Synthesis and characterization of a novel functionalized azanonaborane cluster for boron neutron capture therapy

Article abstract of DOI:10.1039/b503445k

The reactivity of an azanonaborane cluster containing free amino groups {H₂N(CH₂)₄H₂NB₈H ₁₁NH(CH₂)₄NH₂} towards ketones and aldehydes is investigated. In a one step reaction, the reductive amination of some ketones and aldehydes (namely acetone, benzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde, 4-acetoxybenzaldehyde, and 4-acetamidobenzaldehyde) with an azanonaborane cluster in the presence of H ₃BNH₂(CH₂)₄NH₂ gives monoalkylamino derivatives of the azanonaborane cluster {RHN(CH ₂)₄H₂NB₈H₁₁NH(CH ₂)₄NHR} where (R = (Me)₂CH-, C ₆H₄CH₂-, 3-OHC₆H₄CH ₂-, 4-OHC₆H₄CH₂-, 4-NO ₂C₆H₄CH₂-, 4-MeOCOC ₆H₄CH₂-, or 4-NH₂COC ₆H₄CH₂-). The functionalized derivatives of the {B₈N} cluster can be used in boron neutron capture therapy for tumors (BNCT). Similarly, the reductive amination of 5-(4′-formylphenyl)- 10,15,20-triphenylporphyrin with the {B₈N} cluster gave a porphyrin bearing azanonaborane cluster, while a porphyrin dimer linked by an azanonaborane moiety was obtained following the same method, starting with a 2 : 1 molar ratio of porphyrin : {B₈N} cluster. 5,10,15,20- Tetraformylphenylporphyrin gave the chance to increase the percentage of boron in the resulting boronated porphyrin, which is considered an important factor for a BNCT delivery agent. With these compounds, the cell toxicity using V79 cells was carried out to determine whether these compounds would have favorable biological properties. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b503445k

View Article Online / Journal Homepage / Table of Contents for this issue
A R T I C L E
Synthesis and characterization of a novel functionalized
azanonaborane cluster for boron neutron capture therapy
Afaf R. Genady*
Department of Chemistry, Faculty of Science, University of Tanta, 31527-Tanta, Egypt.
E-mail: afafgenady@hotmail.com; Fax: +2-040-3350804; Tel: +2-040-3297974
Received 8th March 2005, Accepted 18th April 2005
First published as an Advance Article on the web 29th April 2005
The reactivity of an azanonaborane cluster containing free amino groups {H2N(CH2)4H2NB8H11NH(CH2)4NH2}
towards ketones and aldehydes is investigated. In a one step reaction, the reductive amination of some ketones and
aldehydes (namely acetone, benzaldehyde, 3-hydroxybenzaldehyde, 4-hydroxybenzaldehyde, 4-nitrobenzaldehyde,
4-acetoxybenzaldehyde, and 4-acetamidobenzaldehyde) with an azanonaborane cluster in the presence of
H3BNH2(CH2)4NH2 gives monoalkylamino derivatives of the azanonaborane cluster {RHN(CH2)4H2NB8-
H11NH(CH2)4NHR} where (R = (Me)2CH–, C6H5CH2–, 3-OHC6H4CH2–, 4-OHC6H4CH2–, 4-NO2C6H4CH2–,
4-MeOCOC6H4CH2–, or 4-NH2COC6H4CH2-). The functionalized derivatives of the {B8N} cluster can be used in
boron neutron capture therapy for tumors (BNCT). Similarly, the reductive amination of 5-(4ꢀ-formylphenyl)-
10,15,20-triphenylporphyrin with the {B8N} cluster gave a porphyrin bearing azanonaborane cluster, while a
porphyrin dimer linked by an azanonaborane moiety was obtained following the same method, starting with a 2 : 1
molar ratio of porphyrin : {B8N} cluster. 5,10,15,20-Tetraformylphenylporphyrin gave the chance to increase the
percentage of boron in the resulting boronated porphyrin, which is considered an important factor for a BNCT
delivery agent. With these compounds, the cell toxicity using V79 cells was carried out to determine whether these
compounds would have favorable biological properties.
Introduction
Boron neutron capture therapy (BNCT) is a bimodal cancer
treatment based on the selective accumulation of certain 10B
carriers in tumors. Subsequent irradiation with thermalized
4
neutrons produces high linear energy transfer particles, He2+
(a-particle) and 7Li3+, that cause severe damage to tumor
cells through ionization processes. Azanonaborane clusters
{(R1H2N)B8H11NHR2} are readily prepared in good yields in
easy steps from nido-B10H14, and the determination of their
structures and unequivocal constitution have been reported.1–3
Fig. 1 Structure of (4-aminobutylamine)-N-aminobutyl)azanonabo-
These compounds have been shown to constitute a good
entry into azacarbaborane4 and azametalloborane chemistry.5
The azanonaborane cluster also undergoes several other
interesting reactions, such as: (i) a ligand-exchange reaction;
(ii) N-deprotonation followed by subsequent N-alkylation;
(iii) a halogenation reaction; (iv) hydrolytic decomposition
to the new 5-vertex compound.6–8 Recently, azanonaboranes
containing free hydroxy groups9 or free amino groups,10 have
been used as a new class of boron clusters and considered as
a promising boron moiety in BNCT. The success of BNCT
depends upon the selective uptake of boron within tumor
cells.11 Porphyrins appear to be particularly promising tumor-
selective compounds because of their demonstrated tendency
to accumulate in neoplastic tissue. Various boron clusters such
as azanonaborane,12 polyhedral closo- and nido-carborane
and closo-dodecaborate anions containing porphyrin have
been synthesized and designed as BNCT agents.13–16 In order
to develop the chemistry of azanonaboranes containing free
amino groups such as (4-aminobutylamine)-N-aminobutyl)-
rane(11) (exo-H atoms are omitted for clarity).
