Myoglobin-Catalyzed C?H Functionalization of Unprotected Indoles

Article abstract of DOI:10.1002/anie.201804779

Functionalized indoles are recurrent motifs in bioactive natural products and pharmaceuticals. While transition metal-catalyzed carbene transfer has provided an attractive route to afford C3-functionalized indoles, these protocols are viable only in the presence of N-protected indoles, owing to competition from the more facile N?H insertion reaction. Herein, a biocatalytic strategy for enabling the direct C?H functionalization of unprotected indoles is reported. Engineered variants of myoglobin provide efficient biocatalysts for this reaction, which has no precedents in the biological world, enabling the transformation of a broad range of indoles in the presence of ethyl α-diazoacetate to give the corresponding C3-functionalized derivatives in high conversion yields and excellent chemoselectivity. This strategy could be exploited to develop a concise chemoenzymatic route to afford the nonsteroidal anti-inflammatory drug indomethacin.

Full text of DOI:10.1002/anie.201804779

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Myoglobin-catalyzed C—H functionalization of unprotected
indoles
Authors: Rudi Fasan, David A Vargas, Antonio Tinoco, and Vikas Tyagi
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201804779
Angew. Chem. 10.1002/ange.201804779
Link to VoR: http://dx.doi.org/10.1002/anie.201804779
http://dx.doi.org/10.1002/ange.201804779

Angewandte Chemie International Edition
10.1002/anie.201804779
COMMUNICATION
Myoglobin-catalyzed C—H functionalization of unprotected indoles
[
b]
[a]
David A. Vargas, Antonio Tinoco, Vikas Tyagi, and Rudi Fasan*
Abstract: Functionalized indoles are recurrent motifs in bioactive
natural products and pharmaceuticals. While transition metal-
catalyzed carbene transfer has provided an attractive route to afford
C3-functionalized indoles, these protocols are viable only in the
presence of N-protected indoles, due to competition from the more
facile N—H insertion reaction. Here, a biocatalytic strategy for
enabling the direct C—H functionalization of unprotected indoles is
reported. Engineered variants of myoglobin provide efficient
biocatalysts for this reaction, which has no precedents in the biological
world, enabling the transformation of a broad range of indoles in the
presence of ethyl α-diazoacetate to give the corresponding C3-
functionalized derivatives in high conversion yields and excellent
chemoselectivity. This strategy could be exploited to develop a
concise chemoenzymatic route to afford the nonsteroidal anti-
inflammatory drug indomethacin.
non-native first-row transition metals (e.g., Co, Mn) are also viable
3
[12]
catalysts for promoting carbene C(sp )—H insertion, a reaction
previously achievable only using precious metals (e.g., Ir).[
These findings prompted us to investigate the reactivity of
11e]
2
myoglobin in the context of the C(sp )—H functionalization of
indoles. Here, we report the successful implementation of a
biocatalytic strategy for the chemoselective functionalization of
the C3 C—H bond in unprotected indoles (Scheme 1).
Previous work:
EWG
[
M]
EWG
N2
R
R
N
PG
N
PG
N-H protection
[M] = Rh, Pd, Cu, Fe
Deprotection
This work:
EWG
Mb
Functionalized indoles are structural motifs found in many
biologically active molecules, including alkaloids, agrochemicals,
and drugs.[1] Because of their relevance as ‘privileged scaffolds’
in medicinal chemistry, methodologies for the synthesis of
functionalized indoles have received significant attention.[2]
R
R
N
EWG
N
H
H
N2
Scheme 1. Metal-catalyzed functionalization of N-protected indoles vs.
biocatalytic functionalization of unprotected indoles reported here.
