Synthesis of [phenyl-13C6]lachnanthocarpone and other 13C-labelled phenylphenalenones

Article abstract of DOI:10.1002/jlcr.808

[phenyl-¹³C₆]Lachnanthocarpone ([phenyl- ¹³C₆]2,6-dihydroxy-9-phenylphenalen-1-one), a hypothetical intermediate in the biosynthesis of various natural phenylphenalenones, was prepared in four steps using [U-

Full text of DOI:10.1002/jlcr.808

JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS
J Label Compd Radiopharm 2004; 47: 147–159.
Published online in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jlcr.808
Research Article
Synthesis of [ phenyl-13C6]lachnanthocarpone and other
13C-labelled phenylphenalenones
1
Felipe Otalvaro , Winston Quinones , Fernando Echeverri and
1
1
!
*
Bernd Schneider2,*
1
! !
Instituto de Quımica, Universidad de Antioquia, Medellın, Colombia
.
Max-Planck-Institut fu.r Chemische Okologie, Beutenberg Campus,
2
.
Hans-Knoll-Str. 8, D-07745 Jena, Germany
Summary
[ phenyl-13C6]Lachnanthocarpone ( [ phenyl-13C6]2,6-dihydroxy-9-phenylphenalen-1-
one), a hypothetical intermediate in the biosynthesis of various natural phenylphe-
nalenones, was prepared in four steps using [U-13C]bromobenzene to introduce the
label. Based on related methodologies further native phenylphenalenones such as
[ phenyl-13C6]anigorufone, [1-13C]anigorufone and [40-O13CH3]40-methoxyanigorufone
were synthesized in labelled form. Copyright # 2004 John Wiley & Sons, Ltd.
Key Words: anigorufone; 13carbon; isotope labelling; Grignard reaction; lachnantho-
carpone; phenylphenalenones
Introduction
Phenylphenalenones are secondary metabolites that have so far been found in
the plant families Haemodoraceae,1 Pontederiaceae,2 Strelitziaceae,3 and
Musaceae.4 In the latter family they are reported as phytoalexins. The
biosynthesis of these compounds is a current research topic, and experimental
evidence has been obtained for their formation from two phenylpropanoid
units through condensation with malonyl-CoA and subsequent cyclization of
the diarylheptanoid intermediate.5,6 Recently, lachnanthocarpone7 (1) has
been hypothesized to be a candidate for the first cyclization product and a
branching point for further biosynthetic conversion.8,9 Two biosynthetic
branches are suggested to start from compound 1: one leading directly to 2-
hydroxy-9-phenylphenalen-1-one (anigorufone, 2) and the other to 1,2,5,6-
.
*Correspondence to: B. Schneider, Max-Planck-Institut fur Chemische Okologie, Beutenberg Campus,
.
Hans-Knoll-Str. 8, D-07745 Jena, Germany. E-mail: schneider@ice.mpg.de
.
Contract/grant sponsor: Colciencias (Bogotu, Colombia)
Copyright # 2004 John Wiley & Sons, Ltd.
Received 23 October 2003
Revised 11 November 2003
Accepted 13 November 2003

´
F. OTALVARO ET AL.
148
tetraoxygenated 9-phenylphenalenones and subsequently to oxa-analogues of
phenylphenalenones. In order to probe hypothetical biosynthetic relationships
of phenylphenalenones by means of 13C NMR spectroscopy, lachnanthocar-
pone (1) and further compounds of this type were required in labelled form.
The first synthesis of lachnanthocarpone (1) was accomplished in 10 steps
starting from 4-(4,5-dimethoxy-2-methylphenyl)-butyric acid.10 Bazan and
Edwards11 used an eight-step procedure to prepare compound 1 from
diacetyldihydrocaffeic acid. However, since the yields are low, this biomimetic
synthesis was only suitable for supporting biosynthetic theories rather than to
provide a straightforward approach to this compound. A partial synthesis of
lachnanthocarpone (1), albeit in low yields, was achieved by treating 6-
methoxy-9-phenylphenalen-1-one with hydrogen peroxide and subsequent
demethylation12 but did not allow introduction of 13C label. Addition of a
Grignard reagent to the 9-position of perinaphthenone, followed by
hydroxylation at C-2 through epoxidation of the 2,3-double bond, according
to the Yang and Finnegan procedure,13 was used by Cooke and Dagley14 to
synthesize 9-phenylphenalenones. This procedure is still the most convenient
and generally useful method for synthesizing phenylphenalenones in very high
yields. However, an attempt to synthesize a closely related compound, 2-
hydroxy-6-methoxy-9-(40-methoxyphenyl)-phenalenone resulted in a very low
yield of 16% in the epoxidation step of the direct precursor, 6-methoxy-9-(40-
methoxyphenyl)-phenalenone. This low yield in a late step is unacceptable for
the synthesis of lachnanthocarpone (1) in a labelled form. In this study,
the Cooke and Dagley method14 has been extended to 6-substituted
phenylphenalenones, and used to prepare [ phenyl-13C6]lachnanthocarpone
([ phenyl-13C6]-1) in high yields.
