A Versatile Boc Solid Phase Synthesis of Daptomycin and Analogues Using Site Specific, On-Resin Ozonolysis to Install the Kynurenine Residue

Article abstract of DOI:10.1002/chem.201903725

A de novo solid-phase synthesis of the cyclic lipodepsipeptide daptomycin via Boc chemistry was achieved. The challenging ester bond formation between the nonproteinogenic amino acid kynurenine was achieved by esterification of a threonine residue with a

Full text of DOI:10.1002/chem.201903725

A Journal of
Accepted Article
Title: A versatile Boc solid phase synthesis of daptomycin and
analogues using site specific, on-resin ozonolysis to install the
kynurenine residue
Authors: Margaret Anne Brimble, Buzhe Xu, Yann Hermant, Sung-
Hyun Yang, and Paul Harris
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Chemistry - A European Journal
RESEARCH ARTICLE
A versatile Boc solid phase synthesis of daptomycin and
analogues using site specific, on-resin ozonolysis to install the
kynurenine residue
Buzhe Xu, Yann Hermant, Sung-Hyun Yang, Paul W. R. Harris,* and Margaret A. Brimble*
Abstract:
A
de novo solid-phase synthesis of the cyclic
lipodepsipeptide daptomycin via Boc chemistry was achieved. The
challenging ester bond formation between the nonproteinogenic
amino acid kynurenine was achieved by esterification of a threonine
residue with a protected tryptophan. Subsequent late-stage on-resin
ozonolysis, inspired by the biomimetic pathway, afforded the
kynurenine residue directly. Synthetic daptomycin possessed potent
antimicrobial activity (MIC100 = 1.0 µg/mL) against S. aureus, while five
other daptomycin analogues containing (2R,3R)-3-methylglutamic
acid, (2S,4S)-4-methylglutamic acid or canonical glutamic acid at
position twelve prepared using this new methodology were all
inactive; clearly establishing that the (2S,3R)-3-methylglutamic acid
plays a key role in the antimicrobial activity of daptomycin.
Introduction
The emergence of multidrug-resistant (MDR) bacteria has
become one of the greatest threats to global public health,
and infectious diseases rank among as the leading causes
of mortality worldwide. Without urgent action, death rates
caused by incurable infections are expected to rise more
than tenfold by 2050, to an extremely disturbing 10 million
every year (exceeding the number of deaths caused by
cancer today).[1] This situation is further aggravated by the
fact that only two new major classes of antibiotics, typified by
linezolid (oxazolidinones) and daptomycin (
have been approved for clinical use in the past 40 years, both
of which have narrow spectrum for Gram-positive
bacteria.[2] This has created a pressing need for the
discovery and development of new antibiotics with novel
chemical scaffolds and different mechanisms of action.
Naturally occurring antimicrobial peptides (AMPs), a
diverse class of molecules produced by most living
organisms, have shown great potential as antibiotic
1) (lipopeptides),
Figure 1. Structure of daptomycin (1) and its non-proteinogenic residues.
a
resistant Staphylococcus aureus (MRSA), vancomycin-
resistant Enterococci (VRE), and several species of
Streptococci.[5] It is a non-ribosomally synthesised peptide
consisting of thirteen amino acids, six of which are non-
proteinogenic residues: Kyn13, (2S,3R)-MeGlu12,
D D-
-Ser11,
Ala8, Orn6 and -Asn2. Ten of the thirteen amino acids form
D
a 31-membered depsipeptide ring, with an ester bond
between the side-chain of Thr4 and the carboxylic acid of
Kyn13. The remaining tripeptide is exocyclic and is capped at
the N-terminus by a decanoyl lipid tail (Figure 1). As a typical
calcium-dependent lipopeptide antibiotic (CDA), the
conserved Asp-Ala-Asp-Gly motif in the macrolactone ring of
candidates.[3] Daptomycin ( )[4], a cyclic lipodepsipeptide
1
natural product, exhibits potent antimicrobial activity against
highly resistant Gram-positive pathogens such as methicillin-
[*] B. Xu, Y. Hermant, S.-H. Yang, P. W. R. Harris, M. A. Brimble
School of Chemical Sciences, The University of Auckland, 23 Symonds
Street, Auckland 1142, New Zealand.
daptomycin (
binding,[6] resulting in the aggregation of
1
, pink residues) is thought to facilitate calcium
to form micelles in
1
E-mail: m.brimble@auckland.ac.nz; paul.harris@auckland.ac.nz
the bacterial cell membrane, which subsequently induces
membrane dissociation and cell death.[7] In 2003,
P. W. R. Harris, M. A. Brimble
School of Biological Sciences, The University of Auckland, 3A Symonds
Street, Auckland 1142, New Zealand.
daptomycin (1) was approved by the FDA as the first CDA
for the treatment of complicated skin and soft tissue
infections caused by Gram-positive pathogens.
