Synthesis, photophysical and electrochemistry of near-IR absorbing bacteriochlorins related to bacteriochlorophyll a

Article abstract of DOI:10.1021/jo301895p

A series of new bacteriochlorins was synthesized using 13 ²-oxo-bacteriopyropheophorbide a (derived from bacteriochlorophyll a) as a starting material, which on reacting with o-phenylenediamine and 1,10-diaminonaphthalene afforded highly conjug

Full text of DOI:10.1021/jo301895p

Article
pubs.acs.org/joc
Synthesis, Photophysical and Electrochemistry of Near-IR Absorbing
Bacteriochlorins Related to Bacteriochlorophyll a
,†
‡
§
⊥
∥
Andrei Kozyrev,* Manivannan Ethirajan, Ping Chen, Kei Ohkubo, Byron C. Robinson,
¶
,⊥,○
,§
,‡
Kathleen M. Barkigia, Shunichi Fukuzumi,*
Karl M. Kadish,* and Ravindra K. Pandey*
†
Nanosyn, Inc., Santa Clara, California 95051, United States
‡
Chemistry Division, PDT Center, Cell Stress Biology, Roswell Park Cancer Institute, Buffalo, New York 14263, United States
§
Department of Chemistry, University of Houston, Houston, Texas 77204-5009, United States
⊥
Department of Material and Life Science, Graduate School of Engineering, Osaka University, ALCA (JST), 2-1 Yamada-oka, Suita,
Osaka 565-0871, Japan
∥
Amgen, Thousand Oaks, California 91320-1799, United States
¶
Brookhaven National Laboratory, Upton, New York 11973, United States
○
Department of Bioinspired Science, Ewha Womans University, Seoul 120-750, Korea
S Supporting Information
*
ABSTRACT: A series of new bacteriochlorins was synthesized
2
using 13 -oxo-bacteriopyropheophorbide a (derived from bacterio-
chlorophyll a) as a starting material, which on reacting with o-
phenylenediamine and 1,10-diaminonaphthalene afforded highly
conjugated annulated bacteriochlorins with fused quinoxaline,
benzimidazole, and perimidine rings, respectively. The absorption
spectra of these novel bacteriochlorins demonstrated remarkably
red-shifted intense Q absorption bands observed in the range of
y
8
1
16−850 nm with high molar extinction coefficients (89,900−
2
36,800). Treatment of 13 -oxo-bacteriopyropheophorbide a methyl ester with diazomethane resulted in the formation of
bacterioverdins containing a fused six-membered methoxy-substituted cyclohexenone (verdin) as an isomeric mixture. The pure
isomers which exhibit long-wavelength absorptions in the near-IR region (865−890 nm) are highly stable at room temperature
with high reactivity with O at the triplet photoexcited state and favorable redox potential and could be potential candidates for
2
use as photosensitizers in photodynamic therapy (PDT).
INTRODUCTION
of fused exocyclic ring(s), directly attached to the reduced
■
porphyrinic skeleton, was found to be beneficial in shifting Q
y
Studies on porphyrins and related compounds as photo-
sensitizers in the field of photodynamic therapy (PDT) suggest
that long-wavelength absorbing chromophores may have
advantages in destroying deeply seated tumors. Porphyrin-
based compounds with absorptions in the far red/near-IR
region of the electromagnetic spectrum may have various
applications as optical materials and sensors or for PDT. The
availability of cheap LED diode lasers in the range of 800−900
nm will make PDT more economical and practical. One
11
absorptions into the near-IR region. Among tetrapyrrolic
systems, bacteriochlorins are of particular interest, because they
1
2
1,2
exhibit intense Q bands in the long-wavelength region.
Earlier, Dolphin and co-workers and Pandey et al.
y
1
3
14
synthesized bacteriochlorins which possessed two fused rings
on the opposite pyrrolic units and had long-wavelength
absorptions in the range of 760−790 nm. Unfortunately,
further studies on these chromophores have not been reported.
