Total synthesis of tubulysin U and N14-desacetoxytubulysin H

Article abstract of DOI:10.1039/d0ob01109f

A concise and efficient procedure for the total synthesis of tubulysin U and N14-desacetoxytubulysin H has been developed with high stereoselectivity on a gram scale. This synthesis features an elegant cascade one-pot process to install the challenging th

Full text of DOI:10.1039/d0ob01109f

View Article Online
View Journal
Organic &
Biomolecular
Chemistry
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: B. Long, C. Tao, Y.
Li, X. B. Zeng, M. Cao and Z. Wu, Org. Biomol. Chem., 2020, DOI: 10.1039/D0OB01109F.
Volume 15
Number 47
21 December 2017
Pages 9945-10124
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Organic &
Biomolecular
Chemistry
Accepted Manuscripts are published online shortly after acceptance,
rsc.li/obc
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
ISSN 1477-0520
PAPER
I . J. Dmochowski et al.
Oligonucleotide modifi cations enhance probe stability for
shall the Royal Society of Chemistry be held responsible for any errors
single cell transcriptome in vivo analysis (TIVA)
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
rsc.li/obc

Please do not adjust margins
Organic & Biomolecular Chemistry
Page 1 of 6
View Article Online
DOI: 10.1039/D0OB01109F
COMMUNICATION
Total Synthesis of Tubulysin U and N14-Desacetoxytubulysin H
Bohua Long, ‡ab Cheng Tao, ‡abd Yinghong Li,a Xiaobin Zeng,*c Meiqun Cao,*ab Zhengzhi Wu*abd
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A concise and efficient procedure for the total synthesis of exhibit extremely potent antiproliferative activity in 1A9
tubulysin U and N14-desacetoxytubulysin H has been developed ovarian cancer cells (IC50 = 0.65 nM), MCF-7 breast cancer cells
with high stereoselectivity on gram scale. This synthesis features (IC50 = 0.4 nM) and for in vitro inhibition of tubulin
an elegant cascade one-pot process to install the challenging polymerization (IC50
thiazole moiety and the employment of stereoselective reductions Desacetoxytubulysin
=
1.9 µM).4 Furthermore, N14-
(2) exhibits consistently potent
H
and a serious of high-yield mild reactions to ensure the requisite activities against leukemia, non-small-cell lung, colon, CNS,
stereochemistry, reaction scale, yield and to avoid the vexing melanoma, ovarian, renal, prostate, and breast cancer cell
epimerization occurring during peptide formation.
lines with IC50 values between 0.074 and 0.548 nM.5 All of
these features rendered tubulysins (1) and
N14-
U
Tubulysins (Figure 1) are a family of architecturally complex
tetrapeptides isolated from the myxobacteria Archangium
gephyra and Angiococus disciformis.1 The unique molecular
architecture of tubulysins comprises four uncommon amino
acid fragments, N-methylpipecolic acid (Mep), isoleucine (Ile),
tubuvaline (Tuv), and tubuphenylalanine (Tup) or Tubutyrosine
(Tut). Biologically, tubulysins exhibit extraordinary anticancer
activities and many members of this family surpass the well-
known chemotherapeutic agents like taxol, epothilones and
vinblastine by a factor of 20–1000 with respect to growth
inhibition potential.2 Furthermore, tubulysins have been
drawing attention as potential payloads for antibody-drug
conjugates (ADCS).3a,b,c Structure-activity relationship studies
of tubulysin derivatives indicated that the N,O-acetal moiety at
R2 position is not essential for picomolar cytotoxicity and
further structural simplifications at this position were
accessiable without abolishing their biological activity.3d
Tubulysins U (1) and the unnatural N14-desacetoxytubulysin H
(2) are representative for the basic structures of the most
potent members in this family. Tubulysin U (1) was found to
desacetoxytubulysin
candidates.
