Synthesis of ether- and carbon-linked polycarboranyl porphyrin dimers for cancer therapies

Article abstract of DOI:10.1016/S0022-328X(03)00391-7

Porphyrin dimers bearing multiple carborane cages for potential use as sensitizers in boron neutron capture therapy (BNCT) and photodynamic therapy (PDT) were synthesized from protoporphyrin dimethyl ester and characterized. Diastereomeric ether-linked di

Full text of DOI:10.1016/S0022-328X(03)00391-7

Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
www.elsevier.com/locate/jorganchem
Synthesis of ether- and carbon-linked polycarboranyl porphyrin
dimers for cancer therapies
Meden F. Isaac, Stephen B. Kahl *
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA 94143-0446, USA
Received 6 March 2002; received in revised form 2 May 2003; accepted 5 May 2003
Dedicated with gratitude and admiration to Professor M. Frederick Hawthorne on the occasion of his 75th birthday
Abstract
Porphyrin dimers bearing multiple carborane cages for potential use as sensitizers in boron neutron capture therapy (BNCT) and
photodynamic therapy (PDT) were synthesized from protoporphyrin dimethyl ester and characterized. Diastereomeric ether-linked
dimers bearing four closo carborane cages (40 boron atoms) were found to be unstable to the acidic conditions necessary for
conversion into water-soluble salts. In contrast, the carbonꢀ/carbon-linked dimers bearing six icosahedral carboranes (60 boron
atoms) were stable to acid and could be isolated as water-soluble sodium salts. In vitro and in vivo studies of these novel molecules
are currently under investigation.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Boron neutron capture therapy; Boronated porphyrin; Carborane; Photodynamic therapy; Porphyrin; Porphyrin dimer
1. Introduction
light absorption by the porphyrin chromophore has a
mean free path of B1 mm, i.e. all less than the average
/
Boron neutron capture therapy (BNCT) and photo-
dynamic therapy (PDT) are binary cancer therapies in
which administration of a sensitizing drug is followed by
local application of an activating agent. BNCT involves
the administration of a non-toxic, tumor-seeking boron
compound followed at an appropriate time by applica-
tion of a low-energy neutron beam. This process yields
metastable 11B nuclei that promptly undergo fission,
producing dense, highly cytotoxic trails of ionizing
radiation [1]. PDT is a similar binary therapy in which
light is used to activate a photophore with local
production of cytotoxic singlet oxygen [2]. One of the
distinctive hallmarks of binary therapies for cancer such
as BNCT and PDT is the selectivity afforded by the
treatment; only cells that take up the sensitizer will be
killed when activated. The fission products resulting
from thermal neutron absorption by 10B have mean free
paths of 5 and 9 mm, and the singlet oxygen produced on
cancer cell diameter. Both therapies can employ boron
cluster compounds, in BNCT as a source of boron
atoms and in PDT as determinants of physicochemical
properties leading to selective tumor uptake of the
photosensitizer. An example is a boronated porphyrin
(BOPP) from our laboratory that has undergone Phase
I/II human trials for PDT of glioma and has also been
under consideration for BNCT treatment of glioma
[3,4].
Porphyrins have been widely observed to accumulate
in malignant cells more than in normal cells [2,5].
Photofrin†-II, a semi-purified form of hematopor-
phyrin derivative (HpD) manufactured and marketed
by Axcan Pharma of Canada, is currently in Phase III
clinical trials worldwide for PDT treatment of a variety
of solid tumors. Chemical analyses of Photofrin†-II
showed that it is a complex mixture of monomeric,
dimeric and oligomeric porphyrins linked with ether [6ꢀ
/
9], ester [10] and/or carbonꢀcarbon linkages [11]. The
/
monomeric fraction was found to be inactive in vivo
while the higher molecular weight components contain-
ing dimers and higher oligomers were biologically active
* Corresponding author. Tel.: ꢁ
0688.
E-mail address: sbkahl@itsa.ucsf.edu (S.B. Kahl).
/
1-415-476-4684; fax: ꢁ1-415-476-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00391-7

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
233
[12]. Detailed structural studies of the chemical nature of
Photofrin†-II have revealed that the major tumor-
localizing fraction contains dimers and trimers with
ether linkages connected between the 2- and 4-positions
of hematoporphyrin IX (2) (Fig. 1). Regioisomerically
pure ether-linked porphyrin dimers and trimers have
been synthesized and characterized by several groups
[12ꢀ16]. It has also been observed that ester-linked
/
porphyrin dimers are biologically inactive and found to
be unstable and readily cleaved under both acidic and
basic conditions at ambient temperature [15,16]. How-
ever, work with carbonꢀ/carbon-linked hematopor-
phyrin dimers indicated that the dimer joined at the 4-
position was extremely active as an anticancer agent,
while the dimer linked at the 2-position showed little
activity [17], indicating a strong relationship between
molecular shape and tumor-localizing ability.
Fig. 2. Carboranyl ether-linked porphyrin dimer target compounds.
preparation of regiochemically pure monomers. Since
we had previous success with exhaustive acylation of
glycol porphyrins [18], the most direct and appealing
route was to start with the 2-(vinyl)-4-(hydroxyethyl)-
deuteroporphyrin monomer (7), dimerize to divinyl
dimer (DVD) isomers 10a and 10b (Fig. 3), convert
the vinyl groups into glycols 11a and 11b by osmylation
and finally acylate with carborane acid chloride. This
route seemed the most direct, but as the light sensitivity
of vinyl porphyrins is well established, a second alter-
native was considered. Beginning with acetyl monomer
4, dimerization would give diacetyl dimer 12a and 12b,
followed by reduction of the acetyl carbonyls to 1-
hydroxyethyl groups as in 13a and 13b. Dehydration to
DVDs 10a and 10b would then be followed as with the
first method by osmylation and carborane acylation.
Lastly, a third route would begin by acylating glycol
monomer 8 to provide the carboranyl porphyrin mono-
mer 14 (Fig. 4). Reduction of the 4-acetyl ketone to
monomer 15 and dimerization would then lead to the
desired target compounds, regiochemically pure dimers
1a and 1b (Fig. 2). Only one of these three strategies
proved successful.
These results prompted us to synthesize regiochemi-
cally pure porphyrin dimers connected with both ether
and carbonꢀ/carbon linkages for evaluation as binary
sensitizers. The porphyrin units were linked specifically
at the 4-position of the macrocycle with both the free
porphyrin ring 2-positions and linker-functional group
atoms providing potential templates for attachment of
polyhedral carborane group attachment. Fig. 2 shows
an example of one such target compound, an ether-
linked hematoporphyrin dimer, bearing four covalently
bound o-carborane cages.
2. Results and discussion
2.1. Synthesis of boronated ether-linked dimers
Three basically similar strategies were apparent for
the preparation of boronated ether-linked dimers such
as 1a and 1b (Fig. 2), each relying on the initial
The sequence of monomeric porphyrin compounds
prepared for the first approach is shown in Fig. 1.
Fig. 1. Porphyrin monomers prepared regioselectively in preparation
for ether-linked porphyrin dimers.
Fig. 3. Diastereomeric ether-linked porphyrin dimers.

