1126 K. SADAOKA ET AL.
reaction temperature was regulated with a Shimadzu
thermo-electric temperature-controlled cell holder TCC-
240A. High-performance liquid chromatography (HPLC)
was performed with a Shimadzu LC-20AT pump, an
SPD-M20A or SPD-20AV detector, and a CTO-20A
column oven. Mass spectra (MS) were measured with a
JEOL JMS700 spectrometer; m-nitorobenzyl alcohol was
used as a matrix. High-resolution mass spectra (HRMS)
were measured with a JEOL GC-mate II spectrometer;
m-nitorobenzyl alcohol and glycerol were used as
(1H, m, 18-H), 4.33–4.28 (1H, m, 17-H), 3.96–3.86 (2H,
m, 8-CH2), 3.58, 3.51, 3.32 (each 3H, s, 2-, 12-, 174-
CH3), 2.65–2.58, 2.56–2.44, 2.30–2.22 (1H + 2H + 1H,
m, 17-CH2CH2), 1.91 (3H, d, J = 6 Hz, 18-CH3), 1.67
(3H, t, J = 7 Hz, 81-CH3). UV-vis (acetone): lmax, nm
659 (relative intensity, 0.26), 606 (0.05), 558 (0.04), 463
(1.00), 437 (0.27). HRMS (FAB): m/z found 626.1555,
calcd. for C33H30N4O5Zn [M]+, 626.1508.
Synthesis of Zn chlorins 2–4. Zn methyl
pyropheophorbide d (Zn 3-formyl-chlorin 2) and Zn
methyl pyropheophorbide a (Zn chlorin 4) were prepared
from Chl a according to previous reports [34, 39, 43,
44]. Zn methyl pyropheophorbide b (Zn 7-formyl-
chlorin 3) was prepared from Chl b [34]. Zn 3-formyl-
chlorin 2. UV-vis (acetone): lmax, nm 680 (relative
intensity, 0.95), 630 (0.12), 586 (0.08), 541 (0.04), 443
(1.00), 390 (0.48). MS (FAB): m/z found 612.4, calcd.
for C33H32N4O4Zn [M]+, 612.2. Zn 7-formyl-chlorin
3. UV-vis (acetone): lmax, nm 637 (relative intensity,
0.30), 587 (0.07), 451 (1.00). MS (FAB): m/z found
624.4, calcd. for C34H32N4O4Zn [M]+, 624.2. Zn chlorin
4. UV-vis (acetone): lmax, nm 655 (relative intensity,
0.69), 607 (0.11), 568 (0.06), 524 (0.04), 425 (1.00), 405
(0.60), 379 (0.37). MS (FAB): m/z found 610.3, calcd. for
C34H34N4O3Zn [M]+, 610.2.
1
matrixes. H NMR spectra were measured with a JEOL
JNM-AL400 NMR spectrometer; chemical shifts were
expressed (in ppm) relative to chloroform (7.26 ppm) as
an internal reference.
Synthesis
Synthesis of diformylated Zn chlorin 1. To a THF
solution (20 mL) of methyl pyropheophorbide b (3, 16.7
mg), which was prepared from Chl b [34, 39], two pieces
of microcapsulated OsO4 [42], which was purchased
from Wako Chemical Industries, Ltd., was added at 0 °C.
A solution of NaIO4 (0.25 g) and CH3COOH (0.32 mL)
in H2O (2.0 mL) was dropped into the ice-chilled THF
solution, and stirred overnight at room temperature.
After extraction of reaction products with CH2Cl2 several
times, the combined organic phases were washed with
NaHCO3-saturated water and distilled water, dried
over anhydrous Na2SO4, and evaporated under reduced
pressure. The residue was purified by flash silica
gel column chromatography and recrystallized from
CH2Cl2 and hexane to give methyl 3-devinyl-3-formyl-
pyropheophorbide b. 3,7-diformyl-chlorin 1′. 8.7 mg,
52% yield. 1H NMR (CDCl3): d, ppm 11.44, 10.95 (each
1H, s, 3-, 7-CHO), 10.38, 9.36, 8.76 (each 1H, s, 5-,
10-, 20-H), 5.33, 5.17 (each 1H, d, J = 20 Hz, 132-H2),
4.57 (1H, dq, J = 2, 7 Hz, 18-H), 4.39 (1H, dt, J = 9, 3
Hz, 17-H), 3.86–3.74 (2H, m, 8-CH2), 3.69, 3.67, 3.63
(each 3H, s, 2-, 12-, 174-CH3), 2.84–2.75, 2.70–2.62,
2.45–2.27 (1H + 1H + 2H, m, 17-CH2CH2), 1.94 (3H,
d, J = 7 Hz, 18-CH3), 1.66 (3H, t, J = 8 Hz, 81-CH3),
-0.60, -2.49 (each 1H, s, NH). UV-vis (acetone): lmax, nm
675 (relative intensity, 0.20), 617 (0.04), 535 (0.08), 449
(1.00), 431 (0.48). HRMS (FAB): m/z found 564.2363,
calcd. for C33H32N4O5 [M]+, 564.2373. Free-base chlorin
1′ (17.7 mg) was dissolved in CH2Cl2 (9 mL) and
Zn(CH3COO)·2H2O-saturated methanol (4 mL) was
added to the CH2Cl2 solution, followed by stirring for 8 h.
The solution was neutralized by aq. 4% NaHCO3, washed
with distilled water several times, dried over anhydrous
Na2SO4, and evaporated under reduced pressure. The
residue was recrystallized from CH2Cl2 and hexane to
afford Zn methyl 3-devinyl-3-formyl-pyropheophorbide
Measurements of demetalation kinetics
A 3.0 mL acetone solution of Zn chlorins 1–4 (Soret
absorbance = 1.0 at the 1-cm pathlength) was mixed with
a 1.0 mL distilled water containing hydrochloric acid.
The proton concentration was calculated by assuming
complete dissociation of hydrochloric acid in a mixture
of acetone and water (3/1, vol/vol), since previous reports
ensured such dissociation at the proton concentration
up to ca. 10-1 M [27, 29]. Demetalation kinetics was
examined by monitoring the absorbances at the Soret
peak positions of Zn chlorins at the proton concentration
of 1.8 × 10-1, 1.2 × 10-1, and 6.0 × 10-2 M for 1–3, as
well as 6.0 × 10-2 M for 4 under the control of reaction
temperature at 25 °C.
Pigment analyses after demetalation reaction
After demetalation reactions, the solution was
neutralized by NaHCO3-saturated water. The reaction
products were extracted with CH2Cl2, washed with
NaCl-saturated water, and dried over anhydrous Na2SO4.
The solution was filtrated and dried with nitrogen gas.
The residue was analyzed by reverse-phase HPLC
column 3C18-EB (4.6 mmf × 150 mm, Nacalai Tesque,
Inc., Kyoto, Japan) with methanol at a flow rate of 0.3
mL.min-1 at 40 °C.
1
b. Zn 3,7-diformyl-chlorin 1. 14.8 mg, 75% yield. H
CONCLUSION
NMR (CDCl3): d, ppm 11.05, 10.70 (each 1H, s, 3-,
7-CHO), 10.04, 9.49, 8.53 (each 1H, s, 5-, 10-, 20-H),
5.01, 4.88 (each 1H, d, J = 20 Hz, 132-H2), 4.51–4.45
This study reveals effects of the formyl groups
conjugated to the A- and B-rings of the chlorin macrocycle
Copyright © 2013 World Scientific Publishing Company
J. Porphyrins Phthalocyanines 2013; 17: 1126–1128