Synthesis and cytotoxicity of 7,9-O-linked macrocyclic C-Seco taxoids

Article abstract of DOI:10.3390/molecules24112161

A series of novel 7,9-O-linked macrocyclic taxoids together with modification at the C2 position were synthesized, and their cytotoxicities against drug-sensitive and P-glycoprotein and βIII-tubulin overexpressed drug-resistant cancer cell lines were eval

Full text of DOI:10.3390/molecules24112161

molecules
Article
Synthesis and Cytotoxicity of 7,9-O-Linked
Macrocyclic C-Seco Taxoids
1
1
2
2
and Wei-Shuo Fang 1,*
Yu Zhao , Tian-En Wang , Alberto Mills , Federico Gago
1
State Key Laboratory of Bioactive Substances and Functions of Natural Medicines, Institute of Materia
Medica, Chinese Academy of Medical Sciences and Peking Union Medical College, 2A Nan Wei Road,
Beijing 100050, China; zhaoyu8410@126.com (Y.Z.); wangtianen@imm.ac.cn (T.-E.W.)
Department of Biomedical Sciences and “Unidad Asociada IQM-CSIC”, School of Medicine and Health
Sciences, University of Alcalá, E-28805 Alcalá de Henares, Madrid, Spain;
2
albertomillsfernandez@gmail.com (A.M.); federico.gago@uah.es (F.G.)
*
Correspondence: wfang@imm.ac.cn; Tel.: +86-10-6316-5229
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: Qiao-Hong Chen
Received: 23 May 2019; Accepted: 6 June 2019; Published: 8 June 2019
ꢀ
ꢁꢂꢃꢄꢅꢆ
Abstract: A series of novel 7,9-O-linked macrocyclic taxoids together with modification at the C2
position were synthesized, and their cytotoxicities against drug-sensitive and P-glycoprotein and
β
III-tubulin overexpressed drug-resistant cancer cell lines were evaluated. It is demonstrated that
C-seco taxoids conformationally constrained via carbonate containing-linked macrocyclization display
increased cytotoxicity on drug-resistant tumors overexpressing both III and P-gp, among which
β
compound 22b, bearing a 2-m-methoxybenzoyl group together with a five-atom linker, was identified
as the most potent. Molecular modeling suggested the improved cytotoxicity of 22b results from
enhanced favorable interactions with the T7 loop region of βIII.
Keywords: taxoids; βIII-tubulin; P-glycoprotein; drug resistance
1
. Introduction
Antitubulin agent paclitaxel (1a, Figure 1) and its semi-synthetic derivative docetaxel (1b, Figure 1)
are successfully used in the clinic for the treatment of ovarian, breast, and non-small cell lung and
prostate cancers and Kaposi’s sarcoma.
2
R O
O
1
R HN
O
O
OH
BocHN
O
OH
OH
O
O
OH
OH
HO
HO
O
O
BzO
BzO
AcO
AcO
1
2
1
1
a R = Bz, R = Ac
2
1
2
b R = Boc, R = H
Figure 1. Structures of paclitaxel (1a), docetaxel (1b), and IDN5390 (2).
However, their clinical uses are severely restricted by drug resistance. Various resistance
mechanisms toward taxane-based anticancer drugs have been revealed, among which only
overexpression of P-glycoprotein (P-gp) and βIII-tubulin have been confirmed clinically [1–4].
A great deal of effort has been made to overcome multi-drug resistance (MDR) mediated
by overexpression of P-gp. Nevertheless, many taxane-based drug candidates targeting P-gp
overexpression did not achieve the expected efficacy in clinical trials [5,6].
Molecules 2019, 24, 2161; doi:10.3390/molecules24112161
www.mdpi.com/journal/molecules

Molecules 2019, 24, 2161
2 of 23
A correlation between
βIII-tubulin overexpression and poor prognosis has been reported in
several human tumors, including various advanced malignancies upon treatment of taxanes, such as
breast, non-small cell lung, and ovarian cancers [ 10]. It was reported that a C-seco taxane IDN5390
, Figure 1) is more active than paclitaxel in several paclitaxel-resistant human ovarian adenocarcinoma
cell lines (e.g., A2780TC1, A2780TC3, and OVCAR-3), expressing high III-tubulin and P-gp levels.
7
–
(2
β
However, IDN5390 was nearly 10-fold less active than paclitaxel in paclitaxel-sensitive cells [11].
To find a modified taxane effective against both paclitaxel-sensitive and -resistant tumors, the
7
,9-O-linked C-seco taxoid
activity enhancement against drug-sensitive Hela and
compared to the C-seco paclitaxel derivative (an analog of IDN5390, Figure 2) [12]. Those macrocyclic
3
(Figure 2) was synthesized in our lab and shown to exhibit significant
β
III-tubulin overexpressing HeLa- III tumor cells
β
4
taxoids provided a successful example for the compromise between structural pre-organization and
sufficient flexibility in the C ring of C-seco taxoids to improve the cytotoxicity against tumor cells that
overexpress βIII tubulin [12].
Figure 2. Structures of the 7,9-O-linked C-seco taxoid 3 and C-seco paclitaxel derivative 4.
It has long been observed that modification of taxane at the C2 position could play a critical role in
its interaction with tubulin. Consistent with this observation, the 7,9-O-linked C-seco taxoid with C2
modification
A2780AD and KB-V1 cells (P-gp overexpression) and Hela-
demonstrated that the meta-substitution (i.e., -OMe, -F, -Cl) of the C2-benzoate moiety of C-seco
taxoids derivatives 7a (Figure 3) could increase the interaction of C-seco-taxoids with III-tubulin to
overcome paclitaxel-resistance [13].
5
(Figure 3) was much more cytotoxic than the C-seco taxoid
6 (Figure 3) in drug-resistant
β
III ( III overexpression) [12]. It was
β
–
c
β
Figure 3. Structures of the 7,9-O-linked C-seco taxoid 5 and C-seco taxoids 6, 7a–c.
In order to explore the effect of macrocyclization in a different way from that employed in our
previous study (i.e., via the carbonate formation to restrict the conformation), the synthesis and

Molecules 2019, 24, 2161
3 of 23
biological activity assessment of a series of 7,9-O-linked macrocyclic taxoids together with modification
at the C2 position were performed and are reported here.
2
. Results and Discussion
2
.1. Chemistry
0
Our synthesis began with the preparation of 2 -tert-butyldimethylsilyl-paclitaxel 12a, which was
then converted to 10-deacetylpaclitaxel 13a upon treatment with hydrazine hydrate in methanol.
0
Synthesis of the analogues 12b
–
e
of 2 -tert-butyldimethylsilyl-paclitaxel with modifications at the
C2 positions was then realized by selective C2 debenzoylation and then elaboration with various
m-substituted benzoyl group. C2-modified 10-deacetylpaclitaxel 13b were afforded in the same
manner as compound 13a. Then the compounds 13a were oxidized by copper (II) diacetate to furnish
4a as a mixture of two epimers. Reductive trapping of the ring C-seco tautomers 15a were obtained
by treatment with l-selectride. Subsequent deprotection with pyridine hydrofluoride (HF-pyridine)
afforded 16a . The 9-OH in 15a was hydroxylalkylated by 2-bromoethanol or 3-bromo-1-propanol
in the presence of potassium carbonate and potassium iodide in N,N-dimethylformamide (DMF).
Cyclization of compounds 17a could be accomplished by treatment with a slight excess of triphosgene,
affording the cyclic carbonate analogues 19a . Desilylation of 19a with HF-pyridine afforded
macrocyclic analogues 21a . Accordingly, macrocyclic taxoids 22a bearing a linkage with one more
carbon atom were synthesized from 18a–e in a similar manner (Scheme 1).
–
e
–
e
1
–
e
–e
–e
–e
–e
–
e
–e
–e
–e
Scheme 1. Cont.

Molecules 2019, 24, 2161
4 of 23
◦
Scheme 1. (a) tert-ButyldiMethylsilyl chloride (TBDMSCl), imidazole, DMF, 2 h, 60 C, and;
triethylchlorosilane (TESCl), imidazole, DMF, overnight, r.t., 90.1%; (b) Triton-B, tetrahydrofuran
◦
0
(
4
THF), 15 min,
−
40 C, 47.7%; (c) (10a) m-anisic acid, N, N -diisopropylcarbodiimide (DIC),
◦
-dimethylaminopyridine (DMAP), toluene, overnight, 60 C, 72.5%; (10b) m-fluorobenzoic acid,
◦
DIC, DMAP, toluene, overnight, 60 C, 91.4%; (10c) m-chlorobenzoic acid, DIC, DMAP, toluene,
◦
◦
overnight, 60 C, 84.2%; (10d) m-trifluoromethyl acid, DIC, DMAP, toluene, overnight, 60 C, 84.2%;
d) HF -pyridine, THF, overnight, r.t.; (11a) 81.8%; (11b) 91.9%; (11c) 85.1%; (11d) 91.0%; (e) TBDMSCl,
(
imidazole, DMF, 4 h, r.t.; (f) NH NH2
·
H O, C H OH, 2 h, r.t. (e and f two steps), (13a) 87.9%, (13b
)
2
2
2
5
99.0%; (13c) 93.5%; (13d) 83.0%; (13e) 90.1%; (g) Cu(OAc)
·
H O, CH OH, overnight, r.t., (14a) 85.8%;
2
2
3
◦
(
(
14b) 69.5%; (14c) 79.0%; (14d) 84.9%; (14e) 81.9%; (h) l-selectride, THF, 15 min,
15b) 88.7%; (15c) 79.2%; (15d) 58.8%; (15e) 76.5%; (i) HF/Py, THF, overnight, r.t., (16a) 77.4%; (16b
−20 C, (15a) 81.2%;
)
)
6
5
4
5.2%; (16c) 59.3%; (16d) 60.3%; (16e) 55.5%; (j) 2-bromoethanol, K CO , KI, DMF, 5–9 h, r.t., (17a
2 3
2.4%; (17b) 56.1%; (17c) 53.2%; (17d) 60.9%; (17e) 49.9%; (k) 3-bromo-1-propanol, K CO , KI, DMF,
2
3
–9 h, r.t., (18a) 72.4%; (18b) 75.3%; (18c) 69.7%; (18d) 52.6%; (18e) 71.8%; (l) triphosgene, pyridine,
◦
DCM, 3–5 h, 0 C to r.t., (19a) 15.9%; (19b) 32.7%; (19c) 32.1%; (19d) 36.1%; (19e) 30.5%; (20a) 24.9%;
(
(
20b) 28.6%; (20c) 27.1%; (20d) 23.6%; (20e) 26.7%; (m) HF/Py, THF, 30 h, r.t., (21a) 46.2%; (21b) 54.1%;
21c) 52.2%; (21d) 48.7%; (21e) 63.7%; (22a) 51.0%; (22b) 59.2%; (22c) 51.5%; (22d) 65.4%; (22e) 59.5%.

Molecules 2019, 24, 2161
5 of 23
2
.2. Bioactivity Evaluation of Taxoids 21a–e and 22a–e
Taxoids 21a 22a , and 16a were evaluated for their in vitro cytotoxicities against cervical
carcinoma HeLa cells and their corresponding drug-resistant cell lines (HeLa-βIII).
As shown in Table 1, all the 7,9-O-linked macrocyclic analogues (21a e, 22a
remarkably higher potency against HeLa and HeLa- III cells than their corresponding C-seco taxoids
analogues 16a . The R/S values (IC50 in drug resistant cells/IC50 in drug sensitive cells) of all
macrocyclic analogues were lower than those of their corresponding C-seco taxoids analogues
6a . These findings demonstrate that conformational restraint via carbonate-containing linked
–
e,
–
e
–e
–
–e) possessed a
β
–
e
1
–e
macrocyclization can improve the cytotoxicity against human carcinoma cell lines overexpressing
βIII tubulin.
Furthermore, all of the 7,9-O-linked macrocyclic analogues bearing the four-atom linker (21a
turned out to be generally more potent against sensitive HeLa cells and HeLa- III cells than the
corresponding macrocyclic analogues bearing the five-atom linker (22a ). Since the cytotoxicity of
1a was approximately equal to that of paclitaxel, these results suggest that a four-atom tether is
optimal in these macrocyclic C-seco taxoids.
For the effect of C2 modifications in these macrocyclic C-seco taxoids, we found similar results as
previously reported [12 13]. Pepe et al. studied the cytotoxicity of a series of C-seco taxoids, whereby
the introduction of a substituent (-OMe, -F, -Cl) to the meta-position of the C2 benzoyl moiety increased
potency against the III-tubulin-overexpressing, paclitaxel-resistant cell line A2780TC3 [13]. Taxoid
–e)
β
–e
2
–d
,
β
6
bearing a 2-(m-azido) benzyloxy group and synthesized in our lab exhibited higher binding affinity for
microtubulin (MT) than its corresponding taxoids bearing a 2-benzyloxy group [12]. The 7,9-O-linked
C-seco taxoid bearing a 2-(m-azido) benzyloxy group
drug-resistant A2780AD, HeLa-βIII, and KB-V1 cells [12].
We investigated this effect in the 7,9-O-linked C-seco taxoids 21b
introduction of a meta substituent (-OMe, -F, -Cl) on derivatives bearing the four-atom linker showed
similar cytotoxicity against HeLa sensitive cell lines and Hela- III cells lines as their corresponding
C-seco taxoid 21a bearing a 2-benzyloxy group. In contrast, the meta-substituted (-OMe, -F, -Cl)
derivatives bearing five-atom linker possessed higher potency against HeLa- III cells lines than its
corresponding C-seco taxoid 22a (by a factor of 3.1–8.9). Nonetheless, the 2-m-CF analogues 21e and
5 was significantly more active than 6 on
–e and 22b–e reported here. Thus,
β
β
3
2
2e were considerably less cytotoxic against both drug sensitive and resistant cells by one to two orders
of magnitude.
The growth inhibition effects of the 7,9-O-linked macrocyclic analogues were also measured on
human breast cancer MCF-7 cells and their corresponding P-gp-overexpressing drug-resistant MCF-7/R
cells. As shown in Table 1, the 7,9-O-linked macrocyclic analogues possessed remarkable potency
against MCF-7/R cells compared to their C-seco counterparts, except for the 2-m-CF derivatives.
3
Strikingly, macrocyclic taxoids bearing the five-atom linker were almost inactive. The cytotoxicity
against MCF-7/R cells of the 7,9-O-linked macrocyclic derivatives (-OMe, -F, -Cl) bearing the five-atom
linker were slightly higher than that of the compouds bearing the four-atom linker. Compounds
2
2b–d (-OMe, -F, -Cl) bearing the five-atom linker and 21a, 21d (-H, -Cl) bearing the four-atom linker
displayed lower R/S values than that of paclitaxel. All in all, 22b turned out to be the best compound
in the whole series.

Molecules 2019, 24, 2161
6 of 23
Table 1. Cytotoxicity of taxoids 16a–e, 21a–e, and 22a–e.
Cytotoxicity (IC , nM)
Ratio
Cytotoxicity (IC , nM)
Ratio
5
0
50
Compound
HeLa
HeLa-βIII
R/S
MCF-7
MCF-7/R
R/S
2
2
2
2
1a
1b
1c
1d
5.97 ± 1.13
5.90 ± 1.47
29.92 ± 2.85
17.61 ± 2.13
5.01 ± 0.48
3.17 ± 0.25
2.83 ± 0.81
2.46 ± 1.24
2.61 ± 0.98
5.74 ± 2.08
1.52 ± 1.34
4.34 ± 1.41
4.35 ± 1.47
2.77 ± 0.89
8.55 ± 1.75
10.48 ± 0.42
20.50 ± 7.54
10.22 ± 1.07
4.77 ± 0.81
2.68 ± 0.28
11.82 ± 1.10
9.93 ± 2.70
6291.33 ± 1252.19
6440.00 ± 1040.85
6411.67 ± 645.71
4126.33 ± 91.92
>10,000
532.26 ± 105.94
648.76 ± 104.85
832.68 ± 83.86
440.85 ± 9.82
7.82 ± 3.10
22.14 ± 6.36
7.70 ± 1.68
7.75 ± 2.24
19.02 ± 9.60
9.36 ± 1.76
2
2
1e
2a
186.03 ± 48.30
28.28 ± 0.47
7.97 ± 1.79
503.40 ± 132.41
162.33 ± 58.80
18.11 ± 2.91
159.80 ± 33.91
19.16 ± 2.39
5.15 ± 0.96
>10,000
2
2
2
2b
2c
2d
2769.00 ± 399.24
4756.33 ± 443.24
3704.67 ± 539.43
>10,000
538.02 ± 77.57
509.79 ± 47.51
255.79 ± 37.24
12.07 ± 0.93
11.53 ± 1.98
89.71 ± 29.80
149.57 ± 31.70
13.63 ± 2.09
22.78 ± 2.20
17.73 ± 1.70
110.14 ± 17.40
4.59 ± 0.55
52.40 ± 16.98
50.11 ± 16.92
267.20 ± 65.38
1423.67 ± 291.75
142.90 ± 5.66
467.13 ± 171.75
181.17 ± 18.92
525.87 ± 88.76
12.31 ± 1.27
9.33 ± 1.44
14.48 ± 3.37
86.00 ± 9.28
103.53 ± 22.21
7.53 ± 0.19
2
1
2e
6a
>10,000
>10,000
>10,000
>10,000
1
6b
6c
6d
6e
Paclitaxel
1
16.90 ± 4.04
15.08 ± 1.65
110.90 ± 13.25
6.21 ± 1.85
1
1
>10,000
3450.00 ± 509.99
555.56 ± 82.12

Molecules 2019, 24, 2161
7 of 23
2
.3. Binding Mode of 22b and Rationale for the Increased Affinity for the βIII Isotype
Inspection of the paclitaxel- -tubulin complex in high-resolution cryo-electron microscopy
cryo-EM) structures of mammalian microtubules reveals a very tight fit between the bulky drug and
β
(
the taxane-binding site, in which the M-loop is structured as an
α
-helix [14]. The oxetane ring oxygen of
0
paclitaxel (1a) accepts a hydrogen bond from the backbone NH of Thr276, whereas the C-3 benzamide
ε
carbonyl oxygen acts as a hydrogen bond acceptor for N of His229. These two hydrogen bonds are
likely to be present in the 22b
binding affinity, but these two residues are common to both
sequence differences that can account for the resistance to taxanes, a lot of emphasis has been placed
on the Ser Ala replacement at position 277, but we believe that the most important replacement in
relation to drug resistance possibly involves Cys241 Ser. The reason is that, as a consequence of this
substitution, disulfide bond formation with Cys356 is precluded in the III isotype and the T7 loop
:β-tubulin complex as well (Figure 4), and definitely contribute to the
β
IIB and III isotypes. In the search for
β
→
→
β
region, which closes over the bound taxane, is likely to be more flexible. By directing the macrocyclic
region of 22b towards this loop, favorable interactions within the taxane-binding site are enhanced and
the affinity towards the
2b relative to 1a, and the other taxanes described here, results from enhanced favorable interactions
with the T7 loop region of III, an isotype in which Cys356 cannot engage in a disulfide bond with the
βIII isotype is improved. We hypothesize that the improved cytotoxicity of
2
β
amino acid present at position 241 (Ser).
Figure 4. 22b docked into homology models of human tubulins IIb and III bound to guanosine
diphosphate (GDP)-Mg2 . Colored in magenta and labeled are those residues close to the taxane-binding
site that differ between these two isotypes.
+
As shown in this modelling study, the binding of these taxoids to microtubules are similar to that
of paclitaxel. Although cyclization does increase the cytotoxicity either in drug-sensitive and -resistant
cells in most cases, the 7,9-O-linked macrocyclic taxoids only showed comparable cytotoxicity to that
of paclitaxel. The enhanced activity is not only arisen from the known C-2 modifications [15
also from the cyclization of the cleaved C-ring of taxane.
,16], but

