Oxidative transformation of the natural lignan hydroxymatairesinol with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone

Article abstract of DOI:10.1016/S0040-4020(03)00683-5

The oxidative transformation of the two isomers of the natural lignan hydroxymatairesinol from Norway Spruce (Picea abies) by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), has been studied. Significant differences in the outcome of the reactions were observed when the pure isomers of hydroxymatairesinol were reacted with DDQ under the same conditions. The different stereoelectronic effects in the two isomers as well as their conformational structures seem to determine the site of reaction, which results in different reaction products. Several products were identified by GC-MS and NMR spectroscopy. Oxomatairesinol was obtained in a yield of 25%.

Full text of DOI:10.1016/S0040-4020(03)00683-5

Tetrahedron 59 (2003) 4515–4523
Oxidative transformation of the natural lignan
hydroxymatairesinol with
2,3-dichloro-5,6-dicyano-1,4-benzoquinone
*
Patrik C. Eklund and Rainer E. Sjoholm
¨
˚
Process Chemistry Group, Department of Organic Chemistry, Abo Akademi University, Piispankatu 8, 20500 Turku, Finland
Received 11 February 2003; revised 3 April 2003; accepted 29 April 2003
Abstract—The oxidative transformation of the two isomers of the natural lignan hydroxymatairesinol from Norway Spruce (Picea abies) by
2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), has been studied. Significant differences in the outcome of the reactions were observed
when the pure isomers of hydroxymatairesinol were reacted with DDQ under the same conditions. The different stereoelectronic effects in the
two isomers as well as their conformational structures seem to determine the site of reaction, which results in different reaction products.
Several products were identified by GC–MS and NMR spectroscopy. Oxomatairesinol was obtained in a yield of 25%. q 2003 Elsevier
Science Ltd. All rights reserved.
1. Introduction
Fig. 2). In the following, the natural mixture of HMR in
Norway spruce (HMR-I/HMR-II,1:3)6 is referred to,
unless otherwise stated.
Many lignans of the a,b-dibenzylbutyrolactone type,
having significant biological effects, can be isolated from
different wood species.1,2 Hydroxymatairesinol (HMR), the
major lignan in Norway spruce (Picea abies), was isolated
as a ca. 1:3 mixture of two isomers by Freudenberg and
Knof in 1957.3 The two isomers were separated, character-
ised and designated by Freudenberg et al. as (2)-allo-HMR
and (2)-HMR, respectively. We separated the two isomers
by chromatography and showed that (2)-allo-HMR is the
minor and (2)-HMR is the major isomer in Norway spruce
wood, here referred to as HMR-I and HMR-II. For both
isomers, the R and R configurations of the lactone ring
carbons H-8 and H-80, respectively, have been established
by comparison of the stereochemistry of stereoselectively
synthesised a-conidendrin4 with that of conidendrin pre-
pared by acidic cyclisation of a natural mixture of HMR
isomers from spruce.3,5 We recently published a paper in
which we showed that the configurations at C-7 in HMR-I
and HMR-II are R and S, respectively.5 The complete
IUPAC name of the minor isomer of hydroxymatairesinol
from Norwa0y spruce is then (2)-(7R,8R,80R)-4,40,7-tri-
hydroxy-3,3 -dimethoxylignano-9,90-lactone (HMR0-I,
Fig. 1) and the major isomer is (2)-(7S,8R,80R)-4,4 7-
trihydroxy-3,30-dimethoxylignano-9,90-lactone (HMR-II,
HMR has been shown to metabolise to the known
mammalian lignan enterolactone, which has antitumouri-
genic properties for hormone dependent cancer forms.7
HMR has also been identified as a powerful antioxidant and
is able to decrease the oxidation of LDL-particles.8 The high
concentration of HMR, especially in the knots and in the
heartwood of branches of Norway spruce, makes HMR
available in large scale.9 Due to its good availability and its
biological properties HMR has been proposed as a
chemopreventive agent against cancers, hormone dependent
diseases and cardiovascular diseases.
During metabolisation, HMR undergoes demethylation and
dehydroxylation by intestinal bacteria. Enterolactone, one
of the main metabolites of HMR, has been widely studied
and its physiological effects have been evaluated.10–13
Jacobs et al.14 have shown that enterolactone undergoes
further oxidative metabolisation by hepatic microsomes,
resulting in hydroxylated products by modifications in the
aliphatic as well as the aromatic parts of the molecule.
However, very little is known about the biotransformation
of HMR and the biological effects of its metabolites.
HMR also undergoes oxidative transformations upon
exposure to light. Kawamura et al.15 reported that the two
isomeric forms can equilibrate and that both are oxidised to
oxomatairesinol, and that they finally form coloured
oligomers when exposed to irradiation by light.
Keywords: hydroxymatairesinol; lignan; oxidative transformation; DDQ;
2,3-dichloro-5,6-dicyano-1,4-benzoquinone; benzylic hydroxylation;
dehydrogenation.
*
Corresponding author. Tel.: þ358-2-2154502; fax: þ358-2-2154866;
e-mail: paeklund@abo.fi
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00683-5

¨
P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4516
Figure 2. Reaction products formed in the reaction between HMR-II and
DDQ.
Figure 1. Reaction products formed in the reaction between HMR-I and
DDQ.
