Biomimetic asymmetric synthesis of (R)-GTRI-02 and (3 S,4 R)-3,4-dihydroxy-3,4-dihydronaphthalen-1(2H)-ones

Article abstract of DOI:10.1021/ol301305p

The NADPH-dependent tetrahydroxynaphthalene reductase (T₄HNR) from Magnaporthe grisea was used for the biomimetic synthesis of (R)-GTRI-02 by stereoselective reduction of 1-(3,6,8-trihydroxy-1-methylnaphthalen-2-yl) ethanone. This also led to t

Full text of DOI:10.1021/ol301305p

ORGANIC
LETTERS
2012
Vol. 14, No. 14
3600–3603
Biomimetic Asymmetric Synthesis of
(R)-GTRI-02 and (3S,4R)-3,4-Dihydroxy-
3,4-dihydronaphthalen-1(2H)-ones
†
Syed Masood Husain, Michael A. Schatzle, Caroline Rohr, Steffen Ludeke, and
†
‡
†
€
€
€
,†
€
Michael Muller*
Institute of Pharmaceutical Sciences, Albert-Ludwigs-University of Freiburg,
Albertstrasse 25, 79104 Freiburg, Germany, and Institute for Inorganic and Analytical
Chemistry, Albert-Ludwigs-University of Freiburg, Albertstrasse 21, 79104 Freiburg, Germany
michael.mueller@pharmazie.uni-freiburg.de
Received May 11, 2012
ABSTRACT
The NADPH-dependent tetrahydroxynaphthalene reductase (T4HNR) from Magnaporthe grisea was used for the biomimetic synthesis of (R)-GTRI-
02 by stereoselective reduction of 1-(3,6,8-trihydroxy-1-methylnaphthalen-2-yl)ethanone. This also led to the isolation of a (3S,4R)-cis-ketodiol
formed by T4HNR-catalyzed reduction of the corresponding hydroxynaphthoquinone. Flaviolin and lawsone also reduced to corresponding cis-
ketodiols in good yields.
Naphthol reductases belong to the large family of short-
chain dehydrogenases/reductases (SDR) and show a
unique ability to catalyze asymmetric NADPH-dependent
reduction of polyhydroxynaphthalenes.1 Although the use
of naphthol reductases as biocatalysts in synthesis looks
promising, so far their application has remained limited to
the reduction of only a few physiological substrates.1À4
Tetrahydroxynaphthalene reductase (T4HNR) from Magna-
porthe grisea has been used by us and others to catalyze the
reduction of 1,3,6,8-tetrahydroxynaphthalene (T4HN, 1) to
(R)-scytalone (2) in 33% yield (Scheme 1, A).1,4,5 T4HNR is
one of the two naphthol reductases involved in the bio-
synthesis of dihydroxynaphthalene melanin.2À4 For naph-
tholic substrates to be reduced by T4HNR, the 1,3-dihydroxy
substitution pattern represents the essential structural
motif.1 Herein, we report the chemoenzymatic synthe-
sis of the natural product GTRI-02 (3) using T4HNR as
well as the unexpected recognition of hydroxynaph-
thoquinones as substrates which are reduced by T4HNR to
cis-ketodiols.
The putatively polyketidic GTRI-02 (3), isolated from
soil actinomycetes Micromonospora sp.,6 has been shown
topossessantioxidant properties. Morerecently, ithas also
been extracted from Streptomyces strain GW4184 and
Streptomyces sp. ANK313.7,8 We proposed that 3 is
biosynthesized via an enzymatic reduction.
† Institute for Pharmaceutical Sciences.
‡ Institute for Inorganic and Analytical Chemistry.
€
(1) Schatzle, M. A.; Flemming, S.; Husain, S. M.; Richter, M.;
€
€
Gunther, S.; Muller, M. Angew. Chem., Int. Ed. 2012, 51, 2643–2646.
(2) Vidal-Cros, A.; Viviani, F.; Labesse, G.; Boccara, M.; Gaudry,
M. Eur. J. Biochem. 1994, 219, 985–992.
(3) Liao, D.-I.; Thompson, J. E.; Fahnestock, S.; Valent, B.; Jordan,
D. B. Biochemistry 2001, 40, 8696–8704.
(4) Simpson, T. J.; Weerasooriya, M. K. B. J. Chem. Soc., Perkin
Trans. 1 2000, 2771–2775.
(5) Thompson, J. E.; Fahnestock, S.; Farrall, L.; Liao, D.-I.; Valent,
(6) Yeo, W. H.; Yun, B. S.; Kim, S. S.; Park, E. K.; Kim, Y. H.; Yoo,
I. D.; Yu, S. H. J. Antibiot. 1998, 51, 952–953.
(7) Maskey, R. P.; Fotso, S.; Lessmann, H.; Grun-Wollny, I.; Lackner,
H.; Laatsch, H. Z. Naturforsch., B 2005, 60, 183–188.
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r
10.1021/ol301305p
Published on Web 06/27/2012
2012 American Chemical Society

