Protecting groups for glucuronic acid: Application to the synthesis of new paclitaxel (taxol) derivatives

Article abstract of DOI:10.1021/jo0612675

To prepare two new glucuronide conjugates, allyl ester and allyl carbonates were used as protecting groups of the glucuronic moiety. In this way, an aniline glycosyl carbamate spacer linked to the 2′-OH of paclitaxel was obtained. By using palladium chemistry, an efficient one-step removal of all the allyl groups at the end of the synthesis afforded the desired compounds in good yields.

Full text of DOI:10.1021/jo0612675

Protecting Groups for Glucuronic Acid: Application to the
Synthesis of New Paclitaxel (Taxol) Derivatives
Abdessamad El Alaoui, Fre´de´ric Schmidt,* Claude Monneret, and Jean-Claude Florent
UMR 176 CNRS/Institut Curie, Centre de Recherche, 26 rue d’Ulm, 75248 Paris Cedex 05, France
frederic.schmidt@curie.fr
ReceiVed June 20, 2006
To prepare two new glucuronide conjugates, allyl ester and allyl carbonates were used as protecting
groups of the glucuronic moiety. In this way, an aniline glycosyl carbamate spacer linked to the 2′-OH
of paclitaxel was obtained. By using palladium chemistry, an efficient one-step removal of all the allyl
groups at the end of the synthesis afforded the desired compounds in good yields.
Introduction
In our ongoing work toward building paclitaxel (Taxol)
glucuronyl prodrugs, one major synthetic problem was to
introduce a â-D-glucuronic acid moiety in the most efficient
possible way. This involved finding a cheap and readily
accessible synthon, coupling it to the cytotoxic unit, and
importantly, removing the protecting groups. New prodrugs
could be obtained in good yields, even in the presence of
sensitive groups, such as in the paclitaxel framework. We report
here the use of a fully allyl protected glucuronyl derivative and
its final deprotection step leading to the planned, tripartite
prodrugs which structure is indicated below (Figure 1).
Synthesis of the Allyl Protected D-Glucuronic Acid De-
rivatives. Glucuronides1 are oxidized forms of glucosides, often
found as metabolites of xenobiotics. They represent a way of
obtaining more water-soluble derivatives. Concerning their
synthesis, due to their own distinctive chemistry, glucuronides
are usually more difficult to prepare than the corresponding
glucopyranosides.2 Several methods are available for the
synthesis of glucuronic acid glycosides, which can be divided
into two broad categories involving either oxidation of the
corresponding glucosides3-8 or direct glycosidation of an
FIGURE 1. Structure of paclitaxel prodrugs.
activated glucuronic acid.2,9-11 Uronic acids are less reactive
than the corresponding glucopyranosides under glycosidation
conditions; moreover, with a leaving group as an acetyl in
position 4, they are prone to give the 4,5-unsaturated byproduct
by elimination of a molecule of carboxylic acid (R1CO2H) under
basic conditions (Scheme 1).
Paclitaxel and Targeting Strategies. We are currently
involved in the preparation of glucuronide prodrugs of paclitaxel
able to release the active compound at the tumor site according
to the Tumor Activated Prodrug (TAP) strategy.12 This consists
of using an activating enzyme that will locally cleave a prodrug
to deliver the antitumor agent. Controlling the selectivity of
cytotoxic drugs like paclitaxel represents a subsidiary advantage.
In this context, the activating enzyme â-D-glucuronidase was
(1) Stachulski, A.; Jenkins, G. Nat. Prod. Rep. 1998, 39, 173-186.
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Keinan, E. J. Org. Chem. 1984, 49, 4988-4993.
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10.1021/jo0612675 CCC: $33.50 © 2006 American Chemical Society
Published on Web 12/01/2006
9628
J. Org. Chem. 2006, 71, 9628-9636

Synthesis of New Paclitaxel (Taxol) DeriVatiVes
SCHEME 1. â-Elimination of the Glucuronic Esters
SCHEME 2. Retrosynthetic Analysis
selected.13 Normally, this endogenous enzyme is exclusively
located in lysosomes, thus avoiding premature liberation of the
drug in the blood. Moreover, â-D-glucuronidase is highly present
in necrotic tumor areas,14 or can be targeted to the non-necrotic
tumor sites via different approaches, such as Antibody Directed
Enzyme Prodrug Therapy (ADEPT), Gene Directed Enzyme
Prodrug Therapy (GDEPT), or Virus Directed Enzyme Prodrug
Therapy (VDEPT), all three involving the use of a conjugate
and a targeted enzyme.15,16
Paclitaxel (Taxol), a potent major anticancer agent that is
widely used in clinics, initiates cell death through multiple
mechanisms, particularly by binding to tubulin and promoting
stable and non-functional microtubule formation.17-20 However,
the clinical usefulness of this drug is particularly hampered by
its poor solubility and lack of selectivity. Improving solubility
and selectivity is therefore a very important goal. In this view,
we undertook and reported the synthesis of paclitaxel prodrugs
designed to be activated by â-D-glucuronidase.21,22 The synthetic
challenges were the control of the â-glycosidic bond and the
choice of the protecting groups of the glucuronic moiety. The
protecting groups had to be easy to introduce, able to control a
â-glycosidic configuration, and overall easy to remove at the
end of the synthesis, especially in the presence of the very
sensitive taxane skeleton. All these reactions had to give high
yields and be versatile enough to be used in a large variety of
different synthetic targets.
glucuronic moiety was crucial. The ester groups (R1 ) acetate)
are most frequently used to protect the 2-, 3-, and 4-hydroxyl
of the glucuronyl moiety with a carboxymethyl or ethyl ester
(R2 ) Me or Et). In this case, the deprotection step at the end
of the synthesis requires the use of basic or nucleophilic
conditions for the cleavage of esters. However, whenever a
sensitive moiety, like paclitaxel, is present in the molecule,
milder conditions are requested.
Another currently used protecting group for the hydroxyls is
the benzyl ether.23,24 In the case of glucuronic acid derivatives,
the most efficient way was to introduce the benzyl ethers into
uronic acid prior to the glucose oxidation stage. However, this
method, which avoids the classic 4,5-elimination under basic
conditions, presents the inconvenience of adding steps to the
synthesis.
Results and Discussion
Retrosynthetic Scheme. For high efficacy, the best choice
consisted of coupling the expensive paclitaxel as late as possible
to an intermediate composed of a â-D-glucuronic acid linked
to a spacer unit.
Synthesis of the Glucuronic Moiety. For the synthesis of
the target molecules, the choice of the protecting groups of the
In a previous work,22 we used tert-butyldimethylsilyl ethers
(TBS) as hydroxy protecting groups (R1 ) TBS) and a benzyl
ester protected carboxyl (R2 ) Bn). The synthetic limitations
observed with these protecting groups were the deprotection
steps, particularly in the case of the benzyl ester under reductive
conditions, when a spacer including a reducible group was
present. This procedure is time-consuming and inelegant because
ester groups must be introduced first and have to be removed
further in the synthesis, and replaced with silyl ester.