Molecules 2019, 24, 2161
8 of 23
3
3
3
. Experimental
.1. Chemical Synthesis
.1.1. General Methods
All chemicals and reagents were purchased from Beijing Innochem Science and Technology
Co. Ltd. (Beijing, China), Sinopharm Chemical Reagent Co. Ltd. (Beijing, China), and thin-layer
chromatography (TCI). The 200–300 mesh silica gel used for flash column chromatography was
purchased from Rushanshi Shuangbang Xincailiao Co. Ltd. (Rushan, Shandong, China). Visualization
on TLC (analytical thin layer chromatography) was achieved by the use of UV light (254 nm) and
treatment with phosphomolybdic acid or KMnO followed by heating. All solvents were purified
4
and dried according to the standard procedures. The purification was performed on flash column
chromatography. The high performance liquid chromatography (HPLC)- electrospray ionization
(
ESI)-mass spectrometry (MS) analysis was carried out in an Agilent 1260 Infinity HPLC system (Agilent
Technologies, Waldbronn, Germany) equipped with a reversed phase 4.68 50 mm (1.8 um) XDB-C18
×
Column and consisted of a binary solvent delivery system, an auto sampler, a column temperature
controller, and an UV detector. The mass spectra were acquired by a 6120 Quadrupole LC-MS mass
spectrometer (Agilent Technologies, Waldbronn, Germany) connected to the HPLC system via an ESI
1
13
interface. Proton and carbon magnetic resonance spectra ( H-NMR and C-NMR) were recorded on a
1
Bruker BioSpin AG 300 or 400 MHz spectrometer or Varian 300, 400, or 600 MHz spectrometer. H-NMR
data were reported as follows: Chemical shifts, multiplicity (s = singlet, d = doublet, t = triplet,
q = quartet, m=multiplet), coupling constant(s) in Hz, integration. All tested compounds 16a
1a , and 22a were 95% pure by HPLC (column XDB C18 4.6 50 mm 1.8 m, mobile phase:
acetonitrile-water (10:90–100:0 gradient in 4.5 min), flow rate 1.0 mL/min, detected at 220 nm).
–e,
2
–
e
–
e
≥
×
µ
3
.1.2. General Experimental Procedure for Compounds 14a–e
0
2
-O-(tert-Butyldimethylsilyl)-10-dehydro-10-deacetylpaclitaxel (14a). To a solution of 13a (261.3 mg,
H O (282 mg, 1.41 mmol). The suspension was
0.282 mmol) in methanol (8 mL) was added Cu(OAc)2
·
2
stirred at room temperature overnight (open air) and then diluted with ethyl acetate. The organic
phase was washed sequentially with saturated aqueous NaCl (50 mL), 2 N NH to remove copper
3
salts and saturated aqueous NH Cl. After drying (Na SO ) and evaporation under reduced pressure,
4
2
4
the crude product was purified by silica gel chromatography (ethyl acetate: petroleum ether = 1:2)
1
to give a 4:1 mixture of epimers 14a (14-
CDCl , 600 MHz)
β
-OH and 14-
α
-OH, 223.8 mg, 85.8% total yield). H-NMR
(
δ
: 8.19 (d, J = 7.8 Hz, 1H, Ar-H), 7.73 (d, J = 7.8 Hz, 2H, Ar-H), 7.48 (m, 11H, Ar-H),
3
7
.06 (d, J = 9.0 Hz, 1H, NH), 6.28 (t, J = 8.7 Hz, 1H, H-13), 5.87 (d, J = 7.2 Hz, 1H, H-2), 5.79 (dd,
0
0
J = 1.5, 8.7 Hz, 1H, H-3 ), 4.93 (m, 1H, H-5), 4.67 (d, J = 1.8 Hz, 1H, H-2 ), 4.50 (d, J = 11.4 Hz, 1H, H-7),
.44 (d, J = 8.4 Hz, 1H, H- 20a), 4.38 (d, J = 9.0 Hz, 1H, H-20b), 4.04 (d, J = 7.2 Hz, 1H, H-3), 3.88 (m,
H, OH-7), 2.67 (s, 3H, CH ), 2.48 (dd, J = 9.6, 15.6 Hz, 1H, H-6a), 2.29 (m, 2H, H-14b, H-14a), 2.19
4
1
3
(
m, 1H, H-6b), 1.86 (s, 3H, CH ), 1.75 (s, 3H, CH ), 1.21 (s, 3H, CH ), 1.13 (s, 3H, CH ), 0.79 (s, 9H,
3
3
3
3
SiC(CH ) ),
http://dx.doi.org/10.1016/j.ejmech.2017.06.001)
−
0.04 (s, 3H, Si(CH )),
−
0.30 (s, 3H, Si(CH )). (For the chemical characterization refer to
3
3
3
3
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-methoxybenzoyl)-7-epi-10-dehydro-10-deacetylpaclitaxel (14b).
1
69.5% yield as a 4:1 mixture of two epimers; H-NMR (CDCl , 400 MHz)
δ: 7.80 (d, J = 7.7 Hz, 1H,
3
Ar-H), 7.74 (d, J = 7.2 Hz, 2H, Ar-H), 7.41 (m, 10H, Ar-H), 7.21 (dd, J = 2.0, 8.0 Hz, Ar-H), 7.09 (d,
J = 9.1 Hz, 1H, NH), 6.27 (t, J = 8.9 Hz, 1H, H-13), 5.89 (d, J = 7.2 Hz, 1H, H-2), 5.79 (dd, J = 2.2, 9.4
0
0
Hz, 1H, H-3 ), 4.94 (m, 1H, H-5), 4.67 (d, J = 2.0 Hz, 1H, H-2 ), 4.50 (d, J = 11.2 Hz, 1H, H-7), 4.47 (d,
J = 8.8 Hz, 1H, H- 20a), 4.38 (d, J = 8.6 Hz, 1H, H-20b), 4.05 (d, J = 7.1 Hz, 1H, H-3), 3.90 (s, 3H, OCH3),
3
.88 (m, 1H, OH-7), 2.67 (s, 3H, CH ), 2.49 (dd, J = 9.8, 15.4 Hz, 1H, H-6a), 2.29 (m, 2H, H-14b, H-14a),
3
1
.86 (s, 3H, CH ), 2.25 (m, 1H, H-6b), 1.75 (s, 3H, CH ), 1.21(s, 3H, CH ), 1.13 (s, 3H, CH ), 0.81 (s, 9H,
3
3
3
3
13
SiC(CH ) ),
−
0.02 (s, 3H, Si(CH )),
−
0.26 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ: 207.8, 188.7,
3
3
3
3
3

Molecules 2019, 24, 2161
9 of 23
1
1
2
72.2, 170.9, 167.0, 166.9, 159.8, 143.3, 141.1, 138.2, 134.1, 131.9, 130.3, 130.0, 128.8 (2C), 128.1, 127.0,
26.4, 122.7, 120.5, 114.4, 82.7, 81.8, 79.2, 77.4, 75.3, 75.1, 70.7, 57.2, 55.5 (2C), 40.3, 39.4, 36.3, 35.4, 26.9,
6.1, 25.5, 22.9, 18.2, 15.0, 14.4, 5.2, 5.8; LC-MS (ESI, m/z): [M + 1], found 954.4, [M + 23], found 976.4,
C H NO Si: 953.40 (see supplementary materials).
−
−
52
63
14
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-fluorobenzoyl)-7-epi-10-dehydro-10-deacetylpaclitaxel (14c).
1
79.0% yield as a 4:1 mixture of two epimers; H-NMR (CDCl , 400 MHz)
δ: 8.02 (d, J = 8.0 Hz, 1H,
3
Ar-H), 7.89–7.86 (m, 1H, Ar-H), 7.73 (d, J = 7.2 Hz, 2H, Ar-H), 7.59–7.33 (m, 10H, Ar-H), 7.07 (d,
J = 9.2 Hz, 1H, BzNH), 6.27 (t, J = 8.8 Hz, 1H, H-13), 5.86 (d, J = 7.2 Hz, 1H, H-2), 5.80 (dd, J = 2.0, 9.2 Hz,
0
0
1
4
(
H, H-3 ), 4.95 (dd, J = 4.0, 8.0 Hz, 1H, H-5), 4.68 (d, J = 2.4 Hz, 1H, H-2 ), 4.48 (d, J = 11.2 Hz, 1H, H-7),
.44 (d, J = 8.8 Hz, 1H, H- 20a), 4.36 (d, J = 8.8 Hz, 1H, H-20b), 4.05 (d, J = 7.2 Hz, 1H, H-3), 3.92–3.88
m, 1H, OH-7), 2.68 (s, 3H, COCH ), 2.48 (dd, J = 9.6, 15.2 Hz, 1H, H-6a), 2.31–2.29 (m, 2H, H-14b,
3
H-14a), 2.22 (dd, J = 8.4, 15.6 Hz, 1H, H-6b), 1.99 (br, 1H, OH), 1.86 (s, 3H, CH ), 1.76 (s, 3H, CH ), 1.22
3
3
(
s, 3H, CH ), 1.13 (s, 3H, CH ), 0.81 (s, 9H, SiC(CH )),
−
0.02 (s, 3H, Si(CH )),
−
0.26 (s, 3H, Si(CH ) );
3
3
3
3
3 2
13
4
C-NMR (CDCl , 100 MHz)
δ
: 207.8, 188.6, 172.3, 171.2, 170.9, 167.0, 165.9 (d, J
= 2.9 Hz), 162.7
3
C-F
1
3
3
(
d, J
= 246.5 Hz), 143.5, 140.9, 138.2, 134.1, 131.9, 131.3 (d, J
= 7.3 Hz), 130.7 (d, J
= 7.6 Hz),
C-F
C-F
C-F
4
2
1
1
28.83 (2C), 128.77 (2C), 128.1, 127.0 (2C), 126.4 (2C), 126.1 (d, J
= 3.1 Hz), 120.0 (d, J
= 21.1 Hz),
C-F
C-F
2
17.1 (d, J
= 23.1 Hz), 82.8, 81.7, 79.4, 75.5, 75.3, 70.6, 57.2, 55.6, 40.3, 39.5, 36.3, 35.4, 26.1, 25.5 (3C),
C-F
2
2.9 (2C), 18.2, 15.0, 14.5, 14.2,
−
5.2, 5.8; LC-MS (ESI, m/z): [M + 1], found 942.4, [M + 23], found 964.3,
−
C H FNO Si: 941.38.
51
60
13
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-chlorobenzoyl)-7-epi-10-dehydro-10-deacetylpaclitaxel (14d).
1
8
4.9% yield as a 4:1 mixture of two epimers; H-NMR (CDCl , 400 MHz)
δ: 8.18 (s, 1H, Ar-H), 8.11 (d,
3
J = 7.6 Hz, 1H, Ar-H), 7.73 (d, J = 7.6 Hz, 2H, Ar-H), 7.62 (d, J = 7.6 Hz, 1H, Ar-H), 7.55–7.50 (m, 2H,
Ar-H), 7.44–7.35 (m, 7H, Ar-H), 7.08 (d, J = 8.8 Hz, 1H, BzNH), 6.25 (t, J = 8.8 Hz, 1H, H-13), 5.84 (d,
0
0
J = 7.2 Hz, 1H, H-2), 5.79 (dd, J = 8.8 Hz, 1H, H-3 ), 4.96 (m, 1H, H-5), 4.67 (d, J = 2.0 Hz, 1H, H-2 ),
.47 (d, J = 11.2 Hz, 1H, H-7), 4.44 (d, J = 8.4 Hz, 1H, H- 20a), 4.35 (d, J = 8.4 Hz, 1H, H-20b), 4.05 (d,
J = 7.2 Hz, 1H, H-3), 3.89 (m, 1H, OH-7), 2.68 (s, 3H, CH ), 2.48 (dd, J = 10.0, 15.4 Hz, 1H, H-6a), 2.29
4
3
(
3
m, 2H, H-14b, H-14a), 2.23 (m, 1H, H-6b), 1.86 (s, 3H, CH ), 1.76 (s, 3H, CH ), 1.22 (s, 3H, CH ), 1.13 (s,
3
3
3
13
H, CH ), 0.82 (s, 9H, SiC(CH ) ),
−
0.02 (s, 3H, Si(CH )),
−
0.26 (s, 3H, Si(CH )); C-NMR (CDCl3,
3
3 3
3
3
1
1
5
00 MHz)
30.3, 128.83 (2C), 128.77 (2C), 128.5, 128.1, 127.0 (2C), 126.5 (2C), 82.7, 81.7, 79.4, 75.4, 75.3, 70.7, 60.4,
7.2, 55.6, 40.2, 39.4, 36.3, 35.3, 29.7, 26.1, 25.5 (2C), 22.9, 22.8, 18.2, 14.9, 14.5, 5.2, 5.8; LC-MS (ESI,
m/z): [M + 1], found 958.4, [M + 23], found 980.4, C H ClNO Si: 957.35.
δ: 207.8, 188.6, 172.2, 170.9, 165.7, 143.5, 140.9, 138.2, 134.9, 134.1, 133.9, 131.9, 130.9, 130.4,
−
−
51
60
13
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-trifluoromethyl)-7-epi-10-dehydro-10-deacetylpaclitaxel (14e).
1
8
1.9% yield as a 4:1 mixture of two epimers; H-NMR (CDCl , 400 MHz)
δ: 8.50 (s, 1H, Ar-H), 8.43 (d,
3
J = 7.6 Hz, 1H, Ar-H), 7.91 (d, J = 8.0 Hz, 1H, Ar-H), 7.72 (d, J = 7.8 Hz, 3H, Ar-H), 7.51 (m, 1H, Ar-H),
.41 (m, 7H, Ar-H), 7.06 (d, J = 9.2 Hz, 1H, BzNH), 6.24 (t, J = 8.6 Hz, 1H, H-13), 5.88 (d, J = 7.6 Hz,
7
0
0
1
H, H-2), 5.78 (dd, J = 1.6, 9.2 Hz, 1H, H-3 ), 4.97 (m, 1H, H-5), 4.67 (d, J = 2.0 Hz, 1H, H-2 ), 4.45 (d,
J = 11.2 Hz, 1H, H-7), 4.42 (d, J = 8.5 Hz, 1H, H-20a), 4.37 (d, J = 8.6 Hz, 1H, H-20b), 4.09 (d, J = 7.6 Hz,
H, H-3), 3.90 (m, 1H, OH-7), 2.66 (s, 3H, CH ), 2.51 (dd, J = 9.6, 15.5 Hz, 1H, H-6a), 2.30 (m, 2H, H-14b,
1
3
H-14a), 2.26 (m, 1H, H-6b), 1.87 (s, 3H, CH ), 1.77 (s, 3H, CH ), 1.23 (s, 3H, CH ), 1.15 (s, 3H, CH ), 0.83
3
3
3
3
1
3
(
1
s, 9H, SiC(CH ) ),
−
0.02 (s, 3H, Si(CH )),
−
0.24 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ: 207.7,
3
3
3
3
3
2
88.6, 172.1, 171.0, 167.1, 165.6, 143.6, 140.9, 138.3, 134.2, 133.6, 131.9, 131.4 (q, J
= 33.2 Hz), 130.3
C-F
3
3
(
q, J = 3.4 Hz), 130.3, 130.1, 129.9, 128.9, 128.8, 128.1, 127.1 (q, J
= 4.0 Hz), 127.0, 126.5, 123.7 (q,
C-F
1
JC-F = 273.6 Hz), 82.8, 81.7, 79.5, 75.6, 75.3, 70.7, 57.2, 55.6, 40.3, 39.5, 36.3, 35.4, 26.1, 25.6, 22.9, 22.7,
8.2, 14.9, 14.5, −5.2, −5.8; LC-MS (ESI, m/z): [M + 1], found 992.0, C H F NO Si: 991.38.
1
52
60
3
13