16 products was detected by GC and GC–MS. However,
when pure isomers (isomeric purity .95%) of HMR-I and
II, respectively, were reacted at the same conditions, the
outcome of the reactions showed great differences (Fig. 3).
In our studies of oxidative transformations of HMR, the use
of a conventional oxidising agent such as PCC lead to
decomposition of the starting material and thereby failed to
oxidise the benzylic alcohol group to the corresponding
ketone. High potential quinones such as DDQ (2,3-dichloro-
5,6-dicyano-1,4-benzoquinone) are known to dehydrogen-
ate benzylic alcohols to ketones and to functionalize
benzylic positions under mild conditions.16–19 DDQ has
previously been shown to react with lignans of the
butyrolactone, aryltetralin and dibenzocyclo-octadiene
series.20–28 However, reactions between DDQ and lignans
containing a benzylic alcohol group have not been reported
previously.
Analysis by GC-FID and GC–MS of the reaction mixtures
(TMS–ether derivatives) showed that HMR-II yielded
oxomatairesinol (6) as the major product. HMR-I yielded
two isomers of the benzylidene lignan 70,80-dehydro-7-
hydroxymatairesinol (8, 9) as the major products and
surprisingly only a few percent of 6 was formed
(Figs. 1–3). When HMR was treated wi0th 0 2 equiv. of
DDQ for 16 h the main product was 7 ,8 -dehydro-7-
oxomatairesinol (11) (Fig. 2).
The products formed in the reactions above, support an
initial formation of benzylic cations by abstraction of
hydride ion by DDQ. The cationic intermediates then
deprotonate to form the dehydrogenated final products. The
difference in the extent of oxidation of the benzylic alcohol
group (formation of 6) of HMR-I (,1%) and HMR-II
(,15%) could be due to different stereoelectronic effects in
the two stereoisomers. As the benzylic C–H bond
approaches an angle of 908 to the plane of the aromatic
ring, the rate of dehydrogenation has been shown to
increase, due to the progressive improvement in overlap
of the empty orbital of the developing benzylic carbonium
ion with the orbitals of the aromatic p-system.17 In our case
the carbonium ion can be further stabilised by the resonance
In this study we performed reactions between HMR and
DDQ in order to obtain oxomatairesinol and other
oxygenated products (possible metabolites) of HMR. We
also aimed at gaining more knowledge of the chemical
properties of HMR. The outcome of the reactions as well as
mechanistic aspects are presented in this paper.
2. Results and discussion
When HMR was reacted with 1.3 equiv. of DDQ in 1,4-
dioxane at room temperature for 6 h, a mixture of altogether

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P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4517
The dehydrogenation at the benzylic alcohol group (C-7),
preferred to dehydrogenation at the benzylic methylene
group (C-70) in HMR-II (note the reverse order in HMR-I),
may be due to a more stabilised carbonium ion formed in the
hydride abstraction step. Besides charge delocalisation to
the aromatic ring, which is possible in each case, some
charge delocalisation to the hydroxyl group oxygen is
possible in the former case. In conclusion, if the
conformational structure and the stereoelectronic arrange-
ment are favourable, DDQ dehydrogenates the alcohol
group prior to the methylene group, by forming a highly
stabilised intermediate in the rate determining hydride
abstraction step.
The low yield of 6 from HMR-I shows that the benzylic
position C-7 is relatively unaffected by DDQ. In the
reactions with HMR-I the formation of benzylic cations
therefore mainly takes place at the other benzylic position
(C-70), as shown by the formation of 8, 9, 10a, 12, and 13
(Fig. 1).
In addition to dehydrogenation, the benzylic cations may
undergo inter- or intramolecular nucleophilic attack in the
presence of a suitable nucleophile (e.g. the solvent).
Functionalization of the benzylic position of para sub-
stituted aromatic systems by DDQ, has been studied by
Ramdayal et al.19 A free OH group at the para position was
found to enhance oxygenation occurring at the benzylic
methylene carbon. Lignan derivatives bearing guaiacyl
groups should therefore be suitable substrates for such
functionalisation reactions by DDQ.
The mass spectra of the peaks 1, 2, 3, 5 and 7 showed
molecular ion peaks indicating the presence of one
additional benzylic OH group in the molecule. Formation
of these products confirmed the attack by water on the
benzylic cation.
Figure 3. GC–MS chromatograms of the reaction mixtures (TMS ether
derivatives) of HMR-I (upper) and HMR-II (lower).
In a closer examination of the mass spectra of the reaction
mixtures, peaks 2 and 3 were identified as the isomeric
compounds 2a and 3a in the reaction of HMR-I and 2b and
3b in the reaction of HMR-II, by their molecular ion peak at
m/z 678 and by the characteristic fragment m/z 297 and also
by the absence of m/z 209 (Fig. 4). The structures of 2b and
3b were confirmed by NMR spectroscopy. Mass spectra of
peaks 5 and 7 (also isomers) had molecular ion peaks at m/z
604 and showed the characteristic fragments m/z 297 and
m/z 223, which indicated one benzylic position containing
an alcohol and the other one a ketone function, i.e.
compounds 5 and 7.
effect of the para hydroxyl group in the aromatic ring of
HMR.
