Methyl-Shifted Farnesyldiphosphate Derivatives Are Substrates for Sesquiterpene Cyclases

Article abstract of DOI:10.1021/acs.orglett.0c01345

New sesquiterpene backbones are accessible after biotransformation of presilphiperfolan-8β-ol synthase (BcBOT2), a fungal sesquiterpene synthase, with non-natural farnesyldiphosphates in which methyl groups are shifted by one position toward the diphosphate terminus. One of the macrocycles formed, a new germacrene A derivative, undergoes a Cope rearrangement to iso-β-elemene. Three of the new terpenoids show olfactoric properties that range from an intense peppery note to a citrus, ozone-like, and fruity scent.

Full text of DOI:10.1021/acs.orglett.0c01345

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Letter
Methyl-Shifted Farnesyldiphosphate Derivatives Are Substrates for
Sesquiterpene Cyclases
§
§
̈
̈
Vanessa Harms, Benjamin Schroder, Clara Oberhauser, Cong Duc Tran, Sven Winkler, Gerald Drager,
and Andreas Kirschning*
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ABSTRACT: New sesquiterpene backbones are accessible after
biotransformation of presilphiperfolan-8β-ol synthase (BcBOT2), a
fungal sesquiterpene synthase, with non-natural farnesyldiphos-
phates in which methyl groups are shifted by one position toward
the diphosphate terminus. One of the macrocycles formed, a new
germacrene A derivative, undergoes a Cope rearrangement to iso-β-
elemene. Three of the new terpenoids show olfactoric properties
that range from an intense peppery note to a citrus, ozone-like, and fruity scent.
ne unique synthetic feature of terpene biosynthesis is
linked with terpene cyclases (TCs). These utilize linear
Scheme 1. Structures of Diphosphate Precursors 1 and 3,
Cyclization Products 2 and 4 Formed by the Sesquiterpene
Cyclase BcBOT2, and Rotundone 5
O
unsaturated methyl-branched precursors activated as terminal
diphosphate esters to yield a diverse range of (oligo)cyclic
products, called monoterpenes (C10), sesquiterpenes (C15),
diterpenes (C20), and sesterpenes (C25). The mechanistic
features of these catalytic transformations are cationic cascade
reactions. These cascades are composed of cyclizations,
hydride shifts, and Wagner−Meerwein rearrangements. Proton
abstraction or trapping of the final carbocation with a
nucleophile, commonly water, terminates these sequences.1
So far, the chemo-, regio-, and stereoselectivity for each step
have not been matched by chemical transformations intended
to mimic TCs.2
In recent years, the substrate specificity of TCs, especially of
mono- and sesquiterpene cyclases, has been championed3
mainly by testing unnatural geranyl- and farnesyldiphosphate
derivatives as substrates.4−7 Commonly, oxygen, sulfur, and
halogen functionalizations have been included in the backbone
of the natural precursor farnesyldiphosphate (FPP 1; PP =
pyrophosphate) when sesquiterpene cyclases (STCs) have
been probed (Scheme 1). A telling example is presilphiperfo-
lan-8β-ol synthase (BcBOT2), a fungal sesquiterpene cyclase
from Botrytis cinerea, which is responsible for the formation of
the tricyclic sesquiterpene presilphiperfolan-8β-ol (2) from
FPP 1.8 When BcBOT2 was exposed to ether derivative 3, the
tricyclic terpenoid 4, whose scent resembles that of rotundone
(5), was isolated in 36% yield instead.5 It has to be noted that
for the formation of 2 and 4 the cascade is initiated by a ring
closure between carbon atoms 1 and 11. Dickschat et al.
reported on isopentenyl diphosphates with an additional
methyl group at C4 that were enzymatically transformed into
methylated terpenes.4h The same group also carried out studies
on the formation of 2-methylisoborneol in myxobacterium
Nannocyctis exedens.9a S-Adenosyl methionine (SAM) was
proposed to be the source of the extra methyl group.
