensities were collected (ω scans with ϑ and κ-offsets), integrated and scaled
with CrysAlisPro [19] suite of programs. The unit cell parameters were obtained by least-
squares refinement (based on the angular settings for all collected reflections with intensities
larger than seven times the standard deviation of measurement errors) using CrysAlisPro.

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Data were corrected empirically for absorption employing the multi-scan method
implemented in CrysAlisPro. The structures were solved by direct methods with the
SHELXS program of the suite SHELX package [20] and the corresponding molecular
models developed by alternated cycles of Fourier methods and full-matrix least-squares
refinement with SHELXL of the same suit of program. All hydrogen atoms were located in
a difference Fourier map phased on the heavier atoms and refined at their found positions
with isotropic displacement parameters. The optimized methyl H-positions converged to
staggered conformations. Crystal data and structure refinement results for both compounds
are summarized in Table 1. Crystallographic structural data have been deposited at the
Cambridge Crystallographic Data Centre (CCDC). Enquiries for data can be direct to:
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, UK, CB2 1EZ or (e-
mail) deposit@ccdc.cam.ac.uk or (fax) +44 (0) 1223 336033. Any request to the Cambridge
Crystallographic Data Centre for this material should quote the full literature citation and the
reference number CCDC 1541924 (3) and CCDC 1541925 (4).
2.4 Computational details
Theoretical calculations were performed using the Gaussian 03 program [21]. Them
were based on the gradient corrected Density Functional Theory (DFT) with the three-
parameter hybrid functional (B3) [22] for the exchange part and the Lee-Yang-Parr (LYP)
correlation function [23]. Scans of the potential energy curves were carried out at the
B3LYP/6-31G(d,p) approximation. Final molecular conformation optimizations and
vibration frequencies were computed employing the 6-311++G(d,p) basis set. The calculated
vibrational properties correspond, in all cases, to potential energy minima with no imaginary
values for the frequencies. Electronic transitions were calculated within the Time-Dependent
Density Functional Theory (TD-DFT) [24] in gas phase and taking into account implicitly
1
13
the solvent effect (ethanol) at B3LYP/6-311+G(2d,p) approximation. The H and C NMR
chemical shifts were calculated at the B3LYP/6-311+G(2d,p) level by the gauge-including
atomic orbital (GIAO) method [25] using the corresponding TMS shielding, calculated at
the same level of theory. The natural bond orbital (NBO) analysis for the molecules was
performed at B3LYP/6-311++G(d,p) approximation by means the NBO 3.1 program
implemented in the Gaussian 03 package.

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2.5 Hirshfeld surface analysis
Hirshfeld surfaces and their associated 2D fingerprint plots were constructed using
CrystalExplorer 3.1 software [26]. The 3D dnorm surfaces were mapped over a fixed color scale
of -0.24 (red) to 0.93 Å (blue). Molecular Hirshfeld surfaces in the crystal structure are
constructed taking into account the electron distribution calculated as the sum of spherical
atom electron densities [27, 28]. The Hirshfeld surface enclosing a molecule is defined by
points where the contribution to the electron density from the molecule of interest is equal to
the contribution from all the other molecules. For each point on that isosurface two distances
are defined: de, the distance from the point to the nearest nucleus external to the surface, and di
the distance to the nearest nucleus internal to the surface. The normalized contact distance
(dnorm) based on both de and di and the vdW radii of the atom, given by eq. (1) enables
identification of the regions of particular importance to intermolecular interactions [28]. A
color scale of red (shorter than vdW separation)-white (equal to vdW separation)-blue (longer
than vdW separation) was used to visualize the intermolecular contacts.
The combination of de and di in the form of a 2D fingerprint plot provides summary of
intermolecular contacts in the crystal [27]. The 2D fingerprint plots were displayed by using
the translated 0.6-2.6 Å range and including reciprocal contacts.
3. RESULTS AND DISCUSSION
3.1 Description of X-ray crystal structure of compounds 3 and 4
ORTEP [29] plots of solid state compounds 3 and 4 are displayed in Figure 1 and their
X-ray geometrical parameters such as bond lengths, angles and dihedral angles, together with
the computed values at B3LYP/6-311++G(d,p) approximation are shown in Tables 1 and 2,
respectively. Observed bond lengths and angles agree with Organic Chemistry’s rules. In
particular, C-C bond lengths in the phenyl ring are in the range from 1.367(2) to 1.401(2) Å in
3 and from 1.378(2) to 1.406(2) Å in 4, as expected for a resonant bond structure. Single C-C

