The absolute configuration of angular 3′-acyloxypyranocoumarins by vibrational circular dichroism exciton chirality

Article abstract of DOI:10.1016/j.tetasy.2014.09.001

A complex mixture of lomatin C-3′ esters and (-)-O-angeloyllomatin 1 was isolated from the seeds of Prionosciadium thapsoides. Since a literature search revealed that some lomatin C-3′ monoesters have positive specific rotations, while others had negative values, the absolute configuration of all of the molecules was determined to be (R) by exciton chirality in the infrared region, and by chemical correlation. A single crystal X-ray study of acetyllomatin 3, using the Flack and Hooft parameters, independently confirmed this absolute configuration.

Full text of DOI:10.1016/j.tetasy.2014.09.001

Tetrahedron: Asymmetry 25 (2014) 1418–1423
Contents lists available at ScienceDirect
Tetrahedron: Asymmetry
journal homepage: www.elsevier.com/locate/tetasy
The absolute configuration of angular 30-acyloxypyranocoumarins
by vibrational circular dichroism exciton chirality
Abigail I. Buendía-Trujillo a, J. Martín Torrres-Valencia b, Pedro Joseph-Nathan c,
Eleuterio Burgueño-Tapia a,
⇑
a Departamento de Química Orgánica, Escuela Nacional de Ciencias Biológicas, Instituto Politécnico Nacional, Prolongación de Carpio y Plan de Ayala, Col. Santo Tomás, México,
D.F. 11340, Mexico
b Área Académica de Química, Universidad Autónoma del Estado de Hidalgo, km 4.5 Carretera Pachuca-Tulancingo, Mineral de la Reforma, Hidalgo 42184, Mexico
c Departamento de Química, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional, Apartado 14-740, México, D.F. 07000, Mexico
a r t i c l e i n f o
a b s t r a c t
A complex mixture of lomatin C-30 esters and (ꢀ)-O-angeloyllomatin 1 was isolated from the seeds of
Prionosciadium thapsoides. Since a literature search revealed that some lomatin C-30 monoesters have
positive specific rotations, while others had negative values, the absolute configuration of all of the
molecules was determined to be (R) by exciton chirality in the infrared region, and by chemical correla-
tion. A single crystal X-ray study of acetyllomatin 3, using the Flack and Hooft parameters, independently
confirmed this absolute configuration.
Article history:
Received 22 August 2014
Accepted 2 September 2014
Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction
values measured in CHCl3 of +7.6,8d +13.7,8c +14.0,8a and even
+210;4b these specific rotations have been used to assign the
Since the very early isolation of coumarin from Nature in
1820,1 hundreds of coumarin derivatives with a huge variety of
substituents have been described,2 from which pyranocoumarins
constitute an important group.
absolute configuration of other lomatin ester derivatives such as
(+)-(S)-O-angeloyllomatin 1,9 and (+)-(R)-O-dodecanoyllomatin
8.10 Compound
2
is also known as jatamansinol,8d and
xanthogalol.8c
Prionosciadium is a genus of herbaceous plants belonging to the
Apiaceae family. It comprises thirty two species from which only
twelve appear in the Missouri Botanical Garden plant list.3 From
this genus, angular-type pyranocoumarins such as lomatin 2 and
chromones have typically been isolated.4 Some lomatin esters have
been evaluated as coronary vasodilatory and spasmolytic agents,5
against lymphocyte H9 cells infected with HIV,6 as phytotoxic com-
pounds,4b and more recently against a specific antigen secreted by
prostate cancer cells.7
In turn, (+)-O-isobutyroyllomatin 4 was isolated as a natural
product following a bioassay guided fractionation of the phytotoxic