234
M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
methyl ester (3) was then dehydrated with benzoyl
chloride in DMF to give 4-acetyl-2-vinyl-deuteropor-
phyrin IX dimethyl ester (6) in quantitative yield.
Reduction of the acetyl group of 6 with sodium
borohydride gave monomer 7, the desired precursor to
DVD 10.
Formation of the 4-linked dimer 10 was achieved
using published procedures [13,15,21]. The hydroxyl
group of porphyrin 7 was transformed into its triflate
with trifluoroacetic anhydride and then converted to its
1-bromoethyl derivative with LiBr. The bromo deriva-
tive was not isolated, but immediately condensed with
the same starting alcoholic monomer 7 to obtain the
desired dimer as a mixture of diastereomers 10a and 10b
in 60% total yield. A similar procedure was used
utilizing methanesulfonyl chloride in which the hydroxyl
group of porphyrin 7 was converted into its mesylate,
which was not isolated, but was immediately reacted
with the original monomer 7. The reaction with
trifluoroacetic anhydride gave a slightly better yield
(66%) than the procedure using mesyl chloride and there
were fewer side products making product isolation
easier. Size exclusion chromatography can effectively
separate the dimers from the monomers, but silica gel
column chromatography was used to separate the
diastereomeric dimers (formed in about 1:2 ratio). Due
to the presence of the vinyl groups, dimers 10a and 10b
were extremely light-sensitive compared to vinyl-con-
taining monomers; hence column chromatography was
performed in the dark.
The origin of these dimeric isomers is of particular
note. Mironov and coworkers [22,23] noted a ‘‘remark-
able observation’’ in their preparation of dimer 13 from
2-acetyl-4-(1-hydroxyethyl) monomer 4. When the re-
sulting dimer was subjected to TLC, it was found to
consist of two stable isomers of significantly differing
chromatographic mobilities, melting points, UV spectra
and, presumably, molecular shapes. Similarly, we found
that dimerization of 2-vinyl-4-(1-hydroxyethyl) mono-
mer 7 resulted in a pair of easily separable isomers. The
mechanism through which dimerization proceeds is
probably initiated when the triflate or mesylate leaves
to form a stable 28 carbonium ion at the 1-position of
the ethyl side chain. A molecule of unesterified alcohol
monomer forms the ether linkage by attack at the planar
sp2 site. Since each monomer contains a chiral atom
from the hydroxy ethyl side chain, the resulting dimer is
composed of two pairs of enantiomers, i.e. a pair of
separable diastereomers. Molecular models show that
the potential orientations of the two planar porphyrin
rings in these diastereomers are quite different. One
direction of attack by the alcohol places the two
porphyrins lying approximately parallel to each other.
This results in the 2- and 2?-vinyl groups being oriented
approximately parallel to each other with the porphyrin
A, B, C and D rings similarly oriented in the two halves
Fig. 4. Carboranyl porphyrin monomers.
Commercially available hematoporphyrin IX dihy-
drochloride (Porphyrin Products) was esterified with
diazomethane to give the starting material hematopor-
phyrin IX dimethyl ester (2) in excellent yields (90%).
The usual esterification procedure for hematoporphyrin
dimethyl ester using methanol/trimethylorthoformate/
sulfuric acid gave variable yields [19]. The strongly
acidic conditions caused dehydration of the hydroxyl
group producing protoporphyrin IX, thereby decreasing
the yield of the esterified product and necessitating an
additional purification step. The preparation of regio-
chemically pure dimers requires the synthesis and
separation of the pure monomeric regioisomers 4-
acetyl-2-(1-hydroxyethyl) deuteroporphyrin IX dimethyl
ester (3) and 2-acetyl-4-(1-hydroxyethyl)-deuteropor-
phyrin IX dimethyl ester (4) [14]. Partial oxidation of
the benzylic-like hydroxyl group of 2 was carried out
smoothly using manganese (IV) oxide [19]. This reaction
gave a mixture of products 3, 4 and 5 which was easily
separated by silica gel column chromatography. The use
of N-methylmorpholine oxide (NMO) as the oxidizing
agent with a catalytic amount of tetra-N-propyl ammo-
nium perruthenate (TPAP) has also been reported
previously [14,21]. In our hands, this reaction gave
varying amounts of the two regioisomers. This reaction
is also considerably faster than oxidation with MnO2
but resulted in uncontrolled formation of the partially
oxidized regioisomers. The completely oxidized by-
product 2,4-diacetyldeuteroporphyrin IX dimethyl ester
(5) eluted first from silica gel, then regioisomer 3
followed closely by regioisomer 4. The fully oxidized
product 2,4-diacetyl-deuteroporphyrin IX dimethyl es-
ter (5) can be reduced back to hematoporphyrin
dimethyl ester (2) with sodium borohydride. Controlled
reduction of 5 using an equimolar amount of sodium
borohydride can be utilized to yield regioisomers 3 and
4, but this method failed to give consistent yields. Pure
4-acetyl-2-(1-hydroxyethyl)-deuteroporphyrin IX di-

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
235
of the dimer, i.e. with A ring above A? ring and so forth
in what might be described as an ‘‘eclipsed’’ manner.
There is then a pseudomirror plane between the two
porphyrin ring planes. This structure consists of the R,S
diastereomer. The R,R diastereomer results from attack
from the opposite side of the carbonium ion and
produces a dimer in which the two porphyrins are
anti-parallel. Such an arrangement leaves the D? ring of
the ‘‘upper’’ porphyrin oriented approximately above
the A ring of the ‘‘lower’’ porphyrin and the 2,2?-
pH-insensitive compounds such as AlPcS4 are also
found to be strongly associated with serum albumin,
which may account for their extracellular locus. For
hydrophobic sensitizers, i.e. those of negligible aqueous
solubility, biodistribution data are strongly affected by
the nature of the delivery vehicle and the resulting state
of aggregation of the drug within its lipid environment,
making structure-based generalizations difficult. Am-
phiphilic boronated porphyrins such as BOPP, where
the carborane ‘‘end’’ of the molecule is hydrophobic and
the propionate residues hydrophilic, are the ultimate
targets of the present work.
substituents at a roughly 90ꢀ1208 angle. Since the
/
resulting diastereomers differ significantly in chromato-
graphic mobility and hence in their potential tumor
uptake, we have undertaken a systematic investigation
of their respective structures by 2D ROESY and low-
temperature proton-NMR and by molecular modeling.
The results of this study will appear in a separate paper.
The question of molecular shape and charge distribu-
tion is of more than simple curiosity. Although the
precise details of the structural requirements and
mechanisms responsible for tumor cell localization of
porphyrins are not completely understood, physico-
chemical properties such as molecular shape and hydro-
phobic character are known to play a major role [24]. In
general, amphiphilic sensitizers constitute the most
potent and largest class of PDT agents. These com-
pounds tend to localize intracellularly and reach max-
The second route to boronated ether-linked dimers
utilized the pure regioisomer, 2-acetyl-4-(1-hydro-
xyethyl) deuteroporphyrin IX dimethyl ester (4). This
was reacted with HBr to form the corresponding
brominated product, which was not isolated but was
immediately reacted with an equimolar amount of 4 to
give two chiral isomeric diacetyl dimers 12a and 12b
formed in 1:3 ratio. These diastereomers were easily
separated by silica gel chromatography since there was a
significant difference in their chromatographic mobili-
ties, the isomer 12a being eluted first. Reduction of the
acetyl group on each of the dimers 12a and 12b was
carried out using sodium borohydride to obtain the
dihematoporphyrin ether (DHE) dimers 13a and 13b,
respectively. Conversion of the acetyl groups of 12a and
12b into hydroxyl groups in this manner introduces
another set of stereocenters into the molecule and
imum tumor concentrations in 24ꢀ
/
48
h
after
administration. There is substantial experimental evi-
dence that this class of sensitizers becomes associated
with lipoproteins on administration, particularly low
(LDL)- and high-density lipoproteins (HDL). This
binding is believed to be responsible for the resulting
intracellular uptake, much like a Trojan horse. Allison
1
considerably complicates the H-NMR spectrum, espe-
cially for 13b. Dehydration of the 28 alcohols in 13a and
13b to give the desired DVDs 10a and 10b proved to be
unsuccessful since the ether linkage was readily cleaved
even under the mildest possible dehydration conditions.
The third approach to the desired compounds in-
volved the initial attachment of the boron cages into the
monomeric porphyrin units followed by dimerization.
The vinyl group of porphyrin 6, obtained by dehydra-
tion of 4-acetyl-2-(1-hydroxyethyl)deuteroporphyrin IX
dimethyl ester (3), was readily converted to its glycol
derivative 8 with OsO4 [18]. Esterification with o-
carborane carboxylic acid chloride gave only 20% yield
of the disubstituted product 14 (Fig. 4). Prolonged
reaction time and increased temperature did not im-
prove the yield considerably. Reduction of 14 to 15 with
NaBH4, which would give the precursor to the boro-
nated ether dimers 1a and 1b, produced a variety of
different products that could not be identified. Hence
this scheme proved unsuccessful. It was also observed
that attaching the carborane molecules during the later
stages of the synthetic scheme gave better yields and
purification steps were easier. The boronated pophyrin
products tend to streak on the plate or in the column
and prolonged contact with silica gel resulted in
decomposition. Using neutral alumina for purifying
et al. [25] have clearly demonstrated that LDLꢀpor-
/
phyrin complexes are transported into cells via the LDL
receptor, and we have demonstrated this to be the mode
of BOPP uptake into malignant glioma cells [26].
Typical biodistribution patterns for amphiphilic por-
phyrins also mirror the LDL and HDL receptors
abundance in organs with liver, spleen, kidney, adrenals
and testes showing the highest levels of uptake. Very
polar anionic compounds with high charge/volume
ratios cannot associate with plasma lipoproteins due to
repulsion between negative charges on the phospholi-
pids on the lipoprotein surface and those on the
sensitizer molecule. Polyanionic hydrophilic com-
pounds, such as aluminum phthalocyanine tetrasulfo-
nate (AlPcS4), are freely soluble at physiologic pH and
often show more rapid tumor uptake and clearance than
amphiphilic porphyrins. They also provide good tu-
mor:blood and tumor:normal tissue ratios. There are
questions, however, as to whether these localize in
stromal and vascular tumor tissue constituents or
intracellularly; AlPcS4 is most likely the former while
the mono- and disulfonates the latter. Highly charged,

