Novel carboranyl C-glycosides for the treatment of cancer by boron neutron capture therapy

Article abstract of DOI:10.1002/chem.200390148

The synthesis of the novel unprotected carboranyl C-glycosides 2 and 20-24 starting from ethynyl C-glycosides 1, 5-8, 10, and 13 is described. The new compounds are highly water-soluble and display only a very low cytotoxicity, which makes them promising

Full text of DOI:10.1002/chem.200390148

FULL PAPER
Novel Carboranyl C-Glycosides for the Treatment of Cancer by Boron
Neutron Capture Therapy
Lutz F. Tietze,*[a] UlrichGriesbach, [a] Ingrid Schuberth,[a] UlrichBothe, [a] Alberto Marra,[b]
and Alessandro Dondoni*[b]
Abstract: The synthesis of the novel unprotected carboranyl C-glycosides 2 and 20
Keywords: alkynes
¥
antitumor
24 starting from ethynyl C-glycosides 1, 5 8, 10, and 13 is described. The new
compounds are highly water-soluble and display only a very low cytotoxicity, which
makes them promising candidates for use in boron neutron capture therapy for the
treatment of cancer.
agents ¥ boron neutron capture ther-
apy ¥ carboranes ¥ drug research ¥
C-glycosides
OH
HO
HO
Introduction
OH
OH
O
HO
HO
O
HO
O
B10H10
OH
OH
O
O
OH
HO
O
Boron neutron capture therapy
(BNCT) is a binary system used
for the treatment of cancer, which
involves administration of a bor-
on compound and subsequent
irradiation with slow neutrons. It
relies on the specific ability of the
O
HO
H
HO
O
4
B10H10
HO
3
= BH
= C
=
B10H10
isotope 10B to react with thermic neutrons to give an a particle
and a Li3‡ ion in a nuclear reaction. If boron is present in a
uptake into tumor cells due to their enhanced hydrophilicities.
They may therefore be used for a selective delivery into
malignant cells by employing glycohydrolases connected to
monoclonal antibodies that bind to tumor-associated antigens.
These glycohydrolases can transform the bisglycosides into
lipophilic compounds.[4]
A possible disadvantage of O-glycosylated carboranes
might be the enzymatic cleavage of such compounds by
glycohydrolases. This problem would not arise with C-
glycosylated carboranes, although, to date, there has been
only one example of a carborane unit connected to the
anomeric carbon atom of a tetrahydropyran ring with the
anomeric carbon atom still bearing a hydroxy group, as
reported by Dahlhoff et al.[5] Such C-linked compounds were
obtained as anomeric mixtures by the addition of monolithio
meta-carborane to trimethylsilyl-protected d-glucono-1,5-lac-
tone or analogous 1,4-lactones.
Herein, we describe the stereoselective synthesis of novel
C-glycosylated carboranes for use in BNCT by reaction of
decaborane(14) with alkynyl C-glycosides, and their biolog-
ical evaluation. We expected the biological and chemical
properties of this new class of configurationally stable
carboranyl C-glycosides to be as good as those of their O-
glycosidic analogues. As already mentioned, the novel C-
glycosides should not be affected by the action of any
glycohydrolase.
7
tumor cell, irradiation with a beam of slow neutrons will cause
destruction of the malign tissue.[1] However, there are several
problems associated with this approach, such as the need to
introduce high levels of boron into the cancer cells. The stable
ortho-carboranes[2] are therefore used as the boron source,
which allow the transport of ten boron atoms per molecule
into the cancer cells. However, the poor solubility in water
and distinct cytotoxicity of most of these compounds has
limited their use in BNCT. In view of their excellent water
solubilities, negligible toxicities, and high rates of uptake into
cancer cells, we have focused our interest on carboranyl O-
glycosides such as maltoside 3 for use in BNCT.[3] Mixed
carboranediyl O-bisglycosides such as 4 show almost no
[a] Prof. Dr. L. F. Tietze, Dr. U. Griesbach, Dr. I. Schuberth, Dr. U. Bothe
Institut f¸r Organische Chemie, Georg-August-
Universit‰t Gˆttingen, Tammannstrasse 2,
37077 Gˆttingen (Germany)
Fax : (‡49)551-399476
E-mail: ltietze@gwdg.de
[b] Prof. Dr. A. Dondoni, Prof. Dr. A. Marra
¡
Universita di Ferrara, Dipartimento di Chimica, Laboratorio di
Chimica Organica, Via L. Borsari 46,
44100 Ferrara (Italy)
Fax : (‡39)0532-291167
E-mail: adn@dns.unife.it
1296
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Chem. Eur. J. 2003, 9, No. 6

1296 1302
1 to the gluconolactone 9 and deoxygenation with Et3SiH/
BF3 ¥ Et2O (Scheme 1). The b-linkage at the anomeric centers
of the two glycoside residues was again confirmed by the
vicinal coupling constant of the anomeric proton (9.2 Hz).
Results and Discussion
The carboranyl-C-glycosides 2, 20 24 were synthesized by a
well-established procedure involving addition of the B10H12 ¥
2CH CN complex to the triple bond of the perbenzylated
3
ethynyl C-glycosides 1, 5 8, 10, and 13, followed by hydro-
genolytic cleavage of the benzyl protecting groups.
OBn
O
OBn
O
BnO
O
BnO
BnO
OBn
OBn
a, b
BnO
BnO
BnO
10
1
+
BnO
52%
BnO
O
Synthesis of C-glycosyl acetylenes: The known perbenzylated
ethynyl b-C-glycoside 1 was readily prepared[6, 7] by a se-
quence of addition of cerium TMS-acetylide to the corre-
sponding gluconolactone, deoxygenation with triethylsilane
9
Scheme 1. Synthesis of 10. a) BuLi, THF, À708C, 1.5 h; b) Et3SiH, BF3 ¥
Et2O, CH 3CN/CH2Cl2, À108C , 1 h.
The synthesis of the ethynyl C-gentiobioside 13 was more
laborious because it involved the stereoselective formation of
two C-glycosidic bonds, one in the assembly of the two sugar
residues, and the other in installing the ethynyl group into the
resulting C-disaccharide. The methyl O-glycoside 11
(Scheme 2) had already been prepared in one of our
OBn
O
OBn
O
OBn
O
BnO
BnO
BnO
BnO
BnO
BnO
BnO
BnO
AcHN
1
5
6
BnO
BnO
OBn
O
OBn
CH3
O
BnO
BnO
OBn
O
OBn
O
BnO
BnO
BnO
BnO
N3
BnO
a, b
BnO
BnO
82%
O
O
BnO
BnO
7
8
BnO
BnO
BnO
BnO
O
OCH3
11
12
and boron trifluoride etherate (Et3SiH/BF3 ¥ Et2O), and cleav-
age of the TMS group with sodium hydroxide.[6, 7] The a-
linked derivatives 5 7 were also obtained as described
previously,[7] by C-glycosidation (ethynylation) of the corre-
sponding sugar acetates using tributylstannyl(trimethylsilyl)-
OBn
O
BnO
BnO
c, d, e
63%
BnO
O
BnO
BnO
ꢀ
ethyne (nBu3SnC CSiMe3) in the presence of trimethylsilyl
BnO
13
triflate (TMSOTf), followed by desilylation. The 1-propynyl
C-glucoside 8 was synthesized in high yield (90%) in one step
by methylation of the lithio derivative of 1 using methyl
triflate as the alkylating agent.[8] The stereointegrity of the b-
linkage at the pseudoanomeric center of 8, as in the precursor
Scheme 2. Synthesis of 13. a) AcOH, H2SO4, 1008C, 75 min; PCC,
CH2Cl2, RT, 1 h; c) TMS-ethyne, BuLi, CeCl3, THF, À788C, 2 h; d) Et3-
SiH, BF3 ¥ Et2O, CH 3CN/CH2Cl2, À108C, 1 h; e) aq. NaOH, CH3OH/THF,
RT, 1 h.
1
C-glycoside 1, was confirmed by H NMR spectroscopy; the
laboratories by Wittig coupling of a sugar aldehyde and a
sugar phosphorane.[9] Acid-catalyzed hydrolysis of the anome-
ric methoxy group in 11, followed by oxidation of the
corresponding hemiacetal with pyridinium chlorochromate
(PCC) afforded the C-gentiobionolactone 12 in very good
overall yield (82%). The ethynyl group was introduced by
following the same reaction sequence as employed for the
ethynylation of monosaccharides, that is addition of cerium
TMS-acetylide, deoxygenation with Et3SiH/BF3 ¥ Et2O, and
desilylation with NaOH. Compound 13 was obtained in 63%
overall yield according to this three-step reaction sequence.