B. Xu, Y. Hermant, P. W. R. Harris, M. A. Brimble
Maurice Wilkins Centre for Molecular Biodiscovery, School of Biological
Sciences, The University of Auckland, Auckland 1142, New Zealand.
Inspired by its potent antimicrobial activity and unique
Supporting information for this article is given via a link at the end of the
document.((Please delete this text if not appropriate))
mode of action, daptomycin (1) is a promising structural motif
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10.1002/chem.201903725
Chemistry - A European Journal
RESEARCH ARTICLE
for the development of novel antibiotics. Thus a general
synthetic method to establish the structure-activity
Trp to install the Kyn residue. Moreover, several daptomycin
analogues were also prepared using this newly-developed
method to probe their biological activities and establish the
contribution of several individual amino acid residues.
relationships (SARs) of daptomycin (1) is of paramount
importance to enable discovery of novel daptomycin-based
antibiotics such as the lipopeptide surotomycin, currently in
phase III clinical trials for Clostridium difficile.[8] Previous
chemoenzymatic
combinatorial biosynthesis[11] of daptomycin only produced a
synthesis,[9] semi-synthesis,[10] and
Results and Discussion
Synthesis of (2S,3R)-3-MeGlu building block
very limited number analogues, leaving much of the chemical
space unexplored. As
biosynthesis, chemical synthesis is a powerful platform for
the construction of native daptomycin ( ) and its analogues,
enabling greater structural variation. However, chemical
synthesis of native daptomycin ( ) has proven to be
a
complementary strategy to
At the outset, we required (2S,3R)-3-MeGlu in a suitably
protected form for use in Boc SPPS protocols. The reported
synthesis of enantiopure (2S,3R)-Fmoc-3-MeGlu(OtBu)-OH
is a step-intensive process, employing extremely sensitive,
explosive and hazardous diazomethane as a methylating
reagent.[12] Thus, we explored an alternative synthetic
strategy for preparing this key building block, which involved
a temperature-dependent asymmetric Michael addition for
accessing (2S,3R)-3-MeGlu (see Supporting Information).[22]
However, Michael addition of camphor-based tricyclic
iminolactone to crotonate to form the crucial (2S,3R)
stereocentres of 3-methyl glutamic acid, could only be
carried out on 50 mg scale in our hands, with moderate to
low yields and poor diastereoselectivity. Hence an
inseparable diastereoisomeric mixture (d.r. = 2/1) of the
desired (2S,3R)-Boc-3-MeGlu(OBn)-OH and (2R,3R)-Boc-3-
MeGlu(OBn)-OH building blocks was obtained. Nonetheless,
we postulated that using the diastereoisomeric mixture for
1
1
historically difficult due to the depsipeptide ester bond and
non-canonical amino acids. For example, the enantiopure
(2S,3R)-3-MeGlu building block is not readily accessible and
its synthesis is labour-intensive.[12]
The first total chemical synthesis of daptomycin (
achieved by Cubist Pharmaceuticals in 2006, involving a
tedious fragment-coupling approach wherein an
1) was
azidobenzene on the side chain of kynurenine was used for
the pivotal esterification step.[13] Li’s group subsequently
reported[14] the functionally critical,[15] but challenging
depsipeptide bond formation between the hydroxyl group on
the side chain of Thr4 and Fmoc-Kyn13(CHO, Boc)-OH could
not be accomplished either on solid support or in solution
phase, owing to the low reactivity of the Kyn residue or the
steric hindrance of the linear peptide precursor.[14] As such,
an alternative strategy was employed, which avoided using
the Kyn13 for direct coupling, but necessitated a step-
intensive, internal-ester fragment synthesis in solution
phase.[14] More recently, Taylor’s group overcame this
problem by using α-azido amino acids, enabling direct on-
resin esterification of a Kyn13 building block at Thr4 using a
truncated linear peptide that contained an N-terminal azido-
masked Asp3 residue (N3-Asp3). The synthesis could then be
completed via Fmoc-SPPS following reduction of the azide
to the amine.[16] However, α-azido amino acids must be
prepared in house and suffer from elimination[17] and triazole
formation[18] during unmasking of the azide. Additionally, the
peptide ester fragment linked to Ser/Thr side chains in
depsipeptides may undergo base-mediated diketopiperazine
formation, or elimination to form dehydrobutyrine residues,
based on the previous findings reported by our group[19] and
others.[20]
SPPS assembly may enable separation of daptomycin (1)
from its Dap-(2R,3R)-MeGlu analogue 16 at the completion
of the synthesis (see Supporting Information).