Results and discussion
Chemistry
The B8N cluster is an interesting starting material for the
synthesis of a wide variety of boron-containing species.
The eight boron atoms offer suitable boron content deriva-
tives and have reasonable water solubility, which makes
them good candidates for the selective delivery of boron
for BNCT.9,10 Functionalization of the azanonaboranes im-
parts a chemical reactivity which can assist their intracellu-
lar retention within tumors or provide the means to attach
them to organic molecules. Azanonaborane clusters contain-
ing free amino groups {H2N(CH2)4H2NB8H11NH(CH2)4NH2}
and H3BNH2(CH2)4NH2 were prepared according to the
literature.10 Addition of carbonyl compounds (1a–g) to a mixture
of B8N cluster with H3BNH2(CH2)4NH2 in tetrahydrofuran
(THF) at room temperature for 24 h (1a) or two days (1b–
g), followed by chromatography, resulted in the isolation
of monoalkylamino derivatives of the azanonaborane cluster
{RHN(CH2)4H2NB8H11NH(CH2)4NHR} (2a–g) in good yields
(Scheme 1). Additionally, the stability of the resulting clus-
ters is higher than the previously reported B8N species10 at
room temperature. The monitoring of the reaction mixture
by NMR spectroscopy showed no evidence of the presence of
azanonaborane(11)
{H2N(CH2)4H2NB8H11NH(CH2)4NH2}
(Fig. 1), we have become interested in the use of these
compounds as starting substrates. Here we report the synthesis
of new compounds containing an azanonaborane cluster
by the reductive amination of some carbonyl compounds
with (4-aminobutylamine)-N-aminobutyl)azanonaborane(11)
{H2N(CH2)4H2NB8H11NH(CH2)4NH2} with the aim of obtain-
ing azanonaboranes with enhanced biological significance.
2 1 0 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
©

View Article Online
Scheme 1
In the case of compound 2a, the 1H NMR spectrum showed a
H3BNH2(CH2)4NH2 {d(11B) = −19.97} after 24 h for compound
2a and two days for compounds 2b–g. The appearance of a new
broad band {d(11B) = −24.65} was attributed to the conversion
of H3BNH2(CH2)4NH2 to H2BNH2(CH2)4NHCHR (Scheme 1).
The constitution and purity of each of the compounds (2a–g)
were established by NMR, mass spectroscopy and elemental
analysis. Clean 11B and 1H NMR spectra were additional criteria
of purity (Table 1). The 11B NMR spectroscopic data of the
series of compounds 2a–g are very similar, although there are
some variations in the proton shielding as the organic moiety
heptet at 2.65–2.9 ppm corresponding to one CH proton and two
doublets at 1.01–1.16 ppm corresponding to six (CH3)2 protons
(Fig. 2). Moreover the ESI-MS spectrum showed the most
intense molecular ion peak (M+) at m/z = 355 corresponding to
the 11B isotope (see experimental section for details).
1
Computed H and 13C NMR chemical shifts, supported by
2D-1H 1H cosy and 2D-1H 13C cosy NMR spectra reflected the
reductive amination of carbonyl compounds by the free amino
groups in the B8N clusters. Additionally the assignments of 13
C
1
NMR signals were based on DEPT experiments and chemical
shift arguments (Fig. 3). The IR spectrum proved the absence of
changes (Table 1). H NMR spectra of all compounds showed
exchangeable singlets corresponding to the NH proton at d =
5.8–6.2 ppm (Fig. 2). Also, 1H and 13C NMR spectra indicate the
appearance of new signals corresponding to the organic moiety
of each carbonyl compound. Mass spectra of all compounds
showed fragments corresponding to the typical pattern of boron
isotopes (10B and 11B).
