Design, synthesis and SAR study of 3rd-generation taxoids bearing 3-CH3, 3-CF3O and 3-CHF2O groups at the C2-benzoate position

Article abstract of DOI:10.1016/j.bioorg.2019.103523

It has been shown that inclusion of CF₃O and CHF₂O groups to drug candidates often improve their pharmacological properties, especially metabolic stability, membrane permeability and PK profile. Moreover, the unique non-spherical structure of the OCHF₂ group can provide interesting and beneficial characteristics. Accordingly, new 3rd-generation taxoids, bearing 3-OCF₃ or 3-OCF₂H (and 3-CH₃ for comparison) at the C2 benzoate moiety, were synthesized and their potencies against drug-sensitive and drug-resistant cancer cell lines examined. In this study, our previous SAR studies on 3rd-generation taxoids were expanded to disclose that CH₃, CF₃O and CHF₂O groups are well tolerated at this position and enhance potency, especially against MDR-cancer cell lines so that these taxoids can virtually overcome MDR. These new taxoids exhibit up to 7 times higher cytotoxicity (IC₅₀) than paclitaxel against drug-sensitive cancer cell lines (MCF7 and LCC6-WT) and 2–3 orders of magnitude higher potency than paclitaxel against drug-resistant ovarian, breast and colon cancer cell lines with MDR-phenotype (NCI/ADR, LCC6-MDR and LDL-1), as well as pancreatic cancer cell line, CFPAC-1. Since it has been shown that a bulky group at this position reduces potency, it is noteworthy that rather bulky CF₃O and CHF₂O groups are well tolerated. Molecular modeling analysis indicated the favorable van der Waals interactions of CF₃O and CHF₂O groups in the binding site. It is also worthy of note that new taxoids, bearing a CHF₂O group at the C2 benzoate position (1-06 series), exhibited the highest potencies against MDR-cancer cell lines and cancer stem cell (CSC)-enriched cancer cell lines. These new 3rd-generation taxoids are promising candidates for highly potent chemotherapeutic agents, as well as payloads for tumor-targeting drug conjugates such as antibody-drug conjugates (ADCs).

Full text of DOI:10.1016/j.bioorg.2019.103523

BioorganicChemistry95(2020)103523
Contents lists available at ScienceDirect
Bioorganic Chemistry
journal homepage: www.elsevier.com/locate/bioorg
Design, synthesis and SAR study of 3rd-generation taxoids bearing 3-CH3,
3-CF3O and 3-CHF2O groups at the C2-benzoate position
Changwei Wanga,b,c,1, Xin Wanga,b,1, Yi Suna,b,1, Adam K. Taouila, Su Yana,b
,
⁎
Galina I. Botchkinab,d, Iwao Ojimaa,b,
a Department of Chemistry, Stony Brook University, Stony Brook, NY 11794-3400, USA
b Institute of Chemical Biology and Drug Discovery, Stony Brook University, Stony Brook, NY 11794-3400, USA
c Drug Discovery Pipeline, Guangzhou Institute of Biomedicine and Health, Chinese Academy of Science, Guangzhou 510530, China
d Department of Pathology, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794-3400, USA
A R T I C L E I N F O
A B S T R A C T
Keywords:
It has been shown that inclusion of CF3O and CHF2O groups to drug candidates often improve their pharma-
cological properties, especially metabolic stability, membrane permeability and PK profile. Moreover, the unique
non-spherical structure of the OCHF2 group can provide interesting and beneficial characteristics. Accordingly,
new 3rd-generation taxoids, bearing 3-OCF3 or 3-OCF2H (and 3-CH3 for comparison) at the C2 benzoate moiety,
were synthesized and their potencies against drug-sensitive and drug-resistant cancer cell lines examined. In this
study, our previous SAR studies on 3rd-generation taxoids were expanded to disclose that CH3, CF3O and CHF2O
groups are well tolerated at this position and enhance potency, especially against MDR-cancer cell lines so that
Taxane
3rd-generation taxoid
SAR study
Multidrug resistance
Cancer stem cells
Fluorine-containing
Trifluoromethoxy
Difluoromethoxy
these taxoids can virtually overcome MDR. These new taxoids exhibit up to 7 times higher cytotoxicity (IC50
)
than paclitaxel against drug-sensitive cancer cell lines (MCF7 and LCC6-WT) and 2–3 orders of magnitude higher
potency than paclitaxel against drug-resistant ovarian, breast and colon cancer cell lines with MDR-phenotype
(NCI/ADR, LCC6-MDR and LDL-1), as well as pancreatic cancer cell line, CFPAC-1. Since it has been shown that
a bulky group at this position reduces potency, it is noteworthy that rather bulky CF3O and CHF2O groups are
well tolerated. Molecular modeling analysis indicated the favorable van der Waals interactions of CF3O and
CHF2O groups in the binding site. It is also worthy of note that new taxoids, bearing a CHF2O group at the C2
benzoate position (1-06 series), exhibited the highest potencies against MDR-cancer cell lines and cancer stem
cell (CSC)-enriched cancer cell lines. These new 3rd-generation taxoids are promising candidates for highly
potent chemotherapeutic agents, as well as payloads for tumor-targeting drug conjugates such as antibody-drug
conjugates (ADCs).
1. Introduction
[3]. Furthermore, Abraxane is effective for the treatment of advanced
pancreatic cancer in combination with gemcitabine [3–5]. Cabazitaxel,
Paclitaxel and docetaxel are two of the most extensively used che-
motherapeutic drugs in clinic for the treatment of various cancers,
particularly for ovarian, lung, and breast cancers in the last quarter
century (Fig. 1) [1,2]. Moreover, the exploration of their new clinical
applications, particularly with new formulations and combination
therapies, are actively underway [1]. Abraxane (nanoparticle albu-
min–bound paclitaxel) is more efficacious than paclitaxel for breast and
non-small cell lung cancer with much muted undesirable side effects
the third FDA-approved taxane (Fig. 1), exhibits good efficacy in hor-
mone-refractory prostate cancer in combination with prednisone [6,7].
However, the first-generation taxane anticancer drugs, i.e., pacli-
taxel and docetaxel, show little efficacy in treating melanoma, pan-
creatic, gastric, brain and renal cancers [2,8]. These limitations are, at
least in part, due to multi-drug resistance (MDR) caused by over-
expression of ABC cassette efflux pumps, overexpression of β-III tubulin
isoform, point mutations in the microtubule binding site and cancer
Abbreviations: MDR, multi-drug resistance; CSCs, cancer stem cells; RI, resistance index; SAR, structure-activity relationship; MOA, mechanism of action; MMPA,
matched molecular pair analysis; HCT116CSC, CSC-enriched colon cancer cell line; PPT2, a patient-derived prostate cancer stem cells; ADCs, antibody-drug con-
jugates; DPBS, Dulbecco's phosphate-buffered saline
⁎ Corresponding author at: Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.
E-mail address: iwao.ojima@stonybrook.edu (I. Ojima).
1 These three authors contributed equally.
https://doi.org/10.1016/j.bioorg.2019.103523
Received 15 October 2019; Received in revised form 18 December 2019; Accepted 18 December 2019
Availableonline20December2019
0045-2068/©2019ElsevierInc.Allrightsreserved.

C. Wang, et al.
BioorganicChemistry95(2020)103523
Fig. 1. Paclitaxel, docetaxel and cabazitaxel.
stem cells [8–10]. In order to address these issues, a number of new
taxoids [11–17], new formulations [18–22] and new combination
therapies [23–28] are currently in different stages of preclinical and
clinical development [1,17]. Nevertheless, it is critical to keep devel-
oping next-generation taxoid anticancer agents with superior pharma-
cological properties and potency against various types of cancers, in
particular drug-resistant and metastatic cancers, as well as cancer stem
cells (CSCs), which are responsible for tumor recurrence and metastasis,
causing major problems in cancer therapy [1,2]. Highly potent taxoids
are also very important as payloads of tumor-targeting drug conjugates
[2,21,29,30].
isopropyl, tert-butyl and CF3 groups based on a computational analysis,
which indicated that bulky substituents at the 3-position of C2-benzoate
caused steric clash with the putative binding site (See Fig. S1 and Table
S1 in the Supplementary Material). Also, we synthesized and evaluated
only one 3-methyl analog, SB-T-121202 (1a-02). Accordingly, in the
present SAR study, we investigated new 3rd-generation taxoids, bearing
a methyl, trifluoromethoxy and difluoromethoxy group at the 3-posi-
tion of the C2-benzoate moiety. As Table 1 shows, SB-T-121303 (1b-
03), bearing a 3-methoxybenzoyl moiety at C2, was identified as the
most potent 3rd-generation taxoid in the study.
In current drug discovery and development, it is quite common to
explore fluorine-containing analogs of lead compounds. This is due to
the fact that a large number of fluorine-containing compounds have
been approved by the FDA for medical and agricultural use [43–48]. In
fact, fluorine is ranked second as the most “favorite heteroatom” only
after nitrogen in current drug discovery [48]. It has been shown that the
replacement of a CeH or CeO bond with a CeF bond in medicinally
active compounds induces or improves desirable pharmacological
properties such as higher metabolic stability, increased binding affinity
to target molecules, and enhanced membrane permeability [49,50].
It has been shown that the OCF3 group in aromatic trifluoromethyl
ethers (Ar-OCF3), e.g., trifluoroanisole, has a strong preference to be
out of plane (i.e., β = 90° in Fig. 2A), while the methyl group in anisole
is mostly in-plane with the phenyl moiety (i.e., β = 18° in Fig. 2A)
[44,51–53]. Furthermore, the conformational preference of the OCHF2
group in Ar-OCHF2 has turned out to be in between the planar OCH3
and the orthogonal OCF3 [44,51] (Fig. 2B) [54]. Since the rotational
barrier in Ar-OCHF2 is considerably lower than that of Ar-OCF3, the
OCHF2 group may serve as a bioisosteric replacement for the OCH3 or
OCF3 moiety, depending on its conformation. Furthermore, the unique
non-spherical feature of the OCHF2 group can provide additionally in-
teresting characteristics. The X-ray crystal structures of Ar-OCHF2 in-
dicate that either one or both of the CeF bonds can be in the anomeric
position to take the endo-exo or endo-endo conformation. In the endo-
endo conformation, the polarities of the CeF bond largely cancel out,
while the polarity of the endo-exo conformation is three times higher
than that of the endo-endo conformation [54]. Thus, Ar-OCHF2 could be
more (endo-endo) or less (endo-exo) lipophilic than their Ar-OCF3
counterparts.
We have been developing 2nd-generation taxoids (modifications at
C10, C3′ and C3′N) [14,16,31–34] and 3rd-generation taxoids (mod-
ifications at C2, C10, C3′ and C3′N) [31,32,35] which exhibit 2–3 or-
ders of magnitude higher potency than paclitaxel and docetaxel against
various drug-resistant cancer cell lines expressing the multidrug-re-
sistance (MDR) phenotype (e.g., LCC6-MDR, breast; NCI-ADR, ovarian;
DLD-1, colon; CFPAC-1, pancreas), as well as point mutations at the
taxane-binding site in β-tubulin (e.g., 1A9PTX10, ovarian) [13]. A re-
presentative 2nd-generation taxoid, SB-T-1214 (1c), as well as its
conjugate with decosahexaenoic acid, DHA-SB-T-1214 (2c) exhibited
impressive efficacy in vivo against DLD-1 tumor xenografts in mice [36].
Also, a nanoemulsion formulation of 2c demonstrated clear efficacy
against PPT2 patient-derived prostate CSC-initiated tumor xenografts in
a mice model and is currently in late stage preclinical development
[37]. We have found that taxoid 1c possesses high potency against CSCs
from colon and prostate cancers by suppressing stemness gene expres-
sions and restoring P21 and P53 expressions through “gene wake-up”
[38].
Through our SAR studies, we found that C2-benzoate modifications
with 3-substitutions with halogens (F, Cl), azide and methoxy groups
enhanced the potency of 2nd-generation taxoids against MDR-cancer
cell lines, leading to the development of 3rd-generation taxoids
[31,35]. The 3-position of the C2-benzoate moiety in paclitaxel was
identified as one of the metabolism site by cytochrome C P450 [39],
and also as a potential van der Waals attractive interaction site with His
229 of β-tubulin, enhancing the binding affinity of paclitaxel [40,41]
and taxoids [32,42].
Select 2nd- and 3rd-generation taxoids investigated in our SAR
studies are shown in Table 1 together with the resistance index, RI (see
Table 1 caption). In those previous SAR studies, we did not include Br, I,
This unique ability of the OCHF2 group to adopt different con-
formations in polar and nonpolar environments would provide unusual
2

C. Wang, et al.
BioorganicChemistry95(2020)103523
Table 1
Cytotoxicity of select 2nd- and 3rd-generation taxoids (IC50 nM).a
Taxoid
R
X
LCC6-WTb
LCC6-MDRc
RId
MCF7e
NCI/ADRf
RId
Paclitaxel
3.1
1.0
–
346
120
–
112
120
–
1.7
300
235
4.0
3.9
4.9
5.3
5.0
2.3
0.33
–
176
235
22
Docetaxel
1.0
SB-T-1213 (1b)
SB-T-1214 (1c)
Et
H
0.18
0.20
0.13
0.14
0.8
c-Pr
Me2N
MeO
Me
H
–
–
–
20
SB-T-1216 (1d)
SB-T-1217 (1e)
H
–
–
–
38
H
–
–
–
38
SB-T-121202 (1a-02)
SB-T-121203 (1a-03)
SB-T-121303 (1b-03)
SB-T-121403 (1c-03)
SB-T-121703 (1e-03)
Me
MeO
MeO
MeO
MeO
1.5
0.6
1.0
1.0
0.6
5.8
2.7
0.9
2.9
1.6
3.9
4.5
0.9
2.9
2.7
6.3
2.9
0.92
–
Me
0.8
Et
0.36
–
c-Pr
MeO
0.4
1.4
3.5
a
Concentration of compound which inhibits 50% (IC50, nM) of the growth of human tumor cell line after 72 h drug exposure.
LCC6-WT: human breast carcinoma cell line (Pgp−).
b
c
d
e
f
LCC6-MDR: mdr1 transduced cell line (Pgp+).
Resistance index = (IC50 for drug resistant cell line)/(IC50 for drug-sensitive cell line).
MCF7: human breast carcinoma cell line.
NCI/ADR: multi-drug resistant human ovarian carcinoma cell line.
combination of attractive properties, such as good aqueous solubility
and cellular permeability. Actually, the matched molecular pair ana-
lysis (MMPA) of the OCHF2 group indicates that this group may be
superior to the OCH3 and OCF3 groups for optimizing ADME properties,
such as metabolic stability and passive transmembrane permeability
[51]. Moreover, the fluorine atom can have multipolar interactions
with the electrophilic carbon of nearby protein amide carbonyl groups
in protein-ligand binding [44]. The importance of such molecular re-
cognition is supported by structural and SAR studies [55–59]. The
significance of the multipolar interaction of fluorine provides a ratio-
nale for the exploitation of the fluorine substitution in lead optimiza-
tions [44].
Table 2
Potency of select taxoids against MCF-7/PTX cell line [60].
Taxane
IC50 (nM)
Paclitaxel
2291
125
1c
80.5
21.7
19.0
34.9
31.4
7.6
2.3
2.0
3.0
2.8
1b-03
SB-T-121205 (1a-05)
SB-T-121405 (1c-05)
SB-T-121605 (1d-05)
exhibited the highest potency, which is 121 times better than that of
paclitaxel, and 1b-03 was the close second. Detailed study on the me-
chanism of action (MOA) for 1a-05 disclosed that this taxoid effectively
suppresses the PI3k/Akt pathway and epithelial-mesenchymal transi-
tion (EMT) by activating PTEN tumor suppressor expression [60]. This
MOA is another new and significant feature associated with new-gen-
eration taxoids against highly drug-resistant cancer cells in addition to
the recently revealed MOA in which new-generation taxoids exhibit
high potency against CSCs by effectively suppressing the stemness gene
expressions, promoting differentiation [38,61].
Accordingly, it would be worthwhile to examine the effects of the
introduction of OCF3 and OCHF2 groups into the 3rd-generation taxoids
on their potencies (i.e., cytotoxicity) in the present work, especially
against drug-resitant cancer cell lines, since the benefits of in-
corporating these groups for pharmacological properties are already
well anticipated as described above. Therefore, we synthesized novel
3rd-generation taxoids, bearing 3-OCF3 and 3-OCHF2 groups at the C2-
benzoate moiety, as well as those taxoids bearing a methyl group at the
same position for comparison.
With highly anticipated benefits of introducing fluorinated methoxy
groups to the 3rd-generation taxoids in ADME properties, as well as
recently disclosed unique MOAs of new-generation taxoids, the dis-
covery and development of potent and efficacious new 3rd-generation
Prior to the full SAR studies, we examined three 3rd-generation
taxoids bearing the 3-CF3O-benzoate moiety at C2 together with pa-
clitaxel, 1c and 1b-03 against the extremely paclitaxel-resistant breast
cancer cell line, MCF-7/PTX. As Table 2 shows, SB-T-121205 (1a-05)
Fig. 2. Conformational characteristics of Ar-OCH3, Ar-OCF3 and Ar-OCHF2.
3

C. Wang, et al.
BioorganicChemistry95(2020)103523
Scheme 1. Synthesis of key intermediates, 7(a-e)-02,05,06.
taxoids has obvious significance.
Then, the subsequent TES protection of the 7-hydroxyl group afforded
the key intermediates, 7(a,b)-02,05,06. In the second method, the C7
hydroxyl group was first selectively protected with TES to give 2-
modified 7-TES-baccatins, 5-02,05,06, which were reacted with
LiHMDS and various acyl chlorides to afford the corresponding key
intermediates, 7(c,d,e)-02,05,06, wherein the C10-acyl groups were
cyclopropanecarbonyl, N,N-dimethylcarbamoyl and methoxycarbonyl.
The new 3rd-generation taxoids, 1(a-e)-02,05,06 (see Table 3),
were synthesized by the Ojima-Holton coupling of the baccatin key
intermediates, 7(a-e)-02,05,06, with β-lactam 8, giving the corre-
sponding 7-TES-2′-TIPSO-taxoids, 9(a-e)-02,05,06, followed by silyl
deprotection with HF/pyridine in good to high yield for 2 steps
(Scheme 2).
2. Results and discussion
2.1. Synthesis of new 3rd-generation taxoids bearing 3-CH3, 3-OCF3 or 3-
OCF2H group at the C2-benzoate moiety
The synthesis of new 3rd-generation taxoids followed the proce-
dures that we developed and reported [30], starting from 10-deace-
tylbaccatin III (10-DAB) and using the β-lactam synthon method in-
cluding the Ojima-Holton coupling, as illustrated in Schemes 1 and 2.
The synthesis of C2-modified baccatins 5-02,05,06 commenced
with the exhaustive triethylsilyl (TES) protection of C7, C10, and C13-
hydroxyl groups (Scheme 1). Due to the highly congested steric en-
vironment, the C1-hydroxyl cannot be protected with a TES group. This
free hydroxyl group allowed the selective cleavage of the C2-benzoate
by Red-Al in high yield. DIC coupling of 3-CH3-, 3-OCF3- or 3-OCF2H-
benzoic acid with tri-TES-baccatin 2 gave 2-modified-tri-TES-baccatins
3-02,05,06. The subsequent HF/pyridine deprotection afforded 2-
modified baccatins 4-02,05,06, bearing a 3-CH3, 3-OCF3 or 3-OCF2H
group at the C2-benzoate moiety (Scheme 1).
2.2. Biological evaluations of new 3rd-generation taxoids
2.2.1. Potency of new 3rd-generation taxoids against human cancer cell
lines
The potency (i.e., cytotoxicity) of the new 3rd-generation taxoids
was evaluated against various drug-sensitive and drug-resistant cancer
cell lines, i.e., MCF-7, NCI/ADR, LCC6-WT, LCC6-MDR, DLD-1 and
CFPAC-1. Results are summarized in Table 4 together with the re-
sistance index (RI). Paclitaxel and extensively studied 2nd-generation
taxoid, 1c, were used as controls. The IC50 values were determined by a
standard MTT assay.
Modification of the C10 position with various acyl groups was
performed by two methods. The first method was the selective acylation
of the 10-hydroxyl moiety by taking advantage of a site-selective Ce3+
complexation to block the 7-hydroxyl moiety, using acetic and propa-
noic anhydrides to give 2,10-modified baccatins, 5(a,b)-02,05,06.
As Table 4 shows, all of the new 3rd-generation taxoids possess two
4