The b-linkage at the anomeric center of 13 was confirmed by
the vicinal coupling constant of J ˆ 9.7 Hz for the signal at d ˆ
3.96 ppm attributable to the pseudoanomeric proton (3-H).
signal of the pseudoanomeric proton (4-H), observed at d ˆ
4.06 ppm, shows a coupling constant of J4,5 ˆ 9.5 Hz, which is
typical for a trans-diaxial arrangement. The bisglycosylated
ethyne 10 was also prepared in good yield (52%) in a
straightforward manner by addition of the lithio derivative of
Abstract in German: Die Synthese der neuartigen ungesch¸tz-
ten Carboranyl-C-Glycoside 2 und 20 24 ausgehend von
Ethinyl-C-Glycosiden wie 1, 5 8, 10 und 13 wird beschrieben.
Die neuen Verbindungen sind wasserlˆslich und zeigen eine
nur sehr geringe Cytotoxizit‰t, was sie zu vielversprechenden
Kandidaten f¸r den Einsatz in der Bor-Neutroneneinfang-
Tumortherapie macht.
Abstract in Italian: Viene descritta la sintesi di una nuova serie
di carboranil C-glicosidi deprotetti 2 e 20 24 a partire dagli
etinil C-glicosidi 1, 5 8, 10 e 13. I nuovi composti oltre ad
Synthesis of carboranyl C-glycosides: To prepare the carbor-
anyl C-glycosides, decaborane(14) (B10H14) was heated in
acetonitrile under reflux for 1 h to give the B10H12 ¥ 2C HCN
3
¡
essere molto solubili in acqua mostrano una bassa citossicita
adduct,[10] which was then treated with the ethynyl C-glyco-
sides 1, 5 8, 10, and 13 in toluene to give the benzyl-protected
carboranyl C-glycosides 14 19 in moderate to excellent
cosÏ che si presentano come promettenti candidati nella terapia
del cancro basata sulla cattura di neutroni da parte del boro.
Chem. Eur. J. 2003, 9, No. 6
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L. Tietze, A. Dondoni et al.
FULL PAPER
yields depending on the substituents in the vicinity of the
triple bond. Thus, starting from the b-ethynyl C-glucoside 1,
the yield of the corresponding carborane 14 was 92%
(Scheme 3), whereas the C2-symmetric carborane 19 was
MeOH. Therefore, the crude products obtained by removal of
the catalyst and evaporation of the solvents were merely
washed with Et2O to give satisfactory purities.
Structure determination of the carboranyl C-glycosides: The
structures of the new compounds were determined by means
OR
O
OBn
O
1
of H and 13CNMR spectroscopy (1D and 2D experiments)
a
RO
RO
BnO
BnO
O
and mass spectrometry. As is typical for carboranes, a broad
signal due to the ten protons attached to boron atoms is seen
at d ˆ 0.5 4.0 ppm in the 1H NMR spectra. Furthermore, the
IR spectra of the novel carboranes feature the typical strong
B10H10
OR
OBn
1
14, R = Bn
2, R = H
b
B
H stretching signal at approximately 2590 cmÀ1. The
Scheme 3. Synthesis of 2. a) B10H14, C HCN, reflux 30 60 min; then 1 in
3
prepared boron compounds contain the natural isotopic
distribution of boron. In the mass spectra of the new
compounds, a broad assembly of peaks is therefore detected,
together with the peak of highest intensity, which correlates to
the most abundant 10B/11B ratio. As proven by NMR experi-
ments on the compounds obtained, upon addition of B10H14 to
the triple bond of the ethynyl C-glycosides and subsequent
deprotection, the configuration at the pseudoanomeric center
is not affected. The b-linkage at the anomeric centers of the
carboranyl C-glycosides 2, 14, 16, 18, 19, 21, 23, and 24 was
also confirmed by the large values (9.0 10.0 Hz) of the vicinal
coupling constant of the doublets attributable to the anomeric
protons, as is typical for a trans-diaxial arrangement. In
contrast, the a-linkage at the pseudoanomeric centers of
compounds 15, 17, 20, and 22 was indicated by the low J values
(1.0 2.0 Hz) observed for the signals of the anomeric protons
due to an equatorial axial arrangement. The C H of the
carborane moiety of C-glycosides with monosubstituted
carboranes gives rise to a characteristic broad singlet at
toluene, reflux, 16 18 h, 92%; b) Pd(OH)2/C, H2 (2 3 bar), MeOH/
EtOAc, RT, 5 8 h, 81%.
obtained in only 13% yield from ethynyl bisglucoside 10 due
to the steric demand of the two sugar moieties. Ethynyl C-
glycosides with terminal triple bonds such as 1, 5, 6, and 13
gave consistently higher yields (64 92%) as compared to the
acetylenes 8 and 10 with internal triple bonds (13 31%).
Astoundingly, in the case of the acetyl amide 6, protection of
the acidic amide NH, as reported in our previous work,[3e] was
not necessary and the corresponding carborane 17 was
obtained in 73% yield. In contrast, starting from azide 7, no
carborane was obtained, presumably due to the thermal
instability of the azido group (Table 1).
Debenzylation was carried out by hydrogenation under
elevated H2 pressure (2 3 bar) in the presence of Pearlman×s
catalyst[11] (Pd(OH)2 on activated charcoal). The deprotected
carboranyl C-glycosides 2, 20 24 were obtained in good
yields in every case (Table 1). The novel compounds 2, 20 24
could not be purified by column chromatography due to
partial degradation under the conditions employed. This
decomposition also occurred on standing for several days in
1
around d ˆ 4.0 in the H NMR spectra. In the case of the C2
symmetric bisglucosides 10, 19, and 24, with an internal triple
bond or carborane moiety, two equivalent carbons give rise to
just one signal in the 13CNMR spectra.
Table 1. Structures and yields of the carboranyl C-glycosides and -bisglycosides.
Reaction conditions for carborane formation and debenzylation were similar to
those given in Scheme 3.
In vitro cytotoxicity tests: The cytotoxicities of the novel
carboranyl C-glycosides 2 and 20 23 were determined using
the MTT test.[12] This test is based on the irreversible
reduction of the yellow tetrazolium salt 3-(4,5-dimethylthia-
zol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) into a dark
blue, water-insoluble but alcohol-soluble formazane deriva-
tive by mitochondrial dehydrogenases of viable cells. MTT is
taken up by viable cells and then reduced. The concentration
of the resulting blue formazane derivative is measured with a
photometer after cell lysis. The optical density of the blue
formazane derivative is proportional to the fraction of the
living, metabolically active cells.[12]
In vitro studies with the new compounds were carried out
on four different cell lines: on human bronchial carcinoma
cells of line A549,[13] on murine melanoma cells of line B-16,
on human pancreas carcinoma cells of line PancTu 1,[14] and on
colonrectal human adeno carcinoma cells of line LoVo.[15]
The results of these in vitro studies are presented in Table 2
and Figure 1. The b- and a-carboranyl C-glucosides 2 and 20,
with ED50 values in the range 227 482mm (ED50 ˆ drug
concentration required for 50% effect on target cells), show
only a low cytotoxicity. The ED50 values for the methylcar-
borane 21 and acetamide 22 are slightly lower, falling in the
Starting Structures of the
carboranes obtained
Yield [%] after
carborane formation hydrogenation
Yield [%] after
(R ˆ Bn)
15, 68
(R ˆ H)
20, 82
5
8
16, 31
17, 73
21, 61
22, 75
7
6
decomp
13
10
18, 64
19, 13
23, 69
24, quant.
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Carboranyl C-Glycosides
1296 1302
Table 2. Cytotoxicities of carboranyl C-glycosides 2 and 20 23 as well as hydroxymethylcarborane 25.
Experimental Section
R1
R2
R3
ED50 Values [mm]
B-16 PancTu 1
Synthesis of the C-glycosides: general:
All moisture-sensitive reactions were
performed under a nitrogen or argon
atmosphere using oven-dried glass-
ware. Anhydrous solvents were dried
over standard drying agents[17] and
were freshly distilled prior to use.
