Chemistry Reference
In-Depth Information
4
7
He +
Li + 2.79 MeV (6%)
3
2
10
5
11
5
B
B+n
7
4
Li +
g
+ 0.48 MeV + 2.31 MeV (94%)
He +
2
3
Fig. 1
The
10
B(n,
)
7
Li neutron capture and fission reactions
ʱ
Fig. 2
Boron delivery agents in BNCT clinical trials
ortho
-,
meta
-, and
para
-C
2
B
10
H
12
, the anionic
closo
-carborane CB
11
H
12
and the
open-cage
nido
-C
2
B
9
H
12
(obtained from base-induced deboronation of
ortho
-
carborane), and the bis(dicarbollide) [3,3
0
-Co(1,2-C
2
B
9
H
11
)
2
]
, have been the clusters
of choice for attachment to porphyrin macrocycles because of their high boron
content, amphiphilic properties, and their high photochemical, kinetic, and hydro-
lytic stabilities. In this chapter we review the synthesis of carboranyl-containing
porphyrins and derivatives that have been reported for application in BNCT, with
particular emphasis on the macrocycles reported in the last decade.
2 Synthetic Strategies and Early Reported Macrocycles
The synthesis of porphyrins
3
and
4
, among other
meso
-tetracarboranylporphyrins,
were first carried out in 1978 by Haushalter and Rudolph [
17
,
18
]. Porphyrin
3
was
prepared in 11% yield by Rothemund condensation of pyrrole with 1-methyl-2-
methylformyl-
ortho
-carborane, and porphyrin
4
was obtained from the reaction of
pre-formed
meso
-tetra(4-aminophenyl)porphyrin with the corresponding
ortho
-
methylcarborane acid chloride. The
closo
-carboranylporphyrins
3
and
4
were
subsequently converted into their corresponding
nido
-carborane derivatives by
base-induced removal of a boron atom from each
ortho
-carborane cage, using a
mixture of pyridine and piperidine. About a decade later several groups reported the
synthesis of carboranylporphyrins for application as boron delivery agents for
BNCT [
19
-
24
]. These macrocycles were obtained from commercially available
protoporphyrin-IX or hematoporphyrin-IX precursors, via functionalization of the
vinyl, hydroxyethyl or the propionic side chains, producing VCDP (
5
)[
21
],
6
[
22
,
23
],