It thus seems, that HMR-II most likely takes a confor-
mation having a nearly orthogonal relationship between the
C–H bond at C-7 and the aromatic plane under the present
conditions. HMR-I would then adopt a structure with a
more parallel relationship, unfavourable for orbital over-
lapping, leading to less dehydrogenation of the alcohol
group.
Dehydrogenation of benzylic alcohols by quinones, has
been proposed to occur via the formation of charge-transfer
complexes.18 In the present case the guaiacyl group with its
high electron density would be a very efficient donor to the
electron deficient aromatic ring of DDQ. In fact, on addition
of DDQ to HMR, the solution turned dark green and then the
colour slowly faded to light yellow. Such transitory colours
observed in reactions with DDQ have been ascribed to p–p
charge-transfer complexes. The structural differences in the
two diastereomers of HMR, could affect the formation of
such complexes. In addition to the stereoelectronic effects
discussed above, this would also affect the rate of the
oxidation of the benzylic alcohol group in HMR-I and
HMR-II, respectively.
Figure 4. The most common characteristic fragment ion peaks in
masspectra of TMS-derivatives of bytyrolactone type lignans derived
from HMR.

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P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4518
Peaks 8 and 9 in the reaction mixture of HMR-I, gave
identical mass spectra and showed molecular ion peaks at
m/z 588 together with a strong fragment ion peak at m/z 297
and were assigned to compounds 8 and 9, which was in
accordance with NMR spectroscopic data. The correspond-
ing compounds, albeit epimers at position 7 were detected as
minor components in the reaction mixture of HMR-II.
Peaks 4 and 11 showed a molecular ion peak at m/z 514 and
a strong fragment peak at m/z 223 and were assigned to the
isomers 4 and 11, also in accordance with NMR spectro-
scopic data.
product 11 is formed from 6. In aqueous conditions
hydroxylation occurred instead of dehydrogenation. Oxo-
matairesinol formation was only slightly affected by the
presence of water. However, the highest yield (25%) of 6
was obtained in 3% aqueous dioxane, and due to the absence
of benzylidene lignans in aqueous conditions, 6 was easily
isolated by chromatography. In a similar reaction (3%
aqueous dioxane), HMR-I was partly unreacted and formed
mainly the dihydroxy compounds 2a, and 3a, but only
detectable amounts of 6 and 10a were formed.
In the photo-oxidation of HMR reported by Kawamura
et al.15 isomerisation between HMR-I and HMR-II and
formation of oxomatairesinol and conidendrin was
explained by light induced radical reactions forming a
quinone methide intermediate. Kawamura et al. did not
report any reactions at the unsubstituted benzylic position.
The additional peaks 10, 12 and 13 detected only in the
reaction mixture of HMR-I, showed mass spectra some-
what different from those of the butyrolactone type lignans.
Peak 10 gave a strong molecular ion at m/z 588 and a weak
fragmentation pattern, which indicated the podophyllo-
toxin-like structure 10a. Peaks 12 and 13 gave fragmenta-
tion patterns related to furo-furan type lignan derivatives
(cf. pinoresinol) and a molecular ion peak at m/z 516. This
indicated the presence of the isomeric lignan derivatives 12
and 13 (Fig. 1).
In our reactions, no isomerisation of HMR and no formation
of conidendrin was detected. The reaction therefore most
likely proceeded via the direct hydride abstraction
mechanism, forming the same quinone methide inter-
mediate (ii) as r0eported by Kawamura et al. (Scheme 2).
Reactions at C-7 also support this mechanism.
Formation of 12 and 13 can be explained by an
intramolecular nucleophilic attack by the hydroxyl group
at position C-7 on the benzylic cation at position C-70
(Scheme 1, route b). Compound 10 could be formed via a
similar attack from C-6 forming the intermediate (i) as
shown in route a of Scheme 1. Alternatively, 10, 12 and 13
can be formed by an intramolecular cyclisation of
compounds 2 and 3. Peaks 1, 14, 15 and 16 have not been
identified.
When the reaction mixtures were analysed by GC-FID,
using a short capillary column (HP-5, 6 m) oligolignans
were detected.9,29 The presence of oligolignans confirmed
the presence of polymerisation reactions, probably also
taking place via polar mechanisms. The total recovery of
monolignan derivatives from the reaction mixtures was
about 60%.
Treatment of HMR with 1.2 equiv. DDQ in anhydrous THF
under Ar for 6 h at room temperature gave a lower yield of
hydroxylated products and a higher yield of 6. To explore
the yields of 6 formed from HMR-II, we performed
reactions in dioxane containing different amounts of water.
The presence of water in the reaction medium affected the
formation of hydroxylated products as well as the formation
of benzylidene lignans. Clearly, more anhydrous conditions
(freshly vacuum dried HMR-II, anhydrous 1,4-dioxane,
flame dried glasware and Ar-gas atmosphere) yielded more
of the benzylidene lignan 11 and less of the hydroxylated
products 5 and 7. The same result was obtained when longer
reaction times were applied. It is therefore likely that
As shown above, HMR undergoes both dehydrogenation,
hydroxylation, cyclisation and polymerisation reactions
when treated with DDQ. Structural differences in HMR-I
and HMR-II direct the formation of benzylic cations to the
most favourable position, yielding different products from
the two isomers. However, the reactions are competitive and
no reaction conditions yielding a single product could be
found.