H
(2) as excellent anticancer drug
HO 1
O
2
O
OR1
4
H
14
HN
N
N
R3
13
11
N
N
R2
17
7
O
S
O
Mep
Tuv
Tut/Tup
Ile
R1
Tubulysin
R3
R2
A
E
CH2OC(O)CH2CH(CH3)2
CH2OC(O)CH2CH2CH3
CH2OC(O)CH2CH3
Ac
Ac
Ac
OH
H
F
H
1
Ac
H
U ( )
H
H
H
H
V
2
( )
Me
Ac
H
Figure 1 Representative members of tubulysins.
In recent years, tubulysin
U
(1)4,6-11 and N14-
desacetoxytubulysin H (2)5,12-15 have garnered considerable
attention and many novel synthetic strategies have been
developed for these two molecules. Each of these works
employed novel strategies or methodologies to ensure the
synthetic efficacy. However, the highly congested
stereochemical complexity and several chemically sensitive
moieties of 1 and 2 coupled with the vexing epimerization
occurring during peptide formation6,16 posed a particular
synthetic challenge and impeded multigram-scale access to
a. The First Affiliated Hospital of Shenzhen University, Shenzhen 518035, China.
b. Shenzhen Institute of Geriatric Medicine, Shenzhen, 518035, China
c. Central Center Lab of Longhua Branch, Department of Infectious Disease,
Shenzhen People's Hospital, 2nd Clinical Medical College of Jinan University,
Shenzhen 518120, China.
d. Integrated Chinese and Western Medicine Postdoctoral Research Station, Jinan
University, Guangzhou 510632 China.
†
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
‡ These authors contributed equally to this work.
Please do not adjust margins

Please do not adjust margins
Organic & Biomolecular Chemistry
Page 2 of 6
COMMUNICATION
Journal Name
issue,7,9,16,26,27 most of these methods suffer fromVoienweAroticrlemOnolirnee
limitations such as tedious operations, mDuOltIi:s1t0e.p10r3e9a/Dc0tiOoBn0s1,1t0h9eF
use of strong dehydrating reagents and low overall yield,
which impeded efficient access to tubulysins. Recently, Du and
co-workers reported a novel method for the synthesis of 2,4-
disubstituted thiazoles.23 This cascade transformation consists
of disulfide cleavage, thiocarbonylation, phosphine-promoted
these compounds. An abundant synthetic supply remains
necessary for further biological evaluation of tubulysins and
their analogues, which prompted us to develop a more
efficient route for these appealing molecules. As part of our
long-term efforts on marine peptides,17-20 we present herein a
conciseꢀandꢀefficient total synthesis of tubulysin U (1) and
N14-desacetoxytubulysin H (2).
intramolecular
Staudinger/aza-Wittig
reaction
and
dehydrogenation to form the corresponding thiazoles, which
promoted us to further explore this methods in the synthesis
of tubulysins. Much to our delight, after numerous
unsuccessful trials, the disired thiazole 7 was successfully
synthesized in a cascade one-pot process under mild condition
with high yield by utilizing a modified procedure of Du et al23.
Then acid-promoted hydrolysis of 7 afforded thiazolyl
ketone 17 in 90% yield. Reduction of thiazolyl ketone 17 with
BH3·SMe2 in the presence of (S)-Me-CBS at room temperature
HO 1
O
2
O
OAc
4
H
HN
14
N
N
N
11
N
O
R2
S
O
17
1
Tubulysins U ( ) (R2 = H)
N14-desacetoxytubulysin H ( ) (R2 = Me)
2
HO
O
2
O
OH
produced Tuv fragment (5) in 72% yield as
a single
N3
O
N
OH
OH
HCl·H2N
CbzHN
11
N
diastereoisomer. As such, the key Tuv fragment (5) was
synthesized from the cheap L-valinol (11) on gram scale in 7
steps with 38.9% overall yield and excellent stereoselectivity.