Commercially available powdered
4 ä molecular sieves (average particle
size 5 mm) was used without further
activation. Reactions were monitored
A549
379
Lovo
410
2
20
b-carboranyl
a-carboranyl
b-carboranylmethyl
a-carboranyl
b-carboranyl
OH
OH
OH
NHAc
OH
OH
OH
OH
OH
X[a]
472 355
[b]
482
178
291
–
203
236
198
227
199
222
21
22
> 124
> 1100
278
> 1100
23
25[16]
> 1100
78
> 1100
[b]
[b]
[b]
[a] X ˆ methylene-b-d-C-glucosyl. [b] Not determined.
by TLCon silica gel 60F
with de-
254
tection using sulfuric acid alone or in
conjunction with vanillin. Flash col-
umn chromatography[18] was per-
formed on silica gel 60 (230
400 mesh). The sugar lactone 9[19] was
prepared by oxidation of the corre-
sponding hemiacetal with pyridinium
chlorochromate.[20]
Melting points were determined with a
capillary apparatus and are uncorrect-
ed. Optical rotations were measured at
20 Æ 28Cin the stated solvent; [ a]D20
values are given in 10À1 degcm2 gÀ1. IR
spectra were recorded on a Bruker
Vector 22 spectrometer. 1H and
13CNMR spectra were recorded on
Varian XL-200, Unity 300, Inova 500,
Unity
Inova 600,
and
Bruker
AMX300 spectrometers, at room tem-
perature unless otherwise specified;
chemical shifts are quoted in ppm (d)
from SiMe4 (TMS) as an internal
standard; assignments were aided by
homo- and heteronuclear two-dimen-
sional experiments. Signals marked
with an asterisk (*) could not be
assigned with certainty. In the
1H NMR data listed below, the n and
m values quoted for geminal or vicinal
proton-proton coupling constants Jn,m
Figure 1. Inhibition of proliferation on different cell lines by the novel carboranyl C-glycosides 2 and 20 23.
denote the number of corresponding sugar protons, where applicable. Mass
spectra were measured on a Finnigan MAT 95 spectrometer. MALDI-TOF
mass spectra were acquired using a-cyano-4-hydroxycinnamic acid as the
matrix. Elemental analysis was carried out in the analytical laboratories of
the universities of Gˆttingen and Ferrara.
range >124 293mm. With ED50 values greater than 1.1mm
with all four cell lines, carboranyl C-gentiobiose 23 displays
the lowest cytotoxicity among the carboranes investigated. In
comparison, hydroxymethylcarboranes such as 25, which we
have investigated in our previous work,[3] have a significantly
higher toxicity. For example, an ED50 value of 78mm was
measured in the case of 25[3c, 16] (Table 2, Figure 1).
4,8-Anhydro-5,6,7,9-tetra-O-benzyl-1,2,3-trideoxy-d-glycero-l-manno-
non-2-ynitol (8): A stirred solution of 1 (549 mg, 1.00 mmol) in anhydrous
THF (10 mL) was cooled to À508C, whereupon butyllithium (1.25 mL,
2.00 mmol, 1.6m solution in hexane) was added dropwise. Stirring was
continued at À508Cfor 10 min, and then methyl trifluoromethanesulfo-
nate (340 mL, 3.00 mmol) was added. After an additional 30 min at À508C,
the reaction mixture was diluted with 1m phosphate buffer at pH 7 (20 mL),
allowed to warm to room temperature, and extracted with Et2O (2 Â
100 mL). The combined organic phases were dried (Na2SO4) and concen-
trated. The residue was chromatographed on a column of silica gel eluting
R3
O
HO
O
HO
HO
B10H10
R1
R2
25
with cyclohexane/EtOAc (9:1) to give 8 (506 mg, 90%) as a syrup. [a]D20
ˆ
In conclusion, we have prepared several novel C-glycosidic
carboranes by way of a short and convenient synthesis from
the corresponding alkynes. As shown by an MTT cytotoxicity
assay, this new class of compounds displays lower cytotox-
icities and an increased water solubility compared to simple
carborane derivatives such as hydroxymethylcarborane 25.
The biological properties of the carboranyl C-glycosides make
them promising candidates for use in boron neutron capture
therapy for the treatment of cancer.
1
‡1.58 (c ˆ 1.2, CHCl3); H NMR (300 MHz, C6D6): d ˆ 1.42 (d, 3H; 1-H),
3.24 (ddd, 1H; 8-H), 3.64 (dd, J8,9b ˆ 2.0 Hz, 1H; 9b-H), 3.66 (dd, J5,6
ˆ
9.0 Hz, 1H; 5-H), 3.68 (dd, J8,9a ˆ 3.5, J9a,9b ˆ 10.8 Hz, 1H; 9a-H), 3.78 (dd,
J7,8 ˆ 9.7, J6,7 ˆ 8.9 Hz, 1H; 7-H), 4.06 (dq, J4,5 ˆ 9.5, J1,4 ˆ 2.0 Hz, 1H; 4-H),
4.34 and 4.47 (2d, J ˆ 12.0 Hz, 2H; PhCH2), 4.60 and 4.86 (2d, J ˆ 11.1 Hz,
2H; PhCH2), 4.80 and 4.91 (2d, J ˆ 11.5 Hz, 2H; PhCH2), 4.82 and 5.05 (2d,
J ˆ 11.0 Hz, 2H; PhCH2), 7.02 7.40 ppm (m, 20H; 4 Ph); 13CNMR
(75 MHz, C6D6): d ˆ 3.2 (C-1), 69.4 (C-9), 70.7 (C-4), 73.6, 74.9, 75.3, and
75.5 (4 PhCH2), 78.2 (C-7), 79.4 (C-8), 77.8 and 82.0 (C-2, C-3), 83.2 (C-5),
86.4 (C-6), 127.6 128.4, 138.9, 139.2, 139.3, and 139.5 ppm (Ph); elemental
Chem. Eur. J. 2003, 9, No. 6
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1299

L. Tietze, A. Dondoni et al.
FULL PAPER
analysis (%) calcd for C37H38O5 (562.7): C76.98, H 6.81; found: C77.20, H
6.71.
cooled to À788C, and then butyllithium (0.55 mL, 0.88 mmol, 1.6m solution
in hexane) was slowly added. The resulting solution was stirred at À788C
for 45 min, and then transferred via a cannula into the stirred suspension of
CeCl3 in THF, prepared immediately prior to use as described above. The
yellow mixture obtained was stirred at À788Cfor 30 min, and then a
solution of lactone 12 (336 mg, 0.35 mmol) in anhydrous THF (2.5 mL) was
added dropwise. The mixture was stirred at À788Cfor an additional 2 h,
then diluted with 0.1m HCl (4 mL), allowed to warm to room temperature,
and extracted with Et2O (3 Â 50 mL). The combined organic layers were
dried (Na2SO4) and concentrated to give the disaccharidic hemiacetal as an
approximately 1:1 mixture of anomers. A stirred mixture of the hemiacetal,
activated 4 ä powdered molecular sieves (0.35 g), and triethylsilane
(232 mL, 1.45 mmol) in anhydrous CH3CN (6 mL) and CH2Cl2 (2 mL)
was cooled to À108C, and then freshly distilled BF3 ¥ Et2O (174 mL,
1.37 mmol) was added dropwise. Stirring was continued at À108Cfor a
further 1 h, and then the mixture was diluted with Et3N (0.6 mL) and
CH2Cl2 (50 mL), filtered through a pad of Celite, and concentrated. A
solution of the residue in CH2Cl2 (100 mL) was washed with H2O, dried
(Na2SO4), and concentrated. A solution of the crude silylated C-disacchar-
ide in CH3OH/THF (1:1; 12 mL) was treated with 1m NaOH (0.7 mL) for
1 h at room temperature, then neutralized with 1m HCl, and concentrated
to remove the organic solvents. The residue was diluted with CH2Cl2
(100 mL), and this solution was washed with H2O, dried (Na2SO4), and
concentrated. The residue was chromatographed on a column of silica gel
eluting with CH2Cl2/Et2O (40:1 ! 30:1) to afford 13 (213 mg, 63%) as a
white solid; m.p. 178 1808C(EtOAc/cyclohexane); [ a]2D0 ˆ ‡7.48 (c ˆ 1.0,
CHCl3); selected 1H NMR data (300 MHz, C6D6): d ˆ 1.99 (d, 1H; 1-H),
1.63 1.69 and 2.25 2.29 (2m, 4H; 2 8-H, 2 9-H), 3.18 3.29 (m, 4H), 3.34
3.40 (m, 1H), 3.45 3.51 (m, 3H), 3.66 3.72 (m, 3H), 3.76 (dd, J4,5 ˆ 8.8,
J5,6 ˆ 9.7 Hz, 1H; 5-H), 3.96 ppm (dd, 1H, J1,3 ˆ 2.2, J3,4 ˆ 9.7 Hz; 3-H);
elemental analysis (%) calcd for C64H66O9 (979.2): C78.50, H 6.79; found:
C78.72, H 6.61.