Among them, indole functionalization via transition metal-
catalyzed carbene transfer provides an attractive route to C3-
substituted indoles, which constitute the core structure of various
We began these studies by testing the activity of wild-type
drugs[ and medicinally important agents. Kerr, Davis, Fox, and
Hashimoto reported the successful application of Rh-based
catalysts for realizing this transformation with diazo compounds.[
More recently, other catalytic systems have been introduced to
enable these reactions.[ Invariably, however, the scope of these
protocols have been limited to the C—H functionalization of
indoles in which the N—H group is masked either through
alkylation or via a protecting group,[5-6] due to inherently higher
reactivity of this functional group toward carbene insertion. The
application of these catalysts to unprotected indoles have indeed
3]
[4]
sperm whale myoglobin (Mb) and its distal histidine variant
Mb(H64V)[
8a, 9a]
toward the conversion of indole (1) to the C3-
5]
functionalized product (3) in the presence of ethyl α-diazoacetate
(2) as the carbene donor (Table 1). However, neither reactions
led to appreciable formation of the desired product 3, a result
comparable to that obtained using other hemoproteins or simple
hemin as the catalyst (0-1% conversion; Table S1). Since
mutation of the amino acid residues within the distal pocket of Mb
6]
was previously found to greatly affect its carbene transfer
reactivity,[
8a, 9]
we then extended these studies to a panel of Mb
resulted in mixtures of N—H, C—H, and double N—H/C—H
variants, in which each of the active site residues Leu29, Phe43,
Val68, and Ile107 is substituted by an amino acid bearing a side
chain group of significantly different size (e.g., Leu29 → Ala or
Phe; Phe43 → Ile or Ser). While the majority of these Mb variants
showed no or only modest improvement in product conversion (0-
5%; Table S1), Mb(H64V,V64A) was found to constitute a
significantly more efficient catalyst for this reaction, producing 3
in 50% yield (Table 1). Importantly, the Mb(H64V,V68A)-
catalyzed reaction proceeds with excellent chemoselectivity,
yielding 3 as the only observable product. This result is in stark
insertion products.[
5a, 6b, 7]
These limitations impose the need of
additional protection/deprotection steps for the functionalization of
indoles using carbene transfer chemistry (Scheme 1).
In previous work, we established that engineered variants of
myoglobin, a small (15 kDa) heme-containing protein, can provide
efficient catalysts for carbene transfer reactions involving α-
[8]
diazoesters, including olefin cyclopropanations and carbene
Y—H insertion (Y = N, S)[
9]
reactions, among others.[10]
Biocatalytic carbene transfer reactions using other hemoproteins
or metalloprotein scaffolds have also been reported.[ More
recently, we established that myoglobin variants incorporating
11]
2 4
contrast with that obtained from reactions with Rh (OAc) as the
catalyst, from which nearly equal amounts of 3 (45%) and N—H
insertion by-product (42%) were formed, along with some double
insertion product (13%; Table 1 and Figure S1). Encouraged by
these results, the Mb(H64V,V68A)-catalyzed transformation was
targeted for optimization. The efficiency of this reaction was found
to have a slight dependence on pH (Table S2), with a pH of 9
[
[
a]
b]
D. A. Vargas, A. Tinoco, Dr. V. Tyagi, Prof. Dr. R. Fasan
Department of Chemistry
University of Rochester
120 Trustee Road, Rochester, NY 14627 (USA)
E-mail: rfasan@ur.rochester.edu
being optimal (Table 1). However,
a
more substantial
Current address: School of Chemistry and Biochemistry, Thapar
Institute of Engineering and Technology, Punjab, India.
Supporting information for this article is given via a link at the end of
the document.
improvement in product yield (54%→85%) was achieved by
increasing the indole : EDA ratio from 1:1 to 1:2 (Table 1). Despite
the excess diazo reagent and the single-addition protocol, no
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201804779
COMMUNICATION
carbene dimerization (to give diethyl maleate/fumarate) or
reaction with water (to give ethyl glycolate) was observed,
highlighting the high chemoselectivity of the biocatalyst toward
these potential side reactions as well.
cell density in these reactions (Table S2), a phenomenon we
tentatively attributed to the sequestration or utilization of the
indole substrate by the cells. Importantly, under optimal
conditions (OD600 = 20), quantitative conversion of the indole
substrate to the desired C—H functionalization product 3 was
achieved (Table 1). The TON values measured in this reaction
was comparable to that obtained with purified protein (82 vs. 106),
Table 1. Activity and selectivity of myoglobin variants and other catalysts
[a]
for the C—H functionalization of indole with ethyl α-diazoacetate (EDA).
