Synthesis of bacterial metabolites of polycyclic aromatic hydrocarbons: Benzochromenones, o-carboxyvinylnaphthoates, and o-substituted aryl-α-oxobutenoates

Article abstract of DOI:10.1080/00397910500214367

Bacterial metabolites of phenanthrene and anthracene include benzochromenones, o-carboxyvinylnaphthoates, and o-substituted aryl α-oxobutenoates, which were synthesized with the Wittig reaction, the Heck reaction, and coupling of aromatic aldehyde with py

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Synthesis of Bacterial
Metabolites of Polycyclic
Aromatic Hydrocarbons:
Benzochromenones,
o‐Carboxyvinylnaphthoates,
and o‐Substituted
Aryl‐α‐Oxobutenoates
Young‐Soo Keum a , Jong‐Su Seo a & Qing X. Li a
a Department of Molecular Biosciences and
Bioengineering, University of Hawaii, Honolulu,
Hawaii, USA
Published online: 22 Aug 2006.
To cite this article: Young‐Soo Keum , Jong‐Su Seo & Qing X. Li (2005): Synthesis
of Bacterial Metabolites of Polycyclic Aromatic Hydrocarbons: Benzochromenones,
o‐Carboxyvinylnaphthoates, and o‐Substituted Aryl‐α‐Oxobutenoates, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:20, 2685-2693
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Synthetic Communicationsw, 35: 2685–2693, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500214367
Synthesis of Bacterial Metabolites of
Polycyclic Aromatic Hydrocarbons:
Benzochromenones,
o-Carboxyvinylnaphthoates, and
o-Substituted Aryl-a-Oxobutenoates
Young-Soo Keum, Jong-Su Seo, and Qing X. Li
Department of Molecular Biosciences and Bioengineering, University
of Hawaii, Honolulu, Hawaii, USA
Abstract: Bacterial metabolites of phenanthrene and anthracene include benzochrome-
nones, o-carboxyvinylnaphthoates, and o-substituted aryl a-oxobutenoates, which
were synthesized with the Wittig reaction, the Heck reaction, and coupling of
aromatic aldehyde with pyruvate.
Keywords: Polycyclic aromatic hydrocarbon, metabolite, benzochromene carbo-
xyvinylnaphthoate, oxobutenoate
Polycyclic aromatic hydrocarbons (PAHs) are global contaminants.
Numerous bacterial species have been reported as PAH degraders. Phenan-
threne (1) and anthracene (2) are frequently used as model compounds in
bacterial metabolism studies. Bacterial degradation usually starts with dioxy-
genation on 1,2-, 3,4-, or 9,10-C of phenanthrene and 1,2-C of anthracene
(Figure 1).[1,2] Dihydrodiols from dioxygenation are metabolized to
benzochromenones (3, 6) and o-hydroxynaphthyl-a-oxobutenoate (4, 7),
and o-carboxyvinylnaphthoates (5, 8), via meta- and ortho-cleavage
Received in the USA January 27, 2005
Address correspondence to Qing X. Li, Department of Molecular Biosciences and
Bioengineering, University of Hawaii, 1955 East-West Road, Honolulu, HI 96822,
USA. Tel.: (808) 956-2011; Fax: (808) 956-3542; E-mail: qingl@hawaii.edu
2685

2686
Y.-S. Keum, J.-S. Seo, and Q. X. Li
Figure 1. Bacterial metabolism of phenanthrene (1) and anthracene (2) via 3,4- and
1,2-dioxygenation.
pathways, respectively. Further degradations result in the formation of
2-(3-carboxy-3-oxoprop-1-enyl)-benzoic acid (9), o-carboxycinnamic acid,
or 4-(2-hydroxyphenyl)-2-oxobut-3-enoic acid (10). These metabolites are
usually identified by gas or liquid chromatography coupled with mass
spectrometry (GC-MS or LC-MS) in their intact form or their ether/ester
derivatives. However, the authentic standards of the intact chemicals
(1–10) or their ether/ester derivatives are not commercially available,
which limits the detailed study of their role in bacterial metabolism. In
addition, their stereochemistry (E- or Z-) is also vague. This study was
intended to provide proper synthetic methods of these metabolites or their
derivatives for more detailed biochemical studies and instrumental analysis.
Benzochromenones and coumarins are prepared by several methods
includinga) couplingof trimethylsilylketene witho-hydroxynaphthaldehyde,[3]
b) cyclization of o-substituted cinnamates,[4,5] and c) thermal oxidation and
cyclization of o-hydroxyarylpropanoic acid.[6]
Benzochromenones 3 and 3a, which are common metabolites of phenan-
threne,[1] were prepared from o-hydroxynaphthaldehyde (11a and 11b)
through a Wittig reaction (Scheme 1). 2H-Benzo[g]chromen-2-one (6) was
synthesized from 11c.[7] The reaction yields were 70, 78, and 69% for 3,
3a, and 6, respectively. Mass spectra and melting points well coincided
with those in the literature.[1,2,7] Crude reaction mixtures of 3 and 3a were
analyzed with GC-MS. Approximately 20–30% of the aldehydes were