bis-p-bromobenzoate derivative of 3 was prepared, and
CD spectroscopy, according to the method of Harada and
Nakanishi (exciton coupling), was used to unambiguously
verify the assignment.10 Since both the natural substance6
and the enzymatically synthesized product show negative
specific rotation, the absolute configuration of the former
must also be (R).
Scheme 1. (A) T4HNR-Catalyzed Reduction of its Physiological
Substrate T4HN (1). (B) Retrosynthetic Proposal for the Bio-
mimetic Enzymatic Synthesis of GTRI-02 (3)
The unexpected side product of the enzymatic reduction,
ketodiol 5, was isolated in 1% yield by column chromato-
graphy. Further analysis of the T4HNR-catalyzed reduc-
tion reaction of 4 led to the detection of the presence of
2-hydroxy-1,4-naphthoquinone 6, possibly formed by
nonenzymatic aerobic oxidation. Although the transfor-
mation was performed under N2, incomplete removal of
oxygen from the buffer solution might account for the
oxidation of compound 4. We assumed that 2-hydroxy-
1,4-naphthoquinone6 could have beenreducedtodiol 5 by
T4HNR, using 2 equiv of NADPH.
In order to prove this assumption, 6 was prepared in 82%
isolated yield by the oxidation of compound 4 using K2CO3
in DMF.11 Hydroxynaphthoquinone 6 was then employed
as a substrate and was reduced by T4HNR to exclusively give
the above-mentioned vicinal diol 5 with 80% conversion
(60% yield, drcis/trans g 99:1) (Scheme 3). The relative con-
figuration of 5 was elucidated by single-crystal X-ray analysis
of the 4-biphenylboronic ester derivative. The absolute
(3S,4R)-configuration was determined by vibrational cir-
cular dichroism (VCD) and quantum chemical calculations
(Gaussian 0912) (see the Supporting Information).
The biomimetic retrosynthetic analysis of 3 guided us to
the acetylated trihydroxynaphthalene 4 as the required
substrate (Scheme 1, B). Compared to T4HN (1), naphthol
4 contains an additional acetyl group, in principle a poten-
tially better substrate unit to be reduced by oxidoreductases.
Compound 4 was synthesized in four straightforward
steps starting from 3,5-dimethoxyphenylacetic acid in an
overall yield of 25% (see the Supporting Information).
Naphthol 4 was then reduced with T4HNR. NADPH was
used as a cofactor and regenerated using glucose and glucose
dehydrogenase (GDH) in all enzyme-catalyzed reactions.
The transformation proceeded as proposed and resulted in
the formation of GTRI-02 (3) as the major product after 24 h
(17% conversion), supporting the argument for the putative
involvement of a similar naphthol reductase in the biosynthe-
sis of 3.9 Unexpectedly, ketodiol 5 was obtained as a side
product in the same transformation (Scheme 2).
Scheme 3. T4HNR-Catalyzed Reduction of
Hydroxynaphthoquinone 6
Scheme 2. T4HNR-Catalyzed Reduction of 4
T4HNR-catalyzed reduction of 2-hydroxy-1,4-naphtho-
quinone 6 to cis-ketodiol 5 also hints at the possible
(10) Harada, N.; Nakanishi, K.; TatSuoka, S. J. Am. Chem. Soc.
1969, 91, 5896–5898.
(11) Synder, S. A.; Tang, Z.-Y.; Gupta, R. J. Am. Chem. Soc. 2009,
131, 5744–5745.
* NADPH was regenerated using glucose/glucose dehydrogenase.
(12) Gaussian 09, Revision B.01: Frisch, M. J.; Trucks, G. W.;
Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.;
Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; Nakatsuji,
H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov, A. F.; Bloino, J.;
Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.; Toyota, K.;
Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro,
F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov,
V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.;
Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam,
N. J.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.;
Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;
Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
GTRI-02 (3) was isolated and purified by preparative
HPLC (RP-18) to provide pure material in 10% isolated
yield. The absolute configuration was determined as
(R) by using circular dichroism (CD). Additionally, the
(9) 2-Acetyl-1,3,6,8-tetrahydroxynaphthalene (a) and 6-hydroxymu-
sizin (b) were synthesized and tested with T4HNR; however, the
transformations did not result in any reduction. (a) Wheeler, M. H.;
Abramczyk, D.; Puchhaber, L. S.; Naruse, M.; Ebizuka, Y.; Fujii, I.;
Szaniszlo, P. J. Eukaryotic Cell 2008, 7, 1699–1711. (b) Harris, T. H.;
Wittek, P. J. J. Am. Chem. Soc. 1975, 97, 3270–3271.
€
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian, Inc., Wallingford, CT, 2009.
Org. Lett., Vol. 14, No. 14, 2012
3601