236
M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
the boronated products did not provide any improve-
ment.
Once the desired dimer precursors were in hand we
were able to proceed to add the carborane cages. Divinyl
dimers 10a and 10b were subjected to dihydroxylation
with osmium tetroxide to give bis-glycol ether dimers
11a and 11b, respectively. Similar to 13a and 13b, the
non-stereoselective introduction of two cis-hydroxyl
substituents creates additional stereocenters in the
molecule; thus, the NMR spectra of bis-glycols 11a
and 11b are very complex. However, as with compounds
11a and 11b, this is not reflected in the appearance of
additional chromatographically separable species. At-
tachment of the carborane cages was accomplished
easily using a procedure [27] previously developed in
our laboratory to give the BOPP ether dimer targets 1a
and 1b. Passing the reaction mixture through a short
silica gel column purified the products 1a and 1b. For
both of the boronated isomers, a minor quantity of
baseline material is always observed during the chro-
matographic separation in the column and on TLC
plates. The IR spectra of 1a and 1b both gave a strong
Fig. 5. Carbonꢀcarbon-linked porphyrin dimers.
/
The regioisomer 2-acetyl-4-(1-hydroxyethyl)deuteropor-
phyrin IX dimethyl ester (4) in dry dichloromethane was
reacted with freshly opened triflic acid to give in 90%
yield the carbonꢀ
/
carbon-linked diacetyl dimer 17, the
structure of which was confirmed by 1H-NMR and mass
spectroscopies. The proposed mechanism for the cou-
pling reaction involves initial protonation of the hy-
droxyl substituent, which is eventually lost as a water
molecule. The porphyrin can form either a vinyl group
through proton elimination or remain a stabilized
carbocation. Dimerization occurs when the vinyl group
acting as a nucleophile attacks the carbonium ion
formed from another molecule. During the course of
the reaction, the stable by-product, 2-acetyl-4-vinyl-
deuteroporphyrin IX dimethyl ester (9) (the dehydrated
form of 4), was observed as a faster-moving band than
dimer 16. This stable vinyl-substituted intermediate 9
can be isolated and, when subjected to the same reaction
absorption at about 2570 cmꢂ1, characteristic of the Bꢀ
/
H stretching frequency of the carborane cage. The mass
spectrum indicated a molecular ion peak at 1948 and the
molecular formula C84H122N8O17B40 was confirmed by
elemental analysis. The boron wt.% in these dimers is
thus in excess of 22%. Comparison of the melting points
of the dimers showed that the dimers 1a, 10a, 11a, 12a
and 13a all melted at a higher temperature than their
corresponding diastereomers.
To ensure efficient transport and biodistribution for
applications in binary cancer therapies, BOPP should be
amphiphilic. In the case of the boronated dimer, water
solubility can be achieved by hydrolysis of the propio-
nate ester groups and then converting their correspond-
ing carboxylic acids into their sodium or potassium
salts. However, the ether linkage of boronated dimers 1a
and 1b did not withstand the conditions for acidic
hydrolysis, and the carborane cage, although stable in
acidic media, decomposes into its open cage form in
basic conditions. Although nido carborane cages are
intrinsically water-soluble, they are also often associated
with significantly increased toxicity. Since our results
showed instability and extreme acid sensitivity of the
ether linkage of the boronated dimer, we turned our
with triflic acid, carbonꢀ
16 was also formed under the same reaction conditions.
Conversion into the carbonꢀcarbon-linked DVD 17 was
/
carbon-linked porphyrin dimer
/
performed easily by sodium borohydride reduction of 16
to the corresponding diol followed by the usual method
of dehydration with benzoyl chloride in dimethylforma-
mide to give 17 in 80% yield. The ‘‘propene’’ dimer
linkage is very stable under these acidic conditions and
no evidence of dimer cleavage was observed. Dimer 17
has three alkene groups that can be transformed into
dihydroxy-substituted functional groups. Indeed, dihy-
droxylation with osmium tetroxide gave the correspond-
ing hexaol 18 (Fig. 6). Despite having five tetrahedral
stereocenters, both 18 and 19 appeared as single spots
upon thin-layer chromatography (TLC). Esterification
of 18 with carboranyl acid chloride using the procedure
attention to BOPP dimers joined by carbonꢀ
/
carbon
bonds.
described above gave the desired carbonꢀ
BOPP dimer 19, which has six carborane cages ap-
pended. The boron wt.% of this dimer is ꢀ28%.
/
carbon-linked
2.2. Synthesis of carbonꢀ/carbon-linked BOPP dimers
/
Subsequent acidic hydrolysis of 19 gave product 20
(Fig. 7), which was found by mass spectral analysis to
contain one less carborane cage, indicating that one of
the ester bonds is acid-labile, presumably one located in
Triflic acid (trifluoromethane sulfonic acid) treatment
of porphyrins has been reported to give carbonꢀcarbon-
linked dimers (Fig. 5) [17]. Such methodology was
utilized in the present work, but the reaction time was
increased to 5 days from the reported time of 30 min.
/
the carbonꢀ
/
carbon linkage. This implies that two

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
237
in vitro and in vivo behavior of this remarkable
compound are currently underway.
3. Conclusions
Porphyrin dimers are potentially useful as boron
delivery agents for BNCT or as photosensitizers in
PDT. We have synthesized a series of ether-linked
diastereomeric porphyrin dimers joined at the 4-posi-
tion, culminating in a diastereomeric pair of boronated
dimers in which four closo carborane cages are ap-
pended. The resulting diastereomers, containing 40
boron atoms, were found to be acid-labile at the ether
link and thus unsuitable for use in binary cancer
Fig. 6. Carbon-linked porphyrin dimers bearing four or six o-
carborane cages.
therapies. In contrast, carbonꢀ
/
carbon-linked dimers
bearing up to six carborane cages (60 boron atoms)
were prepared and found to be acid-stable. Further in
vitro and in vivo investigation of these compounds is
currently in progress.
positional isomers 20a and 20b are formed. The fact that
the dimer is still intact means that the linkage survived
this extremely acidic dehydration condition. Exchanging
the ionizable proton by passing the compound in an ion-
exchange column gave sodium salts 21a and 21b, which
4. Experimental
prove to have surprisingly good solubility in water (ꢀ2
/
mg mlꢂ1). Complete assignment of 1H-NMR spectra of
the hydrolyzed products 20a and 20b and their corre-
sponding salts 21a and 21b is not possible due to the
presence of broad peaks. These are likely results of
positional isomers at the linkage sites brought about by
the hydrolysis reaction, as well as the presence of
multiple stereocenters. Further studies evaluating the
4.1. General
Melting points were measured on Thomas Hoover
capillary melting point apparatus. Electronic absorption
spectra were obtained on a Hewlett-Packard 8452A
spectrophotometer using solutions in dichloromethane.
Routine NMR spectra (1H- and 13C-NMR) were
Fig. 7. Carboranyl porphyrin dimer target compounds.