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bond distances are in the range from 1.485(2) to 1.536(2) Å for 3 and in the 1.483(2)-1.532(2)
Å interval for 4. C=O distance in the ketone group is 1.213(2) Å for 3 and 1.222(2) Å for 4.
Hetero-cycle ring C(sp2)-O and O-C(sp3) bond lengths are respectively 1.356(2) and 1.464(2)
Å in 3, and 1.356(2) and 1.467(2) Å in 4. All the geometrical parameters related to the
chromane moiety are in accordance with the values previously reported for 6-acetyl-2,2-
dimethyl-chromane [9].
In the structure of 3, each molecule participates in four hydrogen bonds and these inter-
molecular interactions necessarily dominate the crystal packing of the compound. In the
crystal packing of 3, neighboring molecules related by a unit cell translation along c-axis are
linked to each other through inter-molecular O-H···O(keto) bonds [d(OH···O) = 2.014 Å,
angle (O-H···O) = 171.7º] giving rise to a polymeric structure along the crystal c-axis (See
Figure 2). The crystal structure of 3 features the characteristic pattern of the
cyclic
hydrogen bond interaction between the O-H···O(keto) and C-H···O(pyrane). Two molecules
are also linked between C-H···O(pyrane) hydrogen bonds into centre-symmetric dimers
stacked, giving (8) graph-set motif as shown in Figure 2a.
The supramolecular assembly also includes the existence of one intermolecular C-
H···π interaction involving the benzene (Cg2 centroid) ring and the H atom bounded to C(10)
as can be seen in Figure 2b. The C10-H···Cg2 interaction [symmetry code: 2-x,1-y,1-z] forms
centre-symmetric dimers with an angle of 172º. The distance between the H and the Cg2
centroid is 2.964 Å.
In 4 the hydroxyl group serves a double stabilizing function acting as a bifurcate H-
bond donor. It forms a weak and bent intra-molecular OH···O(furan) bond [d(OH···O) =
2.505 Å, (O-H…O) = 103.7º] and also links neighboring molecules (symmetry related
through a glide plane) to each other by a much stronger inter-molecular O-H···O(keto) bond
[d(OH···O)=2.051
Å
,
(O-H···O)=151.8º], giving rise to a zig-zag polymeric structure that
extends along the crystal c-axis (see Figure 3).
3.2 Hirshfeld surface analysis
Hirshfeld surface analysis was performed to understand the nature of the molecular
packing, highlighting the contribution of significant inter-molecular interactions that stabilize

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the observed crystal structure. Figure 4 shows the Hirshfeld surfaces (dnorm surfaces) of
compound 3. The normalized contact distance (dnorm) based on both de and di, and the radii of
the atom enable the regions indicating the intermolecular interactions. The active spots shown
in dnorm surfaces characterize the hydrogen-bonding interactions. The large circular spots in
deep red, which are visible on the dnorm surfaces are an indicator of hydrogen bonding contacts
and other visible spots are due to H···H interactions. The dominant H···O and O···H
interactions are visualized in Hirshfeld surfaces by the bright red area labeled 1 and 4 in
Figures 4a and 4b. As was deduced from the crystal structure, these interactions produce a
polymeric structure as can be seen in Figure 4d. The small amount of area and light color on
the surface indicates weaker and longer contacts other than hydrogen bonds. The two red
regions labeled 2 and 3 in the dnorm map are attributed to C-H···O hydrogen bonds involving
the acceptor O15 of the oxopyrane group belonging to two different molecules (see Figure
4c). The red region located in the methy groups labeled 3 in Figure 4b is attributed to C-
H···C non-classical hydrogen bonds. The Hirshfeld surfaces mapped with shape index and
curvedness for compound 3 are reported in the supplementary material. There is neither
touching complementary pair of triangles for shape index surface nor large and green flat
regions for curvedness surfaces which indicate that π-π stacking interactions are absent in the
crystal packing of compound 3.
Figure 5 shows the Hirshfeld surface plots for compound 4. The spots labeled as 1 and
2, with the large and circular depressions (deep red) visible on the front and back views of the
surfaces are indicative of hydrogen-bonding contacts. These interactions are attributed to O-
H···O(keto) interactions. The dominant interactions between C-H and the O atom from the
hydroxyl group can be seen in the Hirshfeld surface as the red areas marked as 3 and 4 in
Figure 5. The interaction labeled 3 is assigned to the C-H···O interaction between the
hydrogen of the methyl from the acetyl group and the O from the hydroxyl whereas the area
marked as 4 is attributed to the interaction between the hydrogen atom from the furan ring and
the oxygen from the hydroxyl group. The small extent of area and light color of surface
indicates weaker and longer contact other than hydrogen bonds.
Two dimensional (2D) fingerprint plots were obtained by calculating the distances
from the Hirshfeld surface to the nearest nucleus inside the surface (di) to the outs of surface
(de) to analyze the molecular interaction around the nearest neighbor molecules. In 2D plots,

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green regions show closer contacts and blue color indicates longer contacts. Complementary
regions are visible in the fingerprint plots where one molecule acts as donor (de > di) and the
other as acceptor (de < di). The fingerprint plots of the main intermolecular interactions for
both structures are shown in Figure 6. The H···H interaction (labeled as 1) in compound 3 is
59.2%, whereas in 4 is 59.6%. These interactions have the major contribution to the crystal
packing of both structures. The proportion of O···H and H···O interactions (labeled as 2)
comprising 11.8 and 10.0 % of the Hirshfeld surface for each molecule of compound 3. In 3,
the H···O interactions are represented by a spike near a (de+di) sum of 1.85 Å in the bottom
left (donor) area of the fingerprint plot (See Figure 6), which represents the interaction
between the hydrogen atom of the hydroxyl group and the carbonyl oxygen. Also, the
interaction between oxygen of the pyrane ring interacts with the hydrogen of the benzene ring
of another molecule. These interactions produce a three-dimensional network of hydrogen
bonds. The O···H interactions are represented by a spike near a (de+di) sum of 1.85 Å in the
botton right (acceptor) region of fingerprint plot, where carbonyl oxygen also acts as acceptor
to the neighboring hydrogen atoms from the hydroxyl groups. These interactions represent the
closest contacts in the structure and can be seen as a pair of large red spots on the dnorm surface
(Figure 4). O···H interactions in compound 4 are represented by spikes near a (de+di) sum of
1.95 Å and represent the interaction between the hydrogen from the hydroxyl group and the O
atom from the carbonyl group. The decomposed fingerprint plot shows C-H···C hydrogen
bonds of which C-H···π interactions appears as a pair of characteristic wings around (de+di)
sum of 3.1 and 3.0 Å in compounds 3 and 4, respectively. The C···H interactions correspond
to 17.4 % and 18.3 % of total contribution to the Hirshfeld surface for compounds 3 and 4,
respectively.
3.3 Structural results derived from quantum chemical calculations
The optimized molecular structures calculated at B3LYP/6-311++G(d,p)
approximation for compounds 3 and 4 are shown in Figures 7(a) and 7(b). The molecules are
characterized primarily by a planar conformation. Tables 2 and 3 give a comparison between
the experimental values of the relevant geometrical parameters and the optimized molecular
structures calculated at B3LYP/6-311++G(d,p) level. The agreement between the
experimental and computed results is very good in all the groups of the molecules. The small