See also SI Tables S1 and S2.
indicating
expressed biocatalyst.
Using the whole cell protocol, the scope of the reaction was
a nearly optimal utilization of the intracellularly
then probed using a panel of indole derivatives. As summarized
in Scheme 2, a variety of 5- (4a-7a), 6- (8a), and 7-substituted
indoles (9a) could be efficiently processed by the Mb variant to
give the corresponding C3-functionalized products 4b-9b in
quantitative conversions (>99%). 9b was isolated in 61% yield. As
an exception, 5-methoxy-indole (7a) was converted to 7b with
only moderate efficiency using the standard protocol (28%).
Significantly improved conversion of 7a to 7b was obtained using
purified Mb(H64V,V68A) and sequential catalyst additions (77%).
For each of the indole substrates, the desired carbene C—H
insertion product represented the only detectable product,
indicating that the metalloprotein catalyst maintains excellent
chemoselectivity toward C—H functionalization over the more
facile carbene N—H insertion reaction regardless of the position
and electronic effect of the substituent on the indole ring.
EDA
equiv
Conv.
% C-H
funct.
Catalyst
TON
[b]
Hemin
Rh (OAc)
Mb
Mb(H64V)
-
1
1
1
1
1
1
1
2
<1%
5%
1
5
n.a.
45[c]
n.a.
n.a.
100
100
100
100
[
c]
2
4
-
Protein
Protein
Protein
Protein
Protein
Protein
<1%
<1%
5%
1
<1
6
Mb(L29A,H64V)
Mb(H64V,V68A)
50%
54%
85%
62
68
106
Mb(H64V,V68A)[d]
Mb(H64V,V68A)[d]
Next, we examined the ability of Mb(H64V,V68A) to accept
C2-substitued (10a), N-methylated (11a), and doubly substituted
indole derivatives such as 12a, 13a, and 14a (Scheme 2).
Although the corresponding C—H functionalization product (10b-
Mb(H64V,V68A)[e]
Protein
2
34%
168
100
Cells[f]
18[h]
Mb(H64V,V68A)
Mb(H64V,V68A)
2
2
70%
100
100
14b) was obtained in each case, the yields were generally modest
Cells[g]
>99%
82[h]
(5-26%), denoting a scope limitation of this Mb variant across this
[
a] Reactions conditions: 20 μM Mb variant or hemin (0.8 mol%), 2.5 mM
subset of indole derivatives. To identify a better catalyst for these
substrates, the original panel of Mb variants was screened against
indole, 2.5 or 5 mM EDA, 10 mM dithionite, 16 h. Reported values are mean
values from n ≥ 2 experiments (SE <15%). [b] GC yield using calibration
curve with authentic 3. [c] Using 0.8 mol% catalyst in CH Cl ; other
2 2
14a, which bears substitutions at both the C2 and C5 positions
and was recognized as a potential precursor for a drug molecule
(vide infra). Interestingly, many of these Mb variants displayed
significantly higher activity (2- to 5-fold) on this substrate
compared to Mb(H64V,V68A) (Table S3) in spite of their inferior
performance in the context of indole (Table S1), thus denoting a
clear preference of these biocatalysts for bulkier indole substrates.
Among them, Mb(F43S,H64V) and Mb(L29F,H64V) emerged as
the most promising catalysts for this reaction, furnishing 14b in
31% and 41% yield, respectively (Table S3). The latter reaction
could be further optimized to give 14b in 80% (Scheme 2).
Gratifyingly, in addition to 14a, Mb(L29F,H64V) was found to
exhibit improved activity also toward 2-methyl-, 5-methyl-N-
methyl-, and 5-chloro-N-methyl-indole, yielding the corresponding
C—H functionalized products 10b, 12b, and 13b, respectively, in
50-85% conversion (Scheme 2). For 12b, this corresponds to a
nearly 8-fold higher catalytic efficiency compared to
Mb(H64V,V68A) (85% vs. 10%). While being complementary in
terms of substrate scope, Mb(L29F,H64V) share with
Mb(H64V,V68A) excellent chemoselectivity for the C—H
functionalization reaction (no detectable N—H insertion product)
products: N—H insertion (42%) and double insertion (13%). [d] pH 9.0. [e]
Using 5 μM protein (0.2 mol%) and pH 9.0. [f] OD600 = 40. [g] OD600 = 20.
n.a. = not available. [h] As determined based on the protein concentration
−
1
−1
in cell lysates using ε410 = 156 mM cm
.