1,2-Bis(2',3',4',6'-tetra-O-benzyl-b-d-glucopyranosyl)ethyne (10): A stirred
solution of 1 (200 mg, 0.36 mmol) in anhydrous THF (3.6 mL) was cooled
to À708C, whereupon butyllithium (0.25 mL, 0.40 mmol, 1.6m solution in
hexane) was added dropwise. Stirring was continued at À708Cfor 15 min,
and then a solution of lactone 9 (194 mg, 0.36 mmol) in anhydrous THF
(3.6 mL) was added. After a further 1.5 h at À708C, the reaction mixture
was diluted with 1m phosphate buffer at pH 7 (20 mL), allowed to warm to
room temperature, and extracted with CH2Cl2 (2 Â 100 mL). The combined
organic layers were dried (Na2SO4) and concentrated to afford the
hemiacetal as a mixture of anomers. A stirred mixture of the crude
hemiacetal, activated 4 ä powdered molecular sieves (0.36 g), and
triethylsilane (240 mL, 1.49 mmol) in anhydrous CH3CN (6.5 mL) and
CH2Cl2 (2.5 mL) was cooled to À108C, and then freshly distilled BF3 ¥ Et2O
(180 mL, 1.40 mmol) was added dropwise. Stirring was continued at À108C
for 1 h, and then the mixture was diluted with Et3N (0.6 mL) and CH2Cl2
(50 mL), filtered through a pad of Celite, and concentrated. The residue
was chromatographed on a column of silica gel eluting with cyclohexane/
EtOAc (12:1 ! 5:1) to give 10 (200 mg, 52%) as a white solid; m.p. 89
908C(cyclohexane/pentane); [ a]2D0 ˆ À20.58 (c ˆ 1.3, CHCl3); 1H NMR
(300 MHz, C6D6): d ˆ 3.21 (ddd, 2H; 2 5'-H), 3.50 (dd, 2H; 2 3'-H), 3.60
(dd, J5',6'b ˆ 1.8 Hz, 2H; 2 6'b-H), 3.65 (dd, J6'a,6'b ˆ 11.2, J5',6'a ˆ 3.6 Hz, 2H; 2
6'a-H), 3.68 (dd, J2',3' ˆ 9.1 Hz, 2H; 2 2'-H), 3.74 (dd, J4',5' ˆ 9.8, J3',4' ˆ 8.7 Hz,
2H; 2 4'-H), 4.08 (d, J1',2' ˆ 9.2 Hz, 2H; 2 1'-H), 4.30 and 4.42 (2d, J ˆ
12.1 Hz, 4H; 2 PhCH2), 4.56 and 4.82 (2d, J ˆ 11.4 Hz, 4H; 2 PhCH2), 4.78
and 4.90 (2d, J ˆ 11.5 Hz, 4H; 2 PhCH2), 4.84 and 5.19 (2d, J ˆ 11.0 Hz,
4H; 2 PhCH2), 7.03 7.32 and 7.47 7.53 ppm (2m, 40H; 8 Ph); 13CNMR
(75 MHz, C6D6): d ˆ 69.3 (2 C-6'), 70.4 (2 C-1'), 74.9, 75.4, and 77.9 (8
PhCH2), 79.6 (2 C-5'), 82.5 (2 C-2'), 84.0 (C-1, C-2), 86.3 (2 C-3'), 127.7
128.7, 138.8, 138.9, 139.2, and 139.5 ppm (Ph); MS (MALDI-TOF): m/z:
1095.6 [M‡H‡Na], 1111.8 [M‡H‡K]; elemental analysis (%) calcd for
C70H70O10 (1071.3): C76.48, H 6.59; found: C76.31, H 6.74.
Synthesis of the perbenzylated carboranyl C-glycosides: general proce-
dure: Decaborane(14) (B10H14, 1.3 1.4 equivalents with respect to the
alkyne as the starting material) was heated in refluxing CH3CN (2 mL per
mmol of the alkyne) for 30 min, in the course of which the solution turned
8,12-Anhydro-2,3,4,9,10,11,13-hepta-O-benzyl-6,7-dideoxy-d-glycero-d-
gulo-d-gluco-tridecopyranolactone (12): A stirred solution of 11 (450 mg,
0.46 mmol) in acetic acid (18 mL) was heated to 1008C, and then 1m
aqueous H2SO4 (1.8 mL) was added dropwise. The solution was stirred at
1008Cfor a further 75 min, and then cooled to room temperature, diluted
with CH2Cl2 (100 mL), and washed with saturated aqueous Na2CO3
solution (5 Â 20 mL). The organic phase was dried (Na2SO4) and concen-
trated. The residue was chromatographed on a column of silica gel eluting
with cyclohexane/EtOAc (8:1 ! 4:1) to give the disaccharidic hemiacetal
as an approximately 1:1 mixture of anomers (370 mg). A mixture of this
product, activated 4 ä powdered molecular sieves (0.38 g), and anhydrous
CH2Cl2 (3.8 mL) was stirred at room temperature for 15 min, and then
pyridinium chlorochromate (410 mg, 1.90 mmol) was added in one portion.
The mixture was vigorously stirred at room temperature for 60 min until
the starting material had been consumed (TLCanalysis), and then diluted
with cyclohexane (3.8 mL) and Et2O (7.6 mL) to precipitate the chromium
salts. Stirring was continued for a further 10 min, and then the brown
suspension was filtered through a pad of silica gel (5 Â 4 cm). Further
elution with Et2O/cyclohexane (2:1; ca. 100 mL) gave 12 as a white solid
(363 mg, 82%); m.p. 117 1198C(cyclohexane); [ a]2D0 ˆ ‡36.38 (c ˆ 0.9,
CHCl3); 1H NMR (300 MHz, C6D6): d ˆ 1.52 1.62 (m, 1H; 7b-H), 1.65
1.75 (m, 1H; 6b-H), 2.12 2.23 (m, 2H; 6a-H, 7a-H), 3.20 3.27 (m, 2H),
3.38 (dd, J4,5 ˆ 8.4 Hz, 1H; 4-H), 3.34 3.40 (m, 1H), 3.65 3.79 (m, 4H),
3.83 (dd, J3,4 ˆ 5.3 Hz, 1H; 3-H), 4.10 (d, J2,3 ˆ 5.4 Hz, 1H; 2-H), 4.38 and
4.46 (2d, J ˆ 12.1 Hz, 2H; PhCH2), 4.39 4.45 (m, 1H; 5-H), 4.28 and 4.47
(2d, J ˆ 11.5 Hz, 2H; PhCH2), 4.32 and 4.51 (2d, J ˆ 11.5 Hz, 2H; PhCH2),
4.50 and 4.84 (2d, J ˆ 11.3 Hz, 2H; PhCH2), 4.54 and 4.93 (2d, J ˆ 11.8 Hz,
2H; PhCH2), 4.65 and 4.90 (2d, J ˆ 11.4 Hz, 2H; PhCH2), 4.90 (s, 2H;
PhCH2), 7.02 7.36 ppm (m, 35H; 7 Ph); elemental analysis (%) calcd for
C62H64O10 (969.2): C76.84, H 6.66; found: C76.60, H 6.92.
yellow, indicating the formation of the adduct B10H12 ¥ 2C HCN. A solution
3
of the alkyne in toluene (2 mL per mmol) was then added and heating was
continued for 16 18 h. For work-up, MeOH (1 mL) was added, the
mixture was heated to reflux for 30 min, cooled to room temperature, and
concentrated in vacuo. Baseline impurities were removed by filtration
through a short plug of silica with EtOAc as eluent. The pure products were
obtained by column chromatography using n-pentane/EtOAc (15:1) as the
eluent.