Therefore, allyl esters and allyl carbonates were finally chosen
for their easy introduction, their mild conditions of removal with
palladium, and also for the possibility to simultaneously
deprotect hydroxy and carboxylic acid functions. Starting from
glucuronic acid, the allyl ester was first prepared by reaction
(13) Chen, X.; Wu, B.; Wang, P. Curr. Med. Chem. Anticancer Agents
2003, 3, 139-50.
(14) Bosslet, K.; Straub, R.; Blumrich, M.; Czech, J.; Gerken, M.;
Sperker, B.; Kroemer, H.; Gesson, J.-P.; Koch, M.; Monneret, C. Cancer
Res. 1998, 58, 1195-1201.
(15) Jung, M. Mini-ReV. Med. Chem. 2001, 1, 399-407.
(16) Bagshawe, K.; Sharma, S.; Begent, R. Expert Opin. Biol. Ther. 2004,
4, 1777-1789.
(17) Gue´nard, D.; Gue´ritte-Voegelein, F.; Potier, P. Acc. Chem. Res. 1993,
26, 160-167.
(18) Nicolaou, K. C.; Dai, W. M.; Guy, R. K. Angew. Chem., Int. Ed.
Engl. 1994, 33, 15-44.
(19) Wang, T. H.; Wang, H. S.; Soong, Y. K. Cancer 2000, 88, 2619-
2628.
(20) Huang, Y.; Fang, Y.; Dziadyk, J. M.; Norris, J. S.; Fan, W. Oncol.
Res. 2002, 13, 113-122.
(21) Schmidt, F.; Ungureanu, I.; Duval, R.; Pompon, A.; Monneret, C.
Eur. J. Org. Chem. 2001, 2129-2134.
(22) Bouvier, E.; Thirot, S.; Schmidt, F.; Monneret, C. Org. Biomol.
Chem. 2003, 1, 3343-3352.
FIGURE 2. Glucuronic acid derivatives.
J. Org. Chem, Vol. 71, No. 26, 2006 9629

El Alaoui et al.
SCHEME 3. Synthesis of the Glucuronic Moiety
SCHEME 4. Synthesis of the Spacer
SCHEME 5. Coupling Between the Glucuronic and the Spacer Moieties
with allyl bromide under basic conditions (DBU).25 The next
step was the protection of all the hydroxy groups by treatment
with an excess of allyloxycarbonyl chloride. Then, selective
cleavage of the anomeric carbonate was performed by treatment
with tributyltin oxide giving 4 as a mixture of anomers (R/â )
3.5/1 according to NMR). These conditions were described for
the removal of anomeric acetates,26 but we applied them to allyl
carbonates. More classical hydroxyl anomer deacylation condi-
tions, such as hydrazine acetate,27 gave nonselective deprotec-
tions of the anomeric allyl-carbonates, thus leading to mixtures
of partially protected glucuronic derivatives.
Synthesis of the Spacer Moiety. The p-nitrobenzyl alcohol
5 was reacted with TBSCl giving the O-silylprotected derivative
6,28,29 and the aromatic nitro group was selectively reduced by
hydrogen transfer (H2, Pd/C, ammonium formate) to avoid
benzylic hydrogenolysis. Next, by using triphosgene,31 the amine
728 was converted into isocyanate 830 which, due to its
instability, was immediately engaged in the coupling with the
sugar moiety.
Synthesis of the Allyl Protected Aniline â-O-Glucuronyl.
According to Scheeren et al.,30 aromatic isocyanates react in
the presence of Et3N with anomerically unprotected per-O-acetyl
glucuronide to highly diastereoselectively afford the correspond-
ing â-O-glycosyl carbamates. This high â-stereoselectivity could
be explained by the fact that the 1-OH group is known to be
more nucleophilic in the â-configuration than in the R-config-
uration. By using these conditions, compound 9 was obtained,
with high â-stereoselectivity as unambiguously determined by
NMR analysis, and in a rather good yield (69%) from the allyl
protected glucuronic acid 4 and p-hydroxybenzyl-silyl isocyanate
8.
The next step was the deprotection of the silyl ether. The
reaction conditions had to be compatible with ester, carbonate,
and carbamate functions. Whereas neither TBAF (which proved
to be too basic) nor HF/Pyr (which afforded the dimer 11 as
the main product) could be used, the TBAF/AcOH32 couple
proved to be the choice reactant to obtain 10 in good yield
(81%).
To activate the benzylic alcohol of 10, it was initially treated
with disuccinimidyl carbonate. However, no succinimidyl
carbonate was obtained, but the unexpected decarboxylated
succinimido derivative 13 was obtained, as is clearly identified
by spectroscopic data. Therefore we turned our attention toward
an activation with 4-nitrophenyl chloroformate and obtained 12
ready for the coupling reaction with paclitaxel.
A possible mechanism of 13 formation could be the loss of
CO2 by the expected compound, followed by succinimide
addition as indicated in Scheme 7.
(23) Keglevic, D.; Pravdic, N.; Tomasic, J. J. Chem. Soc. (C) 1968, 511-
514.
(24) Keglevic, D.; Lievakovic, D. Carbohydr. Res. 1978, 64, 319-322.
(25) Juteau, H.; Gareau, Y.; Labelle, M. Tetrahedron Lett. 1997, 38,
1481-1484.
(26) Nudelman, A.; Herzig, J.; Gottlieb, H.; Keinan, E.; Sterling, J.
Carbohydr. Res. 1987, 162, 145-152.
(27) Excoffier, G.; Gagnaire, D.; Utille, J.-P. Carbohydr. Res. 1995, 39,
368-373.
(28) Luo, C.; Guldi, D.; Imahori, H.; Tamaki, K.; Sakata, Y. J. Am. Chem.
Soc. 2000, 122, 6535-6551.
(29) Shiraishi, M.; Aramaki, Y.; Seto, M.; Imoto, H.; Nishikawa, Y.;
Kanzaki, N.; Okamoto, M.; Sawada, H.; Nishimura, O.; Baba, M.; Fujino,
M. J. Med. Chem. 2000, 43, 2049-2063.
Couplings with Paclitaxel. To link this glucuronylated spacer
to the 2′-OH of paclitaxel, two kinds of carbonates were
envisioned. The choice of a carbonate rather than an ester
(30) Leenders, R.; Ruytenbeek, R.; Damene, E.; Scheeren, H. Synthesis
1996, 1309-1312.
(31) Niculescu-Duvaz, D.; Niculescu-Duvaz, I.; Friedlos, F.; Martin, J.;
Spooner, R.; Davies, L.; Marais, R.; Springer, C. J. Med. Chem. 1998, 41,
5297-5309.
(32) Higashibayashi, S.; Shinko, K.; Ishizu, T.; Hashimoto, K.; Shira-
hama, H.; Nakata, M. Synlett 2000, 9, 1306-1308.