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differences between the calculated and experimental geometrical parameters are attributed to
the fact that the theoretical calculations were performed with isolated molecules in gas phase
whereas the experimental data were based on molecules in the solid state. The acetyl group of
molecules 3 and 4 shows only a small distortion from the molecular plane: the C8-C7-C1-C2
and C8-C7-C1-C2 torsion angles are -179.8º and 0.4155º, respectively for compound 3 and -
179.9º and -0.041º for compound 4. The comparison of the X-ray data of compound 3 with
those of the parent 6-acethyl-2,2-dimethyl chromane [9] indicates that the presence of the
hydroxyl group does not affect the extent of planarity in the phenyl ring and the acetyl group.
The Natural Bond Orbital (NBO) population analysis is an important tool to calculate
donor→ acceptor interactions estimated by the second order perturbation theory [30, 31]. The
lone-pair electron at the carbonyl oxygen atom donates electronic density mainly to the vacant
C1-C7 and C7-C8 anti-bonding orbitals via hyper-conjugative interactions of the type
LPπO(14)→ σ* C-C with energy values of 20.40 and 21.45 kcal mol-1, respectively for
compound 3 and 18.52 and 19.97 kcal mol-1 for compound 4. The mesomeric effect, reflected
mainly by the LPπ O(15) → π* C4-C5 interactions are 28.03 and 28.52 kcal mol-1 for
compounds 3 and 4, respectively. This type of interaction also leads to increased occupation
numbers of the corresponding π* C4-C5 orbitals. In the case of compound 3, the occupation
number is slightly larger (0.39e) than that in compound 4 (0.38e). The described increased
population of the π* C4-C5 orbital in compound 3 reduces the C4-C5 bond strength and, as a
consequence, a bond lengthening (See Tables 2 and 3).
The total atomic charges of compounds 3 and 4 are obtained from natural population
analysis at B3LYP/6-311++G(d,p) level are provided as Supplementary Information. The
atomic charges obtained using the natural population analysis approach revealed that the more
negative charge (-0.74 a.u.) is located at the O(16) atom of the hydroxyl group and the
negative charges -0.57 and -0.56 are located at the O(15) and O(14) atoms, respectively for
compound 3. Similar results were obtained for compound 4. The more negative charge on
O(16) atom makes C(7) atom more positive and acidic (charge of +0.56). The negative
charges mainly located on O(16), O(15) and O(14) atoms could interact with the positive part
of a receptor. In addition, C(7) atom is the most positively charged part and could interact with
the negatively charged part of a receptor easily.

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In order to understand the sites for electrophilic and nucleophilic attacks, we resorted
to molecular electrostatic potential (MEP) calculations [32, 33]. MEP plots of compounds 3
and 4 generated at the optimized geometry of both molecules using GaussView 05 software
are shown in the Supplementary Information. The red and blue regions of MEP represent the
net negative and positive charges, respectively. For compound 3, the red regions are mainly
located on the oxygen atom of the carbonyl group and the oxygen atom of the hydroxyl group.
The atomic charge analysis and MEP calculation confirmed that hydroxyl and carbonyl
oxygen atoms are preferred sites for electrophilic attack. Similar results were obtained for
compound 4. It is evident from the MEP map for compound 3 that the region around the
hydrogen atoms of the hydroxyl group is electron deficient (blue region), in accordance with
NPA charges with a maximum positive value (0.46) for H(19) atom. The blue region is also
observed around the hydrogen atom of the hydroxyl group in compound 4.
3.4 Vibrational results
The FTIR and Raman spectra for the solid sate compounds 3 and 4 are shown in
Figure 8. The observed and computed frequencies (B3LYP/6-311++G(d,p)), together with
the corresponding assignment of bands, are given in Tables 4 and 5. A tentative assignment
of the observed bands in the IR and Raman spectra were carried out by comparison with
theoretical results and also with the frequencies reported for related compounds. A very
good agreement between the experimental and calculated vibration data was observed.
Only the normal modes of the most relevant characteristic functional groups of the
molecules will be discussed.
3.4.1 Assignment of bands
OH modes. For compound 3, the very broad IR absorption band centered at 3427 cm-1 is
assigned to the O-H stretch. This mode was calculated at 3844 cm-1 at the B3LYP/6-
311++G(d,p) approximation. For compound 4, this mode appears as a broad band located at
3435 cm-1 in the IR spectrum and at 3389 cm-1 in Raman. The strong hydrogen bonding
present in the solid state of this compound red-shifts the υ(O-H) frequency. The O-H in-plane
bending mode is observed in the IR spectra at 1180 cm-1 (3) and 1292 cm-1 (4). This mode