The synthesis of stable bacteriochlorins has been a
challenging aspect of photosensitizer development in the field
3
4
5
approach used in the synthesis of long-wavelength absorbing
compounds exploits the strategy of extending the π-conjugated
macrosystem of the porphyrin chromophore. This has been
15−17
6
of PDT. A decade ago, Robinson et al.
reported the
synthesis of a series of bacteriopurpurins, which had previously
been erroneously reported as being so unstable that their
achieved by introducing fused aromatic rings directly attached
7
to the porphyrin, or by building extended cyclic pyrrolic
18
8
,9
characterization was not possible. In this instance, it was
found that the presence of two conjugated electron-with-
drawing cyclopentenyl rings on the bacteriochlorins produced
macrocycles. Another strategy that has been largely adopted
utilizes partial reduction of the porphyrin system to produce
4
chlorins or bacteriochlorins. Introduction of electron-with-
drawing substituents in such systems at an appropriate
position(s) produces significant bathochromic shifts in their
long-wavelength absorptions. In some instances introduction
Received: September 6, 2012
Published: October 22, 2012
10
©
2012 American Chemical Society
10260
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Scheme 1
2
Figure 1. UV/near-IR absorption spectra (in CH Cl ) of bacteriochlorins: (A) 13 -oxo-bacteriopyropheophorbide a (8); (B) quinoxalino-
2
2
bacteriochlorin (10); (C) benzimidazolo-bacteriochlorin (11); (D) perimidino-bacteriochlorin (13).
1
0,22
large bathochromic shifts of their Q -bands, which absorbed in
range.
The utility of these compounds has been extensively
y
17
the range of 846−863 nm. A few years ago, Pandey and co-
investigated by Pandey and co-workers and some of the
analogues have shown excellent PDT efficacy, both in vitro and
in vivo in various tumor models.
1
9
workers extended the osmium tetroxide oxidation approach
followed by the pinacol−pinacolone reaction in developing
certain keto-bacteriochlorins derived from chlorins (pyropheo-
The chemistry involving the enolization of pyropheophor-
23
phorbide a, chlorin e , and purpurinimide). A remarkable
bide was outlined by Pandey and co-workers who showed the
utility of the resulting product in highly conjugated systems.
They followed this approach by first converting the
bacteriochlorophyll a (1) to the corresponding α-diketone 8
which was then attached to a variety of fused aromatic moieties.
This synthetic design followed the strategy of introducing
moieties that extended conjugation on the pyrrolic unit C,
while the opposite pyrrolic unit A contained an electron-
withdrawing substituent (acetyl group). This arrangement of
substituents along the pyrrolic A−C unit axis in bacterio-
chlorins was expected to provide large bathochromic effects on
6
difference in photophysical properties and PDT efficacy was
observed, depending on the position of the keto group at the
position-7 or -8.
Natural bacteriochlorophylls, for example, bacteriochloro-
phyll a (1) and its derivatives, have been shown to possess
2
0
significant potency as photosensitizers. Many of these
21
compounds appear to be unstable during in vivo experiments.
Bacteriochlorins with fused anhydride and imide rings have
been reported to be more stable to photooxidation, while
possessing adequate Q absorptions in the 800−820 nm
y
1
0261
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Scheme 2
10
their Q absorption bands, which could be shifted into the
hypsochromic shift (Figure 1). The electron-withdrawing
y
required near-IR region (above 800 nm). Here we report our
results on the synthesis and spectroscopic, electrochemical, and
photophysical characterization of a series of novel bacterio-
chlorins, bearing fused aromatic units.
nature of the cyclopentyldiketone ring E produced a significant
hyperchromic effect in the Q absorption band (768 nm, ε =
y
87,900) when compared to bacteriopyropheophorbide a (5)
2
(754 nm, ε = 61,700). The presence of the 13 -oxo-
1
functionality was evident in the H NMR spectrum of
bacteriochlorin (8). Thus, when compared with similar
resonances in 5, the signal of the 17-H in 8 was shifted upfield
to 5.00 ppm (Δδ = 0.97 ppm). The 13 -methylene group
resonance, which occurs at 5.33 ppm in 5, was not observed in
RESULTS AND DISCUSSION
■
Annulated Aromatic Bacteriochlorins. Bacteriochloro-
phyll a (1) was isolated from Rhodobacter sphaeroides according
2
24
to a standard procedure. A brief treatment with 0.5% aq HCl
afforded bacteriopheophytine a (2). Attempts to transesterify
bacteriochlorin 2 using 2% sulfuric acid in methanol were
unsuccessful, resulting in the formation of a significant amount
8
as expected.