HMR-II favours the formation of oxomatairesino0l by
oxidation of the 7-OH group but hydroxylation at C-7 is a
competing0reaction in aqueous media while dehydrogena-
tion at C-7 competes in anhydrous media. HMR-I favours
reactions at C-70 yielding 8, 9, 10a and 12 at anhydrous
conditions and the hydroxylated products 2a and 3a together
Scheme 1.
Scheme 2.

¨
P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4519
with 10a in aqueous conditions. The formation of several
products as well as polymeric structures, inevitably lead to
poor yields of single products in the reactions. Only
oxomatairesinol could be isolated in moderate yield.
resulting in coupling constants near the observed values.
Based on couplig constants alone, the stereochemistry at 70
of 2b and 3b can therefore not be determined. The complete
1H NMR signal assignments were based on COSY spectra.
Additional analyses by HPLC-MS gave molecular ion peaks
at m/z 390, in accordance with the proposed structures. It
should be observed that compounds 2b and 3b in the
reactions of HMR-II differ in stereochemistry from 2a and
3a obtained from HMR-I. The stereoisomers show small
differences in retention times in GC and GC/MS analyses,
but identical mass spectra. Attempts to isolate 2a and 3a
from the reaction mixture of HMR-I were unsuccesfull and
due to the small amounts and the impurity of the fractions,
NMR data of these compounds could not be obtained.
Dibenzylbutyrolactone lignans have been reported to form
aryl–aryl coupled dibenzocyclo-octadiene lignans by the
action of DDQ in TFA.28 The possibility to obtain
dibenzocyclo-octadienes in the reactions between HMR
and DDQ by reaction in TFA, is restricted by the formation
of a-conidendrin from HMR in acidic media.3 Treatment of
HMR with TFA resulted in the instantaneous formation of
a-conidendrin as shown by GC–MS and NMR
spectroscopy (unpublished results).
Compounds 4, 8, 9, 10, and 11 are to the best of our
knowledge new compounds and hitherto unreported.
Oxomatairesinol (6), the monoepoxylignanolid (12) and
lignans 2, 3 have been reported as naturally occurring
lignans.3,30,31 Though, the relative stereochemistry of the
reported lignans could differ from our obtained products.
Compounds 8 and 9 were isolated from the reaction of
HMR-I and identified as the E and Z isomers of 70,80-
dehydro-7-hydroxymatairesinol. Compound 8 was assigned
the E configuration, based on the following argument. In the
E isomer the vinylic proton H-70 is positioned in the
deshielding area of the carbonyl group and the signal is
expected to appear downfield (d¼7.45 ppm) from that of
the corresponding Z isomer (d¼6.51 ppm). Consequently,
the H-20 proton in the Z isomer is situated closely to the
carbonyl group and shifted downfield (d¼8.11 ppm)
compared to the E isomer (d¼7.29 ppm). Complete 1H
NMR signal assignments were based on COSY spectra.
2.1. Identification of compounds in the reaction mixtures
From the reaction mixtures, fractions containing minor
products were isolated by repeated column chromatography
and analysed by NMR spectroscopy (Tables 1 and 2). The
analysed fractions were not chromatographically pure and
comprised several components. Hence, no yields of minor
products are given. GC analyses showed that the yields of
the minor products were from a few percent up to 10%.
Compounds 4 and 11 were isolated as a mixture. Similar
effects on the chemical shifts for the H-70and H-20signals in
4 and 11 as in 8 and 9 were observed. Compound 4 was
assigned the Z configuration and compound 11 the E
configuration, respectively. COSY spectra allowed the
Compounds 2b and 3b were isolated as a mixture from the
reaction of HMR-II in aqueous dioxane and identified as
isomers of 7-70-dihydroxymatairesinol, differing in the
stereochemistry at position 70. NMR data of 2b and 3b
showed the absence of benzylic methylene group signals.
Instead, two signals from the benzylic alcohol group protons
appeared as doublets. The signals from H-70 were observed
approximately 0.8 ppm downfield from those of H–7, due
to the anisotropy effect of the carbonyl group. Both
stereoisomers can adopt a conformation with bond angles
1
complete H NMR assignment of 4 and 11 (see Section 4
for NMR data). A fra0ction containing compound 10 together
with isomers of 7,7 -dihydroxy matairesinol was isolated
from the reaction mixture of HMR-I. The magnitude of the
0
0
coupling constant, J7 ,8 ¼11.5 Hz, pointed to a trans (aa)
relation between H-70 and H-80 and an equatorial position of
the guaiacyl group. Likewise, the coupling between H-7 and
H-8 of similar magnitude, J7,8¼9.9 Hz, supported a trans
position of H-7 and H-8 with an equatorial 7-OH group.