Independently, the groups of Cane and Ikeda identified
members of the actinomycetes family that use a combination of
a terpene synthase and a C-methyl transferase for the
generation of 2-methylisoborneol.9b9c
On the basis of these findings, Kampranis and co-workers
showed that the chemical code of terpene biosynthesis can be
expanded to C11 building blocks, namely 2-methyl-geranyldi-
phosphate [2me-GPP (7)], by engineering the GPP
methyltransferase from Pseudanabaena limnetica into a
Saccharomyces cerevisiae strain AM94 (Figure 1).9d 2-
Methylisoborneol (8) is a noncanonical bacterial product
Received: April 22, 2020
https://dx.doi.org/10.1021/acs.orglett.0c01345
© XXXX American Chemical Society
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Scheme 2. Synthesis of New Farnesyldiphosphate Derivative
a
9
Figure 1. Structures of geranyl- and 2-methylgeranyl diphosphates 6
and 7, methylisoborneol (8), and new FPPs 9−12 with shifted methyl
groups.
a
TMS
= trimethylsilyl. cp = cyclopentadienyl. dppf =
that contributes to the musty-earthy fragrant notes of Brie and
Camembert cheeses.10 C11 precursor 7 is generated under the
control of a dedicated methyltransferase that acts at C2 of
geranyldiphosphate 6 (GPP). It was noted that the cyclization
process is unique, because hardly any other C11 terpenoid has
been reported as a major metabolite in bacteria.11,12 The
authors found that for broadening the substrate tolerance of
monoterpene synthases to 2-methyl-branched GPP derivatives
bearing 11 carbon atoms, only a single-residue switch in the
TC was necessary.9d
(diphenylphosphino)ferrocene. NCS = N-chlorosuccinimide.
termini. Thus, a set of standard reactions (bromination, sulfone
introduction, Riley oxidation, reduction of the intermediate
aldehyde, and O-silylation) yielded sulfone 20 starting from
geraniol 19 (Scheme 3). At this stage, the syntheses diverged
Scheme 3. Synthesis of New Farnesyldiphosphate
a
Derivatives 10−12
In 2me-GPP 7, the additional methyl group is located one
position closer to the diphosphate group, which should cause
steric congestion in the key step, Mg-promoted ionization of
the allyldiphosphate moiety, and cyclization.11c So far, 2-
methyl-branched analogues of FPP 1 have rarely been tested in
biotransformations with STCs.13
In this report, we describe the synthesis of four new FPP
derivatives 9−12 bearing one or more methyl groups that are
shifted by one position toward the diphosphate terminus. This
also includes position 2 similar to that of GPP derivative 7. In
diphosphates 10−12, the terminal alkene moiety displays
different patterns of substitution. These serve as substrates for
recombinant and purified BcBOT2, which in our hands shows
promiscuous behavior toward a variety of FPP derivatives.5
The major products formed were commonly isolated by
preparative GC. Preliminary results on their olfactoric
properties were also collected.
a
TBDPS = tert-butyldiphenylsilyl. dppe = 1,2-bis(diphenyl-
phosphino)ethane. KHMDS = potassium bis(trimethylsilyl)amide.
TBAF = tetra-n-butylammonium fluoride. NCS = N-chlorosuccini-
mide.
In FPP derivative 9, one methyl group is shifted from C11 to
C10 compared to natural FPP 1. Our synthesis relied on two
sp2−sp3 Negishi coupling reactions (Scheme 2).14 Homo-
propargyl alcohol 13 was used to prepare both building blocks
1415 and 15,16 which were coupled after transforming iodide
14 into the organozinc species using Pd(dppf)Cl2 as a
precatalyst. Then, the resulting alkyl iodide 16 underwent a
second Negishi cross-coupling reaction with the organozinc
species derived from vinyl bromide 1717 to yield yne-diene
18.18 After desilylation and methyl metalation of the alkyne
group, the trapping of the active organometallic species with
ClCO2Me provided the α,β-unsaturated methylester inter-
mediate. This was reduced to the allyl alcohol, which was
further transformed into diphosphate 9 via the corresponding
allyl chloride.19
toward allyl alcohols 21−23 by alkylation of deprotonated
sulfone 20 with different allyl bromides 24a−c followed by O-
desilylation. The corresponding diphosphates 10−12 were
obtained via the corresponding allyl chlorides according to an
established protocol.19
Next, BcBOT2 was cloned and expressed in Escherichia coli.