Results and discussion
Retrosynthesis of phenylphenalenones
Due to the compact structure of most phenylphenalenones, especially the
tricyclic nucleus, labelling with 13C through a minimum of synthetic steps
requires introducing the label with the lateral phenyl moiety at the peri-
position of the perinaphthenone tricycle. The phenyl ring has to be attached to
the phenalenone tricycle before introducing hydroxyl (at C-2) or deprotecting
methoxyl substituents (at C-6 of lachnanthocarpone precursors). Grignard-
type addition was considered the favored reaction for achieving high yields in
this step (Figure 1). The a-hydroxy group would be established by opening the
epoxide, which can be introduced via epoxidation of the 2,3-double bond of
the 9-phenylphenalen-1-one intermediate by known procedures.13–16 Phenyl-
phenalenones bearing a methoxyl group can be readily labelled in the OCH3
substituent. Removal of unlabelled O-methyl and methylation using a 13C
Copyright # 2004 John Wiley & Sons, Ltd.
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SYNTHESIS OF [PHENYL-13C6]LACHNANTHOCARPONE
149
Figure 1. Retrosynthetic analysis of phenylphenalenones
labelled agent is required during synthesis, which in the other steps proceeds
similarly to synthesis of the unmethylated phenylphenalenones.
Synthesis of lachnanthocarpone
The synthesis of labelled lachnanthocarpone ([ phenyl-13C6]-1) is shown in
Figure 2. A method for the synthesis of 6-hydroxy-perinaphthenone (3) by
condensing 2,7-dihydroxynaphthalene (4) with glycerol in the presence of
phosphoric acid and an oxidizing agent was described earlier.17 Using this
method, compound 3 was obtained in low yields of approximately 8% after
purification. No attempt to optimize this procedure was carried out, since a
sufficient quantity was obtained to proceed and labelling was not yet involved
in this step. Alternatively, compound 3 is accessible by cyclization of b-(4-
methoxy-1-naphthyl)-propionic acid under dehydrogenation conditions.17
Methylation using an ethanol-containing solution of diazomethane gave the
desired methyl ether 5 in a quantitative yield. 6-Methoxy-perinaphthenone (5)
was treated with [U-13C]phenylmagnesium bromide and the crude product was
dehydrogenated by the action of DDQ. [ phenyl-13C6]6-Methoxy-9-phenylphe-
nalen-1-one ([ phenyl-13C6]-6) was obtained in 82% yield after purification by
preparative TLC. The Yang and Finnegan13 procedure for the epoxidation of
a non-labelled sample of 6 was tested but no product was observed after 24 h.
This problem has been overcome by employing the Jacobsen–Katsuki
epoxidation,15,16 which smoothly resulted in 2-hydroxy-6-methoxy-9-phenyl-
phenalen-1-one (7) in 79% yield after purification by TLC. Manganese salen
complexes are mainly used for the highly enantioselective epoxidation of
alkenes, and a practical and economical method for the synthesis of this
catalyst was available.18 In our case, there was no need for an enantioselective
epoxidation. However, the availability of this catalyst and the simplicity of the
procedure made this type of epoxidation ideal for generating a-hydroxy-
ketones from a; b-unsaturated carbonyl compounds such as 6.
No attempt was made to isolate the epoxide because of its lability to acid
treatment, which was concluded from the immediate color change from pale
yellow to deep red that occurred during application to TLC plates of the
dichloromethane fraction containing the crude product. Therefore, compound
7 was isolated directly and purified by preparative TLC. Demethylation of 7
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F. OTALVARO ET AL.
150
Figure 2. Synthesis of [ phenyl-13C6]lachnanthocarpone ([ phenyl-13C6]-1).
[ phenyl-13C6]
=
*
by HBr gave the target molecule, [ phenyl-13C6]lachnanthocarpone ([ phe-
nyl-13C6]-1), in 84% yield. The total yield with respect to the labelled starting
compound, [U-13C]bromophenol, was 36%.
The 1H and 13C NMR signals of the uniformly labelled lateral phenyl ring of
[ phenyl-13C6]lachnanthocarpone ([ phenyl-13C6]-1) and the synthetic intermedi-
ates [ phenyl-13C6]-6 and -7 appear as multiplets. Interestingly, the resonance of
3
3
0
H-8, due to JH-8–H-7 = 8.5 Hz and JH-8–C-1 =3.7 Hz, exhibits a doublet
1
of doublets in the H NMR spectrum (Figure 3). This characteristic coupling
1
pattern represents a sensitive H fingerprint signal, which can be used to
detect metabolites derived from ([ phenyl-13C6]-1) or analogously labelled
compounds in plant crude extracts or semi-purified fractions of biosynthetic
experiments.
Synthesis of phenylphenalenones without substitution at C-6
Labelled anigorufone19 (13C-2) and 40-methoxyanigorufone20 (13C-8) were
synthesized starting from perinaphthenone (9). [U-13C]bromophenol and
[1-13C]bromophenol, respectively, were used to prepare the labelled Grignard
reagents for the introduction of 13C into the lateral phenyl substituent at C-9
of [ phenyl-13C]anigorufone ([ phenyl-13C6]-2) and [10-13C]anigorufone ([10-13C]-
2) (Figure 4).