9630 J. Org. Chem., Vol. 71, No. 26, 2006

Synthesis of New Paclitaxel (Taxol) DeriVatiVes
SCHEME 6. Activation of the Glucuronic Spacer Moiety
SCHEME 7. Mechanism of Formation of Compound 13
SCHEME 8. Coupling of Paclitaxel
function was dictated by the fact that carbonates, and particularly
paclitaxel-2′-carbonates, are more stable as regards hydrolysis
than the corresponding esters.33 The first carbonate derivative
15 could directly be obtained by coupling 12 with paclitaxel.
The second derivative, 19, bearing an additional 2-methylamino
alcohol moiety, was prepared. Its structure was devised accord-
ing to previous observations by us34 and Scheeren35 et al., which
showed that introducing an additional short spacer such as a
diaminoethylene derivative could greatly influence both the
stability and kinetics of cleavage of the prodrugs.
To achieve the synthesis of the first prodrug 15, the activated
p-nitrophenyl carbonate 12 was condensed (71%) with paclitaxel
in the presence of DMAP, followed by simultaneous removal
of both allyl ester and allyloxycarbonyl (alloc) that cleanly
occurred by reacting 14 with Pd(PPh3)4 in the presence of Et3N/
HCO2H.36,37As these conditions avoided the current formation
of byproducts during the classical deprotection of per-O-acetyl
glucuronides, this could be an interesting alternative to other
methods of glucuronide synthesis for base-sensitive compounds.
(33) Ueda, Y.; Wong, H.; Matiskella, J.; Mikkilineni, A.; Farina, V.;
Fairchild, C.; Rose, W.; Mamber, S.; Long, B.; Kerns, E.; Casazza, A.;
Vyas, D. Bioorg. Med. Chem. Lett. 1994, 4, 1861-1864.
(34) Lougerstay-Madec, R.; Florent, J.-C.; Monneret, C.; Nematy, F.;
Poupon, M.-F. Anticancer Drug Des. 1998, 13, 995-1007.
(35) de Groot, F.; Loos, W.; Koekkoek, R.; van Berkom, L.; Busscher,
G.; Seelen, A.; Albrecht, C.; de Bruijn, P.; Scheeren, H. J. Org. Chem.
2001, 66, 8815-8830.
(36) Tsuji, J.; Nisar, M.; Shimizu, I. J. Org. Chem. 1985, 50, 3416-
3417.
J. Org. Chem, Vol. 71, No. 26, 2006 9631

El Alaoui et al.
SCHEME 9. Synthesis of the Second Prodrug 19
SCHEME 10. Cleavage of Paclitaxel Prodrug
TABLE 1. Decomposition of Prodrug 15
is specifically transformed into the active paclitaxel by enzy-
matic cleavage at the tumor site. The unstable prodrug 15
spontaneously releases the active drug, so it could be used as a
soluble form of paclitaxel, but without selectivity toward cancer
cells.
time, h
0
0
0
1
2
8.9
12.6
5
19.8
28.9
24
40
64.7
decomp with PBS, %
decomp with PBS + 10% FCS, %
5.5
6.6
Cytotoxicity Measurements. Cytotoxicity was measured on
HT29 cell lines (colorectal cancer). For the stable prodrug 19,
the IC50 value was 26.3 nM. Under the same conditions, that
of paclitaxel was 0.16 nM, meaning that the free drug is 164-
fold more cytotoxic than the prodrug. This value is compatible
with a TAP strategy where a relatively noncytotoxic prodrug
releases a cytotoxic drug at the tumor site.
As regards the unstable prodrug 15, the actual value could
not be measured due to its decomposition during incubation
(72 h) with the cells.
Enzymatic Cleavage. The release of the paclitaxel from its
prodrug 19 in the presence of the activating enzyme â-D-
glucuronidase was measured by HPLC (UV detection) in either
PBS buffer or PBS + 10% FCS.
Prodrug cleavage and release of free paclitaxel were supposed
to occur according to Scheme 10. E. coli â-D-glucuronidase was
used as the activating enzyme. Cleavage of the prodrug was
To access to the second prodrug 19, glucuronyl p-nitrophenyl
carbonate derivative 12 was reacted with 2-methylamino ethanol
to give the carbamate 16. After activation of the free primary
alcohol function as described above for 10, carbonate 17 was
obtained and condensed with paclitaxel; the glucuronyl unit of
18 was then deprotected by Pd(PPh3)4 in the presence of Et3N/
HCO2H.
Stability Tests. The two prodrugs 15 and 19 (190 µM) were
dissolved in a phosphate buffer (PBS) containing either no or
10% fetal calf serum (FCS) and the evolution of the solution
was followed by HPLC (UV detection) at 37 °C.
In both media, the prodrug 19 proved to be rather stable over
24 h with less than 5% hydrolysis detected, whereas the prodrug
15 was unstable, with spontaneous release of the free paclitaxel.
These differences in stability can be explained, since both
compounds are paclitaxel-2′-carbonates, but in 15, it is a
benzylic carbonate versus an aliphatic carbonate in 19. Kinetics
of decomposition of 15 (recorded as starting material disap-
pearance) are given in Table 1.
(37) Corey, E. J.; Gin, D. Y.; Kania, R. S. J. Am. Chem. Soc. 1996, 118,
9202-9203.
(38) Zhu, J.; Withers, S.; Reichardt, P.; Treadwell, E.; Clausen, T.
Biochem. J. 1998, 332, 367-371.
The use of the two prodrugs will be different: the stable
prodrug 19 can be used in a TAP strategy, where the prodrug
9632 J. Org. Chem., Vol. 71, No. 26, 2006

Synthesis of New Paclitaxel (Taxol) DeriVatiVes
FIGURE 3. Cleavage of prodrug 19 by â-D-glucuronidase.
4.32 (d, 1H, J ) 9.7 Hz), 3.68 (t, 1H, J ) 9.1 Hz), 3.52 (t, 1 H, J
) 9.7 Hz), 3.36 (m, 1H); 1H NMR (300 MHz, MeOD) (â isomer)
δ 5.93 (m, 1H), 5.32 (ddd, 2H, J ) 10.4, 3.1, and 1.5 Hz), 4.50 (d,
1H, J ) 7.6 Hz), 4.66 (m, 2H), 3.85 (d, 1H, J ) 9.7 Hz), 3.68 (t,
1H, J ) 9.1 Hz), 3.52 (t, 1 H, J ) 9.7 Hz), 3.18 (m, 1H); 13C
NMR (75 MHz, MeOD) δ 171.6, 170.4, 133.1, 118.5, 98.7, 94.4,
77.4, 75.8, 74.3, 73.4, 73.1, 72.6, 66.8, 66.7; MS (FAB+) m/z 257
[M + Na]+.
Allyl 1.2.3.4-Tetra-(O-allyloxycarbonyl)-D-glucuronate (3).