238
M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
obtained in CDCl3 or DMSO at 300 MHz (GE QE300)
with chemical shifts reported in ppm relative to internal
standards of tetramethylsilane (0 ppm) or chloroform
(7.258 ppm). Reactions were monitored using TLC on
commercially available Eastman-Kodak silica sheets.
Gravity and flash column chromatography employed
4.3. 4-Acetyl-2-vinyldeuteroporphyrin IX dimethyl ester
(6)
4-Acetyl-2-(1-hydroxyethyl)deuteroporphyrin IX di-
methyl ester (3) (400 mg) was dissolved in anhydrous
dimethyl formamide (120 ml) and benzoyl chloride (4.6
ml) was added to the solution. The solution was heated
at 95 8C for 1 h. The mixture was allowed to cool and
then poured into 3% aqueous triethylamine (460 ml).
The purple black precipitate was filtered in a sintered
glass funnel and then washed with water several times.
The product was dissolved with methylene chloride and
the filtrate was dried over sodium sulfate. The solvent
was evaporated to give 390 mg of 6 (98% yield). m.p.:
either Camag Brockman neutral alumina (70ꢀ230-
/
mesh) or Merck silica gel 60. For preparative TLC,
Analtech 1500 m Silica Gel GF was used and for gel
permeation chromatography, Bio-Beads S-X1 (200ꢀ
/
400-mesh) was utilized.
4.2. 4-Acetyl-2-(1-hydroxyethyl)deuteroporphyrin IX
dimethyl ester (3) and 2-acetyl-4-(1-
hydroxyethyl)deuteroporphyrin IX dimethyl ester (4)
190ꢀ
/
191 8C (lit. [21], 160ꢀ163 8C); lmax (nm) (CH2Cl2):
/
412 (o (dm3 molꢂ1 cmꢂ1): 171 000), 510 (12 000), 550
(9900), 580 (6900), 632 (3800); 1H-NMR (CDCl3, d
ppm): 10.72, 10.21, 9.98, 9.96 (4H, s, meso-H), 8.26ꢀ
8.20 (1H, dd, ꢀCH ꢁCH2), 6.44ꢀ6.23 (2H, dd, CHꢁ
CH2), 4.43ꢀ4.32 (4H, each t, CH2CH2CO2Me), 3.85,
3.71, 3.67, 3.55 (18H, each s, ring Me and CO2CH3),
/
Hematoporphyrin IX dimethyl ester (2, 1.00 g)
(obtained by diazomethane esterification of commer-
cially available hematoporphyrin IX) was dissolved in
dichloromethane (400 ml). Manganese (IV) oxide
(MnO2, 3.0 g) was added and the mixture stirred
overnight. The reaction monitored by TLC was stopped
when almost all the starting porphyrin disappeared. The
black precipitate was filtered-off and the solvent re-
moved. The product was purified by silica gel column
chromatography, eluting with 1% MeOH in methylene
chloride. The first band was 2,4-diacetylporphyrin IX
dimethyl ester (5) which was collected and evaporated to
dryness to give 95 mg of 5 (9.5% yield from 2). The
major band contained the desired isomers; each was
separated and crystallized from dichloromethane/hex-
ane. (A) Fast-running band: 4-acetyl-2-(1-hydro-
/
/
/
/
/
3.31 (3H, s, CH3Cꢁ
/
O), 3.27 (4H, t, CH2CH2CO2Me), ꢂ
/
3.64 (2H, br s, NH); m/z: 607.2 (100%, MHꢁ).
4.4. 4-(1-Hydroxyethyl)-2-vinyldeuteroporphyrin IX
dimethyl ester (7)
4-Acetyl-2-vinyldeuteroporphyrin IX dimethyl ester
(6) (300 mg) was dissolved in dry methylene chloride
(100 ml) and the solution was stirred under argon. A
suspension of sodium borohydride (160 mg) in dry
methanol (10 ml) was added to the mixture. The
reaction was monitored by TLC. When the reaction
was complete, pouring the solution into water quenched
excess sodium borohydride. The organic portion was
washed with aqueous solution of sodium bicarbonate
and then twice with water. The organic layer was dried
over sodium sulfate and then concentrated to give 300
xyethyl)deuteroporphyrin IX dimethyl ester (3)*
/320
mg (32% yield from 2); m.p.: 213ꢀ
/
215 8C (lit. [20], 229ꢀ
/
230 8C); lmax (nm) (CH2Cl2): 410 (o (dm3 molꢂ1 cmꢂ1):
172 000), 508 (10 000), 548 (11 000), 578 (7000), 632
(900); 1H-NMR (CDCl3, d ppm): 10.67, 10.02, 9.79,
mg of the reduced product 7 (100% yield). m.p.: 195ꢀ
/
9.77 (4H, s, meso-H), 6.14 (1H, q, ꢀ
4.33ꢀ4.23 (4H, each t, CH2CH2CO2Me), 3.69, 3.68,
3.67, 3.49, 3.40 (18H, each s, ring Me and CO2CH3),
3.30 (4H, t, CH2CH2CO2Me), 3.19 (3H, s, CH3CꢁO),
2.40 (1H, br s, OH), 1.98 (3H, d, CH(OH)CH3), ꢂ4.11
(2H, br s, NH). (B) Slow-moving band: 2-acetyl-4-(1-
hydroxyethyl)deuteroporphyrin IX dimethyl ester (4)*
350 mg (35% yield from 2); m.p.: 240ꢀ242 8C (lit. [20],
/
CH(OH)ꢀ
/
CH3),
196 8C (lit. [21], 164ꢀ166 8C); lmax (nm) (CH2Cl2): 402
/
(o (dm3 molꢂ1 cmꢂ1): 109 000), 502 (8700), 536 (6300),
572 (3800), 626 (2200); 1H-NMR (CDCl3, d ppm):
/
/
10.09, 9.96, 9.90, 9.89 (4H, s, meso-H), 8.24ꢀ
/8.14 (1H,
/
dd, ꢀCH ꢁCH2), 6.35ꢀ6.14 (2H, dd, CHꢁCH2), 6.05
/
/
/
/
(1H, q, CH(OH)CH3), 4.30 (4H, each t,
CH2CH2CO2Me), 3.66, 3.67, 3.61, 3.51, 3.49, 3.35
(18H, each s, ring Me and CO2CH3), 3.23 (4H, t,
CH2CH2CO2Me), 2.11 (1H, br s, CH(OH)CH3), 2.02
/
/
247ꢀ
249 8C); lmax (nm) (CH2Cl2): 410 (o (dm3 molꢂ1
/
cmꢂ1): 175 000), 508 (10 900), 548 (12 000), 578 (7500),
(3H, d, CH(OH)CH3), ꢂ
/
4.08 (2H, br s, NH); m/z:
632 (1600); 1H-NMR (CDCl3, d ppm): 10.62, 10.22,
609.2 (100%, MHꢁ).
9.85 (4H, s, meso-H), 6.40 (1H, q, ꢀ
/
CH(OH)ꢀ
/
CH3),
4.36, 4.27 (4H, each t, CH2CH2CO2Me), 3.72, 3.69,
3.66, 3.57, 3.49, 3.47 (18H, each s, ring Me and
CO2CH3), 3.26 (4H, t, CH2CH2CO2Me), 3.24 (3H, s,
4.5. Bis {1-[2-vinyldeuteroporphyrin IX 13,17-dimethyl
ester-8-yl]ethyl} ether or DVD (10a and 10b)
CH3Cꢁ
/
O), 2.75 (1H, br s, OH), 2.15 (3H, d,
4.06 (2H, br s, NH).
4-(1-Hydroxyethyl)-2-vinyldeuteroporphyrin IX di-
methyl ester (7) (600 mg) was dissolved in trifluoroacetic
CH(OH)CH3), ꢂ
/