S
OMe
Boc
O
5
Tup fragment (6)
Tuv fragment (
)
3
4
OMe
OMe
O
O
N
CbzHN
OH
OH
5
Tuv fragment (
)
H2N
CbzHN
EtO
S
OMe
CbzCl, NaHCO3
IBX, MeCN
reflux, 2 h
OH
11
OH
O
7
8
L-valinol (11)
H2N
CbzHN
CbzHN
13
THF/H2O (1:1)
0 oC to rt, 10 h
H
L-valinol (
)
12
HO
O
2
HO
H2N
L-phenylalaninol (18)
NaOH
THF/H2O (1:1)
OMe
OMe
O
6
Tup fragment (
)
14
, TMG, DCM
BocHN
BocHN
OMe
OH
CbzHN
CbzHN
reflux, 24 h
80% over 3 steps
reflux, 2 h
O
10
9
8
15
Scheme 1 Retrosynthetic analysis of 1 and 2
OMe
THF/con.HCl (20:1)
rt, 24 h, 90%
FDPP, Et3N, DCM, rt, 0.5 h
The retrosynthetic analysis was depicted in Scheme 1.
Initial disconnection of amide traced the origins of 1 and 2 to
four segments: easily available known coupounds 321, 422, Tuv
fragment (5), and Tup fragment (6). We envisaged that the C4
stereocenter on Tuv fragment (5) could be installed through a
CBS reduction of ketone, which traced the origin of 5 to methyl
enol ether 7. The challenging thiazole moiety could be
prepared from β-azido disulfide with the carboxylic acid 8 via a
O
N
CbzHN
16
then PPh3, , reflux, 10h
then CBrCl3, DBU, rt, 2h, 75%
(one pot)
S
OMe
7
75% with two steps
OH
O
O
N
O
N
(S)-Me-CBS, BMS
THF, rt, 3 h, 72%
CbzHN
CbzHN
S
S
OMe
OMe
17
5
)
Tuv fragment (
cascade one-pot process23, and compound
8 could be
OMe
N3
O
prepared from the commercially available L-valinol 11. Tup
fragment (6) could be prepared through oxidation of alcohol 9,
and C2 stereocenter of 9 could be induced by reduction of α,β-
unsaturated ester 10, which could be easily prepared from the
commercially available L-phenylalaninol (18).
Our synthetic strategy for the Tuv fragment (5)
commenced with L-valinol (11) (Scheme 2). Protection of the
amino group with CbzCl group led to alcohol 12.24 Oxidation of
12 with IBX in refluxing MeCN resulted in the aldehyde 13.
Without purification, aldehyde 13 was subjected to a wittig
olefination with phosphonium reagent 1425 to provide
unsaturated ester 15 in 80% yield over three steps. Hydrolysis
of the methyl ester with sodium hydroxide in refluxing
THF/H2O system delivered acid 8.
MeO
MeO
S
PPh3
Br
S
OMe
O
O
N3
14
16
Scheme 2 Synthesis of Tuv fragment (5)
With the key Tuv fragment (5) in hand, the synthesis of
Tup fragment (6) was then explored. The α,β-unsaturated
eater 10 was prepared in a good overall yield by employing the
three-step protection/oxidation/wittig olefination procedure
similar to that of compound 15. Chemoselective reduction of
the double bond of 10 was performed by using NaBH4/NiCl2 in
MeOH,28 and the hydrogenation product 22 was then
hydrolysized with sodium hydroxide in refluxing THF/H2O
system, after which the generating acid was further reduced
through the mixed anhydride method to give a separable
mixture of alcohol 9 and 9’ (anti:syn = 3:1), as reported by
Wipf er al.27 The desired major isomer 9 could be easily
separated by flash chromatography with 60% overall yield over
With the acid 8 in hand, we next turned our attention to
the synthesis of thiazole 7. The installation of the
configurationally and chemically sensitive thiazole fragment
has proved challenging in the synthesis of tubulysins. Although
a lot of methods have been reported to address this vexing three steps and the spectral data for 9 and 9’ were consistent
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 6
Organic & Biomolecular Chemistry
Please do not adjust margins
Journal Name
with earlier studies27.