=
the free C O group of carbonyl compounds. These observations
suggested a mechanism for the formation of compounds 2a–
g in which the hydroborane H3BNH2(CH2)4NH2 reduction
of ketones and aldehydes most likely proceeds by an initial
complexing of H3BNH2(CH2)4NH2 with carbonyl oxygen17
Table 1 200 MHz (11B, 1H) NMR data in CDCl3 at 20 ◦C for 2a–g, 4a–b and 6
B1
B2
B3
B4
B5
B6
B7
B8
lH(4,5) lH(6,7)
[d(1H)]
NH
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
d(11B)
[d(1H)]
[d(1H)]
Compound
2a
1.62
[2.65]
−55.11
[−0.66]
−19.29
[1.18]
−34.16
[0.69]
−9.93
[2.64]
−9.93
[2.57]
−32.75
[0.69]
−31.41
[0.54]
[−0.66]
−30.95
[0.53]
[−0.71]
−30.67
[0.57]
[−0.67]
−30.59
[0.63]
[−0.59]
−30.06
[0.71]
[−0.62]
−30.26
[0.56]
[−0.67]
−30.76
[0.59]
[−0.68]
−30.25
[0.51]
[−2.17]
[−1.12]
[−1.34]
[−1.42]
[−1.56]
[−1.39]
[−1.52]
[−1.56]
[−1.29]
[−1.46]
[−1.56]
[−2.021]
2b
2c
2d
2e
2f
2g
4a
4b
6
1.54
[2.58]
−54.95
[−0.71]
−18.06
[1.28]
−34.31
[0.78]
−10.88
[2.54]
−10.88
[2.47]
−32.45
[0.78]
[−2.05]
[−2.12]
1.71
[2.52]
−54.98
[−0.67]
−20.16
[1.32]
−33.95
[0.72]
−11.12
[2.56]
−11.14
[2.54]
−31.22
[0.72]
[−2.32]
[−2.29]
1.66
[2.51]
−55.06
[−0.65]
−20.12
[1.21]
−34.06
[0.82]
−11.24
[2.62]
−11.24
[2.57]
−32.75
[0.82]
[−2.39]
[−2.39]
1.72
[2.49]
−55.21
[−0.68]
−20.36
[1.28]
−34.14
[0.81]
−11.21
[2.58]
−11.21
[2.58]
−31.94
[0.81]
[−2.17]
[−2.17]
1.79
[2.56]
−55.56
[−0.67]
−20.66
[1.29]
−34.16
[0.86]
−11.23
[2.52]
−11.23
[2.52]
−33.41
[0.86]
[−2.23]
[−2.025]
1.64
[2.56]
−55.12
[−0.68]
−21.46
[1.18]
−34.05
[0.84]
−10.89
[2.58]
−10.89
[2.58]
−32.36
[0.84]
[−2.22]
[−1.99]
1.59
[2.49]
−54.81
[−0.59]
−19.54
[1.23]
−32.76
[0.72]
−10.16
[2.53]
−10.11
[2.53]
−31.85
[0.72]
[−1.99]
[−1.89]
[−0.59]
−30.52
[0.55]
[−0.66]
−30.72
[0.57]
1.76
[2.57]
−54.61
[−0.66]
−20.46
[1.19]
−33.23
[0.69]
−10.88
[2.53]
−10.89
[2.53]
−32.41
[0.69]
[−2.14]
[−2.03]
1.61
[2.51]
−54.72
[−0.65]
−19.36
[1.18]
−33.15
[0.66]
−10.78
[2.51]
−10.78
[2.51]
−31.87
[0.68]
[−2.11]
[−2.02]
[−0.65]
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8
2 1 0 3

View Article Online
Fig. 2 200 MHz 11B (top) and 11B { H} (bottom) NMR spectra of compound 2a in CDCl3 at 20 ◦C.
1
assigned structures 4a, 4b, and 6. To assess the potential of these
boronated porphyrins in neutron capture therapy (NCT), we
will consider achieving the water solubility of these porphyrins.
Insertion of trivalent metal and addition of 1N HCl may be the
route to our aim.
UV–visible spectra showed that the Soret band of the
boronated porphyrins are red shifted nearly 3–5 nm comparing
to the nonboronated starting porphyrins.
The vibrational frequency of the B–H band m(B–H) or
the B–B band m(B–B) was not found to be sensitive to the
connection of the carbonyl compounds with free amino groups.
For compounds 2a–g, 4a–b and 6, m(B–H) lies in the range of
2521–2512 cm−1, while m(B–B) varies from 1056 to 1048 cm−1.
10
Compared to the frequencies of {B8N} m(B–B) = 2529–
2541 cm−1, m(B–H) = 1065 to 1059 cm−1, only slight differences
were found, indicating that the intracluster bonding is not
perturbed by substitution on the free amino groups.
Fig. 3 200 MHz DEPT 13C NMR spectrum of compound 2a in CDCl3
at 20 ◦C.
followed by an intramolecular hydride shift and removal of H2O
to yield the required products.
Biology
Reaction of azanonaborane clusters with hydroxy acetone
or isophthaloyl chloride under the same reaction conditions
or at a lower temperature (0 ◦C) gave a white precipitate
immediately. However, the monitoring of the reaction mixture
by NMR spectroscopy showed that a progressive loss of the
boron cluster occurred exclusively to give only boric acid. No
reaction was found to occur upon treatment of the B8N cluster
with acetylacetone.
