Synthesis of 3/8-carbonylated chlorophyll derivatives and regiodependent reductivity of their carbonyl substituents

Article abstract of DOI:10.1016/j.tet.2008.04.025

Methyl pyropheophorbide-d possessing a formyl group at the 3-position and its regioisomer having 8-CHO were prepared and their reactivities with a reductant were determined by the ¹H NMR technique: 3-CHO>8-CHO. The regioselective reduction of a synthetic 3,8-diformyl-chlorin also supported the higher reactivity in 3-CHO than in 8-CHO. Regiodependent reduction of the corresponding acetyl-chlorins confirmed that carbonyl groups at the 3-position in chlorophyllous pigments were reduced more rapidly than those at the 8-position. From the reports that reactions of 3-CHO with amines were preferable to those of 7-CHO, the C{double bond, long}O functional groups on the pyrrole A-ring of chlorophylls are more reactive than those on the B-ring.

Full text of DOI:10.1016/j.tet.2008.04.025

Tetrahedron 64 (2008) 5721–5727
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Tetrahedron
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Synthesis of 3/8-carbonylated chlorophyll derivatives and regiodependent
reductivity of their carbonyl substituents
*
Hitoshi Tamiaki , Kazunori Hamada, Michio Kunieda
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Methyl pyropheophorbide-d possessing a formyl group at the 3-position and its regioisomer having
8-CHO were prepared and their reactivities with a reductant were determined by the 1H NMR technique:
3-CHO>8-CHO. The regioselective reduction of a synthetic 3,8-diformyl-chlorin also supported the
higher reactivity in 3-CHO than in 8-CHO. Regiodependent reduction of the corresponding acetyl-
chlorins confirmed that carbonyl groups at the 3-position in chlorophyllous pigments were reduced
more rapidly than those at the 8-position. From the reports that reactions of 3-CHO with amines were
preferable to those of 7-CHO, the C]O functional groups on the pyrrole A-ring of chlorophylls are more
reactive than those on the B-ring.
Received 26 February 2008
Received in revised form 4 April 2008
Accepted 7 April 2008
Available online 10 April 2008
Keywords:
Chlorophyll
Pyropheophorbide
Reduction
Ó 2008 Elsevier Ltd. All rights reserved.
Regioisomer
Substituent effect
1. Introduction
the left of Fig. 1), 3-COMe in bacteriochlorophyll(BChl)-a and BChl-
b, 7-CHO in Chl-b and BChl-e, and 7-COOMe in Chl-c3.2 Such formyl
All naturally occurring chlorophylls have oxygen-functional
groups in a molecule.1 For example, chlorophyll(Chl)-a possesses
one keto-carbonyl group at the 13-position and two ester residues
at the 132- and 172-position (see the left of Fig. 1). The other car-
bonyl groups are found as the peripheral functional groups directly
and acetyl groups are so reactive that their alteration was useful for
in vitro preparation of modified chlorophylls having different
optical and electronic properties from those of the original chlo-
rophylls.3,4 Moreover, biosynthetic reduction of the formyl group
at the 7-position in Chl-b to the corresponding hydroxymethyl
group has been observed in the course of its interconversion to
Chl-a possessing the 7-methyl group.5
conjugating to the chlorophyllous
p-system: 3-CHO in Chl-d (see
The formyl group in natural chlorophylls was conjugated with
the chlorin p-system at the 3- or 7-position and affected the visible
absorption spectra. The reactivities of the 3- and 7-CHO are
assumed to be different and some model systems are available. The
3-CHO of methyl pyropheophorbide-d (PPhe-dM, 1, see the right of
Fig. 1) reacted with amines (RNH2) to give 3-CH2NHR and the re-
ductive amination was reported to occur more rapidly than that in
7-CHO of PPhe-bM.6 The condensation of 3-CHO in zinc complex of
1 with an amine to afford the corresponding imine was performed
eight times more quickly than that of 7-CHO in Zn-PPhe-bM.7 The
difference in reactivities of 3- and 7-CHO is ascribable to a sub-
stituent effect on the asymmetric chlorophyllous macrocyclic
p-
system. An electronic factor would control the observed reactivity
(3-CHO>7-CHO) and the steric factor cannot be ruled out because
the substituents near the 3-CHO (2-methyl and 7-methyl groups)
are sterically less hindered than those near the 7-CHO (8-ethyl and
3-vinyl groups).
Figure 1. Molecular structures of natural chlorophylls (left) and their synthetic
formylated derivatives (right).
Here, 8-formyl-chlorin 2 (see the right of Fig. 1) was prepared
whose formyl group was situated at the same steric environment as
* Corresponding author. Fax: þ81 77 561 2659.
E-mail address: tamiaki@se.ritsumei.ac.jp (H. Tamiaki).
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.04.025

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H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
the 3-CHO in 1; both their first and second neighbor substituents are
methyl groups. The reduction of 1 and 2 to hydroxymethyl-chlorins
was examined and their difference was discussed in consideration
of regioselective reduction of synthetic 3,8-diformyl-chlorin 3.
Moreover, acetyl-chlorins corresponding to formyl-chlorins 1–3
were synthesized and their reductions were similarly investigated.
8-formyl-chlorin 2 mentioned above (see Scheme 1). The isolated
yield of the final oxidation of 10 to 3 (step (i)) was 54% and slightly
lower than that of 9 to 2 (68%). The decrease would be due to the
3-substituent effect: the electron-withdrawing formyl group at the
3-position suppressed the oxidation of the 8-vinyl group. This
effect was pronounced in the double dehydration of 7,8-cis-diols to
8-vinyl-chlorins through cationic species (step (iv)): the yield to
3-formylated 10 (24%) was less than half of that to 3-ethylated 9
(60%).10
2. Results and discussion
2.1. Synthesis of formylated chlorophyll derivatives 1–3
2.2. Synthesis of acetylated chlorophyll derivatives 11–13
One of the 3-formyl-chlorins, methyl pyropheophorbide-d (1)
was prepared according to reported procedures.8 Briefly, naturally
occurring Chl-a was modified to methyl pyropheophorbide-a and
the 3-vinyl group was oxidatively cleaved (see step (i) of Scheme 1)
to give the corresponding 3-formyl compound 1.