COMMUNICATION
A
two-step oxidation/cyclization very difficult to purify by silica gel chromatography. Therefore
View Article Online
DOI: 10.1039/D0OB01109F
procedure was performed as a tandem one-pot process when we attempted to induce the methyl group at final stage.
treating with IBX in refluxing MeCN, and then acidic hydrolysis
After removal of the TBS groups and saponification of the
of the resulting N-Boc-pyrrolidinone 23 delivered the methyl ester, the resulting hydroxyl group then underwent
enantiomerically pure Tup fragment (6) in 83% yield over two acetylation with Ac2O in pyridine to deliver acid 29. Finally,
steps, which was then esterified to yield its carboxylate form removal of the Boc group and the methyl group was then
H-Tup-OMe·HCl (26)29 for subsequent couplings. At this stage, induced by treating with 37% aqueous formaldehyde and
the Tup fragment (6) was successfully prepared from the sodium cyanoborohydride to afford the natural product
cheap L-phenylalaninol (18) on gram scale in 8 steps with tubulysins U (1) in 80% yield over five steps. Tubulysins U (1)
44.8% overall yield.
was subsequently purified by a simple silica gel column
chromatography method that did not result in noticeable
epimerization. The spectral data for synthetic tubulysins U (1)
(1H, 13C NMR and HRMS) were identical to those previously
HO
BocHN
O
HO
IBX
MeCN
H
Boc2O, NaHCO3
BocHN
EtO
H2N
reflux, 2 h
THF/H2O (1:1)
rt, 10 h
19
20
18
L-phenylalaninol (
)
7,9,10
25
reported.
The optical rotation of our product 1 ([α]D -
EtO
10.5, c 0.46, MeOH) corresponded well with the literature
value10 (lit. ([α]D25 -11.7, c 0.21, MeOH).
O
O
OEt
Ph3P
21
NaBH4, NiCl2·6H2O
MeOH, 0 oC, 30 min
O
BocHN
BocHN
DCM, rt, 14 h
90% over 3 steps
MeO
O
10
22
HO
O
OH
OH
OH
N
HO
N
HCl·H2
N
N3
Boc
O
O
1) NaOH, THF/H2O (1:1)
reflux, 12 h
26
4
3'
3
+
BocHN
BocHN
9'
2) IBCF, NMM, THF, 0 oC, 0.5 h
then NaBH4, MeOH, rt, 2 h
OH
TBSOTf
2.6-lutidine
O
OH
1) TFA, relfux, 3 h
O
OMe
O
N
N3
N
9
(60%)
(20%)
O
CbzHN
N
9
60% over three steps for
4
2) , HATU, DIPEA
H
DCM, rt
4 h, 90%
S
OMe
S
DCM, rt, overnight
82% over two steps
24
5
Tuv fragment (
)
IBX, MeCN
reflux, 2 h
HO
MeO
O
TBS
TBS
O
O
O
O
O
1) NaOH, THF/H2O (1:1)
rt, 2 h
6M HCl, reflux, 6 h
83% over two steps
HN
OMe
O
N3
N
HCl·H2N
N3
BocN
N
S
N
N
H
H
S
O
26
2) , HATU, DIPEA
DCM, rt, overnight
80% over two steps
25
27
6
Tup fragment (
)
23
Scheme 3 Synthesis of Tup fragment (6)
MeO
O
TBS
With the efficient access to key Tuv fragment (5) and Tup
fragment (6) realized, we next turned our attention to the
completion of the total synthesis of tubulysins U (1) (Scheme
4). Initially, we attempted to remove the Cbz group of 5 by
Pd/C hydrogenolysis, but no reaction occurred under this
O
O
1) NH4F, MeOH
reflux, overnight
1) PPh3, THF/H2O (20:1)
reflux, 2 h
H
HN
O
N
N
S
N
N
H
3
2) , HATU, DIPEA, DCM
2) NaOH, THF/H2
reflux, 10 h
3) Ac2O, pyridine
O
Boc
O
rt, overnight
76% over two steps
28
rt, 16 h then aq. HCl
HO
O
condition. Gratifyingly, when
5
was heated at reflux
O
OAc
H
HN
in neat trifluoroacetic acid (TFA) for 3 h, the Cbz group was