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appears at 1289 cm-1 in the Raman spectrum of compound 4. The calculated frequencies for
both compounds appear in Tables 4 and 5.
CH3 modes. The Raman dispersion bands observed at 3042, 3003 and 2983 cm-1 in compound
3 are assigned to CH3 asymmetric stretching modes. In compound 4 these bands appear at
2976 cm-1 in the IR spectrum and at 3045, 3006, 2977, 2968 and 2915 cm-1 in Raman. For 3
the CH3 symmetric stretching modes are observed at 2935 cm-1 in the IR spectrum and at 2936
and 2924 cm-1 in Raman. For compound 4, the bands located at 2909 and 2865 cm-1 in the
Raman spectrum are assigned to the mode previously mentioned. The CH3 asymmetric
bending modes are observed in the IR spectra as medium-intensity bands at 1576, 1495 and
1434 cm-1 for 3 and as medium-intensity bands at 1469 and 1440 cm-1 for 4. These frequencies
are in accordance with the data reported in literature [9, 34]. For 3, the Raman dispersion band
located at 1339 cm-1 is assigned to the CH3 symmetric bending mode. For compound 4, the
bands corresponding to the CH3 symmetric bending mode are well defined in the IR and
Raman spectra. This vibration appears at 1380, 1362 and 1314 cm-1 in IR and at 1382 and
1367 cm-1 in Raman. The IR bands located at 1122, 1077, 1010 and 975 cm-1 in compound 3
(1127 cm-1 in Raman) are assigned to the CH3 rocking mode. For 4, these vibrations appear at
1020 and 999 cm-1 in IR and at 1042, 1023 and 999 cm-1 in Raman. This assignment was in
accordance with literature data [9, 34] and it is supported by quantum chemical calculations
(see Tables 5 and 6).
CH2 modes. The CH2 stretching modes are observed in the IR spectrum of 3 as a weak band
located at 2979 cm-1 and as a low-intensity Raman band at 2980 cm-1. A similar feature was
observed for compound 4, in which the weak IR band located at 2935 cm-1 (2939 cm-1 in
Raman) is assigned to the previously mentioned mode. The shoulder observed in the IR
spectrum of 3 at 2911 cm-1 (2916 cm-1 in Raman) is assigned to the CH2 symmetric stretching
mode. This mode was not detected in the IR and Raman spectra of compound 4. The medium-
intensity band located at 1427 cm-1 in the IR spectrum of 3 is assigned to the CH2 bending
mode. For compound 4, this vibration appears as a Raman band located at 1429 cm-1. The
modes corresponding to the wagging, twisting and rocking modes of the methylene group are
all assigned and given in Tables 5 and 6.

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CH modes. The aromatic structure gives rise to C-H stretching vibrations in the frequency
region from 3200 to 3000 cm-1. These modes are not affected by the nature and position of
substituents. In both compounds, two rings are fused together and three C-H stretching
vibrations are expected. The characteristic C-H stretching mode for compound 3 is assigned to
the very weak IR bands observed at 3056 and 3951 cm-1 and at 3072, 3055 and 3052 cm-1 in
Raman. This assignment is in accordance with the theoretical predictions (see Table 5). For
compound 4, the C-H stretching vibration appears as low-intensity bands in the Raman
spectrum at 3068, 3062 and 3051 cm-1.
In compound 3, the IR spectrum shows two absorptions at 1360 and 1267 cm-1, with medium
and very strong intensities, respectively, which are assigned to the in-plane C-H bending
modes of the aromatic ring. The Raman dispersion counterpart appears at 1279 cm-1. For
compound 4, the in-plane C-H stretching modes appear as medium-intensity IR bands at 1235,
1123 and 1112 cm-1 (1229 and 1109 cm-1 in Raman). The out-of-plane C-H deformation
modes are all assigned in Tables 5 and 6.
C=O modes. For 3, the strong IR absorption at 1673 cm-1 (calculated value at 1734 cm-1) is
attributed to the υ(C=O) mode. This vibration corresponds to the medium-intensity Raman
band observed at 1668 cm-1. In compound 4, the υ(C=O) mode appears as a strong IR band at
1668 cm-1 and the Raman counterpart at 1666 cm-1. The spectral features and assignment of
the C=O in-plane and out-of-plane bending vibrations for compounds 3 and 4 are included in
Tables 5 and 6, respectively.
3.5 Electronic spectra and frontier molecular orbitals
The experimental (measured in ethanol solvent) and calculated electronic absorption
spectra of compounds 3 and 4 are shown in the Supplementary Information. The assigned
transitions with major contributions for both compounds are shown in Table 6. A very
good correlation between experimental and calculated spectra was observed. In the
experimental spectrum, the two bands centered at 280 and 289 nm are assigned to the
HOMO→LUMO transitions for 3 and 4, respectively. The bands corresponding to the
HOMO-2→LUMO and HOMO→LUMO+1 were not observed experimentally due to their
lower oscillator strength (see Table 6).