Initial synthetic strategy toward daptomycin (1)
In our initial efforts toward the preparation of daptomycin (1)
(Scheme 1), we attached the first residue, Fmoc-Asp-OtBu to
aminomethyl polystyrene resin equipped with the 4-
(hydroxymethyl)phenylacetic acid (PAM) linker, via its side
chain and obtained an acceptable loading of 0.35 mmol/g
based on the Fmoc-release assay (see Supporting
Information). The resulting PAM handle
2 was treated with
TFA/H2O to remove the tert-butyl (tBu) group on the C-
terminal of Asp9, followed by coupling of TFA-+H3N-Gly-OAllyl
to afford the resin-bound dipeptide
3
, which would then be
via standard Boc-
elongated to give the linear decapeptide
4
SPPS (Scheme 1). Interestingly, it was found that protection
of the side chain of Thr4 was not necessary even though
HATU/DIPEA were used as coupling reagents. Inspired by
the superior advantages of Boc-SPPS over Fmoc-SPPS for
the synthesis of “difficult” peptides, it was envisaged that the
Boc/Bn-solid-phase peptide synthesis (Boc-SPPS) is
considered to possess several advantages over Fmoc-SPPS
such as reducing peptide aggregation and suppressing
aspartimide formation when making “troublesome”
peptides.[21] In addition, Boc-SPPS may be preferred when
synthesising peptides containing base-sensitive moieties
such as depsipeptides. Herein we report an entirely Boc-
based SPPS approach to the total synthesis of daptomycin
ester bond of daptomycin (
be established directly between the free hydroxyl group of a
resin-bound threonine residue Thr4
and Boc-Kyn(CHO)2-
OH, followed by chain elongation to afford the fully
1) (resin-bound peptidyl 5) could
4
assembled
macrocyclization then affords resin-bound peptidyl
cleavage affords the final product daptomycin (
sequence
6
.
Subsequent
on-resin
, and HF
7
(1) employing an on-resin ozonolysis of the corresponding
1
) (Scheme
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Scheme 2. Second synthetic strategy toward daptomycin (1).
the three peptide residues at the N- terminus making the
hydroxyl group of Thr4 less accessible. This result was
consistent with those reported by the Li and Taylor
groups.[14,16]
Second synthetic strategy toward daptomycin (1)
Lohani et al. overcame the difficult Kyn13-Thr4 esterification
using an orthogonal protecting group strategy employing an
azide protected building block Asp3 (N3-Asp-(Trt)-OH) that
was coupled to the resin-bound Thr4 to afford a resin-bound
octapeptide. In this case, esterification proceeded readily on
[16]
the octapeptide
8
.
Similarly, we anticipated that the
esterification reaction between the sterically less hindered,
truncated Nα-Fmoc protected octapeptide
and Boc-
Kyn(CHO)2-OH would be more favourable (Scheme 2).
Disappointingly, in our case, no desired product was
8
9
formed after HF cleavage and analysis by LC-MS (see
Supporting Information).
Synthesis of daptomycin (1)
An alternative synthetic route towards daptomycin (1) was
devised to circumvent the direct esterification of the Kyn
building block. Inspired by the effective synthesis of Kyn-
containing peptide cyclomontanin B via on-resin ozonolysis
of the corresponding Trp residue[24] to a Kyn residue
Scheme 1. Initial synthetic strategy toward daptomycin (1). Reagents and
conditions: (a) i. PAM linker, DIC, 6-Cl-HOBt, DMF/DCM (1/1, v/v), 12 h; ii.
FmocAspOtBu, DIC, DMAP, DMF, 12 h. (b) i. TFA/H2O (95/5, v/v), 1 h; ii. TFA-
+H3NGlyOAllyl, PyBOP, 6-Cl-HOBt, DIPEA, DMF, 3 h. (c) i. 20% piperidine in
DMF (v/v), 5 min x 2; ii. standard Boc-SPPS: 1) HATU, DIPEA, DMF, 5 min; 2)
TFA, 2 min x 2. (d) standard Boc-SPPS. (e) i. cat. Pd(PPh3)4, phenylsilane,
DCM; ii. TFA, 2 min x 2; iii. PyBOP, 6-Cl-HOBt, DIPEA, DMF. (f) HF/p-cresol
(95/5, v/v).