Bacterial Metabolites
2687
Scheme 1.
recovered as unreacted starting materials. o-Hydroxynaphthylpropenoates,
possible Wittig reaction products, were found only at the initial stage
of reaction (,2 h of reflux). Dubuffet et al.[7] prepared 3 and 3a from
o-methoxynaphthaldehyde via a Wittig reaction, followed by boron-
mediated dealkylative ring closure, the methods of which were applied on
the preparation of 6 in this study. Boron trihalide, which is very toxic
and air sensitive, is usually used for the ring closure of o-methoxyaryl
propenoates.[7,8] In this study, o-methoxynaphthldehyde was used for the
synthesis 3 and 3a instead of o-hydroxy analogues. Toluene (bp 1108C),
a commonly used solvent,[7] was replaced by higher boiling xylene
(bp 1388C). In the preliminary experiments for solvent selection, the
reaction yields in benzene and toluene were 10 and 45% of 3, respectively.
The results suggest that higher boiling-point solvents may increase thermal
rearrangement from o-hydroxynaphthyl propenoates to benzochromenones.
Several synthetic methods have been reported for the preparation of
aryl-a-oxobutenoic acids.[9,10] The method of Dujardin et al.[9] was very
simple but required a long reaction time (usually .36 h of reflux).
Coupling of a-ketoylide to arylaldehyde is another possible choice of
the synthesis of aryl-a-oxobutenoates.[11] The previous studies, however,
were limited to the synthesis of nonsubstituted or p-substituted aryl
analogues.[9–11] PAH metabolites, conversely, usually have o-hydroxy or
o-carboxy substituents on their aromatic ring (e.g., 4, 5, 7–10). We
tested the reactivity of five arylaldehydes with o-hydroxy (11a and b),
-methoxy (11c, 12a and b, 14a), and methoxycarbonyl group (14b) in
two different reaction conditions (Scheme 2). The yields of method A or
B with o-methoxy- or o-carboxy-substituted arylaldehyde were 27–40%
(Table 1). o-Hydroxyaryl aldehyde (11a and b) did not react to produce
a-oxobutenoates after 36 h of reflux (Table 1). Longer heating (.72 h)

2688
Y.-S. Keum, J.-S. Seo, and Q. X. Li
Scheme 2.
did not improve the yield. Instead of 4a and 13a, approximately 1–2% of
benzochromenone (3 and 3a) was recovered from reaction mixtures.
Reaction yields of method A with 11c, 12a and b, and 14a and b were
lower than those of nonsubstituted or p-substituted aldehydes,[7] which
may be due to steric effects of ortho-substituents. Among the products
derived from method A, only a single peak in each experiment, except
Table 1. Reaction condition, yield, and GC retention time of o-substituted aryl-a-
oxobutenoates
Reaction
time (h)
GC retention
time (min)
Reactant
Product
4a
13a
Method
Yield (%)a
11a
11b
11c
12a
A
A
A
A
B
A
B
A
A
A
36
36
36
48
5
—
—
NDb
ND
32
31
34
27
38
32
40
1
7a
4b
58.6
54.78
54.79
56.66
56.71
34.28
38.25
35.01
4b
12b
13b
13b
10a
48
5
14a
14b
36
36
36
9a-trans
9a-cis
aReaction yield after column chromatography or thin-layer chromatography.
bNot detected.