1
Table 1. H NMR data of compounds 2b, 3b, 8, 9, 10a and 10b
Protona
Compound, peak position, multiplicity and coupling constants (J values/Hz)
2b
3b
8 (E)
9 (Z)
10a
10b
H-2
H-5
H-6
6.45 d (2.0)
6.73 d (8.1)
6.59 dd (2.0, 8.1)
6.54 d (1.8)
6.77 d (8.1)
6.74 dd (1.8, 8.1)
4.64 d (5.2)
5.15 d (3.8)
2.75 m
6.37 d (2.0)
6.70 d (8.0)
6.46 dd (2.0, 8.0)
6.45 d (1.8)
6.81 d (8.1)
6.78 dd (1.8, 8.1)
4.16 d (7.9)
5.21 d (2.9)
2.73 m
7.05 d (1.8)
6.80 d (8.0)
6.91dd (1.8, 8.0)
7.29 d (1.8)
6.94 d (8.2)
7.26 dd (1.8, 8.2)
5.11 d (2.7)
7.45 d (2.1)
4.10 m
7.04 d (1.9)
6.81 d (8.0)
6.86 dd (1.9, 8.0)
8.11 d (2.0)
6.78 d (8.2)
7.10 dd (2.0, 8.2)
4.80 d (6.7)
6.50 d (1.5)
3.36 m
7.21 s
6.25 s
–
6.83 d (2.0)
6.75 d (8.0)
6.64 dd (2.0, 8.0)
4.96 d (9.9)
4.01 d (11.5)
2.60 m
6.92 s
6.31 s
–
6.87 d (2.0)
6.77 d (8.0)
6.71 dd (2.0, 8.0)
4.85 bs (2.9)
3.91 d (11.5)
2.72 m
H-20
H-50
H-60
H-7
H-70
H-8
H-80
H-9ab
H-9b
OMe
OMe0
2.92 dd (4.4, 3.8)
4.18 dd (8.9, 4.3)
4.30 dd (8.9, 8.4)
3.77 s
2.65 dd (4.4, 2.9)
4.52 dd (8.9, 3.9)
4.33 dd (8.9, 7.6)
3.72 s
–
–
2.92 dd (11.5, 14.7)
4.56 dd (6.7, 8.6)
4.16 dd (8.6, 10.8)
3.77 s
3.22 dd (11.5, 13.9)
4.40 dd (7.2, 8.2)
4.30 dd (8.2, 11.0)
3.78 s
4.51 dd (8.2, 3.2)
4.14 dd (8.2, 8.0)
3.86 s
4.52 dd (9.1, 2.9)
4.29 dd (9.1, 7.6)
3.81 s
3.78 s
3.75 s
3.92 s
3.85 s
3.81 s
3.82 s
Compounds 2b, 3b, 8, 9 and 10a dissolved in CDCl3–(CD3)2CO and compound 10b dissolved in (CD3)2CO.
Numbering according to HMR.
a
b
H-8–H-9 cis.

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P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4520
Table 2. 13C NMR data of compounds 2b, 3b, 8, 9, 10a and 10b
Carbona
Compound
2b
3b
8 (E)
134.65
9 (Z)
135.55
127.23
111.02
115.00
{147.25–147.80
10a
133.73
131.11
107.35
111.46
{143.60–145.62
10b
1
10
{131.67–133.21
{107.18–107.55
{144.25–148.80
{144.25–148.80
{117.02–117.29
{113.00–113.70
{131.67–133.21
{107.18–107.55
{144.25–148.80
{144.25–148.80
{116.75–117.90
{113.00–113.70
{133.85–136.25
127.11
110.03
114.23
148.25
148.05
146.35
149.10
116.07
114.97
118.90
124.80
71.68
137.30
45.67
121.72
66.27
173.00
{56.10–56.40
20
113.90
114.07
{146.16–148.70
2
3
30
4
40
5
50
6
60
7
70
8
80
9
90
OMe
OMe0
146.60
149.00
115.37
115.16
120.06
126.99
75.90
142.35
50.93
123.90
67.30
{143.60–145.62
{146.16–148.70
114.20
113.12
q
120.52
69.57
44.50
44.28
46.06
68.63
173.53
{53.70–54.20
116.60
115.40
131.11
123.00
66.84
73.33
71.76
41.73
48.05
72.63
70.87
41.59
49.84
46.68
46.05
41.62
68.75
70.06
177.98
{54.40–54.90
68.21
177.57
{54.40–54.90
170.88
56.07
56.40
q
{56.10–56.40
Compounds 2b, 3b, 8, 9 and 10a dissolved in CDCl3–(CD3)2CO and compound 10b dissolved in (CD3)2CO.
Numbering according to HMR.
a
Formation of a ring with an equatorial guaiacyl group
should be favoured on stereochemical grounds. An
equatorial 7-OH group confirms the expected R configur-
ation (as in HMR-I) at C-7. This particular isomer of 4,40,7-
trihydroxy-3,30-dimethoxy-6,70-cyclolignano-9,90-lactone
was designated 10a.
4. The identification of compounds 5, 7, 12, and 13 was
based solely on interpretation of mass spectra.
In addition to the compounds above, we also identified
two diastereomers of 70-methoxy-7-oxo-matairesinol
coeluting with oxomatairesinol. HPLC–MS analyses gave
a molecular ion peak at m/z 401.2 and GC–MS analyses
(TMS–ether-derivatives) gave a molecular ion peak at m/z
546 and the fragments m/z 223 and 239. NMR spectroscopic
analyses confirmed the structures (see Section 4).
From the reaction mixture of HMR-II in aqueous dioxane
(See Section 4) a corresponding fraction containing
compound 10 together with isomers of 7, 70-dihydroxy
matairesinol (2b and 3b) was isolated. The masspectrum of
the compound designated 10b was identical with that of
10a. Their NMR spectra, however, were different. In
addition to the shift differences in01H and 13C NMR spectra,
the H-7, H-8 and H-70, H-8 couplings were most
The formation of the methoxy derivatives may be explained
by reactions of residual methanol (originating from the
purification procedure) in the starting material, with reactive
intermediates in the DDQ reaction. Alternatively, the
products were formed when the reaction mixture was
dissolved in methanolic chloroform prior to column
chromatorgaphy. According to this, it seems possible that
various compounds with nucleophilic character may add to
the carbonium ion intermediaties, forming new compounds.