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The frontier molecular orbitals involved in the electronic transitions for compounds
3 and 4 are depicted in Figure 9. As can be observed in Figure 9, the HOMO for both
compounds involves π-bonding orbitals of the aromatic ring and the non-bonding character
of the three oxygen and some carbon atoms from another ring. The LUMO exhibits a π
anti-bonding character of the carbon atoms of the aromatic ring and non-bonding character
of some carbon atoms of the pyran and furan rings. Thus, the HOMO→LUMO transition
has a π→π* nature. The HOMO-1 corresponds to a p-type orbital strongly located on the
oxygen atom of the carbonyl group and the carbon atoms of the acetyl group. The HOMO-2
corresponds to a π-bonding system located over the aromatic ring and a p-type orbital
located on the oxygen and a carbon atom of the hetero-cycle ring. In LUMO+1 the electron
density of π* nature is extended all over the aromatic ring.
3.6 1H NMR spectral study
1
The H NMR spectra of the title compounds have been recorded in CDCl3 and the
chemical shifts for non-equivalent protons relative to TMS are given in the experimental
section (Section 3.1). The signals due to the characteristic aromatic protons were observed
in the region 7.83-7.81 ppm. For compound 3, the signals located at 7.75, 7.73 and 6.85 are
1
assigned to H-7, H-5, H-8, respectively. The H NMR spectra of compound 4 shows two
doublets at 7.81 and 6.82 ppm due to H-6 and H-7, respectively. The signal corresponding
to H-4 appears as a singlet at 7.83 ppm.
The two doublets located at 3.10 and 2.83 ppm in the 1H NMR spectra of compound
3, are attributed to H-4 of the pyran ring and the doublet at 3.22 ppm observed in
compound 4 is assigned to H-3 corresponding to the benzofuran ring. The protons H-9
corresponding to the CH3(CO) group appears as a singlet at 2.54 ppm. The signals observed
at 1.38 and 1.35 ppm in the spectra of compound 3 are assigned to each gem-dimethyl
group. The 1H NMR spectra of compound 4 show two singlets at 1.25 and 1.23 ppm due to
H-4’ and H-5’, respectively. The total of protons calculated from the integration curve is in
accordance with those calculated from the proposed molecular formula.

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4. CONCLUSIONS
The benzopyran 2,2-dimethyl-3-hydroxy-6-acetyl-chromane (compound 3) and
benzofuran 10,11-dihydro-10-hydroxytremetone (compound 4) are structural isomers that
biogenetically are formed from a prenylated p-hydroxyacetophenone precursor. The crystal
structure of both substances was determined by X-ray diffraction methods and the major
packing interactions that help to stabilize each structure were identified. Compound 3
crystallizes in the triclinic P-1 space group and compound 4 in the monoclinic P21/c space
group. The Hirshfeld surfaces and fingerprint plots were used to understand, identify and
quantify the interactions that are responsible for different packing patterns observed in both
compounds. In accordance with Hirshfeld surface analysis, the relative contributions of
H···H interactions are higher than other contacts. Intra- and inter-molecular hydrogen
bonding interactions play a dominant role in structural diversity related to different kinds of
supra-molecular assembly of both compounds. The theoretical results agree with the
experimental observations. The vibrational and electronic properties were fully determined
by combining experimental data and quantum chemical calculations.

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REFERENCES
[1] P. Proksch, E.Rodriguez, Phytochemistry 1983, 22, 2335.
[2] E. Romano, A. Raschi, A.M. González, G. Jaime, M. Fortuna,R. Hernández, H. Bach, A.
Benavente, Plant Physiol. and Biochem. 2001, 49, 671.
[3] K.C. Nicolaou, J.A. Pfefferkorn, A.J. Roecker, G.Q. Cao, S. Barluenga, H.J. Mitchell, J.
Am. Chem. Soc. 2000, 122, 9939.
[4] L. Li, H.-K.Wang, J.-J Chang, A. T. McPhail, D. R. McPhail, H. Terada, T. Konoshima,
M. Kokumai, M. Kozuka, K.-H Lee, J. Nat.Prod. 1993, 56, 690.
[5] S. Kawaii, Y. Tomono, E. Katase, K. Ogawa, M. Yano, Y. Takemura, M. Ju-ichi, C.
Ito, H. Furukawa, J. Nat. Prod. 1999, 62, 587.
[6] S. P. Pillai, S. R. Menon, L. A. Mitscher, C. A. Pillai, D. M. Shankel, J. Nat. Prod.
1999, 62, 1358.
[7] Y. Kashman, K. R. Gustafson, R. W. Fuller, J. H. Cardellina, J. B. McMahon, M. J.
Currens, R. W. Buckheit, S. H. Hughes, G. M. Cragg, M. R. Boyd, J. Med. Chem. 1992, 35,
2735.
[8] A. D. Patil, A. J. Freyer, D. S. Eggleston, R. C. Haltiwanger, M. F. Bean, P. B. Taylor,
M. J. Caranfa, A. L. Breen, H. R. Bartus, J.Med. Chem. 1993, 36, 4131.
[9] E. Lizarraga, D.M. Gil, G.A. Echeverría, O.E. Piro, C.A.N. Catalán, A. Ben Altabef,
Spectrochim.Acta A 2014, 127, 74.
[10] L. Tsung-Jen, E. Ramstad, P. Heinstein, Phytochemistry 1974, 13, 1809.
[11] R. Siebertz, P. Proksch, L. Witte, Phytochemistry 1990, 29, 2135.
[12] R. Siebertz, P. Proksch, V. Wray, L. Witte, Phytochemistry 1989, 28, 789.
[13] L. Margl, C. Ettenhuber, I. Gyurjan, M. H.Zenk, A. Bacher, W. Eisenreich,
Phytochemistry 2005, 66, 887.
[14] T. Garcia de Quesada, B. Rodriguez, S. Valverde, Phytochemistry 1972, 11, 446.
[15] F. Bohlmann, C. Zdero, R.M. King, H. Robinson, Phytochemistry 1980, 19, 1141.
[16] S. Piacente, R. Aquino, N. De Tommasi, O. Lock De Ugaz, H. Chavez Orellana,
Phytochemistry 1992, 31, 2182.