Bacterial Metabolites
2689
the synthesis of 9a, showed an expected mass spectrum of o-substituted aryl
oxobutenoate 2[M]þ 220 or 270, fragments of m/z [M-15 (Me)], [M-31
(MeO)], [M-59 (COOMe)]. In addition to these peaks, a trace amount of
benzochromenones (3 and 3a) was observed. In consideration of the
reaction condition,[11] the C-C double bond in oxobutenoates from
method A may have an E-configuration. Two peaks (GC retention time
[Rt], 35.01 and 38.25 min) with nearly identical mass spectra were found
in the reaction mixture for the synthesis of 9a, which suggests cis- and
trans-isomer, respectively.
The yields from the Wittig reaction (method B) were comparable
with those in literature.[11] Although both methods A and B gave similar
yields, large differences were observed in the chemical profile of reaction
mixtures. More complex reaction mixtures were obtained from method
A—more than 10 reaction products—and were detected in GC-MS analysis.
In comparison with method A, only four to five peaks were observed in GC-
MS chromatograms of reaction mixtures from method B, which can be easily
assigned as unreacted aldehyde, ylide, triphenylphosphine oxide, and
expected products (4b and 13b). The selectivity for E- and Z-isomers in the
Wittig reaction is dependent on various conditions.[12–14] Because ylide
usually exists as a mixture of E- and Z-isomers, isomeric mixture of products
were expected in method B. However, only a single isomer was found (4b)
or one of isomers was the dominant product (13b). Because of the high steric
hindrance of ortho-substituents, the dominant isomer may be the E-isomer.
o-Carboxyvinyl naphthoates (5a, 8a, and 8b) were prepared from a
typical Heck reaction with o-bromonaphthoic acid methyl esters
(Scheme 3). Among the peaks in GC-MS chromatograms of a crude
reaction mixture (5a), only a single peak (Rt 49.50 min) showed a
typical MS spectrum of the predicted product (Mþ, 270). In case of the
synthesis of 8a (Rt 53.93 min), one additional peak (Rt 47.08 min) also
showed a similar MS pattern. In consideration of the reaction mecha-
nisms,[15–17] the double bond in the propenoic acid group of the dominant
product (5a and 8a) may be an E-configuration. The reaction yields were 68
and 73% for 5a and 8a, respectively. Approximately 30% of the reactant
was recovered at the end of reaction. No other products were detected with
GC-MS.
Scheme 3.