Copyright # 2004 John Wiley & Sons, Ltd.
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SYNTHESIS OF [PHENYL-13C6]LACHNANTHOCARPONE
151
OH
O
•
H-8
•
•
•
•
1
1'
•
H-3
8
3J H-8–H-7 = 8.5 Hz
3J H-8–C-1’ = 3.7 Hz
7
H
H
OH
H-4
H-7
H-5
H-8
H-2’–H-6’
δ
7.60
δ
8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2
1
Figure 3. H NMR spectrum of [ phenyl-13C6]lachnanthocarpone ([ phenyl-13C6]-
3
3
1). The multiplicity of H-8 at d 7.59 results from JH–H and JH–C couplings as
=
13C
*
indicated in the magnified detail.
In the first step of the synthesis of [40-O13CH3]40-methoxyanigorufone20 ([40-
O13CH3]-8), a Grignard reaction again led to the attachment of the lateral aryl
moiety to C-9 of perinaphthenone (9). Ether cleavage of 9-(40-methoxyphenyl)-
phenalenone (10) made the 40-O-position available for methylation, which was
achieved by 13CH3I as a labelled precursor. The Yang and Finnegan13
procedure for the epoxidation worked satisfactorily in the case of phenylphe-
nalenones without substituent in position 6.
Conclusions
Phenylphenalenones were prepared in labelled form, bearing 13C in the lateral
substituent attached to C-9 of the phenalenone nucleus. Grignard addition of
the aryl ring and hydroxylation at C-2 via epoxidation of the a; b-double bond
were the key steps of this synthesis. While the Grignard reaction smoothly
resulted in the desired products, two different procedures were needed in order
to obtain appropriate yields in the epoxidation step. The Yang and Finnegan
procedure worked well with phenylphenalenones lacking an O-substituent at
C-6 but did not give satisfying results when 6-methoxy compounds were used.
In contrast, the Jacobsen–Katsuki epoxidation proved superior in this case
and was employed successfully in the synthesis of labelled lachnanthocarpone.
Different labelling patterns of phenylphenalenones are feasible for various
purposes in biosynthetic experiments. For example, the fingerprint signal of
Copyright # 2004 John Wiley & Sons, Ltd.
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´
F. OTALVARO ET AL.
152
Figure 4. Synthesis of [ phenyl-13C6]anigorufone ([ phenyl-13C6]-2), [1-13C]ani-
gorufone [1-13C6]-2 and [40-O13CH3]40-methoxy-anigorufone ([40-O13CH3]-8).
= [ phenyl-13C6],
=
13C
*
*
H-8 in the 1H NMR spectrum (Figure 3) allows sensitive detection of
phenylphenalenones biosynthetically derived from ([ phenyl-13C6]-labelled
1
precursors. In contrast, in the H spectra of singly 10-13C-labelled phenylphe-
nalenones, such as [10-13C]anigorufone ([10-13C]-2), the doublet of H-8 is
1
superimposed by the H resonances of the phenyl moiety and therefore is
13
less useful for biosynthetic studies. Instead, the C signal of C-10 of singly
labelled compounds appears as a singlet and, in comparison with the
multiplets of [ phenyl-13C6]-labelled compounds, is detected more sensitively
by 13C NMR.
Experimental
Preparative TLC was performed on silica gel 60 F254 (1 mm layer thickness)
(Merck, Darmstadt, Germany) and inspected under UV light (254 nm).
Preparative column chromatography was conducted on silica gel 60 (particle
size 0.040–0.063 mm) (Merck) using CH2Cl2 as an eluent. NMR spectroscopy:
1
1H NMR, H-1H COSY, HMBC, and HMQC spectra were recorded on an
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SYNTHESIS OF [PHENYL-13C6]LACHNANTHOCARPONE
153
Avance DRX 500 NMR spectrometer (Bruker, Karlsruhe, Germany)
equipped with a 5 mm TXI CryoProbe. 13C NMR spectra were measured on
a Bruker Avance 400 NMR spectrometer. The samples were measured in
acetone-d6 as a solvent. The spectra were referenced to TMS, which was used
as an internal standard. Electron impact mass spectra (EI-MS) and high-
resolution mass spectra (HREI-MS) were recorded on a MasSpec sector field
mass spectrometer (Micromass Ltd., Manchester, UK) with a direct insertion
probe. Labelled starting materials: ([1-13C]bromobenzene (99% 13C1) was
from Deutero GmbH (Kastellaun, Germany), [U-13C]bromobenzene (99%
13C6) and 13CH3I (99% 13C) were from Aldrich. Unlabelled chemicals were
from Aldrich as well and used without purification.