Molecules 2019, 24, 2161
10 of 23
3
.1.3. General Experimental Procedure for Compounds 15a–e
0
2
-tert-Butyldimethylsilyl-10-dehydro-7-8-seco-10-deacetylpaclitaxel (15a). l-selectride (1M solution in THF,
◦
0.8 mL) was added, dropwise, to a solution of 14a (171.5 mg, 0.186 mmol) in THF (4.1 mL) at
−
20 C.
After 15 min, the reaction was quenched by addition of cold ethyl acetate (50.0 mL) and 2 N H SO
2
4
(4.0 mL). The reaction mixture was extracted with ethyl acetate and the combined organic phases were
washed with a saturated aqueous NaHCO and saturated aqueous NH Cl. The resulting solution was
3
4
dried over anhydrous MgSO and the solvent evaporated under reduced pressure to give a crude
4
product. The crude product was purified by silica gel chromatography (ethyl acetate: petroleum
ether = 1:1) which gave product 15a (139.5 mg, 81.2% yield) as a white solid
0
2
-tert-Butyldimethylsilyl-2-debenzoyl-2-(3-methoxybenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel (15b).
1
White solid; yield 88.7%; H-NMR (CDCl , 400 MHz)
δ: 7.73–7.70 (m, 3H, Ar-H), 7.55 (s, 1H, Ar-H),
3
7
.42 (m, 10H, Ar-H), 7.14 (dd, J = 2.3, 8.2 Hz, 1H, BzNH), 6.47 (s, 1H, OH-9), 6.29 (t, J = 8.0 Hz, 1H,
0
H-13), 5.91 (d, J = 8.8 Hz, 1H, H-3 ), 5.60 (d, J = 9.2 Hz, 1H, H-2), 5.24 (brs, 2H, H-5, H-20a), 4.72 (d,
J = 1.6 Hz, 1H, H-2 ), 4.29 (d, J = 6.8 Hz, 1H, H-3), 4.20 (brs, 1H, H-7a), 3.96 (brs, 1H, OH), 3.85 (s, 4H,
0
OCH , H-7b), 2.82 (brs, 1H, H-6a), 2.71 (brs, 1H, OH), 2.26 (dd, J = 9.6, 15.6 Hz, 2H, H-14a, H-14b),
3
2
.09–2.02 (m, 4H, CH , H-6b), 1.87 (brs, 6H, 2
×
CH ), 1.28 (s, 3H, CH ), 1.10 (s, 3H, CH ), 0.79 (s, 9H,
3 3 3
3
13
SiC(CH ) ),
−
0.11 (s, 3H, Si(CH )),
−
0.28 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ
: 191.2, 171.2,
71.1, 168.9, 167.4, 167.2, 159.8, 148.9, 142.1, 138.2, 133.9, 131.9, 130.5, 130.3, 128.7 (4C), 128.0, 127.1
2C), 126.7 (2C), 124.6, 122.2, 119.5, 115.0, 86.3, 76.1, 75.1, 70.6, 59.2, 55.8, 55.5, 43.1, 36.6, 25.5 (3C), 23.4,
2.2, 21.5, 18.3, 14.8, 14.4, 5.6, 6.0; LC-MS (ESI, m/z): [M + 1], found 956.4, [M + 23], found 978.4,
C H NO Si: 955.42.
3
3
3
3
3
1
(
2
−
−
52
65
14
0
2
-tert-Butyldimethylsilyl-2-debenzoyl-2-(3-fluorobenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel (15c).
1
White solid; yield 79.2%; H-NMR (CDCl , 400 MHz)
δ: 7.94 (d, J = 7.8 Hz, 1H, Ar-H), 7.76 (d,
3
J = 8.7 Hz, 1H, Ar-H), 7.68 (d, J = 7.4 Hz, 2H, Ar-H), 7.53–7.44 (m, 3H, Ar-H), 7.40–7.30 (m, 8H, NH,
0
Ar-H), 6.48 (s, 1H, OH-9), 6.30 (t, J = 8.0 Hz, 1H, H-13), 5.92 (d, J = 9.0 Hz, 1H, H-3 ), 5.60 (d, J = 9.5 Hz,
1
0
H, H-2), 5.25 (brs, 2H, H-5, H-20a), 4.71 (d, J = 2.1 Hz, 1H, H-2 ), 4.30 (d, J = 7.8 Hz, 1H, H-3), 4.19 (brs,
1
H, H-20b), 3.96 (brs, 1H, H-7a), 3.80 (brs, 1H, H-7b), 2.78 (brs, 1H, H-6a), 2.69 (brs, 1H, H-14a), 2.26
(
dd, J = 9.5, 15.6 Hz, 1H, H-14b), 2.10–2.00 (ovelap, 1H, H-6b), 1.90 (s, 3H, CH ), 1.86 (overlap and
3
brs, 6H, 2
×
CH ), 1.27 (s, 3H, CH ), 1.10 (s, 3H, CH ), 0.78 (s, 9H, SiC(CH ) ), 0.09 (s, 3H, Si(CH )),
−
3
3
3
3 3
3
13
−
0.29 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz) δ: 191.1, 171.2, 171.0, 168.8, 167.4, 166.4, 131.0 (d,
3 3
JC-F = 248.1 Hz), 128.8 (2C), 128.1, 127.1, 126.7, 125.8 (d, J
1
4
2
= 2.6 Hz), 124.6, 121.1 (d, J
= 21.3 Hz),
C-F
C-F
1
1
16.7 (d, 2J
4.5,
= 22.6 Hz), 86.5, 80.7, 76.1, 75.5, 70.5, 59.0, 55.8, 44.5, 43.2, 36.7, 25.6, 22.3, 21.6, 18.3, 14.9,
C-F
−
−
5.4, 5.9; LC-MS (ESI, m/z): [M + 1], found 944.4, [M + 23], found 966.4, C H FNO Si: 943.40.
51 62 13
0
2
-tert-Butyldimethylsilyl-2-debenzoyl-2-(3-chlorobenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel (15d).
1
White solid; yield 58.8%; H-NMR (CDCl , 400 MHz) δ: 8.05 (d, J = 7.6 Hz, 2H, Ar-H), 8.01 (s, 1H,
3
Ar-H), 7.68 (d, J = 7.6 Hz, 2H, Ar-H), 7.57 (d, J = 8.0 Hz, 1H, Ar-H), 7.41–7.31 (m, 9H, NH, Ar-H),
0
6
.49 (s, 1H, OH-9), 6.29 (t, J = 8.4 Hz, 1H, H-13), 5.92 (d, J = 9.3 Hz, 1H, H-3 ), 5.59 (d, J = 9.5 Hz, 1H,
0
H-2), 5.23 (brs, 2H, H-5, H-20a), 4.71 (d, J = 1.6 Hz, 1H, H-2 ), 4.30 (d, J = 6.9 Hz, 1H, H-3), 4.18 (brs,
1H, H- 20b), 3.98 (brs, 1H, H-7a), 3.83 (brs, 1H, H-7b), 2.78 (brs, 1H, H-6a), 2.67 (brs, 1H, H-14a), 2.25
(
dd, J = 9.6, 15.6 Hz, 1H, H-14b), 2.05 (m, 1H, H-6b), 1.89 (s, 3H, CH ), 1.85 (brs, 6H, 2
×
CH ), 1.26
3
3
(
s, 3H, CH ), 1.10 (s, 3H, CH ), 0.78 (s, 9H, SiC(CH ) ),
−
0.11 (s, 3H, Si(CH )),
−
0.28 (s, 3H, Si(CH ));
3
3
3 3
3
3
1
3
C-NMR (CDCl , 100 MHz)
δ
: 191.1, 171.0, 168.7, 167.4, 166.3, 148.9, 142.0, 138.0, 137.1, 135.0, 133.9,
31.9, 131.0, 130.6, 129.6, 128.7 (2C), 128.1, 128.0, 127.0 (2C), 126.7 (2C), 124.5, 86.4, 87.0, 80.5, 76.0, 75.4,
0.5, 55.7, 43.1, 36.6, 29.7, 26.9, 25.5 (3C), 22.2, 21.5, 18.3, 14.8, 14.5, 5.5, 6.0; LC-MS (ESI, m/z): [M + 1],
found 960.0, [M + 23], found 981.9, C H ClNO Si: 959.37.
3
1
7
−
−
51
62
13
0
2
(
-tert-Butyldimethylsilyl-2-debenzoyl-2-(3-trifluoromethylbenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel
1
15e). White solid; yield 76.5%; H-NMR (CDCl , 400 MHz)
δ
: 8.38 (d, J = 7.9 Hz, 2H, Ar-H), 7.84 (d,
3
J = 7.9 Hz, 2H, Ar-H), 7.48 (m, 11H, NH, Ar-H), 6.51 (s, 1H, OH-9), 6.29 (t, J = 8.4 Hz, 1H, H-13), 5.89 (d,

Molecules 2019, 24, 2161
11 of 23
0
0
J = 9.3 Hz, 1H, H-3 ), 5.62 (d, J = 9.4 Hz, 1H, H-2), 5.25 (brs, 2H, H-5, H-20a), 4.72 (brs, 1H, H-2 ), 4.32
d, J = 6.8 Hz, 1H, H-3), 4.24 (brs, 1H, H- 20b), 3.94 (brs, 1H, H-7a), 3.76 (brs, 1H, H-7b), 2.78 (brs, 1H,
H-6a), 2.66 (brs, 1H, H-14a), 2.28 (dd, J = 9.5, 15.6 Hz, 1H, H-14b), 2.05 (m, 1H, H-6b), 1.92 (s, 3H,
CH ), 1.85 (brs, 6H, 2 CH ), 1.27 (s, 3H, CH ), 1.11 (s, 3H, CH ), 0.78 (s, 9H, SiC(CH ) ), 0.08 (s,
(
×
−
3
3
3
3
3 3
13
3
1
H, Si(CH )),
−
0.29 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
42.1, 137.9, 133.9, 133.1, 131.9, 131.4 (q, J
Hz), 126.5, 123.5 (q, J
δ
: 191.0, 170.9, 167.5, 166.2, 148.9,
3
3
3
2
3
= 33.3 Hz), 130.2, 128.7, 128.0, 126.9, 126.7 (q, J
= 4.1
C-F
C-F
1
= 273.7 Hz), 87.2, 86.3, 80.6, 75.8, 75.6, 74.5, 70.4, 67.6, 59.0, 55.7, 44.4, 43.2,
C-F
3
8.3, 36.6, 29.7, 29.1, 25.5, 22.1, 21.5, 18.2, 14.8, 14.4,
−
5.5, 6.0; LC-MS (ESI, m/z): [M + 1], found 994.3,
−
[M + 23], found 1016.3, C H F NO Si: 993.39.
52
62
3
13
3
.1.4. General Experimental Procedure for Compounds 16a–e
1
0-Dehydro-7,8-seco-10-deacetylpaclitaxel (16a). To a solution of of 15a (19.8 mg, 0.0214 mmol) in THF
◦
(1.4 mL) was added, dropwise, 0.3 mL of HF-pyridine (v/v = 1:2) at 0 C, and the reaction mixture was
stirred at room temperature for 30 h. The reaction was quenched with saturated aqueous NaHCO3,
diluted with ethyl acetate, washed with saturated NH Cl. The organic layer dried over anhydrous
4
Na SO and then concentrated under reduced pressure. Purification of the crude product by silica
2
4
gel chromatography (ethyl acetate: petroleum ether = 2:1) gave product 16a as a white solid (13.4 mg,
1
7
7.4% yield). H-NMR (CDCl , 400 MHz)
δ: 8.04 (d, J = 7.6 Hz, 2H, Ar-H), 7.69 (d, J = 7.2 Hz, 2H,
3
Ar-H), 7.57 (t, J = 7.4 Hz, 1H, Ar-H), 7.48–7.44 (m, 5H, Ar-H), 7.38–7.27 (m, 6H, NH, Ar-H), 6.47 (s, 1H,
0
OH-9), 6.16 (t, J = 7.5 Hz, 1H, H-13), 5.86 (dd, J = 2.8, 9.4 Hz, 1H, H-3 ), 5.60 (d, J = 9.5 Hz, 1H, H-2), 5.20
(
0
brs, 1H, H-5), 5.16 (d, J = 11.4 Hz, 1H, H-20a), 4.78 (d, J = 3.0 Hz, 1H, H-2 ), 4.27 (d, J = 8.1 Hz, 1H, H-3),
4
.20 (brs, 1H, H-20b), 3.89 (brs, 1H, H-7a), 3.68 (dt, J = 6.2, 10.1 Hz, 1H, H-7b), 2.77 (brs, 1H, H-6a), 2.61
(
(
brs, 1H, H-14a), 2.38 (dd, J = 9.7, 15.9 Hz, 1H, H-14b), 2.29 (brs, 1H, OH), 2.10–2.07 (m, 1H, H-6b), 1.83
13
brs, 6H, 2
×
CH ), 1.75 (s, 3H, CH ), 1.20 (s, 3H, CH ), 1.07 (s, 3H, CH ); C-NMR (CDCl , 100 MHz)
3 3 3 3 3
δ
: 191.0, 172.4, 169.0, 167.3, 167.2, 148.8, 142.2, 138.0, 136.7, 133.8, 133.6, 132.0, 129.7, 129.3, 129.0, 128.8,
1
28.7, 128.1, 127.1, 127.0, 124.6, 86.9, 86.2, 80.5, 74.8, 73.7, 70.7, 59.6, 54.8, 43.0, 36.6, 29.7, 24.9, 22.1, 21.2,
1
8.4, 14.6, 14.5; LC-MS (ESI, m/z): [M + 1], found 812.0, [M + 23], found 834.0, C H NO : 811.32.
45
49
13
2
-Debenzoyl-2-(3-methoxybenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel (16b). White solid; yield 65.2%;
1
H-NMR (CDCl , 400 MHz) δ: 7.72 (d, J = 7.6 Hz, 2H, Ar-H), 7.60 (d, J = 7.1 Hz, 1H, Ar-H), 7.47–7.43
3
(
1
m, 5H, Ar-H), 7.36–7.31 (m, 5H, Ar-H), 7.29–7.25 (m, 1H, Ar-H), 7.10 (d, J = 8.1 Hz, 1H, NH), 6.49 (brs,
0
H, OH-9), 6.09 (t, J = 7.4 Hz, 1H, H-13), 5.81 (d, J = 9.2 Hz, 1H, H-3 ), 5.58 (d, J = 9.5 Hz, 1H, H-2), 5.20
0
(
(
(
(
brs, 1H, H-5), 5.14 (d, J = 11.3 Hz, 1H, H-20a), 4.73 (brs, 1H, H-2 ), 4.24 (d, J = 7.2 Hz, 1H, H-3), 4.19
brs, 1H, H-20b), 3.87 (brs, 1H, H-7a), 3.79 (s, 3H, OCH ), 3.65 (brs, 1H, H-7b), 2.74 (brs, 1H, H-6a), 2.56
3
brs, 1H, H-14a), 2.40 (dd, J = 9.9, 15.9 Hz, 1H, H-14b), 2.35 (brs, 1H, OH-1), 2.09 (m, 1H, H-6b), 1.83
13
brs, 6H, 2
: 191.1, 172.4, 169.0, 167.1, 159.8, 148.8, 142.1, 138.1, 136.7, 133.6, 131.9, 130.7, 130.1, 129.0, 128.7, 128.6,
28.2, 128.1, 127.1, 124.5, 121.8, 119.5, 114.8, 86.9, 86.1, 80.4, 74.8, 73.7, 70.5, 59.7, 55.5, 55.0, 44.5, 42.9,
6.6, 29.8, 29.7, 24.9, 22.2, 21.1, 14.6, 14.5; LC-MS (ESI, m/z): [M + 1], found 842.4, [M + 23], found 864.3,
C H NO : 841.33.
×
CH ), 1.69 (s, 3H, CH ), 1.17 (s, 3H, CH ), 1.06 (s, 3H, CH ); C-NMR (CDCl , 100 MHz)
3 3 3 3 3
δ
1
3
46
51
14
2
-Debenzoyl-2-(3-fluorobenzoyl)-10-dehydro-7, 8-seco-10-deacetylpaclitaxel (16c). White solid; yield 59.3%,
1
H-NMR (CDCl , 300 MHz) δ: 7.90 (d, J = 7.7 Hz, 1H, Ar-H), 7.75–7.68 (m, 3H, Ar-H), 7.48–7.44 (m, 4H,
3
Ar-H), 7.41–7.31 (m, 6H, Ar-H), 7.24 (d, J = 8.0 Hz, 1H, NH), 6.46 (brs, 1H, OH-9), 6.20 (t, J = 7.9Hz,
0
1
H, H-13), 5.88 (d, J = 7.6 Hz, 1H, H-3 ), 5.59 (d, J =9.5 Hz, 1H, H-2), 5.19 (overlap, J = 11.5 Hz, 2H,
0
H-20a, H-5), 4.81 (brs, 1H, H-2 ), 4.46 (brs, 1H, OH), 4.29 (d, J = 7.9Hz, 1H, H-3), 4.22 (brs, 1H, H-20b),
3
.92 (brs, 1H, H-7a), 3.70 (brs, 1H, H-7b), 3.39 (brs, 1H, OH), 2.77 (brs, 1H, H-6a), 2.60 (brs, 1H, H-14a),
2
.37 (dd, J = 9.7, 15.8 Hz, 1H, H-14b), 2.09 (m, 1H, H-6b), 1.85 (brs, 6H, 2
×
CH ), 1.78 (s, 3H, CH ),
3
3
13
1
1
.64 (brs, 1H, OH-1), 1.22 (s, 3H, CH ), 1.09 (s, 3H, CH ); C-NMR (CDCl , 75 MHz)
67.2, 166.2, 162.7 (d, J
δ: 190.9, 172.4,
3
3
3
1
2
= 248.7 Hz), 148.9, 142.1, 137.9, 133.6, 132.0, 131.4 (d, J
= 7.4 Hz), 130.8
C-F
C-F
3
2
(d, J
= 7.9 Hz), 128.9, 128.7, 128.2, 127.0, 126.9, 125.5, 124.4, 121.0 (d, J
= 21.2 Hz), 116.5 (d,
C-F
C-F

Molecules 2019, 24, 2161
12 of 23
2JC-F = 23.5 Hz), 86.8, 86.2, 80.5, 75.2, 74.7, 73.6, 70.7, 59.5, 54.6, 42.9, 36.5, 29.7, 29.3, 24.9, 22.1, 21.2, 14.7,
1
4.5; LC-MS (ESI, m/z): [M + 1], found 830.3, [M + 23], found 852.3, C H FNO : 829.31.
45 48 13
2
-Debenzoyl-2-(3-chlorobenzoyl)-10-dehydro-7, 8-seco-10-deacetylpaclitaxel (16d). White solid; yield 60.3%;
1
H-NMR (CDCl , 400 MHz) δ: 7.98 (d, J = 7.5 Hz, 2H, Ar-H), 7.72 (d, J = 7.0 Hz, 2H, Ar-H), 7.56 (d,
3
J = 8.4 Hz, 1H, Ar-H), 7.47–7.42 (m, 4H, Ar-H), 7.40–7.29 (m, 6H, NH, Ar-H), 6.49 (brs, 1H, OH-9),
0
6
1
.15 (t, J = 7.8 Hz, 1H, H-13), 5.86 (d, J = 8.1 Hz, 1H, H-3 ), 5.58 (d, J = 9.5 Hz, 1H, H-2), 5.21 (brs,
0
H, H-5), 5.14 (d, J =11.0 Hz, 1H, H-20a), 4.79 (d, J = 2.8 Hz, 1H, H-2 ), 4.27 (d, J =7.8 Hz, 1H, H-3),
4
.20 (brs, 1H, H-20b), 3.89 (brs, 1H, H-7a), 3.71–3.67 (m, 1H, H-7b), 2.75 (brs, 1H, H-6a), 2.59 (brs, 1H,
H-14a), 2.38 (dd, J = 9.7, 15.8 Hz, 1H, H-14b), 2.25 (brs, 1H, OH), 2.09 (m, 1H, H-6b), 2.00 (m, 1H,
13
OH), 1.84 (brs, 6H, 2
×
CH ), 1.74 (s, 3H, CH ), 1.20 (s, 3H, CH ), 1.07 (s, 3H, CH ); C-NMR (CDCl3,
3 3 3 3
δ: 191.0, 172.5, 167.2, 166.0, 148.9, 142.1, 138.1, 135.0, 133.8, 133.7, 132.0, 131.1, 130.4, 129.5,
1
1
2
00 MHz)
28.8, 128.7, 128.1, 127.9, 127.0, 124.3, 86.9, 86.2, 80.4, 75.3, 74.7, 73.6, 70.6, 59.6, 54.8, 50.8, 42.9, 36.6,
9.7, 29.5, 29.3, 24.9, 22.2, 21.2, 14.6, 14.5; LC-MS (ESI, m/z): [M + 1], found 845.9, [M + 23], found 867.8,
C H ClNO : 845.28.
45
48
13
2
5
-Debenzoyl-2-(3-trifluoromethylbenzoyl)-10-dehydro-7,8-seco-10-deacetylpaclitaxel (16e). White solid; yield
1
5.5%; H-NMR (CDCl , 400 MHz)
δ: 8.33 (d, J = 7.7 Hz, 1H, Ar-H), 8.25 (brs, 1H, NH), 7.85 (d,
3
J = 7.4 Hz, 1H, Ar-H), 7.68–7.62 (m, 3H, Ar-H), 7.48–7.45 (m, 3H, Ar-H), 7.40–7.29 (m, 6H, Ar-H), 6.47
0
(
5
brs, 1H, OH-9), 6.18 (t, J = 7.9 Hz, 1H, H-13), 5.87 (d, J = 7.6 Hz, 1H, H-3 ), 5.62 (d, J = 9.4 Hz, 1H, H-2),
0
.18 (overlap, J = 11.5 Hz, 2H, H-20a, H-5), 4.80 (d, J = 2.8 Hz, 1H, H-2 ), 4.62 (brs, 1H, OH), 4.28 (d,
J = 7.6 Hz, 1H, H-3), 4.24 (brs, 1H, H-20b), 3.90 (brs, 1H, H-7a), 3.68 (brs, 1H, H-7b), 3.38 (brs, 1H, OH),
2
2
.77 (brs, 1H, H-6a), 2.58 (brs, 1H, H-14a), 2.37 (dd, J = 9.7, 15.7 Hz, 1H, H-14b), 2.05 (brs, 1H, OH),
.03–1.98 (m, 1H, H-6b), 1.84 (brs, 6H, 2 CH ), 1.78 (s, 3H, CH ), 1.22 (s, 3H, CH ), 1.09 (s, 3H, CH );
×
3
3
3
3
1
3
C-NMR (CDCl , 100 MHz)
δ
: 190.9, 172.4, 167.2, 166.0, 148.9, 142.1, 138.0, 133.7, 133.0, 132.0, 131.7,
30.3, 130.0, 129.7, 128.9, 128.7, 128.2, 127.0 (2C), 126.4, 124.8, 124.2, 122.1, 86.9, 86.2, 80.5, 75.4, 74.7, 73.5,
0.7, 59.6, 54.7, 43.0, 36.6, 31.9, 29.7, 25.5, 22.1, 21.2, 14.6, 14.4; LC-MS (ESI, m/z): [M + 1], found 880.0,
M + 23], found 901.9, C H F NO : 879.31.
3
1
7
[
46
48
3
13
3
.1.5. General Experimental Procedure for Compounds 17a–e
0
2
-O-(tert-Butyldimethylsilyl)-9-O-(2-hydroxyethyl)-10-dehydro-7, 8-seco-10-deacetylpaclitaxel (17a). To a
mixture of 15a (50 mg, 0.0540 mmol), potassium carbonate (104 mg, 0.754 mmol), and potassium iodide
◦
(
18 mg, 0.108 mmol) in DMF (0.9 mL) was added 2-bromoethanol (54
µ
L 0.762 mmol), dropwise, at 0 C.
The reaction mixture was stirred for 9 h at room temperature and then was diluted with ethyl acetate.
The organic phase was washed with saturated aqueous NH Cl. The organic layer was dried over
4
anhydrous Na SO and then concentrated under reduced pressure. Purification of the crude product
2
4
by silica gel chromatography (ethyl acetate: petroleum ether = 1:1) gave product 17a as a white solid
1
(
19 mg, 52.4% yield). H-NMR (CDCl , 300 MHz)
δ
: 8.09 (d, J = 7.2 Hz, 2H, Ar-H), 7.62 (d, J = 7.2 Hz,
3
2
H, Ar-H), 7.57 (d, J = 7.5 Hz, 1H, Ar-H), 7.49 (t, J = 7.5 Hz, 2H, Ar-H), 7.36 (m, 8H, Ar-H), 6.30 (t,
0
J = 8.4 Hz, 1H, H-13), 5.88 (d, J = 9.0 Hz, 1H, H-3 ), 5.57 (d, J = 9.6 Hz, 1H, H-2), 5.28 (overlap, 2H, H-5,
H-20a), 4.69 (d, J = 1.8 Hz, 1H, H-2 ), 4.26 (d, J = 7.8 Hz, 1H, H-3), 4.20 (m, 2H, H-20b, OCH2CH2OCO),
0
3.94 (m, 1H, OCH2CH2OCO), 3.87 (m, J = 1.8, 6.3, 8.7, 12.0 Hz, 1H, H-7a), 3.74 (overlap, 2H, H-7b,
O
CH2CH OCO), 3.62 (m, 1H, OCH2CH OCO), 2.71 (m, 2H, H-6a, H-14a), 2.25 (dd, J = 9.3, 15.9 Hz, 2H,
2
2
H-6b, H-14b), 1.97 (s, 3H, CH ), 1.92 (s, 3H, CH ), 1.82 (s, 3H, CH ), 1.27 (s, 3H, CH ), 1.16 (s, 3H, CH ),
3
3
3
3
3
13
0
1
1
.76 (s, 9H, SiC(CH ) ),
−
0.08 (s, 3H, Si(CH )), 0.33 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz) δ:
92.3, 170.7, 168.7, 167.3, 153.8, 144.0, 139.4, 138.0, 133.7 (2C), 131.8, 129.9 (2C), 128.9 (2C), 128.6 (4C),
27.9, 126.9 (2C), 126.4 (2C), 87.1, 87.7, 85.7, 79.9, 75.6, 75.4, 74.6, 73.8, 70.5, 61.8, 58.7, 55.6, 42.9, 36.6,
−
3
3
3
3 3
2
9
5.4 (3C), 22.9, 22.0, 18.1, 15.3, 14.6,
92.4, C H NO Si: 969.43.
−
5.5, 6.1; LC-MS (ESI, m/z): [M + 1], found 970.5, [M + 23], found
−
53
67
14