2690
Y.-S. Keum, J.-S. Seo, and Q. X. Li
EXPERIMENTAL
General Procedures for the Preparation of Benzochromenones
Benzochromenones 3 and 3a were prepared from 11a and b, respectively, by
the procedure of Dubuffet et al.[7] with some modification. Methyl triphenyl-
phosphoranylidene acetate (10 mmol) was added to a solution of o-hydroxy-
naphthaldehyde (10 mmol) in xylene (50 ml). The mixture was refluxed for
4 h. After removing the solvent, the residues were triturated with isopropyl
ether. Insoluble triphenylphosphine oxide was removed and the filtrate was
concentrated. Residue was purified with silica-gel column chromatography
(hexane/ethyl acetate 1/1, v/v). Purities of synthetic compounds were deter-
mined with GC-MS. Melting points were measured with a Fisher-Johns
melting-point apparatus and reported without correction.
3-Methoxy-2-naphthaldehyde (11c) was prepared from (3-methoxy-
naphthalen-2-yl)-methanol by an established method.[18] 2H-Benzo[g]chro-
men-2-one (6) was prepared from 11c, according to the established
procedure.[7]
2H-Benzo[h]chromen-2-one (3). GC-MS Rt (min): 39.53; m/z 196 (Mþ,
1
72), 168 (100), 139 (46); H NMR: 6.51 (d, 1H), 7.51 (d, 1H), 7.65 (m, 2H),
7.70 (d, 1H), 7.83 (d, 1H), 7.88 (m, 1H), 8.47 (m, 1H); purity, 98%; mp:
138–1418C, lit.: 140–1418C.[19]
3H-Benzo[f]chromen-3-one (3a). GC-MS Rt (min): 41.80; m/z 196
1
(Mþ, 88), 168 (100), 139 (56); H NMR: 6.65 (d, 1H), 7.45 (d, 1H), 7.59
(m, 1H), 7.68(t, 1H), 7.91 (d, 1H), 7.98 (d, 1H), 8.32 (d, 1H), 8.50 (d, 1H);
purity, 99%; mp: 116–1188C, lit.: 115–1168C.[7]
2H-Benzo[g]chromen-2-one (6). GC-MS Rt (min): 41.49; m/z 196 (Mþ,
1
100), 168 (73), 139 (60); H NMR: 6.40 (d, 1H), 7.52(m, 1H), 7.68–7.79
(m, 3H), 7.90–8.00 (m, 1H), 8.20 (s, 1H); purity, 97%; mp: 124–1258C.
General Procedures for the Preparation of 4-(o-Methoxyaryl)-2-
oxobut-3-enoates and Related Compounds
Method A: 4-(o-Methoxnaphthyl)-2-oxobut-3-enoates (4b, 7a, and 13b) were
prepared from o-methoxynaphthaldehyde (11c, 12a, and b) according to the
literature method.[9] 4-(o-substituted pheny)-2-oxobut-3-enoates (9a and
10a) were synthesized by the same method, using 14a and b, respectively.
Copper triflate [Cu(OTf)2, 0.2 mmol] and trimethyl orthoformate (1.2 mmol)
were added to a solution of methyl pyruvate (2 mmol) and o-substituted
aldehyde (1 mmol) in dichloromethane (80 ml), and the mixture was heated
to reflux for 36–48 h. After solvent removal, an oily residue was purified by
silica-gel thin-layer chromatography (hexane/ethyl acetate 2/1, v/v).
Method B: Methyl 2-oxo-3-(triphenylphosphoranylidene)propanoate
(TPPP) was prepared by a literature method.[20] TPPP (50 mmol) was added

Bacterial Metabolites
2691
to a solution of aldehyde (10 mmol, 12a and b) in toluene (50 ml), and the
mixture was stirred at 808C for 5 h. After removing the solvent under
reduced pressure, the residue was triturated with isopropyl ether. Insoluble
oxide was removed and the extracts were purified with silica-gel column
chromatography (hexane/ethyl acetate 1/1, v/v).
Methyl (3E)-4-(1-methoxy-2-naphthyl)-2-oxobut-3-enoate (4b). m/z
1
270 (Mþ, 6), 255 (2), 239 (100), 211 (53), 196 (57), 168 (34); H NMR:
3.86 (s, 3H), 3.95 (s, 3H), 7.32 (d, 1H), 7.47 (d, 1H), 7.49–7.60 (m, 3H),
7.85–7.90 (m, 2H), 8.41 (d, 1H); purity 96%; mp 35–368C.
Methyl (3E)-4-(2-methoxy-1-naphthyl)-2-oxobut-3-enoate (13b). m/z
270 (Mþ, 55), 239 (97), 211 (61), 196 (100), 168 (82); 1H NMR: 3.84
(s, 3H), 3.94 (s, 3H), 6.37 (d, 1H), 7.52–7.62 (m, 3H), 7.75 (d, 1H), 7.99
(d, 1H), 8.04 (d, 1H), 8.42 (d, 1H); purity 98%; mp 41–428C.
Methyl (3E)-4-(3-methoxy-2-naphthyl)-2-oxobut-3-enoate (7a). m/z
1
270 (Mþ, 25), 255 (1), 239 (5), 211 (100), 196 (45), 168 (24); H NMR:
3.74 (s, 3H), 3.87 (s, 3H), 7.22 (d, 1H), 7.44 (t, 1H), 7.48 (d, 1H), 7.67
(t, 1H), 7.82 (m, 2H), 8.08 (d, 1H), 8.42 (d, 1H); purity 95%; yellow oil.
Methyl 2-[(1E)-4-methoxy-3,4-dioxobut-1-enyl]benzoate (9a-trans).
1
m/z 248 (Mþ, 4), 233 (3), 217 (2), 189 (100), 145 (50); H NMR: 3.89
(s, 3H), 3.92 (s, 3H), 7.18 (d, 1H), 7.48 (m, 1H), 7.51 (m, 1H), 7.64
(m, 1H), 7.90 (d, 1H), 8.37 (d, 1H); purity 95%; yellow oil.
Methyl 2-[(1Z)-4-methoxy-3,4-dioxobut-1-enyl]benzoate (9a-cis). m/z
248 (Mþ, 4), 233 (4), 217 (2), 189 (100), 145 (44); 1H NMR: 3.90 (s, 3H), 3.95
(s, 3H), 6.28 (d, 1H), 7.46–7.53 (m, 2H), 7.57 (m, 1H), 7.91 (d, 1H), 8.22
(d, 1H); purity 97%; mp 34–378C.
Methyl (3E)-4-(2-methoxyphenyl)-2-oxobut-3-enoate (10a). m/z 220
1
(Mþ, 7), 205 (1), 189 (1), 161 (100); H NMR: 3.86 (s, 3H), 4.30 (s, 3H),
7.44 (d, 1H), 7.06–7.66 (m, 4H), 7.87 (d, 1H); purity 94%; yellow oil.
General Procedures for the Preparation of
o-Carboxyvinylnaphthoates and Benzoates
Methyl esters of o-bromonaphthoic acids (15a and b) were prepared according
to the methods of Look et al.[21] and Seki et al.,[22] followed by esterification
with methyl iodide. Methyl acrylate (60 mmol), triethylamine (TEA,
60 mmol), palladium acetate (1 mmol), and tri-o-tolylphosphine (10 mmol)
were added successively to a solution of o-bromonaphthoate (50 mmol)
in N,N-dimethylformamide (50 ml). The mixture was stirred at 908C for 5 h.
After cooling, the mixture was poured into water (200 ml) and extracted
with dichloromethane (80 ml ꢀ 3). After removing the solvent, residues
were purified by column chromatography (silica gel, hexane/ethyl acetate).
1-[(E)-2-Carboxyvinyl]-2-naphthoic acid dimethyl ester (5a). GC-MS
Rt (min): 49.50; m/z 270 (Mþ, 8), 239 (9), 223 (7), 211 (100), 196 (10), 179
1
(10), 168 (12); H NMR: 3.81 (s, 3H), 3.92 (s, 3H), 6.52 (d, 1H), 7.44–7.50

