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The porphyrin handbook - Kadish K.M.

Kadish K.M. The porphyrin handbook - Academic press, 2000. - 368 p.
Download (direct link): kadishsmishgulilard2000.djvu
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Me---^ vV
-NH N---<

H )= :N HN---
/ ')---
Me'%- 'h i"x)
Me
132

C02phytyl C02Me 133
C. STABLE BACTERIOCHLORINS FROM Rb.
sphaeroides
Chlorins containing anhydride ring systems (e.g., purpurin-18) were
found to be more stable to oxidation than those containing isocyclic ring
systems. With these results in consideration, Pandey and coworkers214
have prepared a series of stable bacteriochlorins 134, 135 and 136
containing anhydride, isoimide and imide ring systems, respectively. In
their approach, Rb. sphaeroides containing bacteriochlorophyll a 132 was
directly (in situ) converted into bacteriopurpurin a 135 in good yield.
Reaction of 134 with various amines produced the corresponding amides
137. Cyclization of the intermediate amides under appro-
184
Pandey and Zheng
Scheme 38. Stable bacteriochlorins from bacteriochlorophyll a.
n-Hexylamine

Rb. sphaeraides (contains bacteriochlorophyll a)
C02C3Hy 137a R = CONH(CH2)6CH3, R1 = COOH 137b R = COOH,
R1 = CONH(CH2)5CH3
DCC
135a X = 0, Y = N(CH2)5CH3 135b X = N(CH2)6CH3, Y = 0
priate reaction conditions afforded the desired bacteriochlorins 135 and
136 with isoimide and imide ring systems, respectively. These compounds
exhibit long-wavelength absorptions in the range of 796-822 nm. The
preliminary in vivo results obtained from these compounds are quite
encouraging (Scheme 38).
VI. Synthetic Bacteriochlorins
Callot et al. 215 have shown that the /?,/? double bonds in porphyrins
are susceptible to cyclopropanation with car-benes. Reaction of H2(TPP)
with a diazoester-derived carbene produces both mono- and di-adducts, 138
and 139, with long-wavelength absorptions at 650 and 720 nm, respectively
(Scheme 39).
Dorough and Miller were the first to show that meso-
tetraphenylbacteriochlorin can be obtained by the catalytic hydrogenation
of meso-tetraphenylchlorin.216 The sole evidence was the similarity of
its optical spectrum with that of bacteriochlorophyll, and its photo-
oxidation to the chlorin with 1,2-naphthoquinone. Seely and Calvin217
reduced Zn(TPP) photochemically with benzoin and obtained a byproduct
that has a tetra-hydro structure on the basis of its dehydrogenation to
the chlorin. Eisner208 prepared octaethyl-bacteriochlorin along with the
corresponding isobacteriochloiin in 30% yield by reducing the adjacent
pyrrole ring with sodium in isoamyl alcohol, a method developed by
Fischer. A 720-nm peak indicated the presence of a pigment of the
"bacterio-" type. A few years later this bacteriochlorin structure was
confirmed by NMR, IR and mass spectra.218
Scheme 39. Formation of stable chlorins and bacteriochlorins from
H2(TPP). Ph
N2CHC02Me
Cul
#
43 / Porphyrins as Photosensitizers in Photodynamic Therapy
185
Scheme 40. Formation of bacteriochlorins and isobacteriochlorins (effect
of metal).
A. Tetrahydrobacteriochlorins
and Isobacteriochlorins
Whitlock et al. developed a new method to synthesize bacteriochlorins and
isobacteriochlorins selectively; it involved diimide reduction of
porphyrins.1X2 Di-imide reduction of metal-free tetraphenyl-chlorin
H2(TPC) afforded tetraphenyl-bacteriochlorin H2(TPBC) 140 in 84% yield,
while reduction of zinc tetraphenyl-chlorin Zn(TPC) produced the Zn(II)
complex of tetraphenyl-isobacteriochlorin 141 in 57% yield (Scheme 40).
It is now accepted that the reduced double bond in chlorins induces a
pathway for the delocalized electrons that "isolates" the diagonal
cross-conjugated pyrrolic double bond, such that reduction of this double
bond is favored due to minimal loss of n energy over the double bond
present in the adjacent. The presence of a metal changes the
delocalization of the electrons, which makes the adjacent pyrrolic ring
more reactive, and diimide reduction produces mainly the corresponding
isobacteriochlorins.
The diimide-reduction approach was later employed by Bonnett et al.
for preparing the m^o-tetra(m-hydroxyphe-nyl)-bacteriochlorin H2(/n-
THPBC).184 In vivo biological assays of tumor response showed that H2(m-
THPBC) was a very active tumor photosensitizer. However, it was
relatively unstable when compared with H2(m-THPC) in vitro. About
25 to 33% of the H2(m-THBPC) within the cells was oxidized to chlorin in
24 hours.219
B. Wc-DIHYDROXYBACTERIOCHLORINS AND
ISOBACTERIOCHLORINS
Chang and Sotiriou189 were the first to show that free-base
octaethlchlorin H2(OEP) 142 or its metalated analogue 143 (without any
electron-withdrawing substituents), upon reaction with 0s04, can be
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