Molecules 2019, 24, 2161
13 of 23
0
2
1
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-methoxybenzoyl)-9-O-(2-hydroxyethyl)-10-dehydro-7,8-seco-
1
0-deacetylpaclitaxel (17b). White solid; yield 56.1%; H-NMR (CDCl , 400 MHz) δ: 7.72–7.66 (m, 3H,
3
Ar-H), 7.54 (s, 1H, Ar-H), 7.47–7.43 (m, 2H, Ar-H), 7.42–7.29 (m, 8H, Ar-H), 7.12 (dd, J = 2.0, 8.4 Hz, 1H,
0
BzNH), 6.29 (t, J = 8.5 Hz, 1H, H-13), 5.88 (d, J = 9.3 Hz, 1H, H-3 ), 5.59 (d, J = 9.6 Hz, 1H, H-2), 5.26
(
0
overlap, 2H, H-5, H-20a), 4.72 (s, 1H, H-2 ), 4.26 (d, J = 6.4 Hz, 1H, H-3), 4.19–4.15 (m, 1H, H-20b),
3
.94–3.64 (m, 9H, OCH , OCH CH OH, H-7a, H-7b), 2.61 (br, 2H, H-6b, H-14b), 2.25 (dd, J = 9.6, 15.6
3 2 2
Hz, 2H, H-6a, H-14a), 2.03 (s, 3H, OAc), 1.93 (s, 6H, 2
×
CH ), 1.26 (s, 3H, CH ), 1.16 (s, 3H, CH ), 0.77
3 3 3
13
(
1
s, 9H, SiC(CH ) ),
−
0.10 (s, 3H, Si(CH )), 0.30 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz) δ: 192.4,
−
3
3
3
3 3
71.2, 170.9, 168.8, 167.3, 167.0, 162.6, 159.7, 144.1, 138.1, 133.8, 131.8, 130.4, 130.2, 128.6 (2C), 127.9,
27.0 (2C), 126.6 (2C), 122.2, 119.5, 114.9, 85.7, 79.8, 75.8, 74.8, 61.8, 58.9, 55.7, 55.5, 42.9, 36.6, 36.5, 31.9,
1
3
1.4, 29.7, 25.5 (3C), 22.9, 22.1, 18.2, 15.2, 14.6,
−
5.5, 6.1; LC-MS (ESI, m/z): [M + 1], found 1000.5,
−
[M + 23], found 1022.5, C H NO Si: 999.44.
54
69
16
0
2
1
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-fluorobenzoyl)-9-O-(2-hydroxyethyl)-10-dehydro-7,8-seco-
1
0-deacetylpaclitaxel (17c). White solid; yield 53.2%; H-NMR (CDCl , 400 MHz)
δ: 7.93 (d, J = 7.8 Hz,
3
1
6
H, Ar-H), 7.76 (d, J = 8.8 Hz, 1H, Ar-H), 7.63 (d, J = 7.6 Hz, 2H, Ar-H), 7.52–7.28 (m, 11H, NH, Ar-H),
0
.29 (t, J = 8.1 Hz, 1H, H-13), 5.89 (d, J = 9.2 Hz, 1H, H-3 ), 5.58 (d, J = 9.6 Hz, 1H, H-2), 5.35–5.15
0
(
overlap, 2H, H-5, H-20a), 4.70 (d, J = 1.9 Hz, 1H, H-2 ), 4.26 (d, J = 7.6 Hz, 1H, H-3), 4.20–4.16 (m, 2H,
H-20b, OCH CH OCO), 3.95 (brs, 1H, OCH CH OCO), 3.89–3.84 (ddd, J = 2.3, 6.8, 8.7, 12.4 Hz, 1H,
2
2
2
2
H-7a), 3.80–3.70 (overlap, 2H, H-7b, OCH CH OCO), 3.60–3.58 (m, 1H, OCH CH OCO), 2.71–2.63 (m,
2
2
2
2
2
H, H-6a, H-14a), 2.25 (dd, J = 9.6, 15.8 Hz, 2H, H-6b, H-14b), 2.03 (s, 3H, CH ), 1.91(s, 3H, CH ), 1.87
3 3
(
brs, 3H, CH ), 1.83 (brs, 2H, 2
×
OH), 1.26 (s, 3H, CH ), 1.15 (s, 3H, CH ), 0.73 (s, 9H, SiC(CH ) ),
3 3 3 3
3
13
−
0.08 (s, 3H, Si(CH )),
67.4, 166.2, 162.7 (d, J
−
0.32 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ
: 192.3, 171.2, 170.8, 168.6,
3
3
3
1
3
1
= 248.3 Hz), 144.0, 137.9, 133.9, 131.9, 131.2 (d, J
= 7.4 Hz), 131.0 (d,
= 21.2 Hz), 116.3
C-F
C-F
2
3J
= 7.7 Hz), 128.7 (2C), 128.0, 127.0, 126.5, 125.8 (d, J
= 22.9 Hz), 85.8, 80.0, 75.7, 75.2, 70.5, 61.9, 58.7, 55.6, 45.7, 42.9, 36.7, 25.5, 22.9, 22.1, 18.2, 15.3,
C-F
4
= 2.6 Hz), 121.0 (d, J
C-F
2
C-F
C-F
(
d, J
1
4.6, 13.7, −5.4, −6.0; LC-MS (ESI, m/z): [M + 1], found 988.0, C H FNO Si: 987.42.
53
66
14
0
2
1
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-chlorobenzoyl)-9-O-(2-hydroxyethyl)-10-dehydro-7,8-seco-
1
0-deacetylpaclitaxel (17d). White solid; yield 60.9%; H-NMR (CDCl , 400 MHz)
δ: 8.06 (d, J = 8.8 Hz,
3
2
7
H, Ar-H), 7.63 (d, J = 7.5 Hz, 2H, Ar-H), 7.57 (d, J = 8.2 Hz, 1H, Ar-H), 7.50–7.43 (m, 3H, Ar-H),
0
.43–7.33 (m, 8H, Ar-H, BzNH), 6.31 (t, J = 8.0 Hz, 1H, H-13), 5.90 (d, J = 9.2 Hz, 1H, H-3 ), 5.59 (d,
0
J = 9.6 Hz, 1H, H-2), 5.32–5.28 (overlap, 2H, H-5, H-20b), 4.71 (d, J = 1.9 Hz, 1H, H-2 ), 4.28 (d, J = 7.6
Hz, 1H, H-3), 4.24–4.20 (m, 2H, H-20a, OCH CH OH), 3.98–3.95 (m, 1H, OCH CH OH), 3.93–3.89 (m,
2
2
2
2
1
H, H-7b), 3.78–3.72 (overlap, 2H, H-7a, OCH CH OH), 3.65 (br, 1H, OCH CH OH), 2.72–2.68 (m, 2H,
2 2 2 2
H-6b, H-14b), 2.26 (dd, J = 7.2, 13.4 Hz, 2H, H-6a, H-14a), 1.98 (s, 3H, CH ), 1.93 (brs, 1H, OH), 1.85
3
(
brs, 2H, OH), 1.29 (brs, 6H, CH ), 1.18 (s, 3H, CH ), 0.78 (s, 9H, SiC(CH ) ), 0.08 (s, 3H, Si(CH )),
0.30 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz) δ: 192.3, 170.8, 167.4, 166.3, 144.0, 137.9, 135.0,
3 3
33.9 (2C), 132.0, 130.8, 130.7, 129.7, 128.8 (2C), 128.7 (2C), 128.2, 128.1, 127.0 (2C), 126.6 (2C), 85.9, 75.8,
−
3
3
3 3
3
13
−
1
7
5.3, 70.5, 62.0, 55.6, 43.0, 36.7, 32.0, 29.7, 29.4, 27.3, 25.5 (3C), 23.0, 22.7, 22.2, 18.3, 15.3, 14.7, 14.2,
−
5.4,
−
6.0; LC-MS (ESI, m/z): [M + 1], found 1004.4, [M + 23], found 1026.4, C H ClNO Si: 1003.39.
53
66
14
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-trifluoromethylbenzoyl)-9-O-(2-hydroxyethyl)-10-dehydro-7,
1
8
-seco-10-deacetylpaclitaxel (17e). White solid; yield 49.9%; H-NMR (CDCl , 400 MHz)
δ
: 7.83 (d,
3
J = 7.7 Hz, 2H, Ar-H), 7.68 (t, J = 7.8 Hz, 1H, Ar-H), 7.58 (d, J = 7.3 Hz, 1H, Ar-H), 7.45 (t, J = 7.4 Hz,
0
2
H, Ar-H), 7.35 (m, 8H, Ar-H), 6.29 (t, J = 8.2 Hz, 1H, H-13), 5.87 (d, J = 8.7 Hz, 1H, H-3 ), 5.60 (d,
0
J = 9.65 Hz, 1H, H-2), 5.26 (overlap, 2H, H-5, H-20a), 4.70 (d, J = 1.3 Hz, 1H, H-2 ), 4.28 (d, J = 6.8 Hz,
1
1
2
H, H-3), 4.19 (m, 2H, H-20b, OCH CH OCO), 3.98 (m, 1H, OCH CH OCO), 3.87 (m, J = 1.8, 6.3, 8.7,
2 2 2 2
2.0 Hz, 1H, H-7a), 3.75 (overlap, 2H, H-7b, OCH CH OCO), 3.66 (m, 1H, OCH CH OCO), 2.65 (m,
2
2
2
2
H, H-6a, H-14a), 2.24 (dd, J = 6.7, 16.3 Hz, 2H, H-6b, H-14b), 1.97 (s, 3H, CH ), 1.92 (s, 3H, CH ), 1.82
3
3
(
(
s, 3H, CH ), 1.26 (s, 3H, CH ), 1.17 (s, 3H, CH ), 0.77 (s, 9H, SiC(CH ) ),
−
0.08 (s, 3H, Si(CH )),
−
0.32
3
3
3
3 3
3
13
s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ: 192.3, 170.8, 167.6, 166.1, 144.1, 137.8, 133.9, 133.2,
3
3

Molecules 2019, 24, 2161
14 of 23
1
32.0, 131.4 (q, 2JC-F = 33.2 Hz), 130.3, 130.2 (q, 3JC-F = 3.5 Hz), 130.0, 128.8, 128.7, 128.1, 126.9, 126.8 (q,
3J = 3.6 Hz), 126.5, 123.6 (q, 1JC-F = 273.8 Hz), 85.8, 75.6, 75.4, 70.5, 62.0, 58.4, 55.6, 43.0, 36.7, 31.9,
C-F
2
9.8, 29.7, 29.6 (2C), 29.3 (2C), 27.2, 25.5, 23.0, 22.7, 22.1, 18.4, 18.2, 15.3, 14.6, 14.1,
−
5.4, 6.0; LC-MS
−
(ESI, m/z): [M + 1], found 1038.4, [M + 23], found 1060.4, C H F NO Si: 1037.42.
54
66
3
14
3
.1.6. General Experimental Procedure for Compounds 19a–e
0
2
-O-(tert-Butyldimethylsilyl)-macrocyclic taxoid (19a). To a solution of 17a (19 mg, 0.0196 mmol) in
dichloromethane (4.2 mL) was added, dropwise, pyridine (22
µ
L, 0.266 mmol) and triphosgene (8.7 mg,
◦
0.0293 mmol) at 0 C, then the reaction mixture was stirred at room temperature for 5 h. The reaction
was diluted with ethyl acetate, washed with saturated NaCl. The organic layer was dried over
anhydrous Na SO and then concentrated under reduced pressure. Purification of the crude product
2
4
by silica gel chromatography (ethyl acetate: petroleum ether = 1:3) gave product 19a as a white solid
1
(
3.1 mg, 15.9% yield). H-NMR (CDCl , 400 MHz)
δ
: 8.17 (d, J = 7.2 Hz, 2H, Ar-H), 7.75 (d, J = 7.2 Hz,
3
2
7
H, Ar-H), 7.63 (t, J = 7.2 Hz, 1H, Ar-H), 7.54 (t, J = 7.6 Hz, 2H, Ar-H), 7.50 (d, J = 7.6 Hz, 1H, Ar-H),
.43 (d, J = 7.6 Hz, 2H, Ar-H), 7.39 (t, J = 7.2 Hz, 2H, Ar-H), 7.34–7.29 (m, 3H, Ar-H), 7.08 (d, J = 9.2 Hz,
0
1H, NH), 6.27 (t, J = 8.8 Hz, 1H, H-13), 5.76 (d, J = 8.4 Hz, 1H, H-3 ), 5.60 (d, J = 7.6 Hz, 1H, H-2), 4.84
0
(
overlap, 2H, H-5, OCH2CH OCO), 4.79 (d, J = 7.6 Hz, 1H, H-3), 4.67 (d, J = 2.0 Hz, 1H, H-2 ), 4.57 (dd,
2
J = 6.8, 12.0 Hz, 1H, OCH2CH2OCO), 4.49 (dd, J = 6.8, 12.0 Hz, 1H, OCH2CH2OCO), 4.46 (d, J = 8.4 Hz,
H, H-20a), 4.35 (d, J = 8.4 Hz, 1H, H-20b), 4.32 (dd, J = 5.2, 13.6 Hz, 1H, OCH2CH OCO), 4.13 (ddd,
1
2
J = 6.4, 10.8, 17.2 Hz, 1H, H-7a), 4.02 (ddd, J = 8.8, 11.6, 17.2 Hz, 1H, H-7b), 2.55 (s, 3H, 4-OAc), 2.35 (m,
3
H, H-6a, H-6b, H-14a), 2.18 (dd, J = 8.8, 15.2 Hz, 1H, H-14b), 1.84 (s, 3H, CH ), 1.25 (s, 3H, CH ), 1.24
3
3
(
s, 3H, CH ), 1.19 (s, 3H, CH ), 0.79 (s, 9H, SiC(CH ) ),
−
0.03 (s, 3H, Si(CH )),
−
0.30 (s, 3H, Si(CH ));
3
3
3 3
3
3
1
3
C-NMR (CDCl , 150 MHz)
δ
: 192.1, 171.0, 169.4, 166.9, 166.8, 152.4, 151.5, 144.5, 139.7, 138.3, 134.6,
34.1, 133.8, 131.8, 130.2 (2C), 129.0, 128.8 (2C), 128.7, 127.9, 127.0 (2C), 126.3 (2C), 89.6, 84.7, 78.6, 76.1,
5.3, 75.2, 71.4, 70.6, 68.9, 65.9, 55.6, 42.9, 42.4, 36.5, 31.0, 26.2, 25.5 (3C), 22.9, 21.6, 18.1, 14.4, 13.6, 5.3,
5.9; LC-MS (ESI, m/z): [M + 1], found 996.4, [M + 23], found 1018.4, C H NO Si: 995.41.
3
1
7
−
2
3
7
−
54
65
15
0
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-methoxybenzoyl)-macrocyclic taxoid (19b). White solid; yield
1
2.7%; H-NMR (CDCl , 400 MHz)
δ
: 7.80 (d, J = 1.2, 7.6 Hz, 1H, Ar-H), 7.77 (d, J = 6.8 Hz, 2H, Ar-H),
3
.67 (dd, J = 1.5, 2.5 Hz, 1H, Ar-H), 7.55–7.51 (m, 1H, Ar-H), 7.49–7.39 (m, 3H, Ar-H), 7.40–7.31 (m, 5H,
Ar-H), 7.20–7.17 (m, 1H, Ar-H), 7.08 (d, J = 9.2 Hz, 1H, BzNH), 6.28 (t, 1H, H-13), 5.76 (dd, J = 1.6, 8.9 Hz,
0
H-3 ), 5.62 (d, J = 7.5 Hz, 1H, H-2), 4.87 (d, J = 7.6 Hz, 1H, H-20b), 4.85 (d, J = 4.8 Hz, 1H, H-5), 4.81 (d,
0
J = 7.5 Hz, 1H, H-20a), 4.68 (d, J = 2.0 Hz, 1H, H-2 ), 4.60–4.32 (m, 5H, H-7a, H-7b, H-16a, H-16b, H-3),
4
.18–4.03 (m, H-15a, H-15b), 3.91 (s, 3H, OCH ), 2.55 (d, J = 1.3 Hz, 6H, 2
×
CH ), 2.41–2.35 (m, 3H,
3
3
H-14b, H-6a, H-6b), 2.24–2.20 (m, 1H, H-14a), 1.84 (d, J = 1.2 Hz, 3H, COCH ), 1.26 (s, 3H, CH ), 1.21 (s,
3
3
13
3H, CH ), 0.81 (s, 9H, SiC(CH ) ),
−
0.008 (s, 3H, Si(CH )), 0.28 (s, 3H, Si(CH )); C-NMR (CDCl3,
δ: 192.2, 171.1, 169.4, 166.9, 166.8, 159.8, 152.5, 151.6, 144.6, 139.7, 138.4, 134.7, 134.2, 131.9,
−
3
3 3
3
3
1
1
7
−
00 MHz)
30.4, 130.0, 128.82 (2C), 128.78 (2C), 128.0, 127.0 (2C), 126.4 (2C), 122.6, 120.3, 114.7, 89.6, 84.8, 78.5,
5.4, 75.3, 71.5, 70.7, 69.0, 65.9, 55.6, 43.0, 42.5, 36.5, 31.1, 29.7, 26.3, 25.6 (3C), 22.9, 21.6, 18.2, 14.4, 13.7,
5.2,−5.8; LC-MS (ESI, m/z): [M + 1], found 1026.4, [M + 23], found 1048.4, C H NO Si: 1025.42.
55
67
16
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-fluorobenzoyl)-macrocyclic taxoid (19c). White solid; yield
1
3
2.1%; H-NMR (CDCl , 400 MHz)
δ: 8.01(d, J = 7.8 Hz, 1H, Ar-H), 7.84–7.87 (m, 1H, Ar-H), 7.75–7.73
3
(
m, 2 H, Ar-H), 7. 56–7.49 (m, 2H, Ar-H), 7.44–7.31 (m, 8H, Ar-H), 7.09 (d, J = 9.0 Hz, 1H, NH), 6.28 (t,
0
J = 8.8 Hz,1H, H-13), 5.78 (dd, J = 1.4, 9.1 Hz, 1H, H-3 ), 5.61 (d, J = 7.6 Hz, 1H, H-2), 4.87–4.82 (overlap,
2
0
H, OCH CH OCO, H-5), 4.83 (d, J = 7.5 Hz, 1H, H-3), 4.69 (d, J = 2.0 Hz, 1H, H-2 ), 4.58 (dd, J = 6.4,
2
2
1
1.9 Hz, 1H, OCH2CH2OCO), 4.51 (dd, J = 6.4, 13.7 Hz, 1H, OCH2CH2OCO), 4.46 (d, J = 8.2 Hz, 1H,
H-20a), 4.36–4.30 (overlap, 2H, OCH2CH OCO, H-20b), 4.16–4.09 (m, 1H, H-7a), 4.06–3.99 (m, 17.2 Hz,
2
1
H, H-7b), 2.57 (s, 3H, COCH ), 2.56 (s, 3H, 4-OAc), 2.39–2.31 (m, 3H, H-6a, H-6b, H-14a), 2.18 (dd,
3
J = 8.4, 15.4 Hz, 1H, H-14b), 1.90 (brs, 1H, OH), 1.84 (s, 3H, CH ), 1.23 (s, 3H, CH ), 1.19 (s, 3H, CH ),
3
3
3
13
0
.80 (s, 9H, SiC(CH ) ),
−
0.29 (s, 3H, Si(CH )), 0.03 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
−
3
3
3
3 3