Compound 2 (9 g, 0.038 mol) was dissolved in anhydrous pyridine
(100 mL). Allyl chloroformate (122 mL, 30 equiv) was added
dropwise in 15 min at 0 °C (strong gas release). The solution turned
brown. After 24 h under stirring, pyridine (30 mL) was added, and
the mixture was stirred for another 24 h. The residue was then
diluted in dichloromethane (250 mL) and washed twice with water,
then three times with a saturated solution of copper sulfate. The
last washing with water, drying over MgSO4, and evaporation gave
a brown oil that was purified over silica gel (eluent: CH2Cl2/acetone
98/2). Compound 3 (10.5 g, 48%) was obtained as an oil: Rf 0.66
(CH2Cl2/acetone 98/2); [R]20D +38 (c 1.0, CHCl3); 1H NMR (300
MHz, CDCl3) (R/â ) 2/3) 6.38 (d, 1H, J ) 3.5 Hz), 5.99-5.81
(m, 5H), 5.72 (d, 1H, J ) 7.3 Hz), 5.54-4.97 (m, 13H), 4.67-
4.52 (m, 11H), 4.31 (d, 1H); 13C NMR (75 MHz, CDCl3) 166.2,
165.8, 153.8, 153.5, 153.4, 152.7, 152.6, 131.0, 130.9, 130.8, 130.7,
130.6, 119.8, 119.7, 119.6, 119.4, 119.3, 119.2, 119.1, 119.0, 94.4,
91.9, 75.2, 73.5, 72.6, 72.5, 72.2, 70.0, 69.4, 69.3, 69.2, 69.1, 69.0,
66.8. MS (CI/NH3) m/z 588 [M + NH4]+; HRMS (FAB + MB +
NaI) (C25H30O15Na) m/z calcd 593.1482, found 593.1478.
Allyl 2.3.4-tri-(O-Allyloxycarbonyl)-D-glucuronate (4). Bis(tri-
n-butyltin) oxide (5.35 mL, 0.01 mol) was added to a solution (6
g, 0.01 mol) of the protected sugar 3 in THF (240 mL), and the
mixture was heated to reflux for 6 h. After evaporation of the
solvent, the residue was chromatographed twice over silica gel
(eluents: first elution CH2Cl2/acetone 96/4; second elution CH2-
Cl2/acetone 95/5) to remove the tin derivatives, leading to compound
4 (2.6 g, 61% of conversion). Isolated byproducts were the starting
material 3 (1 g) and the diprotected compound (900 mg, 19%): Rf
0.47 (CH2Cl2/acetone 98/2); [R]20D +45.8 (c 1.0, CHCl3); 1H NMR
(300 MHz, CDCl3) (R/â ) 3.5/1) δ 5.93-5.77 (m, 4H), 5.57 (d,
1H, J ) 3.3 Hz), 5.40 (t, 1H, J ) 9.7 Hz), 5.32-5.19 (m, 8H),
5.04 (m, 1H), 4.89 (d, 1H, J ) 7.6 Hz), 4.77 (dd, 1H, J ) 10.0 Hz
and J′ ) 3.4 Hz), 4.66-4.49 (m, 9H), 4.21 (d, 1H, J ) 9.4 Hz);
13C NMR (75 MHz, CDCl3) δ 167.7, 166.8, 154.2, 154.0, 153.8,
153.7, 153.6, 131.1, 131.0, 130.9, 119.4, 119.3, 119.1, 118.9, 118.8,
95.0, 89.9, 75.9, 75.4, 73.7, 73.1, 72.9, 72.8, 71.9, 69.1, 69.0, 68.9,
67.5, 66.9, 66.7; MS (CI/NH3) m/z 504 [M + NH4]+; HRMS (FAB
+ MB + NaI) (C21H26O13Na) m/z calcd 509.1271, found 509.1267.
observed with the simultaneous appearance of paclitaxel (Figure
3). The cleavage was faster in buffer than in PBS + serum.
During the HPLC kinetic analysis, we unexpectedly noticed
that no amino alcohol 22 was detected by comparison with an
authentic sample. The cleavage seemed to stop after a while
and a plateau was reached. Our hypothesis is that imine 21 is
not hydrolyzed fast enough, and thus can react first with a
nucleophilic residue on the active site of the enzyme, in the
same way as quinone methides are reported to react with
glucosidases.37 For verification purposes, the enzymatic activity
of â-D-glucuronidase was measured after preincubation with
prodrug 19 and compared to the native enzyme during the same
time. The activity was measured by enzymatic cleavage of
4-nitrophenyl glucuronide. Indeed, the activity was slower after
preincubation with the prodrug, thus demonstrating that the
enzyme is partially inhibited during preincubation with the
prodrug.
Conclusion
Since prodrug therapy based on elevated tumor levels of
endogenous or targeted â-glucuronidase (ADEPT, PMT) has
been the subject of increasing research for several years, finding
an efficient synthesis of glucuronide-containing prodrugs of
antitumor agents is a need. So far, the use of conventional
protection of the glucuronyl moiety could not be applied
whenever acid- or alkali-sensitive groups were present in the
drug or reducible functions. In contrast, the use of allyl ester
and allyl carbonate, as reported in the paper, proved to be
compatible with all these functions and represents a general
pathway.
Experimental Section
Allyl D-Glucuronate (2).25 DBU (17.0 mL, 0.11 mol, 1.1 equiv)
was added dropwise to a solution of D-glucuronic acid (20 g, 0.103
mol) in DMF (200 mL). After the solution was stirred for 15 min
at room temperature, 11 mL (0.12 mmol, 1.2 equiv) of allyl bromide
was added dropwise, and the mixture was stirred overnight. After
evaporation, the residue was purified over silica gel (eluent:
acetone). Compound 2 (19.2 g, 79%) was isolated as an oil: Rf
1
0.76 (acetone). [R]20 +54 (c 1.0; MeOH) (lit. +55.9°; H NMR
D
(300 MHz, MeOD) (R isomer) δ 5.93 (m, 1H), 5.32 (ddd, 2H, J )
10.4, 3.1, and 1.5 Hz), 5.13 (d, 1H, J ) 3.4 Hz), 4.66 (m, 2H),
J. Org. Chem, Vol. 71, No. 26, 2006 9633

El Alaoui et al.
tert-Butyldimethyl-(4-nitrobenzyloxy)silane (6).27,28 To a solu-
tion of 4-nitrobenzylic alcohol 5 (5 g, 0.032 mol) and imidazole
(4.67 g, 0.068 mol, 2.1 equiv) in anhydrous DMF (35 mL) was
added tert-butyldimethylsilyl chloride (4.8 g, 0.032 mol) in small
portions. After stirring for 2 h at room temperature, the mixture
was diluted with EtOAc (250 mL), washed with water (6 × 70
mL), dried over MgSO4, and evaporated. The crude compound was
purified over silica gel (eluent: cyclohexane/EtOAc 8/2). The 8.4
g (98%) yield of product 6 was isolated as an oil: Rf 0.51
(cyclohexane/EtOAc 6/4); 1H NMR (300 MHz, CDCl3) δ 8.20 (d,
2H, J ) 8.7 Hz), 7.49 (d, 2H, J ) 8.7 Hz), 4.82 (s, 2H), 0.95 (s,
9H), 0.12 and 0.11 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 149.0,
146.8, 126.1, 123.4, 63.9, 25.7, 18.2, -5.4; MS (CI/NH3) m/z 285
[M + NH4]+.