involvement of T4HNR or related enzymes in the putative
biosynthetic reduction of flaviolin (7) to 4-hydroxyscyta-
lone (8).13 To support our argument, 7 was synthesized in
80% yield by the oxidation of T4HN (1)11 and was used as
a substrate for T4HNR (Scheme 4).
Scheme 4. T4HNR-Catalyzed Reduction of Flaviolin (7)
The transformation was performed using glucose/GDH
for cofactor regeneration and resulted in the formation of
cis-4-hydroxyscytalone (8) with quantitative conversion
and high diastereoselectivity (drcis/trans = 99:1) (deter-
mined by 1H NMR spectroscopy). A lower isolated yield
of 60% was obtained due to decomposition of 8.
Relativetotransformations performedinthepresenceof
air, much better yields were obtained when the transforma-
tion was performed under N2 and after degassing. cis-4-
Hydroxyscytalone (8) has been isolated previously from
various sources and has also been proposed to be formed
during melanin biosynthesis of Wangiella dermatitidis
along with other naphthalene-based metabolites.9a,13À15
To stress hydroxynaphthoquinones as general substrates
for T4HNR, another natural product, lawsone (9), was used
as a substrate (Scheme 5). This transformation resulted in
quantitative reduction, and the cis-ketodiol 10 was isolated
in 90% yield.
Figure 1. Experimental IR and VCD spectra of the acetonide 11
(150 mM in CDCl3) and the theoretical IR and VCD spectra
calculated12 (B3LYP/6-31G* level) for the (3S,4R)-configured
acetonide 11. Good agreement in frequencies and sign between
the calculated and observed spectra allows for assignment of the
absolute configuration.
Although several studies13b have proposed that cis-4-
hydroxyscytalone (8) is formed by the reduction of flavio-
lin (7), the absolute configuration of 8 and the enzymatic
reduction of flaviolin by T4HNR have now been estab-
lished for the first time.
Acceptance by T4HNR of different hydroxynaphtho-
quinones as substrates and their reduction to homochiral
cis-ketodiols hint at further biosynthetic considerations:
we propose that in the biosynthesis of 3-hydroxy-3,4-
dihydronaphthalen-1(2H)-ones (and the corresponding
anthracenones), e.g., GTRI-02 (3), T4HNR-like enzymes
might be involved. Characterization of these enzymes with
a probably expanded substrate range will broaden the
Scheme 5. Reduction of Lawsone (9) Catalyzed by T4HNR
The same transformation was performed in up to a 100-
mg scale with no significant change in the yield of ketodiol
10. The configuration of 10 was determined by VCD of its
acetonide 11 and assigned as (3S,4R) (Figure 1).
For cis-4-hydroxyscytalone (8), the absolute configura-
tion (3S,4R) was assigned by comparison of the CD
spectra of 8 and 10 (see the Supporting Information).
(13) (a) Sankawa, U.; Shimada, H.; Sato, T.; Kinoshita, T.; Yamasaki,
K. Chem. Pharm. Bull. 1981, 29, 3536–3542. (b) Bell, A. A.; Stipanovic,
R. D.; Puhalla, J. E. Tetrahedron 1976, 32, 1353–1356.
Figure 2. Natural products containing 3-hydroxy-3,4-dihy-
droanthracen-1(2H)-one (12aÀc) and 3,4-dihydroxy-3,4-dihy-
dronaphthalen-1(2H)-one substructures (13À15).
€
(14) Burki, N.; Michel, A.; Tabacchi, R. Phytopathol. Mediterr. 2003,
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(15) Wheeler, M. H.; Stipanovic, R. D. Arch Microbial 1985, 142,
234–241.
3602
Org. Lett., Vol. 14, No. 14, 2012