The isomeric 8-formyl-chlorin 2 was similarly prepared from
oxidation of the 8-vinyl compound 9. Compound 9 was reported in
our previous literature9 and the access was briefly noted. First,
selective hydrogenation of the 3-vinyl group in methyl pyropheo-
phorbide-a to the ethyl group was performed in acetone which
disturbed the undesired reduction of the 13-carbonyl group (see
step (ii) of Scheme 1). The reactive C7]C8 double bond of
the resulting methyl mesopyropheophorbide-a was oxidized to
give cis-diol 19 (step (iii) of Scheme 1) and successive double
dehydration afforded 9 (step (iv) of Scheme 1).
As shown in the upper portion of Scheme 2, 3-acetyl-chlorin 11
was prepared by hydration of the 3-vinyl group of methyl pyro-
pheophorbide-a (step (vii)) and oxidation of the 3-(1-hydroxy-
ethyl) group of the resulting methyl bacteriopheophorbide-d (14)
(step (vi)).11
8-Acetyl-chlorin 12 isomeric to 11 was obtained as follows (see
the lower portion of Scheme 1). Mono-dehydration of cis-diol 19
gave a mixture of primary alcohol 22 and secondary alcohol 15
(step (v)). The acid-catalyzed dehydration proceeded more favor-
ably through secondary cationic species as in 8-CHþMe than pri-
mary 7-CHþ2 species,12 to afford 15 (50%) more effectively than 22
(18%). The isomeric mixture of alcohols was readily separated by
silica gel column chromatography. The major separated product 15
was oxidized to give desired 12 (step (vi)).
3,8-Diformyl-chlorin 3 was prepared from 3-formyl-8-ethyl-
chlorin 1 by the same procedures of 3,8-diethyl-chlorin to 3-ethyl-
By the same procedures as in methyl mesopyropheophorbide-
a/19/15/12 possessing the 3-ethyl group, 3-acetyl-chlorin 11
Scheme 1. Synthesis of 3/8-formyl-, 3,8-diformyl-, and 8-acetyl-chlorophyll derivatives, 1/2, 3, and 12: (i) OsO4–NaIO4/THF–aq AcOH; (ii) H2/Pd–C/Me2CO; (iii) OsO4/C5H5N–CH2Cl2,
H2S/MeOH; (iv) pTsOH/CH2Cl2–C6H6 (rt to reflux); (v) aq HCl/O(CH2CH2)2O (50 ꢀC), FCC separation; (vi) Pr4RuO4–O(CH2CH2)2N(O)Me/CH2Cl2.

H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
5723
Scheme 2. Synthesis of 3-acetyl- and 3,8-diacetyl-chlorophyll derivatives, 11 and 13: (iii) OsO4/C5H5N–CH2Cl2, H2S/MeOH; (v) aq HCl/O(CH2CH2)2O (50 ꢀC), FCC separation;
(vi) Pr4RuO4–O(CH2CH2)2N(O)Me/CH2Cl2; (vii) HBr/AcOH, H2O, CH2N2/Et2O.
was converted to 3,8-diacetyl-chlorin 13 through 20 and 17 (see the
right half of Scheme 2). Alternatively, 13 was prepared from 14 via
21 and 18 (see the left of Scheme 2).12 The latter route was shorter
by one step compared to the former: double one-pot oxidation of 18
to 13 was done in the final stage of the latter, while two oxidations
of 14/11 and 17/13 were needed in the initial and final stages of
the former. In spite of there being fewer steps in the latter route, the
former access to 13 was effective, because 17 was easily separated
from 23 in the isomeric mixture of alcoholic products and separa-
tion of 18 from 24 was troublesome.12 This difference in separation
of isomeric alcohols is ascribable to polarities of the molecules:
diols 18 and 24 are more polar and interacted more strongly with
silica gel than mono-ols 17 and 23, thus the separation of 18 from
24 was more difficult than that of 17 from 23.
desired compound 5 was the main product but the reaction mix-
ture was complex compared with reduction of 1 to 4. By similar
reduction of 3,8-diformyl-chlorin 3, a single mono-ol and diol 8
were obtained as isolated products. The molecular structure of the
isolated mono-ol was determined by 1H NMR and visible absorp-
tion spectra to be regioisomeric 3-hydroxymethyl-8-formyl-chlorin
6. The visible spectrum was especially useful for the determination
because the redmost band of chlorins is sensitive to the 3-sub-
stituent and is much lesser affected by the 8-functional group.4,13
The peak position of the resulting mono-ol in dichloromethane was
situated at 662 nm which was the same as that of 4 (3-CH2OH) and
blue-shifted compared with 695 nm of 1 (3-CHO), indicating that
the mono-ol was 6 possessing the 3-hydroxymethyl group. It is
noteworthy that mono-ol 7 isomeric to 6 could not be detected in
the reaction mixture from the reduction of 3.