gel (eluent: CH2Cl2/acetone 92/8), benzylic alcohol 10 (550 mg,
81%) was obtained as a lacquer: Rf 0.24 (CH2Cl2/acetone 92/8);
1
[R]20 -6.6 (c 1.0, CHCl3); H (NMR 300 MHz, CDCl3) δ 7.29
D
(m, 5H), 5.95-5.79 (m, 5H), 5.37-5.10 (m, 11H), 4.62 (m, 10H),
4.33 (d, 1H, J ) 9.3 Hz), 1.80 (br s, 1H); 13C NMR (75 MHz,
CDCl3) δ 166.3, 153.8, 153.7, 153.5, 150.6, 136.3, 136.2, 130.9,
130.8, 130.7, 127.6, 119.2, 119.1, 119.0, 118.9, 92.1, 75.0, 72.9,
72.3, 71.9, 69.2, 69.0, 66.8, 64.5; MS (FAB + NaI) m/z 658 [M +
Na]+; HRMS (FAB + MB + NaI) (C29H33O15NNa) m/z calcd
658.1748, found 658.1742.
Di[[N-[2,3,4-tri(O-allyloxycarbonyl)allylester-â-D-glucopyra-
nosyl]carbamoyl-4-oxy]benzyl] Oxide (11). HF/pyridine (70%, 0.5
mL) was added to a solution of alcohol 10 (80 mg, 0.106 mmol)
in THF (3 mL). The mixture was stirred for 3 h at room temperature.
A NaHCO3 saturated solution (50 mL) was added and extracted
with EtOAc (3 × 10 mL). After drying over MgSO4 and
evaporation, the compound was purified over silica gel (eluent:
CH2Cl2/acetone 98/2). The dimer 11 (84 mg, 63%) was obtained
tert-Butyldimethyl(4-aminobenzyloxy)silane (7).27 Pd/C (10%,
2.5 g) and ammonium formate (8.6 g) were added to a solution of
the nitro derivative 6 (8.3 g, 0.031 mol) in absolute ethanol (150
mL). After the solution was stirred for 5 h at room temperature,
the catalyst was eliminated by filtration over Celite 545. The filtrate
was evaporated and taken up in EtOAc (200 mL), washed with
water (200 mL), dried over MgSO4, and evaporated to dryness.
The oil was chromatographed over silica gel (eluent: cyclohexane/
EtOAc 8/2). Compound 7 (6.2 g, 84%) was obtained as an oil: Rf
0.34 (cyclohexane/EtOAc 6/4); 1H NMR (300 MHz, CDCl3) δ 7.14
(d, 2H, J ) 8.4 Hz), 6.67 (d, 2H, J ) 8.4 Hz), 4.64 (s, 2H), 3.55
(s, 2H), 0.95 and 0.93 (s, 9H), 0.10 (s, 6H); 13C NMR (75 MHz,
CDCl3) δ 145.2, 131.4, 127.6, 114.9, 64.9, 25.9, 25.6, 18.3, -5.1;
MS (CI/NH3) m/z 255 [M + NH4]+.
as a lacquer: Rf 0.60 (CH2Cl2/acetone 98/2); [R]20 -6.4 (c 1.0,
D
1
CHCl3); H NMR (300 MHz, CDCl3) δ 7.23 (m, 5H), 5.92-5.82
(m, 5H), 5.36-5.20 (m, 11H), 4.62 (m, 8H), 4.41 (s, 2H), 4.35 (d,
1H, J ) 8.6 Hz); 13C NMR (75 MHz, CDCl3) δ 166.4, 153.9, 153.7,
153.6, 150.5, 136.3, 133.4, 131.1, 131.0, 130.9, 130.7, 130.6, 128.3,
119.3, 119.2, 119.0, 118.8, 92.3, 75.0, 72.7, 72.3, 71.9, 71.0, 69.3,
69.0, 66.8, 60.3; MS (FAB + NaI) m/z 1275 [M + Na]+; HRMS
(FAB + MB + NaI) (C58H64N2NaO29) m/z calcd 1275.3493, found
1275.3518.
O-[[N-[2,3,4-Tri(O-allyloxycarbonyl)allylester-â-D-glucopyra-
nosyl]carbamoyl-4-oxy]benzyloxycarbonyl]-4-nitrophenol (12).
At 0 °C, anhydrous pyridine (36 µL, 0.44 mmol, 2 equiv) was added
to a solution of compound 10 (140 mg, 0.22 mmol) in anhydrous
CH2Cl2 (5 mL). Then, 4-nitrophenyl chloroformate (89 mg, 0.44
mmol, 2 equiv) was added and the mixture was stirred for 2 h at
0 °C. After evaporation, the residue was chromatographed over
silica gel (eluent: CH2Cl2/acetone 99/1), giving compound 12 (160
tert-Butyldimethyl(4-isocyanatobenzyloxy)silane (8). To a
solution of the amino 7 compound (1.46 g, 6.1 mmol) and
triethylamine (0.90 mL, 6.3 mmol, 1.05 equiv) in freshly distilled
toluene (40 mL) heated at 70 °C was added triphosgene (0.73 g,
2.4 mmol, 0.4 equiv). The solution became yellow with formation
of a precipitate (triethylamonium salts). The mixture was heated
for 3 h at 70 °C. After filtration, washing with toluene, and
evaporation, isocyanate 8 (1.4 g, 86%) was obtained and directly
used for the next step: Rf 0.78 (CH2Cl2); IR (CHCl3. cm-1) ν 2220
mg, 91%) as a white lacquer: Rf 0.56 (CH2Cl2/acetone 99/1); [R]20
D
1
-7.5 (c 1.0, CHCl3); H NMR (300 MHz, CDCl3) δ 8.27 (d, 2H,
1
(NCO); H NMR (300 MHz, CDCl3) δ 7.28 (d, 2H, J ) 8.3 Hz),
J ) 9.0 Hz), 7.37-7.15 (m, 7H), 5.95-5.77 (m, 5H), 5.37-5.21
(m, 13H), 4.65-4.49 (m, 8H), 4.36 (d, 1H, J ) 9.0 Hz); 13C NMR
(75 MHz, CDCl3) δ 166.2, 155.4, 153.9, 153.7, 153.6, 152.4, 150.3,
145.3, 137.6, 131.0, 130.9, 130.8, 129.7, 125.3, 121.7, 119.4, 119.2,
119.1, 92.3, 75.2, 73.2, 72.4, 72.2, 70.5, 69.3, 69.2, 69.1, 66.9. MS
(MALDI) m/z 823 [M + Na]+ and 839 [M + K]+; HRMS (FAB
+ MB + NaI) (C36H36N2NaO19) m/z calcd 823.1810, found
823.1793.