C. Wang, et al.
BioorganicChemistry95(2020)103523
Scheme 2. Synthesis of new 3rd-generation taxoids, 1(a-e)-02,05,06.
orders of magnitude greater potency against different drug-resistant
cancer cell lines, i.e., NCI/ADR, LCC6/MDR and DLD-1, as compared to
the parent compound, paclitaxel. The results clearly indicate that these
new taxoids can basically overcome multidrug resistance caused by the
overexpression of Pgp and other ABC cassette transporters. Also, all of
these new taxoids exhibit subnanomolar IC50 values against drug-sen-
sitive cell lines, MCF7 and LCC6-WT, as well as CFPAC-1 which is
moderately resistant to paclitaxel.
Table 3
New 3rd-generation taxoids.
Taxoid
R
X
In general, there is a trend in that the potency of these 3rd-gen-
eration taxoids is in the order of preference, OCF2H (1-06) > OCF3 (1-
05) > CH3 (1-02), at the 3-position of the C2-benzoate moiety with
some exceptions in the drug-sensitive cancer cell lines. For example, 1a-
02 and 1d-02 are the two most potent taxoids against LCC6-WT, and
1d-05 and 1e-05 are the two best taxoids against MCF7. However, in all
of the drug-resistant cancer cell lines including CFPAC-1, 1(a-e)-06,
exhibit the highest potency. Also, the potency of 1(a-e)-06 is higher
than that of excellent 2nd-generation taxoid, 1c, in all cancer cell lines
without exception. [Note: The potency of 1-06 is also higher than that
of 1-03 (MeO analogs) (see Table 1) in general. The only minor ex-
ception is 1b-03 (RI = 2.78) vs. 1b-06 (RI = 2.9) in LCC6-WT/LCC6-
MDR, but the difference is within the margin of error. Since the data in
Table 1 need normalization to make a fair comparison, the normalized
values, i.e., IC50 and RI values, are shown in Table S2 in the
Supplementary Material.]
1a-02
1b-02
1c-02
1d-02
1e-02
1a-05
1b-05
1c-05
1d-05
1e-05
1a-06
1b-06
1c-06
1d-06
1e-06
Me
Me
Et
Me
c-Pr
Me2N
MeO
Me
Me
Me
Me
OCF3
OCF3
OCF3
OCF3
OCF3
OCF2H
OCF2H
OCF2H
OCF2H
OCF2H
Et
c-Pr
Me2N
MeO
Ac
Et
c-Pr
Me2N
MeO
Table 4
IC50 values (nM)a of new 3rd-generation taxoids against drug-sensitive and drug-resistant human cancer cell lines.
Taxoid
MCF-7e
NCI/ADRf
RId*
LCC6-WTb
LCC6-MDRc
RId
DLD-1g
CFPAC-1h
PTX
0.9
0.15
0.56
130
2.08
144
1.2
1.81
0.91
0.25
0.42
0.69
0.27
0.47
0.51
0.71
0.58
0.74
0.85
0.42
0.56
0.45
0.40
0.67
0.84
619
129
342
3.5
12
364
3.4
5.6
5.5
3.7
3.4
3.3
3.0
3.1
3.2
3.3
3.1
2.9
3.0
3.1
2.9
3.0
58
60
5.1
0.41
1c
0.74
0.49
0.55
0.56
0.82
0.71
0.98
0.37
0.56
0.28
0.32
0.34
0.60
0.37
0.56
0.41
0.88
0.78
0.59
0.59
0.97
0.76
0.83
0.43
0.42
0.66
0.66
0.45
0.26
0.36
0.42
0.39
0.24
0.53
0.07
0.26
0.33
0.30
0.02
0.20
0.34
0.28
0.18
0.02
0.19
0.11
0.07
0.08
0.24
0.06
0.30
0.18
0.02
0.35
0.18
0.33
0.19
0.06
0.21
0.13
0.25
0.13
0.21
0.03
3.19
2.99
2.43
2.15
3.11
2.49
2.20
2.40
2.11
2.15
1.96
2.01
1.64
1.80
1.77
1.75
0.66
1.07
0.23
0.07
0.93
0.85
0.24
0.44
0.08
0.28
0.31
1.26
0.44
0.71
1.39
0.06
0.52
1.10
0.39
0.75
0.46
0.30
0.39
0.26
0.05
0.56
0.47
0.56
0.58
0.44
0.37
0.41
0.71
0.59
0.91
0.95
0.48
0.61
0.57
0.75
0.79
0.69
0.51
0.48
0.42
0.39
0.44
0.49
1a-02
1b-02
1c-02
1d-02
1e-02
1a-05
1b-05
1c-05
1d-05
1e-05
1a-06
1b-06
1c-06
1d-06
1e-06
0.13
0.27
0.14
0.32
0.07
0.19
0.14
0.16
0.14
0.22
0.21
0.02
0.12
0.3
1.6
0.38
0.74
0.48
0.60
0.61
0.32
0.70
0.17
0.59
0.47
0.26
0.29
0.48
0.25
0.37
1.1
5.8
3.1
12
1.1
1.2
1.1
5.3
4.3
3.4
3.6
2.9
2.3
4.8
2.9
4.0
4.4
2.6
0.85
1.2
0.75
2.4
2.1
1.3
0.43
0.97
0.75
0.95
0.15
a-fSee the captions in Table 1.
g
h
multidrug-resistant (Pgp + ) human colon cancer cell line.
human pancreatic cancer cell line.
5

C. Wang, et al.
BioorganicChemistry95(2020)103523
LCC6-MDR
1.2
1
NCI/ADR
1.2
paclitaxel
PTX
paclitaxel
PTX
1c
SB-T-1214
1a-02
SB-T-121202
1b-02
SB-T-121302
1c-02
SB-T-121402
1d-02
SB-T-121602
1e-02
SB-T-121702
1
0.8
0.6
0.4
0.2
0
1c
SB-T-1214
0.8
0.6
0.4
0.2
0
SB1-aT--01221202
SB1-bT--01221302
SB1-cT--01221402
SB-T-121602
1d-02
SB-T-121702
1e-02
0.1
0.5
2.5
12.5
-0.2
0.1
0.5
2.5
12.5
Drug Concentration
-0.2
Drug Concentration
1.2
1
1.2
1
PTpXaclitaxel
SB1-cT-1214
SB1-aT--01521205
SB1-bT--01521305
SB1-cT--01521405
SB1-dT--01521605
PTX
paclitaxel
SB-T-1214
1c
SB-T-121205
1a-05
SB-T-121305
1b-05
0.8
0.6
0.4
0.2
0
0.8
0.6
0.4
0.2
0
SB-T-121405
1c-05
SB-T-121705
1e-05
SB-T-121605
1d-05
SB-T-121705
1e-05
0.1
0.5
2.5
12.5
-0.2
0.1
0.5
2.5
12.5
Drug Concentration
-0.2
Drug Concentration
1.2
1
0.8
0.6
0.4
0.2
0
PTX
paclitaxel
SB-T-1214
1c
1.2
1
PTpXaclitaxel
SB1-cT-1214
SB1-aT--01621206
SB1-bT--01621306
SB1-cT--01621406
SB1-dT--01621606
SB-T-121206
1a-06
SB1-bT--10261306
1c-06
SB-T-121406
1d-06
SB-T-121606
1e-06
SB-T-121706
0.8
0.6
0.4
0.2
0
SB-T-121706
1e-06
0.1
0.5
2.5
12.5
-0.2
0.1
0.5
2.5
12.5
-0.2
Drug Concentration
Drug Concentration
Fig. 4. Dose response curves of new 3rd-generation taxoids in LCC6-MDR lung
cancer cell line.
Fig. 3. Dose-response (kill) curves of new 3rd-generation taxoids in NCI/ADR
ovarian cancer cell line.
In the DLD-1 drug-resistant colon cancer cell line (Fig. 5), paclitaxel
was, again, essentially inactive (IC50 364 nM, Table 4). At 12.5 nM
paclitaxel concentration, 80% of the cancer cells were alive, while less
than 10% cancer cells were alive after treatment with new 3rd-gen-
eration taxoids at the same concentration. Taxoids 1d-02, 1e-02, 1a-
06, 1d-06, and 1e-06 possess high potency (< 15% cell viability) at
5 nM concentration, and 1d-06 and 1e-06 exhibit most impressive
dose-response (kill) curves as compared to that of paclitaxel and even
1c. Interestingly, the 1-05 series of taxoids did not show distinct dose-
response (kill) curves, compared to that of 1c against this particular
drug-resistant cell line.
2.2.2. Dose-response (kill) curve analysis of new 3rd-generation taxoids in
drug-resistant cancer cell lines
In the NCI/ADR drug-resistant ovarian cancer cell line (Fig. 3),
paclitaxel is essentially inactive (IC50 130 nM, Table 4). The new 3rd-
generation taxoids showed significantly higher potency than paclitaxel
and better dose-response than 2nd-generation taxoid 1c. It is worthy of
note that after 100 nM of paclitaxel treatment, 10% cells were still alive
(data not shown). In contrast, after 12.5 nM of next-generation fluor-
otaxoids treatment, only < 3% cells were alive. Especially, 1b-02, 1c-
02, 1e-02, 1d-05, 1e-05, 1d-06 and 1e-06 possess very high potency
(< 10% cell viability) at 2.5 nM concentration. Overall, 1d-06 and 1d-
05 exhibit impressive dose-response (kill) curves as compared to that of
paclitaxel and even that of 1c.
2.2.3. Potencies of new 3rd-generation taxoids against CSC-enriched colon
cancer cell line HCT-116CSC and patient-derived prostate cancer stem cells
PPT2
In the LCC6-MDR drug-resistant breast cancer cell line (Fig. 4),
paclitaxel was essentially inactive (IC50 619 nM, Table 4) as in the case
of the NCI/ADR cell line. Thus, even after 100 nM of paclitaxel treat-
ment, 10% cells were still alive (data not shown), while only < 3%
cells were alive after 12.5 nM of new 3rd-generation taxoid treatments.
Taxoids 1c-02, 1c-05, 1d-05, 1e-05 and 1a-06 possess high potency
(< 15% cell viability) at 2.5 nM concentration, and exhibit impressive
dose-response (kill) curves as compared to that of paclitaxel.
The potency of select new 3rd-generation taxoids was evaluated
against a CSC-enriched colon cancer cell line, HCT116CSC [62,63] and a
patient-derived prostate cancer stem cells, PPT2 [61], expressing high
levels of CD133, CD44, CD44v6, EpCAM, CD49f and CD166 genes.
Since CSC-enriched cancer cells with CD133+ and CD44+ are highly
resistant to traditional chemotherapeutic drugs, it was interesting to
examine the potency of select new 3rd-generation taxoids against those
6

C. Wang, et al.
BioorganicChemistry95(2020)103523
DLD-1
1.2
1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
PTX
paclitaxel
SB1-Tc-1214
SB1-Ta--10221202
1b-02
SB-T-121302
1c-02
SB-T-121402
1d-02
SB-T-121602
1e-02
SB-T-121702
0.677
0.8
0.6
0.4
0.2
0
0.601
cabazitaxel
CBZ
0.485
0.447
1c
SB-T-1214
S1Bc--T0-5121405
SB-T-121605
1d-05
0.10
0.50
2.50
5.00
12.50
Drug Concentration
10 uM
drug concentration
1.2
1
Fig. 6. Cell death rate induced by select taxoids against HCT116CSC cells.
PTX
paclitaxel
SB-T-1214
1c
SB-T-121205
1a-05
SB-T-121305
1b-05
SB-T-121405
1c-05
SB-T-121605
1d-05
0.8
0.6
0.4
0.2
0
1
0.9
0.8
0.7
0.6
SB-T-121705
1e-05
1b-02
1b-02
0.10
0.50
2.50
5.00
12.50
0.5
0.4
0.3
0.2
0.1
0
1b-05
1b-05
Drug Concentration
1b-06
1b-06
1.2
1
PTX
paclitaxel
SB1-cT-1214
SB1-aT--01621206
SB1-bT--01621306
SB1-cT--01621406
SB1-dT--01621606
0.8
0.6
0.4
0.2
0
10
25
50
100
250
Drug concentration
Fig. 7. Dose response curves of select 3rd-generation taxoids against PPT2
SB-T-121706
1e-06
CSCs.
0.10
0.50
2.50
5.00
12.50
Fig. 7. Taxoid 1b-06, bearing a 3-CHF2O-benzoyl group at C2, exhibited
Drug Concentration
the best potency (IC50 23 nM) among the three. This pilot study implied
Fig. 5. Dose-response (kill) curves of new 3rd-generation taxoids in DLD-1
that the order of potency is 1-06 series (CHF2O)
(CF3O) > 1-02 series (CH3).
> 1-05 series
colon cancer cell line.
Following up with the pilot study, we examined the cell viability of
PPT2 CSCs at 50 nM and 250 nM concentrations of twelve new 3rd-
generation taxoids to compare the potencies of 1-02, 1-05 and 1-06
series and to find if there is a clear structure-activity relationship (SAR).
Results are summarized in Fig. 8. As Fig. 8A shows, there is a clear SAR
among the twelve taxoids examined wherein the order of potency is 1-
06 (CF2HO) > 1-05 (CF3O) > 1-02 (CH3) in all variations at C10
(i.e., b: EtCO; c: cycloPr-CO; d: Me2NCO; e: MeOCO) at 50 nM con-
centration. At 250 nM concentration (Fig. 8B), however, the relative
potency of 1-05 series varies, depending on the C10 substituent al-
though the order of potency among the three series is the same as that
observed at 50 nM concentration. The potencies of 1b-02 and 1c-02 are
close to those of 1b-05 and 1c-05, respectively, while the potencies of
1d-05 and 1e-05 are very close to those of 1d-06 and 1e-06, respec-
tively. Overall, 1e-06 (CF2HO) exhibited the best potency among the
twelve taxoids examined, which caused 62% cell death at 50 nM con-
centration and 78% cell death at 250 nM concentration.
cells.
CSC-enriched colon cancer cell line HCT-116CSC. To maintain its
stemness, the CSC-enriched HCT116CSC cell line [38] was cultured in
mesenchymal stem cell growth medium (MSCGM™). Since HCT116CSC
cells formed 3D spheroids, those cells did not attach well to the bottom
of the wells. Three days after treatment with three select taxoids, 1d-05,
1c-05 and 1c, much less floating 3D spheroids compared to the control
were observed at 10 μM concentration. In the attempted MTT assay
(72 h), the cell death rate with 10 μM of taxoids 1d-05 and 1c-05
showed appreciably higher cytotoxicity than carbazitaxel [6], which is
the most potent taxane approved by FDA (Fig. 6). Taxoid 1d-05 in-
duced 68% cell death, which is 1.5 times more than that by carbazi-
taxel. Although 32–40% of HCT116CSC cells survived after treatment
with select new 3rd-generation taxoids, it was found that those survived
cells showed distinct morphological abnormalities, e.g., enlarged size,
severe vacuolization, knobby projections, prolonged size and multiple
nuclei. Those abnormalities are characteristic to seriously damaged
CSCs, losing pluripotency and ability to form secondary spheroids, re-
ported previously on a HCT116CSC spheroids treated with 1c [38].
Patient-derived prostate cancer stem cells PPT2. PPT2 cells were also
cultivated in the MSCGM™. To estimate approximate IC50 values for the
new 3rd-generaiton taxoids, three taxoids, 1b-02, 1b-05 and 1b-06
were selected for an MTT assay. The dose response curves are shown in
2.3. Molecular modeling analysis of new 3rd-generation taxoids
We generated a β-tubulin-bound structure of 1a from the co-crystal
structure of β-tubulin and paclitaxel (PDB: 1JFF) [64] using the Avo-
gadro molecular editor [65,66] and MMFF94 force field [67–71], which
showed an excellent overlay (see Fig. S1(C) in the Supplementary
7

C. Wang, et al.
BioorganicChemistry95(2020)103523
50 nM drug concentration
Table 5
A
Relative docking energy scores (kcal/mol) of 3rd-generation taxoids in the
1
proximal and distal sites, in comparison to that of 1a (kcal/mol).
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0.79
0.78
0.69
0.67
0.65
0.64
0.62
0.58
0.54
0.48
0.42
0.38
Entry
X
ΔE proximal site
ΔE distal site
1a
H
0
0
1a-02
1a-03
1a-05
1a-06
Me
−0.17
−0.01
−0.54
−0.39
−0.38
−0.34
−0.47
−0.40
MeO
OCF3
OCF2H
250 nM drug concentration
B
groups with hydrophobic amino acid residues, Leu230 and Leu275, in
the proximal binding site.
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
Docking analyses were performed using AutoDock Vina [72]. En-
ergy-minimized structures were directly used as input for re-orienta-
tion. For local search minimization, all possible conformers were used,
and data was collected for the conformer in which the pose was most
geometrically and energetically favorable. The obtained energy scores
of the 4 analogs were compared to that of 1a, and the relative docking
energy scores (ΔE) are summarized in Table 5. Interestingly, the OCF3
and OCF2H analogs, i.e., 1a-05 and 1a-06, orient the X group to the
proximal site, while the Me and OMe analogs , i.e., 1a-02 and 1a-03,
tend to place the X groups to the distal site. It is important to point out
that all those X groups moderately increase the binding energy, in
contrast to bulky X groups such as Br, I, isoPr, tert-Bu and CF3 (see Table
S1 in the Supplementary Material). In the proximal site, there is a clear
difference in ΔE values between Me/OMe groups vs. OCF3/OCF2H
groups, while the difference becomes smaller in the distal site although
the order of enhancement is the same as that in the proximal site. [Note:
The distal site is rather shallow and the deviation of binding poses of 1a
analogs from the canonical 1a structure is large, as compared to that in
the proximal site, which show very little deviation. Thus, the results in
the proximal site appear to be more reliable. Thus, Fig. 9 only shows
docking results in the proximal site.]
0.44
0.42
0.41
0.4
0.39
0.37
0.31
0.29
0.26
0.25
0.23
0.22
Fig. 8. Cell viability of PPT2 CSCs with 50 nM and 250 nM of new 3rd-gen-
eration taxoids (72 h).
Material). Then, the structures of 1a-02, 1a-03, 1a-05 and 1a-06 were
generated, building upon the β-tubulin-bound 1a structure in the same
manner. Fig. 9 shows (A) the overlays of those 5 taxoids in the proximal
binding site and (B) the overlay of 1a-05 and 1a-06, illustrating the
favorable van der Waals (VDW) interactions of the OCF3 and OCF2H
Although the predicted affinity is slightly larger for the OCF3 analog
Fig. 9. (A) Overlay of 1a, 1a-02, 1a-03, 1a-05 and 1a-06 in the proximal binding site; (B) Overlay of 1a-05 and 1a-06, illustrating favorable VDW interactions of the
OCF3 and OCF2H residues in the proximal binding site.
8