2.3. Reduction of 3/8-carbonylated chlorophyll derivatives
to the corresponding alcohols
In similar procedures to the reduction of formyl-chlorins (vide
supra), 3-acetyl-chlorin 11 was reduced to 3-(1-hydroxyethyl)-
chlorin 14. Since an acetyl group is less reactive than a formyl
group, a prolonged reaction time was necessary for conversion of 11
to 14 and a large amount of the reducing reagent was useful for
rapid completion of the reduction. Product 14 has a chiral center at
the 31-position and was a 1:1 epimeric mixture due to achiral
conditions using sole Me3CNH2BH3 as a reducing reagent without
any chiral additives.4,14 The remote chiral induction from 17S and
18S asymmetric carbon atoms could not be observed and product
14 was a diastereomeric mixture. 8-Acetyl-chlorin 12 was reduced
to an equimolar 81-epimeric mixture of 15 similarly with 11/14
and the reduced 15 was predominantly observed as the product in
the initial stage. Reduction of 3,8-diacetyl-chlorin 13 gave mono-ol
3-Formyl-chlorin 1 in chloroform was treated with tert-butyl
amine borane complex at room temperature to afford 3-hydroxy-
methyl-chlorin 4 (see Scheme 3).8 The reduction was clean and
compound 4 was exclusively isolated as product just after disap-
pearance of 1. In the molecule of 1 are three carbonyl groups at 3-,
13-, and 172-position and the 3-formyl group was the most reactive
as expected: –CHO>–COR>–COOR. 8-Formyl-chlorin 2 was simi-
larly reduced to give the corresponding 8-hydroxymethyl-chlorin 5.
In the initial stage of the reduction, compound 5 was solely
obtained as the product and reduction of the 13-keto-carbonyl
group was observed in the latter. After consuming 2 completely,

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H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
Scheme 3. Reduction of 3/8-carbonylated chlorophyll derivatives 1–3/11–13 to the corresponding alcohols 4–8/14–18: (viii) Me3CNH2BH3/CHCl3.
16 and diol 18 and the isomeric mono-ol 17 was not observed. Both
the secondary alcoholic products 16 and 18 were epimeric mixtures
at 31- and 31,81-position, indicating no asymmetric reduction
occurred as expected.
2.4. Regiodependent reductivity of 3/8-carbonyl
substituent(s)
The difference in reductivity between the 3- and 8-formyl
groups was confirmed by NMR techniques. An equimolar solution
of 3-formyl-chlorin 1 and 8-formyl-chlorin 2 in deuterated chlo-
roform was prepared in an NMR sample tube. To the solution was
added a CDCl3 solution of Me3CNH2BH3, and the 1H NMR spectra
were measured at room temperature. The amounts of each formyl-
chlorin were determined by peak areas of low-field shifted protons,
5-, 10-, 20-H and CHO. 3-Formyl-chlorin 1 decreased rapidly and
was fully converted to 4 within 10 min (see open circles of Fig. 2A).
In contrast, 8-formyl-chlorin 2 was consumed slowly and about half
the amount still remained after incubation for 30 min (see closed
squares of Fig. 2A). The 3-formyl group was thus more reductive
than the 8-formyl group. Compared with the initial slopes of curves
in Figure 2A, the reduction rate k of 1 to 4 was about five times
faster than that of 2 to 5. The slow reduction of the 8-formyl group
in 2 led to the undesired reduction of its 13-carbonyl group during
the prolonged reaction time (vide supra).
In the reduction of 3,8-diformyl-chlorin 3, 3-hydroxymethyl-
chlorins 6 and 8 but no 3-formyl-chlorin 7 were isolated as reduced
products. This indicated also that the 3-CHO of 3 was more reactive
in the reduction than its 8-CHO. The doubly reduced product 8 was
prepared by slow reduction of 8-CHO in major 6 and quick re-
duction of 3-CHO in minor 7. In the latter case, the second reduction
of 7 to 8 (3-CHO/3-CH2OH) was more easily achieved than the
first reduction of 3 to 7 (8-CHO/8-CH2OH), and 7 could not be
detected in the reaction mixture.
Figure 2. Consumption of 3-formyl-chlorin 1 (open circles) and 8-formyl-chlorin 2
(closed squares) (A, upper) and that of 3-acetyl-chlorin 11 (closed circles) and 8-acetyl-
chlorin 12 (open squares) (B, lower) by reduction with Me3CNH2BH3 in CDCl3.
more slowly than the 3-CHO of 1 but was quantitatively transferred
to the 1-hydroxyethyl group in 14 within 2 h (see Fig. 2B). The
8-COMe of 12 was reduced to about five times slower in the initial
stage than the 3-COMe of 11. The relative suppression of k-values in
reduction of 12/15 over that of 11/14 was the same as in formyl-
chlorins, k2/5/k1/4¼ca. 1:5. The difference in reductivity of 3- and
8-acetyl-chlorins 11 and 12 was supported by the selective re-
duction of 3,8-diacetyl-chlorin 13 at which products 16 and 18
reduced at the 3-acetyl group were obtained, but no 3-acetyl-
chlorins including 17 were isolated as reduction products from the
reaction mixture.
Under the same conditions as the reduction of formyl-chlorins 1
and 2 with Me3CNH2BH3 in CDCl3, an equimolar solution of 3- and
8-acetyl-chlorins 11 and 12 was examined and their consumed
amounts were determined at intervals by 1H NMR spectroscopy.
The acetyl group at the 3-position of 11 was reduced about 10 times

H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
5725
Figure 4. Enzymatic hydrogenation of divinyl-chlorophyllide-a to chlorophyllide-a in
a biosynthetic route to Chl-a.
Figure 3. A major 18
p
-circuit (red) of chlorophyll derivatives.
a
Table 1
Stretching vibrational peaks
3. Concluding remarks
n
(cmꢁ1
) of carbonyl groups of 3- and 8-carbonyl-
chlorins in CH2Cl2
The present results clearly indicated that the 3-carbonyl group
in synthetic chlorophyll derivatives was reduced more smoothly
than the 8-carbonyl group. The substituent effect is ascribable to
the difference in electronic factor at the substituted positions, not
to the steric factor. Considering the reported data that the 3-formyl
group was more easily reduced than the 7-formyl group (see Sec-
tion 1), the carbonyl groups on an A-ring (see Fig. 3) would be more
reactive than those on a B-ring. The preferable reduction of the
3-carbonyl group is consistent with the report16 that the 3-formyl
group of Chl-d (see Fig. 1) in an aqueous solution was easily altered
by treatment of a weak reductant, sodium dithionite.