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
239
anhydride (180 ml). After stirring the solution under
argon for 15 min, the solvent was evaporated under
vacuum protected from light. The residue was dissolved
in dry dichloromethane (180 ml) after which 600 mg of 7
dissolved in dry dichloromethane (180 ml) was added to
the original mixture. The solution was stirred for 8 h
under argon at room temperature (r.t.), then diluted
with methylene chloride (100 ml) and washed with water
(8 ml) was added and the mixture heated at 75 8C for 1
h. The black precipitate was filtered-off and discarded.
The filtrate was subjected to evaporation under vacuum
and the residue was purified by preparative TLC using
2% methanol in dichloromethane as the solvent. The
major band was the dimer glycol which was collected to
give 75 mg of the product 11a (35% yield). m.p.: ꢁ
/
270 8C; lmax (nm) (CH2Cl2): 402 (o (dm3 molꢂ1 cmꢂ1):
219 000), 502 (19 200), 534 (10 400), 570 (6600), 624
(2ꢃ/). The organic layer was dried over Na2SO4 and the
1
(2200); H-NMR (CDCl3, d ppm): 10.33, 10.08, 10.01,
solvent was removed. The residue was subjected to silica
gel column chromatography in the dark using 2%
tetrahydrofuran (THF) in dichloromethane as the eluent
and increasing to 4% THF in dichloromethane to yield
two fractions in 1:2 mixture (66% total yield). (A) Fast-
9.97 (8H, each s, meso-H), 6.24 (4H, br m,
CH(OH)CH2OH and CH(O)CH3), 4.56, 4.20, 4.05
CH2CH2CO2Me),
ꢀ
/
(4H, m, CH2OH), 4.45 (8H, br t, ꢀ
/
3.67, 3.34 (36H, each s, ring Me and CO2CH3), 2.36
(8H, m, CH2CH2CO2Me), 2.23 (6H, d, CH(O)CH3),
running band, DVD 10a (156 mg; 26% yield)*m.p.:
/
255ꢀ
/
257 8C (decomposed); lmax (nm) (CH2Cl2): 404 (o
2.11 (4H, br s, OH), ꢂ
/
3.67 (4H, br s, NH); m/z: 1268.6
3H2O: C,
(dm3 molꢂ1 cmꢂ1): 230 000), 504 (26 000), 530 (17 000),
572 (10 000), 622 (4600); 1H-NMR (CDCl3, d ppm):
10.19, 10.14, 9.91 (6H, each s, meso-H), 9.80 (2H, br s,
(100%, MHꢁ); Anal. Calc. for C72H82N8O13×
/
65.44; H, 6.71; N, 8.48. Found: C, 65.43; H, 6.57; N,
8.46%.
meso-H), 8.32ꢀ
6.12 (4H, each dd, CHꢁ
CH(O)CH3), 4.48 (8H, br t, CH2CH2CO2Me), 3.93,
3.79, 3.72, 3.64 (30H, each s, ring Me and CO2CH3),
3.34 (8H, m, CH2CH2CO2Me), 2.35ꢀ
/
8.22 (2H, each dd, ꢀ
/
CH ꢁ
/
CH2), 6.38ꢀ
/
The same procedure was followed to give 85 mg of the
product 11b from 200 mg of 10b (40% yield). m.p.:
250 8C (decomposed); lmax (nm) (CH2Cl2): 390 (o (dm3
molꢂ1 cmꢂ1): 195 000), 502 (24 200), 534 (18 500), 570
/
CH2), 6.27ꢀ
/
6.20 (2H, q,
1
/
2.37 (6H, d,
(17 300), 622 (13 300); H-NMR (CDCl3, d ppm): 9.89,
CH(O)CH3), 2.09 (6H, br s, 10-CH3), ꢂ
/
3.67 (4H, br s,
9.78, 9.54, 9.51, 9.35 (8H, each s, meso-H), 6.64ꢀ
/
6.38
NH); m/z: 1199.4 (100%, MHꢁ); Anal. Calc. for
C72H78N8O9: C, 72.08; H, 6.56; N, 9.35. Found: C,
71.84; H, 6.51; N, 9.15%. (B) Slow-moving band, DVD
(4H, br m, ꢀCH(OH)CH2OH and CH(O)CH3), 5.26ꢀ
/
/
4.91 (4H, br m, CH(OH)CH2OH), 4.38 (4H, br t, ꢀ
/
CH2CH2CO2Me), 3.79, 3.67, 3.60, 3.34 (36H, each s,
ring Me and CO2CH3 and 4H, CH2CH2CO2Me), 3.30
10b (320 mg, 40% yield)*
/
m.p.: 127ꢀ130 8C; lmax (nm)
/
(CH2Cl2): 398 (o (dm3 molꢂ1 cmꢂ1): 200 000), 504
(4H, br t, ꢀ
2.49 (4H, m, CH2CH2CO2Me), 2.20 (4H, br s, OH), ꢂ
5.07 (4H, br s, NH); m/z: 1267.7 (100%, MHꢁ); Anal.
3H2O: C, 65.44; H, 6.71; N,
/CH2CH2CO2Me), 2.53 (6H, d, CH(O)CH3),
1
(19 000), 538 (12 000), 576 (6200), 628 (2600); H-NMR
(CDCl3, d ppm): 9.96, 9.63, 9.36 (6H, each s, meso-H),
/
9.81 (2H, br s, meso-H), 8.06ꢀ
CH2), 6.65ꢀ6.59 (2H, q, CH(O)CH3), 6.22ꢀ
each dd, CHꢁCH2), 4.40 (4H, br t, CH2CH2CO2Me),
/
7.96 (2H, each dd, ꢀ
/
CH ꢁ
/
Calc. for C72H82N8O13×
/
/
/
6.03 (4H,
8.48. Found: C, 65.39; H, 6.40; N, 8.52%.
/
3.70, 3.69, 3.49, 3.34 (30H, each s, ring Me and
CO2CH3), 3.40 (4H, br t, CH2CH2CO2Me), 3.24 (4H,
4.7. Bis{1-[2-(1,2-di-o-carboranyl-1-
carboxyethyl)deuteroporphyrin IX 13,17-dimethyl ester-
8-yl]ethyl} ether or ether-linked BOPP (1a and 1b)
overlapping m, CH2CH2CO2Me), 2.52ꢀ
CH(O)CH3), 2.40 (4H, br m, CH2CH2CO2Me), 2.01
(6H, s, 10-CH3), ꢂ4.78 (4H, br s, NH); m/z: 1199.5
(100%, MHꢁ); Anal. Calc. for C72H78N8O9×
2H2O: C,
/2.50 (6H, d,
/
To bis-glycol dimer 11a (70 mg) in dichloromethane
(10 ml) was added carboranyl acid chloride (70 mg). The
solution was stirred for 10 min under argon at r.t.
DMAP (35 mg) was added and stirring was continued
for another hour while the reaction was monitored.
When the starting glycol disappeared as shown by TLC,
the solution was washed twice with water. The residue
after the solvent was removed was redissolved in a small
amount of dichloromethane and then purified by
passing through a short silica gel column using 4%
THF in methylene chloride as the eluent. The faster-
moving band, which was the major component, was
collected to give 38 mg (36% yield) of BOPP ether dimer
/
70.00; H, 6.69; N, 9.07. Found: C, 70.36; H, 6.59; N,
8.92%.
4.6. Bis{1-[2-(1,2-dihydroxyethyl)deuteroporphyrin IX
13,17-dimethyl ester-8-yl]ethyl} ether or bis-glycol dimer
(11a and 11b)
To DVD 10a (200 mg) was added dioxane (60 ml) and
pyridine (18 drops). Argon was bubbled through the
solution for 20 min. A solution of osmium tetroxide (200
mg) in diethyl ether (28 ml) was added to the mixture
and the resulting solution was stirred overnight under
argon atmosphere. The reaction flask was protected
from light by wrapping with aluminum foil. After 16 h
of stirring in the dark, sodium sulfite (800 mg) in water
1a. m.p.: 190ꢀ
molꢂ1 cmꢂ1): 257 000), 504 (24 900), 538 (18 600), 572
(14 000), 628 (7000); IR (in KBr, cmꢂ1): 2607, 2571 (Bꢀ
/
192 8C; lmax (nm) (CH2Cl2): 400 (o (dm3
/
1
H stretch), 1731 (Cꢁ
/
O stretch); H-NMR (CDCl3, d

240
M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
ppm): 10.49, 10.24, 9.95 (6H, each s, meso-H), 9.73 (2H,
v br s, meso-H), 6.37 (2H, m, ꢀCH(O)CH3), 6.34 (4H,
br m, CH2ꢀOCꢁO), 6.13 (2H, br m, CH ꢀOCꢁO), 5.46,
4.99 (4H, br m, ꢀCOOCHꢀCH2ꢀOCO), 4.51 (8H, m, ꢀ
CH2CH2CO2Me), 4.09 (4H, br s, carborane CH), 3.70,
3.59, 3.37 (36H, br s, ring Me and CO2CH3), 2.29 (6H,
d, CH(O)CH3), 2.20 (40 H, v br s, BH), 2.14 and 2.18
NMR (CDCl3, d ppm): 10.84, 10.28, 9.83 (6H, each s,
meso-H), 9.64 (2H, br s, meso-H), 6.25 (2H, q, ꢀ
CH(O)CH3), 4.50 (8H, t, ꢀCH2CH2CO2Me), 4.00,
3.77, 3.69, 3.63 (30H, br s, ring Me and CO2CH3),
3.35 (6H, s, CH3CꢁO), 3.26 (8H, br t, CH2CH2CO2Me),
2.33 (6H, d, CH3CHO), 2.11 (6H, br s, 10-CH3), ꢂ3.54
(4H, br s, NH); 13C-NMR: 199.7 (CH3C ꢁ
O), 173.4
(CH3OC ꢁO), 140.0, 138.9, 138.6, 136.6, 135.7 (aromatic
porphyrin), 101.7, 98.2, 97.2, 95.9 (meso-C), 69.4
(CH(O)CH3), 51.8, 51.7 (CO2CH3), 36.8
(CH2CH2CO2Me), 36.4 (CH3CꢁO), 24.7 (CH3CHO),
/
/
/
/
/
/
/
/
/
/
/
/
/
/
(8H, each m, CH2CH2CO2Me), ꢂ
/
3.68 (4H, br s, NH);
/
m/z: 1949.2 (100%, MHꢁ); Anal. Calc. for
C84H122N8O17B40: C, 51.78; H, 6.31; N, 5.75. Found:
C, 52.15; H, 6.00; N, 6.13%.
/
The same procedure as above was followed to give 65
mg of the product 1b from 70 mg of 11b (62% yield)
except 3% THF in CH2Cl2 was used to elute the product
21.1, 21.7 (CH2CH2CO2Me), 14.5, 11.6, 11.4, 10.5 (ring
Me); m/z: 1231.8 (100%, MHꢁ); Anal. Calc. for
C72H78N8O11: C, 68.23; H, 6.52; N, 8.84. Found: C,
from the silica gel column. m.p.: 165ꢀ
/
168 8C; lmax (nm)
67.81; H, 6.41; N, 8.55%. (B) Slower-moving fraction*
/
(CH2Cl2): 399 (o (dm3 molꢂ1 cmꢂ1): 236 000), 505
(23 000), 540 (19 300), 572 (16 500), 624 (12 100); IR (in
DAD 12b, 60 mg (60% yield); m.p.: 217ꢀ218 8C (lit. [23],
/
265 8C decomposed); lmax (nm) (CH2Cl2): 406 (o (dm3
KBr, cmꢂ1): 2610 (Bꢀ
/
H stretch), 1739 (Cꢁ
/
O stretch);
1H-NMR (CDCl3, d ppm): 10.20, 10.16, 10.09, 9.94,
9.86, 9.85, 9.32, 9.12 (8H, each s, meso-H), 7.58, 7.49
molꢂ1 cmꢂ1): 213 000), 512 (20 100), 536 (19 400), 578
1
(14 000), 636 (6300); H-NMR (CDCl3, d ppm): 10.33,
9.96, 9.07 (6H, each s, meso-H), 9.54 (2H, br s, meso-H),
(2H, br dd, ꢀ
CH(O)CH3), 5.98, 5.45, 5.24 (4H, br m, ꢀ
OCO), 4.39 (8H, m, ꢀCH2CH2CO2Me), 4.07 (4H, br s,
/
COOꢀ
/
CH ꢀ
/
CH2ꢀ
/
OCO), 6.60 (2H, m, ꢀ
/
6.59 (2H, q,
CH2CH2CO2Me), 3.90, 3.71, 3.64, 3.54, 3.47 (30H,
each s, ring Me and CO2CH3), 3.37 (4H, m,
ꢀ
/
CH(O)CH3), 4.33 (4H, t,
ꢀ
/
/
COOꢀCH2ꢀ
/
/
/
carborane CH), 3.73, 3.71, 3.66, 3.55, 3.41 (36H, br s,
CH2CH2CO2Me), 3.22 (6H, s, CH3Cꢁ
CH2CH2CO2Me), 2.52 (6H, d, CH3CHO), 2.39 (4H, m,
CH2CH2CO2Me), 2.04 (6H, br s, 10-CH3), ꢂ4.96 (4H,
br s, NH); 13C-NMR: 199.3 (CH3C ꢁ
O), 173.2
(CH3OC ꢁO), 138.3, 137.1, 136.2 (aromatic porphyrin),
100.8, 97.4, 94.7 (meso-C), 71.2 (CH(O)CH3), 51.7, 51.5
(CO2CH3), 36.6, 35.9 (CH2CH2CO2Me), 33.1 (CH3Cꢁ
/O), 3.18 (4H, m,
ring Me and CO2CH3), 3.28 (8H, m, CH2CH2CO2Me),
2.53 (6H, d, CH(O)CH3), 2.23 (40H, v br s, BH), ꢂ
/
3.99
/
(4H, br s, NH); m/z: 1949.3 (55%, MHꢁ); Anal. Calc.
for C84H122N8O17B40: C, 51.78; H, 6.31; N, 5.75. Found:
C, 52.20; H, 6.52; N, 5.72%.
/
/
/
4.8. Bis{1-[2-acetyldeuteroporphyrin IX 13,17-dimethyl
ester-8-yl]ethyl} ether or diacetyl ether dimer (DAD)
(12a and 12b)
O), 24.2 (CH3CHO), 21.6, 20.8 (CH2CH2CO2Me), 14.4,
11.9, 11.6, 10.2 (ring Me); m/z: 1230.7 (100%, Mꢁ);
Anal. Calc. for C72H78N8O11: C, 70.23; H, 6.38; N, 9.10.
Found: C, 69.96; H, 6.57; N, 9.02%.
2-Acetyl-4-(1-hydroxyethyl)deuteroporphyrin IX di-
methyl ester (4) (100 mg) was dissolved in dry methylene
chloride (80 ml). HBr was bubbled into the solution for
5 min and the solution stirred for another 10 min. The
solvent was evaporated and the residue was dissolved in
dry methylene chloride (80 ml) after which a solution of
100 mg of the starting monomeric alcohol 4 (100 mg) in
dry methylene chloride (20 ml) was added. The resulting
mixture was stirred for 20 min, then diluted with
methylene chloride (100 ml). The solution was washed
with water, then with aqueous sodium bicarbonate, then
again with water. The solution was concentrated and the
dimers were separated from the monomers by using gel
permeation chromatography. The dimeric fraction was
eluted first with dichloromethane followed by the
monomeric fraction. The diastereomeric dimers were
separated by silica gel chromatography eluting with 4%
THF in dichloromethane to give two fractions. (A)
4.9. Bis{1-[2-(1-hydroxyethyl)deuteroporphyrin IX
13,17-dimethyl ester-8-yl]ethyl} ether or DHE dimer
(13a and 13b)
These compounds (13a and 13b) were prepared in
quantitative yield from diacetyl porphyrin dimer 12a
and 12b, respectively, using sodium borohydride as the
reducing agent. The procedure for the preparation of 7
was followed. (A) DHE 13a*
/
m.p.: 289ꢀ291 8C; lmax
/
(nm) (CH2Cl2): 404 (o (dm3 molꢂ1 cmꢂ1): 185 000), 502
1
(20 500), 534 (11 500), 572 (7520), 622 (4700); H-NMR
(CDCl3, d ppm): 10.46, 10.40, 10.16, 9.93 (6H, each s,
meso-H), 9.78 (2H, br s, meso-H), 6.56 (2H, br q, ꢀ
CH(OH)CH3), 6.32 (2H, br q, ꢀCH(O)CH3), 4.47
(8H, t, ꢀCH2CH2CO2Me), 3.71, 3.69, 3.64 (36H, each
/
/
/
s, ring Me and CO2CH3), 3.35 (8H, br t,
CH2CH2CO2Me), 3.16, 2.92 (2H, br s, OH), 2.35 (6H,
Faster-moving fraction*
/
DAD 12a, 20 mg (20% yield);
d, CH(OH)CH3), 2.22 (6H, d, CH(O)CH3), ꢂ
br s, NH); m/z: 1235.6 (100%, Mꢁ); Anal. Calc. for
C72H82N8O11×2H2O: C, 68.01; H, 6.82; N, 8.81. Found:
C, 67.75; H, 6.52; N, 8.59%. (B) DHE 13b*m.p.: 198ꢀ
/
3.72 (4H,
m.p.: 271ꢀ
/
272 8C (lit. [23], 293ꢀ294 8C); lmax (nm)
/
(CH2Cl2): 408 (o (dm3 molꢂ1 cmꢂ1): 242 000), 512
/
(24 500), 548 (23 400), 578 (15 200), 628 (5900); 1H-
/
/