Molecules 2019, 24, 2161
15 of 23
1
δ
: 192.1, 171.1, 169.4, 167.0, 165.7, 162.7 (d, J
= 247.8 Hz), 152.5, 151.6, 144.5, 139.8, 138.4, 134.5,
= 7.6 Hz), 128.8 (2C), 128.0, 127.0, 126.5, 126.0 (d,
= 23.3 Hz), 89.6, 84.7, 78.6, 76.1, 75.7, 75.3, 71.5,
C-F
C-F
3
3
134.2, 131.9, 131.3 (d, J
= 7.6Hz), 130.6 (d, J
C-F
2
C-F
4J
= 3.0 Hz), 121.0 (d, J
= 21.4 Hz), 117.1 (d, J
2
C-F
C-F
7
0.7, 68.9, 65.9, 55.6, 43.0, 42.5, 36.4, 31.0, 26.3, 25.6, 22.8, 21.6, 18.2, 14.4, 13.6,
−
5.2, 5.8; LC-MS (ESI,
−
m/z): [M + 1], found 1014.4, [M + 23], found 1036.4, C H FNO Si: 1013.40.
54
64
15
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-chlorobenzoyl)-macrocyclic taxoid (19d). White solid; yield
1
3
6.1%; H-NMR (CDCl , 400 MHz)
δ: 8.19 (t, J = 1.6 Hz, 1H, Ar-H), 8.10–8.07 (m, 1H, Ar-H), 7.77–7.75
3
(
m, 2H, Ar-H), 7.64–7.61 (m, 1H, Ar-H), 7.55–7.49 (m, 2H, Ar-H), 7.46–7.33 (m, 7H, Ar-H), 7.08 (d,
0
J = 9.2 Hz, 1H, BzNH), 6.25 (m, 1H, H-13), 5.76 (dd, J = 1.6, 9.0 Hz, 1H, H-3 ), 5.59 (d, J = 7.6 Hz, 1H,
H-2), 4.89–4.81 (m, 3H, OCH2CH OCO, H-5, H-3), 4.68 (d, J = 2.0 Hz, 1H, H-2 ), 4.57 (dd, J = 6.6,
0
2
1
1.9 Hz, 1H, OCH2CH2OCO), 4.50 (dd, J = 6.5, 11.8 Hz, 1H, OCH2CH2OCO), 4.44 (d, J = 8.0 Hz, 1H,
H-20a), 4.38–4.32 (m, 2H, OCH2CH OCO, H-20b), 4.15–4.10 (m, 1H, H-7a), 4.07–4.01 (m, J = 17.2 Hz,
2
1
H, H-7b), 2.56 (s, 3H, CH ), 2.55 (s, 3H, CH ), 2.41–2.30 (m, 3H, H-6a, H-6b, H-14a), 2.25–2.18 (m, 1H,
3 3
H-14b), 1.84 (d, J = 1.2 Hz, 3H, CH ), 1.25 (s, 3H, CH ), 1.20 (s, 3H, CH ), 0.82 (s, 9H, SiC(CH ) ),
−
0.01
: 192.1, 171.1, 169.4, 165.6, 152.5,
51.7, 144.5, 139.8, 138.4, 134.9, 134.5, 133.6, 131.8, 131.0, 130.3, 128.81 (2C), 128.79 (2C), 128.4, 128.0,
27.0 (2C), 126.5 (2C), 89.6, 84.7, 78.7, 77.3, 75.6, 75.3, 70.8, 69.0, 55.7, 43.0, 42.5, 36.4, 29.7, 26.3, 25.6 (3C),
2.8, 21.6, 18.2, 14.4, 13.6, 5.2, 5.8; LC-MS (ESI, m/z): [M + 1], found 1030.4, [M + 23], found 1052.4,
C H ClNO Si: 1029.37.
3
3
3
3 3
13
(
1
1
s, 3H, Si(CH )), 0.26 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz) δ
−
3
3 3
2
−
−
54
64
15
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-trifluoromethylbenzoyl)-macrocyclic taxoid (19e). White solid;
1
yield 30.5%; H-NMR (CDCl , 400 MHz)
δ: 8.51 (s, 1H, Ar-H), 8.41 (d, J = 7.8 Hz, 1H, Ar-H), 7.92
3
(
d, J = 7.8 Hz, 1H, Ar-H), 7.76–7.72 (m, 3H, Ar-H), 7.55–7.51 (m, 1H, Ar-H), 7.47–7.40 (m, 4H, Ar-H),
7
9
.37–7.33 (m, 3H, Ar-H), 7.09 (d, J = 9.1 Hz, 1H, NH), 6.24 (t, J = 8.8 Hz, 1H, H-13), 5.76 (dd, J = 1.0,
0
.0 Hz, 1H, H-3 ), 5.63 (d, J = 7.6 Hz, 1H, H-2), 4.91–4.84 (m, 3H, H-3, H-5, OCH2CH OCO), 4.67 (d,
2
0
J = 1.8 Hz, 1H, H-2 ), 4.58 (dd, J = 6.8, 11.8 Hz, 1H, OCH2CH2OCO), 4.52 (dd, J = 6.8, 13.7 Hz, 1H,
O
CH2CH OCO), 4.44 (d, J = 8.1 Hz, 1H, H-20a), 4.38–4.33 (m, 2H, OCH2CH2OCO, H-20b), 4.11–4.18
2
(
m, 1H, H-7a), 4.09–4.02 (m, J = 17.2 Hz, 1H, H-7b), 2.55 (s, 3H, 4-OAc), 2.42–2.36 (m, 3H, H-6a, H-6b,
H-14a), 2.29–2.20 (m,1H, H-14b), 1.94 (s, 1H, OH), 1.86 (d, J = 1.04 Hz, 3H, CH ), 1.29 (s, 3H, CH ), 1.26
3
3
(
s, 3H, CH ), 1.22 (s, 3H, CH ), 0.84 (s, 9H, SiC(CH ) ),
−
0.004 (s, 3H, Si(CH )),
−
0.24 (s, 3H, Si(CH ));
3
3
3 3
3
3
1
3
C-NMR (CDCl , 100 MHz)
δ
: 192.0, 171.1, 169.3, 167.0, 165.4, 152.5, 151.6, 144.5, 139.8, 138.4, 134.4,
3
2
3
1
1
34.3, 133.6, 131.8, 131.4 (q, J
= 33.2 Hz), 130.3 (q, J
= 3.4 Hz), 130.2, 129.7, 128.8, 128.0, 127.0,
C-F
C-F
3
1
26.9 (q, J
= 4.3 Hz), 126.5, 123.7 (q, J
= 273.8 Hz), 89.6, 84.7, 78.7, 76.0, 75.8, 75.2, 71.5, 70.8, 69.0,
C-F
C-F
6
5.9, 55.7, 43.0, 42.4, 36.4, 31.0, 29.0, 26.3, 25.6, 22.7, 21.6, 18.2, 14.4, 13.6,
−
5.2, 5.8; LC-MS (ESI, m/z):
−
[M + 1], found 1064.4, [M + 23], found 1086.4, C H F NO Si: 1063.40.
55
64
3
15
3
.1.7. General Procedure for the Syntheses of Compounds 21a–e
Macrocyclic taxoid (21a)
To a solution of of 19a (32.3 mg, 0.0464 mmol) in THF (8 mL) was added, dropwise, 1.53 mL of
◦
HF-pyridine (v/v = 1:2) at 0 C, and the reaction mixture was stirred at room temperature for 30 h.
The reaction was quenched with saturated aqueous NaHCO , diluted with ethyl acetate, and washed
3
with saturated NH Cl. The organic layer was dried over anhydrous Na SO and then concentrated
4
2
4
under reduced pressure. Purification of the crude product by silica gel chromatography (ethyl acetate:
1
petroleum ether = 2:1) gave product 21a as a white solid (13.2 mg, 46.2% yield). H-NMR (CDCl ,
3
400 MHz)
δ: 8.14 (d, J = 7.0 Hz, 2H, Ar-H), 7.73 (d, J = 8.6 Hz, 2H, Ar-H), 7.62 (t, J = 7.5 Hz, 1H, Ar-H),
7
.52–7.45 (m, 5H, Ar-H), 7.40–7.30 (m, 5H, Ar-H), 7.22 (d, J = 9.1 Hz, 1H, NH), 6.20 (t, J = 8.5 Hz, 1H,
0
0
H-13), 5.78 (dd, J = 2.5, 9.1 Hz, 1H, H-3 ), 5.58 (d, J = 7.5 Hz, 1H, H-2), 4.80–4.74 (overlap, 4H, H-5, H-2 ,
H-3, OCH2CH OCO), 4.52 (dd, J = 6.4, 12.0 Hz, 1H, OCH2CH2OCO), 4.45–4.44 (overlap, 2H, H-20a,
2
OCH2CH2OCO), 4.31-4.25 (overlap, 2H, H-20b, OCH2CH OCO), 4.07–3.91 (overlap, 2H, H-7b, H-7a),
2

Molecules 2019, 24, 2161
16 of 23
0
.56 (br, 1H, OH-2 ), 2.51 (s, 3H, CH ), 2.35 (s, 3H, CH ), 2.33–2.25 (overlap, 4H, H-14a, H-14b, H-6a,
3 3
2
13
H-6b), 1.68 (s, 3H, CH ), 1.18 (s, 3H, CH ), 1.16 (s, 3H, CH ); C-NMR (CDCl , 150 MHz)
δ: 191.8,
3
3
3
3
1
1
72.4, 169.7, 166.9, 166.8, 152.4, 151.5, 144.8, 138.6, 137.9, 135.0, 133.9, 133.6, 132.0, 130.1 (2C), 129.0 (2C),
28.8 (4C), 128.3, 127.0 (2C), 89.4, 84.7, 78.4, 76.1, 75.1, 73.1, 71.8, 71.5, 68.9, 65.8, 54.8, 42.8, 42.4, 36.4,
30.9, 29.7, 26.3, 22.5, 21.2, 14.0, 13.7; LC-MS (ESI, m/z): [M + 1], found 882.8, [M + 23], found 904.4,
C H NO : 881.33.
48
51
15
1
2
-Debenzoyl-2-(3-methoxybenzoyl)-macrocyclic taxoid (21b). White solid; yield 54.1%; H-NMR (CDCl ,
3
4
00 MHz)
δ
: 7.76–7.74 (m, 3H, Ar-H), 7.66-7.65 (m, 1H, Ar-H), 7.53–7.46 (m, 8H, Ar-H), 7.36–7.32 (m,
0
1
H, Ar-H), 7.03 (d, J = 8.9 Hz, 1H, NH), 6.17 (t, J = 8.2 Hz, 1H, H-13), 5.79 (dd, J = 2.3, 9.0 Hz, 1H, H-3 ),
0
5.59 (d, J = 7.5 Hz, 1H, H-2), 4.84–4.77 (overlap, 4H, H-5, H-2 , H-3, OCH2CH OCO), 4.55 (dd, J = 6.5,
2
1
1.9 Hz, 1H, OCH2CH2OCO), 4.45 (dd, J = 6.6, 13.2 Hz, 1H, OCH2CH2OCO), 4.43 (d, J = 7.5 Hz, 1H,
H-20a), 4.36 (d, J = 8.29 Hz, 1H, H-20b), 4.32 (dd, J = 5.2, 13.8 Hz, 1H, OCH2CH OCO), 4.12–3.96 (m,
2
0
2
H, H-7b, H-7a), 3.88 (s, 3H, OAc), 3.62 (brs, 1H, OH-2 ), 2.53 (s, 3H, CH ), 2.36 (s, 3H, CH ), 2.40–2.27
3
3
(
1
overlap, 4H, H-14a, H-14b, H-6a, H-6b), 1.93 (brs, 1H, OH-1), 1.68 (d, 3H, CH ), 1.23 (s, 3H, CH ),
3 3
.18 (s, 3H, CH3); 13C-NMR (CDCl , 100 MHz)
δ: 191.9, 172.4, 169.7, 167.0, 166.7, 159.8, 152.4, 151.5,
3
1
44.8, 138.6, 138.0, 135.1, 133.7, 132.0, 130.3 (2C), 130.0, 129.8, 129.7, 129.0 (2C), 128.7 (4C), 128.3, 127.0
(
3
2C), 122.5, 120.0, 115.0, 89.4, 84.7, 78.4, 76.2, 75.3, 73.2, 71.7, 71.5, 68.9, 65.8, 55.5, 54.9, 42.8, 42.4, 36.4,
1.9, 30.9, 29.7, 26.3, 22.5, 21.2, 14.0, 13.7; LC-MS (ESI, m/z): [M + 1], found 912.3, [M + 23], found 934.3,
C H NO : 911.34.
49
53
16
1
2
-Debenzoyl-2-(3-fluorobenzoyl)-macrocyclic taxoid (21c). White solid; yield 52.2%; H-NMR (CDCl ,
3
4
00 MHz) δ: 7.97–7.92 (m, 1H, Ar-H), 7.86–7.83 (ddd, J = 1.5, 2.5, 9.2 Hz, 1H, Ar-H), 7.75–7.72 (m, 2H,
Ar-H), 7.54–7.47 (m, 4H, Ar-H), 7.43–7.39 (m, 4 H, Ar-H), 7.37–7.32 (m, 2H, Ar-H), 7.02 (d, J = 9.1 Hz, 1H,
0
NH), 6.17 (dd, J = 7.5, 8.8 Hz, 1H, H-13), 5.79 (dd, J = 2.4, 9.0 Hz, 1H, H-3 ), 5.57 (d, J = 7.6 Hz, 1H, H-2),
0
4
4
(
.84–4.78 (overlap, 4H, H-5, H-2 , H-3, OCH2CH OCO), 4.55 (dd, J = 6.4, 11.9 Hz, 1H, OCH2CH2OCO),
.47–4.40 (m, 2H, H-20b, H-20a), 4.34–4.29 (m, 2H, OCH2CH2OCO), 4.12–3.96 (m, 2H, H-7b, H-7a), 3.62
d, J = 4.9 Hz, 1H, OH-2 ), 2.53 (s, 3H, CH ), 2.36 (s, 3H, CH ), 2.35–2.25 (m, 4H, H-14a, H-14b, H-6a,
2
0
3
3
1
3
H-6b), 1.93 (brs, 1H, OH-1), 1.68 (d, J = 1.2 Hz, 3H, CH ), 1.23 (s, 3H, CH ), 1.18 (s, 3H, CH ); C-NMR
3
3
3
1
(
CDCl , 100 MHz)
δ
: 191.8, 172.4, 169.6, 167.1, 165.6 (d, JC-F = 3.2 Hz, CO), 162.4 (d, J
= 7.6 Hz), 130.5 (d, J
= 3.9 Hz), 129.7, 129.0, 128.7, 128.4, 127.0, 126.0, 121.0 (d, J
= 247.8 Hz),
= 7.8 Hz),
= 21.3 Hz), 117.0 (d,
C-F
3
C-F
3
3
1
1
52.4, 151.6, 144.7, 138.7, 138.0, 134.8, 133.7, 132.0, 131.3 (d, J
C-F
C-F
4
2
29.9 (d, J
2J
C-F
= 23.3 Hz), 89.5, 84.7, 78.5, 76.0, 75.5, 73.2, 71.7, 71.5, 68.9, 65.7, 55.0, 42.8, 42.4, 36.3, 30.9, 26.3,
C-F
25.5, 22.7, 22.4, 21.2, 14.1, 14.0, 13.6; LC-MS (ESI, m/z): [M + 1], found 900.0, [M + 23], found 922.0,
C H FNO : 899.32.
48
50
15
1
2
4
8
-Debenzoyl-2-(3-chlorobenzoyl)-macrocyclic taxoid (21d). White solid; yield 48.7%; H-NMR (CDCl ,
3
00 MHz) δ: 8.16 (t, 1H, Ar-H), 8.06–8.03 (m, 1H, Ar-H), 7.75–7.72 (m, 2H, Ar-H), 7.61 (ddd, J = 1.1, 2.1,
.0 Hz, 1H, Ar-H), 7.53–7.45 (m, 4H, Ar-H), 7.43–7.39 (m, 4 H, Ar-H), 7.36–7.32 (m, 1H, Ar-H), 7.01
d, J = 9.1 Hz, 1H, NH), 6.17 (td, J =1.3, 8.7 Hz, 1H, H-13), 5.78 (dd, J = 2.3, 9.0 Hz, 1H, H-3 ), 5.56 (d,
J = 7.6 Hz, 1H, H-2), 4.84–4.78 (overlap,4H, H-5, H-2 , H-3, OCH2CH OCO), 4.55 (dd, J = 6.4, 11.9 Hz,
0
(
0
2
1
H, OCH2CH2OCO), 4.47–4.38 (m, 2 H, H-20b, H20a), 4.34–4.29 (m, 2H, OCH CH2OCO), 4.11–3.96
2
0
(m, 2H, H-7b, H-7a), 3.62 (brs, 1H, OH-2 ), 2.52 (s, 3H, CH ), 2.37 (s, 3H, CH ), 2.42–2.27 (overlap, 4H,
3
3
H-14a, H-14b, H-6a, H-6b), 2.0 (brs, 1H, OH-1), 1.68 (d, J = 1.2 Hz, 3H, CH ), 1.23 (s, 3H, CH ), 1.18 (s,
3
3
3
1
7
(
H, CH3); 13C-NMR (CDCl , 100 MHz)
δ
: 191.8, 172.4, 169.6, 167.1, 165.5, 152.4, 151.6, 144.7, 138.7,
38.0, 134.8 (2C), 133.8, 133.7, 132.0, 130.9, 130.2 (2C), 129.0, 128.7, 128.4 (2C), 127.1, 127.0, 89.4, 84.7,
8.4, 76.0, 75.5, 73.1, 71.7, 71.5, 68.9, 65.7, 55.0, 42.8, 42.4, 36.3, 30.9, 26.2, 22.4, 21.2, 14.0, 13.6; LC-MS
ESI, m/z): [M + 1], found 916.3, [M + 23], found 938.3, C H ClNO : 915.29.
3
48
50
15
1
2
-Debenzoyl-2-(3-trifluoromethylbenzoyl)-macrocyclic taxoid (21e). White solid; yield 63.7%; H-NMR
: 8.47 (s, 1H, Ar-H), 8.36 (d, J = 7.9 Hz, 1H, Ar-H), 7.90 (d, J = 7.8 Hz, 1H, Ar-H),
.73–7.67 (m, 3H, Ar-H), 7.46–7.52 (m, 3 H, Ar-H), 7.43–7.32 (m, 5H, Ar-H), 6.94 (d, J = 9.0 Hz, 1H,
(CDCl , 400 MHz) δ
3
7