Compound
n
(3-C]O)
n
(8-C]O)
n
(13-C]O)
n
(172-C]O)
1 (3-CHO)
2 (8-CHO)
11 (3-COMe)
12 (8-COMe)
1677
1697
1697
1695
1696
1734
1734
1734
1734
1663
1657
1671
a
Errors were within 1 cmꢁ1
.
2.5. The reduction reactivity of 3-C]O>8-C]O
As mentioned above, the 3-carbonyl group of chlorin chromo-
phores is more reactive with a reducing agent than the 8-carbonyl
Recently, Tanaka and his colleagues reported that the 8-vinyl
group of divinyl-chlorophyllide-a in
a biosynthetic route to
Chl-a was hydrogenated to the 8-ethyl group (see Fig. 4),17 in spite
of the presence of the 3-vinyl group. Such an enzymatic reduction
is exclusively performed at the 8-substituent, not at the 3-sub-
stituent. This is in sharp contrast with the regiodependent re-
activity based on the present reduction of C]O to CHOH. One
of the reasons for the reverse selectivity is the high site-recogni-
tion of the substrate (divinyl-chlorophyllide-a) by the enzyme
(divinyl reductase). The other is the difference between regiode-
pendent reactivities in reduction of carbonyl groups in pyro-
chlorophyll derivatives lacking 132-COOMe and hydrogenation of
vinyl groups in the chlorophyllide possessing 132-COOMe;10,18 the
8-vinyl group would be hydrogenated more easily than the 3-vinyl
group.
group. The difference is explained by consideration of a chlorin
conjugated system. The major aromatic 18 -circuit of a chlorin
chromophore is drawn by the red line of Figure 3.15 The 3-C]O is
attached on the largely delocalized 18 -system and the 8-C]O is
bonded with the relatively isolated double bond C7]C8, giving
that the conjugation of the 3-C]O with the 18 -system would be
weaker than that of the 8-C]O with C7]C8. Therefore, the 3-C]O
is more isolated from the adjacent -system than the 8-C]O, and
p-
p
p
p
p
the former is a more reactive carbonyl substituent than the latter.
This explanation was confirmed by their FTIR and 13C NMR spectra
as follows.
In dichloromethane, the stretching vibrational band of the 3-
formyl carbonyl group in 1 was observed at
n
¼1677 cmꢁ1 and
n of
the 8-formyl carbonyl group in 2 was 1663 cmꢁ1 (see Table 1). The
lower wavenumber shift (Dn¼14 cmꢁ1) in 1/2 showed that the
4. Experimental
4.1. General
peripheral 3-CHO was less conjugated with the adjacent p-system
than the 8-CHO. In acetyl-chlorins 11 and 12, the same shift was
observed [Dn¼1671 (for 11)ꢁ1657 (for 12)¼14 cmꢁ1] and less
conjugation of 3-COMe than 8-COMe was ascertained.
All melting points were measured with a Yanagimoto micro
melting apparatus and were uncorrected. Visible absorption spec-
tra were measured with a Hitachi U-3500 spectrophotometer. 1H
NMR spectra in CDCl3 were measured with a Bruker AC-300
(300 MHz) and JEOL ECA-600 (600 MHz) spectrometers at room
In chloroform-d, the chemical shift
d
of 3-formyl carbon atom in
1 was 188.14 ppm and the
d
of C81 in 2 was 187.15 ppm (see Table
2). The low-field shift in 2/1 indicated that the C31 of 1 was more
deshielded and electropositive than the C81 of 2, and the 3-CHO
was more reactive with a nucleophile than the 8-CHO. The similar
temperature; chemical shifts (d) are expressed in parts per million
d
of C31 in 11
relative to CHCl3 (7.26 ppm) as an internal reference. 13C NMR
spectra in CDCl3 were measured with a JEOL ECA-600 (150 MHz)
tendency was observed in acetyl-chlorins 11 and 12;
and C81 in 12 was 199.39 and 198.96, respectively.
spectrometer; ds are expressed in parts per million relative to
13CDCl3 (77.0 ppm) as an internal reference. FABMS spectra were
measured with a JEOL GCmate II spectrometer; FABMS samples
were dissolved in CH2Cl2, m-nitrobenzyl alcohol was used as the
matrix and PEG600 was added as an external reference for HRMS
measurements. FTIR spectra were measured with a Shimadzu FTIR-
8600 spectrophotometer; samples in CH2Cl2 were measured in
a KBr cell.
All synthetic procedures were done in the dark under N2. THF
was distilled from CaH2 before use and CH2Cl2 was distilled without
moisture before use. Flash column chromatography (FCC) was
Table 2
Chemical shifts
in CDCl3
d
(ppm)a of carbonyl carbon-13 atoms of 3- and 8-carbonyl-chlorins
(C31) (C81) (C131) (C173)
Compound
d
d
d
d
1 (3-CHO)
2 (8-CHO)
11 (3-COMe)
12 (8-COMe)
188.14
195.94
195.77
196.09
196.07
173.36
173.36
173.44
173.44
187.15
198.96
199.39
a
Errors were within 0.02 ppm.
performed on silica gel, Kieselgel 60 (Merck, 40–63 mm).

5726
H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
4.2. Materials
3.28 (each 3H, s, 2-, 12-CH3, COOCH3), 2.63–2.68, 2.51–2.56, 2.19–
2.33 (1Hþ1Hþ2H, m, 17-CH2CH2), 1.79 (3H, d, J¼7 Hz, 18-CH3), 1.73,
1.72 (each 3H, t, J¼8 Hz, 31-, 81-CH3), 0.47, ꢁ1.67 (each 1H, s, NHꢂ2).