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
241
200 8C; lmax (nm) (CH2Cl2): 396 (o (dm3 molꢂ1 cmꢂ1):
195 000), 502 (18 800), 534 (10 600), 570 (9500), 622
(4500); 1H-NMR (CDCl3, d ppm): 9.94, 9.93, 9.91, 9.86,
9.68, 9.43, 9.31 (8H, each s, meso-H), 6.62, 6.58 (2H, br
organic layer was washed several times with water and
then dried over sodium sulfate. After evaporation, the
residue was treated with diazomethane. The product was
purified on a short pad of silica gel eluting with
chloroform to remove monomeric fraction and then
the eluting solvent was changed to 2% MeOH/CHCl3 to
elute the second band which is the dimeric fraction to
q, ꢀ
/
CH(OH)CH3), 6.07, 5.93 (2H, br q, ꢀ
/
CH(O)CH3),
CH2CH2CO2Me), 3.73, 3.69, 3.50 (36H,
4.40 (8H, t, ꢀ
/
each s, ring Me and CO2CH3), 3.27 (8H, br t,
CH2CH2CO2Me), 2.94 (2H, br s, OH), 2.48 (6H, d,
yield 350 mg of 16 (88% yield). m.p.: 240ꢀ242 8C; lmax
/
CH(OH)CH3), 2.22 (6H, d, CHꢀ
4.90, ꢂ4.98 (4H, each br s, NH); m/z: 1235.7 (100%,
2H2O: C, 68.01;
/
Oꢀ
/
CH3), ꢂ
/
4.80, ꢂ
/
(nm) (CH2Cl2): 410 (o (dm3 molꢂ1 cmꢂ1): 297 000), 512
(27 100), 548 (20 800), 578 (17 400), 636 (5000); 1H-
NMR (CDCl3, d ppm): 11.03, 10.82, 10.68, 10.22, 10.10,
/
MHꢁ); Anal. Calc. for C72H82N8O11×
/
H, 6.82; N, 8.81. Found: C, 68.38; H, 6.54; N, 8.62%.
10.07, 10.04, 9.90 (8H, each s, meso-H), 8.43 (1H, d, ꢀ
CH ꢁCHꢀCH), 8.00 (1H, dd, ꢀCHꢁCH ꢀCH), 5.99
(1H, br m, ꢀCHꢁCHꢀCH), 4.49, 4.31, 4.23, 4.09 (8H,
t, ꢀCH2CH2CO2Me), 4.05, 3.94, 3.86, 3.76, 3.71, 3.64,
3.61, 3.55, 3.53, 3.38, 3.36 (36H, each s, ring Me and
CO2CH3), 3.28 (6H, s, CH3CꢁO), 3.31, 3.23, 3.12, 3.03
(8H, br t, CH2CH2CO2Me), 2.72 (3H, d, CHꢁCHꢀ
3.61 (4H, br s, NH); m/z: 1213.6
/
/
/
/
/
/
4.10. 4-Acetyl-2-(1,2-dihydroxyethyl)deuteroporphyrin
/
/
/
IX dimethyl ester (8)
/
This compound was prepared from 6 similar to the
preparation of 1 in 30% yield with osmium tetroxide as
/
/
/
the hydroxylating agent. m.p.: 210ꢀ
/
211 8C; lmax (nm)
CHCH3), ꢂ
/
3.42, ꢂ
/
(CH2Cl2): 410 (o (dm3 molꢂ1 cmꢂ1): 141 000), 508
(9400), 546 (8300), 576 (5700), 634 (1600); 1H-NMR
(CDCl3, d ppm): 10.52, 9.68, 9.52, 8.98 (4H, each s,
(100%, MHꢁ); Anal. Calc. for C72H76N8O10: C, 71.25;
H, 6.32; N, 9.24. Found: C, 70.80; H, 6.39; N, 8.86%.
meso-H), 5.08 (1H, br t, ꢀ
each t, ꢀCH2CH2CO2Me), 3.68, 3.59, 3.42, 3.15, 2.97,
2.82 (18H, each s, ring Me and CO2CH3), 3.76 (2H, br d,
/
CH(OH)CH2OH), 4.47 (4H,
4.13. 2-Acetyl-4-vinyldeuteroporphyrin IX dimethyl ester
(9)
/
CH(OH)CH2OH),
CH2CH2CO2Me), 2.25, 2.10 (2H, br s, OH), ꢂ
(2H, br s, NH); m/z: 641.2 (100%, MHꢁ).
3.20
(4H,
overlapping
t,
4.62
This is the monomeric fraction isolated upon forma-
/
tion of the above CCD 16. m.p.: 250ꢀ252 8C (lit. [21],
/
256ꢀ
258 8C); lmax (nm) (CH2Cl2): 414 (o (dm3 molꢂ1
/
cmꢂ1): 140 000), 512 (13 000), 550 (12 000), 582 (7000),
4.11. 4-Acetyl-2-(1,2-dicarboranyl)deuteroporphyrin IX
dimethyl ester (14)
634 (3500); 1H-NMR (CDCl3, d ppm): 10.82, 10.08,
9.96 (4H, each s, meso-H), 8.32ꢀ
CH2), 6.46ꢀ6.22 (2H, dd, CHꢁCH2), 4.45ꢀ
each t, CH2CH2CO2Me), 3.87, 3.75, 3.67, 3.54 (18H,
each s, ring Me and CO2CH3), 3.31 (3H, s, CH3CꢁO),
3.65 (2H, br s, NH); m/
/
8.22 (1H, dd, CH ꢁ
/
/
/
/
4.28 (4H,
This product was prepared from 8 similar to the
preparation of 1 in 30% yield. m.p.: 165ꢀ
/
167 8C; lmax
/
(nm) (CH2Cl2): 410 (o (dm3 molꢂ1 cmꢂ1): 141 000), 508
(9400), 546 (8300), 576 (5700), 634 (1600); 1H-NMR
(CDCl3, d ppm): 10.81, 10.33, 10.09, 10.04 (4H, each s,
3.25 (4H, t, CH2CH2CO2Me), ꢂ
/
z: 607.3 (100%, MHꢁ); Anal. Calc. for C36H38N4O5: C,
71.27; H, 6.31; N, 9.23. Found: C, 70.78; H, 6.42; N,
9.13%.
meso-H), 7.65 (1H, t, ꢀ
d, ꢀCH(O)CH2ꢀOꢀ), 4.35 (4H, t, CH2CH2CO2Me),
4.18, 4.12 (2H, each br s, carborane CꢀH), 3.99, 3.79,
3.64, 3.37 (18H, each s, ring Me and CO2CH3), 3.27
(3H, s, CH3CꢁO), 3.20 (4H, overlapping t,
CH2CH2CO2Me), 2.63 (20H, br, BH), ꢂ3.48 (2H, br
s, NH); m/z: 981.6 (100%, MHꢁ).
/
CH(O)CH2Oꢀ/), 5.78, 5.01 (2H,
/
/
/
/
4.14. Bis[1-(2-vinyldeuteroporphyrin IX 13,17-dimethyl
ester-8-yl)]-3-methylpropene or carbonꢀ
/
carbon-linked
/
divinyl dimer (CCDV) (17)
/
To a solution of CCD 16 (300 mg) in dry methylene
chloride (80 ml) was added sodium borohydride (300
mg) and dry methanol (10 ml). The solution was stirred
at r.t. under argon atmosphere and the progress of the
reaction monitored by TLC. When only one slow-
moving spot was observed, the reaction was quenched
by pouring the solution into water. The organic layer
was washed twice with aqueous sodium bicarbonate,
dried over sodium sulfate, solvent removed and the
residue dissolved in anhydrous dimethyl formamide (90
ml). Benzoyl chloride (3.6 ml) was added and the
mixture was heated at 95 8C for 1 h under argon
atmosphere. After the solution was allowed to cool, it
4.12. Bis[1-(2-acetyldeuteroporphyrin IX 13,17-dimethyl
ester-8-yl)]-3-methylpropene or carbonꢀcarbon-linked
diacetyl dimer (CCD) (16)
/
2-Acetyl-4-vinyldeuteroporphyrin IX dimethyl ester
(4) (400 mg) was dissolved in dry methylene chloride (40
ml). Argon was bubbled through the solution and triflic
acid (4 ml) was added. The green-colored mixture was
stirred for 5 days. The solution was neutralized slowly
with aqueous solution of sodium bicarbonate and the
product was extracted with methylene chloride. The