C. Wang, et al.
BioorganicChemistry95(2020)103523
(1a-05) than the OCF2H analogs (1a-06), the observed cytotoxicity of
1a-06 is slightly higher than that of 1a-05 (Table 4). This might be
ascribable to a possible difference in cell membrane permeability, i.e.,
1a-06 might have a better permeability than 1a-05 though those dif-
ferences could be within the margin of error.
Shimadzu LC-2010A machine with a Phenomenex C18 column, Curosil-
B 250 × 4.60 mm (acetonitrile-water; flow rate: 0.6 mL/min; UV at 254
and 220/215 nm).
4.2. Materials
The chemicals were purchased from Aldrich Co. and Sigma.
Tetrahydrofuran was freshly distilled from sodium metal and benzo-
phenone. Dichloromethane was also distilled immediately prior to use
under nitrogen from calcium hydride. 10-DAB III was a gift from the
Fujian Yew Park Biological Co. Ltd. (+)-(3R,4S)-1-Boc-3-TIPS-O-4-(2-
methylpropen-1-yl)azetidin-2-one (8) [34,75], 7,10,13-tris(triethyl-
silyl)-2-debenzoyl-10-deacetylbaccatin III (2) [31], 7,10,13-tris(trie-
thylsilyl)-2-debenzoyl-2-(3-methylbenzoyl)-10-deacetylbaccatin III (3-
02) [31], 2-debenzoyl-2-(3-methylbenzoyl)-10-deacetylbaccatin III (4-
02) [31], 2-debenzoyl-2-(3-methylbenzoyl)-10-propanoyl-7-triethyl-
silyl-10-DAB III (5a-02) [31], 2-debenzoyl-2-(3-methylbenzoyl)-10-
propanoyl-10-deacetylbaccatin III (7a-02) [31], (2′R,3′S)-2-debenzoyl-
2-(3-methylbenzoyl)-7-TES-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-Boc-N-
3′-dephenyldocetaxel (9a-02) [31], (2′R,3′S)-2-debenzoyl-2-(3-methyl-
benzoyl)-3′-(2-methylpropen-1-yl)-3′-Boc-N-3′-dephenyldocetaxel (1a-
02) [31] and cabazitaxel [76,77] were prepared by the literature
methods. All medium components, buffer and other reagents were ob-
tained from Thermo Fisher Scientific, unless otherwise indicated. 3-
(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT),
hydrochloric acid and isopropyl alcohol were purchased from Aldrich
Co. and Sigma.
3. Conclusion
New 3rd-generation taxoids, bearing 3-CH3, 3-OCF3 or 3-OCF2H at
the C2 benzoate moiety, were synthesized and fully characterized.
These taxoids exhibit up to 7 times better potency (IC50) than paclitaxel
against drug-sensitive cancer cell lines, MCF7 (breast) and LCC6-WT
(breast), and are 2–3 orders of magnitude more potent than paclitaxel
against drug-resistant cancer cell lines, NCI/ADR (ovarian), LCC6-MDR
(breast) and LDL-1 (colon) in which P-glycoprotein (Pgp) and other
efflux pumps are overexpressed (MDR-phenotype), as well as CFPAC-1
(pancreas). This profile is largely in agreement with those for other 3rd-
generation taxoids reported by us previously, wherein the 3-sub-
stituents in the C2-benzoate moiety were F, Cl, N3, MeO and vinyl
[31,32]. The new series of taxoids reported in this study expand the
SAR studies on 3rd-gneration taxoids, disclosing that CH3, CF3O and
CHF2O groups are well tolerated at this position and enhance potency,
especially against MDR-cancer cell lines. Importantly, these new tax-
oids can virtually overcome MDR. Since it has been shown that a vinyl
group at this position reduces potency although this group is mildly
tolerated, it is a significant finding that rather bulky CF3O and CHF2O
groups are well tolerated. Molecular modeling analysis of the docked
structures and predicted affinity of the new 3rd-generation taxoids, 1a-
05 and 1a-06, in comparison to 1a-02 and 1a-03, indicated a con-
siderably favorable VDW interactions of OCF3 and OCF2H groups with
hydrophobic amino acid residues in the binding site, as compared to Me
and OMe groups. It has also been shown that inclusion of CF3O and
CHF2O groups to drug candidates often improve their pharmacological
properties, especially metabolic stability, membrane permeability and
PK profile [73,74]. Also, the unique non-spherical structure of the
OCHF2 group can provide interesting characteristics [54]. Therefore,
our finding in this study that the 1-06 series of taxoids, bearing a
CHF2O group at the C2 benzoate position, exhibited the highest po-
tencies against MDR-cancer cell lines and CSC-enriched cancer cell line,
HCT-116CSC (colon), as well as patient derived PPT2 CSCs (prostate), is
noteworthy. These new 3rd-generation taxoids are promising candi-
dates for highly potent chemotherapeutic agents with proper formula-
tions, especially nanoformulations, and also as payloads (warheads) for
tumor-targeting drug conjugates, e.g., antibody-drug conjugates
(ADCs).
4.3. Chemical synthesis
4.3.1. 7,10,13-TriTES-2-debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-
deacetyl-baccatin III (3-05)
Compound 2 (6.086 g, 7.77 mmol), DMAP (7.594 g, 62.16 mmol)
and 3-trifluromethoxybenzoic acid (12.812 g, 62.16 mmol) were dis-
solved in CH2Cl2 (81 mL), and purged with nitrogen. To the mixture
DIC (9.71 mL, 62.16 mmol) was added dropwise under inert conditions.
The mixture was stirred at room temperature and the reaction progress
was monitored by TLC (hexanes:ethyl acetate = 80:20). Upon com-
pletion, the reaction was quenched with saturated aqueous NH4Cl
(12 mL), diluted with H2O (720 mL) and extracted with ethyl acetate
(3 × 720 mL). The organic layers were collected, washed with brine
(3 × 720 mL), dried over anhydrous MgSO4, and concentrated in vacuo.
Purification of the crude product by column chromatography on silica
gel (hexanes:ethyl acetate = 90:10) to afford 3-05 (7.094 g, 7.31 mmol,
94%) as a white solid: m.p. 189–190 °C; 1H NMR (400 MHz, CDCl3,
ppm) δ 0.56–0.71 (m, 18H), 0.95–1.04 (m, 27H), 1.14 (s, 3H), 1.20 (s,
3H), 1.49 (s, 1H), 1.66 (s, 3H), 1.86–1.93 (m, 1H), 1.99 (d, J = 1.0 Hz,
1H), 2.07–2.24 (m, 2H), 2.28 (s, 3H), 2.50–2.57 (m, 1H), 3.88 (d,
J = 7.1 Hz, 1H), 4.14 (AB, JAB = 8.0 Hz, 1H), 4.26 (AB, JAB = 8.0 Hz,
1H), 4.43 (dd, J1 = 10.5 Hz, J2 = 6.6 Hz, 1H), 4.91–4.97 (m, 2H), 5.21
(s, 1H), 5.61 (d, J = 7.1 Hz, 1H), 7.44 (d, J = 8.0 Hz, 1H), 7.53 (t,
J = 8.0 Hz, 1H), 7.99 (s, 1H), 8.03 (d, J = 8.0 Hz, 1H); 19F NMR
(376 MHz, CDCl3, 25 °C) δ −57.92 (3F). HRMS (TOF) m/z: Calcd. For
C48H77F3O11Si3H+, 971.4799. Found, 971.4788.
4. Experimental section
4.1. General methods
Melting points were measured on a Thomas Hoover Capillary
melting point apparatus and are uncorrected. NMR spectra were re-
corded on a Bruker Ascend 700 spectrometer operating at 700 MHz for
1H and 175 MHz for 13C, a Bruker 500 Advance spectrometer operating
at 500 MHz and 125 MHz for 1H and 13C, respectively, or a Bruker 400
Nanobay spectrometer operating at 400 MHz, 100 MHz, and 376 MHz
for 1H, 13C, and 19F, respectively. Mass to charge values were measured
by flow injection analysis on an Agilent Technologies LC/MSD VL. High
resolution mass spectrometry (HRMS) analysis was carried out on an
Agilent LC-UV-TOF mass spectrometer at the Institute of Chemical
Biology and Drug Discovery, Stony Brook, New York. TLC was per-
formed on Merck DC-alufolien with Kieselgel 60F-254 and column
chromatography was carried out on silica gel 60 (Merck; 230–400 mesh
ASTM). Compound purity was verified by reverse phase HPLC on a
4.3.2. 7,10,13-TriTES-2-debenzoyl-2-(3-difluromethoxybenzoyl)-10-
deacetyl-baccatin III (3-06)
In the same manner as that for 3-05, 3-06 was synthesized from 2
(1.818 g, 2.32 mmol) and 3-difluromethoxybenzoic acid (1.746 g,
9.28 mmol) in 86% yield (1.903 g) as a white solid: 1H NMR (400 MHz,
CDCl3, ppm) δ 0.55–0.70 (m, 18H), 0.94–1.03 (m, 27H), 1.12 (s, 3H),
1.17 (s, 3H), 1.59 (bs, OH), 1.64 (s, 3H), 1.84–1.91 (m, 1H), 1.98 (s,
3H), 2.06–2.12 (m, 1H), 2.18–2.24 (m, 1H), 2.27 (s, 3H), 2.48–2.56 (m,
1H), 3.86 (d, J = 7.0 Hz, 1H), 4.14 (AB, JAB = 8.2 Hz, 1H), 4.26 (AB,
9

C. Wang, et al.
BioorganicChemistry95(2020)103523
JAB = 8.2 Hz, 1H), 4.43 (dd, J1 = 10.5 Hz, J2 = 6.6 Hz, 1H), 4.90–4.95
(m, 2H), 5.19 (s, 1H), 5.59 (d, J = 7.0 Hz, 1H), 5.59 (d, J = 73.3 Hz,
1H), 7.34 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.47 (t, J = 8.0 Hz, 1H),
7.88 (s, 1H), 7.94 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm)
δ 5.02, 5.42, 6.15, 7.05, 7.13, 10.59, 14.76, 20.75, 22.42, 26.49, 37.45,
39.97, 43.15, 47.09, 58.40, 68.47, 72.82, 75.95, 76.17, 76.70, 79.76,
80.92, 84.20, 113.23, 115.83, 118.43, 120.94, 125.14, 127.37, 130.27,
131.68, 135.89, 139.70, 151.23, 166.14, 170.23, 205.79.
(d, J = 8.4 Hz, 1H), 4.46 (m, 1H), 4.88 (dd, J = 7.2 Hz, J = 12.2 Hz,
1H), 4.98 (d, J = 8.0 Hz, 1H), 5.59 (d, J = 7.1 Hz, 1H), 6.33 (s, 1H),
7.35 (t, J = 7.6 Hz, 1H), 7.41 (d, J = 7.6 Hz, 1H), 7.89 (d, J = 7.6 Hz,
1H), 7.91 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 9.2, 9.6, 15.8, 21.1,
21.6, 22.7, 27.2, 27.8, 35.8, 38.8, 42.9, 46.3, 58.9, 68.2, 72.6, 75.0,
76.2, 76.7, 79.3, 81.0, 84.6, 127.4, 128.7, 129.4, 131.0, 132.1, 134.6,
138.6, 146.4, 167.4, 170.8, 174.9, 204.4. HRMS (TOF) Calcd for
C
33H42O11NH4+: 632.3065, Found: 632.3066.
4.3.3. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-10-deacetylbaccatin III
(4-05)
4.3.6. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)baccatin III (5a-05)
In the same manner as that for 5b-02, 5a-05 was synthesized from
4-05 (473 mg, 0.752 mmol) and acetic anhydride (0.71 mL,
7.52 mmol)) in 90% yield (453 mg) as a white solid: m.p. 209–210 °C;
1H NMR (400 MHz, CDCl3, ppm) δ 1.11 (s, 6H), 1.67 (s, 3H), 1.83–1.90
(m, 1H), 2.06 (s, 3H), 2.24–2.29 (m, 8H), 2.53–2.61 (m, 1H), 3.89 (d,
J = 7.0 Hz, 1H), 4.14 (AB, JAB = 8.2 Hz, 1H), 4.28 (AB, JAB = 8.2 Hz,
1H), 4.47 (dd, J1 = 10.8 Hz, J2 = 6.8 Hz, 1H), 4.89 (t, 1H), 4.99 (d,
J = 8.8 Hz, 1H), 5.60 (d, J = 7.0 Hz, 1H), 6.33 (s, 1H), 7.46 (d,
J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 7.99 (s, 1H), 8.04 (d,
J = 8.0 Hz, 1H); 13C NMR δ (100 MHz, CDCl3, ppm) 9.60, 15.83, 21.05,
21.10, 22.56, 27.16, 35.77, 38.71, 42.86, 46.34, 58.87, 68.05, 72.51,
75.71, 76.40, 76.49, 77.44, 79.36, 80.90, 84.66, 119.34, 121.91,
122.35, 126.39, 128.73, 130.50, 131.58, 131.90, 146.75, 149.49,
Compound 3-05 (1.107 g, 1.14 mmol) was dissolved in a 1:1 mix-
ture of acetonitrile:pyridine (50 mL total; 45 mL) and cooled to 0 °C
under inert conditions. To the mixture excess HF (70%) in pyridine
(11 mL), was added dropwise. The reaction mixture was stirred at room
temperature and monitored by TLC (hexanes:ethyl acetate = 50:50).
Upon completion, the reaction was quenched with 10% aqueous citric
acid (22 mL), diluted with water (220 mL) neutralized with NaHCO3(s)
and extracted with ethyl acetate (2 × 220 mL). The organic layer was
collected, washed with saturated CuSO4 solution (3 × 70 mL), water
(70 mL) and brine (3 × 70 mL). The extract was then dried over an-
hydrous MgSO4, filtered and the filtrate concentrated in vacuo.
Purification of the crude product by column chromatography on silica
gel (hexanes:ethyl acetate
=
50:50) to afford 4-05 (688 mg,
165.77, 170.85, 171.54, 204.28; 19F NMR (376 MHz, CDCl3, 25 °C) δ
1.095 mmol, 96%) as a white solid: m.p. 224–225 °C; 1H NMR
(400 MHz, CDCl3, ppm) δ 0.94 (s, 6H), 1.53 (s, 3H), 1.62–1.68 (m, 1H),
1.90 (s, 3H), 2.13–2.17 (m, 5H), 2.25–2.33 (m, 1H), 3.82 (d,
J = 7.1 Hz, 1H), 4.02 (s, 2H), 4.06–4.12 (m, 1H), 4.47 (s, 1H),
4.61–4.62 (m, 1H), 4.78 (d, J = 2.0 Hz, 1H), 4.93 (d, J = 9.1 Hz, 1H),
5.00 (d, J = 7.1 Hz, 1H), 5.14 (d, J = 2.0 Hz, 1H), 5.23 (d, J = 4.4 Hz,
1H), 5.39 (d, J = 7.1 Hz, 1H), 7.72–7.73 (m, 2H), 7.91 (s, 1H), 8.02 (d,
J = 8.4 Hz, 1H); 13C NMR (100 MHz, DMSO, ppm) δ 9.66, 14.83,
20.09, 22.03, 26.73, 36.55, 42.39, 46.48, 57.01, 65.98, 70.91, 74.38,
75.39, 75.59, 76.92, 80.08, 83.70, 118.87, 121.41, 126.00, 128.56,
131.11, 132.38, 134.41, 141.59, 148.31, 163.78, 169.39, 210.20; 19F
NMR (376 MHz, CDCl3, 25 °C) δ −56.92 (3F). HRMS (TOF) m/z: Calcd.
For C30H35F3O11H+, 629.2204. Found, 629.2201.
−57.86 (3F). HRMS (TOF) m/z: Calcd. For
C
32H37F3O12NH4
,
+
688.2575. Found, 688.2574.
4.3.7. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-10-propanoyl-10-
deacetylbaccatin III (5b-05)
In the same manner as that for 5a-05, 5b-05 was synthesized from
4-05 (431 mg, 0.686 mmol) and propanoic anhydride (0.76 mL,
5.88 mmol) in 88% yield (415 mg) as a white solid: m.p. 124–127 °C;
1H NMR (400 MHz, CDCl3, ppm) δ 1.10 (s, 6H), 1.23 (t, J = 7.6 Hz,
3H), 1.60 (s, 1H), 1.66 (s, 3H), 1.91–1.79 (m, 1H), 2.05 (s, 3H), 2.25
(m, 6H), 2.64–2.47 (m, 4H), 3.89 (d, J = 7.0 Hz, 1H), 4.13 (d,
J = 8.2 Hz, 1H), 4.27 (d, J = 8.2 Hz, 1H), 4.49–4.44 (m, 1H),
4.90–4.85 (m, 1H), 4.99 (d, J = 8.1 Hz, 1H), 5.59 (d, J = 7.0 Hz, 1H),
6.33 (s, 1H), 7.45 (d, J = 8.6 Hz, 1H), 7.53 (dd, J1 = 8.0 Hz,
J2 = 2.0 Hz, 1H), 7.98 (s, 1H), 8.03 (d, J = 7.7 Hz, 1H); 13C NMR δ
(100 MHz, CDCl3, ppm) δ 9.03, 9.39, 15.62, 20.86, 22.36, 26.96, 27.60,
35.56, 38.51, 42.65, 46.15, 58.67, 67.85, 72.34, 75.51, 76.00, 76.29,
79.17, 80.70, 84.48, 120.42 (q, J = 259 Hz), 122.15, 126.18, 128.53,
130.30, 131.38, 131.76, 146.43, 149.29, 165.56, 170.65, 174.70,
4.3.4. 10-Deacetyl-2-debenzoyl-2-(3-difluromethoxybenzoyl)baccatin III
(4-06)
In the same manner as that for 4-05, 4-06 was synthesized from 3-
06 (904 mg, 0.948 mmol) in 95% yield (550 mg) as a white solid: m.p.
218–219 °C; 1H NMR (400 MHz, CDCl3, ppm) δ 1.10 (s, 3H), 1.26 (m,
3H), 1.75 (s, 3H), 1.89–1.78 (m, 1H), 2.07 (s, 1H), 2.08 (s, 3H), 2.27 (d,
J = 7.7 Hz, 3H), 2.61 (m, 1H), 4.01 (d, J = 7.0 Hz, 1H), 4.20–4.06 (m,
4H), 4.31 (d, J = 8.4 Hz, 1H), 4.87 (s, 1H), 4.99 (d, J = 9.3 Hz, 1H),
5.25 (s, 1H), 5.62 (d, J = 7.0 Hz, 1H), 6.57 (t, J = 73.1 Hz, 1H), 7.38
(d, J = 8.0 Hz, 1H), 7.51 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.90 (s,
204.16; 19F NMR (376 MHz, CDCl3, 25 °C) δ −57.86 (3F). HRMS for
+
C
33H39F3O12 calcd: 684.2637. Found: 684.2389 (Δ = 0.4 ppm).
4.3.8. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)baccatin III (5a-06)
In the same manner as that for 5a-05, 5a-06 was synthesized from
4-06 (130 mg, 0.213 mmol) and acetic anhydride (0.2 mL, 2.213 mmol)
in 98% yield (133 mg) as a white solid: m.p. 128–130 °C; 1H NMR
(700 MHz, CDCl3, ppm) δ 1.07 (m, 6H), 1.23 (m, 3H), 1.63 (s, 3H),
1.85–1.77 (m, 1H), 2.02 (m, 6H), 2.30–2.16 (m, 9H), 2.53 (m, 1H), 3.85
(d, J = 7.0 Hz, 1H), 4.07 (m, 1H), 4.10 (d, J = 8.3 Hz, 1H), 4.26 (d,
J = 8.3 Hz, 1H), 4.43 (dd, J = 10.8, 6.8 Hz, 1H), 4.86 (t, J = 7.8 Hz,
1H), 4.96 (d, J = 8.8 Hz, 1H), 5.57 (d, J = 7.0 Hz, 1H), 6.29 (s, 1H),
6.55 (t, J = 73.1 Hz, 1H), 7.35 (d, J = 8.1 Hz, 1H), 7.47 (dd,
1H), 7.96 (d,
J = 8.0 Hz, 1H). HRMS (TOF) m/z: Calcd. For
C
30H36F2O11H+, 611.2298. Found, 611.2278.
4.3.5. 2-Debenzoyl-2-(3-methylbenzoyl)-10-deacetyl-10-
propanoylbaccatin III (5b-02)
To a solution of 4-02 (92 mg, 0.165 mmol) and cerium(III) chloride
hexahydrate (6 mg, 0.017 mmol) in THF (4 mL) was added acetic an-
hydride (0.16 mL, 1.65 mmol) at 0 °C, the mixture was stirred at room
temperature for 3 h. The progress of the reaction was monitored by
TLC. Upon completion, the reaction was quenched with saturated
NH4Cl (10 mL), and the aqueous layer was extracted with ethyl acetate
J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.86 (s, 1H), 7.93 (d, J = 7.8 Hz, 1H).
+
HRMS for
C
32H38F2O12
calcd: 652.2336. Found: 652.2331
(Δ = −0.7 ppm).
(3
× 30 mL). The combined extracts were washed with brine
(3 × 30 mL), dried over MgSO4 and concentrated in vacuo. The residue
was purified by flash chromatography on silica gel to afford 5b-02
(89 mg, 88%) as a white solid: m.p. 105–107 °C; 1H NMR (500 MHz,
CDCl3) δ 1.10 (s, 6H), 1.23(t, J = 7.6 Hz, 3H), 1.66 (m, 6H), 1.86 (m,
1H), 2.04 (s, 3H), 2.19 (d, J = 5 Hz, 1H), 2.28 (m, 5H), 2.42 (s, 3H),
2.53 (m, 5H), 3.87 (d, J = 7.1 Hz, 1H), 4.14 (d, J = 6.4 Hz, 1H), 4.30
4.3.9. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)-10-propanoyl-10-DAB III
(5b-06)
In the same manner as that for 5a-05, 5b-06 was synthesized from
4-06 (316 mg, 0.518 mmol) and propanoic anhydride (0.70 mL,
5.42 mmol) in 95% yield (328 mg) as a white solid: m.p. 140–142 °C;
1H NMR (400 MHz, CDCl3, ppm) δ 1.12 (s, 6H), 1.24 (t, 3H), 1.59 (bs,
10