extracts of Prionosciadium watsoni,4b and its (R)-absolute configu-
ration was assigned using Mosher esters. However, an O-isobuty-
royllomatin sample in our hands, obtained after esterification of
(+)-lomatin 2 with i-butyroyl chloride showed [
a
]D = ꢀ9.1. In addi-
tion, Murray in a classical review about naturally occurring couma-
rin2 accounts nine lomatin C-30 monoesters, from which two
showed positive and three showed negative specific rotations
when measured in CHCl3. Although the specific rotation of an
enantiomerically pure sample is frequently used to identify the
absolute configuration of natural products, its dependence on
temperature, concentration, solvent used for the measurement,
and impurities in the sample has led to a literature with many
examples of incorrect values for compounds considered to be
enantiomerically pure.11 Furthermore, the absolute configuration
of (ꢀ)-(R)-4,5-dimethyl-3-hydroxy-2(5H)-furanone and (+)-(R)-
5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone was confirmed by
VCD emphasizing the risk of assignments based on the comparison
of the specific rotation sign of similar structures.12 Therefore, in
a continuation of our studies of natural compound structural
analysis,4a,13 we herein assign the absolute configuration of several
(+)-Lomatin 2 was isolated from Lomatium nuttallii in 1964,8e
and its absolute configuration was established by comparison of
the specific rotation of (+)-(R)-3,5-dinitrobenzoyloxy-5,5-dimethyl-
dihydrofuran-2(3H)-one, obtained after esterification of the ozon-
olysis product of (+)-2, with the respective derivative generated
by ozonolysis of the angular dihydrofuranocoumarin (+)-(S)-8,9-
dihydrooroselol 9 of known absolute configuration.8b Although
the literature shows a wide range of specific rotations for 2, with
⇑
Corresponding author. Tel.: +52 55 5729 6300x62413; fax: +52 55 5747 7137.
E-mail address: eleuteriobt@gmail.com (E. Burgueño-Tapia).
http://dx.doi.org/10.1016/j.tetasy.2014.09.001
0957-4166/Ó 2014 Elsevier Ltd. All rights reserved.

A.I. Buendía-Trujillo et al. / Tetrahedron: Asymmetry 25 (2014) 1418–1423
1419
30-acyloxypyranocoumarins using an independent and reliable
methodology.
frequencies. The amplitudes given in Table 1 correspond to a coun-
terclockwise orientation of the two carbonyl groups, and therefore
we can conclude that the absolute configuration of all these mole-
cules is (R).
The method of choice was vibrational circular dichroism exciton
chirality (VCDEC)14 for which it has been shown that the Harada–
Nakanishi rule holds. Similar to the well-established electronic cir-
cular dichroism chirality methodology,15 VCDEC is based on the
through-space interaction of two or more IR chromophores, which
yield a pair of VCD signals with opposite signs around the absorp-
tion region of the chromophores. The sign of this split-type VCD
signal reflects the absolute configuration of the molecule.14c Thus,
when the interacting chromophores are counterclockwise ori-
ented, the long-wavelength component of the associated exciton
couplet can be expected to exhibit a negative Cotton effect, while
when they are clockwise oriented, the long-wavelength Cotton
effect is positive.
Table 1
VCDEC couplet data for the two carbonyl groups of 1 and 3–8
a
a
Compd
M
D
e1 (v[cmꢀ1])
D
e2 (v[cmꢀ1])
Ab
1
3
4
5
6
7
8
0.08
0.09
0.06
0.06
0.08
0.08
0.06
ꢀ0.07 (1722)
ꢀ0.07 (1724)
ꢀ0.10 (1722)
ꢀ0.10 (1724)
ꢀ0.09 (1715)
ꢀ0.09 (1703)
ꢀ0.09 (1720)
+0.04 (1734)
+0.05 (1745)
+0.07 (1740)
+0.06 (1742)
+0.05 (1724)
+0.05 (1730)
+0.05 (1744)
ꢀ0.11
ꢀ0.12
ꢀ0.17
ꢀ0.16
ꢀ0.14
ꢀ0.14
ꢀ0.14
a
In Mꢀ1 cmꢀ1
.
b
D
e1
ꢀ De2.