(2R,3R,4R,5S,6S)-3,4,5-Tris(benzyloxy)-2-benzyloxymethyl-6-(1C,2C-
dicarba-closo-dodecaboran(12)ylethyl)tetrahydropyran (14): 92% from 1,
colorless solid; Rf (n-pentane/EtOAc, 15:1) ˆ 0.52; [a]2D0 ˆ ‡32.08 (c ˆ 0.2,
CHCl3); IR (KBr): nÄ ˆ 2866, 2584 (B H), 1362, 1098 cmÀ1; UV (C HCN);
3
lmax (lge) ˆ 205.0 (4.462), 257.5 nm (2.930); 1H NMR (300 MHz, CDCl3):
d ˆ 1.00 3.20 (brs, 10H; BH), 3.42 (ddd, J ˆ 9.3, 3.7, 3.2 Hz, 1H; 2-H), 3.54
(dd, J ˆ 9.2, 8.0 Hz, 1H; 4-H), 3.59 3.69 (m, 3H; 5-H, CH2OBn), 3.72 (dd,
J ˆ 9.3, 8.0 Hz, 1H; 3-H), 3.79 (d, J ˆ 9.4 Hz, 1H; 6-H), 4.09 (brs, 1H;
carborane-CH), 4.52 (s, 2H; PhCH2OCH2), 4.62 and 4.76 (2d, J ˆ 10.8 Hz,
2H; PhCH2), 4.72 and 5.02 (2d, J ˆ 11.0 Hz, 2H; PhCH2), 4.77 and 4.98 (2d,
J ˆ 11.4 Hz, 2H; PhCH2), 7.16 7.39 ppm (m, 20H; 4 Ph); 13CNMR
(50 MHz, CDCl3): d ˆ 59.42 (carborane-CH), 68.14 (CH2OBn), 73.09
(PhCH2OCH2), 73.61 (PhCH2), 74.76 (carborane-C-1'), 74.94 (PhCH2),
75.26 (PhCH2), 77.64 (C-5), 77.88 (C-6), 79.01 (C-2), 79.97 (C-4), 87.31 (C-
3), 127.3 128.5, 137.4, 137.6, 137.8, 137.9 (Ph); MS (DCI): m/z (%): 685
‡
(100) [M‡NH4] ; elemental analysis (%) calcd for C36H46B10O5 (666.9): C
64.84, H 6.95; found: C64.72, H 6.82.
(2R,3R,4R,5S,6R)-3,4,5-Tris(benzyloxy)-2-benzyloxymethyl-6-(1C,2C-
dicarba-closo-dodecaboran(12)yl-ethyl)tetrahydropyran (15): 68% from 5,
colorless oil; Rf (n-pentane/EtOAc, 15:1) ˆ 0.35; [a]2D0 ˆ ‡24.28 (c ˆ 0.6,
CHCl3); IR (film): nÄ ˆ 3031 (C H), 2865, 2582 (B H), 1497, 1454, 1362,
3,7:10,14-Dianhydro-4,5,6,11,12,13,15-hepta-O-benzyl-1,2,8,9-tetradeoxy-
d-erythro-l-talo-d-gulo-pentadec-1-ynitol (13): Commercially available
CeCl3 ¥ 7H2O (261 mg, 0.70 mmol) was heated in a reaction flask at
1208C/0.1 mbar for 1 h and at 1408C/0.1 mbar for 1 h, and then cooled to
08Cunder an argon atmosphere. It was taken up in anhydrous THF
(2.8 mL), the suspension was stirred at room temperature for 2 h, and then
cooled to À788C. Meanwhile, a stirred solution of commercially available
trimethylsilylacetylene (122 mL, 0.88 mmol) in anhydrous THF (1 mL) was
1095 cmÀ1; UV (C HCN): lmax (lge) ˆ 191.0 (5.124), 205.5 (4.477), 257.5 nm
3
1
(2.914); H NMR (300 MHz, CDCl3): d ˆ 1.00 3.20 (brs, 10H; BH), 3.58
(dd, J ˆ 10.6, 4.0 Hz, 1H; CHaHbOBn), 3.61 3.73 (m, 3H; 3-H, 5-H,
CHaHbOBn), 3.85 (dd, J ˆ 3.8, 2.7 Hz, 1H; 4-H), 4.08 4.17 (m, 2H;
carborane-CH, 2-H), 4.35 (d, J ˆ 1.8 Hz, 1H; 6-H), 4.36 and 4.54 (2d, J ˆ
10.8 Hz, 2H; PhCH2), 4.46 4.53 (m, 6H; 3 PhCH2), 7.19 7.41 ppm (m,
1300
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
0947-6539/03/0906-1300 $ 20.00+.50/0
Chem. Eur. J. 2003, 9, No. 6

Carboranyl C-Glycosides
1296 1302
20H; 4 Ph); 13C NMR (75 MHz, CDCl3): d ˆ 58.10 (carborane-CH), 68.50
(CH2OBn), 71.37 (C-6), 71.76, 72.05, 72.69, 73.16 (4 PhCH2), 74.45 (C-5*),
74.97 (carborane-C-1'), 75.28, 76.08, 76.31 (C-2, C-3, C-4*), 127.4 128.7,
136.6, 137.1, 137.8, 138.0 ppm (Ph); MS (DCI): m/z (%): 685 (100)
(lge) ˆ 191.5 (5.388), 257.0 nm (2.850); 1H NMR (300 MHz, CDCl3): d ˆ
1.00 3.20 (brs, 10H; BH), 3.48 3.67 (m, 10H; 2 CH2OBn, 2a-H, 2b-H,
3a-H, 3b-H, 4a-H, 4b-H, 5a-H, 5b-H), 4.14 (d, J ˆ 9.0 Hz, 2H; 6a-H, 6b-
H), 4.46 (d, J ˆ 12.2 Hz, 2H; PhCH), 4.53 (d, J ˆ 12.2 Hz, 2H; PhCH), 4.53
(d, J ˆ 11.2 Hz, 2H; PhCH), 4.60 (d, J ˆ 11.2 Hz, 2H; PhCH), 4.61 (d, J ˆ
10.9 Hz, 2H; PhCH), 4.69 (d, J ˆ 10.9 Hz, 2H; PhCH), 4.80 (d, J ˆ 11.2 Hz,
2H; PhCH), 4.90 (d, J ˆ 11.2 Hz, 2H; PhCH), 7.13 7.40 ppm (m, 40H; 8
‡
‡
[M‡NH4] , 594 (20) [M À Bn‡NH4] ; C36H46B10O5 (666.9).
(2R,3R,4R,5S,6S)-3,4,5-Tris(benzyloxy)-2-benzyloxymethyl-6-(1C,2C-
dicarba-closo-dodecaboran(12)ylpropyl)tetrahydropyran (16): 31% from
8, colorless solid; Rf (n-pentane/EtOAc, 12:1) ˆ 0.29; [a]2D0 ˆ ‡23.98 (c ˆ
0.6, CHCl3); IR (film): nÄ ˆ 3031, 2868, 2582 (B H), 1736, 1497, 1362,
Ph); 13CNMR (75 MHz, CDCl
3): d ˆ 69.01 (2 CH2OBn), 72.66 (2
PhCH2OCH2), 73.46 (2 PhCH2), 74.34 (2 PhCH2), 74.86 (2 PhCH2), 76.67
(C-5a, C-5b), 77.57 (C-6a, C-6b), 78.98 (C-2a, C-2b), 79.82 (C-4a, C-4b),
80.27 (2 carborane-C), 86.92 (C-3a, C-3b), 127.3 128.5, 137.7, 137.8, 137.9,
1097 cmÀ1; UV (C HCN): lmax (lge) ˆ 191.0 (4.958), 251.5 (2.768), 257.0 nm
3
1
(2.785); H NMR (500 MHz, CDCl3): d ˆ 1.00 3.20 (brs, 10H; BH), 1.96
‡
138.0 ppm (Ph); MS (ESI): m/z (%): 1212 (100) [M‡Na] ; C70H80B10O10
(s, 3H; CH3), 3.42 (ddd, J ˆ 9.3, 4.1, 3.1 Hz, 1H; 2-H), 3.65 3.71 (m, 5H;
CH2OBn, 3-H, 5*-H, 6-H), 3.72 (ddd, J ˆ 9.0, 5.8, 1.5 Hz, 1H; 4*-H), 4.46
and 4.57 (2d, J ˆ 12.2 Hz, 2H; PhCH2OCH2), 4.62 and 4.77 (2d, J ˆ
11.0 Hz, 2H; PhCH2), 4.74 and 5.01 (d, J ˆ 10.9 Hz, 1H; PhCH2), 4.76
and 4.98 (2d, J ˆ 11.0 Hz, 2H; PhCH2), 7.18 7.38 ppm (m, 20H; 4 Ph);
13CNMR (50 MHz, CDCl 3): d ˆ 23.27 (CH3), 68.63 (CH2OBn), 73.31
(PhCH2OCH2), 73.43, 74.73 (2 PhCH2), 74.79 and 78.15 (carborane-C),
75.05 (PhCH2), 76.86 (C-5), 77.54 (C-6), 79.26 (C-2), 79.62 (C-4), 87.37 (C-
3), 127.3 128.5, 137.6, 137.7, 137.9, 138.0 ppm (Ph); MS (DCI): m/z (%): 699
(1189.5).