C. Wang, et al.
BioorganicChemistry95(2020)103523
1H), 1.68 (s, 3H), 1.84–1.91 (m, 1H), 2.06 (d, J = 1.0 Hz, 3H),
2.28–2.30 (m, 5H), 2.48–2.62 (m, 3H), 3.90 (d, J = 7.0 Hz, 1H), 4.15
(AB, JAB = 8.2 Hz, 1H), 4.31 (AB, JAB = 8.2 Hz, 1H), 4.80 (dd,
concentrated in vacuo. The residue was purified by flash chromato-
graphy on silica gel to afford 7b-02 (64 mg, 75%) as a white solid: m.p.
105–107 °C; 1H NMR (700 MHz, CDCl3) δ 0.57 (m, 6H), 0.91 (t,
J = 8.0 Hz, 9H), 1.02 (s, 3H), 1.20 (m, 6H), 1.67 (m, 4H), 1.86 (m, 1H),
2.18 (d, J = 4.8 Hz, 1H), 2.19 (d, J = 1.1 Hz, 3H), 2.28 (m, 5H), 2.42
(m, 3H), 2.52 (m, 2H), 3.87 (d, J = 7.0 Hz, 1H), 4.13 (d, J = 8.5 Hz,
1H), 4.29 (d, J = 8.5 Hz, 1H), 4.48 (dd, J = 6.7 Hz, J = 10.5 Hz, 1H),
4.82 (m, 1H), 4.96 (d, J = 8.2 Hz, 1H), 5.60 (d, J = 7.1 Hz, 1H), 6.47
(s, 1H), 7.35 (t, J = 7.5 Hz, 1H), 7.40 (d, J = 7.5 Hz, 1H), 7.90 (d,
J = 7.5 Hz, 1H), 7.93 (s, 1H); 13C NMR (175 MHz, CDCl3) δ 5.5, 6.9,
9.4, 10.1, 15.1, 20.3, 21.6, 22.8, 27.0, 37.4, 38.4, 42.9, 47.5, 58.8, 68.1,
72.6, 74.8, 76.0, 76.7, 79.0, 81.1, 84.4, 127.4, 128.7, 129.5, 131.0,
132.9, 134.6, 138.5, 144.1, 167.4, 170.9, 173.0, 202.45. HRMS (TOF)
J
1 = 10.8 Hz, J2 = 6.8 Hz, 1H), 4.90 (t, 1H), 5.00 (d, J = 7.8 Hz, 1H),
5.61 (d, J = 7.0 Hz, 1H), 6.35 (s, 1H), 6.58 (d, J = 73.2 Hz, 1H), 7.38
(d, J = 7.8 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 7.91 (s, 1H), 7.97 (d,
J = 7.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 9.26, 9.61, 15.82,
21.08, 22.64, 27.20, 27.82, 35.80, 38.72, 42.89, 46.34, 58.93, 68.15,
72.56, 75.59, 76.20, 76.55, 79.38, 80.97, 84.70, 113.19, 115.79,
118.40, 121.18, 126.37, 127.42, 130.41, 131.41, 132.09, 146.51,
151.23, 166.15, 170.92, 174.88, 204.37; 19F NMR (376 MHz, CDCl3,
25 °C) δ −81.54 to −80.63 (2F). HRMS (TOF) m/z: Calcd. For
C33H40F2O12NH4+, 684.2826. Found, 684.2833.
Calcd
for
C
39H56O11SiH+
729.3665,
Found:
729.3669
4.3.10. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-7-triethylsilyl-10-
deacetylbaccatin III (6-05)
(Δ = −0.55 ppm).
Compound 4-05 (2.118 g, 3.37 mmol) was dissolved in DMF
(46 mL) and cooled to 0 °C under inert conditions. To this mixture was
added 4 eq of imidazole (990 mg, 14.60 mmol) and allowed to stir
5 min. Then TES-Cl (1.84 mL, 10.95 mmol) was added dropwise. The
mixture was stirred and allowed to warm to room temperature while
being monitored by TLC (hexanes: ethyl acetate = 60:40). Upon
completion the reaction was quenched with saturated NH4Cl (12 mL)
and extracted with ethyl acetate (3 × 200 mL). The organic layer was
collected, washed with brine (3 × 250 mL), dried over anhydrous
MgSO4, and concentrated in vacuo. Purification of the crude product by
column chromatography on silica gel (hexanes: ethyl acetate = 65:35)
to afford 6-05 (2.302 g, 3.10 mmol, 92%) as a white solid: 1H NMR
(400 MHz, CDCl3, ppm) δ 0.53–0.62 (m, 6H), 0.93–0.97 (m, 9H), 1.09
(s, 6H), 1.74 (s, 3H), 1.88–1.94 (m, 1H), 2.05–2.06 (m, 1H), 2.09 (s,
3H), 2.25–2.27 (m, 5H), 2.45–2.53 (m, 1H), 3.97 (d, J = 7.0 Hz, 1H),
4.3.13. 2-Debenzoyl-7-TES-2-(3-methylbenzoyl)-10-deacetyl-10-
cyclopropane-carbonylbaccatin III (7c-02)
To a solution of 6-02 (193 mg, 0.287 mmol) in THF (6 mL) was
added LiHMDS (1.0 M in THF, 0.32 mL, 0.320 mmol) dropwise at −40
°C. The mixture was stirred at −40 °C for 5 min. Then cyclopropane-
carbonyl chloride (27 μl, 0.301 mmol) was added dropwise and the
reaction mixture was stirred at −40 °C for 30 min. The progress of the
reaction was monitored by TLC. Upon completion, the reaction was
quenched with saturated NH4Cl (10 mL), and the aqueous layer was
extracted with ethyl acetate (3 × 30 mL). The combined extracts were
washed with brine (3 × 30 mL), dried over MgSO4 and concentrated in
vacuo. The residue was purified by flash chromatography on silica gel
to afford 7b-02 (178 mg, 84%) as a white solid: m.p. 132–133 °C; 1H
NMR (500 MHz, CDCl3) δ 0.56 (m, 6H), 0.91 (m, 10H), 1.02 (m, 5H),
1.17 (m, 4H), 1.67 (m, 4H), 1.75 (m, 1H), 1.87 (m, 1H), 2.19 (s, 3H),
2.26 (m, 6H), 2.41 (s, 3H), 2.51 (m, 1H), 3.87 (d, J = 7.0 Hz, 1H), 4.13
(d, J = 8.4 Hz, 1H), 4.30 (d, J = 8.4 Hz, 1H), 4.47 (dd, J = 6.8 Hz,
J = 10.5 Hz, 1H), 4.82 (t, J = 8.0 Hz, 1H), 4.96 (d, J = 8.7 Hz, 1H),
5.61 (d, J = 7.1 Hz, 1H), 6.45 (s, 1H), 7.35 (t, J = 7.7 Hz, 1H), 7.40 (d,
J = 7.7 Hz, 1H), 7.89 (d, J = 7.7 Hz, 1H), 7.93 (s, 1H); 13C NMR
(125 MHz, CDCl3) δ 5.5, 7.0, 8.8, 8.9, 10.1, 13.2, 15.1, 20.4, 21.6, 22.8,
27.0, 37.4, 38.4, 43.0, 47.5, 58.8, 68.2, 72.6, 74.8, 75.7, 76.8, 79.0,
81.1, 84.4, 127.4, 128.7, 129.5, 131.0, 133.0, 134.6, 138.5, 144.1,
4.15 (AB, JAB
= 8.2 Hz, 1H), 4.25–4.30 (m, 2H), 4.42 (dd,
J1 = 10.5 Hz, J2 = 6.6 Hz, 1H), 4.86–4.89 (m, 1H), 4.97 (d, J = 8.0 Hz,
1H), 5.18 (d, J = 2.0 Hz, 1H), 5.58 (d, J = 7.0 Hz, 1H), 7.46 (d,
J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 8.00 (s, 1H), 8.05 (d,
J = 8.0 Hz, 1H). HRMS (TOF) m/z: Calcd. For C36H49F3O11SiH+
,
743.3069. Found, 743.3072.
4.3.11. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)-7-triethylsilyl-10-
deacetylbaccatin III (6-06)
167.4,
170.9,
173.4,
202.5.
HRMS
(TOF)
Calcd
for
In the same manner as that for 6-02, 6-06 was synthesized from 4-
06 (1.195 g, 1.96 mmol) and TES-Cl (0.40 mL, 2.35 mmol) in 97% yield
(1.377 g) as a white solid: 1H NMR (400 MHz, CDCl3, ppm) δ; δ
0.52–0.62 (m, 6H), 0.92–0.96 (m, 9H), 1.09 (s, 6H), 1.74 (s, 3H),
1.87–1.94 (m, 1H), 2.02–2.09 (m, 4H), 2.25–2.29 (m, 5H), 2.45–2.53
(m, 1H), 3.96 (d, J = 7.0 Hz, 1H), 4.15 (AB, JAB = 8.2 Hz, 1H), 4.25 (d,
J = 2.0 Hz, 1H), 4.15 (AB, JAB = 8.2 Hz, 1H), 4.41 (dd, J1 = 10.5 Hz,
J2 = 6.6 Hz, 1H), 4.86–4.88 (m, 1H), 4.97 (d, J = 8.0 Hz, 1H), 5.18 (d,
J = 2.0 Hz, 1H), 5.59 (d, J = 7.0 Hz, 1H), 6.57 (d, J = 73.2 Hz, 1H),
7.36 (d, J = 8.0 Hz, 1H), 7.50 (t, J = 8.0 Hz, 1H), 7.90 (s, 1H), 7.94 (d,
J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 5.02, 5.42, 6.15,
7.05, 7.13, 10.59, 14.76, 20.75, 22.42, 26.49, 37.45, 39.97, 43.15,
47.09, 58.40, 68.47, 72.82, 75.95, 76.17, 76.70, 79.76, 80.92, 84.20,
113.23, 115.83 (t, J = 260 Hz), 118.43, 120.94, 125.14, 127.37,
130.27, 131.68, 135.89, 139.70, 151.23, 166.14, 170.23, 205.79; 19F
NMR (376 MHz, CDCl3, 25 °C) δ −80.99 (ABq, J = 167 Hz, 2F).
C
40H57O11Si+:741.3665, Found: 741.3673 (Δ = −1.08 ppm).
4.3.14. 2-Debenzoyl-7-TES-2-(3-methylbenzoyl)-10-deacetyl-10-N,N-
dimethyl-carbamoyl-baccatin III (7d-02)
In the same manner as that for 7c-02, 7d-02 was synthesized from
6-02 (101 mg, 0.150 mmol) and N,N-dimethylcarbamoyl chloride
(15 μl, 0.158 mmol) in 94% yield (454 mg) as a white solid: m.p.
146–148 °C; 1H NMR (500 MHz, CDCl3) δ 0.58 (m, 6H), 0.91 (t,
J = 8.1 Hz, 9H), 1.04 (s, 3H), 1.19 (s, 3H), 1.64 (s, 1H), 1.65 (s, 3H),
1.67 (s, 3H), 1.86 (m, 1H), 2.12 (d, J = 4.8 Hz, 1H), 2.25 (m, 8H), 2.41
(s, 3H), 2.51 (m, 1H), 2.93 (s, 3H), 3.07 (s, 3H), 3.88 (d, J = 7.0 Hz,
1H), 4.13 (d, J = 8.3 Hz, 1H), 4.29 (d, J = 8.3 Hz, 1H), 4.47 (dd,
J = 6.8 Hz, J = 10.5 Hz, 1H), 4.81 (br s, 1H), 4.96 (d, J = 8.1 Hz, 1H),
5.60 (d, J = 7.1 Hz, 1H), 6.37 (s, 1H), 7.34 (t, J = 7.6 Hz, 1H), 7.39 (d,
J = 7.6 Hz, 1H), 7.89 (d, J = 7.6 Hz, 1H), 7.93 (s, 1H); 13C NMR
(125 MHz, CDCl3) δ 5.4, 5.5, 6.9, 10.1, 15.0, 20.4, 21.6, 22.8, 27.1,
36.4, 36.7, 37.4, 38.4, 42.9, 47.5, 58.6, 68.2, 72.5, 74.8, 76.8, 79.0,
81.1, 84.5, 127.4, 128.7, 129.5, 131.0, 133.4, 134.5, 138.5, 143.8,
155.5, 167.4, 170.9, 203.5. HRMS (TOF) Calcd for C39H57NO11SiNa+
766.3593, Found: 766.3594 (Δ = −0.1 ppm).
4.3.12. 2-Debenzoyl-7-TES-2-(3-methylbenzoyl)-10-deacetyl-10-
propanoylbaccatin III (7b-02)
To a solution of 5b-02 (72 mg, 0.117 mmol) and imidazole (32 mg,
0.469 mmol) in DMF (6 mL) was added TES-Cl (58 µl, 0.351 mmol)
dropwise at 0 °C. The mixture was stirred at 0 °C for 45 min. The
progress of the reaction was monitored by TLC. Upon completion, the
reaction was quenched with saturated NH4Cl (10 mL), and the aqueous
layer was extracted with ethyl acetate (3 × 30 mL). The combined
extracts were washed with brine (3 × 30 mL), dried over MgSO4 and
4.3.15. 2-Debenzoyl-7-TES-2-(3-methylbenzoyl)-10-deacetyl-10-
methoxycarbonyl-baccatin III (7e-02)
In the same manner as that for 7c-02, 7e-02 was synthesized from
6-02 (102 mg, 0.152 mmol) and methyl chloroformate (13 μl,
0.159 mmol) in 72% yield (80 mg) as a white solid: m.p. 110–112 °C 1H
11

C. Wang, et al.
BioorganicChemistry95(2020)103523
NMR (500 MHz, CDCl3) δ 0.59 (m, 6H), 0.93 (t, J = 8.2 Hz, 9H), 1.05
(s, 3H), 1.17 (s, 3H), 1.63 (s, 1H), 1.68 (s, 3H), 1.88 (m, 1H), 2.10 (br s,
1H), 2.20 (s, 3H), 2.27 (m, 5H), 2.42 (s, 3H), 2.53 (m, 1H), 3.81 (s, 3H),
3.84 (d, J = 7.1 Hz, 1H), 4.13 (d, J = 8.4 Hz, 1H), 4.30 (d, J = 8.4 Hz,
1H), 4.48 (dd, J = 6.9 Hz, J = 10.5 Hz, 1H), 4.86 (m, 1H), 4.96 (d,
J = 8.2 Hz, 1H), 5.60 (d, J = 7.1 Hz, 1H), 6.28 (s, 1H), 7.35 (t,
J = 7.7 Hz, 1H), 7.41 (d, J = 7.7 Hz, 1H), 7.89 (d, J = 7.7 Hz, 1H),
7.93 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 5.4, 5.5, 6.9, 10.1, 15.0,
20.4, 21.6, 22.8, 27.1, 36.4, 36.7, 37.4, 38.4, 42.9, 47.5, 58.6, 68.2,
72.5, 74.8, 76.8, 79.0, 81.1, 84.5, 127.4, 128.7, 129.5, 131.0, 133.4,
134.5, 138.5, 143.8, 155.5, 167.4, 170.9, 203.5. HRMS (TOF) Calcd for
followed by the dropwise addition of 1.2 equiv. of cyclopropane-
carbonyl chloride (19 μl, 0.199 mmol). The mixture was stirred and the
progress of the reaction was monitored by TLC (hexanes:ethyl
acetate = 70:30). Upon completion, the reaction was quenched with
saturated NH4Cl (5 mL), diluted with water and extracted with ethyl
acetate (3 × 5 mL). The organic layers were collected and combined,
washed with brine (2 × 5 mL), dried over anhydrous MgSO4, and
concentrated in vacuo. Purification of the crude product by column
chromatography on silica gel (hexanes:ethyl acetate = 67:33) to afford
7c-05 (0.154 mmol, 93%) as a white solid: m.p. 201–202 °C; 1H NMR
(400 MHz, CDCl3, ppm) δ 0.65–0.50 (m, 6H), 0.92 (t, J = 7.9 Hz, 9H),
1.06 (s, 3H), 1.20 (s, 3H), 1.68 (s, 2H), 1.76 (m, 1H), 1.83–1.93 (m,
1H), 2.20 (d, J = 1.2 Hz, 2H), 2.30–2.23 (m, 4H), 2.53 (ddd, J = 14.4,
9.6, 6.8 Hz, 1H), 3.89 (d, J = 7.0 Hz, 1H), 4.13 (d, J = 7.7 Hz, 1H),
4.27 (d, J = 8.1 Hz, 1H), 4.48 (dd, J = 10.4, 6.7 Hz, 1H), 4.84 (t,
J = 8.1 Hz, 1H), 4.97 (d, J = 7.8 Hz, 1H), 5.61 (d, J = 7.1 Hz, 1H),
6.47 (s, 1H), 7.45 (d, J = 8.9 Hz, 1H), 7.53 (dd, J = 10.6, 5.3 Hz, 1H),
8.00 (s, 1H), 8.04 (dd, J = 7.7, 1.2 Hz, 1H); 13C NMR (100 MHz, CDCl3,
ppm) δ 5.42, 6.91, 8.72, 8.84, 10.05, 13.15, 15.08, 20.29, 22.53, 26.91,
37.32, 38.42, 42.86, 47.43, 58.71, 67.90, 72.49, 75.53, 75.71, 76.52,
78.97, 80.86, 84.41, 119.28, 121.85 (q, J = 259 Hz), 122.29, 126.24,
128.67, 130.40, 131.64, 132.60, 144.53, 149.42, 165.71, 170.81,
173.36, 202.62; 19F NMR (376 MHz, CDCl3) δ −57.87 (s, 3F). HRMS
(TOF) m/z: Calcd. For C40H53F3O12SiNa+, 833.3150. Found, 833.3150.
C
37H56NO12Si+ 748.3723, Found: 748.3727 (Δ = −0.53 ppm).
4.3.16. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-7-TES-baccatin III (7a-
05)
Compound 5a-05 (400 mg, 0.596 mmol) was dissolved in DMF
(8 mL) and cooled to 0 °C under inert conditions. To this mixture was
added 4 equiv. of imidazole (162 mg, 2.39 mmol) and the mixtures was
allowed to stir for 5 min. Then, TES-Cl (0.30 mL, 1.79 mmol) was added
dropwise. The mixture was stirred and allowed to warm to room tem-
perature while being monitored by TLC (hexanes: ethyl
acetate = 60:40). Upon completion the reaction was quenched with
saturated aqueous NH4Cl (2 mL) and extracted with ethyl acetate
(3 × 35 mL). The organic layer was collected, washed with brine
(3 × 45 mL), dried over anhydrous MgSO4, and concentrated in vacuo.
Purification of the crude product by column chromatography on silica
gel (hexanes: ethyl acetate = 60:40) to afford 7a-05 (409 mg,
0.521 mmol, 88%) as a white solid: 1H NMR (400 MHz, CDCl3, ppm) δ
0.56–0.62 (m, 6H), 0.93 (t, J = 8.0 Hz, 9H), 1.05 (s, 3H), 1.20 (s, 3H),
1.69 (s, 3H), 1.85–1.92 (m, 1H), 2.07 (d, J = 4.8 Hz, 1H), 2.19 (s, 3H),
2.20 (d, J = 1.0 Hz, 1H), 2.26–2.27 (m, 4H), 2.51–2.59 (m, 1H), 3.90
(d, J = 7.0 Hz, 1H), 4.14 (AB, JAB = 8.1 Hz, 1H), 4.28 (AB,
JAB = 8.1 Hz, 1H), 4.47 (dd, J1 = 10.5 Hz, J2 = 6.8 Hz, 1H), 4.83–4.86
(m, 1H), 4.98 (d, J = 8.1 Hz, 1H), 5.62 (d, J = 7.0 Hz, 1H), 6.47 (s,
1H), 7.46 (d, J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 8.00 (s, 1H),
8.04 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 5.50, 6.96,
10.12, 15.20, 20.25, 21.16, 22.68, 27.04, 37.43, 38.36, 42.95, 47.47,
58.86, 68.12, 72.57, 75.53, 75.96, 76.60, 77.44, 79.05, 81.02, 84.44,
122.40, 126.35, 128.77, 130.46, 131.66, 132.84, 144.23, 149.50,
165.84, 169.56, 170.96, 202.29. HRMS (TOF) m/z: Calcd. For
4.3.19. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-7-TES-10-(N,N-
dimethylcarbamoyl)-10-deacetylbaccatin III (7d-05)
In the same manner as that for 7c-05, 7d-05 was synthesized from
6d-05 (394 mg, 0.530 mmol) and N,N-dimethylcarbamoyl chloride
(0.059 mL, 0.636 mmol) in 77% yield (332 mg) as a white solid: 1H
NMR (400 MHz, CDCl3, ppm) δ 0.57–0.64 (m, 6H), 0.91–0.95 (m, 9H),
1.06 (s, 3H), 1.20 (s, 9H), 1.69 (s, 3H), 1.85–1.91 (m, 1H), 2.26–2.27
(m, 7H), 2.51–2.58 (m, 1H), 2.95 (s, 3H), 3.09 (s, 3H), 3.92 (d,
J = 7.0 Hz, 1H), 4.14 (AB, JAB = 8.2 Hz, 1H), 4.28 (AB, JAB = 8.2 Hz,
1H), 4.50 (dd, J1 = 10.4 Hz, J2 = 6.7 Hz, 1H), 4.84 (t, J = 8.0 Hz, 1H),
4.98 (d, J = 8.3 Hz, 1H), 6.40 (s, 1H), 5.62 (d, J = 7.0 Hz, 1H), 7.46 (d,
J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 8.01 (s, 1H), 8.06 (d,
J = 8.0 Hz, 1H);13C NMR (100 MHz, CDCl3, ppm) δ 5.49, 6.95, 10.14,
15.09, 20.39, 22.70, 27.10, 36.44, 36.78, 37.42, 38.35, 42.92, 47.48,
58.64, 68.20, 72.56, 75.60, 76.62, 77.43, 79.13, 81.05, 84.51, 121.92,
122.42, 126.33, 128.75, 130.44, 131.71, 133.28, 143.92, 149.49,
155.52, 165.86, 170.94, 203.39.
C
38H51F3O12SiH+, 785.3175. Found, 785.3178.
4.3.17. 2-Debenzoyl-7-TES-2-(3-trifluromethoxybenzoyl)-10-propanoyl-
10-deacetylbaccatin III (7b-05)
4.3.20. 10-Deacetyl-2-debenzoyl-10-methoxycarbonyl-7-TES-2-(3-
trifluoromethoxybenzoyl)-baccatin III (7e-05)
In the same manner as that for 7a-05, 7b-05 was synthesized from
5b-05 (400 mg, 0.605 mmol) and TES-Cl (0.32 mL, 1.82 mmol) in 94%
yield (454 mg) as a white solid: m.p. 202–205 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 0.58 (d, J = 7.1 Hz, 6H), 0.92 (t, J = 7.8 Hz, 9H), 1.03
(s, 3H), 1.25–1.19 (m, 6H), 1.65 (m, 3H), 1.87 (m, 1H), 2.26 (m, 9H),
2.39–2.60 (m, 4H), 3.89 (d, J = 6.8 Hz, 1H), 4.12 (d, J = 8.0 Hz, 1H),
4.26 (d, J = 8.0 Hz, 1H), 4.49 (dd, J = 9.8, 6.9 Hz, 1H), 4.83 (s, 1H),
4.96 (d, J = 9.0 Hz, 1H), 5.61 (d, J = 6.8 Hz, 1H), 6.47 (s, 1H), 7.45 (d,
J = 7.6 Hz, 1H), 7.52 (dd, J = 8.0, 2.0 Hz, 1H), 7.99 (s, 1H), 8.04 (d,
J = 7.5 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 5.3, 6.7, 9.2, 9.9,
14.9, 20.1, 26.8, 27.7, 37.2, 42.7, 47.3, 58.6, 67.8, 72.3, 75.3, 75.6,
76.4, 76.7, 77.2, 77.3, 116.5, 116.7, 121.7 (q, J = 259 Hz), 122.2,
124.5, 126.1, 128.5, 130.2, 131.5, 132.6, 144.1, 149.3, 165.6, 170.7,
172.7, 202.2; 19F NMR (376 MHz, CDCl3) δ −57.87 (s, 3F). HRMS
(TOF) m/z: Calcd. For C39H53F3O12Si+, 798.3445. Found, 798.3477
(Δ = 4.0 ppm).
In the same manner as that for 7c-05, 7e-05 was synthesized from
6e-05 (364 mg, 0.490 mmol) and methyl chloroformate (0.045 mL,
0.59 mmol) in 89% yield (351 mg) as a white solid: 1H NMR (400 MHz,
CDCl3, ppm) δ 0.58–0.64 (m, 6H), 0.90–0.97 (m, 9H), 3.04 (s, 3H), 1.18
(s, 3H), 1.70 (s, 3H), 1.86–1.92 (m, 1H), 2.21 (d, J = 1.0 Hz, 1H),
2.26–2.28 (m, 5H), 2.52–2.59 (m, 1H), 3.83 (s, 3H), 3.86 (d,
J = 7.0 Hz, 1H), 4.13 (AB, JAB = 8.2 Hz, 1H), 4.28 (AB, JAB = 8.2 Hz,
1H), 4.50 (dd, J1 = 10.4 Hz, J2 = 6.7 Hz, 1H), 4.87 (t, J = 8.0 Hz, 1H),
4.98 (d, J = 8.1 Hz, 1H), 5.61 (d, J = 7.0 Hz, 1H), 6.30 (s, 1H), 7.46 (d,
J = 8.2 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 8.00 (s, 1H), 8.05 (dd,
J1 = 7.7 Hz, J2 = 1.2 Hz, 1H).
4.3.21. 2-Debenzoyl-7-TES-2-(3-difluromethoxybenzoyl)baccatin III (7a-
06)
In the same manner as that for 7a-05, 7a-06 was synthesized from
5a-06 (133 mg, 0.204 mmol) and TES-Cl (0.11 mL, 0.61 mmol) in 93%
yield (148 mg) as a white solid: m.p. 197–198 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 0.55–0.61 (m, 6H), 0.92 (t, J = 7.9 Hz, 9H), 1.04 (s, 3H),
1.19 (s, 3H), 1.57 (d, J = 8.1 Hz, 2H), 1.68 (s, 3H), 1.84–1.96 (m, 1H),
2.07 (d, J = 5.0 Hz, 1H), 2.18 (m, 6H), 2.26 (d, J = 7.5 Hz, 5H),
2.49–2.57 (m, 1H), 3.88 (d, J = 7.0 Hz, 1H), 4.13 (d, J = 8.2 Hz, 1H),
4.3.18. 2-Debenzoyl-2-(3-trifluromethoxybenzoyl)-7-TES-10-
cyclopropanecarbonyl-10-deacetyl-baccatin III (7c-05)
Compound 6c-05 (123 mg, 0.166 mmol) was dissolved in THF
(3.7 mL) and cooled to −40 °C under inert conditions. To the mixture
1.0 M LiHMDS in tert-butyl methyl ether (0.2 mL) was added dropwise,
12