MS (FAB) found: m/z 566, calcd for C34H38N4O4: Mþ, 566. Com-
pound 15: black solid; mp 128–130 ꢀC; vis (CH2Cl2) lmax¼654 (rel,
39), 599 (7), 538 (7), 507 (9), 413 (100), 397 (71) nm; 1H NMR
Methyl pyropheophorbide-d (1),8 methyl 3-devinyl-3-hydroxy-
methyl-pyropheophorbide-a (4),8 methyl 8-deethyl-8-hydroxy-
methyl-mesopyropheophorbide-a (5),9 methyl 31-oxo-mesopyro-
pheophorbide-a (11),11 methyl bacteriopheophorbide-d (14),19 and
31,81-dihydroxy-mesopyropheophorbide-a (18)12 were prepared
according to reported procedures.
(CDCl3)
d
¼10.00/9.99, 9.25, 8.48 (each 1H, s, 5-,10-, 20-H), 6.26 (1H,
q, J¼7 Hz, 8-CH), 5.24, 5.09 (each 1H, d, J¼19 Hz, 131-CH2), 4.47 (1H,
dq, J¼2, 8 Hz, 18-H), 4.27 (1H, dt, J¼9, 2 Hz, 17-H), 3.85 (2H, q,
J¼8 Hz, 3-CH2), 3.67, 3.61, 3.36, 3.30 (each 3H, s, 2-, 7-, 12-CH3,
COOCH3), 2.66–2.70, 2.53–2.57, 2.25–2.33 (1Hþ1Hþ2H, m, 17-
CH2CH2), 2.14 (3H, d, J¼7 Hz, 81-CH3), 1.80 (3H, d, J¼8 Hz, 18-CH3),
1.73 (3H, t, J¼8 Hz, 31-CH3), 0.44, ꢁ1.73 (each 1H, s, NHꢂ2). MS
(FAB) found: m/z 566, calcd for C34H38N4O4: Mþ, 566. HRMS (FAB)
found: m/z 566.2879, calcd for C34H38N4O4: Mþ, 566.2893.
4.3. Synthesis of 3/8-carbonylated chlorophyll derivatives
4.3.1. Methyl 8-deethyl-8-formyl-mesopyropheophorbide-a (2)
To 8-vinyl-chlorin 9 (48.5 mg, 88
(2.3 mg) was added with stirring and cooled to 0 ꢀC. A solution of
NaIO4 (48.8 mg) and AcOH (64 l) in H2O (1.0 ml) was dropped into
m
mol)9 in THF (25.0 ml), OsO4
m
the above ice-chilled THF solution, stirred overnight at room tem-
perature, and poured into ice-water. After extraction with CH2Cl2
several times, the combined organic phase was washed with aq 4%
NaHCO3 and water, dried over Na2SO4, and evaporated under re-
duced pressure. The residue was purified by FCC (5% Et2O/CH2Cl2)
and recrystallized from CH2Cl2 and hexane to give 8-formyl-chlorin
2 (33.0 mg, 68% yield);9 black solid; mp 243–246 ꢀC; vis (CH2Cl2)
lmax¼659 (relative intensity, 27), 606 (5), 571 (3), 522 (4), 435
4.3.4. Methyl 81-oxo-mesopyropheophorbide-a (12)
To 8-(1-hydroxyethyl)chlorin 15 (17.0 mg, 31 mmol) in CH2Cl2
(15 ml), N-methylmorphorine N-oxide (12.4 mg) and tetra-n-pro-
pylammonium perruthenate (4.0 mg) were added and stirred for
2 h at room temperature. The reaction mixture was poured into
water and extracted with CH2Cl2. The organic phase was washed
with water, and dried over Na2SO4. After evaporation under re-
duced pressure, the residue was purified by FCC (5% Et2O/CH2Cl2)
and recrystallized from CH2Cl2 and hexane to give 12 (10.0 mg, 59%
yield); black solid; mp 98–101 ꢀC; vis (CH2Cl2) lmax¼656 (rel, 29),
602 (6), 559 (4), 517 (6), 430 (100), 411 (44) nm; 1H NMR (CDCl3)
(100), 413 (36) nm; 1H NMR (CDCl3)
d¼11.12 (1H, s, CHO), 10.36,
9.31, 8.56 (each 1H, s, 5-, 10-, 20-H), 5.26, 5.11 (each 1H, d, J¼19 Hz,
131-CH2), 4.51 (1H, dq, J¼2, 7 Hz, 18-H), 4.31 (1H, dt, J¼6, 2 Hz, 17-
H), 3.85 (2H, q, J¼8 Hz, 3-CH2), 3.64, 3.63, 3.60, 3.26 (each 3H, s, 2-,
7-, 12-CH3, COOCH3), 2.70–2.76, 2.56–2.62, 2.26–2.35 (1Hþ1Hþ2H,
m, 17-CH2CH2), 1.84 (3H, d, J¼7 Hz, 18-CH3), 1.75 (3H, t, J¼8 Hz, 31-
CH3), ꢁ0.05, ꢁ1.94 (each 1H, s, NHꢂ2). MS (FAB) found: m/z 550,
calcd for C33H34N4O4: Mþ, 550. HRMS (FAB) found: m/z 550.2592,
calcd for C33H34N4O4: Mþ, 550.2580.
d
¼10.18, 9.23, 8.51 (each 1H, s, 5-, 10-, 20-H), 5.21, 5.06 (each 1H, d,
J¼19 Hz, 131-CH2), 4.47 (1H, dq, J¼2, 8 Hz, 18-H), 4.26 (1H, dt, J¼9,
2 Hz, 17-H), 3.79 (2H, q, J¼8 Hz, 3-CH2), 3.63, 3.58, 3.49, 3.29, 3.07
(each 3H, s, 2-, 31-, 7-, 12-CH3, COOCH3), 2.66–2.72, 2.54–2.60,
2.24–2.33 (1Hþ1Hþ2H, m, 17-CH2CH2), 1.82 (3H, d, J¼8 Hz, 18-
CH3), 1.71 (3H, t, J¼8 Hz, 31-CH3), 0.06, ꢁ2.00 (each 1H, s, NHꢂ2).