Deprotection of the perbenzylated carboranyl C-glycosides: general
procedure: The benzylated sugar derivative was dissolved in EtOAc/
MeOH (1:5; 1 mL/25 mmol of the C-glycoside), Pd(OH)2/C(10%, 1 mg/
mmol of the C-glycoside) was added, and the resulting mixture shaken
under H2 atmosphere (up to 3 bar) in a Parr apparatus for 5 8 h. The
progress of the reaction was monitored by TLC. The catalyst was carefully
filtered off (danger of spontaneous combustion when dry!), the solvents
were removed, and the residue was washed with Et2O to obtain the
deprotected compound.
‡
(100) [M‡NH4] ; elemental analysis (%) calcd for C37H48B10O5 (680.9): C
65.27, H 7.11; found: C65.42, H 7.01.
(2R,3S,4R,5R,6R)-N-[4,5-Bis(benzyloxy)-6-benzyloxymethyl-2-(1C,2C-
dicarba-closo-dodecaboran(12)yl-ethyl)tetrahydropyran-3-yl]acetamide
(2R,3S,4R,5R,6S)-3,4,5-Tris(hydroxy)-2-hydroxymethyl-6-(1C,2C-dicar-
ba-closo-dodecaboran(12)ylethyl)tetrahydropyran (2): 81% from 14, col-
orless solid; Rf (EtOAc/MeOH, 4:1) ˆ 0.29; [a]2D0 ˆ ‡11.68 (c ˆ 0.5,
MeOH); IR (KBr): nÄ ˆ 3396 (O H), 2916 (C H), 2581 (B H), 1339,
(17): 73% from 6, colorless oil; Rf (toluene/acetone, 10:1) ˆ 0.37; [a]D20
ˆ
À19.08 (c ˆ 0.5, CHCl3); IR (film): nÄ ˆ 3424 (N H), 3032, 2920 (C H),
2579 (B H), 1660 (C O), 1454, 1030 cmÀ1; UV (C HCN): lmax (lge) ˆ
ˆ
1094 cmÀ1
;
UV (C HCN): lmax (lge) ˆ 275.0 nm (1.929); 1H NMR
3
3
192.5 nm (5.079), 251.5 (3.176), 257.0 (3.206); 1H NMR (300 MHz, CDCl3):
(300 MHz, CD3OD): d ˆ 1.00 3.00 (brs, 10H; BH), 3.16 (dd, J ˆ 9.2,
9.2 Hz, 1H; 5-H), 3.18 3.15 (m, 3H; 2-H, 3-H, 4-H), 3.57 (dd, J ˆ 12.4,
6.3 Hz, 1H; CHaHbOH), 3.71 (d, J ˆ 9.2 Hz, 1H; 6-H), 3.84 (dd, J ˆ 12.4,
2.0 Hz, 1H; CHaHbOH), 4.60 ppm (brs, 1H; carborane-CH); 13CNMR
(50 MHz, CD3OD): d ˆ 61.56 (carborane-CH), 62.72 (CH2OH), 70.83 (C-
5), 74.66 (C-3), 76.73 (carborane-C-1'), 79.39 (C-6), 82.02 (C-4), 82.44 ppm
(C-2); MS (ESIÀ): m/z (%): 612 (10) [2M À H]À, 305 (100) [M À H]À;
C8H22B10O5 (306.4).
d ˆ 1.00 3.20 (brs, 10H; BH), 1.83 (s, 3H; CH3 of NAc), 3.33 (brs, 1H;
5-H*), 3.49 (dd, J ˆ 10.4, 6.2 Hz, 1H; CHaHbOBn), 3.73 (brs, 1H; 4-H*),
3.83 (dd, J ˆ 10.4, 8.2 Hz, 1H; CHaHbOBn), 4.01 (brs, 1H; carborane-CH),
4.28 4.23 (m, 3H; 2-H, 3-H, PhCH), 4.39 4.53 (m, 5H; 6-H,
PhCH2OCH2, 2 PhCH), 4.64 (d, J ˆ 11.9 Hz, 1H; PhCH), 6.26 (d, J ˆ
10.1 Hz, 1H; NH), 7.14 7.40 ppm (m, 15H; 3 Ph); 13CNMR (75 MHz,
CDCl3): d ˆ 23.25 (CH3 of NAc), 46.82 (C-3), 58.16 (carborane-CH), 66.35
(CH2OBn), 67.67 (C-2), 71.69 (PhCH2), 72.42 (PhCH2), 72.64 (C-4*), 73.31
(PhCH2OCH2), 73.46 (carborane-C-1'), 73.92 (C-5*), 77.83 (C-6), 127.7
(2R,3S,4R,5R,6R)-3,4,5-Tris(hydroxy)-2-hydroxymethyl-6-(1C,2C-dicar-
ba-closo-dodecaboran(12)ylethyl)tetrahydropyran (20): 82% from 15,
colorless solid; Rf (EtOAc/MeOH, 4:1) ˆ 0.10; [a]2D0 ˆ ‡7.78 (c ˆ 0.1,
MeOH); IR (KBr): nÄ ˆ 3417 (O H), 2928 (C H), 2583 (B H), 2361,
ˆ
128.6, 136.7, 136.9, 137.8, 137.4 (Ph), 169.8 ppm (C O); MS (DCI): m/z (%):
‡
‡
‡
636 (100) [M‡NH4] , 619 (25) [M‡H] , 547 (25) [M À Bn‡NH4] , 529 (5)
‡
[M À Bn‡H] ; C31H43B10NO5 (617.8).
1384, 1038 cmÀ1; UV (C HCN): lmax (lge) ˆ 195.0 nm (3.267); 1H NMR
3
(2aS,3aS,4aR,5aR,6aR,2bS,3bS,4bR,5bR,6bR)-2a-(1C,2C-Dicarba-
closo-dodecaboran(12)yl-ethyl)-3a,4a,5a-tris(benzyloxy)-6a-{2-
(500 MHz, CD3OD): d ˆ 1.20 3.00 (brs, 10H; BH), 3.52 (mc, 1H; 3-H*),
3.63 (dd, J ˆ 12.0, 4.0 Hz, 1H; CHaHbOH), 3.69 (mc, 1H; 5-H), 3.85 (mc,
1H; 4-H*), 3.92 (dd, J ˆ 12.0, 8.3 Hz, 1H; CHaHbOH), 3.98 4.06 (m, 1H;
2-H), 4.34 (d, J ˆ 0.9 Hz, 1H; 6-H), 4.70 ppm (brs, 1H; carborane-CH);
13CNMR (50 MHz, CDCl 3): d ˆ 60.32 (carborane-CH), 60.64 (CH2OH),
69.54, 70.43, 71.17, 71.44 (C-3, C-4, C-5, C-6), 76.97 (carborane-C-1'),
82.63 ppm (C-2); MS (ESIÀ): m/z (%): 612 (10) [2M À H]À, 351 (100)
[M‡EtOH À H]À, 306 (80) [M À H]À; C8H22B10O5 (306.4).