5
4
6
3
Although VCDEC does not require quantum chemistry calcula-
tions, we carried out the VCD calculation21 of (R)-3 in order to con-
firm the absolute configuration. After Monte Carlo conformational
searching at the MMFF94 level of theory, two conformers with a
0.55 kcal/mol energy difference, accounting for the total conforma-
tional population were observed, since the third conformer was
7.6 kcal/mol less stable. The two conformers were submitted to
single point energy calculations using density functional theory
(DFT) with the B3LYP/6-31G(d) functional and basis set, followed
by complete geometry optimization at the DFT B3LYP/DGDZVP
level, whereby they converged into the single conformation shown
O
O
O
1
4'
O
4''
3''
5'
Ang =
3'
6'
1''
OR
5''
O
1''
O
R
4''
Sen =
Tgl =
O
O
5''
O
1
2
Ang
H
3''
Ac
3
4
5
6
OH
1''
3''
4''
C(=O)−i-Pr
i-Val
5''
in Figure 1. This most stable conformation showed H–C30–C40–H
a
O
9
Dodecanoyl=
Sen
10
Tgl
7
8
Dodecanoyl
2. Results and discussion
After column chromatography of the EtOAc extract of the seeds of
Prionosciadium thapsoides, (ꢀ)-O-angeloyllomatin 18c,d,16 was iso-
lated along with a complex mixture of lomatin derivatives in which
1 and O-isobutyroyllomatin 4 could be identified. Compound 1
showed [
a
]
D = ꢀ7.6 and its 1H and 13C NMR spectra were in agree-
6.7 Å
ment with those described for the (S)-enantiomer isolated from
Selinum cryptotaenium,9 whose specific rotation was [
A portion of the lomatin ester mixture was subjected to alkaline
hydrolysis to afford (+)-2 ([
D = +12.4), whose 1H and 13C NMR
a]D = +6.2.
(a)
a
]
data were essentially the same as those described.8d,17 A solution
of (+)-2 was treated at room temperature with acetyl, isobutyroyl,
isovaleroyl, senecioyl, and dodecanoyl chlorides to afford the
(ꢀ)-3,7,5a,8c,d,18 (ꢀ)-4,4 (+)-5,19 (+)-6,8a,19,20 and (+)-810 esters,
respectively. Treatment of (+)-2 with angeloyl chloride only affor-
ded (+)-O-tigloyllomatin 7. The identity of (+)-2 and the lomatin
C-30 esters was confirmed by 1D and 2D NMR, including COSY,
HSQC, and HMBC experiments, and by comparison of their spectro-
scopic properties with those described. It is important to note that
the specific rotation for 4 of ꢀ10.6 (c 0.16, CHCl3), measured herein
using two different instruments, was opposite to that described for
θ = −30°
the (R)-enantiomer ([
a]
D = +20.0).4b A sample of (ꢀ)-4 was sub-
jected to alkaline hydrolysis to afford (+)-2 ([a]D = +11.5).
The C-30 lomatin esters, which contain two carbonyl groups, are
ideal candidates to be studied by vibrational circular dichroism exci-
ton chirality (VCDEC) to determine their absolute configuration.
The VCD spectra of (ꢀ)-1, (ꢀ)-3, (ꢀ)-4, (+)-5, (+)-6, (+)-7, and
(+)-8 showed a strong bisignate VCD signal in the carbonyl stretch-
ing region, with a negative–positive couplet from lower to higher
(b)
Figure 1. DFT B3LYP/DGDZVP most stable conformer of (R)-3 showing (a) the syn-
relationship of the ester carbonyl group and H30, and (b) the counterclockwise twist
of the two carbonyl groups’ orientation. The through space intercarbonyl distance is
calculated from the center of the carbonyl groups.