Molecules 2019, 24, 2161
17 of 23
0
NH), 6.16 (dd, J = 7.5, 8.8 Hz, 1H, H-13), 5.77 (dd, J = 2.0, 8.9 Hz, 1H, H-3 ), 5.60 (d, J = 7.5 Hz,
0
1
H, H-2), 4.85–4.78 (overlap, 4H, H-5, H-2 , H-3, OCH CH OCO), 4.55 (dd, J = 6.6, 12.0 Hz, 1H,
2
2
OCH CH OCO), 4.45 (dd, J = 6.7, 13.6 Hz, 1H, OCH CH OCO), 4.39 (d, J = 8.0 Hz, 1 H, H-20b),
2
2
2
2
4
.33 (dd, 1H, OCH CH OCO), 4.31 (d, J = 7.7 Hz, 1H, H-20a),4.12-3.97 (m, 2H, H-7b, H-7a), 3.53 (d,
2 2
0
J = 6.9 Hz, 1H, OH-2 ), 2.53 (s, 3H, CH ), 2.34 (s, 3H, CH ), 2.46–2.28 (m, 4H, H-14a, H-14b, H-6a,
H-6b), 1.93 (brs, 1H, OH-1), 1.70 (d, J = 1.2 Hz, 3H, CH ), 1.24 (s, 3H, CH ),1.15 (s, 3H, CH ); C-NMR
3
3
13
3
3
3
(
1
3J
CDCl , 100 MHz)
δ
: 192.0, 171.1, 169.3, 167.0, 165.4, 152.5, 151.6, 144.5, 139.8, 138.4, 134.4, 134.3, 133.6,
3
2
3
31.8, 131.4 (q, J
= 33.2 Hz), 130.3 (q, J
= 3.4 Hz), 130.2, 129.7, 128.8, 128.0, 127.0, 126.9 (q,
C-F
C-F
1
= 4.3 Hz), 126.5, 123.7 (q, J
= 273.8 Hz), 89.6, 84.7, 78.7, 76.0, 75.8, 75.2, 71.5, 70.8, 69.0, 65.9,
C-F
C-F
5
5.7, 43.0, 42.4, 36.4, 31.0, 29.0, 26.3, 25.6, 22.7, 21.6, 18.2, 14.4, 13.6,
−
5.2, 5.8; LC-MS (ESI, m/z): [M + 1],
−
found 950.3, [M + 23], found 972.3, C H F NO : 949.31.
49
50
3
15
3
.1.8. General Experimental Procedure for Compounds 18a–e
0
2
-O-(tert-Butyldimethylsilyl)-9-O-(3-hydroxyethyl)-10-dehydro-7, 8-seco-10-deacetylpaclitaxel (18a). To a
mixture of 15a (65 mg, 0.0703 mmol), potassium carbonate (67.8 mg, 0.491 mmol) and potassium
iodide (11.7 mg, 0.0705 mmol) in DMF (0.65 mL) was added 3-bromo-1-propanol (44
dropwise, at 0 C. The reaction mixture was stirred for 4 h at room temperature and then was diluted
µ
L 0.487 mmol),
◦
with ethyl acetate. The organic phase was washed with saturated aqueous NH Cl. The organic layer
4
was dried over anhydrous Na SO and then concentrated under reduced pressure. Purification of the
2
4
crude product by silica gel chromatography (ethyl acetate: petroleum ether = 1:1) gave product 18a
1
as a white solid (50 mg, 72.4% yield). H-NMR (CDCl , 400 MHz)
δ
: 8.10 (d, J = 7.6 Hz, 2H, Ar-H),
3
7
7
.62 (d, J = 7.6 Hz, 2H, Ar-H), 7.58 (t, J = 7.2 Hz, 1H, Ar-H), 7.47 (dd, J = 7.6, 14.8 Hz, 2H, Ar-H),
.43–7.40 (m, 1H, Ar-H), 7.38–7.36 (m, 4H, Ar-H), 7.30–7.29 (m, 3H, Ar-H), 6.30 (t, J = 8.4 Hz, 1H,
0
H-13), 5.88 (d, J = 9.6 Hz, 1H, H-3 ), 5.57 (d, J = 9.6 Hz, 1H, H-2), 5.30–5.27 (overlap, 2H, H-5, H-20a),
4
0
.69 (d, J = 2.0 Hz, 1H, H-2 ), 4.26 (d, J = 7.6 Hz, 1H, H-3), 4.20 (brs, 1H, H-20b), 4.00-3.95 (m, 2H,
OCH CH2CH2OCO), 3.91–3.83 (m, 3H, OCH2CH CH OCO, H-7a), 3.76 (brs, 1H, H-7b), 2.75–2.64 (m,
2
2
2
2H, H-6a, H-14a), 2.27–2.21 (m, 2H, H-6b, H-14b), 1.92–1.90 (m, 5H, CH , OCH2CH2CH OCO), 1.96 (s,
3 2
3
H, CH ), 1.81 (brs, 3H, CH ), 1.27 (s, 3H, CH ), 1.18 (s, 3H, CH ), 0.76 (s, 9H, SiC(CH ) ),
−
0.08 (s, 3H,
3
3
3
3
3 3
13
Si(CH )),
−
0.33 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ
: 191.6, 170.7, 168.7, 167.3 (2C), 153.1,
3
3
3
1
7
−
2
52.8, 144.1, 137.9, 133.8, 133.7, 131.9, 129.9 (2C), 128.9 (2C), 128.7 (4C), 128.6, 127.9 (2C), 126.5 (2C), 82.1,
9.9, 75.7, 74.7, 70.5, 68.8, 60.4, 59.3, 58.8, 55.6, 42.8, 36.6, 32.2, 25.4 (3C), 23.2, 22.1, 18.2, 14.9, 14.2, 5.5,
6.1; LC-MS (ESI, m/z): [M + 23], found 1006.0, C H NO Si: 983.45.
−
54
69
14
0
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-methoxybenzoyl)-9-O-(3-hydroxyethyl)-10-dehydro-7,8-seco-
1
1
0-deacetylpaclitaxel (18b). White solid; yield 75.3%; H-NMR (CDCl , 400 MHz)
δ: 7.71–7.65 (m, 3H,
3
Ar-H), 7.53 (m, 1H, Ar-H), 7.46–7.41 (m, 2H, Ar-H), 7.11 (dd, J = 2.4, 8.0 Hz, 1H, BzNH), 6.28 (t,
0
J = 8.6 Hz, 1H, H-13), 5.87 (d, J = 9.2 Hz, 1H, H-3 ), 5.58 (d, J = 9.5 Hz, 1H, H-2), 5.29–5.26 (overlap,
0
2
4
H, H-5, H-20a), 4.72 (d, J = 2.1 Hz, 1H, H-2 ), 4.26 (d, J = 6.6 Hz, 1H, H-3), 4.21 (brs, 1H, H-20b),
.00-3.95 (m, 2H, OCH CH2CH2O), 3.98–3.86 (m, 3H, OCH2CH CH O, H-7b), 3.83 (overlap, 4H,
2
2
2
OCH , H-7a), 2.77–2.66 (m, 2H, H-6b, H-14b), 2.27–2.21 (m, 2H, H-6a, H-14a), 1.96 (s, 3H, CH ), 1.92
3
3
(
brs, 2H, OCH2CH2CH O), 1.83 (m, 2H, OH), 1.84 (brs, 3H, CH ), 1.26 (s, 3H, CH ), 1.19 (s, 3H, CH ),
2 3 3 3
0
1
1
.78 (s, 9H, SiC(CH ) ),
−
0.09 (s, 3H, Si(CH )), δ:
−
0.29 (s, 3H, Si(CH )); 13C-NMR (CDCl , 100 MHz)
3
3
3
3 3
91.6, 171.2, 170.9, 168.9, 167.3, 167.2, 159.8, 144.4, 138.1, 133.8, 131.9, 130.4, 130.3, 128.7 (2C), 128.7 (2C),
28.0, 127.0 (2C), 126.7 (2C), 122.3, 119.6, 114.9, 85.8, 79.9, 75.8, 74.9, 70.7, 68.8, 59.3, 59.0, 55.7, 55.5, 42.8,
3
6.6, 32.3, 25.5 (3C), 25.2, 23.2, 22.2, 18.2, 14.9, 14.5,
−
5.5, 6.0; LC-MS (ESI, m/z): [M + 1], found 1014.4,
−
[M + 23], found 1036.4, C H NO Si: 1013.46.
55
71
16
0
2
1
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-fluorobenzoyl)-9-O-(3-hydroxyethyl)-10-dehydro-7, 8-seco-
1
0-deacetylpaclitaxel (18c). White solid; yield 69.7%; H-NMR (CDCl , 400 MHz)
δ: 7.93 (d, J = 7.6 Hz,
3
1
6
H, Ar-H), 7.75 (d, J = 8.9 Hz, 1H, Ar-H), 7.63 (d, J = 7.5 Hz, 1H, Ar-H), 7.52–7.28 (m, 11H, NH, Ar-H),
.29 (t, J = 8.1 Hz, 1H, H-13), 5.89 (d, J = 9.2 Hz, 1H, H-3 ), 5.57 (d, J = 9.6 Hz, 1H, H-2), 5.28–5.26
0

Molecules 2019, 24, 2161
18 of 23
0
(
overlap, 2H, H-5, H-20a), 4.70 (d, J = 2.0 Hz, 1H, H-2 ), 4.27 (d, J = 8.1 Hz, 1H, H-3), 4.19 (brs, 1H,
H-20b), 3.99–3.94 (m, 2H, OCH CH2CH2OH), 3.88–3.81 (m, 3H, OCH2CH CH OH, H-7a), 3.76 (brs,
2
2
2
1
1
3
H, H-7b), 2.72–2.63 (m, 2H, H-6a, H-14a), 2.24 (dd, 1H, J = 9.5, 15.8 Hz, H-14b), 2.06– 1.98 (overlap,
H, H-6b), 1.95 (s, 3H, CH ), 1.93–1.87 (m, 4H, CH , OCH2CH2CH OH), 1.83 (brs, 3H, CH ), 1.26 (brs,
3
3
2
3
H, CH ), 1.17 (s, 3H, CH ), 0.77 (s, 9H, SiC(CH ) ),
−
0.09 (s, 3H, Si(CH )),
−
0.32 (s, 3H, Si(CH ));
3
3
3 3
3
3
1
3
1
C-NMR (CDCl , 100 MHz)
δ
: 191.5, 171.2, 170.8, 168.6, 167.4, 166.3, 162.7 (d, J
= 248.2 Hz), 144.3,
3
C-F
2
3
1
1
37.9, 133.9, 131.9, 131.2 (d, J
25.8 (d, J
= 7.3 Hz), 131.0 (d, J
= 7.7 Hz), 128.8, 128.7, 128.0, 127.0, 126.5,
C-F
C-F
4
2
2
= 2.6 Hz), 121.0 (d, J
= 21.2 Hz), 116.6 (d, J
= 22.8 Hz), 85.9, 80.0, 75.8, 75.2, 70.5,
C-F
C-F
C-F
6
8.9, 59.3, 55.6, 42.8, 36.7, 32.3, 25.5, 23.2, 22.1, 18.2, 15.0, 14.5,
−
5.4, 6.0; LC-MS (ESI, m/z): [M + 1],
−
found 1002.0, [M + 23], found 1025.0, C H FNO Si: 1001.44.
54
68
14
0
2
1
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-chlorobenzoyl)-9-O-(3-hydroxyethyl)-10-dehydro-7,8-seco-
1
0-deacetylpaclitaxel (18d). White solid; yield 52.6%; H-NMR (CDCl , 400 MHz)
δ: 8.03 (d, J = 7.6 Hz,
3
1H, Ar-H), 8.00–7.96 (m, J = 7.6 Hz, 1H, Ar-H), 7.65 (d, J = 7.6 Hz, 2H, Ar-H), 7.54 (t, J = 7.2 Hz, 1H,
Ar-H), 7.48–7.44 (m, 2H, Ar-H), 7.43–7.40 (m, 1H, Ar-H), 7.38–7.36 (m, 4H, Ar-H), 7.39–7.28 (m, 7H,
0
Ar-H), 6.30 (t, J = 8.4 Hz, 1H, H-13), 5.88 (d, J = 9.6 Hz, 1H, H-3 ), 5.57 (d, J = 9.6 Hz, 1H, H-2), 5.30–5.27
(
0
overlap, 2H, H-5, H-20a), 4.71 (s, 1H, H-2 ), 4.26 (d, J = 7.6 Hz, 1H, H-3), 4.18 (brs, 1H, H-20b),
3
.99–3.93 (m, 2H, OCH CH2CH2O), 3.79–3.40 (m, 3H, OCH2CH CH O, H-7a), 3.73–3.64 (brs, 1H,
2
2
2
H-7b), 2.94 (s, 3H, CH ), 2.84 (s, 3H, CH ), 2.66 (br, 2H, H-6a, H-14a), 2.29–2.22 (m, 2H, H-6b, H-14b),
3
3
1
.93 (s, 3H, CH ), 1.93–1.86 (m, 5H, CH , OCH2CH2CH O), 1.82 (brs, 3H, CH ), 1.24 (s, 3H, CH ), 1.16
3 3 2 3 3
s, 3H, CH ), 0.76 (s, 9H, SiC(CH ) ), −0.11 (s, 3H, Si(CH )), −0.31 (s, 3H, Si(CH )); 3C-NMR (CDCl3,
1
(
1
1
3
3 3
3
3
00 MHz)
δ: 191.5, 171.1, 170.8, 167.4, 165.9, 162.5, 144.3, 137.9, 134.8, 133.9, 133.7, 131.8, 131.0, 130.6,
29.5, 128.7 (2C), 128.6 (2C), 128.1, 127.9, 126.9 (2C), 126.5 (2C), 85.8, 75.7, 75.2, 70.5, 68.8, 67.9, 60.4, 59.2,
5.6, 42.7, 36.6, 36.4, 32.3, 31.4, 25.4 (3C), 23.2, 22.1, 21.0, 18.2, 14.5, 14.2, 5.5, 6.1; LC-MS (ESI, m/z):
M + 1], found 1018.4, [M + 23], found 1040.4, C H ClNO Si: 1017.41.
5
[
−
−
54
68
14
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-trifluoromethylbenzoyl)-9-O-(3-hydroxyethyl)-10-dehydro-7,
1
8-seco-10-deacetylpaclitaxel (18e). White solid; yield 71.8%; H-NMR (CDCl , 400 MHz):
δ
8.38 (d,
3
J = 7.8 Hz, 2H, Ar-H), 7.83 (d, J = 7.7 Hz, 2H, Ar-H), 7.68 (t, J = 7.8 Hz, 1H, Ar-H), 7.44 (dd, J = 15.4,
8
.0 Hz, 2H, Ar-H), 7.47–7.41 (m, 1H, Ar-H), 7.40–7.36 (m, 4H, Ar-H), 7.30–7.29 (m, 3H, Ar-H), 6.29
0
(t, J = 8.5 Hz, 1H, H-13), 5.86 (d, J = 8.6 Hz, 1H, H-3 ), 5.59 (d, J = 9.5 Hz, 1H, H-2), 5.26 (overlap,
0
2
4
H, H-5, H-20a), 4.70 (d, J = 2.0 Hz, 1H, H-2 ), 4.29 (d, J = 7.3 Hz, 1H, H-3), 4.21 (brs, 1H, H-20b),
.00–3.96 (m, 2H, OCH CH2CH2OH), 3.90–3.87 (m, 3H, OCH2CH CH OH, H-7a), 3.75 (brs, 1H,
2
2
2
H-7b), 2.70–2.60 (m, 2H, H-6a, H-14a), 2.28–2.22 (m, 2H, H-6b, H-14b), 1.97 (s, 3H, CH ), 1.94–1.92 (m,
3
5
H, CH , OCH2CH2CH OH), 1.81 (brs, 3H, CH ), 1.27 (s, 3H, CH ), 1.19 (s, 3H, CH ), 0.76 (s, 9H,
3
2
3
3
3
13
SiC(CH ) ),
−
0.08 (s, 3H, Si(CH )),
−
0.32 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ: 191.5, 170.8,
3
3
3
3
3
2
3
1
1
4
67.5, 144.3, 137.9, 133.9, 133.2, 132.0, 131.4 (q, J = 33.3 Hz), 130.2 (q, J = 4.0 Hz), 130.0, 128.8,
28.1, 126.9, 126.8 (q, J = 3.9 Hz), 126.5, 123.6 (q, J = 274.2 Hz), 85.9, 75.6, 75.4, 70.5, 59.4, 55.6,
2.9, 36.7, 32.3, 25.5, 18.2, 14.6,
C-F C-F
3
1
C-F
C-F
−
5.4,
−
6.0; LC-MS (ESI, m/z): [M + 1], found 1052.4, [M + 23], found
1
074.4, C H NO F Si: 1051.44.
55 68 14 3
3
.1.9. General Experimental Procedure for Compounds 20a–e
0
2
-O-(tert-Butyldimethylsilyl)-macrocyclic taxoid (20a). To a solution of 18a (26.2 mg, 0.0266 mmol) in
dichloromethane (5.7 mL) was added, dropwise, pyridine (11
µ
L, 0.133 mmol) and triphosgene (8.7 mg,
◦
0
.0293 mmol) at 0 C, then the reaction mixture was stirred at room temperature for 3.5 h. The reaction
was diluted with ethyl acetate, then washed with saturated NaCl. The organic layer was dried over
anhydrous Na SO and then concentrated under reduced pressure. Purification of the crude product
2
4
by silica gel chromatography (ethyl acetate: petroleum ether = 1:3) gave product 20a as a white solid
1
(
6.7 mg, 24.9% yield). H-NMR (CDCl , 400 MHz)
δ
: 8.17 (d, J = 8.0 Hz, 2H, Ar-H), 7.75 (d, J = 7.6 Hz,
3
2
H, Ar-H), 7.63 (t, J = 7.2 Hz, 1H, Ar-H), 7.56–7.49 (m, 3H, Ar-H), 7.44–7.29 (m, 7H, Ar-H), 7.09 (d,
0
J = 9.2 Hz, 1H, NH), 6.27 (t, J = 8.8 Hz, 1H, H-13), 5.76 (d, J = 8.8 Hz, 1H, H-3 ), 5.60 (d, J = 8.0 Hz, 1H,