C. Wang, et al.
BioorganicChemistry95(2020)103523
4.29 (d, J = 8.2 Hz, 1H), 4.49 (dd, J = 10.4, 6.7 Hz, 1H), 4.83 (dd,
J = 13.0, 6.8 Hz, 1H), 4.96 (d, J = 7.9 Hz, 1H), 5.61 (d, J = 7.0 Hz,
1H), 6.46 (s, 1H), 6.66 (t, J = 72.0 Hz, 1H), 7.37 (d, J = 7.8 Hz, 1H),
7.49 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.90 (s, 1H), 7.96 (d,
J = 7.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 5.29, 6.75, 9.92,
14.97, 20.05, 20.95, 22.52, 26.83, 37.23, 38.19, 42.76, 47.25, 58.66,
67.93, 72.36, 75.20, 75.76, 76.44, 76.70, 77.22, 77.34, 78.81, 80.81,
84.24, 115.60 (t, J = 263 Hz), 120.97, 125.10, 127.23, 130.16, 131.28,
132.65, 144.00, 151.02, 165.98, 169.35, 170.82, 202.11; 19F NMR
(376 MHz, CDCl3) δ −81.06 (ABq, J = 169 Hz, 2F). HRMS (TOF) m/z:
Calcd. For C38H52F2O12Si+, 766.3212. Found, 767.322 (Δ = 1 ppm).
144.06, 151.18, 151.21, 155.51, 166.16, 170.95, 203.46. 19F NMR
(376 MHz, CDCl3, 25 °C) δ −81.06 (ABq, J = 167 Hz, 2F).
4.3.25. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)-10-deacetyl-10-
methoxycarbonyl-7-TES-baccatin III (7e-06)
In the same manner as that for 7c-05, 7e-06 was synthesized from
6e-06 (355 mg, 0.462 mmol) and methyl chloroformate (53 mg,
0.554 mmol) in 87% yield (321 mg) as a white solid: m.p. 115–117 °C;
1H NMR (400 MHz, CDCl3, ppm) δ 0.58–0.64 (m, 6H), 0.92–0.96 (m,
9H), 1.06 (s, 3H), 1.18 (s, 3H), 1.69 (s, 3H), 1.85–1.91 (m, 1H), 2.20 (s,
3H), 2.26–2.28 (m, 5H), 2.51–2.59 (m, 1H), 3.82 (s, 3H), 3.86 (d,
J = 7.0 Hz, 1H), 4.13 (AB, JAB = 8.2 Hz, 1H), 4.29 (AB, JAB = 8.2 Hz,
1H), 4.50 (dd, J1 = 10.4 Hz, J2 = 6.8 Hz, 1H), 4.86 (t, 1H), 4.97 (d,
J = 9.0 Hz, 1H), 5.61 (d, J = 7.0 Hz, 1H), 6.30 (s, 1H), 6.58 (d,
J = 73.2 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.49 (t,
J = 8.0 Hz, 1H), 7.90 (s, 1H), 8.05 (d, J = 8.0 Hz, 1H); 13C NMR
(100 MHz, CDCl3, ppm) δ 5.55, 6.98, 10.10, 15.27, 20.15, 22.71, 26.93,
37.41, 38.38, 42.86, 47.40, 55.26, 58.74, 68.10, 72.57, 75.36, 76.64,
77.43, 79.00, 79.36, 80.98, 84.42, 113.20, 115.81, 118.41, 121.15,
125.30, 127.43, 130.36, 131.46, 132.50, 145.05, 151.19, 151.22,
155.05, 166.15, 171.04, 201.79; 19F NMR (376 MHz, CDCl3, 25 °C) δ
−81.06 (ABq, J = 167 Hz, 2F). HRMS (TOF) m/z: Calcd. For
4.3.22. 2-Debenzoyl-7-TES-2-(3-difluromethoxybenzoyl)-10-propanoyl-
10-deacetyl-baccatin III (7b-06)
In the same manner as that for 7a-05, 7b-06 was synthesized from
5b-06 (323 mg, 0.484 mmol) and TES-Cl (0.25 mL, 1.45 mmol) in 85%
yield (321 mg) as a white solid: m.p. 104–106 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 0.56–0.62 (m, 6H), 0.91–0.95 (m, 9H), 1.04 (s, 3H),
1.20–1.24 (m, 6H), 1.59 (bs, OH), 1.68 (s, 3H), 1.85–1.91 (m, 1H), 2.21
(s, 3H), 2.26–2.28 (m, 5H), 2.40–2.55 (m, 1H), 3.90 (d, J = 7.0 Hz,
1H), 4.14 (AB, JAB = 8.2 Hz, 1H), 4.30 (AB, JAB = 8.2 Hz, 1H), 4.50
(dd, J1 = 10.4 Hz, J2 = 6.7 Hz, 1H), 4.84 (t, 1H), 4.98 (d, J = 8.1 Hz,
1H), 5.62 (d, J = 7.0 Hz, 1H), 6.49 (s, 1H), 6.58 (d, J = 73.2 Hz, 1H),
7.37 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.50 (t, J = 7.8 Hz, 1H), 7.91
(s, 1H), 7.97 (d, J = 7.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ
5.50, 6.97, 9.44, 10.13, 15.17, 20.28, 22.77, 27.03, 27.91, 37.43,
38.40, 42.95, 47.46, 58.84, 68.13, 72.56, 75.42, 75.77, 76.65, 77.43,
79.04, 81.02, 84.46, 113.20, 115.80, 118.41, 121.17, 125.29, 127.43,
130.36, 131.48, 132.90, 144.17, 151.22, 166.19, 171.02, 172.98,
202.41; 19F NMR (376 MHz, CDCl3) δ −81.06 (ABq, J = 167 Hz, 2F).
HRMS (TOF) m/z: Calcd. For C39H54F2O12SiH+, 781.3425. Found,
781.3425.
C
38H52F2NO13SiNH4+, 800.8483. Found, 800.8486.
4.3.26. 2-Debenzoyl-2-(3-methylbenzoyl)-7-TES-10-deacetyl-10-
propanoyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel (9b-02)
To a solution of 7b-02 (64 mg, 0.088 mmol) and 8 (42 mg,
0.105 mmol) in THF (2 mL) was added LiHMDS (1.0 M in THF, 105 µl,
0.105 mmol) dropwise at −40 °C. The mixture was stirred at −40 °C
for 2 h. The progress of the reaction was monitored by TLC. Upon
completion, the reaction was quenched with saturated NH4Cl (10 mL),
and the aqueous layer was extracted with ethyl acetate (3 × 30 mL).
The combined extracts were washed with brine (3 × 30 mL), dried over
MgSO4 and concentrated in vacuo. The residue was purified by flash
chromatography on silica gel to afford 9b-02 (83 mg, 84%) as a white
solid: m.p. 140–142 °C; 1H NMR (500 MHz, CDCl3) δ 0.57 (m, 6H), 0.91
(t, J = 8.1 Hz, 9H), 1.11 (m, 21H), 1.16 (s, 3H), 1.17 (s, 1H), 1.21 (m,
6H), 1.25 (s, 1H), 1.33 (s, 9H), 1.59 (s, 1H), 1.67 (m, 4H), 1.74 (s, 3H),
1.78 (d, J = 0.9 Hz, 3H), 1.88 (m, 1H), 2.01 (d, J = 0.9 Hz, 3H), 2.36
(m, 5H), 2.42 (s, 3H), 2.52 (m, 3H), 3.84 (d, J = 7.1 Hz, 1H), 4.18 (d,
J = 8.6 Hz, 1H), 4.31 (d, J = 8.5 Hz, 1H), 4.43 (d, J = 2.9 Hz, 1H),
4.47 (dd, J = 6.7 Hz, J = 10.6 Hz, 1H), 4.78 (m, 2H), 4.94 (d,
J = 8.2 Hz, 1H), 5.33 (d, J = 8.7 Hz, 1H), 5.67 (d, J = 7.1 Hz, 1H),
6.08 (t, J = 9.3 Hz, 1H), 6.49 (s, 1H), 7.34 (t, J = 7.7 Hz, 1H), 7.41 (d,
J = 7.7 Hz, 1H), 7.90 (d, J = 7.7 Hz, 1H), 7.93 (s, 1H); 13C NMR
(125 MHz, CDCl3) δ 5.5, 7.0, 9.4, 10.3, 12.8, 14.6, 18.2, 18.3, 18.8,
21.5, 21.6, 22.8, 25.9, 26.5, 27.8, 28.5, 29.9, 35.7, 37.4, 43.5, 47.0,
52.2, 58.6, 72.1, 72.5, 75.1, 75.1, 75.6, 76.8, 79.1, 79.6, 84.5, 122.4,
127.6, 128.7, 129.5, 131.0, 133.6, 134.5, 136.4, 138.5, 141.1, 155.4,
167.2, 170.0, 172.1, 172.9, 202.2. HRMS (TOF) m/z: Calcd. For
C60H95NO15Si2Na+ 1148.6132, Found: 1148.6133 (Δ = −0.04 ppm).
4.3.23. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)-7-TES-10-deacetyl-10-
cyclopropane-carbonylbaccatin III (7c-06)
In the same manner as that for 7c-05, 7c-06 was synthesized from
6e-06 (338 mg, 0.466 mmol) and cyclopropanecarbonyl chloride
(58 mg, 0.559 mmol) in 86% yield (318 mg) as a white solid: 1H NMR
(400 MHz, CDCl3, ppm) δ 0.56–0.61 (m, 6H), 0.93 (t, J = 7.9 Hz, 9H),
1.06 (s, 3H), 1.20 (s, 3H), 1.69 (s, 2H), 1.73 (m, 1H), 1.80–1.91 (m,
1H), 2.20 (d, J = 1.2 Hz, 2H), 2.26–2.28 (m, 4H), 2.50–2.54 (m, 1H),
3.89 (d, J = 7.0 Hz, 1H), 4.14 (d, J = 8.0 Hz, 1H), 4.30 (d, J = 8.0 Hz,
1H), 4.48 (dd, J = 10.4, 6.7 Hz, 1H), 4.85 (t, J = 8.1 Hz, 1H), 4.97 (d,
J = 7.8 Hz, 1H), 5.62 (d, J = 7.0 Hz, 1H), 6.47 (s, 1H), 6.58 (t,
J = 73.1 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.48 (t,
J = 8.0 Hz, 1H), 7.91 (s, 1H), 7.97 (d, J = 8.0 Hz, 1H); 19F NMR
(376 MHz, CDCl3) δ −57.87 (s, 3F). 19F NMR (376 MHz, CDCl3, 25 °C)
δ −81.05 (ABq, J = 167 Hz, 2F).
4.3.24. 2-Debenzoyl-2-(3-difluromethoxybenzoyl)-7-TES-10-deacetyl-10-
N,N-demthyl-carbamoylbaccatin III (7d-06)
In the same manner as that for 7c-05, 7d-06 was synthesized from
6d-06 (349 mg, 0.481 mmol) and N,N-demthylcarbamoyl chloride
(62 mg, 0.577 mmol) in 84% yield (321 mg) as a white solid: H-NMR
(400 MHz, CDCl3, ppm) δ 0.56–0.62 (m, 6H), 0.90–0.94 (m, 9H), 1.04
(s, 3H), 1.18 (s, 3H), 1.67 (s, 3H), 1.82–1.92 (m, 1H), 2.24 (s, 3H),
2.26–2.28 (m, 5H), 2.48–2.57 (m, 1H), 2.93 (s, 3H), 3.07 (s, 3H), 3.90
(d, J = 7.0 Hz, 1H), 4.13 (AB, JAB = 8.2 Hz, 1H), 4.28 (AB,
JAB = 8.2 Hz, 1H), 4.49 (dd, J1 = 10.4 Hz, J2 = 6.8 Hz, 1H), 4.81 (t,
1H), 4.97 (d, J = 8.2 Hz, 1H), 5.61 (d, J = 7.0 Hz, 1H), 6.39 (s, 1H),
6.57 (d, J = 73.2 Hz, 1H), 7.36 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H),
7.48 (t, J = 8.0 Hz, 1H), 7.90 (s, 1H), 7.96 (d, J = 8.0 Hz, 1H); 13C
NMR (100 MHz, CDCl3, ppm) δ 5.45, 5.98, 6.77, 6.92, 10.11, 15.05,
17.88, 20.38, 22.69, 22.80, 27.04, 36.40, 37.39, 38.42, 42.89, 47.44,
58.60, 68.09, 72.52, 75.48, 76.64, 77.43, 79.05, 80.98, 84.49, 113.19,
115.79, 118.39, 121.12, 125.22, 127.37, 130.32, 131.51, 133.15,
4.3.27. 2-Debenzoyl-2-(3-methylbenzoyl)-7-TES-10-deacetyl-10-
cyclopropane-carbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-
dephenyldocetaxel (9c-02)
In the same manner as that for 9b-02, 9c-02 was synthesized from
7c-02 (178 mg, 0.240 mmol) and 8 (115 mg, 0.289 mmol) in 81% yield
(222 mg) as a white solid: m.p. 153–154 °C; 1H NMR (500 MHz, CDCl3)
δ 0.56 (m, 6H), 0.91 (m, 11H), 1.10 (m, 21H), 1.19 (m, 4H), 1.23 (s,
3H), 1.33 (s, 9H), 1.68 (m, 4H), 1.74 (m, 4H), 1.77 (d, J = 1.1 Hz, 3H),
1.88 (m, 1H), 2.00 (d, J = 1.1 Hz, 3H), 2.36 (m, 5H), 2.41 (s, 3H), 2.49
(m, 1H), 3.83 (d, J = 7.1 Hz, 1H), 4.17 (d, J = 8.4 Hz, 1H), 4.30 (d,
J = 8.4 Hz, 1H), 4.45 (m, 2H), 4.76 (m, 1H), 4.81 (m, 1H), 4.94 (d,
J = 7.8 Hz, 1H), 5.33 (d, J = 8.7 Hz, 1H), 5.67 (d, J = 7.2 Hz, 1H),
6.08 (t, J = 8.9 Hz, 1H), 6.48 (s, 1H), 7.34 (t, J = 7.7 Hz, 1H), 7.40 (d,
J = 7.7 Hz, 1H), 7.90 (d, J = 7.7 Hz, 1H), 7.93 (s, 1H); 13C NMR
13