1). However, numerous attempts to form the crucial ester
linkage (Thr4-Kyn13) including using carbodiimide chemistry,
acyl fluoride, modified Yamaguchi conditions,[23] and other
conditions, failed (see Supporting Information). This was
purported to caused either by the low reactivity of the Kyn
residue, or the steric hindrance of the bulky lipid chain and
Scheme 3. On-resin ozonolysis of Trp to install Kyn residue. AA = amino
acid.[24]
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(Scheme 3), and a previous report on the high efficiency of
the esterification reaction between Fmoc-Trp(Boc)-OH and a
resin-bound threonine-containing decapeptide[25]
adopted this combined strategy for the solid-phase synthesis
of native daptomycin ( ) (Scheme 4).
Nonapeptide 10 was prepared via standard Boc-SPPS
conditions, employing Fmoc-
-Asn2(Trt)-OH as residue two
in order to achieve orthogonality to Boc-chemistry.
,
we
1
D
Remarkably, Boc-Trp(CHO)-OH was attached to the side
chain of the Thr4 residue in peptide 10 to form the ester bond
quantitatively using double coupling with DIC/cat. DMAP for
1 h. Subsequent peptide chain elongation from Trp13 was
smoothly carried out by standard Boc-SPPS to afford resin-
bound peptidyl 11. The mixture (d.r. = 2/1) of (2S,3R)-Boc-3-
MeGlu(OBn)-OH and (2R,3R)-Boc-3-MeGlu(OBn)-OH was
used for the Glu12 coupling. The allyl group on Gly10 was then
removed by cat. Pd(PPh3)4 and phenylsilane in DCM with
microwave irradiation for 30 min (2 x), followed by treatment
with TFA to remove the Nα-Boc group on Ser11. On-resin
macrolactamisation was then conducted using PyBOP, 6-Cl-
HOBt, DIPEA in DMF for 2 h, affording resin-bound peptide
12 quantitatively.
Next, we attempted to construct the Kyn-containing
peptide 13 via on-resin ozonolysis of the corresponding Trp
residue in peptide 12. The resin-bound peptide 12 was
directly treated with ozone (O3, -78 ℃ , DCM, 5 min;
subsequently, Me2S, 2 h, rt), followed by washing of the resin
with DCM and DMF. Fortunately, LC-MS analysis of a
cleaved resin sample showed that the Trp-containing peptide
12 was quantitatively converted into Kyn-containing peptide
13 without noticeable formation of side-products.
Having established a reliable site-specific method to
convert the Trp to Kyn residue on-resin, the rest of the
synthesis was expected to be straightforward requiring Fmoc
deprotection of peptide 13, followed by coupling of Boc-Trp-
OH and finally acylation with decanoic acid to afford resin-
bound peptide 14. Unfortunately, utilization of 10-20%
piperidine in DMF (v/v) for Fmoc-removal from the Fmoc-D-
Asn2 residue followed by the subsequent coupling of the final
two residues (Trp, decanoic acid) and HF cleavage did not
afford the desired product 15. LC-MS analysis of the crude
peptide indicated that unidentified, inseparable side products
were the main component of the reaction mixture (Table S1,
entry 1, see Supporting Information). This was not a
surprising result as ester bonds in depsipeptides are
susceptible to basic conditions.[19-20] Hence, deprotection of
the N-terminal Fmoc group of peptide 13 needed further
investigation (Scheme S4, see Supporting Information).
Direct HPLC analysis of the deprotected peptide 13 was
difficult as it was not sufficiently retained on the HPLC
column, hence we decided to complete the synthesis by
installing the decanoyl lipid tail on the N-terminus, thereby
enabling monitoring of the reaction by HPLC-MS. Several
conditions were investigated for the Fmoc deprotection
(Table S1, see Supporting Information). 2-Methylpiperidine
Scheme 4. Synthesis of daptomycin (1) and Dapt-(2R,3R)-MeGlu analogue 16
.