6-Hydroxy-perinaphthenone (3)
A mixture of 2,7-dihydroxynaphthalene (4) (2 g), sodium nitrobenzenesulpho-
nate (2.5 g), glycerol (5 g), H3PO4 (98%, 15 g), FeSO4 (0.6 g) and B(OH)3 (1 g)
was heated at 1608C for 35 min. The mixture was poured into water and
filtered. The residue was extracted with hot aqueous sodium carbonate and
filtered, and the resulting solution was acidified with HCl to precipitate the
product 3. The solid was then washed with water and dried. The crude
precipitate (0.5 g) was purified by column chromatography. TLC: Rf=0.3
(Et2O: n-hexane 7:1); EI-MS: m/z (rel. int.) 196 [M]+ (100); HR-MS: found
1
196.051903 (calculated for C13H8O2: 196.052430); H NMR: d 8.69 (H-7, d,
J=8.0 Hz), 8.57 (H-9, d, J = 8.0 Hz), 7.85 (H-8, dd, J=8.0, 8.0 Hz), 7.83 (H-3,
d, J = 9.4 Hz), 7.80 (H-4, d, J=8.0 Hz), 7.08 (H-5, d, J=8.0 Hz), 6.48 (H-2, d,
J=9.4 Hz); 13C NMR: d 185.4 (C-1), 159.6 (C-6), 143.0 (C-3), 134.8 (C-4),
131.1 (C-7), 130.8 (C-9a), 130.3 (C-9), 129.8 (C-9b), 126.8 (C-8), 126.7 (C-2),
125.6 (C-6a), 121.2 (C-3a), 110.4 (C-5).
6-Methoxy-perinaphthenone (5)
An ethanol-containing solution of diazomethane was prepared from Diazald1
using the standard procedure. This solution was added dropwise to 6-hydroxy-
perinaphthenone (3) (20 mg, 0.1 mmol) until gas evolution had ceased. The
reaction mixture was dried under a stream of nitrogen gas and used directly in
the next step. TLC: Rf=0.25; EI-MS: m/z (rel. int.) 210 [M]+ (100), 195 (26);
1
HR-MS: found 210.067098 (calculated for C14H10O2: 210.068080); H NMR:
d 8.65 (H-7, dd, J = 8.4, 1.3 Hz), 8.56 (H-9, d, J = 7.4, 1.3 Hz), 7.91 (H-4, d,
J = 8.0 Hz), 7.86 (H-3, d, J = 9.7 Hz), 7.86 (H-8, dd, J = 8.4, 7.4 Hz), 7.15
(H-5, d, J = 8.0 Hz), 6.51 (H-2, d, J = 9.7 Hz), 4.16 ð6-OCH3; sÞ; 13C NMR: d
185.2 (C-1), 160.5 (C-6), 142.9 (C-3), 134.9 (C-4), 131.0 (C-9), 130.4 (C-9a),
129.9 (C-7), 129.6 (C-9b), 127.5 (C-8), 127.4 (C-2), 126.2 (C-6a), 121.6 (C-3a),
106.5 (C-5), 57.0 ð6-OCH3Þ:
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154
[phenyl-13C6]6-Methoxy-9-phenylphenalen-1-one ([phenyl-13C6]-6)
[U-13C]Bromobenzene (0.17 ml, 1.6 mmol) was dissolved in dry THF (1 ml).
This solution was added during a period of 20 min with a 1-ml syringe to small
pieces of magnesium (39 mg, 1.6 mmol) in a 10-ml round-bottomed flask
containing dry THF (0.5 ml) and a small crystal of iodine under N2
atmosphere. After the addition, the solution was stirred for 20 min. An
aliquot of this solution (0.15 ml, 0.15 mmol) was transferred to a 5-ml round-
bottomed flask with a syringe purged with argon and cooled to ꢀ708C in an
acetone-dry ice bath. 6-Methoxy-perinaphthenone (5) (0.1 mmol, 21 mg) was
dissolved in dry THF and added to the cold Grignard solution over a period of
10 min with stirring. The solution was warmed up to 58C for 5 min and
quenched with a saturated aqueous solution of NH4Cl. After the crude
mixture was partitioned with CH2Cl2 (50 ml) and water (50 ml), the organic
phase was separated, dried with Na2SO4, and filtered. DDQ (23 mg, 0.1 mmol)
was added and the solution refluxed for 15 min. Preparative TLC gave
[ phenyl-13C6]6-methoxy-9-phenylphenalen-1-one ([ phenyl-13C6]-6) (24 mg,
82%). The rest of the Grignard reagent was used for the synthesis of
[ phenyl-13C6]anigorufone ([ phenyl-13C6]-2) as described below. TLC: Rf =
0.70 (Et2O: n-hexane 7:1). The labelled compound [ phenyl-13C6]-6 was
completely used up in the next step and no analytical data were recorded.