cleaved successfully to give the corresponding amine, which
was then condensed with 430 by using HATU in the presence of
Hünig’s base to generate dipeptide 24 in 82% yield over two
steps. Treatment of 24 with TBSOTf in the presence of 2,6-
lutidine resulted in the corresponding silyl ether 25 in 90%
yield. Then saponification of 25 followed by coupling with H-
Tup-OMe·HCl (26)29 afforded azide 27 in 80% yield over two
steps. Then a Staudinger reduction of azide 27 with PPh3 in
THF-H2O system was performed followed by a condensation
of the resulting amine with N-Boc-D-pipecolinic acid 321 to
afford tetrapeptide 28 in 76% overall yield for the two steps,
1) TFA/DCM, rt, 4 h
N
N
N
N
H
1
Tubulysin U (
)
Boc
O
S
2) 37% aq.HCHO, NaBH3CN
MeCN/MeOH (1:1)
O
27 steps, 7.7% overall yield
1.51 g scale
29
HOAc, rt, overnight
80% over 5 steps
Scheme 4 Total synthesis of tubulysins U (1)
As shown in Scheme 5, treatment of 25 with NaH and MeI
in DMF resulted in the formation of N14-methylated product 30
in 90% yield, as reported by Ellman et al.31 Using a
similar synthesis route
described
above,
N14-
desacetoxytubulysin H (2) was prepared successfully. The
detailed procedures, see Electronic Supporting Information.
The spectral data for synthetic 2 (1H, 13C NMR and HRMS) were
identical to those previously reported.5,12-15,31a The optical
which
was
easily
separated
25
rotation of our product 2 ([α]D -14.4, c 0.26, MeOH)
corresponded well with the literature value31a (lit. ([α]D25 -19.2,
by flash column chromatography on silica gel in EtOAc/Hex
(1:4). Interestingly, introduction of the methyl group at this
step turned out to be fruitless: when the amine was coupled
with N-methyl-D-pipecolinic acid 3’6 under the same condition,
the reaction was sluggish and unclean, and the product was
c 0.9, MeOH).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Organic & Biomolecular Chemistry
Page 4 of 6
COMMUNICATION
Journal Name
TBS
O
TBS
O
O
O
Notes and references
1
View Article Online
14
N
OMe
O
14
N
H
OMe
O
N3
N3
N
N
NaH, MeI, DMF
F. Sasse, H. Steinmetz, H. Höfle anDdOHI: .10R.1e0i3c9h/eDm0ObBa0c1h1,09JF.
Antibiot., 2000, 53, 879-885.
S
0 oC to rt, 2 h, 90%
S
30
25
2
H. Steinmetz, N. Glaser, E. Herdtweck, F. Sasse, H.
Reichenbach, and G. Hӧfle, Angew. Chem. Int. Ed. 2004, 43,
4888 –4892.
HO
O
3
a) K. C. Nicolaou, R. D. Erande, J. Yin, D. Vourloumis, M.
Aujay, J. Sandoval, S. Munneke, J. Gavrilyuk, J. Am. Chem. Soc.
2018, 140, 3690−3711; b) R. V. J. Chari, M. L. Miller, W. C.
Widdison, Angew. Chem. Int. Ed. 2014, 53, 3796 – 3827; c) J.
S. Parker, M. McCormick, D. W. Anderson, B. A. Maltman, L.
Gingipalli, D. Toader, Org. Process Res. Dev. 2017, 21, 1602-
1609; d) Z. Wang, P. A. McPherson, B. S. Raccor, R.
Balachandran, G. Zhu, B. W. Day, A. Vogt and P. Wipf, Chem.
Biol. Drug Des., 2007, 70, 75-86.
O
H
OAc
HN
N
N
N
N
O
S
O
41% over 9 steps
N14-Desacetoxytubulysin H (
2)
28 steps, 6.5% overall yield
1.83 g scale
Scheme 5 Total synthesis of N14-desacetoxytubulysin H (2)
4
5
R.Balasubramanian, B. Raghavan, A. Begaye, D. L. Sackett
and R. A. Fecik, J. Med. Chem., 2009, 52, 238-240.