scope of asymmetric “phenol”-reducing methods. More-
over, the biosynthesis of 3,4-dihydroxy-3,4-dihydronaphtha-
len-1(2H)-ones (and the corresponding anthracenones) might
proceed through T4HNR-like transformations, as shown
above for the reduction of hydroxy-1,4-naphthoquinones 6,
7, and 9.
Several natural products with similar substructures
show interesting biological activities. For example, 12a
isolated from Dendrobium sp.16 and 12b and 12c isolated
from the roots of Lomatophyllum17 possess the 3-hydroxy-
3,4-dihydroanthracen-1(2H)-one substructure (Figure 2).
cis-Ketodiols contain a 3,4-dihydroxy-1-tetralone sub-
structure which is also a part of several natural pro-
ducts. Such an example is 3,4,8-trihydroxy-1-tetralone (13)
which has been isolated from several fungal species and
shows antifungal activity.18À20 Chrysanthone A (14)21 and
cladosporol D (15)22 are further examples of natural products
with a vicinal cis-diol containing a similar substructure.23
In summary, T4HNR was successfully applied for the
chemoselective reduction of naphtholic substrates; no re-
duction of the acetyl side chain present in compounds 4
and 6 was observed. We have shown that the enzymatic
reduction of aromatic hydroxy groups and, especially,
2-hydroxy-1,4-naphthoquinones can be used for the asym-
metric synthesis of related compounds.23 Moreover, the
discussed biosynthetic considerations will help to identify
related enzymes.
Acknowledgment. We thank Volker Brecht from the
University of Freiburg for measurement of NMR spectra
and the Black Forest Grid initiative for the use of their
computing resources. We thank the German Research
Council DFG for financial support within the framework
of project IRTG 1038.
(16) Hu, J.-M.; Zhao, Y.-X.; Miao, Z.-H.; Zhou, J. Bull. Korean
Chem. Soc. 2009, 30, 2098–2100.
(17) Van Wyk, B.-E.; Yenesew, A.; Dange, E. Biochem. Syst. Ecol.
1995, 23, 805–808.
Supporting Information Available. Experimental pro-
cedures and full spectroscopic data for all new com-
pounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
ꢀ
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Cavalheiro, A. J.; Bolzani, V. D. S.; Young, M. C. M.; Pfenning,
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L. H.; Araujo, A. R. Biochem. Syst. Ecol. 2006, 34, 822–824.
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(19) Krohn, K.; Biele, C.; Drogies, K.-H.; Steingrover, K.; Aust,
H.-J.; Draeger, S.; Schulz, B. Eur. J. Org. Chem. 2002, 2331–2336.
(20) Yamaguchi, Y.; Masuma, R.; Kim, Y.-P.; Uchida, R.; Tomado,
H.; Omura, S. Mycoscience 2004, 45, 9–16.
(21) Albinati, A.; Arnone, A.; Assante, G.; Mille, S. V.; Nasini, G.
Phytochemistry 1989, 28, 923–927.
(23) The nonenzymatic synthesis of such ketodiols is tedious and time
consuming. Mukherjee, P.; Roy, S. J. S.; Sarkar, T. K. Org. Lett. 2010,
12, 2472–2475.
(22) Nasini, G.; Arnone, A.; Assante, G.; Bava, A.; Moricca, S.;
Ragazzi, A. Phytochemistry 2004, 65, 2107–2111.
The authors declare no competing financial interest.
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