In vitro enzyme tests for determining enzyme activity and for
optimizing substrate tolerance were conducted on small scales
(150 μM substrate and 0.01 mg/mL enzyme) using natural
precursor FPP 1 (see the Supporting Information). The key
parameters to be optimized were the temperature and the pH
value. To study possible inhibitory effects or denaturation,
substrate and enzyme concentrations were also part of this
study (see the Supporting Information). Interestingly, non-
natural FPP derivatives 9−12 require higher temperatures for
achieving the best yields of new biotransformed products (vide
supra). This can be ascribed to the increased conformational
The underlying synthetic concept toward FPP derivatives
10−12 is based on the idea of moving the diphosphate moiety
to the opposite terminus of GPP. The original hydroxyl group
in geraniol 19 then served to introduce different new C-
B
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flexibility of the protein allowing the easier fit of unnatural
substrates.20
The outcome of biotransformations with FPP derivatives 9−
12 with BcBOT2 is summarized in Scheme 4. Derivative 10
Scheme 5. Proposed Mechanisms for the BcBOT2-
Promoted Formation of Macrocyclic Terpenoids 25−28
from FPP Derivatives 9, 11, and 12 (cases A−C,
a
respectively)
a
Scheme 4. Formation of Cyclization Products 25−28
a
The configurations of the double bonds were determined by NOESY
experiments.
a
NOE correlations for (Z,E,E)-25 and isomeric macrocycles 26 and
macrocyclization followed by deprotonation at C9 to yield
26 (Scheme 5B). The formation of isomer 27 could be the
result of a monoprotic intramolecular hydrogen transfer either
initially for 11 or at a late stage with isomer 26. Precedence for
such a hydride transfer was reported for sesquiterpene cyclase
pentalenene synthase (PenA) and the diterpene taxadiene
cyclase (TDC1).21 When pure terpenoid 26 was exposed to
BcBOT2, GC-MS analysis revealed no formation of 27 so that
its late stage formation can be excluded.22
Here, FPP derivative 12 behaves remarkably. It is the first
example of an unnatural FPP derivative that is transformed by
BcBOT2 into a 10-membered macrocycle, although the
substitution patterns of the terminal alkene in FPP 1 and
derivative 12 are identical. It is remarkable that the shift of the
two methyl groups (at C3 and C7) by one position closer to
the diphosphate terminus has a profound influence on the type
of cyclization. The possibility that the system first undergoes a
1 → 11 cyclization8 followed by a Wagner−Meerwein
rearrangement cannot be ruled out (Scheme 5C).
A common feature of the cyclodecadiene ring system of
germacrenes is its fit in two preferred conformations. The
conformation of germacrene A (29) shown in Scheme 6 finds
the propenyl group in a pseudo-equatorial orientation. It is
established that this conformation is subject to a facile [3,3]-
sigmatropic Cope rearrangement, which leads to the 1,2-
divinylcyclohexane elemene (30).23 The new germacrene A
derivative 28 behaves in a similar manner yielding what we call
here “iso-β-elemene” (31) as a single diastereoisomer. This can
27 are given. Cyclization product 28 was commonly accompanied by
small amounts of Cope product 31.
that lacks any methyl group at the terminal alkene (C10−C11)
gave a complex mixture with no major product that could be
detected by GC-MS. However, the other three FPP derivatives
9, 11, and 12 yielded defined cyclization products 25−28 in
amounts sufficient for isolation and structural elucidation (25,
13%; 26 and 27, 33%; 28, 31%).