[3b,4b,5b-tris(benzyloxy)-6b-benzyloxymethyl-tetrahydropyran-2b-yl]-
ethyl}tetrahydropyran (18): 64% from 13, colorless foam; Rf (n-pentane/
EtOAc, 5:1) ˆ 0.74; [a]2D0 ˆ ‡19.48 (c ˆ 0.5, CHCl3); IR (KBr): nÄ ˆ 3030
(C H), 2862, 2577 (B H), 1454, 1361, 1095 cm À1; UV (C HCN): lmax
3
(lge) ˆ 191.5 nm (5.331); 1H NMR (500 MHz, CDCl3): d ˆ 1.20 2.80 (brs,
10H; BH), 1.45 (mc, 2H; 2''-H2), 1.97 (dt, J ˆ 9.0, 2.3 Hz, 1H; 1''-Ha), 2.06
2.14 (m, 1H; 1''-Hb), 3.15 3.25 (m, 3H; 5a-H, 6a-H, 3b-H), 3.33 (td, J ˆ
9.0, 3.0 Hz, 1H; 2b-H), 3.39 (ddd, J ˆ 9.0, 4.4, 2.3 Hz, 1H; 6b-H), 3.49 (dd,
J ˆ 9.3, 8.4 Hz, 1H; 4a-H), 3.58 (dd, J ˆ 9.3, 9.3 Hz, 1H; 3a-H), 3.62 (dd,
J ˆ 8.8, 8.4 Hz, 1H; 4b-H), 3.64 (m, 1H; CHaHbOBn), 3.66 (dd, J ˆ 10.8,
2.3 Hz, 1H; CHaHbOBn), 3.67 (dd, J ˆ 9.0, 8.8 Hz, 1H; 5b-H), 3.75 (d, J ˆ
9.3 Hz, 1H; 2a-H), 4.09 (brs, 1H; carborane-CH), 4.48 and 4.54 (2d, J ˆ
12.2 Hz, 2H; PhCH2), 4.55 and 4.70 (2d, J ˆ 10.9 Hz, 2H; PhCH2), 4.59 and
4.74 (2d, J ˆ 10.9 Hz, 2H; PhCH2), 4.60 and 4.81 (2d, J ˆ 10.9 Hz, 2H;
PhCH2), 4.68 and 4.87 (2d, J ˆ 10.6 Hz, 2H; PhCH2), 4.90 4.93 (m, 3H;
PhCH2OCH2, PhCH), 5.01 (d, J ˆ 10.9 Hz, 1H; PhCH), 7.10 7.34 ppm (m,
35H; 7 Ph); 13C NMR (75 MHz, CDCl3): d ˆ 27.64, 28.10 (C-1'', C -2''), 59.20
(carborane-CH), 69.29 (CH2OBn), 73.41, 73.52, 75.02, 75.20, 75.49, 75.57,
76.88 (7 PhCH2), 77.29 (carborane-C-1'), 77.74, 78.64, 78.74, 79.49, 79.74,
80.26, 81.94, 82.20, 87.23, 87.27 (C-2a, C-2b, C-3a, C-3b, C-4a, C-4b, C-5a,
C-5b, C-6a, C-6b), 127.3 128.6, 137.5, 137.6, 137.8, 137.9, 138.0, 138.1,
(2R,3S,4R,5R,6S)-3,4,5-Tris(hydroxy)-2-hydroxymethyl-6-(1C,2C-dicar-
ba-closo-dodecaboran(12)ylpropyl)tetrahydropyran (21): 61% from 16,
colorless solid. Rf (EtOAc/MeOH, 4:1) ˆ 0.16; [a]2D0 ˆ ‡2.08 (c ˆ 0.3,
MeOH); IR (KBr): nÄ ˆ 3417 (O H), 2936 (C H), 2581 (B H), 1385,
1092 cmÀ1
;
1H NMR (300 MHz, CD3OD): d ˆ 1.20 3.00 (brs, 10H; BH),
2.05 (s, 3H; CH3), 3.17 3.15 (m, 4H; 2-H, 3-H, 4-H, 5-H), 3.59 (dd, J ˆ
12.0, 6.0 Hz, 1H; CHaHbOH), 3.65 (d, J ˆ 10.0 Hz, 1H; 6-H), 3.84 ppm (dd,
J ˆ 12.0, 2.0 Hz, 1H; CHaHbOH); 13CNMR (75 MHz, CD 3OD): d ˆ 23.63
(CH3), 62.80 (CH2OH), 70.91 (C-5), 74.31 (C-3), 76.39 (carborane-C-1'*),
77.89 (C-6), 80.05 (carborane-C-2'*), 80.39, 82.06 (C-2, C-4); MS (ESIÀ):
m/z (%): 639 (100) [2M À H]À, 319 (20) [M À H]À; C9H24B10O5 (320.4).
(2R,3R,4R,5S,6R)-N-[4,5-Bis(hydroxy)-6-hydroxymethyl-2-(1C,2C-di-
carba-closo-dodecaboran(12)ylethyl)tetrahydropyran-3-yl]acetamide (22):
75% from 17, colorless solid; Rf (EtOAc/MeOH, 4:1) ˆ 0.09; [a]2D0 ˆ ‡28.28
(c ˆ 0.5, MeOH); IR (KBr): nÄ ˆ 3407 (N H, O H), 2925 (C H), 2584
‡
138.5 ppm (Ph); MS (ESI): m/z (%): 1120 (100) [M‡Na] ; elemental
(B H), 1656 (C O), 1384, 1054 cmÀ1; UV (C HCN): lmax (lge) ˆ 254.0 nm
analysis (%) calcd for C64H76B10O9 (1097.4): C70.05, H 6.98; found: C70.36,
H 6.75.
ˆ
3
(2.373); 1H NMR (500 MHz, CD3OD): d ˆ 1.00 3.20 (brs, 10H; BH), 1.99
(2aR,3aR,4aR,5aS,6aS,2bR,3bR,4bR,5bS,6bS)-1,2-Bis[3,4,5-tris(benzy-
loxy)-2-benzyloxymethyltetrahydropyran-6-yl]-1C,2C-dicarba-closo-do-
decaborane(12) (19): 13% from 10, yellowish wax-like solid; Rf (n-pentane/
EtOAc, 6:1) ˆ 0.78; [a]2D0 ˆ ‡33.38 (c ˆ 0.5, CHCl3); IR (KBr): nÄ ˆ 3031
(s, 3H; CH3 of NAc), 3.52 (ddd, J ˆ 2.6, 1.3, 1.3 Hz, 1H; 4-H*), 3.60 (dd, J ˆ
11.9, 4.5 Hz, 1H; CHaHbOH), 3.73 (dd, J ˆ 2.6, 2.6 Hz, 1H; 5-H*), 3.98 (dd,
J ˆ 11.9, 9.0 Hz, 1H; CHaHbOH), 4.02 4.07 (m, 2H; 3-H, 6-H), 4.58 (d, J ˆ
1.1 Hz, 1H; 2-H), 4.66 (brs, 1H; carborane-CH), 7.47 ppm (d, J ˆ 9.9 Hz,
1H; NH); 13CNMR (150 MHz, CD 3OD): d ˆ 23.02 (CH3 of NAc), 51.81
(C H), 2866, 2574 (B H), 1497, 1454, 1362, 1101 cm À1; UV (C HCN): lmax
3
Chem. Eur. J. 2003, 9, No. 6
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1301

L. Tietze, A. Dondoni et al.
FULL PAPER
(C-3), 60.11 (CH2OH), 60.63 (carborane-CH), 68.50, 68.68, 70.94 (C-2, C-4,
chemicals by Aventis S.A., BASF AG, Bayer AG, Degussa AG, and
Wacker AG are gratefully acknowledged. The authors would also like to
thank Ms. Maria Grazia Zampolli and Ms. Stefanie Heidrich for their help
in the synthesis of ethynyl C-glycosides and with the in vitro cytotoxicity
tests.
À
ˆ
C-5), 75.98 (carborane-C-1'), 83.88 (C-6), 172.7 ppm (C O); MS (ESI ):
m/z (%): 694 (50) [2M À H]À, 384 (70) [M‡H2O‡H2O À H]À, 346 (100)
[M À H]À; C10H25B10NO5 (347.4).
(2aS,3aR,4aS,5aS,6aR,2bS,3bS,4bR,5bS,6bR)-2a-(1C,2C-Dicarba-
closo-dodecaboran(12)yl-ethyl)-3a,4a,5a-tris(hydroxy)-6a-{2-[3b,4b,5b-
tris(hydroxy)-6b-hydroxymethyltetrahydropyran-2b-yl]ethyl}tetrahydro-
pyran (23): 69% from 18, colorless solid containing traces of impurities; Rf
(EtOAc/MeOH, 4:1) ˆ 0.09; [a]2D0 ˆ ‡16.58 (c ˆ 0.6, MeOH); IR (KBr):
[1] For reviews, see: a) R. F. Barth, A. H. Soloway, R. G. Fairchild,
Cancer 1992, 70, 2995 3007; b) M. F. Hawthorne, Angew. Chem. 1993,
105, 997 1033; Angew. Chem. Int. Ed. Engl. 1993, 32, 950 984; c) C.
Morin, Tetrahedron 1994, 50, 12521 12569; d) D. Gabel, Chem.
Unserer Zeit 1997, 31, 235 240; e) A. H. Soloway, W. Tjarks, B. A.
Barnum, F.-G. Rong, R. F. Barth, I. M. Codogni, J. G. Wilson, Chem.