Analytical data of the unlabelled compound 6, which was prepared under
identical conditions: EI-MS: m/z (rel. int.) 285 [M-1]+ (100), 279 (48); HR-
1
MS: found 286.099107 (calculated for C20H14O2: 286.099380); H NMR: d
8.61 (H-7, d, J = 8.3 Hz), 7.90 (H-4, d, J = 8.0 Hz), 7.77 (H-3, d, J = 9.7 Hz),
7.56 (H-8, d, J = 8.3 Hz), 7.16 (H-5, d, J = 8.0 Hz), 7.41-7.31 (H-20–H-60, m),
6.34 (H-2, d, J = 9.7 Hz), 3.73 ð6-OCH3; sÞ: 13C NMR: d 185.7 (C-1), 160.3 (C-
6), 148.2 (C-9), 144.3 (C-10), 141.0 (C-3), 134.2 (C-4), 131.4 (C-8), 128.9 (C-30/
50), 128.1 (C-7), 127.9 (C-2), 127.7 (C-20/60), 127.3 (C-40), 127.0 (C-9a), 125.7
(C-6a), 123.1 (C-9b), 122.5 (C-3a), 105.7 (C-5), 56.6 ð6-OCH3Þ:
[phenyl-13C6]2-Hydroxy-6-methoxy-9-phenylphenalen-1-one ([phenyl-13C6]-7)
[ phenyl-13C6]6-Methoxy-9-phenylphenalen-1-one ([ phenyl-13C6]-6) (24 mg,
82 mmol), (S,S)-(+)-N,N0-bis-(3,5-di-tert-butylsalicylidene)-1,2-diamino-cyclo-
hexane manganese-(III)-chloride (Mn salen, 2.2 mg, 4 mmol) and 4-phenylpyr-
idine-N-oxide (3.4 mg, 20 mmol) were dissolved in dichloromethane (5 ml) and
the resulting solution cooled in an ice-water bath (solution A). Sodium
hypochlorite solution (NaOCl, 5 ml, ca. 0.9M) was buffered with 2 ml of a
sodium phosphate solution (0.05M) and the solution cooled in an ice-water
bath (solution B). Solution B was promptly added to solution A under
vigorous stirring and allowed to react for 3 h at 08C. The mixture was
separated, and the organic layer dried and applied directly to a preparative
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SYNTHESIS OF [PHENYL-13C6]LACHNANTHOCARPONE
155
TLC plate. Separation using the solvent system Et2O: n-hexane 7:1 resulted in
a red zone (Rf=0.9), which gave 20 mg (79%) of ([ phenyl-13C6]-7. EI-MS: m/z
12
(rel. int.) 307 [M-1]+ (100); HR-MS: found 308.112038 (calculated for
C
14
13C6H14O3: 308.114424); 1H NMR: d 8.71 (H-7, d, J = 8.5 Hz), 7.80 (H-4, d,
J = 7.8 Hz), 7.58 (H-8, dd, J = 8.4, 3.8 Hz), 7.67-7.51 and 7.30-7.13 (H-20– H-
60, m), 7.14 (H-5, d, J = 7.8 Hz), 7.11 (H-3, s), 4.13 ð6-OCH3; sÞ; 13C NMR: d
180.7 (C-1), 158.0 (C-6), 150.1 (C-2), 149.8 (C-9), 144.2 (C-1’, m), 133.2 (C-4),
131.5 (C-8), 129.9-127.0 (C-2’ - C-6’, C-7, C-9a, C-9b, m), 125.8 (C-6a), 123.0
(C-3a), 113.8 (C-3), 106.6 (C-5), 56.6 ð6-OCH3Þ: Analytical data of the
unlabelled compound 7, which was prepared under identical conditions: EI-
MS: m/z (rel. int.) 301 [M-1]+ (100); HR-MS: found 302.095491 (calculated
1
for C20H14O3: 302.094294); H NMR: d 8.71 (H-7, d, J = 8.5 Hz), 7.80 (H-4,
d, J = 7.8 Hz), 7.58 (H-8, d, J = 8.5 Hz), 7.35-7.45 (H-20– H-60, brm), 7.14 (H-
5, d, J = 7.8 Hz), 7.11 (H-3, s), 4.13 ð6-OCH3; sÞ; 13C NMR: d 180.7 (C-1),
158.0 (C-6), 150.1 (C-2), 149.8 (C-9), 144.2 (C-10), 133.2 (C-4), 131.5
(C-8), 129.9 (C-7), 129.2 (C-30/50), 128.9 (C-20/60), 128.2 (C-40), 127.2 (C-9a),
127.0 (C-9b), 125.8 (C-6a), 123.0 (C-3a), 113.8 (C-3), 106.6 (C-5), 56.6
ð6-OCH3Þ:
[phenyl-13C6]2,6-Dihydroxy-9-phenylphenalen-1-one ([phenyl-13C6]lachnantho-
carpone, [phenyl-13C6]-1)
Compound ([ phenyl-13C6]-7 (20 mg, 65 mmol) was refluxed in a N2 atmosphere
with AcOH (4.4 ml) and 48% HBr (0.56 ml) for 10 h. After cooling to room
temperature, the crude product was subjected to liquid–liquid distribution
between H2O (10 ml) and CH2Cl2 (10 ml). Preparative TLC of the organic
phase resulted in [ phenyl-13C6]lachnanthocarpone ([ phenyl-13C6]-1) (16 mg,
84%). TLC: Rf=0.8 (Et2O: n-hexane 7:1); EI-MS: m/z (rel. int.) 293 [M-1]+
12
(100); HR-MS: found 294.100182 (calculated for
1
C
13
13C6H12O3:
294.098773); H NMR: d 8.75 (H-7, d, J = 8.5 Hz), 7.67-7.51 and 7.30-7.13
3
(H-20–H-60, brm), 7.70 (H-4, d, J = 8.0 Hz), 7.59 (H-8, dd, JH-8–C-1 =3.7 Hz,
0
3JH-8–H-7=8.5 Hz), 7.11 (H-3, s), 7.08 (H-5, d, J = 8.0 Hz); 13C NMR: d 180.3
1
(C-1), 157.1 (C-6), 149.6 (C-9, d, JC-9–C-1 = 55 Hz), 149.5 (C-2), 144.1 (C-10,
0
3
0
m), 133.4 (C-4), 130.9 (C-8), 130.3 (C-7, d, JC-7–C-1 =3.7 Hz), 129.8-126.6
(C20–C60, C-9a, C-9b, m), 124.9 (C-6a), 122.0 (C-3a), 113.8 (C-3), 110.5 (C-5).