1-[[N-[2,3,4-Tri-(O-allyloxycarbonyl)allylester-â-D-glucopyra-
nosyl]carbamoyl-4-oxy]benzyl]pyrrolidine-2.5-dione (13). To a
solution of compound 10 (54 mg, 0,085 mmol) in freshly distilled
CH2Cl2 (5 mL) were added (iPr)2NEt (37 µL, 0.212 mmol, 2.5
equiv) then DSC (33 mg, 0.127 mmol, 1.5 equiv). The mixture
was stirred for 24 h at room temperature. One supplementary
equivalent of DSC was added and stirring was continued for an
additional 3 h. After evaporation, the residue was chromatographed
over silica gel (CH2Cl2/acetone 96/4), to obtain the product 13 (20
mg, 40% conversion) as well as 10 mg of starting material: Rf
0.63 (CH2Cl2/acetone 95/5); [R]20D -6.8 (c 1.0, CHCl3); 1H NMR
(300 MHz, CDCl3) δ 7.36 (m, 4H), 7.29 (s, 1H), 5.94-5.82 (m,
5H), 5.36-5.08 (m, 11H), 5.05 (s, 2H), 4.58 (m, 8H), 4.35 (d, 1H,
J ) 9,2 Hz), 2.64 (s, 4H); 13C NMR (75 MHz, CDCl3) δ 171.2,
166.0, 153.8, 153.7, 153.5, 150.2, 138.0, 130.9, 130.8, 129.0, 128.8,
128.2, 119.4, 119.2, 119.1, 118.6, 92.2, 77.9, 75.3, 73.4, 72.4, 72.3,
69.2, 69.1, 66.9, 25.4; MS (FAB + NaI) m/z 755 [M + Na]+;
HRMS (FAB + MB + NaI) (C33H36N2NaO17) m/z calcd 755.1912,
found 755.1927.
7.05 (d, 2H, J ) 8.3 Hz), 4.74 (s, 2H), 0.91 (s, 9H), 0.08 (s, 6H);
MS (CI/NH3) m/z 264 [M + H]+.
N-[4-(tert-Butyldimethylsilanyloxymethyl)phenyl]-O-[2,3,4-tri-
(O-allyloxycarbonyl)allylester-â-D-glucopyranosyl]carbamate (9).
To a sugar 4 solution (1.8 g, 3.70 mmol) in freshly distilled toluene
(100 mL) was added triethylamine (0.52 mL, 3.70 mmol) dropwise
at 0 °C under argon, then isocyanate 8 (1.26 g, 4.81 mmol, 1.3
equiv) in toluene (10 mL), and the mixture was stirred for 1.5 h at
0 °C. After evaporation, the residue was chromatographed over
silica gel (eluent: CH2Cl2/acetone 99/1). The coupling product 9
(1.92 g, 69%) was isolated as an oil: Rf 0.66 (CH2Cl2/acetone 98/
1
2); [R]20 -3.8 (c 1.02, CHCl3); H NMR (300 MHz, CDCl3) δ
D
7.25 (m, 4H), 6.98 (br s, 1H), 5.94-5.82 (m, 5H), 5.36-5.10 (m,
11H), 4.63 (m, 10H), 4.33 (d, 1H, J ) 9.4 Hz), 0.92 (s, 9H), 0.08
(s, 6H); 13C NMR (75 MHz, CDCl3) δ 166.2, 153.8, 153.6, 153.5,
150.4, 136.7, 135.6, 131.1, 130.9, 130.8, 130.7, 130.6, 126.4, 119.2,
119.1, 119.0, 118.9, 118.8, 92.1, 75.0, 72.8, 72.3, 71.9, 69.1, 68.9,
66.7, 64.4, 26.1, 25.8, 25.5, 18.2, -5.3, -5.4; MS (CI/NH3) m/z
767 [M + NH4]+; HRMS (FAB + MB + NaI) (C35H47NNaO15Si)
m/z calcd 772.2613, found 772.2609.
N-[4-(Hydroxymethyl)phenyl]-O-[2,3,4-tri(O-allyloxycarbony-
l)allylester-â-D-glucopyranosyl]carbamate (10). Compound 9
(800 mg, 1.067 mmol) and glacial acetic acid (80 µL, 1.387 mmol,
1.3 equiv) were dissolved in anhydrous THF (50 mL) at 0 °C. TBAF
(1 M, 420 µL, 1.387 mmol, 1.3 equiv) in THF was added dropwise.
After the solution was stirred for 18 h at room temperature, an
additional 0.2 equiv of acetic acid and TBAF was added and the
stirring was continued for 2 h. After cooling at 0 °C, the mixture
was diluted in dichloromethane and washed with a NaHCO3
saturated solution, then with water. The organic phase was dried
over MgSO4 and evaporated to dryness. After purification over silica
2′-O-[N-[2,3,4-tri-(O-allyloxycarbonyl)allylester-â-D-glucopy-
ranosyl]carbamoyl-4-oxy]benzyloxycarbonylpaclitaxel (14). 4-Ni-
trophenyl carbonate 12 (43 mg, 0.053 mmol) and paclitaxel (32
mg, 0.037 mmol, 0.7 equiv) were dissolved in freshly distilled CH2-
Cl2 (7 mL). Then, DMAP (9.8 mg, 0.080 mmol, 1.5 equiv) was
9634 J. Org. Chem., Vol. 71, No. 26, 2006

Synthesis of New Paclitaxel (Taxol) DeriVatiVes
added under argon and the mixture was stirred for 24 h at room
temperature. After evaporation, the compound obtained was purified
over silica gel (CH2Cl2/acetone 9:1), giving the coupled product
mmol) in anhydrous dichloromethane (5 mL) were added pyridine
(15 µL, 0.19 mmol, 2 equiv) then 4-nitrophenyl chloroformate (38
mg, 0.19 mmol, 2 equiv) at 0 °C under stirring. Stirring was
continued at 0 °C for 2 h, then 24 h at room temperature. The
mixture was diluted with dichloromethane and washed with a
saturated cupper sulfate solution, and with water. After drying on
MgSO4, the solution was evaporated to dryness. Purification over
silica gel (eluent: CH2Cl2/acetone 97:3) afforded the activated
compound 17 (40 mg, 71% conversion) as a white solid. The
starting material 16 (24 mg) was also isolated (eluent: CH2Cl2/
14 (40 mg, 71%) as a white solid; mp 188 °C; Rf 0.47 (CH2Cl2/
1
acetone 9/1); [R]20 -31 (c 1.2, CHCl3); H NMR (300 MHz,
D
CDCl3) δ 8.14 (d, 2H, J ) 7.2 Hz), 7.72 (d, 2H, J ) 7.1 Hz),
7.59-7.17 (m, 16H), 6.28 (m, 2H), 5.99-5.79 (m, 6H), 5.69 (d,
1H, J ) 6.8 Hz), 5.44 (d, 1H, J ) 2.4 Hz), 5.36-5.17 (m, 10H),
5.12-5.02 (m, 3H), 4.99 (d, 1H, J ) 9.2 Hz), 4.62 (m, 8H), 4.43
(m, 1H), 4.32 (m, 2H), 4.20 (d, 1H, J ) 8.3 Hz), 3.81 (d, 1H, J )
6.6 Hz), 2.62 (m, 1H), 2.44 (s, 3H), 2.21 (s, 3H), 2.16 (s, 2H),
1.89 (s, 3H), 1.83 (br s, 1H), 1.67 (s, 3H), 1.22 (s, 3H), 1.13 (s,
3H); 13C NMR (75 MHz, CDCl3) δ 203.8, 171.2, 169.8, 167.8,
167.2, 167.0, 166.3, 166.0, 154.0, 153.9, 153.7, 153.5, 150.2, 142.5,
137.4, 136.6, 133.7, 133.4, 132.8, 132.0, 131.0, 130.9, 130.2, 129.8,
129.7, 129.5, 129.1, 128.7, 128.5, 127.1, 126.5, 126.0, 131.0, 130.9,
119.4, 119.3, 119.0, 119.1, 92.2, 84.4, 81.0, 79.1, 77.2, 76.8, 75.5,
75.3, 75.0, 73.4, 72.4, 72.0, 70.3, 69.4, 69.2, 69.1, 66.9, 58.4, 52.7,
45.6, 43.1, 35.5, 29.6, 26.8, 22.7, 22.1, 20.8, 14.7, 9.6; MS (FAB
+ MB + NaI) m/z 1538 [M + Na]+; HRMS (C77H82O23N2Na) m/z
calcd 1537.4850, found 1537.4812.