Molecules 2019, 24, 2161
19 of 23
0
H-2), 4.80 (d, J = 7.6 Hz, 2H, H-5, H-3), 4.67 (brs, 1H, H-2 ), 4.63 (m, 1H, OCH2CH CH OCO), 4.53 (dd,
2
2
J = 6.4, 11.6 Hz, 1H, OCH CH2CH2OCO), 4.47 (d, J = 8.4 Hz, 1H, H-20a), 4.42 (dd, J = 4.0, 7.2 Hz, 1H,
2
OCH CH2CH2OCO), 4.34 (d, J = 8.4 Hz, 1H, H-20b), 4.11 (overlap, 2H, H-7a, OCH2CH CH OCO),
2
2
2
3
.98 (dt, J = 6.0, 11.6 Hz, 1H, H-7b), 2.66 (m, 1H, H-6a), 2.56 (s, 3H, CH ), 2.52 (s, 3H, CH ), 2.42–2.11
3 3
(
m, 5H, H-6b, H-14a, H-14b, OCH2CH2CH O), 1.82 (s, 3H, CH ), 1.24 (s, 3H, CH ), 1.17 (s, 3H, CH ),
2
3
3
3
0
δ
.79 (s, 9H, SiC(CH ) ),
−
0.04 (s, 3H, Si(CH )),
−
0.31 (s, 3H, Si(CH )); 13C-NMR (CDCl , 150 MHz)
3
3
3
3
3
: 191.6, 170.7, 169.7, 169.3, 166.7, 166.6, 153.6, 152.4, 144.1, 138.8, 138.1, 135.5, 133.6, 131.6, 130.2 (2C),
30.0, 128.7, 128.6, 128.5, 127.7, 126.8 (2C), 126.1 (2C), 90.3, 84.4, 78.4, 76.1, 75.2, 75.0, 70.4, 68.9, 65.8,
4.2, 55.4, 42.6 (2C), 36.4, 30.8, 28.8, 25.9, 25.3 (3C), 22.5, 21.5, 17.9, 14.5, 14.1, 5.5, 6.1; LC-MS (ESI,
m/z): [M + 23], found 1032.0, C H NO Si: 1009.43.
1
6
−
−
55
67
15
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-methoxybenzoyl)-macrocyclic taxoid (20b). White solid; yield
1
2
7
7
8.6%; H-NMR (CDCl , 400MHz)
.67–7.66 (m, 1H, Ar-H), 7.55–7.50 (m, 1H, Ar-H), 7.48–7.42 (m, 3H, Ar-H), 7.40–7.29 (m, 5H, Ar-H),
.19–7.16 (m, 1H, Ar-H), 7.09 (d, J = 8.8 Hz, 1H, BzNH), 6.27 (t, J = 8.8 Hz, 1H, H-13), 5.76 (dd,
δ: 7.79 (d, J = 7.6 Hz, 1H, Ar-H), 7.76 (d, J = 7.2 Hz, 2H, Ar-H),
3
0
J = 1.5, 9.0 Hz, 1H, H-3 ), 5.62 (d, J = 7.64 Hz, 1H, H-2), 4.85–4.82 (m, 2H, H-5, H-3), 4.69–4.63 (m, 2H,
H-2 , OCH2CH CH OCO), 4.56–4.51 (m, 1H, OCH CH2CH2OCO), 4.48–4.38 (m, 3H, H-20a, H-20b,
0
2
2
2
OCH CH2CH2OCO), 4.16–4.07 (m, 2H, H-7a, OCH2CH CH OCO), 4.01–3.96 (m, 1H, H-7b), 3.90 (s,
2
2
2
3
2
H, OCH ), 2.72–2.62 (m, 1H, H-6a), 2.57 (s, 3H, CH ), 2.53 (s, 3H, CH ), 2.43–2.36 (m, 1H, H-6b),
3 3 3
.35–2.28 (m, 1H, H-14a), 2.16–2.14 (m, 2H, H-14b, OCH2CH2CH O), 1.82 (d, J = 1.1 Hz, 3H, CH ), 1.25
2
3
(
s, 3H, CH ), 1.18 (s, 3H, CH ), 0.88 (s, 9H, SiC(CH ) ),
−
0.014 (s, 3H, Si(CH )),
−
0.29 (s, 3H, Si(CH ));
3
3
3 3
3
3
1
3
C-NMR (CDCl , 100 MHz)
δ
: 190.8, 171.3, 171.2, 169.2, 166.9, 166.8, 159.8, 144.8, 138.3, 134.2, 131.8,
30.6, 130.1, 128.8 (2C), 128.7 (2C), 128.0, 127.0 (2C), 126.6 (2C), 122.3, 120.0, 114.5, 85.1, 77.4, 77.3, 76.8,
5.3, 74.9, 70.8, 67.8, 60.4, 55.8, 55.5, 42.8, 41.6, 40.4, 36.6, 33.0, 29.7, 25.5 (3C), 23.2, 22.4, 21.0, 18.2, 14.5,
4.2, 5.3, 5.8; LC-MS (ESI, m/z): [M + 1], found 1040.5, [M + 23], found 1062.5, C H NO Si: 1039.44.
3
1
7
1
−
−
5
6
69
16
0
2
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-fluorobenzoyl)-macrocyclic taxoid (20c). White solid; yield
1
7.1%; H-NMR (CDCl , 400 MHz)
δ: 8.00 (d, J = 7.7 Hz, 1H, Ar-H), 7.87 (d, J = 8.8 Hz, 1H, Ar-H), 7.77
3
(
d, J = 7.32 Hz, 1H, Ar-H), 7.57–7.51 (m, 2H, Ar-H), 7.46–7.33 (m, 8H, Ar-H), 7.10 (d, J = 9.0 Hz, 1H,
0
NH), 6.26 (t, J = 8.5 Hz, 1H, H-13), 5.78 (d, J = 8.5 Hz, 1H, H-3 ), 5.60 (d, J = 7.7 Hz, 1H, H-2), 4.85–4.82
0
(
overlap, 2H, H-5, H-3), 4.72–4.63 (overlap, 2H, OCH2CH CH OCO, H-2 ), 4.55 (dt, J = 5.5, 10.3 Hz,
2
2
1
1
2
H, OCH CH2CH2OCO), 4.47–4.42 (overlap, 2H, OCH CH2CH2OCO, H-20a), 4.37 (d, J = 8.2 Hz,
2
2
H, H-20b), 4.14–4.10 (overlap, 2H, H-7a, OCH2CH CH OCO), 3.99 (dt, J = 6.4, 11.3 Hz, 1H, H-7b),
2
2
.73–2.64 (m, 1H, H-6a), 2.57 (s, 3H, CH ), 2.54 (s, 3H, CH ), 2.42–2.18 (m, 5H, H-6b, H-14a, H-14b,
3
3
OCH2CH2CH O), 2.10 (brs, 1H, OH), 1.83 (s, 3H, CH ), 1.25 (s, 3H, CH ), 1.18 (s, 3H, CH ), 0.82 (s,
2
3
3
3
1
3
9
H, SiC(CH ) ),
−
0.008 (s, 3H, Si(CH )),
−
0.27 (s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ
: 191.8,
3
3
3
3
1
3
5
1
1
1
71.0, 169.5, 166.9, 165.7 (d, J
38.4, 135.5, 134.2, 131.8, 131.3 (d, J
26.4, 126.0 (d, J
= 3.0 Hz, ArCO), 162.6 (d, J
= 247.8 Hz), 153.8, 152.6, 144.3, 139.1,
= 7.7 Hz), 128.8, 128.7, 127.9, 127.0,
C-F
C-F
C-F
3
3
= 7.5 Hz), 130.6 (d, J
C-F
4
2
2
= 2.6 Hz), 120.9 (d, J
= 21.1 Hz), 117.0 (d, J
= 23.2 Hz), 90.6, 84.6, 78.6,
C-F
C-F
C-F
7
2
7.4, 77.1, 76.7, 76.2, 75.8, 75.3, 70.6, 69.2, 66.0, 64.4, 55.6, 42.8 (2C), 36.5, 31.0, 29.0, 26.1, 25.5 (3C),
2.7, 21.7, 18.2, 14.7, 14.4, 5.2, 5.8; LC-MS (ESI, m/z): [M + 1], found 1028.4, [M + 23], found 1050.4,
−
−
C H FNO Si: 1027.42.
55
66
15
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-chlorobenzoyl)-macrocyclic taxoid (20d). White solid; yield
1
2
3.6%; H-NMR (CDCl , 400 MHz)
δ
: 8.20 (t, J = 1.6 Hz, 1H, Ar-H), 8.12–8.09 (m, 1H, Ar-H), 7.77 (d,
3
J = 7.2 Hz, 1H, Ar-H), 7.65–7.62 (m, 1H, Ar-H), 7.56–7.51 (m, 2H, Ar-H), 7.47–7.33 (m, 7H, Ar-H), 7.09 (d,
0
J = 9.0 Hz, 1H, BzNH), 6.26 (t, J = 8.8 Hz, 1H, H-13), 5.77 (dd, J = 1.5, 8.98 Hz, 1H, H-3 ), 5.60 (d, J = 7.8 Hz,
1
H, H-2), 4.85–4.82 (dd, J = 3.5, 11.0 Hz, 2H, H-5, H-17b), 4.72–4.64 (m, 2H, OCH2CH CH OCO,
2 2
0
H-2 ), 4.59–4.53 (m, 1H, OCH CH2CH2OCO), 4.49–4.43 (m, 2H, OCH CH2CH2OCO, H-20a), 4.38
2
2
(
d, J = 8.4 Hz, 1H, H-20b), 4.15–4.10 (m, 2H, OCH CH2CH2OCO, H-20a), 4.02–3.96 (m, 1H, H-7b),
2
2
.74–2.65 (m, 1H, H-6a), 2.57 (s, 3H, CH ), 2.55 (s, 3H, CH ), 2.42–2.20 (m, 5H, H-6b, H-14a, H-14b,
3 3
OCH2CH2CH O), 1.84 (d, J = 1.0 Hz, 3H, CH ), 1.26 (s, 3H, CH ), 1.19 (s, 3H, CH ), 0.83 (s, 9H,
2
3
3
3

Molecules 2019, 24, 2161
20 of 23
SiC(CH ) ),
−
0.005 (s, 3H, Si(CH )),
−
0.26 (s, 3H, Si(CH )); 13C-NMR (CDCl , 100 MHz)
δ
: 190.7, 171.2,
3
3
3
3
3
169.1, 167.0, 165.7, 144.8, 138.3, 135.5, 135.0, 134.3, 133.9, 131.8, 131.1, 130.5, 129.9, 128.8 (2C), 128.7 (2C),
28.2, 128.0, 127.0 (2C), 126.7 (2C), 90.6, 84.6, 78.7, 76.2, 75.8, 75.3, 70.7, 67.8, 55.7, 42.8, 41.6, 36.5, 34.7,
1
3
1.6, 29.7, 25.6 (3C), 22.7, 22.4, 18.2, 14.5, 14.1,
−
5.3, 5.8; LC-MS (ESI, m/z): [M + 1], found 1044.0,
−
[M + 23], found 1065.9, C H ClNO Si: 1043.39.
55
66
15
0
2
-O-(tert-Butyldimethylsilyl)-2-debenzoyl-2-(3-trifluoromethylbenzoyl)-macrocyclic taxoid (20e). White solid;
1
yield 26.7%; H-NMR (CDCl , 400MHz)
δ
: 8.50 (s, 1H, Ar-H), 8.41 (d, J = 7.8 Hz, 1H, Ar-H), 7.92 (d,
3
J = 7.9 Hz, 1H, Ar-H), 7.55–7.51 (m, 1H, Ar-H), 7.48–7.33 (m, 8H, Ar-H), 7.09 (d, J = 9.0 Hz, 1H, NH),
0
6
2
4
.26–6.21 (m, 1H, H-13), 5.76 (dd, J =1.4, 9.1 Hz, 1H, H-3 ), 5.64 (d, J = 7.8 Hz, 1H, H-2), 4.89–4.83 (m,
0
H, H-5, H-3), 4.69–4.63 (m, 2H, OCH2CH CH OCO, H-2 ), 4.60–4.55 (m, 1H, OCH CH2CH2OCO),
.49–4.43 (m, 2H, OCH CH2CH2OCO, H-20a), 4.37 (d, J = 8.0 Hz,1H, H-20b), 4.13 (t, J = 7.7 Hz, 2H,
2
2
2
2
H-7a, OCH2CH CH OCO), 2.75–2.67 (m, 1H, H-6a), 4.02–3.96 (m, 1H, H-7b), 2.58 (s, 3H, CH ), 2.53 (s,
2
2
3
3
H, CH ), 2.45–2.18 (m, 5H, H-6b, H-14a, H-14b, OCH2CH2CH O), 1.84 (d, J =1.0 Hz, 1H, CH ), 1.26
3
2
3
(
(
s, 3H, CH ), 1.25 (s, 3H, CH ), 1.20 (s, 3H, CH ), 0.83 (s, 9H, SiC(CH ) ),
−
0.006 (s, 3H, Si(CH )),
−
0.25
3
3
3
3 3
3
13
s, 3H, Si(CH )); C-NMR (CDCl , 100 MHz)
δ
: 191.7, 171.1, 167.0, 165.5, 153.9, 152.7, 135.4, 134.3,
3
3
2
3
1
33.6, 131.8, 131.4 (q, J = 33.3 Hz), 130.9, 130.3 (q, J = 3.9 Hz), 130.2, 129.7, 128.8, 128.0, 127.0, 126.9 (q,
3
1
J = 3.8 Hz), 126.5, 123.7 (q, J = 273.8 Hz), 90.6, 84.7, 78.7, 76.2, 75.8, 75.3, 70.8, 69.2, 66.0, 64.5, 55.7,
4
2.9, 42.8, 36.5, 31.0, 29.0, 26.1, 22.6, 21.6, 18.2, 14.6, 14.4,
−
5.2, 5.8; LC-MS (ESI, m/z): [M + 1], found
−
1
078.4, [M + 23], found 1100.4, C H F NO Si: 1077.42.
56
66
3
15
3
.1.10. General Procedure for the Syntheses of Compounds 22a–e
Macrocyclic taxoid (22a)
To a solution of of 20a (29.6 mg, 0.0293 mmol) in THF (8 mL) was added, dropwise, 0.47 mL of
◦
HF-pyridine (v/v = 1:2) at 0 C, and the reaction mixture was stirred at room temperature for 30 h.
The reaction was quenched with saturated aqueous NaHCO , diluted with ethyl acetate, and washed
3
with saturated NH Cl. The organic layer was dried over anhydrous Na SO and then concentrated
4
2
4
under reduced pressure. Purification of the crude product by silica gel chromatography (ethyl acetate:
1
petroleum ether = 2:1) gave product 22a as a white solid (13.4 mg, 51.0% yield). H-NMR (CDCl ,
3
400 MHz) δ: 7.16 (d, J = 7.1 Hz, 2H, Ar-H), 7.75 (d, J = 7.0 Hz, 2H, Ar-H), 7.64 (t, J = 7.5 Hz, 1H,
Ar-H), 7.54–7.50 (m, 3H, Ar-H), 7.49–7.47 (m, 2H, Ar-H), 7.43–7.39 (m, 4H, Ar-H), 7.36–7.32 (m,1H,
0
Ar-H), 7.04 (d, J = 9.1 Hz, 1H, NH), 6.18 (dd, J = 8.7 Hz, 1H, H-13), 5.81 (dd, J = 2.4, 9.1 Hz, 1H, H-3 ),
5
0
.59 (d, J = 7.7 Hz, 1H, H-2), 4.81–4.79 (overlap, 3H, H-5, H-3, H-2 ), 4.61 (dt, J = 5.4, 11.0 Hz, 1H,
O
CH2CH CH OCO), 4.52 (dt, J = 6.9, 12.0 Hz, 1H, OCH CH2CH2OCO), 4.44 (overlap, 2H, H-20a,
2 2 2
OCH CH2CH2OCO), 4.41–4.33 (m, 1H, H-20b), 4.34–4.28 (overlap, J = 6.7 Hz, H-7a), 4.08 (overlap,
2
0
2
2
H, H-7a, OCH2CH CH OCO), 3.95 (m, 1H, H-7b), 3.58 (brs, 1H, OH-2 ), 2.66–2.61 (m, 1H, H-6a),
2
2
.55 (s, 3H, CH ), 2.37–2.33 (brs, 3H, CH ), 2.30–2.12 (overlap, 3H, H-6b, H-14a, H-14b), 1.67 (brs, 2H,
3
3
13
OCH2CH2CH OCO), 1.23 (s, 3H, CH ), 1.16 (s, 3H, CH ); C-NMR (CDCl , 100 MHz) δ: 191.6, 172.4,
2
3
3
3
1
1
69.8, 167.0, 166.9, 153.8, 152.6, 144.6, 138.0 (2C), 136.1, 133.9, 133.7, 130.2 (2C), 129.1, 129.0 (2C), 128.9,
28.8 (2C), 128.7 (2C), 128.3, 127.0 (2C), 90.5, 84.7, 78.5, 76.3, 75.3, 73.2, 71.7, 69.2, 65.6, 64.4, 54.8, 42.9,
4
9
2.7, 36.5, 31.0, 29.0, 26.2, 22.4, 21.3, 14.7, 14.0; LC-MS (ESI, m/z): [M + 1], found 896.3, [M + 23], found
18.3, C H NO : 895.34.
49
53
15
1
2
4
7
-Debenzoyl-2-(3-methoxybenzoyl)-macrocyclic taxoid (22b). White solid; yield 59.2%; H-NMR (CDCl ,
00 MHz)
3
δ: 7.75 (d, J = 7.4 Hz, 3H, Ar-H), 7.65 (dd, J =1.42, 2.3 Hz, 1H, Ar-H), 7.52–7.38 (m, 9H, Ar-H),
.17 (dd, J = 2.1, 8.2 Hz, 1H, Ar-H), 7.06 (d, J = 9.0 Hz, 1H, NH), 6.15 (t, J = 8.2 Hz, 1H, H-13), 5.78 (dd,
J = 2.1, 8.9 Hz, 1H, H-3 ), 5.59 (d, J = 7.6 Hz, 1H, H-2), 4.80–4.76 (overlap, 3H, H-5, H-3, H-2 ), 4.60 (dt,
J = 5.6, 11.2 Hz, 1H, OCH2CH CH OCO), 4.51 (dt, J = 5.7, 11.2 Hz, 1H, OCH CH2CH2OCO), 4.44–4.37
0
0
2
2
2
(
overlap, J = 5.6 Hz, 2H, OCH CH2CH2OCO, H-20a), 4.36 (d, J = 8.3 Hz, 1H, H-20b), 4.07 (overlap, 2H,
2
0
H-7a, OCH2CH CH OCO), 3.97–3.91 (m, 1H, H-7b), 3.87 (s, 3H, OCH ), 3.66 (d, J = 4.1 Hz, 1H, OH-2 ),
2
2
3