MS (FAB) found: m/z 564, calcd for C34H36N4O4: Mþ, 564. HRMS
(FAB) found: m/z 564.2737, calcd for C34H36N4O4: Mþ, 564.2735.
4.3.2. Methyl 8-deethyl-8-formyl-pyropheophorbide-d (3)
Similar to the synthesis of 2, oxidation of 3-formyl-8-vinyl-
chlorin 10 (24.0 mg, 44
(60.5 mg) in THF (10.0 ml), H2O (1.0 ml), and AcOH (77
m
mol)10 by OsO4 (3.2 mg) and NaIO4
ml) [using
4.3.5. Methyl 71-hydroxy-31-oxo-mesopyropheophorbide-a (23)
and methyl 81-hydroxy- 31-oxo-mesopyropheophorbide-a (17)
Similar to the synthesis of 22/15, dehydration of 7,8-cis-diol 20
CHCl3 as extracted and recrystallized solvents instead of CH2Cl2]
gave 3,8-diformyl-chlorin 3 (13.0 mg, 54% yield); dark brown solid;
mp>300 ꢀC; vis (CH2Cl2) lmax¼685 (rel, 32), 625 (6), 542 (9), 455
(10.0 mg, 16 m ml),
mol)4 in 1,4-dioxane (10 ml), aq concd HCl (20
(100) nm; 1H NMR (CDCl3)
d¼11.53, 11.18 (each 1H, s, CHO), 10.58,
and H2O (2 ml) gave 23 (1.7 mg, 18% yield) and 17 (3.4 mg, 38%
yield, 81R/S¼1:1). Compound 23: black solid; vis (CH2Cl2) lmax¼678
(rel, 43), 619 (5), 549 (9), 518 (14), 421 (100) nm; 1H NMR (CDCl3)
10.49, 8.88 (each 1H, s, 5-, 10-, 20-H), 5.35, 5.20 (each 1H, d,
J¼19 Hz, 131-CH2), 4.60 (1H, dq, J¼2, 7 Hz, 18-H), 4.41 (1H, dt, J¼9,
2 Hz, 17-H), 3.80, 3.74, 3.72, 3.64 (each 3H, s, 2-, 7-, 12-CH3,
COOCH3), 2.74–2.79, 2.61–2.66, 2.27–2.38 (1Hþ1Hþ2H, m, 17-
CH2CH2), 1.87 (3H, d, J¼7 Hz, 18-CH3), ꢁ0.45, ꢁ2.08 (each 1H, s,
NHꢂ2). MS (FAB) found: m/z 550, calcd for C32H30N4O5: Mþ, 550.
HRMS (FAB) found: m/z 550.2592, calcd for C32H30N4O5: Mþ,
550.2216.
d
¼10.15, 9.67, 8.78 (each 1H, s, 5-, 10-, 20-H), 5.81 (2H, s, 7-CH2),
5.31, 5.21 (each 1H, d, J¼20 Hz, 131-CH2), 4.54–4.57 (1H, m, 18-H),
4.34–4.37 (1H, m,17-H), 3.84 (2H, q, J¼8 Hz, 8-CH2), 3.70, 3.64, 3.62,
3.31 (each 3H, s, 2-, 31-, 12-CH3, COOCH3), 2.57–2.70, 2.27–2.35
(each 2H, m, 17-CH2CH2), 1.83 (3H, d, J¼7 Hz, 18-CH3), 1.63 (3H, t,
J¼8 Hz, 81-CH3), ꢁ2.02 (1H, s, NH) [another NH was too broad to be
observed]. MS (FAB) found: m/z 580, calcd for C34H38N4O5: Mþ, 580.
Compound 17:20 black solid; vis (CH2Cl2) lmax¼680 (rel, 45), 621
4.3.3. Methyl 71-hydroxy-mesopyropheophorbide-a (22) and
methyl 81-hydroxy-mesopyropheophorbide-a (15)
(7), 548 (9), 518 (12), 419 (100) nm; 1H NMR (CDCl3)
d
¼10.16, 10.03,
To 7,8-cis-diol 19 (50.0 mg, 86
m
mol)9 in 1,4-dioxane (20 ml), aq
8.78 (each 1H, s, 5-, 10-, 20-H), 6.26 (1H, q, J¼7 Hz, 8-CH), 5.31, 5.21
(each 1H, d, J¼20 Hz, 131-CH2), 4.54–4.57 (1H, m, 18-H), 4.34–4.37
(1H, m, 17-H), 3.70, 3.66, 3.61, 3.37, 3.30 (each 3H, s, 2-, 31-, 7-, 12-
CH3, COOCH3), 2.57–2.70, 2.27–2.35 (each 2H, m, 17-CH2CH2), 2.15/
2.13 (3H, d, J¼7 Hz, 81-CH3), 1.83 (3H, d, J¼7 Hz, 18-CH3), ꢁ2.10 (1H,
s, NH) [another NH was too broad to be observed]. MS (FAB) found:
m/z 580, calcd for C34H38N4O5: Mþ, 580.