The observation that porphyrins have both selective uptake
and persistence within tumors encouraged us to synthesize
a series of pure compounds of porphyrins containing the
B8N cluster that may be useful in cancer treatment. We have
found that the reductive amination of 5-(4ꢀ-formylphenyl)-
10,15,20-triphenylporphyrin (3a)18 with a B8N cluster con-
taining free amino groups in THF for two days followed
by chromatography afforded both porphyrin monomer (4a)
and dimer (4b) containing 9.5% and 5.6% boron by weight,
respectively (Scheme 2). To achieve the incorporation of mul-
tiple azanonaborane cluster units, we started with 5,10,15,20-
tetraformylphenylporphyrin 5, affording boronated porphyrin
bearing four azanonaborane clusters (6) in the para-position
(Scheme 3). Compound 6 may be more useful as a boron carrier
in BNCT than both compounds 4a and 4b, where it contains
20% boron by weight. The structures of the new compounds
synthesized possess spectroscopic data in accord with the
Polyamines such as putrescine, spermidine (SPD), and spermine
(SPM) are important biochemical constituents that are essential
for cell growth and differentiation19,20 and their depletion has
a growth inhibitory effect on tumors.21 They accumulate in the
tumor cells22 and have transport systems which increase their up-
take in malignant cells.23 The potential of N-benzylpolyamines
as vectors of boron for tumor targeting is evidenced by a
recent in vitro study.24 The in vitro toxicity test was carried
out to determine whether these compounds were sufficiently
nontoxic. In vitro toxicity was evaluated by exposing V79 cells
(Chinese hamster fibroblasts) for 16 h to the test compounds,
and comparing the number of surviving cells to the number
of surviving cells not exposed to the test compounds. Cells
exposed to the B8N clusters 2b and 2e at a concentration of
0.607 mM did not survive while 2d, 2f and 6 were not toxic
at this concentration, and 2a already showed some toxicity. We
conclude, in agreement with others, that the incorporation of
a hydrophobic group into the chain of polyamines increases
the compound’s toxicity.25 The survival ratio for 2c, 2f and 2g
decreased when its concentrations in the medium increased from
0.607 to 3.5 mM with LD50 >1000 lM. The LD50 of SPD is
880 lM, which is higher than the LD50 of SPM, which is below
600 lM (Fig. 4, Table 2). According to these results, a major
limitation in the use of the present compounds appears to be
their cellular toxicity, especially compounds such as 2a or 2b
2 1 0 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8

View Article Online
Scheme 2
Scheme 3
and 2e with hydrophobic groups. The in vitro toxicities of these
compounds with LD50 values below 607 lM were not measured
at lower concentrations because the achievable concentration of
boron would not be effective for BNCT.
at room temperature is advantageous over previously reported
azanonaboranes. The B8N clusters 2d, 2f and 6 appear not to be
toxic at suitable boron concentrations. These compounds might
be useful as delivery agents for BNCT.
Experimental
Conclusion
Material and methods
In conclusion, we have succeeded in synthesizing functional-
ized azanonaborane clusters via reductive amination of some
aldehydes and ketones by a one step process. New types of
compounds containing both porphyrin macrocycles and polyhe-
dral azanonaborane units in one molecule have been prepared.
These compounds might be suitable for use in BNCT. As
compared with azanonaboranes containing free amino groups,
results reported in this study have shown that their stability
The reagents, dry solvents THF and dichloromethane, were
used as presented directly without further purification. All
aldehydes and ketones (1a–g) were commercially available.
5-(4ꢀ-Formylphenyl)-10,15,20-triphenylporphyrin, 5,10,15,20-
tetraformylphenylporphyrin, (4-aminobutylamine)-N-amino-
butyl)azanonaborane(11) cluster {H2N(CH2)4H2NB8H11NH-
(CH2)4NH2} and H3BNH2(CH2)4NH2 were prepared as
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8
2 1 0 5

View Article Online
Table 2 In vitro toxicity of B8N clusters by V79 Cellsa
Cmedia
Percentage of survival (%)
(lg of B/mL)
(mM)
2a
2b
2d
2e
2f
6
50
75
100
150
225
300
0.607
0.868
1.736
2.343
2.864
3.472
<1
—
—
—
—
—
<1
—
—
—
—
—
65.15 5.3
41.45 3.0
24.17 3.2
17.25 1.6
12.57 1.2
6.72 1.0
<1
—
—
—
—
—
59 1.7
82 0.87
35.23 1.3
18.13 1.56
10.11 0.93
7.23 0.67
60.2 2.68
38.1 0.85
22.2 1.28
16.3 0.45
7.0 0.77
4
0.87
a V79 cells were incubated with boronated compounds for 16 h at compound concentrations corresponding to the boron amounts indicated. Cells
were washed (PBS), trypsinized and seeded out for colony formation. After one week, colonies were washed, stained, washed again (ethanol) and
counted.
1472m, 1442m, 1402m, 1157m, 1115s, 745m, (d, c, CH2-groups);
dH(200 MHz; CDCl3; Me4Si) +6.35 (2H, bs, HN–), +3.93
(2H, bs, H2N–B8), +2.82 (6H, t, –H2CHN), +2.75 (2H, hept,
–HCNH), +2.61 (2H, m, CH2NH2–B8), +1.38–1.61 (8H, m,
–CH2CH2–, –CH2CH2–), +1.13 (6H, d, (CH3)2), +1.01 (6H,
d, (CH3)2); dC(200 MHz; CDCl3; Me4Si) 51.76 (CH2HNB8),
50.54 (CH2NH2–B8), 49.59, 49.17 (2C, CH2NH), 47.2, 46.95
(2C, HNCH), 29.93, 29.14, 27.66, 26.65 (4C, –CH2CH2–), 23.4,
22.56 (4C, CH3); m/z (ESI) 355 (M+, 10%).