acetone 85/15): mp 78 °C; Rf 0.54 (CH2Cl2/acetone 95/5); [R]20
D
1
-6.5 (c 1.0, CHCl3); H NMR (300 MHz, CDCl3) δ 8.26 (d, 2H,
J ) 9.0 Hz), 7.30 (m, 7H), 5.96-5.77 (m, 5H), 5.36-5.14 (m,
11H), 5.06 (s, 2H), 4.64-4.49 (m, 8H), 4.41 and 4.35 (m, 3H, J )
9.2 Hz), 3.65 (br s, 2H), 3.0 (s, 3H); 13C NMR (75 MHz, CDCl3)
δ 166.1, 156.3, 153.9. 153.7, 153.6, 152.4, 150.3, 145.4, 136.8,
132.2, 131.0, 130.9, 130.8, 128.8, 128.2, 125.3, 121.8, 121.7, 119.4,
119.2, 119.1, 92.2, 75.2, 75.3, 72.4 and 72.2, 69.2, 69.1, 66.9, 66.8,
47.9, 47.4, 35.7, 35.3; MS (MALDI-TOF) m/z 924 [M + Na]+
and 940 [M + K]+; HRMS (FAB + MB + NaI) (C40H43N3NaO21)
m/z calcd 924.2287, found 924.2285.
2′-O-(N-â-D-Glucopyranosylcarbamoyl-4-oxy)benzyloxycar-
bonylpaclitaxel (15). The protected prodrug 14 (31 mg, 0.020
mmol) was dissolved in anhydrous THF (2 mL). A solution of NEt3
(9 µL, 0.061 mmol, 3 equiv)/HCOOH (2 µL, 0.040 mmol, 2 equiv)
was added in THF (50 µL) and the mixture was stirred for 10 min
under argon, then Pd(PPh3)4 (4.6 mg, 0.00 4 mmol, 0.2 equiv) was
added. After the solution was stirred for 30 min at 0 °C, then for
2 h at room temperature, the solvents were evaporated, and the
product was purified over silica gel (eluent: CH3CN/H2O 95:5).
After lyophilisation, prodrug 15 (17 mg, 68%) was obtained as a
O-[[N-[2,3,4-Tri-(O-allyloxycarbonyl)allylester-â-D-glucopy-
ranosyl]carbamoyl-4-oxy]benzyloxycarbonyl]-2-aminoethyloxy-
carbonylpaclitaxel (18). The activated carbonate 17 (40 mg, 0.044
mmol) and paclitaxel (30 mg, 0.035 mmol, 0.8 equiv) were
dissolved in 7 mL of freshly distilled CH2Cl2, then DMAP (8 mg,
0.066 mmol, 1.5 equiv) was added under argon. The mixture was
stirred at room temperature for 24 h. After evaporation, the
compound was purified over silica gel (eluent: CH2Cl2/acetone 94/6
then 90/10) to give the coupling product 18 (35 mg, 77%) as a
white solid: mp 198-200 °C; Rf 0.32 (CH3CN/H2O 9/1); [R]20
D
white solid: mp 163 °C; Rf 0.34 (CH2Cl2/acetone 85/15); [R]20
D
1
-31 (c 1.2, MeOH); H NMR (300 MHz, CDCl3) δ 8.11 (d, 2H,
-26 (c 1.0, CHCl3); 1H NMR (300 MHz, CDCl3) δ 8.13 (d, 2H, J
) 7.2 Hz), 7.72-7.22 (m, 18H), 6.30 (br s, 2H), 6.00-5.81 (m,
6H), 5.70 (d, 1H, J ) 6.7 Hz), 5.40-5.14 (m, 11H), 5.09-4.98
(m, 4H), 4.62 (br s, 8H), 4.43 (m, 1H), 4.31-4.18 (m, 5H), 3.83
(d, 1H, J ) 6.4 Hz), 3.55 (m, 2H), 2.91 (d, 3H, J ) 8.7 Hz), 2.62
(m, 2H), 2.45 (s, 3H), 2.21 (s, 3H), 1.93 and 1.88 (2s, 5H), 1.68 (s,
3H), 1.22 (s, 3H), 1.14 (s, 3H); 13C NMR (75 MHz, CDCl3) δ
203.7, 171.2, 169.9, 167.8, 167.2, 167.0, 165.9, 156.3, 156.2, 153.9,
153.8, 153.5, 150.3, 142.5, 136.7, 136.5, 132.8, 133.6, 133.4, 132.0,
131.0, 130.8, 130.2, 129.1, 128.7, 128.5, 127.1, 126.5, 126.1, 119.4,
119.2, 119.1, 118.9, 118.7, 118.6, 92.2, 84.3, 81.0, 79.0, 77.2, 75.5,
75.2, 75.0, 73.4, 72.5, 72.1, 69.2, 69.1, 66.9, 66.8, 66.6, 58.4, 52.6,
48.1, 47.3, 45.6, 43.1, 35.5, 26.7, 22.7, 22.1, 20.8, 14.7, 9.6; MS
(FAB+) m/z 1638.6 [M + Na]+; HRMS (C81H89O32N3Na) m/z calcd
1638.5309, found 1638.5327.