C. Wang, et al.
BioorganicChemistry95(2020)103523
(125 MHz, CDCl3) δ 5.5, 7.0, 8.8, 9.0, 10.3, 12.7, 13.2, 14.5, 18.17,
18.24, 18.8, 21.5, 22.7, 25.9, 26.5, 28.5, 35.7, 37.4, 43.4, 47.0, 52.2,
58.5, 72.1, 72.4, 75.0, 75.1, 75.5, 76.8, 79.1, 79.6, 81.3, 84.5, 122.4,
127.6, 128.7, 129.5, 131.0, 133.6, 134.5, 136.3, 138.4, 141.1, 155.3,
167.2, 169.9, 172.1, 173.3, 202.3. HRMS (TOF) m/z: Calcd. For
71.96, 72.39, 75.00, 75.49, 75.68, 76.60, 115.93, 120.41, 122.23,
124.87, 127.41, 130.35, 131.48, 133.44, 136.39, 141.19, 151.42,
155.37, 165.95, 170.06, 172.10, 172.81, 202.12.
4.3.31. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-7-TES-10-
C
61H95NO15Si2Na+ 1160.6132, Found: 1160.6132 (Δ = 0.07 ppm).
cyclopropanecarbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-
dephenyldocetaxel (9c-05)
4.3.28. 2-Debenzoyl-2-(3-methylbenzoyl)-7-TES-10-deacetyl-10-N,N-
dimethyl-carbamoyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-
In the same manner as that for 9b-02, 9c-05 was synthesized from
7c-05 (121 mg, 0.15 mmol) and 8 (72 mg, 0.18 mmol) in 88% yield
(159 mg) as a white solid: 1H NMR (400 MHz, CDCl3) δ 0.55 (m, 6H),
0.90 (m, 9H), 1.10 (s, 21H), 1.33 (s, 3H), 1.61–1.79 (m, 9H), 2.01 (d,
J = 8.4 Hz, 3H), 2.33 (s, 5H), 2.50 (m, 1H), 3.84 (d, J = 6.4 Hz, 1 H),
4.06–4.17(m, 2 H), 4.26 (d, J = 8.0 Hz, 1 H), 4.44 (m, 2 H), 4.74 (s,
1H), , 4.83 (m, 1 H), 4.94 (d, J = 8.8 Hz, 1 H), 5.32 (d, J = 8.4 Hz, 1
H), 5.66 (d, J = 6.8 Hz, 1H), 6.04 (t, J = 8.8 Hz, 1 H), 6.48 (s, 1H),
7.44 (d, J = 7.6 Hz, 1 H), 7.51 (t, J = 7.6 Hz, 1H), 7.97 (s, 1H), 8.04 (d,
J = 7.6 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ 201.98, 173.01, 171.93,
171.12, 169.71, 165.32, 155.16, 149.15, 141.08, 136.32, 133.16,
131.44, 130.19, 128.66, 125.95, 122.14, 121.94, 121.67, 119.10,
84.26, 80.98, 79.36, 78.79, 77.32, 77.20, 77.00, 76.68, 76.34, 75.51,
75.26, 74.74, 72.18, 71.89, 60.35, 58.27, 52.00, 46.67, 43.18, 37.09,
35.30, 28.19, 26.21, 25.58, 22.30, 21.21, 20.97, 18.33, 17.98, 17.91,
14.31, 14.14, 12.90, 12.51, 9.95, 8.71, 8.61, 6.70, 5.26; 19F NMR
(376 MHz, CDCl3) δ −57.83 (s, 3 F).
dephenyldocetaxel (9d-02)
In the same manner as that for 9b-02, 9d-02 was synthesized from
7-02d (67 mg, 0.090 mmol) and 8 (43 mg, 0.108 mmol) in 92% yield
(94 mg) as a white solid: m.p. 167–169 °C; 1H NMR (700 MHz, CDCl3) δ
0.58 (m, 6H), 0.90 (t, J = 8.0 Hz, 9H), 1.11 (m, 21H), 1.18 (s, 3H), 1.21
(s, 3H), 1.32 (s, 9H), 1.67 (s, 3H), 1.73 (m, 4H), 1.76 (s, 3H), 1.87 (m,
1H), 2.04 (s, 3H), 2.31 (m, 1H), 2.38 (m, 7H), 2.50 (m, 1H), 2.92 (s,
3H), 3.04 (s, 3H), 3.84 (d, J = 7.0 Hz, 1H), 4.17 (d, J = 8.5 Hz, 1H),
4.29 (d, J = 8.5 Hz, 1H), 4.42 (d, J = 2.9 Hz, 1H), 4.46 (dd,
J = 6.7 Hz, J = 10.5 Hz, 1H), 4.75 (br s, 1H), 4.81 (br s, 1H), 4.93 (d,
J = 7.9 Hz, 1H), 5.32 (d, J = 8.8 Hz, 1H), 5.66 (d, J = 7.2 Hz, 1H),
6.08 (t, J = 8.6 Hz, 1H), 6.39 (s, 1H), 7.32 (t, J = 7.7 Hz, 1H), 7.38 (d,
J = 7.7 Hz, 1H), 7.88 (d, J = 7.7 Hz, 1H), 7.92 (s, 1H); 13C NMR
(175 MHz, CDCl3) δ 5.5, 6.9, 10.2, 12.7, 14.5, 18.1, 18.2, 18.8, 21.5,
21.6, 22.7, 25.9, 26.5, 28.4, 35.7, 36.3, 36.8, 37.3, 43.4, 46.9, 58.3,
72.0, 72.4, 75.1, 75.4, 76.5, 76.7, 79.0, 79.5, 81.2, 84.5, 122.3, 127.5,
128.6, 129.5, 130.9, 133.9, 134.5, 136.3, 138.4, 140.8, 155.3, 167.2,
169.9, 172.0, 203.2. HRMS (TOF) m/z: Calcd. For C60H96N2O15Si2H+
calcd: 1141.6422, Found: 1141.6422 (Δ = −0.26 ppm).
4.3.32. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-7-TES-10-N,N-
dimethylcarbamoyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel
(9d-05)
In the same manner as that for 9b-02, 9d-05 was synthesized from
7d-05 (110 mg, 0.135 mmol) and 8 (65 mg, 0.162 mmol) in 91% yield
(149 mg) as a white solid: 1H NMR (500 MHz, CDCl3) δ 0.57–0.62 (m,
6H), 0.90–0.93 (m, 9H), 1.10–1.14 (m, 21H), 1.19 (s, 3H), 1.23 (s, 3H),
1.33 (s, 9H), 1.65–1.68 (m, 4H), 1.74 (s, 3H), 1.76 (s, 3H), 1.86–1.91
(m, 1H), 2.06 (s, 3H), 2.34–2.39 (m, 1H), 2.49–2.55 (m, 1H), 2.94 (s,
3H), 3.06 (s, 3H), 3.87 (d, J = 7.0 Hz, 1H), 4.16 (AB, JAB = 8.2 Hz,
1H), 4.28 (AB, JAB = 8.2 Hz, 1H), 4.42 (d, J = 2.7 Hz, 1H), 4.47 (dd,
J1 = 10.5 Hz, J2 = 6.7 Hz, 1H), 4.75–4.84 (m, 2H), 4.96 (d, J = 8.6 Hz,
1H), 5.33 (d, J = 8.6 Hz, 1H), 5.68 (d, J = 7.0 Hz, 1H), 6.07 (t,
J = 8.8 Hz, 1H), 6.42 (s, 1H), 7.45 (d, J = 8.0 Hz, 1H), 7.52 (t,
J = 8.0 Hz, 1H), 7.99 (s, 1H), 8.05 (d, J = 8.0 Hz, 1H);13C NMR
(125 MHz, CDCl3) δ 5.25, 5.49, 5.72, 6.93, 10.21, 12.51, 12.75, 12.99,
14.31, 14.53, 18.16, 18.24, 18.58, 20.89, 21.60, 22.56, 22.85, 25.47,
25.83, 26.46, 28.44, 31.79, 34.86, 35.60, 36.37, 36.79, 37.33, 43.40,
46.91, 52.19, 58.33, 72.05, 72.40, 75.45, 75.82, 75.82, 76.50, 76.60,
79.10, 79.53, 81.23, 84.54, 117.54, 119.60, 121.65, 122.22, 122.40,
123.70, 126.19, 128.89, 130.43, 131,70, 133.73, 136.50, 141.11,
149.40, 149.41, 155.35, 165.61, 169.91, 172.05, 203.19.
4.3.29. 2-Debenzoyl-2-(3-methylbenzoyl)-7-TES-10-deacetyl-10-
methoxycarbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel
(9e-02)
In the same manner as that for 9b-02, 9e-02 was synthesized from
7e-02 (67 mg, 0.092 mmol) and 8 (44 mg, 0.110 mmol) in 84% yield
(87 mg) as a white solid: m.p. 151–152 °C; 1H NMR (500 MHz, CDCl3) δ
0.58 (m, 6H), 0.92 (t, J = 8.1 Hz, 9H), 1.11 (m, 21H), 1.19 (s, 3H), 1.20
(s, 3H), 1.33 (s, 9H), 1.68 (s, 3H), 1.76 (m, 7H), 1.89 (m, 1H), 2.02 (s,
3H), 2.36 (m, 5H), 2.40 (s, 3H), 2.50 (m, 1H), 3.80 (m, 4H), 4.17 (d,
8.4 Hz, 1H), 4.30 (d, J = 8.4 Hz, 1H), 4.45 (m, 2H), 4.76 (m, 1H), 4.81
(m, 1H), 4.93 (d, J = 8.3 Hz, 1H), 5.33 (d, J = 8.8 Hz, 1H), 5.66 (d,
J = 7.2 Hz, 1H), 6.08 (t, J = 8.6 Hz, 1H), 6.27 (s, 1H), 7.33 (t,
J = 7.7 Hz, 1H), 7.40 (d, J = 7.7 Hz, 1H), 7.89 (d, J = 7.7 Hz, 1H),
7.92 (s, 1H). 13C NMR (125 MHz, CDCl3) δ 5.6, 7.0, 10.2, 12.5, 12.7,
14.6, 18.0, 18.1, 18.17, 18.24, 18.8, 21.3, 21.5, 22.7, 23.5, 24.9, 25.9,
26.4, 28.5, 29.9, 35.6, 36.8, 37.4, 43.4, 46.9, 52.2, 55.3, 58.5, 72.1,
72.5, 75.0, 75.5, 76.8, 78.8, 79.0, 79.7, 81.3, 84.4, 122.4, 127.5, 128.7,
129.5, 131.0, 133.2, 134.5, 136.4, 138.4, 141.9, 155.1, 155.4, 167.2,
170.0, 172.1, 201.5; HRMS (TOF) m/z: Calcd. For C59H93NO16Si2H+
calcd: 1128.6106. Found: 1128.6093 (Δ = 1.15 ppm).
4.3.33. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-7-TES-10-
methoxycarbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel
(9e-05)
4.3.30. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-7-TES-10-propanoyl-
2′-TIPS-3′-(2-methyl-propen-1-yl)-3′-dephenyldocetaxel (9b-05)
In the same manner as that for 9b-02, 9e-05 was synthesized from
7e-05 (351 mg, 0.438 mmol) and 8 (225 mg, 0.567 mmol) in 91% yield
(474 mg) as a white solid: m.p. 103–105 °C; 1H NMR (400 MHz, CDCl3,
ppm) δ 0.57–0.63 (m, 6H), 0.94 (m, 9H), 1.11–1.12 (m, 21H), 1.20 (s,
3H), 1.21 (s, 3H), 1.34 (s, 9H), 1.69 (s, 3H), 1.72 (s, 2H), 1.75 (s, 3H),
1.76 (s, 3H), 1.87–1.93 (m, 1H), 2.03 (s, 3H), 2.31–2.38 (m, 5H),
2.50–2.58 (m, 1H), 3.83 (m, 4H), 4.16 (AB, JAB = 8.2 Hz, 1H), 4.28
(AB, JAB = 8.2 Hz, 1H), 4.42–4.49 (m, 2H), 4.76–4.84 (m, 2H), 4.95 (d,
J = 8.6 Hz, 1H), 5.33 (d, J = 8.6 Hz, 1H), 5.67 (d, J = 7.0 Hz, 1H),
6.07 (t, J = 8.8 Hz, 1H), 6.30 (s, 1H), 7.46 (d, J = 8.0 Hz, 1H), 7.53 (t,
J = 8.0 Hz, 1H), 7.98 (s, 1H), 8.06 (d, J = 8.0 Hz, 1H);13C NMR
(100 MHz, CDCl3, ppm) δ 5.57, 6.96, 10.18, 12.76, 14.65, 18.16, 18.23,
18.59, 21.27, 22.56, 25.83, 26.37, 28.45, 35.45, 37.33, 43.37, 46.87,
52.24, 55.29, 58.47, 72.16, 72.45, 75.52, 75.67, 76.59, 77.43, 78.78,
79.02, 79.64, 81.22, 84.46, 119.35, 121.92, 122.19, 122.38, 126.22,
In the same manner as that for 9b-02, 9b-05 was synthesized from
7b-05 (307 mg, 0.393 mmol) and 8 (188 mg, 0.472 mmol) in 77% yield
(355 mg) as a white solid: 1H NMR (400 MHz, CDCl3, ppm) δ 0.54–0.60
(m, 1H), 0.90 (t, J = 8.0 Hz, 1H), 1.11 (s, 21H), 1.16 (s, 3H), 1.17–1.26
(m, 6H), 1.31 (s, 9H), 1.68 (s, 3H), 1.73–1.76 (m, 7H), 1.75 (s, 3H),
1.85–1.92 (m, 1H), 2.02 (s, 3H), 2.23–2.41 (m, 5H), 2.41–2.53 (m, 1H),
3.82 (d, J = 7.0 Hz, 1H), 4.16 (AB, JAB = 8.3 Hz, 1H), 4.30 (AB,
JAB = 8.3 Hz, 1H), 4.43 (d, J = 2.68 Hz, 1H), 4.45–4.50 (m, 1H),
4.76–4.85 (m, 2H), 4.95 (d, J = 8.2 Hz, 1H), 5.32 (d, J = 8.7 Hz, 1H),
5.67 (d, J = 7.0 Hz, 1H), 6.08 (t, J = 8.9 Hz, 1H), 6.49 (s, 1H), 7.35
(dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.47 (t, J = 8.0 Hz, 1H), 7.88 (s,
1H), 7.95 (d, J = 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3, ppm) δ 5.50,
6.93, 9.37, 10.22, 12.74, 14.52, 18.14, 18.22, 18.64, 21.48, 22.64,
22.83, 25.85, 27.80, 28.41, 35.52, 37.32, 43.42, 46.87, 52.15, 58.51,
14

C. Wang, et al.
BioorganicChemistry95(2020)103523
130.45, 131.67, 133.03, 136.57, 142.12, 149.40, 155.04, 155.39,
165.55, 170.02, 172.20, 201.46; 19F NMR (376 MHz, CDCl3) δ −57.81
(3F). HRMS (TOF) m/z: Calcd. For C59H90F3NO17Si2Na+, 1220.5592.
Found, 1220.5587.
46.91, 52.18, 58.53, 71.98, 72.41, 74.97, 75.51, 75.70, 76.60, 77.43,
79.16, 79.60, 81.23, 84.52, 113.36, 115.95, 118.54, 120.47, 122.27,
124.94, 127.47, 130.40, 131.49, 133.44, 136.42, 141.29, 151.45,
155.39, 166.02, 170.09, 172.13, 173.28, 202.25; 19F NMR (376 MHz,
CDCl3) δ −81.08 (ABq, J = 167 Hz, 2F). HRMS (TOF) m/z: Calcd. For
C61H93F2NO16Si2H+, 1190.6074. Found, 1190.6075.
4.3.34. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-7-TES-10-acetyl-2′-
TIPS-3′-(2-methyl-propen-1-yl)-3′-dephenyldocetaxel (9a-06)
In the same manner as that for 9b-05, 9a-06 was synthesized from
7a-06 (150 mg, 0.186 mmol) and 8 (92 mg, 0.222 mmol) in 92% yield
(199 mg) as a white solid: m.p. 123–125 °C; 1H NMR (400 MHz, CDCl3)
δ 0.60–0.54 (m, 6H), 0.92 (m, 9H), 1.14–1.07 (m, 21H), 1.20 (d,
J = 12.9 Hz, 6H), 1.31 (s, 9H), 1.67 (s, 6H), 1.75 (d, J = 8.2 Hz, 6H),
1.94–1.84 (m, 1H), 2.00 (s, 3H), 2.17 (s, 3H), 2.36 (s, 3H), 2.55–2.48
(m, 1H), 3.84 (d, J = 7.0 Hz, 1H), 4.16 (d, J = 8.2 Hz, 1H), 4.30 (d,
J = 8.2 Hz, 1H), 4.43 (d, J = 2.7 Hz, 1H), 4.47 (dd, J = 10.6, 6.6 Hz,
1H), 4.86–4.76 (m, 2H), 4.95 (d, J = 7.9 Hz, 1H), 5.32 (d, J = 8.6 Hz,
1H), 5.67 (d, J = 7.0 Hz, 1H), 6.08 (t, J = 8.8 Hz, 1H), 6.47 (s, 1H),
6.75 (t, J = 73.4 Hz, 1H), 7.35 (d, J = 7.8 Hz, 1H), 7.48 (t, J = 7.8 Hz,
1H), 7.88 (s, 1H), 7.96 (d, J = 7.8 Hz, 1H). 13C NMR (126 MHz, CDCl3)
δ5.31. 6.74, 10.04, 12.55, 14.34, 17.97, 18.03, 18.47, 20.87, 21.29,
22.46, 25.67, 26.30, 28.23, 29.71, 34.67, 35.32, 37.14, 43.25, 46.68,
51.94, 58.35, 71.73, 72.21, 75.03, 75.31, 75.47, 76.42, 76.77, 77.28,
78.89, 79.42, 81.00, 84.27, 115.74 (t, J = 263 Hz), 120.23, 122.04,
124.73, 127.25, 130.18, 131.27, 133.16, 136.24, 141.09, 151.23,
155.20, 165.79, 169.25, 169.91, 171.90, 201.89.19F NMR (376 MHz,
CDCl3) δ −81.57 (dd, J = 526 Hz, 169 Hz, 2F). HRMS (TOF) m/z:
Calcd. For C59H91F2 NO16Si2+, 1164.5917. Found: 1164.5908.
4.3.37. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-7-TES-10-N,N-
dimethyl-carbamoyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-
dephenyldocetaxel (9d-06)
In the same manner as that for 9b-02, 9d-06 was synthesized from
7d-06 (268 mg, 0.337 mmol) and 8 (161 mg, 0.404 mmol) in 85% yield
(341 mg) as a white solid: 1H NMR (700 MHz, CDCl3, ppm) δ 0.56–0.62
(m, 6H), 0.90–0.93 (m, 9H), 1.06–1.14 (m, 21H), 1.19 (s, 3H), 1.21 (s,
3H), 1.31 (s, 9H), 1.68 (s, 4H), 1.74 (s, 3H), 1.76 (s, 3H), 1.84–1.90 (m,
1H), 2.06 (s, 3H), 2.31–2.38 (m, 5H), 2.50–2.55 (m, 1H), 2.94 (s, 3H),
3.06 (s, 3H), 3.86 (d, J = 7.0 Hz, 1H), 4.16 (AB, JAB = 8.4 Hz, 1H),
4.30 (AB, JAB = 8.4 Hz, 1H), 4.43 (d, J = 2.8 Hz, 1H), 4.47 (dd,
J1 = 10.5 Hz, J2 = 6.7 Hz, 1H), 4.77–4.84 (m, 2H), 4.95 (d, J = 8.7 Hz,
1H), 5.32 (d, J = 8.7 Hz, 1H), 5.68 (d, J = 7.0 Hz, 1H), 6.10 (t,
J = 8.8 Hz, 1H), 6.41 (s, 1H), 7.35 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H),
7.48 (t, J = 8.0 Hz, 1H), 7.88 (s, 1H), 8.05 (d, J = 8.0 Hz, 1H);13C NMR
(175 MHz, CDCl3, ppm) δ 5.29, 5.46, 5.62, 6.92, 10.23, 12.56, 12.73,
12.90, 14.47, 18.15, 18.22, 18.64, 21.66, 22.65, 25.87, 26.49, 28.41,
35.57, 36.36, 36.78, 37.30, 43.39, 46.86, 52.07, 58.27, 71.89, 72.35,
75.42, 75.73, 76.45, 76.60, 79.12, 79.53, 81.18, 84.51, 114.44, 115.92,
117.40, 120.33, 122.22, 124.86, 127.40, 130.35, 131,47, 133.75,
136.34, 141.00, 151.42, 155.38, 165.98, 170.02, 171.99, 203.19; 19F
NMR (376 MHz, CDCl3) δ −81.12 (ABq, J = 167 Hz, 2F). HRMS (TOF)
m/z: Calcd. For C60H94F2N2O16Si2Na+, 1215.6002. Found, 1215.5994.
4.3.35. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-7-TES-10-propanoyl-
2′-TIPS-3′-(2-methyl-propen-1-yl)-3′-dephenyldocetaxel (9b-06)
In the same manner as that for 9b-05, 9b-06 was synthesized from
7b-06 (307 mg, 0.393 mmol) and 8 (188 mg, 0.472 mmol) in 77% yield
(355 mg) as a white solid: 1H NMR (400 MHz, CDCl3, ppm) δ 0.54–0.60
(m, 1H), 0.90 (t, J = 8.0 Hz, 1H), 1.11 (s, 21H), 1.16 (s, 3H), 1.17–1.26
(m, 6H), 1.31 (s, 9H), 1.68 (s, 3H), 1.73–1.76 (m, 7H), 1.75 (s, 3H),
1.85–1.92 (m, 1H), 2.02 (s, 3H), 2.23–2.41 (m, 5H), 2.41–2.53 (m, 1H),
3.82 (d, J = 7.0 Hz, 1H), 4.16 (AB, JAB = 8.3 Hz, 1H), 4.30 (AB,
JAB = 8.3 Hz, 1H), 4.43 (d, J = 2.7 Hz, 1H), 4.45–4.50 (m, 1H),
4.76–4.85 (m, 2H), 4.95 (d, J = 8.2 Hz, 1H), 5.32 (d, J = 8.7 Hz, 1H),
5.67 (d, J = 7.0 Hz, 1H), 6.08 (t, J = 8.9 Hz, 1H), 6.49 (s, 1H), 6.66 (t,
J = 73.4 Hz, 1H), 7.35 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.47 (t,
J = 8.0 Hz, 1H), 7.88 (s, 1H), 7.95 (d, J = 8.0 Hz, 2H); 13C NMR
(100 MHz, CDCl3, ppm) δ 5.50, 6.93, 9.37, 10.22, 12.74, 14.52, 18.14,
18.22, 18.64, 21.48, 22.64, 22.83, 25.85, 27.80, 28.41, 35.52, 37.32,
43.42, 46.87, 52.15, 58.51, 71.96, 72.39, 75.00, 75.49, 75.68, 76.60,
115.93, 120.41, 122.23, 124.87, 127.41, 130.35, 131.48, 133.44,
136.39, 141.19, 151.42, 155.37, 165.95, 170.06, 172.10, 172.81,
202.12.
4.3.38. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-7-TES-10-
methoxycarbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel
(9e-06)
In the same manner as that for 9b-02, 9e-06 was synthesized from
7e-06 (148 mg, 0.190 mmol) and 8 (84 mg, 0.228 mmol) in 69% yield
(155 mg) as a white solid: m.p. 115–117 °C; 1H NMR (400 MHz, CDCl3,
ppm) δ 0.59–0.63 (m, 6H), 0.92–0.96 (m, 9H), 1.11–1.14 (m, 21H),
1.21 (s, 6H), 1.32 (s, 9H), 1.63 (s, 3H), 1.67 (s, 1H), 1.70 (s, 3H), 1.75
(s, 3H), 1.77 (s, 3H), 1.87–1.94 (m, 1H), 2.03 (s, 3H), 2.34–2.37 (m,
5H), 2.50–2.58 (m, 1H), 2.94 (s, 3H), 3.81–3.83 (m, 4H), 4.17 (AB,
JAB = 8.4 Hz, 1H), 4.32 (AB, JAB = 8.4 Hz, 1H), 4.44–4.50 (m, 2H),
4.77–4.97 (m, 2H), 5.33 (d, J = 8.7 Hz, 1H), 5.68 (d, J = 7.0 Hz, 1H),
6.11 (t, J = 8.8 Hz, 1H), 6.29 (s, 1H), 6.66 (t, J = 73.4 Hz, 1H), 7.37
(dd, J = 8.0 Hz, J = 2.0 Hz, 1H), 7.48 (t, J = 8.0 Hz, 1H), 7.89 (s, 1H),
7.97 (d, J = 8.0 Hz, 1H);13C NMR (100 MHz, CDCl3, ppm) δ 5.58, 6.97,
10.22, 12.78, 14.62, 18.18, 18.25, 18.68, 21.36, 22.67, 25.89, 26.43,
28.45, 35.46, 37.35, 43.39, 46.86, 52.19, 55.30, 58.46, 72.02, 72.43,
75.52, 75.62, 76.63, 77.44, 78.76, 79.09, 79.67, 81.21, 84.47, 113.37,
115.96, 118.55, 120.46, 122.24, 124.94, 127.48, 130.39, 131,48,
133.08, 136.44, 142.07, 151.44, 155.06, 155.41, 165.96, 170.15,
4.3.36. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-7-TES-10-
cyclopropanecarbonyl-2′-TIPS-3′-(2-methylpropen-1-yl)-3′-
dephenyldocetaxel (9c-06)
172.15, 201.48; 19F NMR (376 MHz, CDCl3)
δ −81.07 (ABq,
In the same manner as that for 9b-02, 9c-06 was synthesized from
7c-06 (312 mg, 0.393 mmol) and 8 (188 mg, 0.472 mmol) in 90% yield
(422 mg) as a white solid: m.p. 127–129 °C; 1H NMR (400 MHz, CDCl3,
ppm) δ 0.52–0.62 (m, 6H), 0.90–0.94 (m, 9H), 1.11–1.14 (m, 21H),
1.21 (s, 3H), 1.24 (s, 3H), 1.33 (s, 9H), 1.59 (s, 3H), 1.69 (s, 3H),
1.75–1.77 (m, 7H), 1.86–1.93 (m, 1H), 2.02 (s, 3H), 2.32–2.37 (m, 5H),
2.48–2.54 (m, 1H), 3.86 (d, J = 7.0 Hz, 1H), 4.17 (AB, JAB = 8.1 Hz,
1H), 4.32 (AB, JAB = 8.1 Hz, 1H), 4.44–4.50 (m, 2H), 4.77–4.83 (m,
2H), 4.96 (d, J = 8.0 Hz, 1H), 5.33 (d, J = 8.6 Hz, 1H), 5.68 (d,
J = 7.0 Hz, 1H), 6.10 (t, J = 8.8 Hz, 1H), 6.50 (s, 1H), 6.67 (d,
J = 73.4 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J1 = 2.0 Hz, 1H), 7.49 (t,
J = 8.0, 1H), 7.89 (s, 1H), 7.97 (d, J = 7.8 Hz, 1H);13C NMR (100 MHz,
CDCl3, ppm) δ 5.53, 6.98, 8.88, 8.99, 10.25, 12.78, 13.17, 14.52, 18.18,
18.26, 18.69, 21.56, 22.68, 25.89, 26.53, 28.45, 35.56, 37.36, 43.45,
J = 167 Hz, 2F). HRMS (TOF) m/z: Calcd. For C59H91F2NO17Si2Na+
,
1202.5686. Found, 1202.5673.
4.3.39. 2-Debenzoyl-2-(3-methylbenzoyl)-10-propanoyl-3′-(2-
methylpropen-1-yl)-3′-dephenyl-docetaxel (1b-02)
To a solution of 9b-02 (74 mg, 0.066 mmol) in 5 mL pyridine/
acetonitrile (1/1) was added dropwise HF/pyridine (70%, 0.74 mL) at 0
°C. The mixture was stirred at room temperature for 21 h. The progress
of the reaction was monitored by TLC. Upon completion, the reaction
was quenched with saturated aqueous NaHCO3. The reaction mixture
was diluted with EtOAc, washed with aqueous saturated CuSO4 and
water, dried over MgSO4, and concentrated in vacuo. The residue was
purified by flash chromatography on silica gel to afford 1b-02 (44 mg,
77%) as a white solid: m.p. 169–172°C; 1H NMR (700 MHz, CDCl3) δ
15

