Chemistry Reference
In-Depth Information
Porphyrin
33
containing three
ortho
-carboranes and a poly(ethylene glycol)
group was synthesized in low yields by conjugation of the corresponding tri
(carboranyl)porphyrin bearing a free amino group with a poly(ethylene glycol)
monomethyl ether (MeOPEG550) chloroformate [
78
]. A higher yield was recently
achieved for the synthesis of pegylated porphyrin
34
of larger boron content, via
conjugation of a low molecular weight tri-PEG group to a
meso
-tetraarylporphyrin
bearing six Co(III)-bis(dicarbollides) [
60
]. The precursor porphyrin was prepared by
a mixed condensation of 3,5-dimethoxybenzaldehyde and methyl 4-formylbenzoate
with pyrrole using Lindsey's method, followed by deprotection of the methoxy
and ester groups with BBr
3
in 10% overall yield. The resulting free carboxylic
acid group was conjugated to glycine
tert
-butyl ester followed by functionalization
of the six hydroxyl groups with zwiterionic [3,3
0
-Co(8-C
4
H
8
O
2
-1,2-C
2
B
9
H
10
)
(1
0
,2
0
-C
2
B
9
H
11
)] and deprotection using TFA in 65% yield (three steps). Porphyrin
34
was obtained by conjugation of the PEG
tert
-butyl ester using HATU/HOBt/
DIEA and deprotection with TFA in 19% overall yield.
Recently, boronated porphyrin
35
bearing a tri-PEGwas prepared in higher yields
using an alternative conjugation procedure, involving nucleophilic substitution of