Under
catalyst-limited
conditions
(0.2
mol%),
Mb(H64V,V68A) catalyzes about 168 turnovers (TON). These
TON values are lower than those supported by this variant in other
carbene transfer reactions with EDA (1,000-10,000),[
8a, 9-10]
but
they compare favourably (3- to 6-fold higher) with those reported
using Pd- or Cu-based catalysts for the C3 functionalization of N-
protected indoles.[6c, 6d] From time course experiments, the
Mb(H64V,V68A)-catalyzed
conversion of indole to 3 was
determined to proceed with an initial rate of about 10
turnovers/min and that it reaches completion in less than 15
minutes (Figure S2). Control reactions confirmed that the ferrous
form of Mb(H64V,V68A) is responsible for catalysis.
Given the feasibility of performing Mb-catalyzed carbene
transfer reactions directly in whole cells,[8b, 13] we next investigated
the viability of this approach for the biocatalytic C—H
-
1
functionalization
of
indole.
Accordingly,
whole-cell
and comparable kinetics (initial rate: 7-10 TON/min ).
biotransformations were carried out using Mb(H64V,V68A)-
expressing E. coli cells (C41(DE3))[ in the presence of the
optimized indole:EDA ratio of 1:2. Interestingly, a progressive
improvement in product yields was observed upon decreasing the
Mb-catalyzed carbene transfer reactions are believed to
14]
proceed via the formation of an electrophilic heme-bound carbene
intermediate,[
8a, 15]
which can react with various nucleophiles such
as olefins,[8a] amine,[9a] thiols,[9b] or phosphines[10]. Based on the
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201804779
COMMUNICATION
expected. On the other hand, no observable formation of a C2/C3
cyclopropane intermediate disfavours an alternative scenario
involving a cyclopropanation/fragmentation pathway.[6b] Overall,
the proposed mechanism shares similarities with those proposed
for related reactions promoted by Rh-[5c] and Fe-based
catalysts[
6a]
but differs from that reported for indole
functionalization with diazo reagents with Cu-complexes.[
6b]
Scheme 3. Proposed mechanism for the Mb-catalyzed C—H functionalization
of indoles. The relative position of the Phe29 residue in Mb(L29F,H64V) is
shown (grey).
By comparison with Mb(H64V) (Table 1), the enhanced
reactivity of Mb(H64V,V68A) toward in this reaction can be largely
attributed to the V68A mutation. This amino acid substitution
expands the active site in proximity of heme cofactor, which could
facilitate attack of the heme-bound carbene by the indole (II→III),
as previously observed for other nucleophiles.[9] At the same time,
the diminished reactivity of Mb(H64V,V68A) toward C2-
substituted indoles (i.e., 10b and 14a; Scheme 2) can be
rationalized based on increased steric interactions between the
C2 substituent and the porphyrin ring in the hemoprotein
Scheme 2. Substrate scope for Mb(H64V,V68A)- and Mb(L29F,H64V)-
catalyzed C—H functionalization of indoles. Reaction conditions: 2.5 mM indole
derivative, 5 mM EDA, whole cells at OD600 = 20 in 50 mM phosphate buffer (pH
7), RT. [a] Using 75 μM Mb(H64V,V68A) in 50 mM phosphate buffer (pH 9)
containing 10 mM Na (sequential catalyst addition protocol). [b] As in [a]
2 2 4
S O
but using 85 μM Mb(L29F,H64V). Reported conversions are mean values from
n ≥ 2 experiments (SE <10%)
(
Scheme 3). Interestingly, this substrate scope limitation was
effectively overcome using Mb(L29F,H64V). From the structure-
activity data gathered for closely related Mb variants (e.g.,
Mb(H64V), Mb(L29A,H64V); Table S3), the superior reactivity of
Mb(L29F,H64V) toward C2-substituted or other bulky indole
substrates appear to depend upon the presence of a Phe residue
at position 29. A molecular model of Mb(L29F,H64V) shows that
Phe29 projects its side-chain phenyl group above the heme
cofactor (Figure S3). This arrangement is well suited to potentially
favor the interaction (e.g., via π stacking) and/or affect the
orientation of the indole substrate during attack to the heme-
carbene intermediate (II→III, Scheme 3), possibly reducing
steric clashes between the C2 substituent and heme ring. Similar
protein/substrate interactions could also help dictate the high
chemoselectivity of the biocatalyst toward C3 functionalization
over N—H carbene insertion, although further studies are clearly
warranted to elucidate these aspects in more detail.