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(2-MP) has been reported to remove the Fmoc group
mitigating the risk of ester bond cleavage.[16] 1,8-
Diazabicyclo[5.4.0]undec-7-ene (DBU), a non-nucleophilic
base, has also been used as an alternative Fmoc-
deprotection reagent for difficult or sensitive peptide
sequences.[26] The milder base piperazine (5% in DMF)
containing 0.1 M 6-Cl-HOBt as an acidic additive has been
found to be effective at suppressing aspartimide formation on
peptides containing aspartic acid and asparagine.[27]
Disappointingly, use of these Fmoc-removal reagents
presented above proved fruitless (Table S1, entry 1-4, see
Supporting Information) although some of the desired
product (ca. 40%) was observed with piperazine/6-Cl-HOBt
(entry 4). This suggested that amine bases with a lower pKa
(DBU, pKa = 13.5; piperidine, pKa = 11; piperazine, pKa =
9.8) would be beneficial. Pleasingly, we found that use of
morpholine (pKa = 8.5) (50% in DMF, v/v) was able to
deprotect the Fmoc group rapidly (10 mins, 90% complete;
16 mins, 100% complete) without formation of any notable
side products (Table S1, entries 5-6, see Supporting
Information). Subsequent coupling of Boc-Trp-OH and final
capping with decanoic acid afforded resin-bound peptide 14
(Scheme 4). HF cleavage from the resin with simultaneous
removal of side chain protecting groups gave peptide 15
without noticeable aspartimide formation or ester bond
cleavage.
Figure 2. Structures of daptomycin analogues 17-20.
replacement of Orn6 by Lys6 was beneficial to the
antimicrobial activity. daptomycin analogue Dapt-
A
Lys6/Glu12 18, containing Lys at position six, Glu at position
twelve but conserving the Kyn amino acid was thus also
prepared (3.5 mg, overall yield, 8.6 %). Due to the fact that
mutation of Kyn13 to Trp13 in daptomycin (
1) caused
decreased antibacterial activity,[11] the double Kyn
substituted analogues Dapt-Kyn1/Glu12 19 containing
substitution of Kyn1 for Trp1 (3.8 mg, overall yield, 9.4 %) and
Dapt-Kyn1/Lys6/Glu12 20 which contained an additional
substitution, Lys6 for Orn6 (4.8 mg, overall yield, 11.8 %) were
also prepared.
Notably only one formyl protecting group on the aniline
nitrogen of the Kyn residue of peptide 13 was removed upon
treatment with morpholine, leaving the other one intact during
peptide elongation and HF cleavage. Pleasingly,
deformylation of peptide 15 proceeded quantitatively under
acidic conditions TFA/H2O/CH3CN (0.05/1/1, v/v/v) to afford
native daptomycin and its (2R,3R)-MeGlu congener.
Biological evaluation of daptomycin (1) and analogues 16-
Fortunately, daptomycin (
RP-HPLC from its Dapt-(2R,3R)-MeGlu analogue 16, giving
a 9.4 % overall yield (Dapt , 2.5 mg, 6.3%; Dapt-(2R,3R)-
MeGlu analogue 16, 1.3 mg, 3.1%). Synthetic daptomycin (
1) could be readily separated by
20
Table 1. MICs of Daptomycin (1) and Dapt-analogues 16-20
1
MIC100 (µg/mL)[a]
1
)
Peptides
S. aureus ATCC 29213
was identical to authentic daptomycin (HRMS, co-injection
HPLC, 1H NMR spectrum; see Supporting Information).
Authentic daptomycin
Synthetic daptomycin (1)
Dapt-(2R,3R)-MeGlu 16
Dapt-(2S,4S)-MeGlu 17
Dapt-Lys6/Glu12 18
0.5
1.0
Synthesis of daptomycin analogues 17-20
We next adapted our successful synthesis of daptomycin (1)
>128
>128
64
to prepare four daptomycin analogues (Figure 2). The
presence of (2S,3R)-3-MeGlu at position twelve of
daptomycin (1
) is crucial to its bioactivity,[11, 16, 28] however the
biological significance of this particular amino acid has yet to
be further investigated. Analogue 17 containing a (2S,4S)-4-
MeGlu residue was therefore synthesized via this approach
(Scheme 4, 5.0 mg, overall yield, 12.3 %) in order to probe
the effect of substitution at this position on the antimicrobial
activity. The MICs of a daptomycin analogue containing the
substitutions of Lys at position six, Glu at position twelve and
Trp at position thirteen (Dapt-Lys6/Glu12/Trp13) were reported
to be quite close to native daptomycin when assayed against
B. subtilis and S.aureus strains,[25] indicating that
Dapt-Kyn1/Glu12 19
>128
>128
Dapt-Kyn1/Lys6/Glu12 20
[a] 1.25 mM CaCl2 and 0.5 mM MgCl2.