242
M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ243
/
was poured into a cold solution of 3% aqueous
triethylamine (400 ml). The precipitate was filtered-off
and it was purified in a short pad of silica gel to obtain
230 mg of the product 17 (80% yield). In some instances
when precipitation of the product did not occur, it was
extracted with dichloromethane from the aqueous solu-
br s, NH); m/z: 1283.7 (100%, MHꢁ); Anal. Calc. for
C72H82N8O14: C, 67.36; H, 6.44; N, 8.73. Found: C,
67.64; H, 6.24; N, 8.87%.
4.16. Bis{1-[2-(1,2-di-o-carboranyl-1-carboxyethyl)-
deuteroporphyrin IX 13,17-dimethyl ester-8-yl]}-1,2-di-
(o-carboranyl-1-carboxyl)-3-methylpropane or
tion. m.p.: ꢁ
270 8C; lmax (nm) (CH2Cl2): 408 (o (dm3
/
molꢂ1 cmꢂ1): 244 000), 504 (25 800), 540 (20 500), 576
1
(12 100), 636 (4350); H-NMR (CDCl3, d ppm): 10.77,
10.84, 10.22, 10.20, 10.18, 10.10, 9.98 (8H, each s, meso-
boronated carbonꢀ
/
carbon-linked dimer (CCDB) (19)
The above porphyrin 18 was treated with carborane
acid chloride following the procedure described for the
preparation of 1 except that after stirring overnight, the
reaction mixture was washed with H2O, then with 0.1 M
HCl and then twice with aqueous sodium bicarbonate.
The residue was observed to contain unidentified boron-
containing by-products which were detected when a
TLC plate spotted with the sample was exposed to an
acidic solution of PdCl2. The fast-running BOPP was
isolated using alumina column chromatography eluting
with chloroform. The product obtained in 25% yield,
however, was found to decompose on the column if
allowed to remain longer and if a less-polar solvent such
H), 8.54ꢀ
each dd, ꢀ
CH), 6.46, 6.17 (4H, each dd, ꢀ
/
8.49 (1H, d, ꢀ
/
CH ꢁ
7.91 (1H, dd, ꢀ
CHꢁCH2), 5.99 (1H, br
/
CHꢀ
/
CH), 8.38, 8.26 (2H,
/
CH ꢁCH2), 7.97ꢀ
/
/
/
CHꢁCH ꢀ
/
/
/
/
m, ꢀ
/
CHꢁ
/
CHꢀ
/
CH), 4.46, 4.38, 4.26, 4.19 (8H, each t, ꢀ
/
CH2CH2CO2Me), 4.01, 3.66, 3.63, 3.58, 3.53, 3.44 (36H,
each s, ring Me and CO2CH3), 3.32, 3.25, 3.08, 3.01 (8H,
each t, CH2CH2CO2Me), 2.70 (3H, d, CHꢁ
CHCH3), ꢂ3.54, ꢂ3.73 (4H, br s, NH); m/z: 1181.5
(100%, MHꢁ), 591.2 (28%); Anal. Calc. for
3H2O: C, 70.00; H, 6.69; N, 9.07. Found:
/
CHꢀ
/
/
/
C72H76N8O8×
/
C, 70.39; H, 6.46; N, 8.67%.
4.15. Bis{1-[2-(1,2-dihydroxyethyl)deuteroporphyrin IX
13,17-dimethyl ester-8-yl]}-1,2-dihydroxy-3-
as dichloromethane was used. m.p.: 147ꢀ150 8C; lmax
/
(nm) (CH2Cl2): 386 (o (dm3 molꢂ1 cmꢂ1): 228 000), 506
(16 900), 538 (14 200), 570 (13 200), 624 (6000); IR (KBr,
methylpropane or Trisꢀ
dimer (18)
/
glycol carbonꢀ/carbon-linked
cmꢂ1): 2608, 2580 (Bꢀ
/
H stretch), 1740 (Cꢁ
1H-NMR (DMSO, d ppm): 10.24, 10.20, 10.15, 10.09,
10.01 (8H, each b s, meso-H), 6.40 (4H, br m, ꢀ
CH(O)CH2Oꢀ and CH(O)ꢀCH(O)ꢀCHMe), 6.30
(4H, br m, ꢀ CH(Me)CHꢀ
/
O stretch);
To CCDV 17 (350 mg) was added of dioxane (75 ml)
and pyridine (12 drops). Ar was bubbled into the
solution for 20 min. A solution of osmium tetroxide
(500 mg) in diethyl ether (30 ml) was added to the
previous mixture and then the resulting solution was
stirred overnight under argon atmosphere. The reaction
flask was protected from light by wrapping with
aluminum foil. After 16 h of stirring in the dark, sodium
sulfite (1.0 g) in water (15 ml) was added to the mixture
and then heated at 75 8C for 1 h. The black precipitate
was filtered-off and then discarded. The filtrate was
subjected to evaporation under vacuum and the residue
was passed through a short silica gel pad washing with
chloroform and a small amount of THF. The solvent
was evaporated and the residue was again purified by
preparative TLC using 10% methanol in dichloro-
methane as the solvent. The major band was the dimer
/
/
/
/
/
CH2OH), 5.00 (1H, br m, ꢀ
/
/
O), 4.31 (8H, m, CH2CH2CO2Me), 4.10 (6H, br s,
carborane CH), 3.65, 3.36 (36H, br s, ring Me and
CO2CH3), 2.97 (3H, s, CH(O)ꢀ
br s, ꢀBꢀH), 2.31 (8H, each m, CH2CH2CO2Me), ꢂ
4.02 (4H, br s, NH); m/z: 2304.8 (30%, Mꢁ), 679.4
(100%); Anal. Calc. for C90H142N8O20B60×4H2O: C,
/
CHꢀ
/
CH3), 2.32 (60H, v
/
/
/
/
45.47; H, 6.56; N, 4.71. Found: C, 44.15; H, 6.47; N,
4.59%.
4.17. Bis{1-[2-(1,2-di-o-carboranyl-1-
carboxyethyl)deuteroporphyrin IX 13,17-dicarboxylic
acid-8-yl]}-1,2-di-(o-carboranyl-1-carboxyl)-2-hydroxy-
3-methylpropane (20)
Trisꢀ
/
glycol which was collected to give 120 mg of the
The above porphyrin 19 was hydrolyzed by dissolving
the compound (33 mg) in reagent grade anhydrous
diethyl ether (12 ml) followed by adding 25% aqueous
HCl (12 ml). The mixture was stirred overnight. Addi-
tional 25% aqueous HCl (25 ml) was added and the
resulting reaction was monitored by TLC in 20% MeOH
in methylene chloride. When the reaction was observed
to be complete, ether (50 ml) was added and the solution
product 18 (35% yield). m.p.: 217ꢀ219 8C; lmax (nm)
/
(CH2Cl2): 392 (o (dm3 molꢂ1 cmꢂ1): 205 000), 502
1
(19 000), 536 (10 900), 572 (8200), 622 (3600); H-NMR
(CDCl3, d ppm): 10.52, 10.46, 10.28, 10.19, 10.01 (8H,
each s, meso-H), 6.38ꢀ
CH(OH)CH2OH and CH(OH)CH(OH)ꢀ
(4H, br m, ꢀCH2OH), 5.54 (1H, br m, ꢀ
OH), 5.20 (6H, br s, OH), 4.34 (8H, br t,
CH2CH2CO2Me), 3.68, 3.59, 3.47, 3.38 (36H, each s,
ring Me and CO2CH3), 2.94 (3H, br s, ꢀCH(OH)ꢀCHꢀ
CH3), 2.31 (8H, each m, CH2CH2CO2Me), ꢂ4.24 (4H,
/
6.15 (4H, br m,
CHMe), 6.20
CH(Me)CH-
ꢀ
/
/
/
/
ꢀ
/
was washed with H2O (3ꢃ
evaporated to obtain 10 mg of the hydrolyzed free acid
product 20a and 20b (35% yield). m.p.: 190ꢀ193 8C; IR
(KBr, cmꢂ1): 3444 (Oꢀ
H stretch), 2585 (BꢀH stretch),
/
). The ether extract was then
/
/
/
/
/
/
/