Each of the two FPP derivatives, 9 and 12, yielded one
major product. In contrast, substrate 11 is transformed into
two main isomeric macrocycles 26 and 27 along with five
unidentifiable byproducts. The two isomers 26 and 27 were
separated by preparative GC. Our work revealed that BcBOT2
commonly initiates a C1 → C11 macrocyclization with FPP 1,
including all unnatural FPP derivatives studied so far (see also
1 → 4).5 Likewise, new FPP derivative 9 supports this
observation. Deprotonation at C9 leads to macrocycle 25
[70.9% purity (GC-FID) before pGC] (Scheme 5A). The
formation of a (Z)-configured olefinic double bond was proven
by determining a NOE correlation between the methyl group
at C10 and 9-H. Other NOE correlations provided insight into
the preferred conformation of the macrocycle in C6D6.
FPP derivative 11 bears three methyl groups that are shifted
by one position. It yielded macrocycles 26 (92.8% purity after
pGC) and 27 (86.5% purity after pGC). The two isomers
differ in the position of one of the three olefinic double bonds.
The cationic cascade also starts with a C1 → C11
C
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Scheme 6. Considerations of Germacrene A (29) (top) and
“Iso-germacrene A” (28) (bottom) Conformations for Cope
Rearrangements to β-Elemene 30 and “Iso-β-elemene A” 31,
Scheme 7. Possible and Found Stable Conformations of
“Iso-germacrene A” (28) and Key NOE Correlations (blue
a
arrows)
a
Respectively
a
GAS = germacrene A synthase. For analysis of other conformers, see
Scheme 7.
be rationalized if one assumes that the conformation of 28
depicted in Scheme 6 is the preferred one.24−28 The first
evidence of this Cope rearrangement was obtained during GC
analysis of “iso-germacrene A” (28) (for details about GC
analyses, see the Supporting Information). “Iso-β-elemene”
(31) was collected when the pGC was operated in a hot-
injection mode that initiated quantitative (98.4%) rearrange-
ment to 31.26,27
a
Encircled numbers in red refer to the relative abundance at 255 K
(for further details about NMR analyses, including NOESY and NOE
correlations, see the Supporting Information). Relative abundances of
four conformers (DD, UD, UU, and DU) obtained by computational
analysis in toluene (MM3 force field).
conformer has an up−down (UD) orientation, and the up−up
conformer (UU) was also unequivocally determined.
The (E,E)-germacrenes, including 29,29−32 have widely been
studied in solution with respect to their conformational
dynamics around the cyclodecandiene core. Stable conformers
are interconverted through rotation of the two double bonds
and the C7−C9 segment. These conformers can be studied at
lower temperatures by NMR spectroscopy.30,32,33 It was found
that the iso-propenyl group commonly is positioned in an
equatorial or pseudo-equatorial orientation,26,30 and that this
prerequisite can result in four distinct conformations,
commonly labeled DD, UU, UD, and DU (with respect to
the orientation of the methyl groups, D = down and U = up).
Also, the isolated “iso-germacrene A” (28) exists in different
stable conformers as judged by several cross-couplings and
saturation transfers in the NOESY and NOE. Although NMR
spectra were poorly resolved at rt, the carbon backbone of 28
was identified for the major conformer by COSY and HMBC
spectroscopy.
Thus, “iso-germacrene A” (28) preferentially adopts two
crossed alkene conformations (DD and UU, 71.4%) and one
with a parallel orientation of the two alkenes (UD, 28.6%) at
low temperatures. The relative preference was supported by
MM3 force field calculations at 300 and 255 K (Scheme 7). In
contrast, germacrene A (29) parallel and crossed conforma-
tions are distributed in a nearly equal ratio.30
Chromatography with a chiral stationary phase was
performed for “iso-β-elemene” 31 with a heptakis(6-O-
TBDMS-2,3-di-O-Me)-β-CD column, known to separate the
enantiomers of β-elemene. The analysis revealed only one
signal, indicating the presence of one enantiomer.26,35 Due to
the stereospecificity of the Cope rearrangement, it is
reasonable to propose that also “iso-germacrene A” was
formed as a single enantiomer.