2b. Yield: (0.58 g, 47%) as a colorless oil; Rf = 0.32;
(found: C, 58.95; H, 9.01; N, 12.37. B8H41C22N4 requires C, 59.0;
H, 9.16; N, 12.51%); mmax(KBr disc)/cm−1 3239s (NH2/NH),
2526s (BH), 1667w (d, NH2/NH), 1339s (BN), 2976m, 2895m,
1515m, 1467m, 1448m, 1166m, 1116s, 745m (d, c of CH2-
groups); dH(200 MHz; CD3CN; Me4Si) +6.35 (2H, bs, HN–),
+6.5–7.12 (10Harom, m, CH), +3.86 (2H, bs, H2N–B8), +2.78
(2H, t, –H2CHN–B8), +2.71 (4H, m, –H2CNH), +2.67
Fig. 4 Percentage ( SD) of the in vitro survival cell with respect to the
(2H, m, –H2CH2N–B8), +1.4–1.65 (8H, m, –CH2CH2–,
concentration of the B8N cluster compounds, SPD, and SPM. The data
for SPD and SPM were taken from ref. 10.
–CH2CH2–); dC(200 MHz; CD3CN; Me4Si) 130.12, 130.02,
125.2, 117.1, 115.25, 115.12, 115.08 (Carom), 51.63 (CH2HNB8),
50.34 (H2CH2N–B8), 48.98, 49.4 (2C, CH2NH), 30.02, 29.55,
described in the literature.18,10 Plate chromatography was con-
ducted on silica gel 60 (Fluka). Elemental analyses were per-
28.23, 26.95 (4C, –CH2CH2–); m/z (DCI) 449 (M+, 8%).
formed by a Perkin-Elmer 2400 automatic elemental analyzer.
2c. Yield: (0.56 g, 38%) as a colorless solid; Rf = 0.28;
All compounds gave elemental analysis within 0.4%. UV–
visible data were measured on a Varian Cary 50 bio instrument.
(found: C, 55.12; H, 8.05; N 11.56. B8H39C22N4O2 requires C,
55.39; H, 8.16; N, 11.73%); mmax(KBr disc)/cm−1 3612s (OH),
3239s (NH2/NH), 2522s (BH), 1661s (d, NH2/NH), 1336s (BN),
2973m, 2895m, 1513m, 1463m, 1446m, 1163m, 1115s, 742m (d,
c of CH2-groups); dH(200 MHz; CD3CN; Me4Si) +6.35 (2H, bs,
HN–), +6.97 (2H, s, OH), +6.7–7.19 (8Harom, m, CH), +3.95
(2H, bs, H2N–B8), +2.88 (2H, t, –H2CHN–B8), +2.75 (4H, m,
–H2CNH), +2.71 (2H, m, –H2CH2N–B8), +1.38–1.65 (8H, m,
–CH2CH2–, –CH2CH2–); dC(200 MHz; CD3CN; Me4Si) 156.8,
156.49, 130.41, 130.12, 125.83, 117.8, 115.54, 115.48, 115.43
(Carom), 51.21 (CH2HNB8), 50.54 (H2CH2N–B8), 48.98, 47.25
(2C, CH2NH), 30.19, 29.24, 28.13, 27.25 (4C, –CH2CH2–); m/z
(DCI) 479 (M+, 12%).
1
The measurements for NMR (11B, H and 13C) were carried
out on a Bruker DPX 200 spectrometer. The chemical shifts
d are given in ppm relative to DE = 100 MHz for d (1H)
(nominally SiMe4), and DE = 32.083972 MHz for d (11B)
(nominally F3BOEt2) in CDCl3 or CD3CN. IR (cm−1) spectra
were determined as a KBr disc on a Biorad FTS-7 spectrometer.
Electron spray ionization (ESI) and direct chemical ionization
(DCI, reactant gas NH3) mass spectra were recorded on a
Finnigan MAT 8222. Only the most intense molecular ion
peak (M+) corresponding to the 11B isotope was taken into
consideration.
2d. Yield: (0.64 g, 43%) as a colorless oil; Rf = 0.31; (found:
C, 55.09; H, 8.13; N, 11.43. B8H39C22N4O2 requires C, 55.39;
H, 8.16; N, 11.73%); mmax(KBr disc)/cm−1 3605s (OH), 3238s
(NH2/NH), 2521s (BH), 1665w (d, NH2/NH), 1335s (BN),
2976m, 2894m, 1512m, 1458m, 1438m, 1152m, 1113s, 745m
(d, c of CH2-groups); dH(200 MHz; CD3CN; Me4Si) +6.35
(2H, bs, HN–), +6.95 (2H, s, OH), 6.5–7.12 (8Harom, m, CH),
+3.86 (2H, bs, H2N–B8), +2.78 (2H, t, –H2CHN–B8), +2.71
(4H, m, –H2CNH), +2.67 (2H, m, –H2CH2N–B8), +1.4–1.65
(8H, m, –CH2CH2–, –CH2CH2–); dC(200 MHz; CD3CN; Me4Si)
156.23, 156.2, 130.12, 130.02, 125.2, 117.1, 115.25, 115.12,
115.08 (Carom), 51.45 (CH2HNB8), 50.35 (H2CH2N–B8), 48.89,
49.51 (2C, CH2NH), 29.56, 28.95, 27.56, 26.53 (4C, –CH2CH2–
); m/z (ESI) = 479 (M+, 10%).