1420
A.I. Buendía-Trujillo et al. / Tetrahedron: Asymmetry 25 (2014) 1418–1423
and H–C30–C40–Hb dihedral angles of ꢀ71.8 and +43.2 degrees,
respectively. Furthermore, the ester carbonyl group is syn-oriented
with H30; the interchromophoric distance, measured from the cen-
ter of the carbonyl groups, is 6.7 Å (a in Fig. 1), and the dihedral
angle between the carbonyl groups is ꢀ30° (b in Fig. 1). The ther-
mochemical parameters and the IR and VCD frequencies at 298 K
and 1 atm were calculated, and compared with the experimental
VCD frequencies (Fig. 2), and showed excellent similarity. Numer-
ical comparison of the experimental and calculated VCD spectra of
(R)-3, using the CompareVOA software,22 gave a similarity index
(SIR) value of 95.2. The calculated spectra for (R)-3 were compared
with the experimental spectra of (ꢀ)-1, (ꢀ)-4, (+)-5, (+)-6, (+)-7,
and (+)-8, providing SIR values of 86.0, 76.9, 81.4, 80.1, 83.9, and
39.7, respectively (Table 2).
1280 cmꢀ1 is mainly due to an asymmetric H–C30–C40–H2 bending
along with asymmetric O30–C100 and C100–C200 stretchings. In the
absorption centered at 1259 cmꢀ1, three positive vibrations can
be identified: a band at 1269 cmꢀ1 due to asymmetric O10–C20
and C20–C30 stretchings, along with a symmetric H–C30–C40–H2
bending; a band at 1259 cmꢀ1 due to asymmetric O30–C100 and
C100–C200 stretching, along with a symmetric H–C30–C40–H2 bend-
ing; and a band at 1256 cmꢀ1 due to asymmetric O30–C100 and
C100–C200 stretchings, along with a small asymmetric H–C30–C40–
H2 bending; and an asymmetric coumarin ring stretching. The
observed vibration at 1052 cmꢀ1 arises mainly from asymmetric
H–C30–C40–H2 bending and C30–O stretching. These calculated
vibrational modes for 3 also show good similarity with the exper-
imental VCD frequencies (Fig. 3) for (ꢀ)-1, (ꢀ)-4, (+)-5, (+)-6, (+)-7,
In addition to the observed strong bisignate VCD couplet, some
vibrational modes were identified for 3. Thus, the negative band at
0,1
0,1
0,05
0,05
0,15
0,1
0,1
0,05
0
7
6
1
0
0
-0,05
-0,1
-0,05
-0,1
0,05
0
3
-0,05
-0,1
0,1
-0,05
0,05
0
0,05
0
80
30
80
ε
-0,05
-0,1
-0,05
-0,1
30
DFT
-20
-70
-20
-70
0,15
0,1
0,05
0
-0,05
-0,1
-0,15
0,05
0
860
710
560
410
260
110
580
480
380
280
180
80
-0,05
-0,1
ε
0,1
0,05
0
0,1
3
20
0,05
0
190
140
90
190
140
90
8
-0,05
-0,1
-0,05
-0,1
ε
0,1
0,05
0
40
40
0,1
DFT
0,05
0
-10
1850
-10
1700
1400
1250
1100
950
−1
5
4
-0,05
-0,1
ν / cm
-0,05
-0,1
Figure 2. Comparison of the experimental IR and VCD spectra for (ꢀ)-3 with the
DFT B3LYP/DGDZVP calculated IR and VCD spectra for (R)-3.
0,1
0,1
0,05
0
0,05
0
Table 2
Confidence level data comparison of the experimental spectra with the calculated IR
and VCD spectra of (30R)-3 at the B3LYP/DGDZVP level of theory
-0,05
-0,1
-0,05
-0,1
Compd
aanH
bSIR
cSE
dS
eESI
fC
ꢀE
1
3
4
5
6
7
8
0.981
0.982
0.977
0.981
0.978
0.986
0.980
86.0
95.2
76.9
81.4
80.1
83.9
39.7
79.2
91.4
70.1
72.5
69.4
77.2
73.0
18.2
19.8
14.7
17.0
17.6
19.2
15.7
61.0
71.6
55.4
55.6
51.8
57.9
57.3
100
100
100
100
98
80
30
80
30
DFT
-20
-20
-70
-120
100
100
-70
a
b
c
d
e
f
-120
Anharmonicity factor.