Finally, the sensoric profile of new terpenoids was
determined by GCO analysis (Table 1). Macrocycle 25 exerts
At 255 K in toluene-d8, three sets of well-resolved signals in
1
a ratio of 10:6:5 were visible in the H NMR spectrum that
Table 1. Olfactoric Properties of New Terpenoids 25−2836
refer to three conformations (Scheme 7). The relative
orientations of the methyl groups (three groups each with
three signals that differed in signal intensities) were
determined from selected one-dimensional NOE correlation
experiments.
The relative orientation of the proton at C10 was established
by reference to the relative configuration of the Cope-
rearranged product iso-β-elemene (31) that had formed as a
single diastereoisomer via a chairlike transition state from the
DD isomer 28, similar to that reported for the rearrangement
of germacrene A (29) to β-elemene (30) (Scheme 6).26,29 The
stereochemical course of such Cope rearrangement, which
proceeds through a chairlike transition state of the DD
conformer, was recently elegantly confirmed using stereo-
specifically deuterated probes.34 Our analyses revealed that the
main conformer of 28 is down−down (DD) (see Scheme 7
and the Supporting Information). The second most abundant
compound
olfactoric analysis
25
26
27
28
31
intensive, peppery
no profile
no profile
citrus, ozone-like, fruity
citrus, ozone-like
an intense peppery smell comparable to that of terpenoid
rotundone (5). Isomers 26 and 27 did not reveal any sensory
properties. Finally, “iso-β-elemene” (31) was found to show a
citrus and ozone-like odor, whereas the olfactoric property of
the thermal precursor “iso-germacrene A” (28) is similar to
that of 31, except that it additionally shows a fruity note.
In summary, we demonstrate that sesquiterpene cyclases like
BcBOT2 can accept and transform FPP derivatives with an
D
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(3) Harms, V.; Kirschning, A.; Dickschat, J. Nat. Prod. Rep. 2020,
DOI: 10.1039/C9NP00055K.
(4) (a) Jin, Y.; Williams, D. C.; Croteau, R.; Coates, R. M. J. Am.
altered methyl group substitution pattern compared to that of
farnesyl diphosphate (1). Remarkably, a shift of the methyl
group from C3 to C2 does not suppress activation of the
diphosphate moiety and initiation of cyclization cascades.
Olfactoric analyses revealed the practical opportunities of
employing unnatural substrates in biotransformations with
terpene synthases.
́
Chem. Soc. 2005, 127, 7834−7842. (b) Cascon, O.; Touchet, S.;
Miller, D. J.; Gonzalez, V.; Faraldos, J. A.; Allemann, R. K. Chem.
Commun. 2012, 48, 9702−9704. (c) Touchet, S.; Chamberlain, K.;
Woodcock, C. M.; Miller, D. J.; Birkett, M. A.; Pickett, J. A.;
Allemann, R. K. Chem. Commun. 2015, 51, 7550−7553. (d) Demiray,
M.; Tang, X.; Wirth, T.; Faraldos, J. A.; Allemann, R. K. Angew. Chem.,
Int. Ed. 2017, 56, 4347−4350. (e) Tang, X.; Demiray, M.; Wirth, T.;
Allemann, R. K. Bioorg. Med. Chem. 2018, 26, 1314−1319. (f) Huynh,
F.; Grundy, D. J.; Jenkins, R. L.; Miller, D. J.; Allemann, R. K.
ChemBioChem 2018, 19, 1834−1838. (g) Loizzi, M.; Miller, D. J.;
Allemann, R. K. Org. Biomol. Chem. 2019, 17, 1206−1214. (h) Hou,
A.; Lauterbach, A. L.; Dickschat, J. S. Chem. - Eur. J. 2020, 26, 2178−
2182.