General procedure for the synthesis of compounds 2a–g, 4a–b,
and 6
Carbonyl compound (5 mmol) was added dropwise to a solution
of azanonaborane cluster (1 mmol) and H3BNH2(CH2)4NH2
(2 mmol) in 30 ml dry THF at room temperature. The reaction
mixture was stirred for 24 h in the case of compound 2a and
two days in the case of compounds 2b–g, 4a–b, and 6. The
solution was filtered off and all volatile components of the filtrate
were removed under vacuum to give the desired compounds.
The residue was chromatographed on silica gel using THF and
CH2Cl2 (1 : 2) as an eluent to yield the desired product.
2a. Yield (0.5 g, 45%) as a colorless oil; Rf = 0.3; (found:
C, 47.33; H, 12.08; N, 15.71. B8H43C14N4 requires C, 47.53;
H, 12.16; N, 15.84%); mmax(KBr disc)/cm−1 3238s (NH2/NH),
2521s (BH), 1657w (d, NH2/NH), 1338s (BN), 2963m, 2898m,
2e. Yield: (0.74 g, 45%) as a colorless oil; Rf = 0.32; (found:
C, 49.12; H, 6.87; N, 15.48. B8H37C22N6O4 requires C, 49.3;
2 1 0 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8

View Article Online
H, 6.91; N, 15.68%); mmax(KBr disc)/cm−1 3228s (NH2/NH),
2527 (sBH), 1597w (d, NH2/NH), 1332s (BN), 2978m, 2895m,
1517m, 1468m, 1449m, 1167m, 1112s, 744m (d, c of CH2-
groups); dH(200 MHz; CD3CN; Me4Si) +6.28 (2H, bs, HN–),
+6.5–7.18 (8Harom, m, CH), +3.95 (2H, bs, H2N–B8), +2.88
(2H, t, –H2CHN–B8), +2.76 (4H, m, –H2CNH), +2.61 (2H,
m, –H2CH2N–B8), +1.4–1.65 (8H, m, –CH2CH2–, –CH2CH2–);
dC(200 MHz; CD3CN; Me4Si) 155.25, 130. 12, 130.02, 125.2,
117.1, 115.25, 115.12, 115.08 (Carom), 52.05 (CH2HNB8), 50.86
(H2CH2N–B8), 48.89, 49.41 (2C, CH2NH), 29.69, 29.58, 27.95,
26.85 (4C, –CH2CH2–); m/z (DCI) 537 (M+, 15%).
6. Yield: (0.35 g, 45%) as a deep violet crystalline solid;
Rf = 0.21; kmax(CHCl3)/nm 424, 526, 564, 600, and 661 (10−3
e/dm3 mol−1cm−1 369.9, 16.6, 5.1, 5.1, and 2.5); dC(200 MHz;
CDCl3; Me4Si) −2.71 (2H, bs, HN–), +4.2 (8H, bs, H2N–B8),
+3.82 (8H, s, CH2), +7.05–8.25 (19H, m, Harom), 8.68–8.92
(8H, m, b-pyrrole), +2.84 (8H, t, H2CNH), +2.75 (12H, m,
–H2CNH2), +1.38–1.65 (16H, m, –CH2CH2–); dC(200 MHz;
CDCl3; Me4Si) 150.75, 149.28, 137.12, 136.14, 132.83, 130.82,
128.73, 126.23, 118.18, 115.03, 112.01, 108.75 (Cporphyrin),
51.36 (CH2HNB8), 50.25–48.17 (4CH2NH2–B8), 53.19–51.05
(8C, CH2NH), 48.1–42.15 (8C, HNCH), 32.15–25.16 (16C, –
CH2CH2–); m/z (ESI) 1747 (M+, 21%), 1446 (M-272, 18), 630
(M-1088, 100).
2f. Yield: (0.74 g, 42%) as a colorless solid; Rf = 0.28; (found:
C, 55.23; H, 7.38; N, 11.12. B8H43C26N4O4, requires C, 55.57; H,
7.65; N, 11.4%); mmax(KBr disc)/cm−1 3232s (NH2/NH), 2523s
(BH), 1310s (CO), 1615w (d, NH2/NH), 1336s (BN), 2984m,
2892m, 1511m, 1452m, 1437m, 1156m, 1115s, 745m (d, cof CH2-
groups); dH(200 MHz; CD3CN; Me4Si) +6.26 (2H, bs, HN–),
+6.56–7.12 (8Harom, m, CH), +3.67 (2H, bs, H2N–B8), +2.68
(2H, t, –H2CHNB8), +2.65 (4H, m, –H2CNH), +2.67 (2H,
m, –H2CH2NB8), 2.48 (6H, s, CH3OCO), +1.4–1.66 (8H, m,
–CH2CH2–, –CH2CH2–); dC(200 MHz; CD3CN; Me4Si) 186.12,
186.15 (2C, CO), 176.23, 132.11, 131.25, 126.15, 117.25, 116.23,
115.12, 115.29 (Carom), 52.21 (CH2HNB8), 51.56 (H2CH2N–B8),
49.35, 48.58 (2C, CH2NH), 31.59, 30.15, 27.46, 27.38 (4C,
–CH2CH2–), 26.22, 26.13 (2C, CH3); m/z (DCI) 563 (M+, 10%).