IR spectral similarity.
VCD spectral similarity for the correct enantiomer.
VCD spectral similarity for the incorrect enantiomer.
1850
1700
1400
1250
1100
950
−1
ν / cm
Enantiomer similarity index, calculated as the SE – S difference.
Confidence level for the stereochemical assignments.
ꢀE
Figure 3. Comparison of the VCD spectra of 1 and 4–8 with the calculated spectrum
of 3 (bottom). Carbonyl couplets were measured from less concentrated solutions.

A.I. Buendía-Trujillo et al. / Tetrahedron: Asymmetry 25 (2014) 1418–1423
1421
and (+)-8, thus corroborating the validity of the conclusion based
on VCDEC.
In an independent and complementary approach for determin-
ing the absolute configuration of 3, a single crystal X-ray diffraction
study was undertaken. A crystal was mounted on a diffractometer
matography separations and reactions were monitored with Merck
silica gel 60 F254 TLC plates. Visualization was achieved with the
UV light (254 nm) and by a ceric sulfate reagent followed by
heating.
equipped with Cu K
a
graphite monochromated radiation and a
4.2. Plant material
large charge coupled device detector. Compound 3 crystallized in
the monoclinic system, space group P21. The molecular structure
(Fig. 4) was solved by direct methods and refined to a discrepancy
index of 3.4%. The complete sphere data set was used to calculate
the Flack parameter,23 which for the (R)-enantiomer was x = 0.0
(2), and the Hooft parameter,24 which was y = 0.03 (9). The Flack
and Hooft parameters for the (S)-enantiomer were x = 1.0 (2) and
y = 0.97 (9), respectively, which again indicates that the absolute
configuration of (ꢀ)-acetyllomatin is (R), which is in agreement
with the VCDEC results.
Seeds of Prionosciadium thapsoides were collected from
Chiquihuite hill, México City, during September 2009. A whole
plant was authenticated by Professor M. González Ledesma at
Herbario del Centro de Investigaciones Biológicas, UAEH, Pachuca,
Hidalgo, Mexico (Voucher number 1836).
4.3. Isolation of natural compounds
The air-dried seeds of Prionosciadium thapsoides (600 g) were
extracted with EtOAc at room temperature for three weeks to give
a pale orange viscous oil, which was dissolved in acetone, kept at
4 °C for 12 h, and filtered to remove fatty materials. The filtrate
was evaporated under vacuum to afford 32 g of the defatted
extract. A portion of 16 g of this extract was chromatographed over
silica-gel (mesh 300–400) using hexanes, hexanes/EtOAc gradient
(9:1, 4:1, 7:3, 1:1), and EtOAc as eluents. Fractions of 1 L of each
polarity were collected, monitored by TLC, and identified as A
(0.29 g), B (0.24 g), C (1.41 g), D (1.83 g), E (0.2 g), and F (0.41 g).
1H NMR spectra of fractions A and B showed fatty material.
Re-chromatography of fraction C gave (ꢀ)-1 (90 mg), and a com-
plex mixture of esters whose 1H NMR analysis allowed us to iden-
tify O-angeloyllomatin 1, and O-isobutyroyllomatin 4 as the major
components. Fraction D also showed this inseparable mixture of
lomatin esters.
C4
C5
C1
C6
C3
C7
C8
C9
C2
O7
C1
O1
O2
C1
C1
C1
4.4. Preparation of acyllomatin derivatives
C1
O12
C1
C1
A solution of fraction C (0.5 g) in EtOH (5 mL), was treated with
KOH/EtOH (5%) and stirred at room temperature for 48 h, and then
neutralized with HCl (5%). The EtOH was evaporated, the residue
was extracted with EtOAc, and then washed with water. The
organic layer was subjected to column chromatography to afford
0.26 g of (+)-2.