ASSOCIATED CONTENT
* Supporting Information
■
sı
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.orglett.0c01345.
Detailed experimental procedures and spectral data
(PDF)
̈
(5) Oberhauser, C.; Harms, V.; Seidel, K.; Schroder, B.;
Ekramzadeh, K.; Beutel, S.; Winkler, S.; Lauterbach, L.; Dickschat,
J. S.; Kirschning, A. Angew. Chem., Int. Ed. 2018, 57, 11802−11806.
(6) (a) Rabe, P.; Rinkel, J.; Klapschinski, T. A.; Barra, L.; Dickschat,
J. S. Org. Biomol. Chem. 2016, 14, 158−164. (b) Rinkel, J.; Rabe, P.;
Garbeva, P.; Dickschat, J. S. Angew. Chem. 2016, 128, 13791−13794.
(c) Gonzalez, V.; Touchet, S.; Grundy, D. J.; Faraldos, J. A.;
Allemann, R. K. J. Am. Chem. Soc. 2014, 136, 14505−14512.
(7) Andersen-Ranberg, J.; Kongstad, K. T.; Nielsen, M. T.; Jensen,
N. B.; Pateraki, I.; Bach, S. S.; Hamberger, B.; Zerbe, P.; Staerk, D.;
Bohlmann, J.; Møller, B. L.; Hamberger, B. Angew. Chem., Int. Ed.
2016, 55, 2142−2146.
AUTHOR INFORMATION
Corresponding Author
■
Andreas Kirschning − Institute of Organic Chemistry and
Center of Biomolecular Drug Research (BMWZ), Leibniz
̈
Universitat Hannover, 30167 Hannover, Germany;
orcid.org/0000-0001-5431-6930;
Email: andreas.kirschning@oci.uni-hannover.de
Authors
Vanessa Harms − Institute of Organic Chemistry and Center of
Biomolecular Drug Research (BMWZ), Leibniz Universitat
Hannover, 30167 Hannover, Germany
(8) Wang, C.-M.; Hopson, R.; Lin, X.; Cane, D. E. J. Am. Chem. Soc.
2009, 131, 8360−8361.
̈
(9) (a) Dickschat, J. S.; Nawrath, T.; Thiel, V.; Kunze, B.; Muller, R.;
̈
Schulz, S. Angew. Chem., Int. Ed. 2007, 46, 8287−8290. (b) Wang, C.-
M.; Cane, D. E. J. Am. Chem. Soc. 2008, 130, 8908−8909.
(c) Komatsu, M.; Tsuda, M.; Omura, S.; Oikawa, H.; Ikeda, H.
Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 7422−7427. (d) Ignea, C.;
Pontini, M.; Motawia, M. S.; Maffei, M. E.; Makris, A. M.; Kampranis,
S. C. Nat. Chem. Biol. 2018, 14, 1090−1098.
̈
Benjamin Schroder − Institute of Organic Chemistry and
Center of Biomolecular Drug Research (BMWZ), Leibniz
̈
Universitat Hannover, 30167 Hannover, Germany
Clara Oberhauser − Institute of Organic Chemistry and Center
of Biomolecular Drug Research (BMWZ), Leibniz Universitat
Hannover, 30167 Hannover, Germany
Cong Duc Tran − Institute of Organic Chemistry and Center of
Biomolecular Drug Research (BMWZ), Leibniz Universitat
̈
(10) Karahadian, C.; Josephson, D. B.; Lindsay, R. C. J. Agric. Food
Chem. 1985, 33, 339−343.
̈
(11) (a) Dickschat, J. S.; Nawrath, T.; Thiel, V.; Kunze, B.; Muller,
̈
Hannover, 30167 Hannover, Germany
R.; Schulz, S. Angew. Chem., Int. Ed. 2007, 46, 8287−8290. (b) Brock,
N. L.; Ravella, S. R.; Schulz, S.; Dickschat, J. S. Angew. Chem., Int. Ed.
2013, 52, 2100−2104. (c) Kschowak, M. J.; Wortmann, H.;
Dickschat, J. S.; Schrader, J.; Buchhaupt, M. PLoS One 2018, 13,
No. e0196082.