ability of this reactive intermediate to give rise to sulfonium ylides
upon reaction with thiol/thioether nucleophiles[
9b, 16]
and the well
established nucleophilicity of indoles at the C3 site,[17] a proposed
mechanism for the Mb-catalyzed indole C—H functionalization is
shown in Scheme 3. According to it, reaction of the catalytically
active ferrous Mb (I) with the diazo reagent leads to the heme-
carbene intermediate II, which undergoes nucleophilic attack by
the indole substrate to yield the zwitterionic species III. From this
intermediate, the final product can then arise from a [1,2]-proton
shift from the C3 atom to the ester α-carbon atom or, alternatively,
through dissociation of the zwitterionic enolate followed by
protonation by the solvent. To discriminate between these
pathways, the enzymatic reaction was performed with 1-methyl-
3-deutero-indole (11a-3-d). Insightfully, the product of this
reaction showed complete loss of the deuterium label (Figure S4),
thus supporting the involvement of solvent-mediated protonation.
This result, along with the absence of a kinetic isotope effect (KIE)
in reactions with 11a-3-d vs. 11a (Figure S4-S5), also rule out a
carbene C—H insertion process, as in the latter case retention of
the deuterium label in the product and a positive KIE[ would be
To further assess the synthetic value of the present method,
the synthesis of the non-steroidal anti-inflammatory drug
indomethacin (16) was targeted via a chemoenzymatic route
integrating Mb-catalyzed indole C—H functionalization (Scheme
4). Starting from commercially available 2-methyl-5-methoxy-
18]
indole (14a), preparative-scale (1 mmol) reaction with
a
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201804779
COMMUNICATION
Mb(L29F,H64V)-expressing cells afforded ~0.1 g of the desired
C3-functionalized product 14b in 40% isolated yield. N-acylation
of this intermediate with p-chlorobenzoyl chloride, followed by
hydrolysis afforded the target drug. This chemoenzymatic
sequence furnishes a more concise route than that originally
[2]
a) J. B. Chen, Y. X. Jia, Org. Biomol. Chem. 2017, 15, 3550-3567; b) M.
Bandini, A. Eichholzer, Angew. Chem. Int. Ed. 2009, 48, 9608-9644.
a) E. Shaw, J. Am. Chem. Soc. 1955, 77, 4319-4323; b) T. Y. Shen, S.
Lucas, L. H. Sarett, A. Rosegray, G. W. Nuss, J. D. Willett, R. L. Ellis, F.
W. Holly, A. R. Matzuk, A. N. Wilson, C. A. Winter, T. B. Windholz, et al.,
J. Am. Chem. Soc. 1963, 85, 488-&.
[
[
[
3]
4]
5]
[3b]
reported for the synthesis of this molecule (3 vs. 5 steps) and a
viable alternative to more recent syntheses involving precious
metal catalysts.[ More importantly, these results provide a proof-
of-principle demonstration of the scalability of the Mb-catalyzed
transformation disclosed here.
a) D. J. Rawson, K. N. Dack, R. P. Dickinson, K. James, Bioorg. Med.
Chem. Lett. 2002, 12, 125-128; b) D. G. Batt, J. X. Qiao, D. P. Modi, G.