C. Wang, et al.
BioorganicChemistry95(2020)103523
1.14 (s, 3H), 1.23 (m, 6H), 1.34 (s, 9H), 1.67 (s, 3H), 1.74 (s, 3H), 1.76
(s, 3H), 1.87 (m, 4H), 2.37 (m, 5H), 2.42 (s, 3H), 2.53 (m, 4H), 3.39 (br
s, 1H), 3.81 (d, J = 7.1 Hz, 1H), 4.17 (d, 8.5 Hz, 1H), 4.20 (dd,
J = 2.5 Hz, J = 6.7 Hz, 1H), 4.30 (d, J = 8.5 Hz, 1H), 4.42 (m, 1H),
4.74 (t, J = 6.9 Hz, 1H), 4.81 (d, J = 8.7 Hz, 1H), 4.96 (d, J = 8.1 Hz,
1H), 5.32 (d, J = 7.6 Hz, 1H), 5.64 (d, J = 7.1 Hz, 1H), 6.16 (t,
J = 9.0 Hz, 1H), 6.31 (s, 1H), 7.34 (t, J = 7.6 Hz, 1H), 7.41 (d,
J = 7.6 Hz, 1H), 7.89 (d, J = 7.6 Hz, 1H), 7.92 (s, 1H); 13C NMR
(700 MHz) δ 9.3, 9.7, 15.1, 18.8, 21.5, 22.0, 22.5, 25.9, 26.8, 27.8,
28.4, 35.7, 35.8, 43.4, 45.9, 51.7, 58.7, 72.4, 72.6, 73.9, 75.1, 75.6,
76.7, 79.3, 80.1, 81.3, 84.6, 120.8, 127.5, 128.7, 129.3, 131.0, 133.1,
134.6, 138.0, 138.5, 142.7, 155.6, 167.2, 170.2, 173.4, 174.8, 204.0.
HRMS (TOF) m/z: Calcd. For C45H61NO15H+ calcd: 856.4129. Found:
856.4129 (Δ = 0.01 ppm).
4.39 (m, 1H), 4.75 (m, 2H), 5.32 (d, J = 7.4 Hz, 1H), 5.65 (d,
J = 7.1 Hz, 1H), 6.12 (s, 1H), 6.16 (t, J = 9.0 Hz, 1H), 7.35 (t,
J = 7.7 Hz, 1H), 7.41 (d, J = 7.7 Hz, 1H), 7.89 (d, J = 7.7 Hz, 1H),
7.93 (s, 1H); 13C NMR (175 MHz) δ 9.6, 15.2, 18.7, 21.5, 21.9, 22.5,
25.9, 26.7, 28.4, 35.7, 35.8, 43.3, 45.8, 51.7, 55.8, 58.7, 72.3, 72.5,
73.9, 75.0, 76.6, 77.0, 77.2, 77.4, 78.5, 79.3, 80.1, 81.2, 84.5, 120.8,
127.5, 128.7, 129.3, 131.0, 132.7, 134.7, 138.0, 138.5, 143.7, 155.6,
156.0, 167.2, 170.3, 173.3, 204.2. HRMS (TOF) m/z: Calcd. For
C
44H59NO16Na+ calcd: 880.3726. Found: 880.3742 (Δ = −1.8 ppm).
4.3.43. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-acetyl-3′-(2-
methylpropen-1-yl)-3′-dephenyldocetaxel (1a-05)
In the same manner as that for 9b-02, 9a-05 was synthesized from
7a-05 (188 mg, 0.241 mmol) and 8 (101 mg, 0.253 mmol) as a white
solid, which was immediately subjected to deprotection with HF-pyr-
idine in the same manner as that for 1b-02 to give 1a-05 (202 mg,
0.221 mmol, 92% for 2 steps) as a white solid: m.p. 149–151 °C; 1H
NMR (400 MHz, CDCl3, ppm) δ 1.16 (s, 3H), 1.27 (s, 3H), 1.35 (s, 9H),
1.65 (s, 1H), 1.69 (s, 3H), 1.74 (s, 3H), 1.77 (s, 3H), 1.85–1.91 (m, 4H),
2.25 (s, 3H), 2.27–2.46 (m, 5H), 2.50 (broad, OH), 2.53–2.61 (m, 1H),
3.34 (d, J = 6.5 Hz, 1H), 3.84 (d, J = 7.0 Hz, 1H), 4.16–4.20 (m, 2H),
4.29 (AB, JAB = 8.2 Hz, 1H), 4.43 (t, J = 7.0 Hz, 1H), 4.71–4.76 (m,
2H), 4.99 (d, J = 7.8 Hz, 1H), 5.34 (d, J = 4.5 Hz, 1H), 5.66 (d,
J = 7.0 Hz, 1H), 6.15 (t, J = 8.5 Hz, 1H), 6.32 (s, 1H), 7.47 (d,
J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 7.99 (s, 1H), 8.06 (d,
J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 9.69, 15.20, 18.60,
21.06, 21.99, 22.39, 25.87, 26.79, 28.40, 35.60, 35.74, 43.37, 45.85,
51.80, 58.76, 72.39, 72.59, 73.84, 75.83, 76.51, 77.43, 79.40, 80.10,
81.21, 84.63, 119.34, 120.73, 121.91, 122.36, 126.37, 128.86, 130.53,
131.49, 132.86, 138.28, 143.10, 149.46, 149.48, 155.59, 165.67,
170.23, 171.48, 173.48, 203.90; 19F NMR (376 MHz, CDCl3, 25 °C) δ
4.3.40. 2-Debenzoyl-2-(3-methylbenzoyl)-10-cyclopropanecarbonyl-3′-(2-
methylpropen-1-yl)-3′-dephenyldocetaxel (1c-02)
In the same manner as that for 1b-02, 1c-02 was synthesized from
9c-02 (195 mg, 0.171 mmol) and HF/pyridine (70%, 2.2 mL) in 77%
yield (115 mg) as a white solid: m.p. 178–179 °C; 1H NMR (500 MHz,
CDCl3) δ 0.99 (m, 2H), 1.14 (m, 5H), 1.25 (s, 3H), 1.34 (s, 9H), 1.66 (s,
3H), 1.71 (s, 1H), 1.77 (m, 7H), 1.86 (m, 4H), 2.37 (m, 5H), 2.41 (s,
3H), 2.52 (m, 1H), 2.57 (d, J = 4.0 Hz, 1H), 3.38 (d, J = 5.3 Hz, 1H),
3.80 (d, J = 7.1 Hz, 1H), 4.17 (d, J = 8.5 Hz, 1H), 4.20 (dd,
J = 6.9 Hz, J = 6.9 Hz, 1H), 4.30 (d, J = 8.5 Hz, 1H), 4.40 (m, 1H),
4.74 (m, 1H), 4.80 (d, J = 6.4 Hz, 1H), 4.96 (d, J = 4.3 Hz, 1H), 5.32
(d, J = 8.4 Hz, 1H), 5.64 (d, J = 7.1 Hz, 1H), 6.17 (t, J = 9.0 Hz, 1H),
6.30 (s, 1H), 7.35 (t, J = 7.7 Hz, 1H), 7.41 (d, J = 7.7 Hz, 1H), 7.89 (d,
J = 7.7 Hz, 1H), 7.93 (s, 1H); 13C NMR (125 MHz) δ 9.4, 9.6, 9.7, 13.2,
15.2, 18.8, 21.6, 22.2, 22.5, 25.9, 26.9, 28.4, 35.7, 35.8, 43.4, 45.9,
51.7, 58.7, 72.4, 72.6, 73.9, 75.1, 75.6, 76.7, 79.4, 80.1, 81.3, 84.6,
120.9, 127.5, 128.7, 129.3, 131.0, 133.1, 134.6, 138.0, 138.5, 142.8,
155.6, 167.3, 170.2, 173.3, 175.3, 204.1. HRMS (TOF) m/z: Calcd. For
−57.82 (3F). HRMS (TOF) m/z: Calcd. For
C
44H56F3NO16H+
,
912.3624. Found, 912.3629.
C
46H61NO15H + calcd: 868.4114. Found: 868.4122 (Δ = −0.94 ppm).
4.3.44. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-propanoyl-3′-(2-
4.3.41. 2-Debenzoyl-2-(3-methylbenzoyl)-10-N,N-dimethylcarbamoyl-3′-
(2-methylpropen-1-yl)-3′-dephenyldocetaxel (1d-02)
methylpropen-1-yl)-3′-dephenyldocetaxel (1b-05)
In the same manner as that for 1b-02, 1b-05 was synthesized from
9b-05 (246 mg, 0.207 mmol) and HF/pyridine (70%, 2.5 mL) in 94%
yield (180 mg) as a white solid: 1H NMR (500 MHz, CDCl3) 1.17 (s, 3H),
1.32 (m, 6H),1.36 (s, 9H), 1.71 (m, 3H),1.77 (m, 3H), 1.92 (s, 3H), 2.35
(s, 3H), 2.06 (s, 1H), 2.63–2.47 (m, 4H), 3.37 (s, 1H), 3.85 (d,
J = 7.0 Hz, 1H), 4.14 (q, J = 8.0 Hz, 1H), 4.18 (d, J = 8.0 Hz, 1H),
4.21 (d, J = 4.7 Hz, 1H), 4.30 (d, J = 8.3 Hz, 1H), 4.47–4.43 (m,
1H),4.75 (dt, J = 8.5, 5.4 Hz, 2H), 5.00 (d, J = 8.1 Hz, 1H), 5.35 (d,
J = 7.4 Hz, 1H), 5.67 (d, J = 7.0 Hz, 1H), 6.17 (t, J = 8.8 Hz, 1H),
6.34 (s, 1H), 7.48 (d, J = 8.0 Hz, 1H), 7.55 (dd, J = 8.0, 2.0 Hz, 1H),
8.00 (s, 1H), 8.07 (d, J = 8.0 Hz, 1H). 13C NMR (125 MHz, CDCl3) δ
9.03, 9.48, 14.95, 18.38, 21.79, 22.17, 25.27, 25.65, 26.57, 27.56,
28.18, 34.66, 35.42, 35.54, 43.15, 45.69, 51.58, 58.50, 72.18, 72.37,
73.64, 75.43, 75.66, 76.29, 79.15, 79.84, 80.99, 84.45,119.86 (q,
J = 259 Hz), 121.44, 122.15, 126.13,128.65, 130.31, 131.30, 137.98,
132.74,142.71, 149.24, 155.38, 165.44,170.02, 173.28, 174.60,
203.74. 19F NMR (376 MHz, CDCl3) δ −57.83 (s, 3F). HRMS (TOF) m/
z: Calcd. For C45H58F3NO16+, 926.3780. Found, 926.3791.
In the same manner as that for 1b-02, 1d-02 was synthesized from
9d-02 (93 mg, 0.082 mmol) and HF/pyridine (70%, 1.0 mL) in 89%
yield (63 mg) as a white solid: m.p. 158–160°C; 1H NMR (700 MHz,
CDCl3) δ 1.15 (s, 3H), 1.24 (s, 3H), 1.34 (s, 9H), 1.66 (s, 3H), 1.74 (s,
3H),1.75 (s, 3H) 1.85 (m, 3H), 1.91 (s, 3H), 2.36 (m, 5H), 2.41 (s, 3H),
2.52 (m, 1H), 2.95 (s, 3H), 3.04 (s, 3H), 3.24 (br s, 1H), 3.46 (br s, 1H),
3.80 (d, J = 7.0 Hz, 1H), 4.17 (d, 8.5 Hz, 1H), 4.20 (d, J = 3.9 Hz, 1H),
4.30 (d, J = 8.5 Hz, 1H), 4.44 (dd, J = 6.8 Hz, J = 10.9 Hz, 1H), 4.74
(t, J = 7.6 Hz, 1H), 4.83 (d, J = 8.6 Hz, 1H), 4.97 (d, J = 8.4 Hz, 1H),
5.32 (d, J = 7.8 Hz, 1H), 5.63 (d, J = 7.1 Hz, 1H), 6.17 (t, J = 8.9 Hz,
1H), 6.25 (s, 1H), 7.34 (t, J = 7.7 Hz, 1H), 7.40 (d, J = 7.7 Hz, 1H),
7.89 (d, J = 7.7 Hz, 1H), 7.92 (s, 1H); 13C NMR (175 MHz) δ 9.5, 15.2,
18.7, 21.5, 22.5, 25.9, 27.0, 28.4, 35.6, 35.8, 36.2, 36.8, 43.4, 45.8,
51.7, 58.6, 72.7, 73.9, 75.2, 76.4, 76.6, 77.0, 77.2, 77.4, 79.4, 80.1,
81.3, 84.8, 120.8, 127.5, 128.7, 129.3, 131.0, 133.4, 134.6, 138.0,
138.5, 143.1, 155.6, 156.3, 167.2, 170.1, 173.3, 205.9. HRMS (TOF)
m/z: Calcd. For C45H62N2O15Na + calcd: 893.4042. Found: 893.4054
(Δ = −1.3 ppm).
4.3.45. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-
4.3.42. 2-Debenzoyl-2-(3-methylbenzoyl)-10-methoxycarbonyl-3′-(2-
methylpropen-1-yl)-3′-dephenyldocetaxel (1e-02)
cyclopropanecarbonyl-3′-(2-methyl-propen-1-yl)-3′-dephenyldocetaxel (1c-
05)
In the same manner as that for 1b-02, 1e-02 was synthesized from
9e-02 (81 mg, 0.072 mmol) and HF/pyridine (70%, 1.1 mL) in 84%
yield (52 mg) as a white solid: m.p. 150–152 °C; 1H NMR (700 MHz,
CDCl3) δ 1.15 (s, 3H), 1.24 (s, 3H), 1.34 (s, 9H), 1.64 (s, 1H), 1.69 (s,
3H), 1.71 (s, 1H), 1.75 (s, 3H), 1.76 (s, 3H), 1.88 (m, 1H), 1.93 (s, 3H),
2.36 (m, 5H), 2.42 (s, 3H), 2.46 (d, J = 4.1 Hz, 1H), 2.56 (m, 1H), 3.39
(br s, 1H), 3.78 (d, J = 7.1 Hz, 1H), 3.87 (s, 3H), 4.17 (d, J = 8.5 Hz,
1H), 4.21 (dd, J = 2.7 Hz, J = 7.1 Hz, 1H), 4.31 (d, J = 8.5 Hz, 1H),
In the same manner as that for 1b-02, 1c-05 was synthesized from
9c-05 (670 mg, 0.55 mmol) and HF/pyridine (70%, 6.5 mL) in 98%
yield (511 mg) as a white solid: m.p. 145–146 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 0.99–1.01 (m, 1H), 1.12–1.17 (m, 4H), 1.27 (s, 3H), 1.36
(s, 9H), 1.60 (s, 3H), 1.64 (s, 1H), 1.68 (s, 3H), 1.75 (s, 3H), 1.78 (s,
3H), 1.79–1.82 (m, 1H), 1.85–1.91 (m, 4H), 2.32–2.45 (m, 5H),
2.53–2.59 (m, 2H), 3.32 (d, J = 6.4 Hz, 1H), 3.83 (d, J = 7.0 Hz, 1H),
4.17 (AB, JAB = 8.2 Hz, 1H), 4.19 (d, J = 9.6 Hz, 1H), 4.29 (AB,
16