ACCEPTED MANUSCRIPT
[17] J.R. Soberón, E. Lizarraga, M.A. Sgariglia, M.B. Carrasco Juárez, D.A. Sampietro, A.
Ben Altabef, C.A.N. Catalán, M.A. Vattuone, Antonie van Leeuwenhoek Journal of
Microbiology 2015, 108, 1047-1057.
[18] T. Tomas-Barberán, E. Iniesta-Sanmartin, F. Tomás-Lorente, A. Rumbero,
Phytochemistry 1990, 29, 1093.
[19] CrysAlisPro, Oxford Diffraction Ltd., version 1.171.33.48 (release 15-09-
2009CrysAlis171.NET).
[20] G. M. Sheldrick, ActaCrystallogr. 2008, A64, 112.
[21] M. J. Frisch, J. A. Pople, J. S. Binkley, J. Chem. Phys. 1984, 80, 3265. M. J. Frisch, G.
W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A.
Montgomery Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J.
Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H.
Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J.
B. Cross, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin,
R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O.
Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz,
I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng, A.
Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C.
González, J. A. Pople, Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
[22] A.D. Becke, J. Chem. Phys. 1993, 98, 5648.
[23] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B, 1988, 37, 785.
[24] P. Elliot, F. Furche, K. Burke, Rev. Comp. Chem. 2009, 26, 91.
[25] J.R. Cheeseman, G.W. Trucks, T.A. Keith, M.J. Frisch, Chem. Phys. 1996, 104, 5497.
[26] J.J. McKinnon, M.A. Spackman, A.S. Mitchel, Acta Crystallogr., 2004, B60, 627.
[27] M.A. Spackman, P. G. Byrom, Chem. Phys. Lett. 1997, 267, 215.
[28] M.A. Spackman, J.J. McKinnon, CrystEngComm. 2002, 4, 378.
[29] L. J. Farrugia, J. Appl. Cryst. 1997, 30, 565.
[30] A.E. Reed, L.A. Curtis, F. Weinhold, Chem. Rev. 1988, 88, 899.

ACCEPTED MANUSCRIPT
[31] J.P. Foster, F. Weinhold, J. Am. Chem. Soc. 1980, 102, 7211.
[32] N. Okulik, A.H. Jubert, Internet Electron J. Mol. Des. 2005, 4, 17.
[33] J. Sponer, P. Hobza, Int. J. Quantum Chem. 1996, 57, 959.
[34] D. Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Grasselli. The Handbook of Infrared and
Raman Characteristic Frequencies of Organic Molecules.Academic Press, Inc. United
Kingdom. 1991.

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Acknowledgments
This work was supported by SCAIT (D542/2), CONICET (PIP 0205 and PIP 1529) and
ANPCyT (PME06 2804, PICT06 2315 and PICT0697) of Argentina.

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Table 1: Crystal data and structure refinement results for compounds 3and 4.
Compound
(3)
C13 H16 O3
220.26
293(2)
1.54184
Triclinic
P-1
(4)
C13 H16 O3
220.26
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
293(2)
1.54184
Monoclinic
P21/c
6.4289(6)
8.7120(6)
10.952(1)
92.280(7)
95.738(7)
103.973(7)
590.96(9)
11.2891(6)
9.1902(4)
12.4272(7)
90.00
113.689(7)
90.00
b (Å)
c (Å)
α
β
γ
(º)
(º)
(º)
3
1180.7(1)
Volume (Å )
Z, calculated density (Mg/m )
3
2, 1.238
0.708
4, 1.239
0.708
-1
Absorption coefficient (mm )
F(000)
236
472
3
0.142 x 0.238 x
0.312
0.138 x 0.289 x
0.368
Crystal size (mm )
ϑ
-range (º) for data collection
5.24 to 70.99
4.28 to 72.33
Index ranges
-7
10, -13
3525
≤
h
≤
7, -9
≤
10
k
≤
-13
≤
h
≤
11, -10
15
4677
≤
15
k ≤
≤
l
≤
≤
l
≤
Reflections collected
Independent reflections
2247 [R(int) =
0.0176]
2300 [R(int) =
0.0223]
Observed reflections [I>2
Completeness (%)
σ
(I)]
1817
1930
ϑ = 72.33°)
98.3 (to
ϑ
= 70.99°) 98.7 (to
Refinement method
Full-matrix least-
Full-matrix least-
2
2
squares on F
squares on F
Data / restraints / parameters
2247 / 0 / 209
1.046
2300 / 0 / 209
1.053
2
Goodness-of-fit on F
a
R1 = 0.0477, wR2
= 0.1338
R1 = 0.0422, wR2
= 0.1158
Final R indices [I>2
σ(I)]
R indices (all data)
R1 = 0.0567, wR2
= 0.1481
R1 = 0.0503, wR2
= 0.1264
Largest diff. peak and hole
-3
0.193 and -0.185
0.164 and -0.206
(e.Å )
a
R1=
Σ||Fo|-|Fc||/
Σ
|Fo|, wR2=[
Σ
w(|Fo|2-|Fc|2)2/
Σ
w(|Fo|2)2]1/2