concd HCl (40 l) and H2O (4 ml) were added. After being stirred for
m
30 min at 50 ꢀC, the reaction mixture was poured into ice-water
and extracted with CH2Cl2. The organic phase was washed with aq
4% NaHCO3 and water, and dried over Na2SO4. After evaporation
under reduced pressure, the residue was purified by FCC (1.0–1.2%
MeOH/CH2Cl2 for 22 and 0.3–0.5% MeOH/CH2Cl2 for 15) and
recrystallized from CH2Cl2 and hexane to give 22 (9.0 mg, 18% yield)
and 15 (25.0 mg, 50% yield, 81R/S¼1:1). Compound 22: dark green
solid; mp 113–116 ꢀC; vis (CH2Cl2) lmax¼651 (rel, 35), 597 (7), 538
4.3.6. Methyl 31,81-dioxo-mesopyropheophorbide-a (13)
Similar to the synthesis of 12, oxidation of 3-acetyl-8-(1-
hydroxyethyl)-chlorin 17 gave 13;20 black solid; mp 194–197 ꢀC
(lit.20 198–199 ꢀC); vis (CH2Cl2) lmax¼675 (rel, 31), 617 (5), 529 (9),
(6), 506 (8), 414 (100), 397 (66) nm; 1H NMR (CDCl3)
d
¼9.45, 9.43,
8.46 (each 1H, s, 5-, 10-, 20-H), 5.75 (2H, s, 7-CH2), 5.19, 5.05 (each
1H, d, J¼19 Hz, 131-CH2), 4.44 (1H, dq, J¼2, 7 Hz, 18-H), 4.27 (1H, dt,
J¼8, 2 Hz, 17-H), 3.83, 3.76 (each 2H, q, J¼8 Hz, 3-, 8-CH2), 3.61, 3.57,
442 (100), 386 (70) nm; 1H NMR (CDCl3)
9.76 (1H, s, 5-H), 8.72 (1H, s, 20-H), 5.21, 5.04 (each 1H, d, J¼19 Hz,
d
¼9.85 (1H, s, 10-H),

H. Tamiaki et al. / Tetrahedron 64 (2008) 5721–5727
5727
131-CH2), 4.54 (1H, dq, J¼2, 8 Hz, 18-H), 4.31 (1H, dt, J¼10, 2 Hz,
17-H), 3.66 (3H, s, 17-COOCH3), 3.62 (3H, s, 2-CH3), 3.41 (3H,
s, 12-CH3), 3.27 (3H, s, 7-CH3), 3.21 (3H, s, 31-CH3), 2.91 (3H, s,
81-CH3), 2.72–2.78, 2.61–2.66, 2.36–2.41, 2.24–2.31 (each 1H, m,
17-CH2CH2), 1.89 (3H, d, J¼8 Hz, 18-CH3), ꢁ1.15, ꢁ2.71 (each 1H, s,
NHꢂ2). MS (FAB) found: m/z 578, calcd for C34H34N4O5: Mþ, 578.
3.63, 3.59, 3.50/3.49, 3.43/3.42, 3.09/3.08 (each 3H, s, 2-, 7-, 81-,
12-CH3, COOCH3), 2.55–2.71, 2.21–2.39 (each 2H, m, 17-CH2CH2),
2.15/2.14 (3H, d, J¼7 Hz, 31-CH3), 1.83/1.78 (3H, d, J¼7 Hz, 18-
CH3), ꢁ0.36/0.44, ꢁ2.18/2.24 (each 1H, s, NHꢂ2). MS (FAB) found:
m/z 553, calcd for C32H33N4O5: MHþ, 553.
Acknowledgements
4.4. Reduction of carbonyl group
We thank Ms. Kiharu Yamada of Ritsumeikan University for her
assistance in the experiments. This work was partially supported by
Grant-in-Aid for Scientific Research (B) (No. 19350088) from the
Japan Society for the Promotion of Science (JSPS) as well as by the
‘Academic Frontier’ Project for Private Universities: matching fund
subsidy from the Ministry of Education, Culture, Sports, Science and
Technology (MEXT) of the Japanese Government, 2003–2007.
Carbonylated chlorin in CHCl3 was reduced by Me3CNH2BH3 (3–
5 equiv for aldehyde and >10 equiv for ketone) with stirring at
room temperature. The reaction was monitored by visible spectra
and/or TLC. After disappearance of the starting chlorin, the reaction
mixture was quenched by aq dil HCl at 0 ꢀC, washed with aq 4%
NaHCO3 and water, and dried over Na2SO4. After evaporation under
reduced pressure, the residue was purified by FCC (0.6–0.8% MeOH/
CH2Cl2 for mono-ol and 1.2–1.5% MeOH/CH2Cl2 for diol) and
recrystallization (CH2Cl2/hexane) to give the corresponding alco-
hol. All the 1-hydroxyethylated compounds prepared by reduction
of acetyl group gave a diastereomeric mixture.
References and notes
1. Scheer, H. Chlorophylls and Bacteriochlorophylls: Biochemistry, Biophysics, Func-
tions and Applications; Grimm, B., Porra, R. J., Ru¨ diger, W., Scheer, H., Eds.;
Springer: Dordrecht, The Netherlands, 2006; Chapter 1, pp 1–26.
2. Tamiaki, H.; Shibata, R.; Mizoguchi, T. Photochem. Photobiol. 2007, 83, 152.
3. Johnson, S. G.; Small, G. J.; Johnson, D. G.; Svec, W. A.; Wasielewski, M. R. J. Phys.
Chem. 1989, 93, 5437; Osuka, A.; Marumo, S.; Wada, Y.; Yamazaki, I.; Shirakawa,
Y.; Nishimura, Y. Bull. Chem. Soc. Jpn. 1995, 68, 2909; Zheng, G.; Pandey, R. K.;
Forsyth, T. P.; Kozyrev, A. N.; Dougherty, T. J.; Smith, K. M. Tetrahedron Lett. 1997,
38, 2409; Tamiaki, H.; Kouraba, M. Tetrahedron 1997, 53, 10677; Holzwarth, A.
R.; Katterle, M.; Mu¨ ller, M. G.; Ma, Y.-Z.; Prokhorenko, V. Pure Appl. Chem. 2001,
73, 469; Yagai, S.; Miyatake, T.; Shimono, Y.; Tamiaki, H. Photochem. Photobiol.
2001, 73, 153; Li, G.; Dobhal, M. P.; Shibata, M.; Pandey, R. K. Org. Lett. 2004, 6,
2393; Tamiaki, H.; Kitamoto, H.; Nishikawa, A.; Hibino, T.; Shibata, R. Bioorg.
Med. Chem. 2004, 12, 1657; Sasaki, S.; Kotegawa, Y.; Tamiaki, H. Tetrahedron Lett.
2006, 47, 4849.