C. Wang, et al.
BioorganicChemistry95(2020)103523
JAB = 8.2 Hz, 1H), 4.43 (dd, J1 = 10.8 Hz, J2 = 6.6 Hz, 1H), 4.74 (d,
J = 3.4 Hz, 1H), 4.99 (d, J = 7.9 Hz, 1H), 5.34 (s, 1H), 5.66 (d,
J = 7.0 Hz, 1H), 6.16 (t, J = 8.0 Hz, 1H), 6.32 (s, 1H), 7.47 (d,
J = 8.0 Hz, 1H), 7.55 (t, J = 8.0 Hz, 1H), 8.00 (s, 1H), 8.06 (d,
J = 8.0 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 9.43, 9.67, 13.24, 15.23,
18.61, 22.11, 22.40, 25.88, 26.86, 28.41(3C of the t-butyl group),
35.62, 35.68, 43.38, 45.84, 51.78, 58.77, 72.47, 72.65, 73.84, 75.63,
75.84, 76.51, 79.44, 80.12, 81.23, 84.68, 119.61, 120.72, 121.66,
122.37, 126.39, 128.87, 130.54, 131.49, 132.93, 138.32, 143.15,
149.47, 155.59, 165.68, 170.21, 174.10, 175.37, 204.09; 19F NMR
(376 MHz, CDCl3, 25 °C) δ −57.83 (3F). HRMS (TOF) m/z: Calcd. For
C46H58F3NO16H+, 938.3780. Found, 938.3778.
4.44–4.38 (m, 1H), 4.74 (dd, J = 8.8, 2.5 Hz, 1H), 4.82 (d, J = 8.8 Hz,
1H), 4.96 (d, J = 7.8 Hz, 1H), 5.32 (d, J = 8.3 Hz, 1H), 5.64 (d,
J = 7.0 Hz, 1H), 6.16 (dd, J = 9.1, 7.9 Hz, 1H), 6.29 (s, 1H), 6.66 (t,
J = 73.2 Hz, 1H), 7.35 (d, J = 8.0 Hz, 1H), 7.47 (t, J = 8.0 Hz, 1H),
7.86 (s, 1H), 7.94 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3) δ
9.52, 14.19, 14.92, 18.46, 20.85, 21.04, 21.86, 22.27, 25.69, 26.62,
28.19, 35.43, 35.53, 43.16, 45.63, 51.46, 58.49, 60.41, 72.11, 72.30,
73.63, 75.57, 75.61, 76.32, 76.72, 77.36, 79.17, 79.85, 80.97, 84.42,
115.69 (t, J = 263 Hz), 124.88, 127.20, 130.24, 131.09, 132.75,
137.91, 142.74, 151.21, 155.40, 165.81, 170.14, 171.26, 203.70; 19F
NMR (376 MHz, CDCl3) δ −81.23 (ABq, J = 167 Hz, 2F); HRMS (TOF)
m/z: Calcd. for C44H57F2NO16+, 94.3718. Found: 894.3727.
4.3.46. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-N,N-
4.3.49. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-10-propanoyl-3′-(2-
methylpropen-1-yl)-3′-dephenyl-docetaxel (1b-06)
dimethylcarbamoyl-3′-(2-methylpropen-1-yl)-3′-dephenyldocetaxel
(1d-
05)
In the same manner as that for 1b-02, 1b-06 was synthesized from
9b-06 (350 mg, 0.297 mmol) and HF/pyridine (70%, 3.4 mL) in 92%
yield (248 mg) as a white solid: m.p. 126–128 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.15 (s, 3H), 1.21–1.26 (m, 6H), 1.33 (s, 9H), 1.68 (s,
3H), 1.75 (s, 3H), 1.77 (s, 3H), 1.85–1.92 (m, 4H), 2.30–2.38 (m, 5H),
2.47–2.60 (m, 3H), 3.83 (d, J = 7.0 Hz, 1H), 4.17 (AB, JAB = 8.3 Hz,
1H), 4.21 (d, J = 2.2 Hz, 1H), 4.31 (AB, JAB = 8.3 Hz, 1H), 4.44 (dd,
J1 = 10.8 Hz, J2 = 6.7 Hz, 1H), 4.75–4.81 (m, 2H), 4.98 (d, J = 7.8 Hz,
1H), 5.34 (d, J = 7.8 Hz, 1H), 5.66 (d, J = 7.0 Hz, 1H), 6.18 (t,
J = 8.5 Hz, 1H), 6.67 (d, J = 73.4 Hz, 1H), 7.36–7.38 (dd, J1 = 8.0 Hz,
J2 = 2.0 Hz, 1H), 7.49 (t, J = 8.0 Hz, 1H), 7.89 (s, 1H), 7.96 (d,
J = 7.8 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 9.23, 9.72,15.12,
18.67, 22.08, 22.48, 25.89, 26.83, 27.77, 28.39, 35.63, 35.73, 43.37,
45.83, 51.66, 58.72, 72.37, 72.54, 73.83, 75.61, 75.76, 76.53, 77.43,
79.42, 80.07, 81.18, 84.65, 113.29, 115.88, 118.48, 120.36, 120.77,
125.11, 127.41, 130.45, 131.28, 133.01, 138.17, 142.84, 151.42,
155.59, 166.03, 170.33, 173.48, 174.82, 203.98; 19F NMR (376 MHz,
CDCl3, 25 °C) δ −81.13 (ABq, J = 167 Hz, 2F); HRMS (TOF) m/z:
Calcd. For C45H59F2NO16H+, 908.3875. Found, 908.3882.
In the same manner as that for 1b-02, 1d-05 was synthesized from
9d-05 (491 mg, 0.405 mmol) and HF/pyridine (70%, 5 mL) in 96%
yield (366 mg) as a white solid: m.p. 170–172 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.17 (s, 3H), 1.26 (s, 3H), 1.35 (s, 9H), 1.67 (s, 3H), 1.75
(s, 3H), 1.77 (s, 3H), 1.86–1.93 (m, 4H), 2.29–2.42 (m, 5H), 2.51–2.59
(m, 1H), 2.97 (s, 3H), 3.05 (s, 3H), 3.83 (d, J = 7.0 Hz, 1H), 4.16–4.20
(m, 2H), 4.28 (AB, JAB = 8.2 Hz, 1H), 4.46 (dd, J1 = 10.8 Hz,
J2 = 6.6 Hz, 1H), 4.73–4.79 (m, 2H), 4.99 (d, J = 8.2 Hz, 1H), 5.34 (d,
J = 6.3 Hz, 1H), 5.65 (d, J = 7.0 Hz, 1H), 6.17 (t, J = 8.7 Hz, 1H),
6.27 (s, 1H), 7.47 (d, J = 8.0 Hz, 1H), 7.54 (t, J = 8.0 Hz, 1H), 8.00 (s,
1H), 8.06 (d, J = 8.0 Hz, 1H); 13C NMR (100 MHz, CDCl3, ppm) δ 9.51,
15.27, 18.60, 22.39, 25.87, 27.00, 28.41, 35.55, 35.66, 36.23, 36.86,
43.38, 45.80, 51.81, 58.71, 72.65, 72.70, 73.86, 75.96, 76.41, 76.51,
77.43, 79.52, 80.08, 81.29, 84.86, 120.75, 122.39, 126.34, 128.86,
130.51, 131.52, 133.23, 138.29, 143.41, 149.46, 155.59, 156.33,
165.69, 170.16, 173.47, 205.87; 19F NMR (376 MHz, CDCl3, 25 °C) δ
−57.82 (3F). HRMS (TOF) m/z: Calcd. For C45H59F3N2O16H+
,
941.3889. Found, 941.3893.
4.3.47. 2-Debenzoyl-2-(3-trifluoromethoxybenzoyl)-10-methoxycarbonyl-
4.3.50. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-10-
3′-(2-methyl-propen-1-yl)-3′-dephenyldocetaxel (1e-05)
cyclopropanecarbonyl-3′-(2-methylpropen-1-yl)-3′-dephenyl-docetaxel (1c-
06)
In the same manner as that for 1b-02, 1e-05 was synthesized from
9e-05 (246 mg, 0.207 mmol) and HF/pyridine (70%, 2.5 mL) in 95%
yield (183 mg) as a white solid: m.p. 121–123 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.16 (s, 3H), 1.25 (s, 3H), 1.35 (s, 9H), 1.70 (s, 3H), 1.74
(s, 3H), 1.77 (s, 3H), 1.86–1.94 (m, 4H), 2.29–2.50 (m, 5H), 2.53–2.61
(m, 1H), 3.81 (d, J = 7.0 Hz, 1H), 3.88 (s, 3H), 4.17–4.21 (m, 2H), 4.32
(AB, JAB = 8.4 Hz, 1H), 4.46 (dd, J1 = 10.8 Hz, J2 = 6.6 Hz, 1H),
4.73–4.79 (m, 2H), 4.98 (d, J = 8.2 Hz, 1H), 5.34 (d, J = 7.1 Hz, 1H),
5.66 (d, J = 7.0 Hz, 1H), 6.13 (s, 1H), 6.18 (t, J = 8.8 Hz, 1H), 6.67 (t,
J = 73.4 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.50 (t,
J = 8.0 Hz, 1H), 7.89 (s, 1H), 7.96 (d, J = 8.0 Hz, 1H); 13C NMR
(100 MHz, CDCl3, ppm) δ 9.67, 15.23, 18.68, 21.99, 22.48, 25.90,
26.76, 28.40, 35.57, 35.78, 43.27, 45.79, 51.67, 55.81, 58.75, 72.27,
72.48, 73.84, 75.69, 76.53, 77.49, 78.49, 79.43, 80.11, 81.14, 84.60,
113.30, 115.89, 118.48, 120.34, 120.75, 125.13, 127.42, 130.46,
131.26, 132.60, 138.20, 143.85, 151.43, 155.61, 155.98, 166.03,
170.38, 173.54, 204.16; 19F NMR (376 MHz, CDCl3) δ −57.82 (s, 3F);
HRMS (TOF) m/z: Calcd. For C44H56F3NO17H+, 928.3573. Found,
928.3576.
In the same manner as that for 1b-02, 1c-06 was synthesized from
9c-06 (418 mg, 0.351 mmol) and HF/pyridine (70%, 4.1 mL) in 91%
yield (294 mg) as a white solid: m.p. 145–147 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 0.98–1.02 (m, 2H), 1.11–1.15 (m, 4H), 1.26 (s, 3H), 1.32
(s, 9H), 1.66 (s, 3H), 1.74 (s, 3H), 1.76 (s, 3H), 1.78–1.82 (m, 1H),
1.86–1.89 (m, 4H), 2.30–2.38 (m, 5H), 2.50–2.58 (m, 2H), 3.81 (d,
J = 7.0 Hz, 1H), 4.16 (AB, JAB = 8.3 Hz, 1H), 4.20 (d, J = 2.6 Hz, 1H),
4.29 (AB, JAB = 8.3 Hz, 1H), 4.39–4.43 (m, 1H), 4.72–4.77 (m, 1H),
4.83 (d, J = 8.7 Hz, 1H), 4.97 (d, J = 8.0 Hz, 1H), 5.33 (d, J = 8.4 Hz,
1H), 5.65 (d, J = 7.0 Hz, 1H), 6.17 (t, J = 9.0 Hz, 1H), 6.66 (t,
J = 73.4 Hz, 1H), 7.36 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.48 (t,
J = 8.0 Hz, 1H), 7.87 (s, 1H), 7.95 (d, J = 7.8 Hz, 1H); 13C NMR
(100 MHz, CDCl3, ppm) δ 9.20, 9.43, 9.50, 13.04, 14.93, 18.46, 21.97,
22.27, 25.69, 26.68, 28.19, 35.46, 35.49, 43.17, 45.64, 51.45, 58.49,
72.14, 72.34, 73.63, 75.40, 75.60, 76.33, 77.25, 79.18, 79.87, 80.99,
84.47, 113.10, 115.69, 118.29, 120.15, 120.59, 124.88, 127.20,
130.24, 131.10, 132.83, 137.92, 142.74, 151.21, 155.41, 165.81,
170.13, 173.27, 175.12, 203.86; 19F NMR (376 MHz, CDCl3) δ −81.24
(ABq,
J
=
167 Hz, 2F); HRMS (TOF) m/z: Calcd. For
4.3.48. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-10-acetyl-3′-(2-
methylpropen-1-yl)-3′-dephenyl-docetaxel (1a-06)
C
46H59F2NO16Na+, 942.3694. Found, 942.3694.
In the same manner as that for 1b-02, 1a-06 was synthesized from
9a-06 (187 mg, 0.163 mmol) and HF/pyridine (70%, 1.6 mL) in 96%
yield (140 mg) as a white solid: 1H NMR (400 MHz, CDCl3) δ1.14 (s,
3H), 1.24 (m, 3H), 1.31 (s, 9H), 1.66 (s, 3H), 1.74 (m, 3H), 1.77 (m,
3H), 1.84–1.80 (m, 1H), 1.87 (m, 3H), 2.03 (s, 1H), 2.23 (s, 3H), 2.36
(m, 6H), 2.58–2.50 (m, 2H), 3.40 (d, J = 6.7 Hz, 1H), 3.81 (d,
J = 7.0 Hz, 1H), 4.15 (d, J = 8.3 Hz, 1H), 4.29 (d, J = 8.3 Hz, 1H),
4.3.51. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-10-N,N-
dimethylcarbamoyl-3′-(2-methyl-propen-1-yl)-3′-dephenyl-docetaxel (1d-
06)
In the same manner as that for 1b-02, 1d-06 was synthesized from
9d-06 (157 mg, 0.132 mmol) and HF/pyridine (70%, 1.7 mL) in 92%
yield (112 mg) as a white solid: m.p. 150–152 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.16 (s, 3H), 1.26 (s, 3H), 1.33 (s, 9H), 1.67 (s, 3H), 1.75
17

C. Wang, et al.
BioorganicChemistry95(2020)103523
(s, 3H), 1.77 (s, 3H), 1.85–1.92 (m, 4H), 2.30–2.41 (m, 5H), 2.50–2.58
(m, 1H), 2.96 (s, 3H), 3.05 (s, 3H), 3.82 (d, J = 7.0 Hz, 1H), 4.16–4.21
(m, 2H), 4.30 (AB, JAB = 8.3 Hz, 1H), 4.46 (dd, J1 = 10.9 Hz,
J2 = 6.6 Hz, 1H), 4.75–4.82 (m, 2H), 4.99 (d, J = 7.9 Hz, 1H), 5.33 (d,
J = 8.1 Hz, 1H), 5.65 (d, J = 7.0 Hz, 1H), 6.19 (t, J = 8.0 Hz, 1H),
6.67 (t, J = 73.4 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.49
(t, J = 8.0 Hz, 1H), 7.88 (s, 1H), 7.96 (d, J = 7.80 Hz, 1H); 13C NMR
(100 MHz, CDCl3, ppm) δ 9.54, 15.19, 18.67, 22.48, 25.89, 27.02,
28.39, 35.55, 35.68, 36.23, 36.85, 43.37, 45.77, 51.65, 58.66, 72.62,
73.84, 75.89, 76.39, 76.52, 77.43, 79.51, 80.05, 81.24, 84.86, 113.30,
115.89, 118.48, 120.36, 120.78, 125.08, 127.40, 130.43, 131.31,
133.30, 138.16, 143.26, 151.42, 155.60, 156.33, 166.04, 170.27,
Emax model in Sigmaplot 12.5 to calculate IC50 value of a given com-
pound.
4.5. Molecular modeling analysis
The structures of 3rd-generation taxoids were adapted from the co-
crystal coordinates of paclitaxel in β-tubulin (PDB ID: 1JFF) [64]. The
Avogadro molecular editor [79] was used to fix co-crystal structure of
paclitaxel, manually build each functional group augmentation, assign
Marsilli-Gasteiger partial charges [65,66], and minimize the un-
constrained atoms with the organic molecule force field MMFF94
[67–71]. For most taxoids, only two conformers were generated, with
the C2 benzoate group substituent orientated to the proximal and distal
binding sites. However, for more complicated substituents with added
rotatable bonds, e.g. OCF3 and OCF2H, relevant gauche and eclipsed
conformations were also identified and built in accordance to the local
minima from the force field.
173.48, 205.86; 19F NMR (376 MHz, CDCl3)
δ −81.23 (ABq,
J = 167 Hz, 2F). HRMS (TOF) m/z: Calcd. For C45H60F2N2O16Na+
,
945.3803. Found, 945.3794.
4.3.52. 2-Debenzoyl-2-(3-difluoromethoxybenzoyl)-10-methoxycarbonyl-
3′-(2-methyl-propen-1-yl)-3′-dephenyl-docetaxel (1e-06)
Docking calculations were performed using AutoDock Vina [72]
where typical re-orientation calculations, the local search algorithm,
and direct rescoring were utilized. Energy-minimized structures were
directly used as input for re-orientation calculations. For local search
minimization and rescoring calculations, the adapted crystal coordinate
structures for all conformers were used. Data was collected for the
conformer in which the pose was geometrically and energetically most
favorable. All calculations used default parameters (see Supplementary
Material) of the scoring function. All visualization and analysis of
binding poses was performed in UCSF Chimera [80].
In the same manner as that for 1b-02, 1e-06 was synthesized from
9e-06 (89 mg, 0.075 mmol) and HF/pyridine (70%, 0.9 mL) in 90%
yield (61 mg) as a white solid: m.p. 170–172 °C; 1H NMR (400 MHz,
CDCl3, ppm) δ 1.16 (s, 3H), 1.26 (s, 3H), 1.33 (s, 9H), 1.70 (s, 3H), 1.75
(s, 3H), 1.77 (s, 3H), 1.86–1.94 (m, 4H), 2.30–2.42 (m, 5H), 2.53–2.61
(m, 1H), 3.81 (d, J = 7.0 Hz, 1H), 3.88 (s, 3H), 4.17–4.21 (m, 2H), 4.32
(AB, JAB = 8.4 Hz, 1H), 4.46 (dd, J1 = 10.8 Hz, J2 = 6.6 Hz, 1H),
4.73–4.79 (m, 2H), 4.98 (d, J = 8.2 Hz, 1H), 5.34 (d, J = 7.1 Hz, 1H),
5.66 (d, J = 7.0 Hz, 1H), 6.13 (s, 1H), 6.18 (t, J = 8.8 Hz, 1H), 6.67 (t,
J = 73.4 Hz, 1H), 7.37 (dd, J1 = 8.0 Hz, J2 = 2.0 Hz, 1H), 7.50 (t,
J = 8.0 Hz, 1H), 7.89 (s, 1H), 7.96 (d, J = 7.80 Hz, 1H); 13C NMR
(100 MHz, CDCl3, ppm) δ 9.67, 15.23, 18.68, 21.99, 22.48, 25.90,
26.76, 28.40, 35.57, 35.78, 43.27, 45.79, 51.67, 55.81, 58.75, 72.27,
72.48, 73.84, 75.69, 76.53, 77.49, 78.49, 79.43, 80.11, 81.14, 84.60,
113.30, 115.89, 118.48, 120.34, 120.75, 125.13, 127.42, 130.46,
131.26, 132.60, 138.20, 143.85, 151.43, 155.61, 155.98, 166.03,
170.38, 173.54, 204.16; 19F NMR (376 MHz, CDCl3) δ −81.24 (ABq,
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
J = 167 Hz, 2F); HRMS (TOF) m/z: Calcd. For C44H57F2NO17H+
,
910.3667. Found, 910.3671.
This work was supported by grants from the National Cancer
Institute (CA 103314 to IO) and the Natural Science Foundation of
Guangdong Province, China (2015B020211012 and 2016A050502039
to CW). The authors would like to thank Dr. Bela Ruzsiczka, Institute of
Chemical Biology and Drug Discovery, Stony Brook University, for his
advice and technical help for LC/HRMS analysis and the Fujian Yew
Park Biological Co. Ltd., China for generous gift of 10-deacetylbaccatin
III used in this work.
4.4. In vitro cell growth inhibition assay
Tumor cell growth inhibition was determined according to the
method established by Skehan et al. [78]. Human cancer cells DLD-1,
NCI/ADR, LCC6-MDR were cultured and maintained in Roswell Park
Memorial Institute growth medium RPMI1640 supplemented by 10%
fetal bovine serum (FBS) and 1% penicillin (PenStrip). Human cancer
cells CFPAC-1 were cultured and maintained in Iscove's modified Dul-
becco's medium (IDMEM) supplemented by 2 mM glutamine and 10%
fetal bovine serum (FBS). CSC-enriched HCT116CSC colon cancer cells
were cultured in Mesenchymal stem cell growth medium (MSCGM™).
Patient-derived CSC-enriched PPT2 prostate cancer cells were cultured
in serum-free Mesenchymal stem cell basal medium (MSCBM).
Appendix A. Supplementary material
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.bioorg.2019.103523.
References
Cells were plated at a density of 2000–5000 cells/well in 96-well
plates and allowed to attach overnight and reach 50% confluency.
Taxoids were dissolved in sterilized DMSO and further diluted with the
corresponding medium. The concentration of DMSO was restricted to
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Optical density (OD) was tested under 570 nm. A dose-response (kill)
curve was built by applying gradient drug concentration as x axis and
related cell viability as y axis. The curve was then fitted with Sigmoid-
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