C. Houghton, D. A. Pierson, K. A. Rossi, J. M. Luettgen, R. M. Knabb, P.
K. Jadhav, R. R. Wexler, Bioorg. Med. Chem. Lett. 2004, 14, 5269-5273.
a) R. Gibe, M. A. Kerr, J. Org. Chem. 2002, 67, 6247-6249; b) Y. J. Lian,
H. M. L. Davies, J. Am. Chem. Soc. 2010, 132, 440-+; c) A. DeAngelis,
V. W. Shurtleff, O. Dmitrenko, J. M. Fox, J. Am. Chem. Soc. 2011, 133,
19]
1650-1653; d) T. Goto, Y. Natori, K. Takeda, H. Nambu, S. Hashimoto,
Tetrahedr. Asymm. 2011, 22, 907-915.
[
6]
a) Y. Cai, S. F. Zhu, G. P. Wang, Q. L. Zhou, Adv. Synth. Cat. 2011, 353,
2939-2944; b) M. Delgado-Rebollo, A. Prieto, P. J. Perez, Chemcatchem
2014, 6, 2047-2052; c) X. Gao, B. Wu, Z. Yan, Y. G. Zhou, Org. Biomol.
Chem. 2016, 14, 8237-8240; d) X. Gao, B. Wu, W. X. Huang, M. W. Chen,
Y. G. Zhou, Angew. Chem. Int. Ed. 2015, 54, 11956-11960.
[
[
7]
8]
H. Keller, E. Langer, H. Lehner, Monatsh. Chem. 1977, 108, 123-131.
a) M. Bordeaux, V. Tyagi, R. Fasan, Angew. Chem. Int. Ed. 2015, 54,
1744–1748; b) P. Bajaj, G. Sreenilayam, V. Tyagi, R. Fasan, Angew.
Chem. Int. Ed. 2016, 55, 16110–16114.
[
9]
a) G. Sreenilayam, R. Fasan, Chem. Commun. 2015, 51, 1532-1534; b)
V. Tyagi, R. B. Bonn, R. Fasan, Chem. Sci. 2015, 6, 2488-2494.
[
[
10] V. Tyagi, R. Fasan, Angew. Chem. Int. Ed. 2016, 55, 2512-2516
11] a) P. S. Coelho, E. M. Brustad, A. Kannan, F. H. Arnold, Science 2013,
339, 307-310; b) E. W. Reynolds, T. D. Schwochert, M. W. McHenry, J.
Scheme 4. Chemoenzymatic synthesis of indomethacin.
W. Watters, E. M. Brustad, Chembiochem 2017, 18, 2380-2384; c) J. G.
Gober, S. V. Ghodge, J. W. Bogart, W. J. Wever, R. R. Watkins, E. M.
Brustad, A. A. Bowers, ACS Chem. Biol. 2017, 2, 1726–1731; d) P.
Srivastava, H. Yang, K. Ellis-Guardiola, J. C. Lewis, Nat. Commun. 2015,
In summary, we have reported the first example of a
biocatalytic strategy for carbene-mediated functionalization of
indoles. This approach could be applied to the C3
6, 7789; e) P. Dydio, H. M. Key, A. Nazarenko, J. Y. Rha, V.
functionalization of unprotected indoles,
a
goal previously
Seyedkazemi, D. S. Clark, J. F. Hartwig, Science 2016, 354, 102-106; f)
S. B. J. Kan, R. D. Lewis, K. Chen, F. H. Arnold, Science 2016, 354,
1048-1051; g) A. Rioz-Martinez, J. Oelerich, N. Segaud, G. Roelfes,
Angew. Chem. Int. Ed. 2016, 55, 14136-14140; h) M. J. Weissenborn, S.
A. Low, N. Borlinghaus, M. Kuhn, S. Kummer, F. Rami, B. Plietker, B.
Hauer, Chemcatchem 2016, 8, 1636-1640; i) M. W. Wolf, D. A. Vargas,
N. Lehnert, Inorg. Chem. 2017, 56, 5623-5635; j) K. Ohora, H. Meichin,
L. M. Zhao, M. W. Wolf, A. Nakayama, J. Hasegawa, N. Lehnert, T.
Hayashi, J. Am. Chem. Soc. 2017, 139, 17265-17268; k) K. Chen, X. Y.