The formation of the hydroxy and methoxy derivatives in
the above reactions, also indicate that hydroxymatairesinol
effectively binds water and/or methanol (small amounts of
these products were detected, even if hydroxymatairesinol
was dried under high vacuum and the reactions were
performed under anhydrous conditions).
0
0
informative. The large coupling constant, J7 ,8 ¼11.5 Hz,
again indicated the expected trans relationship of H-70 and
H-80 and an equatorial guajacyl group. However, in this case
J7,8 was 2.9 Hz indicating a cis (ae) relation and the
expected S configuration at C-7 (as in HMR-II). This
strongly supports our previous results which showed that the
configuration at C-7 is S in HMR-II and R in HMR-I.5 The
identification of 10a and 10b in fractions containing
dihydroxymatairesinol, strongly indicate a formation of
these by an intramolecular cyclisation reaction of com-
pounds 2 and 3.
13C NMR signals were assigned by 1H–13C-correlation
spectroscopy (HMQC, HMBC) and by chemical shifts. Due
to the complexity of the mixtures of products resulting in
overlapping and poor quality HMBC spectra, the
unambiguous assignments of quaternary carbons could not
be made. Therefore, their chemical shifts are reported as
intervals and unresolved quaternary carbon signals are
denoted by a q in Table 2.
3. Conlusions
We have shown that DDQ reacts with the benzylic positions
in HMR by a hydride abstraction mechanism. We also
showed that the reaction of DDQ has regioselective
properties, which probably depend on stereoelectronic
effects as well as on the conformational structure of the
substrate. This was demonstrated by the different reaction
modes of the two known diastereomers of natural hydroxy-
matairesinol from Norway spruce. Although a definitive
Compounds 6 and 11 were isolated as pure substances, the
spectroscopic and spectrometric data are reported in Section

¨
P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4521
explanation to the differences in the reactions could not be
4.2. Reaction of HMR in anhydrous THF
given, it seems resonable to suppose that the two isomers
can behave differently in mammalian metabolism. Accord-
ing to our results, regioselective functionalisation of
benzylic positions in non-rigid phenolic compounds such
as lignans may be accomplished by DDQ.
All glassware was flame dried under argon before use.
To a solution of freshly distilled THF (20 mL) and HMR
(1.5 g, 4.01 mmol) under Ar, was added dropwise DDQ
(1.09 g, 4.81 mmol) dissolved in 20 mL THF (the mixture
turned dark green). The reaction mixture was stirred for 6 h
at room temperature and then quenched by pouring it into
30 mL of 10% NaHSO3. The mixture was extracted with
CH2Cl2 (50þ30 mL) and dried with NaSO4. The organic
phase was evaporated to dryness. The residue was then
re-dissolved in CH2Cl2 and filtered trough a sintered glass
filter to remove undissolved DDQH2. Evaporation of the
solvent gave a light yellow residue.
4. Experimental
2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) (Fluka
purum ,97%), 1,4-dioxane (LAB-SCAN, max. water
0.05%) and 1,4-dioxane (Aldrich, anhydrous 99.8%) were
purchased from the manufacturers and used as received.
THF (LAB SCAN) was freshly distilled from sodium
benzophenone ketyl. All other commercially available
chemicals were used as supplied by the manufacturers.
2.5 g of a reaction mixture obtained as above was
chromatographed on a silica column using EtOAc–Hexane
(1:1 v/v) yielding a fraction containing (6). The fraction was
then re-chromatographed using CH2Cl2 containing 2%
methanol yielding (410 mg, 16.5%) 6 as a pale yellow
powder; mp 68–708C (CHCl3).
All experiments were monitored by thin layer chromato-
graphy using pre-coated aluminium based sheets (Merck, 60
F254).
The reaction mixtures were silylated using BSTFA (bis-
(trimethylsilyl)-trifluoroacetamide) and TMCS (trimethyl-
chlorosilane) in pyridine and quantitatively analysed by gas
chromatography using a HP-5 capillary column (25m,
Temp. progr. 1508C 0.5 min, 78C/min!2308C,
108C/min!2908C 10 min) and betulinol as an internal
standard. Mass spectra were recorded using a HP-5 capillary
column GC-system equipped with a HP-5973 mass detector.