We next assessed the antimicrobial activities of
analogues 16 20 (Table 1). Synthetic daptomycin
exhibited inhibitory activity against S. aureus (MIC100 = 1.0
1 and its five
-
(1)
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10.1002/chem.201903725
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RESEARCH ARTICLE
[1]
[2]
J. O'Neill, Tackling drug-resistant infections globally: final report and
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Blaskovich, M. A. Cooper, J. Antibiot. 2017, 70, 3-24.
a) N. Strempel, J. Strehmel, J. Overhage, Curr. Pharm. Des. 2015,
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R. H. Baltz, Curr. Opin. Chem. Biol. 2009, 13, 144-151.
a) M. Strieker, M. A. Marahiel, Chembiochem 2009, 10, 607-616; b)
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µg/mL), which was close to the MIC100 data (0.5 µg/mL) for
authentic daptomycin. However, the analogue Dapt-(2R,3R)-
MeGlu 16 that contains the opposite stereochemistry at the
α-carbon and analogue Dapt-(2S,4S)-MeGlu 17 that
relocates the methyl group from the C-3 to the C-4 position
on the Glu side chain, displayed no antibacterial activity
(>128 µg/mL) against S.aureus, which confirmed the finding
that both the absolute stereo-configuration and the position
of the methyl group in the MeGlu residue were critical to the
[3]
[4]
activity of daptomycin (1). Evaluation of compounds 18-20
[5]
[6]
revealed that Dapt-Lys6/Glu12 18 displayed 128-fold less
activity (64 µg/mL) than authentic daptomycin with S.aureus
strain. While analogues 19 and 20 exhibited no antibacterial
activity (>128 µg/mL) against S.aureus.
[7]
[8]
Conclusion
[9]
J. Grünewald, S. A. Sieber, C. Mahlert, U. Linne, M. A. Marahiel, J.
Am. Chem. Soc. 2004, 126, 17025-17031.
In summary, we have developed a robust and entirely solid-
[10]
J. Hill, J. Siedlecki, I. Parr, M. Morytko, X. Yu, Y. Zhang, J. Silverman,
N. Controneo, V. Laganas, T. Li, J.-J. Lai, D. Keith, G. Shimer, J.
Finn, Bioorg. Med. Chem. Lett. 2003, 13, 4187-4191.
K. T. Nguyen, D. Ritz, J. Q. Gu, D. Alexander, M. Chu, V. Miao, P.
Brian, R. H. Baltz, Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 17462-
17467.
phase strategy for the synthesis of daptomycin (1) and
analogues using Boc-chemistry. To the best of our
knowledge, this is the first total synthesis of a cyclic
lipodepsipeptide via Boc-SPPS. The crucial depsipeptide
[11]
[12]
[13]
C. Milne, A. Powell, J. Jim, M. Al Nakeeb, C. P. Smith, J. Micklefield,
J. Am. Chem. Soc. 2006, 128, 11250-11259.
bond in the macrolactone ring of daptomycin (1) was
established by esterification between the side chain of Thr4
and Trp13, followed by conversion of Trp13 to Kyn13 via site-
specific on-resin ozonolysis, which circumvented the
multistep solution-phase synthesis of a Kyn-containing
tetrapeptide fragment. The preference to use Fmoc SPPS
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Acknowledgements
We gratefully acknowledge the RSNZ Marsden Fund for a
doctoral scholarship support to Buzhe Xu and the support of
the New Zealand Health Research Council (HRC, Grant No
16/010).
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Keywords: solid-phase synthesis • daptomycin • Boc chemistry
• on-resin ozonolysis • cyclic lipodepsipeptide
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10.1002/chem.201903725
Chemistry - A European Journal
RESEARCH ARTICLE
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RESEARCH ARTICLE
An entirely solid-phase peptide
synthesis of daptomycin via Boc
chemistry was achieved, which paves
the way for rapid generation of
daptomycin analogues containing the
Thr(OKyn) fragment, as well as other
Buzhe Xu, Yann Hermant, Sung-Hyun
Yang, Paul W. R. Harris,* and Margaret
A. Brimble*
Page No. – Page No.
cyclic
products
proteinogenic Kyn residue.
lipodepsipeptide
featuring the
natural
non-
A versatile Boc solid phase synthesis
of daptomycin and analogues using
site specific, on-resin ozonolysis to
install the kynurenine residue
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RESEARCH ARTICLE
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Title
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This article is protected by copyright. All rights reserved.