Huang, S. B. J. Kan, R. K. Zhang, F. H. Arnold, Science 2018, 360, 71-
75.
unattainable using synthetic transition metal catalysts due to
competition from the inherently more favourable carbene N—H
insertion reaction. Using two engineered Mb variants with
complementary substrate profile, a broad range of variously
substituted indole derivatives, including C2-substituted and
doubly substituted indoles, could be processed with high
efficiency and excellent chemoselectivity. This newly developed
Mb-catalyzed transformation could be further leveraged to
implement a concise chemoenzymatic route for the synthesis of a
drug molecule. This study expands the range of abiotic
[12] G. Sreenilayam, E. J. Moore, V. Steck, R. Fasan, Adv. Synth. Cat. 2017,
59, 2076–2089.
[13] A. Tinoco, V. Steck, V. Tyagi, R. Fasan, J. Am. Chem. Soc. 2017, 139,
293-5296.
3
transformations accessible through engineered and artificial
metalloenzymes.[20]
5
[
[
[
[
14] M. Bordeaux, R. Singh, R. Fasan, Bioorg. Med. Chem. 2014, 22, 5697-
5704.
Acknowledgements
15] Y. Wei, A. Tinoco, V. Steck, R. Fasan, Y. Zhang, J. Am. Chem. Soc. 2018,
140, 1649-1662.
This work was supported by the U.S. National Institute of Health
grant GM098628. A.T. acknowledges support from the Ford
16] V. Tyagi, G. Sreenilayam, P. Bajaj, A. Tinoco, R. Fasan, Angew. Chem.
Int. Ed. 2016, 55, 13562-13566.
Foundation
instrumentation was supported by the U.S. NSF grant CHE-
946653.
Graduate
Fellowship
Program.
LC-MS
17] R. J. Sundberg, in Heterocyclic Scaffolds II:. Topics in Heterocyclic
Chemistry, Vol. 26 (Ed.: G. Gribble), Springer, Berlin, Heidelberg, 2010,
pp. 47-115.
0
[
[
18] S. D. Babu, M. D. Hrytsak, T. Durst, Can. J. Chem. 1989, 67, 1071-1076.
19] a) Y. Kasaya, K. Hoshi, Y. Terada, A. Nishida, S. Shuto, M. Arisawa, Eur.
J. Med. Chem. 2009, 4606-4613; b) C. Mukai, Y. Takahashi, Org. Lett.
References
2
005, 7, 5793-5796.
20] a) O. F. Brandenberg, R. Fasan, F. H. Arnold, Curr. Opin. Biotech. 2017,
7, 102-111; b) F. Schwizer, Y. Okamoto, T. Heinisch, Y. F. Gu, M. M.
[
1]
a) V. Sharma, P. Kumar, D. Pathak, J. Heterocyclic Chem. 2010, 47, 491-
[
502; b) A. J. Kochanowska-Karamyan, M. T. Hamann, Chem. Rev. 2010,
110, 4489-4497; c) M. Z. Zhang, Q. Chen, G. F. Yang, Eur. J. Med. Chem.
2015, 89, 421-441.
4
Pellizzoni, V. Lebrun, R. Reuter, V. Kohler, J. C. Lewis, T. R. Ward, Chem.
Rev. 2018, 118, 142-231.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201804779
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
David A. Vargas, Antonio Tinoco, Vikas
Tyagi, and Rudi Fasan*
Page No. – Page No.
Myoglobin-catalyzed C—H
functionalization of unprotected
indoles
Catalysis without protection: A novel biocatalytic strategy for the synthesis of C3-
functionalized indoles via myoglobin-catalyzed carbene transfer is reported. This
approach enabled the transformation of a broad range of indole derivatives bearing
unprotected N—H groups with high efficiency and excellent chemoselectivity and it
could be integrated into a chemoenzymatic scheme for the synthesis of a drug
molecule (indomethacin) at the preparative scale.
This article is protected by copyright. All rights reserved.