K. C. Nicolaou, J. Yin, D. Mandal, R. D. Erande, P. Klahn, M.
Jin, M. Aujay, J. Sandoval, J. Gavrilyuk, and D. Vourloumis, J.
Am. Chem. Soc. 2016, 138, 1698-1708.
A. Dömling, B. Beck, U. Eichelberger, S. Sakamuri, S. Menon,
Q-Z. Chen, Y. Lu, and L. A. Wessjohann, Angew. Chem. Int.
Ed., 2006, 45, 7235-7239; Angew. Chem. Int. Ed., 2007, 46,
2337-2348 (Corrigendum).
It should be noted that, the present route turned out to be
rather practical, and we developed an effcient and cost effective
large-scale process for the total synthesis of tubulysin U (1) and N14-
desacetoxytubulysin H (2) with high stereoselectivity by employing
the mild reactions and cheap reagents.
6
7
8
9
M. Sani, G. Fossati, F. Huguenot, and M. Zanda, Angew.
Chem. Int. Ed., 2007, 46, 3526-3529
P. S.Shankar, S. Bigotti, P. Lazzari, I. Manca, M. Spiga, M.
Sani, M. Zanda, Tetrahedron Lett., 2013, 54, 6137-6141.
S.P. Shankar, M. Jagodzinska, L. Malpezzi, P. Lazzari, I.
Manca, I. R. Greig, M. Sani, and M. Zanda, Org. Biomol.
Chem., 2013, 11, 2273-2287.
Conclusions
In summary, we established a convenient and scalable
procedure for the total synthesis of tubulysin U (1) (27 steps
with 7.7% overall yield, 1.51
g
scale) and N14-
Desacetoxytubulysin H (2) (28 steps with 6.5% overall yield,
1.83 g scale). Some of the key features of our synthesis
include: 1) the challenging thiazole segment was elegantly
installed via a cascade one-pot process under mild condition,
2) stereoselective reductions and a serious of high-yield mild
reactions were employed to ensure the requisite
stereochemistry, reaction scale, yield and to avoid the vexing
epimerization occurring during peptide formation. The present
route made a significant progress in the stereoselectivity,
production scale, reagent cost and reaction yield. On the basis
of the current work, the diversity-oriented syntheses and the
biological investigation of tubulysin derivatives is ongoing in
our laboratory.
10 T. Shibue, T. Hirai, I. Okamoto, N. Morita, H. Masu, I.
Azumaya, and O. Tamura, Chem. Eur. J., 2010, 16, 11678-
11688.
11 X. Yang, C. Dong, J. Chen, Y. Ding, Q. Liu, X. Ma, Q. and Y.
Chen, Chem. Asian J., 2013, 8, 1213-1222.
12 A. W. Patterson, H. M. Peltier, and J. A. Ellman, J. Org. Chem.,
2008, 73, 4362-4369
13 D. Toader, F. Wang, L. Gingipalli, M. Vasbinder, M. Roth, S.
Mao, M. Block, J. Harper, S. Thota, M. Su, J. Ma, V. Bedian,
and A. Kamal, J. Med. Chem., 2016, 59, 10781-10787
14 P. Wipf and Z. Wang, Org. Lett., 2007, 9, 1605-1607.
15 T. M. Vishwanatha, B. Giepmans, A. Domling, ChemRxiv,
2020, doi.org/10.26434/chemrxiv.11536053.v1
16 W. Tao, W. Zhou, Z. Zhou, C. Si, X. Sun, B. Wei, Tetrahedron,
2016, 72, 5928-5933.
17 B. Long, S. Tang, L. Chen, S. Qu, B. Chen, J. Liu, A. R. Maguire,
Z. Wang, Y. Liu, H. Zhang, Z. Xu and T. Ye, Chem. Commun.,
2013, 49, 2977-2979.