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Table 2: Experimental and calculated bond lengths (Å), bond angles (º), and dihedral angles (º) for
compound 3.
Compound 1
Parameters
Experimentala Calculatedb
Bond lengths
C7-C8
C7=O14
C7-C1
C1-C2
C2-C3
C3-C4
C4-C5
C5-C6
C6-C1
C5-C11
C11-C10
C10-C9
C9-O15
C9-C12
C9-C13
C10-O16
C4-O15
1.494(4)
1.213(3)
1.485(2)
1.399(3)
1.386(2)
1.401(2)
1.400(2)
1.387(2)
1.393(2)
1.507(2)
1.513(2)
1.536(2)
1.464(2)
1.513(3)
1.513(3)
1.421(2)
1.356(2)
1.519
1.219
1.493
1.406
1.381
1.403
1.402
1.395
1.398
1.511
1.522
1.550
1.458
1.526
1.531
1.427
1.362
Bond angles
C8-C7-C1
119.8(2)
120.2(2)
120.0(2)
112.3(1)
117.7(1)
107.1(1)
111.7(1)
107.2(1)
112.2(2)
118.9
120.2
120.9
111.1
118.9
107.6
112.2
107.4
111.2
C8-C7=O14
C1-C7=O14
C5-C11-C10
C4-O15-C9
O15-C9-C10
C9-C10-O16
O16-C10-C11
C13-C9-C12
Dihedral angles
C8-C7-C1-C2
C8-C7-C1-C6
179.6(2)
-1.5(3)
-60.5(2)
179.8
0.4155
-60.28
C11-C10-C9-O15
a Experimental values determined by X-ray diffraction methods.
b Calculated at B3LYP/6-311++G(d,p) approximation.

ACCEPTED MANUSCRIPT
Table 3: Experimental and calculated bond lengths (Å), bond angles (º), and dihedral angles (º) for
compound 4.
Compound 2
Parameters
Experimentala Calculatedb
Bond lengths
C7-C8
C7=O14
C7-C1
C1-C2
C2-C3
C3-C4
C4-C5
C5-C6
C6-C1
1.507(3)
1.222(2)
1.483(2)
1.406(2)
1.378(2)
1.392(2)
1.385(2)
1.381(3)
1.396(3)
1.506(2)
1.532(2)
1.467(2)
1.356(2)
1.527(2)
1.521(3)
1.519(3)
1.429(2)
1.519
1.219
1.494
1.408
1.384
1.395
1.391
1.390
1.405
1.509
1.547
1.468
1.361
1.541
1.535
1.529
1.434
C3-C9
C9-C10
C10-O15
C4-O15
C10-C11
C11-C13
C11-C12
C11-O16
Bond angles
C8-C7-C1
118.8(1)
120.3(2)
120.9(1)
102.1(1)
116.9(1)
105.8(1)
107.5(1)
109.8(1)
110.9(1)
118.8
120.1
121.0
102.0
116.6
105.6
107.9
109.2
110.8
C8-C7=O14
C1-C7=O14
C3-C9-C10
C9-C10-C11
C9-C10-O15
C10-O15-C4
C10-C11-O16
C13-C11-C12
Dihedral angles
C8-C7-C1-C6
C8-C7-C1-C2
C3-C9-C10-O15
C9-C10-C11-O16
O15-C10-C11-O16
163.7(2)
-15.1(2)
18.5(1)
-56.0(2)
63.0(1)
179.9
-0.041
17.64
-56.66
61.96
a Experimental values determined by X-ray diffraction methods.
b Calculated at B3LYP/6-311++G(d,p) approximation.

ACCEPTED MANUSCRIPT
Table 4: Observed and calculated frequencies (in cm-1) and tentative assignments of modes for
compound 3.
Experimental
Calculatedc
Scaled
3779
3148
3132
3118
3088
3067
3059
3056
3050
3037
3019
2993
2982
2981
2975
2945
1704
1575
1539
1459
1450
1440
1430
1422
1420
1419
1410
1389
1363
1356
1343
1327
1316
1293
1279
1246
1232
1228
1218
1210
1170
1140
1119
1113
Mode
Tentative assignmentd,e
O-H
C-H (R1)
C-H (R1)
C-H (R1)
νa CH3(CO)
νa CH3 (R2)
νa CH3 (R2)
νa CH3 (R2)
νa CH3 (R2)
νa CH3 (CO)
νa CH2 (R2)
νs CH3 (R2)
νs CH3 (R2)
νs CH3 (CO)
νs CH2 (R2)
IR (solid)a Raman (solid)b Unscaled
IR int
41
4
2
7
1
2
3
4
5
6
7
8
3427 bd
-
3844
3203
3186
3172
3141
3120
3112
3109
3103
3090
3071
3045
3034
3033
3027
2996
1734
1644
1606
1524
1514
1503
1493
1484
1482
1481
1472
1450
1423
1415
1402
1385
1374
1350
1335
1301
1286
1282
1271
1263
1221
1190
1168
1162
ν
ν
ν
ν
-
3072 (12)
3056 vw
3055 (20)
3051 vw
3052 sh
-
-
-
-
-
-
3042 (14)
-
3003 (15)
-
2983 (27)
-
2980 (26)
-
15
17
25
6
22
9
17
10
22
4
18
24
258
106
142
42
6
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
2979 w
-
2935 w
-
2936 (39)
2924 (41)
2911 sh
2879 sh
1673 s
1663 s
1604 m
1576 m
1495 m
1434 sh
1427 m
-
2916 (37)
2891 (19)
1668 (32)
1648 (46)
1600 (100)
1574 (41)
-
-
ν
ν
ν
ν
C10-H
C=O
C-C (R1) +
C-C (R1) +
δ
δ
C-H (R1)
C-H (R1)
δa CH3 (R2) +
δa CH3 (R2)
δa CH3 (R2)
δ C-H (R1)
4
9
2
2
1429 (16)
-
δ
CH2 (R2) + δa CH3 (R2)
δa CH3 (R2) + δ CH2 (R2)
δ CH2 (R2) + δa CH3 (R2)
δa CH3 (CO)
δa CH3 (CO)
-
-
-
-
-
-
12
15
26
6
14
22
57
3
28
64
56
85
220
43
47
63
1
1383 w
1366 sh
1360 m
-
-
-
-
-
ν
δ
δ
C-C (R1) +
OCH + δs CH3 (R2) +
C-H (R1) + δs CH3 (R2)
δ
C-H (R1) +
ω CH2
δ
O-H
δs CH3 (R2)
δs CH3(CO)
OCH
C-C (R1)
δ C-H (R1) + ω CH2 (R2) + δ O-H
-
1339 (11)
1316 (13)
1300 (14)
1279 (24)
1250 (43)
-
1318 w
1301 vw
1267 vs
1251 sh
-
δ
ν
ω
CH2 (R2) +
τω CH2 + C-H (R1) +
C-H (R1)
C-O +
CH3 (R2)
COH + νa C(CH3)2
C5-C11 + C-H (R1)
CH2 + CH3 (R2)
CH3 (R2) + C-H (R1)
δ C-H (R1)
δ
δ
O-H
1226 w
-
-
1180 w
-
1140 m
1122 m
1226 (10)
-
-
ν
δ
ν
δ
ν
ρ
ρ
C4-O15 +
C-H (R2) +
C9-C10 +
δ
ν
ρ
CH2
ρ
-
1169 (8)
1143 sh
1127 (19)
δ
153
6
ρ
δ