Sven Winkler − Symrise AG, 37603 Holzminden, Germany
̈
Gerald Drager − Institute of Organic Chemistry and Center of
̈
Biomolecular Drug Research (BMWZ), Leibniz Universitat
Hannover, 30167 Hannover, Germany
(12) Dickschat, J. S. Nat. Prod. Rep. 2016, 33, 87−100.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.orglett.0c01345
́
(13) Cascon, O.; Touchet, S.; Miller, D. J.; Gonzalez, V.; Faraldos, J.
A.; Allemann, R. K. Chem. Commun. 2012, 48, 9702−9704.
(14) (a) Colacot, J., Ed. New Trends in Cross-Coupling: Theory
and Applications. RSC Catalysis Series; 2014; Vol. 21. (b) Geist, E.;
Kirschning, A.; Schmidt, T. Nat. Prod. Rep. 2014, 31, 441−448.
(15) (a) Dickner, T.; Laschat, S. J. Prakt. Chem. 2000, 342, 804−
Author Contributions
§V.H. and B.S. contributed equally to this work.
Notes
̈
̈
811. (b) Berkessel, A.; Kramer, J.; Mummy, F.; Neudorfl, J. M.; Haag,
R. Angew. Chem., Int. Ed. 2013, 52, 739−743. (c) Frei, R.; Wodrich,
M. D.; Hari, D. P.; Borin, P.-A.; Chauvier, C.; Waser, J. J. Am. Chem.
Soc. 2014, 136, 16563−16573.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
The authors thank J. Fohrer (Institute of Organic Chemistry,
Leibniz Universitat Hannover) for expert NMR spectroscopic
support. The analytical research center (ACR, Symrise AG) is
gratefully acknowledged for NMR and prep GC support.
■
(16) Penner, M.; Rauniyar, V.; Kaspar, L. T.; Hall, D. G. J. Am.
Chem. Soc. 2009, 131, 14216−14217.
(17) (a) Bordwell, F. G.; Landis, P. S. J. Am. Chem. Soc. 1957, 79,
1593−1597. (b) Richards, J.; Beach, W. J. Org. Chem. 1961, 26, 623−
624.
̈
(18) Negishi, E.; Liou, S.-Y.; Xu, C.; Huo, S. Org. Lett. 2002, 4, 261−
264.
REFERENCES
■
́
(19) (a) Lopez-Gallego, F.; Wawrzyn, G. T.; Schmidt-Dannert, C.
(1) (a) Christianson, D. W. Chem. Rev. 2017, 117, 11570−11648.
(b) Dickschat, J. S. Nat. Prod. Rep. 2016, 33, 87−110. (c) Baunach,
M.; Franke, J.; Hertweck, C. Angew. Chem., Int. Ed. 2015, 54, 2604−
2626.
Appl. Environ. Microbiol. 2010, 76, 7723−7733. (b) Lopez-Gallego, F.;
Agger, S. A.; Abate-Pella, D.; Distefano, M. D.; Schmidt-Dannert, C.
ChemBioChem 2010, 11, 1093−1106. (c) Agger, S. A.; Lopez-Gallego,
F.; Schmidt-Dannert, C. Mol. Microbiol. 2009, 72, 1181−1195.
(2) Yoder, R. A.; Johnston, J. N. Chem. Rev. 2005, 105, 4730−4756.
E
https://dx.doi.org/10.1021/acs.orglett.0c01345
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
pubs.acs.org/OrgLett
Letter
(20) (a) Gerhards, T.; Mackfeld, U.; Bocola, M.; von Lieres, E.;
Wiechert, W.; Pohl, M.; Rother, D. Adv. Synth. Catal. 2012, 354,
2805−2820. (b) Vihinen, M. Protein Eng., Des. Sel. 1987, 1, 477−480.