4.4.1. Methyl 3,8-dediethyl-8-formyl-3-hydroxymethyl-
pyropheophorbide-a (6)
Black solid; vis (CH2Cl2) lmax¼662 (rel, 27), 608 (5) 571 (3), 522
(4), 436 (100), 415 (37) nm; 1H NMR (CDCl3)
d
¼10.85 (1H, s, CHO),
9.87, 9.36, 8.62 (each 1H, s, 5-, 10-, 20-H), 5.90 (2H, s, 3-CH2), 5.17,
5.03 (each 1H, d, J¼19 Hz, 131-CH2), 4.51 (1H, dq, J¼2, 8 Hz, 18-H),
4.27 (1H, dt, J¼10, 2 Hz, 17-H), 3.67, 3.46, 3.43, 3.42 (each 3H, s, 2-,
7-, 12-CH3, COOCH3), 2.70–2.75, 2.59–2.65, 2.36–2.40, 2.23–2.29
(each 1H, m, 17-CH2CH2), 1.87 (3H, d, J¼8 Hz, 18-CH3), ꢁ0.87, ꢁ2.41
(each 1H, s, NHꢂ2). MS (FAB) found: m/z 581, calcd for C34H37N4O5:
MHþ, 581.
4. Sasaki, S.; Omoda, M.; Tamiaki, H. J. Photochem. Photobiol., A: Chem. 2004, 162,
307.
5. Tanaka, A.; Tanaka, R. Curr. Opin. Plant Biol. 2006, 9, 248.
6. Efimov, A.; Tkachenko, N. V.; Vainiotalo, P.; Lemmetyinen, H. J. Porphyrins
Phthalocyanines 2001, 5, 835.
4.4.2. Methyl 3,8-dediethyl-3,8-bis(hydroxymethyl)-
pyropheophorbide-a (8)
7. Rau, H. K.; Snigula, H.; Struck, A.; Robert, B.; Scheer, H.; Haehnel, W. Eur. J.
Biochem. 2001, 268, 3284.
8. Tamiaki, H.; Amakawa, M.; Shimono, Y.; Tanikaga, R.; Holzwarth, A. R.;
Schaffner, K. Photochem. Photobiol. 1996, 63, 92.
9. Yagai, S.; Miyatake, T.; Tamiaki, H. J. Photochem. Photobiol., B: Biol. 1999, 52, 74.
10. Kunieda, M.; Mizoguchi, T.; Tamiaki, H. Tetrahedron 2004, 60, 11349.
11. Tamiaki, H.; Yagai, S.; Miyatake, T. Bioorg. Med. Chem. 1998, 6, 2171.
12. Tamiaki, H.; Omoda, M.; Saga, Y.; Morishita, H. Tetrahedron 2003, 59, 4337.
13. Sasaki, S.; Tamiaki, H. Bull. Chem. Soc. Jpn. 2004, 77, 797; Sasaki, S.; Tamiaki, H.
J. Org. Chem. 2006, 71, 2648.
14. Tamiaki, H.; Kouraba, M.; Takeda, K.; Kondo, S.; Tanikaga, R. Tetrahedron:
Asymmetry 1998, 9, 2101.
15. Steiner, E.; Fowler, P. W. ChemPhysChem 2002, 3, 114.
16. Tomo, T.; Suzuki, T.; Hirano, E.; Tsuchiya, T.; Miyashita, H.; Dohmae, N.; Mimuro,
M. Chem. Phys. Lett. 2006, 423, 282.
17. Nagata, N.; Tanaka, R.; Tanaka, A. Plant Cell Physiol. 2007, 48, 1803.
18. Struck, A.; Cmiel, E.; Katheder, I.; Scha¨fer, W.; Scheer, H. Biochim. Biophys. Acta
1992, 1101, 321.
Black solid; mp 148–151 ꢀC; vis (CH2Cl2) lmax¼660 (rel, 44), 604
(7), 539 (7), 508 (9), 415 (100) nm; 1H NMR (CDCl3)
d
¼9.71, 9.52, 8.60
(each 1H, s, 5-,10-, 20-H), 5.94, 5.76 (each 2H, s, 3-, 8-CH2), 5.16, 5.04
(each 1H, d, J¼19 Hz, 131-CH2), 4.48 (1H, dq, J¼2, 8 Hz, 18-H), 4.24
(1H, dt, J¼10, 2 Hz, 17-H), 3.64, 3.63, 3.44, 3.38 (each 3H, s, 2-, 7-,
12-CH3, COOCH3), 2.55–2.65, 2.28–2.32, 2.17–2.24 (2Hþ1Hþ1H, m,
17-CH2CH2), 1.79 (3H, d, J¼8 Hz, 18-CH3), ꢁ0.10, ꢁ1.96 (each 1H, s,
NHꢂ2). MS (FAB) found: m/z 554, calcd for C32H34N4O5: Mþ, 554.
4.4.3. Methyl 31-hydroxy-81-oxo-mesopyropheophorbide-a (16)
Black solid (31R/S¼1:1); mp 78–84 ꢀC; vis (CH2Cl2) lmax¼659
(rel, 29), 604 (5), 559 (3), 517 (5), 431 (100) nm; 1H NMR (CDCl3)
19. Tamiaki, H.; Takeuchi, S.; Tsudzuki, S.; Miyatake, T.; Tanikaga, R. Tetrahedron
1998, 54, 6699.
20. Inhoffen, H. H.; Ja¨ger, P.; Ma¨hlhop, R.; Mengler, C.-D. Liebigs Ann. Chem. 1967,
704, 188.
d
¼10.183/10.179, 9.85/9.82, 8.56/8.54 (each 1H, s, 5-, 10-, 20-H),
6.40–6.45 (1H, m, 3-CH) 5.18/5.13, 5.04/5.01 (each 1H, d, J¼19 Hz,
131-CH2), 4.46–4.54 (1H, m, 18-H), 4.20–4.27 (1H, m, 17-H), 3.66/