ACCEPTED MANUSCRIPT
45
46
47
48
49
50
51
52
53
54
55
56
57
58
58
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
1089 sh
1077 w
-
1059 w
1010 vvw
975 vw
958 w
948 w
937 sh
917 vvw
-
881 w
-
853 vw
829 w
785 vw
732 vw
-
703 vw
646 vw
617 vw
592 vw
560 vvw
536 vvw
524 sh
479 vvw
-
-
1134
1092
1079
1055
1042
1027
996
988
961
959
943
929
903
886
853
792
745
732
713
652
626
611
555
531
524
500
454
442
427
413
364
315
296
294
276
270
254
236
217
192
142
140
125
105
50
1086
1046
1034
1011
998
984
954
947
920
919
903
889
865
849
817
759
714
701
683
625
600
585
532
509
502
479
435
423
409
396
349
302
284
282
264
259
243
226
208
184
139
134
120
101
48
103
6
157
4
1
16
3
19
48
69
7
3
8
12
29
3
2
3
1
11
8
26
1
10
3
δ
ρ
ν
ν
ρ
ρ
γ
γ
C-H (R1)
CH3(CO) +
C10-O16
δ
C-H (R1)
1068 (37)
-
-
970 (16)
955 (17)
-
930 (3)
913 (3)
898 (5)
-
C9-C10 +
CH3(CO)
CH3 (R2)
C-H (R1)
C-H (R1)
δ O-H
ν C9-O15 + ρ CH3(R2) + γ C-H (R1)
ν
C7-C8 +
ρ
CH3(CO)
νs C(CH3)2
δ
γ
ν
γ
δ
γ
δ
δ
δ
CCC (R1) +
C-H (R1)
C9-O15
C-H (R1)
O15-C9-C12 +
CCC (R1) + C-H (R1)
CCC (R1) + νs C(CH3)2
COC (R2)
CCC (R1) + δ CCC (R2)
γ
C-H (R1)
-
852 (3)
-
780 (2)
722 (41)
710 (52)
-
641 (2)
612 (2)
590 (3)
556 (5)
531 (9)
520 (8)
474 (3)
-
435 (8)
408 (3)
δ CCC (R1)
γ
γ C=O + γ CCC (R1) + γ C-H (R1)
δ
δ
δ
γ
δ
γ
δ
δ
δ
δ
γ
τ
γ
τ
τ
τ
τ
τ
τ
τ
τ
τ
τ
τ
τ
CC=O +
CCC (R2)
C10-C9-C12
δ CCC (R1)
CCC (R1) +
CCC (R1)
CCC (R1) +
COC (R2) +
CCO (R2) +
C8-C7-C1 +
C(CH3)2
CCC (R2) +
CH3 (R2)
O-H
O-H
CH3 (R2) +
C9-C10
CH3 (R2)
CH3 (R2) +
γ
C=O
6
1
5
1
12
1
2
-
γ
δ
δ
γ
C-H (R1)
C(CH3)2
C8-C7-C1
COC (R2)
443 vw
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
388 (4)
375 (5)
304 (6)
-
γ
O-H
1
-
36
14
56
4
14
<1
3
1
2
1
1
262 (8)
-
-
222 (9)
-
176 (20)
-
τ
O-H
O-H
τ
C5-C11 +
CH3(CO)
CH3(CO)
τ CH3 (R2)
-
125 (42)
CCCC (R1) +
CCCC (R1) +
C7-C1
τ
τ
CCCC (R2)
COCC (R2)
-
-
-
4
1
46
44
CCOC (R2)
a sh: shoulder, s: strong, w: weak, m: medium, v: very,
b Relative band heights in parenthesis,