O16
To a solution of 25 mg (0.1 mmol) of lomatin in CH2Cl2 (3 mL)
and 6.1 mg of dimethylaminopyridine (0.05 mmol), the corre-
sponding acyl chloride (0.12 mmol) was added. Each reaction mix-
ture was stirred at room temperature for 3 h, after which water
was added (5 mL), and the organic layer was extracted with EtOAc
(3 ꢁ 5 mL), washed with water (3 ꢁ 5 mL), and dried over anhy-
drous Na2SO4. The solvent was evaporated, and the residue was
purified by column chromatography to afford 23.7 mg (81.7%) of
(ꢀ)-3, 25.0 mg (77.9%) of (ꢀ)-4, 30.5 mg (91.1%) of (+)-5, 28.0 mg
(84.8%) of (+)-6, 26.0 mg (80.0%) of (+)-7, and 40.3 mg (92.6%) of
(+)-8.
Figure 4. Perspective view of the X-ray crystal structure of 3.
3. Conclusion
The (R)-absolute configuration of (ꢀ)-1, (ꢀ)-3, (ꢀ)-4, (+)-5, (+)-
6, (+)-7, and (+)-8, was assigned using vibrational circular dichro-
ism exciton chirality, and confirmed both by VCD DFT B3LYP/
DGDZVP calculations, and by X-ray Flack and Hooft parameter
determination for (R)-3.
4.4.1. O-Angeloyllomatin 1
4. Experimental
4.1. General
[
a]
22 = ꢀ7.6 (c 0.07, CHCl3), ([
a]
D = ꢀ24.1).8d 1H and 13C NMR
D
data were essentially the same as those of the (S)-enantiomer
([a]
D = +6.2).9
The 1H, 13C, and 2D NMR spectra were acquired in CDCl3 solu-
tions on a Varian System 500 (125 MHz for 13C) spectrometer at
298 K. Chemical shifts are expressed in ppm (d) relative to TMS
as the internal reference and J values are given in Hz. High resolu-
tion mass spectra were obtained in the electron impact mode at
70 eV on a Jeol GCMateII spectrometer. Optical rotations were
determined in CHCl3 using Perkin Elmer 341 and Jasco DIP-370
polarimeters. Column chromatography separations were carried
out on Natland silica gel 60 (200–300 Mesh ASTM). Column chro-
4.4.2. Lomatin 2
22 = +12.4 (c 0.10, CHCl3), [([
[
a]
a]
D = +7.6),8d ([
a]
D = +13.7),8c
D
([a] a]
D = +14.0),8a ([ D = +210)4b]. 1H and 13C NMR data were identi-
cal to those reported.8c,d
4.4.3. O-Acetyllomatin 3
[
a]
22 = ꢀ6.2 (c 0.15, CHCl3), ([
a]
D = ꢀ6.8).8d 1H NMR data were
D
essentially the same as reported;5a 13C NMR d 161.1 (C-2), 112.6
(C-3), 143.3 (C-4), 112.2 (C-4a), 126.7 (C-5), 114.3 (C-6), 156.2

1422
A.I. Buendía-Trujillo et al. / Tetrahedron: Asymmetry 25 (2014) 1418–1423
(C-7), 106.9 (C-8), 153.4 (C-8a), 76.5 (C-20), 69.4 (C-30), 23.1 (C-40),
23.0 and 24.6 (C-50, C-60), 170.2 (C-100), 21.0 (C-200).
reflections 2902 (Rint 0.01%), observed reflections 2580. The struc-
ture was resolved by direct methods using the SHELXS-97 program
included in the WingGX v1.70.01 crystallographic software pack-
age. For the structural refinement, the non-hydrogen atoms were
treated anisotropically, and the hydrogen atoms, included in the
structure factor calculation, were refined isotropically. The R indi-
4.4.4. O-Isobutyroyllomatin 4
[
a]
22 = ꢀ10.6 (c 1.7, CHCl3), ([
a]
D = +20.0).4 1H and 13C NMR data
D
were essentially the same as reported.4a
ces were [I > 2r(I)] R1 = 3.4% and wR2 = 8.6%. The largest difference
4.4.5. O-Isovaleroyllomatin 5
peak and hole were 0.137 and ꢀ0.129 eÅ3. The Olex2 v1.15 soft-
ware allowed us to calculate the Flack parameter x = 0.0(2) and
the Hooft parameter y = 0.97(9). For the inverted structure these
parameters were x = 1.0(2) and y = 0.97(9), respectively. Crystallo-
graphic data (excluding structure factors) have been deposited at
the Cambridge Crystallographic Data Centre CCDC number
1020904. Copies of the data can be obtained free of charge on
application to the CCDC, 12 Union Road, Cambridge CB2 IEZ, UK.