Molecules 2019, 24, 2161
21 of 23
2
2
3
1
7
.67–2.56 (m, 1H, H-6a), 2.55 (s, 3H, CH ), 2.34 (s, 3H, CH ), 2.40–2.30 (m, 2H, OCH2CH2CH OCO),
3 3 2
.28–2.12 (m, 3H, H-6b, H-14a, H-14b), 2.02 (brs, 1H, OH-1), 1.65 (s, 3H, CH ), 1.22 (s, 3H, CH ), 1.15 (s,
3
3
H, CH3); 13C-NMR (CDCl , 100 MHz)
δ
: 191.6, 172.3, 169.8, 167.0, 166.8, 159.8, 153.7, 152.6, 144.6,
38.1, 137.9, 136.1, 133.7, 132.0, 130.3, 129.8, 129.0, 128.7, 128.3, 127.1, 127.0, 122.4, 112.0, 115.0, 90.4, 84.7,
8.4, 76.3, 75.3, 73.3, 71.7, 69.2, 66.0, 64.4, 55.5, 54.9, 42.8, 42.7, 36.5, 31.0, 29.0, 26.1, 22.4, 21.2, 14.7, 14.0;
LC-MS (ESI, m/z): [M + 1], found 926.3, [M + 23], found 948.3, C H NO : 925.35.
3
50
55
16
1
2
4
7
-Debenzoyl-2-(3-fluorobenzoyl)-macrocyclic taxoid (22c). White solid; yield 51.5%; H-NMR (CDCl ,
3
00 MHz) δ: 7.96 (d, J = 7.69 Hz, 1 H, Ar-H), 7.84 (d, J = 9.1 Hz, 1H, Ar-H), 7.74 (d, J = 7.7 Hz, 2H, Ar-H),
.53–7.46 (m, 4 H, Ar-H), 7.40 (t, J = 7.5 Hz, 4H, Ar-H), 7.36–7.32 (m, 2H, Ar-H), 7.05 (d, J = 9.0 Hz, 1H,
NH), 6.15 (t, J = 8.6 Hz, 1H, H-13), 5.78 (dd, J = 2.0, 9.0 Hz, 1H, H-3 ), 5.57 (d, J = 7.7 Hz, 1H, H-2),
.81–4.79 (overlap, 3H, H-5, H-3, H-2 ), 4.60 (dt, J = 5.3, 10.7 Hz, 1H, OCH2CH CH OCO), 4.52 (dt,
0
0
4
2
2
J = 5.4, 10.8 Hz, 1H, OCH CH2CH2OCO), 4.44–4.40 (ovelap, 2H, H-7a, OCH CH2CH2OCO), 4.40 (d,
2
2
J = 8.0 Hz, 1H, H-20a), 4.32 (d, J = 8.1 Hz, 1H, H-20b), 4.07 (t, J = 7.5 Hz, 2H, OCH2CH CH OCO), 3.93
2
2
0
dt, J = 5.9, 11.9 Hz, 1H, H-7b), 3.69 (brs, 1H, OH-2 ), 2.68–2.58 (m, 1H, H-6a), 2.54 (s, 3H, CH ), 2.34 (s,
3
(
3
H, CH ), 2.33–2.26 (m, 2H, OCH CH CH OCO), 2.24–2.16 (m, 3H, H-6b, H-14a, H-14b), 1.97 (brs, 1H,
3 2 2 2
13
OH-1), 1.65 (br, 3H, CH ), 1.22 (s, 3H, CH ), 1.15 (s, 3H, CH ); C-NMR (CDCl , 100 MHz)
δ
: 191.5,
=247.9 Hz), 153.8, 152.6, 144.5, 138.1 (2C),
C-F
3
3
3
3
1
1
1
72.4, 169.7, 167.0, 165.7 (d, J
35.9, 133.8, 131.9, 131.3 (d, J
= 2.8 Hz, CO), 162.6 (d, J
= 7.5 Hz), 130.5 (d, J
= 21.3 Hz), 116.9 (d, J
C-F
3
3
= 7.6 Hz), 129.0, 128.7, 128.3, 127.0 (2C), 126.0
= 23.3 Hz), 90.5, 84.6, 78.5, 76.2, 75.6, 73.3,
C-F
C-F
4
2
2
(
d, J
= 2.9 Hz), 121.0 (d, J
C-F
C-F
C-F
71.6, 69.2, 66.0, 64.4, 55.0, 42.8, 42.7, 36.4, 30.9, 29.3, 29.0, 26.1, 22.3, 21.3, 14.6, 14.0; LC-MS (ESI, m/z):
[
M + 1], found 914.3, [M + 23], found 936.3, C H FNO : 913.33.
49 52 15
1
2
-Debenzoyl-2-(3-chlorobenzoyl)-macrocyclic taxoid (22d). White solid; yield 65.4%; H-NMR (CDCl ,
3
4
00 MHz) δ: 8.16 (t, J = 1.8 Hz, 1H, Ar), 8.06–8.04 (m, 1 H, Ar-H), 7.75–7.73 (m, 2H, Ar-H), 7.61 (ddd,
J =1.0, 2.0, 8.0 Hz, 1H, Ar-H), 7.43–7.39 (m, 4H, Ar-H), 7.52–7.45 (m, 4 H, Ar-H), 7.37–7.32 (m, 1H,
Ar-H), 7.01 (d, J = 9.0 Hz, 1H, NH), 6.15 (dd, J = 7.4, 8.7 Hz, 1H, H-13), 5.78 (dd, J = 2.3, 9.0 Hz,
0
0
1
H, H-3 ), 5.57 (d, J = 7.7 Hz, 1H, H-2), 4.81–4.79 (overlap, 3H, H-5, H-3, H-2 ), 4.60 (dt, J = 5.3, 10.7
Hz, 1H, OCH2CH CH OCO), 4.53 (dt, J = 5.5, 11.3 Hz, 1H, OCH CH2CH2OCO), 4.45–4.44 (m, 1H,
2
2
2
OCH CH2CH2OCO), 4.39 (d, J = 8.2 Hz, 1H, H-20a), 4.33 (d, J = 8.2 Hz, 1H, H-20b), 4.08 (overlap,
2
0
J = 7.62 Hz, 2H, H-7a, OCH2CH CH OCO), 3.96–3.90 (m, 1H, H-7b), 3.60 (brs, 1H, OH-2 ), 2.68–2.58
2
2
(
(
(
m, 1H, H-6a), 2.54 (s, 3H, CH ), 2.35 (s, 3H, CH ), 2.44–2.30 (m, 2H, OCH2CH2CH OCO), 2.28–2.16
3 3 2
m, 3H, H-6b, H-14a, H-14b), 1.97 (brs, 1H, OH-1), 1.65 (d, J =1.7 Hz, 3H, CH ), 1.23 (s, 3H, CH ), 1.16
3
3
s, 3H, CH3); 13C-NMR (CDCl , 100 MHz)
δ
: 191.5, 172.4, 169.7, 167.0, 165.5, 153.8, 152.6, 144.5, 138.0,
3
1
7
35.9, 134.8, 133.8, 133.7, 132.0, 130.9, 130.2 (2C), 129.0, 128.7, 128.4, 127.1, 127.0, 90.4, 84.6, 78.5, 76.1,
5.5, 73.2, 71.7, 69.2, 65.9, 64.4, 55.0, 42.8, 42.7, 36.4, 30.9, 29.0, 26.1, 22.3, 21.2, 14.6, 14.0; LC-MS (ESI,
m/z): [M + 1], found 930.3, [M + 23], found 952.3, C H ClNO : 929.30.
49
52
15
1
2
-Debenzoyl-2-(3-trifluoromethylbenzoyl)-macrocyclic taxoid (22e). White solid; yield 59.5%; H-NMR
(
CDCl , 400 MHz) : 8.46 (s, 1 H, Ar), 8.36 (d, J = 7.8 Hz, 1H, Ar-H), 7.90 (d, J =7.7 Hz, 1H, Ar-H),
δ
3
7
.73–7.67 (m, 3 H, Ar-H), 7.51–7.47 (m, 3H, Ar-H), 7.42–7.32 (m, 5H, Ar-H), 6.98 (d, J = 9.0 Hz, 1H,
0
NH), 6.15 (t, J = 8.1 Hz, 1H, H-13), 5.77 (dd, J = 2.0, 9.0 Hz, 1H, H-3 ), 5.61 (d, J = 7.7 Hz, 1H, H-2),
0
4
.84–4.78 (overlap, 3H, H-5, H-3, H-2 ), 4.62–4.51 (m, 2H, OCH2CH2CH2OCO), 4.45–4.41 (m, 2H, H-7a,
OCH CH2CH2OCO), 4.39 (d, J = 8.0 Hz, 1H, H-20a), 4.31 (d, J = 8.2 Hz, 1H, H-20b), 4.07 (t, J = 7.6 Hz,
2
0
1
H, OCH2CH CH OCO), 3.93 (dt, J = 6.9, 11.6 Hz, 1H, H-7b), 3.62 (brs, 1H, OH-2 ), 2.66–2.58 (m, 1H,
2
2
H-6a), 2.54 (s, 3H, CH ), 2.44–2.35 (m, 2H, OCH2CH2CH OCO), 2.32 (s, 3H, CH ), 2.28–2.16 (m, 3H,
3
2
3
H-6b, H-14a, H-14b), 1.97 (brs, 1H, OH-1), 1.67 (br, 3H, CH ), 1.23 (s, 3H, CH ), 1.17 (s, 3H, CH );
3
3
3
1
3
C-NMR (CDCl , 75 MHz)
δ
: 191.6, 172.4, 169.7, 167.0, 165.4, 153.7, 152.6, 144.5, 138.1 (2C), 135.8, 133.7,
= 3.7 Hz), 130.1, 129.6, 129.0, 128.7, 128.4, 127.1,
C-F
= 3.2 Hz), 125.5, 90.5, 84.6, 78.5, 76.1, 75.6, 73.1, 71.7, 69.2, 66.0, 64.4, 55.0, 42.8, 42.7,
3
2
3
1
1
33.6, 131.9, 131.3 (d, J
27.0, 126.9 (d, J
= 33.2 Hz), 130.3 (d, J
C-F
3
C-F
3
9
6.3, 30.9, 29.3, 28.9, 26.1, 22.2, 21.2, 14.6, 14.0; LC-MS (ESI, m/z): [M + 1], found 964.4, [M + 23], found
86.3, C H F NO : 963.33.
50
52
3
15

Molecules 2019, 24, 2161
22 of 23
3
.2. Cell Assays
Cell viability after taxoids treatment was evaluated using CCK-8 assay. Briefly, 3000 cells per well
were seeded in 96-well plates and incubated under normal conditions for 24 h. Cells were treated
with different concentrations of the test agent for 72 h, then the medium was removed, 100
CCK-8 working solution was added to each well for 1 h at 37 C. The absorbance was measured
at 450 nm with a microplate reader (Tecan Trading, AG, Switzerland). Vehicle-only treated cells
µ
L of
◦
served as the indicator of 100% cell viability. The 50% inhibitory concentration (IC ) was defined
50
as the concentration that reduced the absorbance of the vehicle-only treated wells by 50% in the
3
-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.
3
.3. Model Building and Molecular Dynamics Simulations
The X-ray crystal structure of paclitaxel provided a template for the construction of 18b and
2b using the molecular editing tools implemented in PyMOL [17]. Geometry optimization of 18b
2
and 22b was achieved by means of the updated AM1 hamiltonian implemented in the sqm program,
which also produced atomic charge distributions for both ligands that can reproduce the molecular
electrostatic potential. The ff14SB AMBER force field was used to assign bonded and non-bonded
parameters to protein and ligand atoms [18,19]. 18b was immersed in a cubic box containing TIP3P
water molecules and simulated under periodic boundary conditions for 50 ns at 300 K. Subsequent
gradual cooling, from 300 to 273 K over 1 ns, of snapshots taken regularly every 2.5 ns, followed by
energy minimization until the root-mean-square of the Cartesian elements of the gradient was less
− −1
1
than 0.1 kcal
·
mol
·
Å , provided representative structures of this molecule; those displaying the
shortest distance between the free hydroxyl groups were chosen to build 22b by means of a C=O
linkage. The simulated macromolecular ensemble representing a short piece of a microtubule with
bound 22b was constructed as previously reported for D-seco taxol derivatives [20].
4
. Conclusions
In summary, this study demonstrated that C-seco taxoids conformationally constrained via
carbonate-containing linked macrocyclization display increased cytotoxicity on drug-resistant tumors
overexpressing both III and P-gp, compared to the non-cyclized C-seco taxoid counterparts Among
β
them, compound 22b, bearing a 2-m-methoxybenzoyl group together with a five-atom linker, was
identified as the most potent compound in the series.
Supplementary Materials: The supplementary materials are available online, cell lines and culture [21],
establishment of model multidrug-resistant breast cancer cell line MCF-7/ADR. Copies of ESI-MS, HPLC,
1
13
H-NMR and C-NMR spectra for representative compounds.
Author Contributions: Y.Z. performed most of the experiments; T.-N.W. carried out the bioassays; A.M. and
F.G. carried out the molecular modeling studies; writing—original draft preparation, Y.Z., T.-N.W. and A.M.;
writing—review and editing, W.-S.F. and F.G.; W.-S.F. planned, designed, and organized the whole research of this
study. All authors read and approved the final version of the manuscript.
Funding: CAMS Innovation Fund for Medical Sciences (CIFMS Grant No. 2016-I2M-1-01) and the Drug Innovation
Major Project (Grant Nos. 2018ZX09711001-001-001 and 2018ZX09711001-001-003) by MOST of China (W.-S.F.)
and Spanish MEC/MICINN for grant SAF2015-64629-C2-2 (F.G.) are acknowledged.
Conflicts of Interest: The authors declare no conflicts of interest regarding the publication of this paper.
References
1.
2.
3.
Fojo, T.; Coley, H.M. The role of efflux pumps in drug-resistant metastatic breast cancer: New insights and
treatment strategies. Clin. Breast Cancer 2007, 7, 749–756. [CrossRef] [PubMed]
Kavallaris, M. Microtubules and resistance to tubulin-binding agents. Nat. Rev. Cancer 2010, 10, 194–204.
[
CrossRef] [PubMed]
Kamath, K.; Wilson, L.; Cabral, F.; Jordan, M.A.
reduced effects on microtubule dynamic instability. J. Biol. Chem. 2005, 280, 12902–12907. [CrossRef] [PubMed]
βIII-tubulin induces paclitaxel resistance in association with

Molecules 2019, 24, 2161
23 of 23
4
5
6
7
.
.
.
.
Orr, G.A.; Verdier-Pinard, P.; McDaid, H.; Horwitz, S.B. Mechanisms of Taxol resistance related to microtubules.
Oncogene 2003, 22, 7280–7295. [CrossRef] [PubMed]
Ferlini, C.; Gallo, D.; Scambia, G. New taxanes in development. Expert Opin. Investig. Drugs 2008, 17, 335–347.
[CrossRef] [PubMed]
Ojima, I.; Lichtenthal, B.; Lee, S.; Wang, C.; Wang, X. Taxane anticancer agents: A patent perspective.
Expert Opin. Ther. Pat. 2016, 26, 1–20. [CrossRef] [PubMed]
Paradiso, A.; Mangia, A.; Chiratti, A.; Tommasi, S.; Zito, A.; Latorre, A.; Schittulli, F.; Lorusso, V. Biomarkers
predictive for clinical efficacy of taxol-based chemotherapy in advanced breast cancer. Ann. Oncol. 2005, 16,
1
4–19. [CrossRef] [PubMed]
Seve, P.; Mackey, J.; Isaac, S.; Tredan, O.; Souquet, P.-J.; Perol, M.; Lai, R.; Voloch, A.; Dumontet, C. Class
III -tubulin expression in tumor cells predicts response and outcome in patients with non-small cell lung
8
9
1
1
1
.
β
cancer receiving paclitaxel. Mol. Cancer Ther. 2005, 4, 2001–2007. [CrossRef] [PubMed]
Mozzett, S.; Ferlini, C.; Conocolino, P.; Filippetti, F.; Raspaglio, G.; Prislei, S.; Gallo, D.; Martinelli, E.;
.
Ranelletti, F.O.; Ferrandina, G.; et al. Class III
paclitaxel resistance in ovarian cancer patients. Clin. Cancer Res. 2005, 11, 298–305.
0. Ferrandina, G.; Zannoni, G.F.; Martinelli, E.; Paglia, A.; Gallotta, V.; Mozzetti, S.; Scambia, G.; Ferlini, C.
Class III -tubulin overexpression is a marker of poor clinical outcome in advanced ovarian cancer patients.
β-tubulin overexpression is a prominent mechanism of
β
Clin. Cancer Res. 2006, 12, 2774–2779. [CrossRef]
1. Ferlini, C.; Raspaglio, G.; Mozzetti, S.; Cicchillitti, L.; Filippetti, F.; Gallo, D.; Fattorusso, C.; Campiani, G.;
Scambia, G. The Seco-Taxane IDN5390 Is able to target class III
β-Tubulin and to overcome paclitaxel
resistance. Cancer Res. 2005, 65, 2397–2405. [CrossRef]
2. Tang, Y.; Rodriguez-Salarichs, J.; Zhao, Y.; Cai, P.; Estevez-Gallego, J.; Balaguer-Perez, F.; Horcajo, M.R.;
Lucena-Agell, D.; Barasoain, I.; Diaz, J.F.; et al. Modification of C-seco taxoids through ring tethering and
substituent replacement leading to effective agents against tumor drug resistance mediated by βIII-Tubulin
and P-glycoprotein (P-gp) overexpressions. Eur. J. Med. Chem. 2017, 137, 488–503. [CrossRef] [PubMed]
1
1
1
3. Pepe, A.; Sun, L.; Zanardi, I.; Wu, X.Y.; Ferlini, C.; Fontana, G.; Bombardelli, E.; Ojima, I. Novel C-seco-taxoids
possessing high potency against paclitaxel-resistant cancer cell lines overexpressing class III β-tubulin.
Bioorg. Med. Chem. Lett. 2009, 19, 3300–3304. [CrossRef] [PubMed]
4. Alushin, G.M.; Lander, G.C.; Kellogg, E.H.; Zhang, R.; Baker, D.; Nogales, E. High resolution microtubule
structures reveal the structural transitions in alpha-beta tubulin upon GTP hydrolysis. Cell 2014, 157,
1
117–1129. [CrossRef] [PubMed]
5. Chaudhary, A.G.; Gharpure, M.M.; Rimoldi, J.M.; Chordia, M.D.; Gunatilaka, A.A.L.; Kingston, D.G.I.
Unexpectedly facile hydrolysis of the 2-benzoate group of taxol and syntheses of analogs with increased
activities. J. Am. Chem. Soc. 1994, 116, 4097–4098. [CrossRef]
1
1
1
1
2
6. Kingston, D.G.I.; Chaudhary, A.G.; Chordia, M.D. Synthesis and biological evaluation of 2-acyl analogues of
paclitaxel (taxol). J. Med. Chem. 1998, 41, 3715–3726. [CrossRef] [PubMed]
7. Vella-Zarb, L.; Baisch, U.; Dinnebier, R.E. Small molecule, big difference: The role of water in the crystallization
of paclitaxel. J. Pharm. Sci. 2013, 102, 674–683. [CrossRef]
8. Walker, R.C.; Crowley, M.F.; Case, D.A. The implementation of a fast and accurate QM/MM potential method
in Amber. J. Comput. Chem. 2008, 29, 1019–1031. [CrossRef]
9. Kaus, J.W.; Pierce, L.T.; Walker, R.C.; McCammon, J.A. Improving the efficiency of free energy calculations in
the Amber molecular dynamics package. J. Chem. Theory Comput. 2013, 9, 4131–4139. [CrossRef]
0. Wang, S.R.; Yang, C.G.; S
Fang, W.S. Restoration of Microtubule Interaction and Cytotoxicity in D-seco Taxanes upon Incorporation of
0-Hydroxymethyl-4-allyloxy Groups. Org. Lett. 2015, 17, 6098–6101. [CrossRef]
ánchez-Murcia, P.A.; Snyder, J.P.; Yan, N.; Sáez-Calvo, G.; Díaz, J.F.; Gago, F.;
2
2
1. Cai, P.; Lu, P.; Sharom, F.J.; Fang, W.S. A semisynthetic taxane Yg-3-46a effectively evades P-glycoprotein and
beta-III tubulin mediated tumor drug resistance in vitro. Cancer Lett. 2013, 341, 214–223. [CrossRef] [PubMed]
Sample Availability: Not available.
©
2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access
article distributed under the terms and conditions of the Creative Commons Attribution
(CC BY) license (http://creativecommons.org/licenses/by/4.0/).