Analytical data of the unlabelled compound 1, which was prepared under
identical conditions: EI-MS: m/z (rel. int.) 287 [M-1]+ (100); HR-MS: found
1
288.078178 (calculated for C19H12O3: 288.078644); H NMR: d 8.75 (H-7, d,
J = 8.5 Hz), 7.70 (H-4, d, J = 8.0 Hz), 7.59 (H-8, d, 8.5 Hz, ), 7.35-7.45 (H-20–
H-60, m), 7.11 (H-3, s), 7.08 (H-5, d, J = 8.0 Hz); 13C NMR: d 180.3 (C-1),
157.1 (C-6), 149.6 (C-9), 149.5 (C-2), 144.1 (C-10), 133.4 (C-4), 130.9 (C-8),
130.3 (C-7), 129.2 (C-30/50), 128.6 (C-20/60), 127.8 (C-40), 128.6 (C-9a), 126.9
(C-9b), 124.9 (C-6a), 122.0 (C-3a), 113.8 (C-3), 110.5 (C-5).
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F. OTALVARO ET AL.
156
[phenyl-13C6]9-phenylphenalen-1-one ([phenyl-13C6]-11)
The Grignard reagent (1.35 ml, 1.35 mmol) prepared from [U-13C]bromophe-
nol as described above was also used for the synthesis of [ phenyl-13C6]9-
phenylphenalen-1-one ([ phenyl-13C6]-11) which was obtained in ca. 80% yield
1
(168 mg). TLC: Rf = 0.8 (Et2O: n-hexane 7:1); H NMR: d 8.37 (H-7, d,
J = 8.3 Hz), 8.22 (H-6, dd, J = 8.2, 1.1 Hz), 7.98 (H-4, dd, J = 8.2, 1.1 Hz),
7.89 (H-3, d, J = 9.7 Hz), 7.73 (H-5, dd, J = 8.2, 8.2 Hz), 7.60 (H-8, dd,
3
3
JH-8–C-1 =3.8 Hz, JH-8–H-7 = 8.3 Hz), 7.41-7.36 (H-20–H-60, m), 6.51 (H-2, d,
0
J = 9.7 Hz); 13C NMR: d 185.2 (C-1), 147.7 (C-9), 143.7 (C-10, m), 140.7 (C-3),
134.2 (C-7, d, 3JC-7–C-1 = 3.7 Hz), 132.4 (C-6a), 132.2 (C-6), 132.0 (C-4), 131.9
0
(C-8), 130.5 (C-2), 129.8-126.8 (C-20–C-60, C-3a, C-5, C-9a, C-9b). Analytical
data of the unlabelled compound 11, which was prepared under identical
conditions: EI-MS: m/z (rel. int.) 256 [M]+ (100); HR-MS: found 256.087554
1
(calculated for C19H12O: 256.088815); H NMR: d 8.37 (H-7, d, J = 8.3 Hz),
8.22 (H-6, dd, J = 8.2, 1.1 Hz), 7.98 (H-4, dd, J = 8.2, 1.1 Hz), 7.89 (H-3, d,
J = 9.7 Hz), 7.73 (H-5, dd, J = 8.2, 8.2 Hz), 7.60 (H-8, d, J = 8.3 Hz), 7.41-
7.36 (H-20–H-60, m), 6.51 (H-2, d, J = 9.7 Hz); 13C NMR: d 185.2 (C-1), 147.7
(C-9), 143.7 (C-10), 140.7 (C-3), 134.2 (C-7), 132.4 (C-6a), 132.2 (C-6), 132.0
(C-4), 131.9 (C-8), 130.5 (C-2), 129.0 (C-3a), 128.7 (C-9b), 128.5 (C-20/C-60),
128.3 (C-30/C-50), 127.2 (C-40), 127.1 (C-5), 126.2 (C-9a).