Rev. 1998, 98, 1515 1562.
nÄ ˆ 3406 (O H), 2920 (C H), 2590 (B H), 1384, 1087 cm À1
;
1H NMR
(500 MHz, CD3OD): d ˆ 1.00 3.00 (brs, 10H; BH), 1.32 1.48, 2.05 2.20
(2m, 2 Â 2H; 1''-H2, 2''-H2), 3.00 3.40 (m, 9H; 2b-H, 3a-H, 3b-H, 4a-H,
4b-H, 5a-H, 5b-H, 6a-H), 3.60 (dd, J ˆ 12.1, 5.8 Hz, 1H; CHaHbOH), 3.69
(d, J ˆ 9.0 Hz, 1H; 2a-H), 3.83 (dd, J ˆ 12.1, 2.4 Hz, 1H; CHaHbOH), 3.84
(m, 1H; 6b-H), 4.62 ppm (brs, 1H; carborane-CH); 13CNMR (75 MHz,
[2] L. F. Tietze, U. Griesbach, O. Elsner, Synlett 2002, 1109 1110.
[3] a) L. F. Tietze, U. Bothe, Chem. Eur. J. 1998, 4, 1179 1183; b) G. B.
Giovenzana, L. Lay, D. Monti, G. Palmisano, L. Panza, Tetrahedron
1999, 55, 14123 14136; c) L. F. Tietze, U. Bothe, I. Schuberth, Chem.
Eur. J. 2000, 6, 836 842; d) L. F. Tietze, U. Bothe, U. Griesbach, M.
Nakaichi, T. Hasegawa, H. Nakamura, Y. Yamamoto, Bioorg. Med.
Chem. 2001, 9, 1747 1752; e) L. F. Tietze, U. Griesbach, U. Bothe, H.
Nakamura, Y. Yamamoto, ChemBioChem 2002, 3, 219 225.
[4] L. F. Tietze, U. Bothe, U. Griesbach, M. Nakaichi, T. Hasegawa, H.
Nakamura, Y. Yamamoto, ChemBioChem 2001, 2, 326 334.
[5] W. V. Dahlhoff, J. Bruckmann, K. Angermund, C. Kr¸ger, Liebigs
Ann. Chem. 1993, 831 835.
[6] T. Lowary, M. Meldal, A. Helmboldt, A. Vasella, K. Bock, J. Org.
Chem. 1998, 63, 9657 9668.
[7] A. Dondoni, G. Mariotti, A. Marra, J. Org. Chem. 2002, 67, 4475
4486.
[8] Somewhat surprisingly, the alkylation of ethynyl C-glycosides has
been reported to occur in very low yield or not at all under similar
conditions. See: T. M. Davis, T. L. Lowary, Carbohydr. Res. 2000, 324,
210 217.
[9] A. Dondoni, P. P. Giovannini, A. Marra, J. Chem. Soc. Perkin Trans. 1
2001, 2380 2388.
[10] R. Schaeffer, J. Am. Chem. Soc. 1957, 79, 1006 1007.
[11] a) W. M. Pearlman, Tetrahedron Lett. 1967, 17, 1663 1664; b) Hand-
book of Reagents for Organic Synthesis - Oxidizing and Reducing
Agents, (Eds.: S. D. Burke, R. L. Danheiser), Wiley, Chichester, 1999.
[12] a) L. M. Greene, J. L. Reade, C. F. Ware, J. Immunol. Meth. 1984, 70,
257 268; b) T. Mosmann, J. Immunol. Meth. 1983, 65, 5563 5574.
[13] Cell line A 549 (ATCC CCL 185) was kindly provided by the Institut
f¸r Zellbiologie, Universit‰t Essen (Germany).
[14] Cell line PancTu 1 was kindly provided by the Institut f¸r Onkologie,
Georg-August-Universit‰t Gˆttingen (Germany).
[15] Cell line ATCC CCL 229.
[16] U. Bothe, Ph.D. thesis, Georg-August-Universit‰t Gˆttingen (Ger-
many), 1999.
[17] W. L. F. Armarego, D. D. Perrin, Purification of Laboratory Chem-
icals, 4th ed., Butterworth-Heinemann, Oxford, 1996.
CD3OD): d ˆ 28.80, 28.81 (C-1'',
C -'2'), 61.11 (carborane-CH), 63.10
(CH2OH), 71.94 (C-3a), 74.43, 74.74 (C-2b, C-6a), 75.33 (C-4a*), 76.93
(carborane-C-1'), 79.24 (C-4b*), 79.50 (C-2a), 79.72, 81.02 (C-5a, C-3b),
81.39 (C-5b*), 81.47 ppm (C-6b); MS (ESIÀ): m/z (%): 465 (100) [M À H]À;
C15H34B10O9 (466.5).
(2aR,3aS,4aR,5aR,6aS,2bR,3bS,4bR,5bR,6bS)-1,2-Bis[3,4,5-tris(hy-
droxy)-2-hydroxymethyltetrahydropyran-6-yl]-1C,2C-dicarba-closo-do-
decaborane(12) (24): Quantitative from 19, colorless solid; Rf (EtOAc/
MeOH, 4:1) ˆ 0.06; [a]2D0 ˆ ‡7.58 (c ˆ 0.1, MeOH); IR (KBr): nÄ ˆ 3385
(O H), 2925 (C H), 2574 (B H), 1339, 1094 cm À1; UV (C HCN): lmax
3
(lge) ˆ 191.0 (3.847), 248.5 (3.376), 280.0 (2.965), 326.0 nm (3.278);
1H NMR (500 MHz, CD3OD): d ˆ 1.50 3.00 (brs, 10H; BH), 3.14 (dd,
J ˆ 9.2, 9.2 Hz, 2H; 5a-H, 5b-H), 3.26 (ddd, J ˆ 9.5, 7.3, 2.2 Hz, 2H; 2a-H,
2b-H), 3.33 3.39 (m, 4H; 3a-H, 3b-H, 4a-H, 4b-H), 3.58 (dd, J ˆ 12.1,
7.3 Hz, 2H; 2 CHaHbOH), 3.67 (d, J ˆ 9.1 Hz, 2H; 6a-H, 6b-H), 3.89 ppm
(dd, J ˆ 12.1, 2.2 Hz, 2H; 2 CHaHbOH); 13CNMR (125 MHz, CD 3OD):
d ˆ 63.15 (2 CH2OH), 71.17 (C-5a, C-5b), 74.61 (C-3a, C-3b), 77.49 (C-6a,
C-6b), 80.49 (C-4a, C-4b), 81.75 (2 carborane-C), 82.47 ppm (C-2a, C-2b);
‡
‡
MS (ESI): m/z (%): 960 (100) [2M‡Na] , 492 (45) [M‡Na] ; C14H32B10O10
(468.5).
Cytotoxicity tests: Adherent cells of the human bronchial carcinoma cell
line A549, of the murine melanoma cell line B-16, of the human pancreas
carcinoma cell line PancTu 1, and of the colorectal human adeno carcinoma
cell line LoVo were seeded in 96-well plates (TCMicrowell 96F, Nunc) and
cultivated at 378Cunder air with a CO
content enriched to 7.5% in
2
Dulbecco×s modified Eagle×s medium (DMEM, Biochrom) supplemented
with l-glutamine (4mm, Gibco), NaHCO3 (44mm, Biochrom), and 10%
fetal calf serum (FCS, heat-inactivated for 30 min at 568C, Gibco). The cells
were incubated with compounds 2 and 20 23 at various concentrations for
24 h in a serum-free medium (Ultra Culture, Cambrex) containing 1%
DMSO. After five days of cultivation, the cells were treated with MTT
(final concentration 0.5 mg mLÀ1) for 4 h, and with a solubilizing solution
(10% SDS in 0.1m HCl) overnight. The optical density of the resulting blue
formazane derivative was measured with a photometer (thermo max
microplate reader, Molecular Devices) after cell lysis. The measured
optical density is proportional to the fraction of the living, metabolically
active cells. The experiments were performed in duplicate.
[18] W. C. Still, M. Kahn, A. Mitra, J. Org. Chem. 1978, 43, 2923 2925.
[19] H. Kuzuhara, H. Fletcher, J. Org. Chem. 1967, 32, 2531 2534.
[20] E. J. Corey, J. W. Suggs, Tetrahedron Lett. 1975, 2647 2650.
Acknowledgement
This work was generously supported by the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie. Kind donations of
Received: September 16, 2002 [F4431]
1302
¹ 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Chem. Eur. J. 2003, 9, No. 6