Biological studies
All tests were repeated 2–3 times. For each compound, Petri
dishes were seeded with V79 cells (Chinese hamster fibroblasts)
in an F10 essential medium containing 5% fetal calf serum.
Dishes were incubated overnight at 37 ◦C in a humidified
atmosphere containing 5% CO2. The medium was replaced
with a medium containing varying concentrations of the boron
compounds (the solubility of 6 was enhanced using 1N HCl)
and incubated for an additional 16 h at 37 ◦C. When cells were
grown in SPD or SPM, 2 mM aminoguanidine was added as an
inhibitor of serum amine oxidases.26 The medium was removed
from the dishes. The cells were suspended by trypsinization,
counted and seeded out into new dishes at different dilutions.
The numbers of colonies formed after one week were compared
to the numbers of colonies formed in the control without
boron. The medium was removed, washed with PBS, dyed with
GIEMSA for 10–15 minutes and washed again with ethanol.
2g. Yield: (0.73 g, 45%) as a colorless oil; Rf = 0.25; (found:
C, 53.96; H, 7.56; N, 15.65. B8H41C24N6O2 requires C, 54.19;
H, 7.71; N, 15.8%); mmax(KBr disc)/cm−1 3270s (NHCO), 3232s
(NH2/NH), 2525s (BH), 1715s (CO), 1614w (d, NH2/NH),
1337s (BN), 2986m, 2895m, 1515m, 1456m, 1432m, 1155m,
1115s, 745m (d, cof CH2-groups); dH(200 MHz; CD3CN; Me4Si)
+6.45 (2H, bs, HN–), +7.3 (2H, s, HNCO), 6.67–7.89 (8Harom
,
Acknowledgements
m, CH), +4.01 (2H, bs, H2N–B8), +2.89 (2H, t, –H2CHN–B8),
+2.76 (4H, m, H2CNH), +2.65 (2H, m, –H2CH2N–B8), +1.4–
1.65 (8H, m, –CH2CH2–, –CH2CH2–); dC(200 MHz; CD3CN;
Me4Si) 198.12, 198.08, (2C, HNCO), 177.89, 135.12, 133.02,
128.2, 118.1, 117.25, 116.12, 115.85 (Carom), 51.98 (CH2HNB8),
50.58 (H2CH2N–B8), 49.58, 48.47 (2C, CH2NH), 31. 95, 30.51,
28.63, 27.87 (4C, –CH2CH2–); m/z (DCI) 533 (M+, 15%).
The author thanks Professor Detlef Gabel, Department of
Chemistry, University of Bremen, Bremen, Germany, for pro-
viding facilities for recording the NMR and mass spectra.
References
1 B. M. Graybill, A. R. Pitochelli and M. F. Hawthorne, Inorg. Chem.,
1962, 1, 626–631.
4a. Yield: (0.97 g, 37%) as a deep violet crystalline solid;
Rf = 0.28; kmax(CHCl3)/nm 420, 525, 564, 601 and 660 (10−3
e/dm3 mol−1cm−1 370.3, 16.8, 5.4, 5.2, and 2.6); dH(200 MHz;
CDCl3; Me4Si) −2.7 (2H, bs, HN–), +4.15 (2H, bs, H2N–
B8), +4.2 (2H, s, CH2), +7.05–8.25 (19H, m, Harom), 8.68–
8.92 (8H, m, b-pyrrole), +2.82 (2H, t, H2CNH), +2.75 (6H,
m, –H2CNH2), +1.4–1.62 (8H, m, –CH2CH2–, –CH2CH2–);
dC(200 MHz; CDCl3; Me4Si) 149.37, 148.82, 136.92, 135.8,
133.83, 130.82, 128.37, 125.32, 117.8, 115.03, 112.01, 108.75
(Cporphyrin), 51.36 (CH2HNB8), 50.25 (CH2NH2–B8), 47.86 (C,
CH2), 49.19, 48.45 (2C, CH2NH), 47.81, 46.19 (2C, HNCH),
30.18, 28.26, 27.13, 26.12 (4C, –CH2CH2–); m/z (ESI) = 902
(M+, 30%), 630 (M–B8H11NH(CH2)4NH2, 100).
2 R. Lewin, P. G. Simpson and W. N. Lipscomb, J. Chem. Phys., 1963,
39, 1532–1537.
3 U. Do¨rfler, J. D. Kennedy and M. Thornton-Pett, J. Chem. Soc.,
Dalton Trans., 1997, 2547–2550.
4 U. Do¨rfler, D. L. Ormsby, R. Greatrex and J. D. Kennedy, Inorg.
Chim. Acta, 2000, 304, 268–273.
5 U. Do¨rfler, P. A. Salter, X. L. R. Fontaine, N. N. Greenwood, J. D.
Kennedy and M. Thornton-Pett, Collect. Czech. Chem. Commun.,
1999, 64, 947–958.