(c) Fields, P. A. Comp. Biochem. Physiol., Part A: Mol. Integr. Physiol.
2001, 129, 417−431.
(21) (a) Lin, X.; Hezari, M.; Koepp, A. E.; Floss, H. G.; Croteau, R.
Biochemistry 1996, 35, 2968−2977. (b) Cane, D. E.; Abell, C.;
Harrison, P. H. M.; Hubbard, B. R.; Kane, C. T.; Lattman, R.; Oliver,
J. S.; Weiner, S. W. Philos. Trans. R. Soc., B 1991, 332, 123−129.
(22) Tantillo, D. J. Angew. Chem. 2017, 129, 10172−10178.
(23) (a) Takeda, K. Tetrahedron 1974, 30, 1525−1534. (b) Adio, A.
M. Tetrahedron 2009, 65, 1533−1552.
(24) Faraldos, J. A.; Wu, S.; Chappell, J.; Coates, R. M. Tetrahedron
2007, 63, 7733−7742.
(25) (a) Weinheimer, A. J.; Youngblood, W. W.; Washecheck, P. H.;
Karns, T. K. B.; Ciereszko, L. S. Tetrahedron Lett. 1970, 11, 497−500.
(b) Nishino, C.; Bowers, W. S.; Montgomery, M. E.; Nault, L. R.;
Nielson, M. W. J. Chem. Ecol. 1977, 3, 349−357. (c) Takeda, K.
Tetrahedron 1974, 30, 1525−1534.
̈
(26) de Kraker, J.-W.; Franssen, M. C. R.; de Groot, A.; Konig, W.
A.; Bouwmeester, H. J. Plant Physiol. 1998, 117, 1381−1392.
̈
(27) Adio, A. M.; Paul, C.; Kloth, P.; Konig, W. A. Phytochemistry
2004, 65, 199−206.
(28) Miller, D. J.; Yu, F.; Knight, D. W.; Allemann, R. K. Org. Biomol.
Chem. 2009, 7, 962−975.
(29) Rabe, P.; Barra, L.; Rinkel, J.; Riclea, R.; Citron, C. A.;
Klapschinski, T. A.; Janusko, A.; Dickschat, J. S. Angew. Chem., Int. Ed.
2015, 54, 13448−13451.
(30) Faraldos, J. A.; Wu, S.; Chappell, J.; Coates, R. M. Tetrahedron
2007, 63, 7733−7742.
(31) (a) Huynh, F.; Grundy, D. J.; Jenkins, R. L.; Miller, D. J.;
Allemann, R. K. ChemBioChem 2018, 19, 1834−1838. (b) Faraldos, J.
A.; Zhao, Y.; O’Maille, P. E.; Noel, J. P.; Coates, R. M. ChemBioChem
2007, 8, 1826−1833.
(32) Miller, D. J.; Yu, F.; Allemann, R. K. ChemBioChem 2007, 8,
1819−1825.
́
(33) Faraldos, J. A.; Miller, D. J.; Gonzalez, V.; Yoosuf-Aly, Z.;
́
Cascon, O.; Li, A.; Allemann, R. K. J. Am. Chem. Soc. 2012, 134,
5900−5908.
(34) Rinkel, J.; Dickschat, J. S. Org. Lett. 2019, 21, 2426−2429.
(35) Konig, W. A.; Rieck, A.; Hardt, I.; Gehrcke, B.; Kubeczka, K.-
̈
H.; Muhle, H. J. High Resolut. Chromatogr. 1994, 17, 315−320.
(36) (a) Theime, E. T. Fragrance Chemistry: The Science of the Sense
of Smell; Elsevier, 2012. (b) Sell, C. S. Chemistry and the Sense of Smell;
John Wiley & Sons, 2014.
F
https://dx.doi.org/10.1021/acs.orglett.0c01345
Org. Lett. XXXX, XXX, XXX−XXX