Fax: +44 (0)1223 336033 or e-mail: deposit@ccdc.cam.ac.ik.
[a] a]
22 = +28.0 (c 0.91, CHCl3), ([ D = +30.0).19 1H NMR data were
D
essentially the same as those reported.19 13C NMR d 161.1 (C-2),
112.6 (C-3), 143.0 (C-4), 112.1 (C-4a), 126.7 (C-5), 114.3 (C-6),
156.3 (C-7), 107.0 (C-8), 153.4 (C-8a), 76.5 (C-20), 69.2 (C-30), 23.1
(C-40), 22.7 and 24.1 (C-50 and C-60), 172.2 (C-100), 43.4 (C-200),
25.7 (C-300), 22.4 (C-400), 22.3 (C-500).
4.4.6. O-Senecioyllomatin 6
[a] a]
22 = +69.3 (c 0.84, CHCl3), ([ D = +71.8).8a 1H NMR data were
D
essentially the same as those reported;8a 13C NMR d 161.1 (C-2),
112.5 (C-3), 143.8 (C-4), 112.1 (C-4a), 126.6 (C-5), 143.8 (C-6),
156.4 (C-7), 107.2 (C-8), 153.4 (C-8a), 76.7 (C-20), 68.3 (C-30), 23.1
(C-40), 22.9 and 24.6 (C-50 and C-60), 165.3 (C-100), 115.5 (C-200),
158.3 (C-300), 20.3 (C-400), 27.4 (C-500).
Acknowledgments
Partial financial support from CONACYT-Mexico (Grants 168066
and 152994), and SIP-IPN (Grants 20120855 and 20130969)
is acknowledged. AIB-T thanks CONACYT for a fellowship (No.
231817). We are grateful to Professor M. González Ledesma
(Herbario del Centro de Investigaciones Biológicas, UAEH, Pachuca,
Hidalgo, Mexico) for identifying the plant material.
4.4.7. O-Tigloyllomatin 7
[a]
22 = +30.8 (c 0.11, CHCl3), 1H NMR d 7.62 (1H, d, J 9.5 Hz, H4),
D
7.26 (1H, d, J 8.5 Hz, H5), 6.80 (1H, d, J 8.5 Hz, H6), 6.80 (1H, qq,
J 7.0, 1.5 Hz, H300), 6.23 (1H, d, J 9.5 Hz, H3), 5.18 (1H, dd, J 5.2,
5.2 Hz, H30), 3.23 (1H, dd, J 17.9, 5.2 Hz, H40a), 2.99 (1H, dd,
J 17.9, 5.2 Hz, H40b), 1.80 (3H, dq, J 1.5, 1.5 Hz, H400), 1.76 (3H, dq,
J 7.0, 1.5 Hz, H500), 1.38, 1.36 (3H each, s, Me-50, Me-60). 13C NMR
d 161.1 (C-2), 112.6 (C-3), 143.8 (C-4), 112.1 (C-4a), 126.6 (C-5),
114.2 (C-6), 156.3 (C-7), 107.2 (C-8), 153.4 (C-8a), 77.2 (C-20),
69.4 (C-30), 23.1 (C-40), 24.8 and 22.8 (C-50 and C-60), 167.0
(C-100), 128.3 (C-200), 138.2 (C-300), 12.0 (C-400), 14.4 (C-500). EIHRMS
m/z calcd for C19H20O5 ([M]+): 328.1311, found: 328.1310.
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