6 U. Do¨rfler, C. Bauer, D. Gabel, P. N. Rath, L. Barton and D. J.
Kennedy, J. Organomet. Chem., 2000, 614–615, 215–222.
7 C. Bauer, D. Gabel, T. D. McGrath and U. Do¨rfler, Inorg. Chim.
Acta, 2002, 332, 181–185.
8 C. Bauer, D. Gabel, T. Borrmann, J. D. Kennedy, C. A. Kilner, M.
Thornton-Pett and U. Do¨rfler, J. Organomet. Chem., 2002, 657, 205–
216.
4b. Yield: (0.22 g, 39%) as a deep violet crystalline solid;
Rf = 0.25; kmax(CHCl3)/nm 422, 525, 562, 600, and 660 (10−3
e/dm3 mol−1cm−1 370.1, 16.8, 5.2, 5.1, and 2.6); dH(200 MHz;
CDCl3; Me4Si) −2.72 (4H, bs, HN–), +4.1 (2H, bs, H2N–
B8), +4.32 (4H, s, CH2), +6.98–8.35 (38H, m, Harom), 8.38–
9.01 (16H, m, b-pyrrole), +2.92 (2H, t, H2CNH), +2.75 (6H,
m, –H2CNH2), +1.4–1.62 (8H, m, –CH2CH2–, –CH2CH2–
); dC(200 MHz; CDCl3; Me4Si) 149.8, 148.07, 139.22, 137.2,
136.78, 135.8, 135.05, 134.62, 133.72, 131.38, 130.71, 130.32,
129.55, 128.73, 128.3, 127.32, 125.62, 117.32, 116.01, 115.6,
111.43, 108.8 (Cporphyrin), 51.21 (CH2HNB8), 50.14 (CH2NH2–
B8), 49.46 (2C, CH2), 49.18, 48.42 (2C, CH2NH), 47.63, 46.12
(2CH, HNCH), 30.19, 29.26, 28.13, 26.95 (4C, –CH2CH2–); m/z
(ESI) 1531 (M+, 15%), 901 (M-630, 23), 630 (M-901, 100).
9 C. Bauer, U. Do¨rfler and D. Gabel, Eur. J. Med. Chem., 2002, 37,
649–657.
10 M. E. El-Zaria, U. Do¨rfler and D. Gabel, J. Med. Chem., 2002, 45,
5817–5817.
11 G. Oenbrink, P. Ju¨rgenlimke and D. Gabel, Photochem. Photobiol.,
1988, 48, 451–456.
12 D. Gabel, C. Bauer, M. E. El-Zaria, A. R. Genady and U. Do¨rfler,
J. Organomet. Chem., 2003, 680, 23–26.
13 S. B. Kahl and M.-S. Koo, J. Chem. Soc., Chem. Commun., 1990,
1769–1771.
14 V. I. Bregadze, I. B. Sivaev, D. Gabel and D. Wo¨hrle, J. Porphyrins
Phthalocyanines, 2001, 5, 767–781.
15 R. Lauceri, R. Purrello, S. J. Shetty and M. G. H. Vicente, J. Am.
Chem. Soc., 2001, 123, 5835–5836.
16 A. P. Phadke and A. R. Morgan, Tetrahedron Lett., 1993, 34, 1725–
1728.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8
2 1 0 7

View Article Online
17 W. M. Jones, J. Am. Chem. Soc., 1960, 82, 2528–2532.
18 A. D. Pomogailo, V. F. Razumov and I. S. Voloshanovskii, J. Por-
phyrins Phthalocyanines, 2000, 4, 45–64.
19 A. E. Pegg and P. P. McCann, Am. J. Physiol.: Cell Physiol., 1982,
243, C212–C221.
23 N. Seiler, J. G. Delcros and J. P. Moulinoux, Int. J. Biochem. Cell
Biol., 1996, 28, 843–861.
24 B. Martin, F. Posseme, C. Le Barbier, F. Carreaux, B. Carboni, N.
Seiler, J.-P. Moulinoux and J.-G. Delcros, J. Med. Chem., 2001, 44,
3653–3664.
20 C. W. Tabor and H. Tabor, Annu. Rev. Biochem., 1984, 53, 749–790.
21 J. P. Moulinoux, F. Darcel, V. Quemener, R. Havouis and N. Seiler,
Anticancer Res., 1991, 11, 175–180.
22 Y. Li, J. L. Eisenman, D. L. Sentz, F. A. Rogers, S. S. Pan, L. T. Hu,
M. L. Egorin and P. S. Callery, J. Med. Chem., 1996, 39, 339–341.
25 R. J. Bergeron, J. S. McManis, C. Z. Liu, Y. Feng, W. R. Weimar,
G. R. Luchetta, Q. Wu, J. Ortiz-Ocasio, J. R. Vinson, D. Kramer and
C. J. Porter, J. Med. Chem., 1994, 37, 3464–3476.
26 P. A. Shore and V. H. Cohn Jr., Biochem. Pharmacol., 1960, 5,
91–99.
2 1 0 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 2 1 0 2 – 2 1 0 8