[phenyl-13C6]2-Hydroxy-9-phenylphenalen-1-one ([phenyl-13C6]anigorufone,
([phenyl-13C6]-2)
[ phenyl-13C6]9-Phenylphenalen-1-one ([ phenyl-13C6]-11) (168 mg, 0.6 mmol)
was subjected to Yang and Finnegan peroxidation13 (for a protocol see Cooke
and Dagley),14 which after separation by preparative TLC resulted in
[ phenyl-13C6]anigorufone ([ phenyl-13C6]-2, 110 mg, 66%). TLC: Rf = 0.86
(Et2O: n-hexane 7:1); EI-MS: m/z (rel. int.) 277 [M-1]+ (100); HR-MS: found
12
1
278.103359 (calculated for
(H-7, d, J = 8.2 Hz), 8.09 (H-6, d, J = 8.2 Hz), 7.88 (H-4, d, J = 7.1 Hz), 7.70
C
13C6H12O2: 278.103859); H NMR: d 8.41
13
3
(H-5, dd, J = 8.2, 7.1 Hz), 7.63 (H-8, dd, JH-8–C-1 =3.8 Hz, JH-8–H-7
3
0
=
8.2 Hz), 7.61-7.49 and 7.33-7.21 (H-20–H-60, brm), 7.18 (H-3, s); 13C NMR: d
1
180.7 (C-1), 151.3 (C-2), 149.1 (C-9, brd, JC-9–C-1 =55 Hz), 143.6 (C-1 , m),
0
0
3
136.2 (C-7, d, JC-7–C-1 =3.7 Hz), 132.5 (C-6a), 132.0 (C-8), 131.0 (C-4),
0
130.2 (C-6), 130.0 (C-3a), 129.6-127.1 (m, C-20–C-60,C-5), 125.8 (C-9b, d,
3
0
JC-9b–C-1 =3.7 Hz), 124.7 (C-9a), 113.1 (C-3). Analytical data of the
unlabelled compound 2, which was prepared under identical conditions, were
identical with those of the natural product.21
[1’-13C]9-phenylphenalen-1-one ([1’-13C]-11)
The procedure used for the synthesis of [ phenyl-13C6]9-phenylphenalen-1-one
([ phenyl-13C6]-11) was used analogously, except that the Grignard reagent
Copyright # 2004 John Wiley & Sons, Ltd.
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SYNTHESIS OF [PHENYL-13C6]LACHNANTHOCARPONE
157
(1.5 ml, 1.5 mmol) was prepared from [1-13C]bromophenol. [10-13C]9-Phenyl-
phenalen-1-one ([10-13C]-11) was obtained in 82% yield (316 mg). TLC:
Rf=0.8 (Et2O: n-hexane 7:1); EI-MS: m/z (rel. int.) 256 [M-1]+ (100); HR-MS:
found 257.090149 (calculated for
C
18
13CH12O: 257.092170); H and 13C
12
1
NMR data matched those of unlabelled compound 11 except the enhanced 13
signal of C-10 at d 143.7.
C
[1’-13C]2-Hydroxy-9-phenylphenalen-1-one ([1’-13C]anigorufone, [1’-13C]-2)
[10-13C]Anigorufone ([10-13C]-2) (80 mg, 60%) was synthesized from [10-13C]9-
phenylphenalen-1-one ([10-13C]-11) using the procedure described above. EI-
MS: m/z (rel. int.) 273 [M]+ (100), 272 [M-1]+ (64); HR-MS: found
13CH12O2: 273.087085); H and 13C NMR
12
1
273.087662 (calculated for
C
18
data matched those of unlabelled anigorufone21 (2) except the enhanced signal
of C-10 at d 143.6
9-(40-Methoxyphenyl)-phenalen-1-one (10)
A Grignard solution (15 ml, 5.2 mmol) was prepared from 4-bromoanisol
(0.7 ml, 5.2 mmol) and used for the synthesis of 9-(40-methoxyphenyl)-
phenalen-1-one22 (10), which was obtained from perinaphthenone (9) in
65% yield (950 mg). TLC: Rf = 0.53 (Et2O: n-hexane 7:1); EI-MS: m/z (rel.
int.) 285 [M-1]+ (100), 271 (27); HR-MS: found 286.101036 (calculated for
C20H14O2: 286.099380); 1H NMR: d 8.32 (H-7, d, J = 8.3 Hz), 8.19 (H-6, dd,
J=8.2, 1.1 Hz), 7.94 (H-4, dd, J=7.1, 1.1 Hz), 7.85 (H-3, d, J = 9.7 Hz), 7.70
(H-5, dd, J = 8.2, 7.1 Hz), 7.61 (H-8, d, J = 8.3 Hz), 7.32 (H-20/60, d,
J = 8.7 Hz), 6.94 (H-30/50, d, J = 8.7 Hz), 6.50 (H-2, d, J = 9.7 Hz), 3.87
13
ðOCH3; sÞ; C NMR: d 185.6 (C-1), 160.1 (C-40), 147.9 (C-9), 141.0 (C-3),
136.0 (C-10), 134.6 (C-7), 132.8 (C-8), 132.7 (C-6a), 132.6 (C-6), 132.4 (C-4),
131.1 (C-2), 130.6 (C-20/60), 129.4 (C-3a), 129.4 (C-9b), 127.4 (C-5), 126.7
(C-9a), 114.3 (C-30/50), 55.5 ðOCH3Þ:
9-(40-Hydroxyphenyl)-phenalen-1-one (12)
9-(40-Methoxyphenyl)-phenalen-1-one (10) (900 mg, 3.1 mmol) was treated
with 48% HBr (7 ml) in acetic acid (55 ml) and refluxed for 6 h. The resulting
9-(40-hydroxyphenyl)-phenalen-1-one (12) was purified by column chromato-
graphy (760 mg, 90%). TLC: Rf=0.37 (Et2O: n-hexane 7:1); EI-MS: m/z (rel.