4.2.1. Oxomatairesinol (6). [a]2D3¼þ44.3 (c 0.01 g/mL in
THF), lit. [a]2D5¼þ42.6 (c 4.0 in THF).3 dH (500 MHz,
CDCl3, 308C) 2.90 (1H, dd, J¼7.0, 14.3 Hz, H-70a), 2.96
(1H, dd, J¼5.5, 14.3 Hz, H-70b), 3.44 (1H, m, H-80), 3.67
(3H, s, OMe0), 3.86 (3H, s, OMe), 4.00 (1H, m, H-8), 4.04
(1H, t, J¼8.1 Hz, H-90a), 4.30 (1H, t, J¼8.1 Hz, H-90b), 5.43
(1H, s, OH0), 6.13 (1H, s, OH), 6.48 (1H, dd, J¼2.0, 7.9 Hz,
H-600), 6.54 (1H, d, J¼2.0 Hz, H-20), 6.65 (1H, d, J¼7.9 Hz,
H-5 ), 6.81 (1H, d, J¼8.3 Hz, H-5), 7.13 (1H, dd, J¼2.0,
8.3 Hz, H-6), 7.27 (1H, d, J¼2.0 Hz, H-2); dC (125 MHz,
CDCl3, 308C) 34.51 (C-70), 44.98 (C-80), 46.58 (C-8), 55.85
(OMe0), 56.22 (OMe), 69.40 (C-9), 110.12 (C-2), 111.81
(C-20), 113.97 (C-5), 114.42 (C-50), 122.35 (C-600), 123.61
(C-6), 128.73 (C-1), 128.98 (C-10), 144.71 (C-40), 146.71
(C-30), 147.12 (C-3), 151.49 (C-4), 177.38 (C-9 ), 195.06
(C-7); m/z (EIMS) 372 (Mþ, 90%), 221 (17), 194 (100), 177
(20), 151 (70), 137 (55), 123 (13), 77 (8); HRMS: found
372.1211 (Mþ). C20H20O7 requires 372.1209.
1
HRMS were recorded on a ZabSpecETOF system. H and
13C NMR spectra were recorded on a JEOL JNM-A500
spectrometer at 500 and 125 MHz, respectively. TMS was
used as an internal standard and 2D experiments were
recorded using standad JEOL pulse sequences. The 1H and
13C NMR spectra of the compounds were assigned using
homonuclear and heteronuclear direct and long-range
chemical shift-correlation spectroscopy (COSY, HMQC,
HMBC). Chemical shifts are reported in ppm (d) downfield
from TMS.
Optical rotations were measured with a Perkin Elmer 241
digital polarimeter, using a 1 dm–1 mL cell.
4.2.2. 70-Methoxy-7-oxo-matairesinol.0 (isomer I) dH
(500 MHz, CDCl3, 308C) 3.28 (3H, s, 7 -MeO), 3.41 (1H,
dd, J¼2.9, 7.5 Hz, H-80), 3.59 (3H, s, OMe0), 3.82 (3H, s,
OMe),4.00–4.10 (1H, dd, overlapping, H-9b), 4.44 (1H, m,
H-8), 4.50 (1H, dd, J¼8.9.17.0 Hz, H-9b), 4.76 (1H, d,
J¼2.9 Hz, H-70), 6.56 (1H, d, J¼1.8 Hz, H-20), 6.65 (01H, dd,
J¼1.8, 8.0 Hz, H-60), 6.69 (1H, d, J¼8.0 Hz, H-5 ), 6.79
(1H, d, J¼8.3 Hz, H-5), 7.07 (1H, dd, J¼2.0, 8.3 Hz, H-6),
7.16 (1H, d, J¼2.0 Hz, H-2); dC (125 MHz, CDCl3, 308C)
42.09 (C-8), 51.51 (C-80), 55.70 (MeO00), 56.20 (MeO),
57.99 (70-MeO), 69.65 (C-9), 80.33 (C-70), 108.18 (C-200),
110.10 (C-2), 113.79 (C-5), 114.64 (C-50), 118.89 (C-60),
123.43 (C-6), 128.57 (C-1), 130.40 (C-1 ), 145.32 (C-40),
146.70-147.10 (C-3, C-30), 151.18 (C-4), 176.17 (C-9 ),
195.18 (C-7); (isomer II) dH (500 MHz, CDCl3, 308C) 3.25
(3H, s, 70-MeO), 3.70 (1H, dd, J¼4.3, 6.7 Hz, H-80), 3.77
(3H, s, MeO0), 3.85 (1H, dd, overlapping, H-9b), 4.00–4.10
(1H, dd, overlapping, H-9a), 3.90 (3H, s, 0MeO), 4.12 (1H,
m, H-8), 4.68 (1H, d, J¼4.3 Hz, H-7 ), 6.75 (1H, d,
J¼1.8 Hz, H-20), 6.780(1H, dd, J¼1.8, 7.5 Hz, H-60), 6.84
(1H, d, J¼7.5 Hz, H-5 ), 6.89 (1H, d, J¼8.3 Hz, H-5), 7.37
Preparative chromatography was performed on silica gel
columns (Merk, Kiselgel 60). Hydroxymatairesinol was
isolated from Norway spruce as described by Ekman.5
4.1. Reactions with pure isomers of HMR-I and II
To a stirred solution of HMR (160 mg, 0.43 mmol of isomer
I or II) in dioxane (10 mL) a solution of DDQ (127 mg,
0.56 mmol) in dioxane (10 mL) was added dropwise. On
addition of DDQ, the reaction mixture turned dark green,
then slowly turned to yellow. The mixture was allowed to
react at room temperature for 6 h. The reaction was then
quenched by adding 25 mL CH2Cl2 and filtering trough a
sintered glass filter to remove precipitated DDQH2. The
mixture was extracted with 10 mL CH2Cl2 and 30 mL 10%
NaHSO3. The CH2Cl2 phase was washed with 20 mL
saturated NaCl-solution and dried with NaSO4. Evaporation
of the solvent gave a light brown-yellow residue.