J ) 7.1 Hz), 7.77 (d, 2H, J ) 7.0 Hz), 7.68-7.26 (m, 16H), 6.44
(s, 1H), 6.03 (m, 1H), 5.82 (d, 1H, J ) 6.4 Hz), 5.64 (d, 1H, J )
7.2 Hz), 5.47 (d, 2H, J ) 6.5 Hz), 5.15 (s, 2H), 5.01 (d, 1H, J )
8.8 Hz), 4.34 (q, 1H, J ) 10.7 Hz and J′ ) 8.7 Hz), 4.18 (s, 2H),
3.82 (d br, 2H, J ) 7.1 Hz), 3.68-3.42 (m, 3H), 2.48 (m, 1H),
2.40 (s, 3H), 2.17 (m, 4H), 1.89 (s, 3H), 1.86 (m, 2H), 1.65 (s,
3H), 1.13 and 1.12 (s, 6H); 13C NMR (75 MHz, CDCl3) δ 205.2,
171.7, 171.3, 170.5, 170.2, 167.6, 155.8, 142.2, 138.1, 135.4, 134.9,
134.6, 133.1, 133.0, 132.9, 131.4, 131.2, 130.5, 130.1, 129.9, 129.7,
129.6, 129.5, 129.2, 128.6, 119.9, 96.0, 85.9, 82.2, 79.0, 78.5, 77.5,
76.8, 76.2, 73.7, 73.2, 71.3, 59.2, 56.0, 55.4, 54.8, 47.9, 44.6, 37.5,
36.4, 32.1, 30.7, 29.5, 26.9, 26.5, 23.3, 22.4, 20.8, 15.5, 11.1; MS
(ESI+) m/z 1246 [M + Na]+; MS (ESI-) m/z 1222 [M - H]+;
HRMS (C62H66O24N2Na) m/z calcd 1245.3903, found 1245.3923.
O-[[N-[2,3,4-Tri-(O-allyloxycarbonyl)allylester-â-D-glucopy-
ranosyl]carbamoyl-4-oxy]benzyloxycarbonyl]-2-aminoethanol (16).
To a solution of 12 (110 mg, 0.137 mmol) and N-methylethanol
(12.2 µL, 0.151 mmol, 1.1 equiv) in dichloromethane (7 mL) was
added DMAP (20 mg, 0.164 mmol, 1.2 equiv) at 0 °C. The mixture
was stirred for 15 min at 0 °C, then for 30 min at room temperature.
After evaporation, the product was purified over column (eluent:
CH2Cl2/acetone 9/1 then 85/15). Compound 16 (80 mg, 79%) was
O-[[N-[â-D-Glucopyranosyl]carbamoyl-4-oxy]benzyloxycar-
bonyl]-2-aminoethyloxycarbonylpaclitaxel (19). The protected
prodrug 18 (30 mg, 0.018 mmol) was dissolved in anhydrous THF
(2 mL), then a solution of Et3N (11 µL, 0.074 mmol, 4 equiv)/
HCCOH (2 µL, 0.055 mmol, 3 equiv) in THF (50 µL) was added
at 0 °C under argon. After the solution was stirred for 10 min under
a stream of argon, palladium(tetrakistriphenylphosphine) (4.2 mg,
0.0036 mmol, 0.2 equiv) was added, and stirring was pursued for
30 min at 0 °C, then for 2 h at room temperature. After evaporation
of the solvent, the product was purified over silica gel (eluent: CH3-
CN/H2O 95/5), and lyophilisation isolated prodrug 19 (20 mg, 81%)
isolated as an oil: Rf 0.3 (CH2Cl2/acetone 85/15); [R]20 -6.7 (c
D
1
1.0, CHCl3); H NMR (300 MHz, CDCl3) δ 7.67 (br s, 1H, NH),
7.25 (m, 4H), 5.93-5.80 (m, 5H), 5.35-5.18 (m, 11H), 5.02 (s,
2H), 4.64-4.51 (m, 8H), 4.36 (d, 1H, J ) 9.1 Hz), 3.74 (br s, 2H),
3.42 (br s, 2H), 2.96 (s, 3H), 2.49 (br s, 1H); 13C NMR (75 MHz,
CDCl3) δ 166.3, 157.5, 153.9, 153.8, 153.6, 150.5, 136.8, 132.0,
131.0, 130.9, 130.8, 128.9, 128.7, 119.4, 119.2, 119.0, 92.2, 75.2,
73.1, 72.4, 72.1, 69.2, 69.1, 66.9, 61.0, 60.6, 51.8, 50.9, 35.7, 35.3;
MS (MALDI-TOF) m/z 759 [M + Na]+ and 775 [M + K]+; HRMS
(FAB + MB + NaI) (C33H40N2NaO17) m/z calcd 759.2225, found
759.2212.
as a white solid: mp 204-206 °C; Rf 0.32 (CH3CN/H2O 9/1); [R]20
D
-38 (c 0.8, MeOH); 1H NMR (300 MHz, MeOD) δ 9.19 (t, 1H, J
) 10.0 Hz), 8.12 (d, 2H, J ) 7,2 Hz), 7.78-7.25 (m, 18H), 6.45
(s, 1H), 6.06 (t, 1H, J ) 9,1 Hz), 5.84 (d, 1H, J ) 4.0 Hz), 5.65
(d, 1H, J ) 6.9 Hz), 5.52 (m, 2H), 5.03 (d, 1H, J ) 8.3 Hz), 4.94
(s, 2H), 4.31 (m, 3H), 4.18 (s, 2H), 3.83 (d, 2H, J ) 6.8 Hz), 3.73-
3.45 (m, 5H), 2.89 (s, 3H), 2.45 (m, 1H), 2.40 (s, 3H), 2.17 (2 s,
4H), 1.94 (m, 5H), 1.65 (s, 3H), 1.13 (s, 6H); 13C NMR (75 MHz,
CDCl3) δ 203.7, 170.5, 170.2, 167.6, 158.2, 157.9, 155.8, 154.0,
O-[[N-[2,3,4-Tri-(O-allyloxycarbonyl)allylester-â-D-glucopy-
ranosyl]carbamoyl-4-oxy]benzyloxycarbonyl]-2-aminoethanol-
carbonyl-4-nitrophenol (17). To compound 16 (70 mg, 0.095
J. Org. Chem, Vol. 71, No. 26, 2006 9635

El Alaoui et al.
142.2, 139.7, 138.1, 135.4, 134.9, 134.6, 133.8, 133.1, 133.0, 132.9,
132.8, 131.4, 131.2, 130.1, 129.9, 129.7, 129.5, 129.3, 129.1, 129.0,
128.9, 128.7. 128.6, 128.3, 128.2, 128.1, 128.0, 127.9, 119.9, 119.5,
96.4, 85.9, 82.3, 79.0, 78.6, 78.5, 77.9, 77.8, 77.7, 77.4, 76.8, 76.2,
73.8, 76.2, 73.8, 73.3, 73.2, 72.3, 68.9, 68.2, 67.5, 59.2, 55.2, 50.1,
49.9, 45.1, 37.1, 35.9, 26.5, 25.0, 22.8, 21.9, 20.4, 14.5, 11.1; MS
(MALDI-TOF) m/z 1346 [M + Na]+ and 1362 [M + K]+; HRMS
(C66H73O26N3Na) m/z calcd 1346.4380, found 1346.4325.
Acknowledgment. We express our thanks to Ms. Sylvie
Thirot for HPLC measurements.
Supporting Information Available: General experimental
information and 1H and 13C NMR spectra for the new compounds.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO0612675
9636 J. Org. Chem., Vol. 71, No. 26, 2006