int.) 271 [M-1]+ (100); HR-MS: found 272.084846 (calculated for C19H12O2:
1
272.083730); H NMR: d 8.31 (H-7, d, J = 8.3 Hz), 8.18 (H-6, dd, J = 8.2,
1.1 Hz), 7.94 (H-4, dd, J = 7.1, 1.1 Hz), 7.85 (H-3, d, J = 9.7 Hz), 7.69 (H-5,
dd, J = 8.2, 7.1 Hz), 7.61 (H-8, d, J = 8.3 Hz), 7.35 (H-20/60, d, J = 8.7 Hz),
6.89 (H-30/50, d, J = 8.7 Hz), 6.50 (H-2, d, J = 9.7 Hz); 13C NMR: d 185.6
(C-1), 157.7 (C-40), 148.3 (C-9), 140.9 (C-3), 134.9 (C-10), 134.6 (C-7), 133.0
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(C-8), 132.64 (C-6a), 132.61 (C-6), 132.3 (C-4), 131.2 (C-9b), 130.7 (C-20/60),
129.4 (C-3a), 130.8 (C-2), 127.3 (C-5), 126.7 (C-9a), 115.8 (C-30/50).
[40-O13CH3]9-(40-Methoxyphenyl)-phenalen-1-one ([40-O13CH3]-10)
9-(40-Hydroxyphenyl)-phenalen-1-one (12) (170 mg, 0.7 mmol) was dissolved
in acetone (20 ml). 13CH3I (0.46 ml, 0.8 mmol) and K2CO3 (482 mg, 0.7 mmol)
were added and the mixture refluxed for 4 h. The resulting [40-O13CH3]9-(40-
methoxyphenyl)-phenalen-1-one ([40-O13CH3]-10) was purified by column
chromatography (110 mg, 55%). TLC: Rf = 0.53 (Et2O: n-hexane 7:1); EI-
MS: m/z (rel. int.) 286 [M-1]+ (100); HR-MS: found 287.099998 (calculated
for 12C1913CH14O2: 287.098264); 1H and 13C NMR data matched those of the
unlabelled compound 10 except that the methoxyl signal (d 3.87) appeared as a
1
doublet (1JC–H=143.8 Hz) in the H NMR spectrum and the signal of 40-
OCH3 at d 55.5 was enhanced in the 13C NMR spectrum.
[40-O13CH3]2-Hydroxy-9-(40-methoxyphenyl)-phenalen-1-one ([40-O13CH3]-8)
The introduction of the hydroxyl group at C-2 of [40-O13CH3]9-(40-
methoxyphenyl)-phenalen-1-one ([40-O13CH3]-10) (50 mg, 0.17 mmol) was
achieved using the Yang and Finnegan13 procedure. The resulting [40-
O13CH3]2-hydroxy-9-(40-methoxyphenyl)-phenalen-1-one ([40-O13CH3]-8) was
obtained in 75% yield (40 mg) after purification by TLC: Rf = 0.58 (Et2O:
n-hexane 7:1); EI-MS: m/z (rel. int.) 302 [M-1]+ (100), 287 (34), 272 (58);
13CH14O3: 303.097649);
12
HR-MS: found 303.097991 (calculated for
C
19
1H NMR: d 8.38 (H-7, d, J = 8.3 Hz), 8.07 (H-6, dd, J = 8.2, 1.0 Hz), 7.86
(H-4, dd, J = 7.2, 1.0 Hz), 7.68 (H-5, dd, J = 8.2, 7.2 Hz), 7.64 (H-8, d,
J = 8.3 Hz), 7.36 (H-20/60, d, J = 8.8 Hz), 7.02 (H-30/50, d, J = 8.8 Hz), 3.89
ðOCH3; d; JCꢀH ¼ 143:8 HzÞ; 13C NMR data matched those of the natural
1
product20 except the enhanced signal of 40-OCH3 at d 55.6
Acknowledgements
$
$
We thank Dr Ales Svatos and Sybille Koch (Jena, Germany) for mass spectral
analyses and Emily Wheeler (Jena) for linguistic support in the preparation of
this manuscript. This investigation was financially supported by Colciencias
(Bogota, Colombia).
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