18 B. Long, J. Zhang, X. Tang and Z. Wu, Org. Biomol.Chem.,
2016, 14, 9712-9715.
Conflicts of interest
There are no conflicts to declare.
19 B. Long, J. Zhang, X. Wang, X. Tang and Z. Wu, Chem. Res.
Chin. Univ., 2017, 33, 890-894.
20 K. Sun, C. Tao, B. Long, X. Zeng, Z. Wu, R. Zhang, RSC Adv.,
2019, 9, 32017-32020.
21 G. Xia, L. Liu, H. Liu, J. Yu, Z. Xu, Q. Chen, C. Ma, P. Li, B.
Xiong, X. Liu, and J. Shen, ChemMedChem 2013, 8, 577 – 581.
22 J. T. Lundquist, and J. C. Pelletier, Org. Lett., 2001, 3, 781-783.
23 a) Y. Liu, X. Sun, X. Zhang, J. Liu and Y. Du, Org. Biomol.
Chem., 2014, 12, 8453-8461; 2) X. Sun, Y. Liu, J. Liu, G. Gu
and Y. Du, Org. Biomol. Chem., 2015, 13, 4271-4277; c) Y. Liu,
J. Liu, X. Qi, and Y. Du, J. Org. Chem., 2012, 77, 7108-7113; d)
Y. Liu, P. He, Y. Zhang, X. Zhang, J. Liu, and Y. Du, J. Org.
Chem., 2018, 83, 3897-3905.
Acknowledgments
We thank the Health and Family Planning Commission of
Shenzhen Municipality (201601053), Shenzhen Science and
Technology
Program
(JCYJ20160428110124165,
JCYJ20160428110235852, JCYJ20170413161352000), NSFC
(81673837, 81574038), Guangdong Science and Technology
Program (2016A020226039, 2015B020211001), Guangdong
Basic
and
Applied
Basic
Research
Foundation
(2019A1515110874) and Sanming Project of Medicine in
Shenzen (SZSM201612049) for financial support.
24 B.Wei, J. Gunzner-Toste, H. Yao, T. Wang, J. Wang, Z. Xu, J.
Chen, et al, J. Med. Chem., 2018, 61, 989-1000
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 6
Organic & Biomolecular Chemistry
Please do not adjust margins
Journal Name
COMMUNICATION
25 P. Seneci, I. Leger, M. Souchet, G. Nadler, Tetrahedron, 1997,
53, 17097-17114.
View Article Online
DOI: 10.1039/D0OB01109F
26 S. Chandrasekhar, B. Mahipal, and M. Kavitha, J. Org. Chem.,
2009, 74, 9531-9534.
27 P. Wipf, T. Takada, and M. J. Rishel, Org. Lett., 2004, 6, 4057-
4060.
28 T. Nagasawa, S. Kuwahara, Org. Lett., 2009, 11, 761-764.
29 Compound 26 was prepared without purification and used
for next step directly. See Supporting Information for
detailed procedures.
30 J.T. Lundquist IV and J. C. Pelletier, Org. Lett., 2001, 3, 781-
783
31 a) A. W. Patterson, H. M. Peltier, F. Sasse, J. A. Ellman, Chem.
Eur. J., 2007, 13, 9534-9541; b) H. M. Peltier, J. P. McMahon,
A. W. Patterson, J. A. Ellman, J. Am. Chem. Soc. 2006, 128,
16018 –16019.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Organic & Biomolecular Chemistry
Page 6 of 6
View Article Online
DOI: 10.1039/D0OB01109F
HO 1
O
O
2
N3
O
H
OAc
OH
OH
4
N
HN
14
N
N
N
11
N
Boc
O
O
R
S
O
HO
17
OH
H2N
Tubulysins U (R = H), 27 steps, 7.7% yield
N14-desacetoxytubulysin H (R = Me), 28 steps, 6.5% yield
H2N
gram-scale synthesis
high stereoselectivity and reaction yield
mild reaction conditions and cheap reagents
a concise and practical synthetic protocol for tubulysins