2692
Y.-S. Keum, J.-S. Seo, and Q. X. Li
(m, 2H), 7.65 (m, 1H), 7.83 (d, 1H), 7.95 (d, 1H), 8.15 (d, 1H), 8.43 (d, 1H);
purity 97%; mp 54–568C.
3-[(E)-2-Carboxyvinyl]-2-naphthoic acid dimethyl ester (8a). GC-MS
Rt (min): 53.93; m/z 270 (Mþ, 14), 255 (3), 239 (9), 223 (26), 211 (100), 196
1
(13), 168 (16); H NMR: 3.55 (s, 3H), 3.82 (s, 3H), 6.13 (d, 1H), 7.44–7.74
(m, 3H), 7.84–8.06 (m, 2H), 8.21 (d, 1H), 8.43 (s, 1H); purity 97%; mp
77–788C.
3-[(Z)-2-Carboxyvinyl]-2-naphthoic acid dimethyl ester (8b). GC-MS
Rt (min): 47.08; m/z 270 (Mþ, 24), 255 (5), 239 (8), 223 (29), 211 (100), 196
(18), 168 (16); purity 91%.
Instrumental Analysis
GC-MS analyses were performed with a Varian QP-5000 gas chromatograph
and a Saturn-2000 Ion trap mass spectrometer. ZB-1 column (60 m, 0.25 mm)
was used. Initial column temperature was set at 1208C (held for 2 min) and
raised to 2808C at a rate of 28C/min (held for 10 min). Injector and detector
temperatures were 270 and 2808C, respectively. Helium was the carrier gas
at a rate of 2 ml/min. Melting point was measured with a Fisher-Johns
1
melting-point apparatus and is reported without correction. H NMR spectra
were recorded on a Varian Mercury-Plus 300-MHz NMR for solutions in
CDCl3.
ACKNOWLEDGMENTS
This work was supported in part by US-EPA Grant No. 989512-01-1 and
USDA/CSREES/TSTAR Grant No. 0034135-9576.
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