M.F. Isaac, S.B. Kahl / Journal of Organometallic Chemistry 680 (2003) 232ꢀ
/243
243
[3] J.S. Hill, S.B. Kahl, S.S. Stylli, Y. Nakamura, M.-S. Koo, A.H.
Kaye, Proc. Natl. Acad. Sci. USA 92 (1995) 12126.
[4] M.A. Rosenthal, B. Kavar, J.S. Hill, D.J. Morgan, R.L. Nation,
M. Daniel, G. Varigos, M. Searle, S.S. Stylli, R.L. Basser, S.
Uren, H. Geldard, M.D. Green, S.B. Kahl, A.H. Kaye, J. Clin.
Oncol. 19 (2001) 519.
1730 (Cꢁ
10.10 (8H, br s, meso-H and 4H, COOH), 7.5ꢀ
br m, CH(O)ꢀCH2ꢀOꢀ CH(O)ꢀCH(O)ꢀCHMe),
4.44, 4.43, 4.16 (8H, br m, CH2CH2CO2H), 3.66, 3.55
(24H, each v br s, ring Me), 2.28 (50H, v br s, BꢀH and
CH2CH2CO2H), ꢂ4.00 (4H, br s, NH); m/z: 2079.8
(MHꢁ).
/
O stretch); 1H-NMR (DMSO, d ppm): 10.50ꢀ
6.5 (9H,
/
/
/
/
/
,
/
/
/
[5] M.D. Daniell, J.S. Hill, Aust. NZ J. Surg. 61 (1991) 340.
[6] R.K. Pandey, T.J. Dougherty, K.M. Smith, Tetrahedron Lett. 29
(1988) 4657.
/
[7] I.K. Morris, A.D. Ward, Tetrahedron Lett. 29 (1988) 2501.
[8] P.A. Scourides, R.M. Bohmer, A.H. Kaye, G. Morstyn, Cancer
Res. 47 (1987) 3439.
4.18. Bis{1-[2-(1,2-di-o-carboranyl-1-carboxyethyl)-
deuteroporphyrin IX 13,17-dicarboxy-8-yl]}-1,2-di-(o-
carboranyl-1-carboxyl)-2-hydroxy-3-methyl-propane
tetrasodium salt (21)
[9] Y.-K. Ho, R.K. Pandey, J.R. Missert, T.J. Dougherty, Photo-
chem. Photobiol. 52 (1990) 1085.
[10] R.K. Pandey, T.J. Dougherty, Cancer Res. 49 (1989) 2042.
[11] C.J. Byrne, A.D. Ward, Tetrahedron Lett. 30 (1989) 6211.
[12] R.K. Pandey, F.-Y. Shiau, T.J. Dougherty, K.M. Smith, Tetra-
hedron 47 (1991) 9571.
Diacid 20 (10 mg) was dissolved in 80% acetone in
water and was passed through a Dowex 50X2-400 ion-
exchange resin (Aldrich). The eluate was passed through
the ion exchanger again eluting with 50% acetone in
water, and then once again through the resin with water.
Acetone was removed and the product was lyophilized.
The boronated dimer obtained in 95% yield was soluble
in water: 2 mg mlꢂ1. m.p.: 230 8C (decomposed); lmax
(nm) (DMSO): 398 (o (dm3 molꢂ1 cmꢂ1): 185 000), 502
(29 400), 534 (22 100), 564 (18 500), 620 (16 100); IR
[13] R.K. Pandey, F.-Y. Shiau, C.J. Medforth, T.J. Dougherty, K.M.
Smith, Tetrahedron Lett. 31 (1990) 7399.
[14] F.-Y. Shiau, R.K. Pandey, S. Ramaprasad, T.J. Dougherty, K.M.
Smith, J. Org. Chem. 55 (1990) 2190.
[15] C.J. Byrne, A.D. Ward, Aust. J. Chem. 44 (1991) 411.
[16] C.J. Byrne, I.K. Morris, A.D. Ward, Aust. J. Chem. 43 (1990)
1889.
[17] R.K. Pandey, F.-Y. Shiau, C.J. Medforth, T.J. Dougherty, K.M.
Smith, Tetrahedron Lett. 31 (1990) 789.
[18] S.B. Kahl, J.J. Schaeck, M.-S. Koo, J. Org. Chem. 62 (1997) 1875.
[19] C.J. Byrne, A.D. Ward, Tetrahedron Lett. 29 (1988) 1421.
[20] P.S. Clezy, T.T. Hai, R.W. Henderson, L. Van Thuc, Aust. J.
Chem. 33 (1980) 585.
(KBr, cmꢂ1): 2580 (Bꢀ
/
H stretch), 1709, 1653 (Cꢁ
/O
stretch).
[21] R.K. Pandey, K.M. Smith, T.J. Dougherty, J. Med. Chem. 33
(1990) 2032.
Acknowledgements
[22] A.S. Brandis, A.N. Kozyrev, A.F. Mironov, Tetrahedron 48
(1992) 6485.
We gratefully acknowledge the support of this work
by the United States National Institutes of Health
National Cancer Institute in the form of grant CA82478.
[23] A.F. Mironov, A.N. Nizhnik, I.V. Deruzhenko, Tetrahedron
Lett. 31 (1990) 6409.
[24] R.W. Boyle, D. Dolphin, Photochem. Photobiol. 64 (1996) 469.
[25] B.A. Allison, P.H. Pritchard, J.G. Levy, Br. J. Cancer 69 (1994)
833.
[26] D.E. Callahan, T.M. Forte, S.M.J. Afzal, D.F. Deen, S.B. Kahl,
K.A. Bjornstad, W.L. Bauer, E.A. Blakely, Int. J. Radiat. Oncol.
Biol. Phys. 45 (1999) 761.
References
[1] M.F. Hawthorne, Angew. Chem. Int. Ed. Engl. 32 (1993) 950.
[2] T.F. Dougherty, Crit. Rev. Oncol. Hematol. 2 (1984) 83.
[27] S.B. Kahl, M.-S. Koo, J. Chem. Soc. Chem. Commun. (1990)
1769.