¨
P. C. Eklund, R. E. Sjoholm / Tetrahedron 59 (2003) 4515–4523
4522
(1H, dd, J¼2.0, 8.3 Hz, H-6), 7.58 (1H, d, J¼2.0 Hz, H-2);
dC (125 MHz, CDCl3, 308C) 43.34 (C-8), 49.52 (C-80),
56.06 (MeO0), 56.20 (MeO), 57.30 (70-MeO), 68.78 (C-9),
81.40 (C-70), 109.70 (C-20), 110.56 (C-2), 114.04 (C-5),
114.46 (C-500), 119.72 (C-600), 123.98 (C-6), 128.28 (C-1),
129.14 (C-1 ), 145.80 (C-4 ), 146.70–147.10 (C-3, C-30),
151.41 (C-4), 176.17 (C-90), 195.35 (C-70).
(C-800), 125.32 (C-6), 127.10 (C-1), 127.70 (C-600), 128.99
(C-10), 143.01 (C-70), 147.74 (C-3), 148.90 (C-3 ), 149.71
(C-4 ), 153.23 (C-4), 169.28 (C-90), 196.63 (C-7). HRMS:
found 370.1050 (Mþ). C20H18O7 requires 370.1052.
4.4. Reaction of HMR-II in aqueous 1,4-dioxane
HMR-II (1 g, 2.67 mmol) was dissolved in 30 mL aqueous
dioxane (5%). DDQ (0.789 g, 3.48 mmol) was dissolved in
20 mL dioxane and added dropwise to the solution above.
After 8 h the reaction was quenched by adding 10%
NaHSO3 (50 mL). The mixture was then extracted with
CH2Cl2 (50 mL) and EtOAc (50 mL). The organic phases
were combined, dried with NaSO4 and the solvents were
removed under reduced pressure. The residue was chro-
matographed on a Biotage 40i flash chromatographic
system using CHCl3:MeOH (99:1, v/v) as eluent, yielding
6 (248 mg, 25%) as a pale yellow powder.
4.3. Reaction of HMR with 2 equiv. of DDQ in 1,4-
dioxane
HMR (2 g, 5.35 mmol) was dissolved in 50 mL dioxane and
DDQ (2.43 g, 10.7 mmol) was added to the solution in small
portions. The reaction mixture was stirred at room
temperature for 16 h and then passed trough a sintered
glass filter to remove precipitated DDQH2. The mixture was
washed with 130 mL 10% NaHSO3 and extracted with
100 mL CH2Cl2. The CH2Cl2 phase was dried with NaSO4
and evaporated under reduced pressure to leave a yellow
residue. The recovery of lignans from the residue was very
poor, which showed that higher molar ratios of DDQ result
in more polymerized material.
Acknowledgements
The authors thank Hormos Nutraceuticals Ltd., Turku,
Finland for the financial support of this work, Mr
M. Reunanen, Mrs N. Granholm, Mr C. Eckerman,
Compound 11 (150 mg, 7.6%) was isolated by column
chromatography using CHCl3–MeOH (99:1 v/v) as eluent;
mp.1508C, decomp. (CHCl3). NMR analysis showed one
pure product. GC and GC–MS showed two peaks 4 and 11
indicating thermal isomerisation of the E and Z isomers.
Thermal isomerisation of closely related benzylidene-
lactone lignans has been reported earlier.24 Small amounts
of the Z isomer (4), were detected in remaining fractions
from the above purification and the compound was
identified by NMR.
˚
Laboratory of Forest Product Chemistry, Abo Akademi
University, Turku, Finland for the GC, GC–MS analyses
and for the supply of HMR. We also thank Mr M. Roslund
for recording some of the NMR spectra.
References
4.3.1.
(7E0)-70,80-Dehydro-7-oxomatairesinol
(11).
[a]2D3¼þ252.3 (c 0.01 g/mL in THF). dH (500 MHz,
CDCl3, 308C) 3.51 (3H, s, OMe0), 3.88 (3H, s, OMe), 4.31
(1H, dd, J¼3.8, 9.3 Hz, H-9a), 4.65 (1H, t, J¼9.3 Hz, H-9b),
5.08 (1H, ddd J, 3.8, 9.3, 2.3 Hz, H-8), 5.77 (1H, s, OH0),
6.15 (1H, s, OH), 6.73 (1H, d, J¼2.0 Hz, H-20), 6.750(1H, d,
J¼8.3 Hz, H-50), 6.86 (1H, dd, J¼2.0, 8.3 Hz, H-6 ), 6.94
(1H, d, J¼8.3 Hz, H-5), 7.44 (1H, dd, J¼2.0, 8.3 Hz, H-6),
7.46 (1H, d, J¼2.0 Hz, H-2), 7.67 (1H, d, J¼2.3 Hz, C-700);
dC (125 MHz, CDCl3, 308C) 46.76 (C-8), 55.55 (OMe ),
56.20 (OMe), 67.69 (C-9), 110.50 (C-2), 111.56 (C-20),
114.20 (C-50), 114.86 (C-500), 119.83 (C-80), 123.39 (C-6),
125.20 (C-60), 126.30 (C-1 ), 127.84 (C-1), 140.20 (C-70),
146.59 (C-30), 147.31 (C-3), 147.92 (C-40), 151.52 (C-4),
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