Condensation of bacteriochlorin 8 with 1,2-phenylenedi-
amine 9 in pyridine in the presence of catalytic amounts of
27−29
TFA
afforded two bacteriochlorins, which were isolated
(
more than 50%) of 3-acetyl-3-devinyl-pheophorbide a (3).
Other researchers have also reported difficulties working with
bacteriochlorins in the presence of strong acids.
and purified by column and thin-layer chromatography. The
minor product identified as quinoxalino-bacteriochlorin (10)
25,26
The phytyl
1
1
(
29%) based on HRMS and H NMR spectroscopy data. A H
ester group was cleaved efficiently using 80% aqueous TFA
25
NMR spectrum of 10 displayed characteristic resonances from
the aromatic protons of the quinoxaline fused ring at 7.49 and
under an inert atmosphere, and the resulting bacteriopheo-
phorbide a was esterified using diazomethane to give methyl
ester 4 in 89% yield.
7
.96 ppm, while a mass ion (M + H) at m/z 653.3 was
observed consistent with the structure.It was interesting to
observe the effects induced by introduction of fused quinoxa-
line ring system in its UV−near-IR absorption spectrum
A small amount of chlorin 3 (2%) was separated using
chromatography on silica. Demethoxycabonylation of bacterio-
chlorin 4 in collidine afforded bacteriopyropheophorbide a (5)
in 95% yield. A minor byproduct, isolated chromatographically
as a faster moving band, was identified as 3-acetyl-3-devinyl-
(
Figure 1). The extension of conjugation at ring E in
bacteriochlorin 10 caused a significant bathochromic effect in
2
the Q absorption band, shifted it to 816 nm. The high
pyropheophorbide a (6) (3% yield). The synthesis of 13 -oxo-
y
extinction coefficient (ε = 107,600) indicated a strong
bacteriopyropheophorbide a (8) followed the approach
outlined for the autooxidation of related pyropheophorbide a
hyperchromic effect in the Q absorption band, due to the
y
23
annulated polycyclic quinoxaline system in the chromophore
and phylloerythrin compounds. Hence, in situ autooxidation
of the bacteriopyropheophorbide a (5) using aqueous LiOH in
THF for 24 h followed by an acidic workup and re-esterification
with diazomethane, afforded bacteriochlorin α-diketone (8) in
1
1
0. The major product (54%) was identified as bacteriochlorin
1, possessing a conjugated benzimidazole ring. The structure
of this product was assigned on the basis of mass spectral and
27
1
H NMR data. Thus, the signal of the 17-H atom resonance at
6
8% yield (see Scheme 1). Surprisingly, no other oxidized
byproducts (chlorins or porphyrins) or peripheral oxidation
products were isolated from the reaction mixture as was
observed in the LiOH-promoted allomerization of pyropheo-
5.43 ppm indicated the presence of the carbonyl function at the
3
27
13 -position. A similar deshielding effect on the 17-H
3
resonance from the neighboring 13 -keto group was reported
in a bacteriopurpurin a imide series. Signals from the
2
3
22
phorbide a. As expected, bacteriochlorin (8) demonstrated a
moderate bathochromic shift of the Q and Soret absorption
aromatic protons of benzimidazole moiety resonated at δ
y
bands, while the Qx band was depressed and has a
7.30, 7.86, and 8.06 ppm, which is similar in chemical shift to
1
0262
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Scheme 3
2
8
values reported in a pyropheophorbide a series. By UV−near-
IR spectroscopy, it is evident that the extended conjugation due
to annulated benzimidazole in the bacteriochlorin chromo-
phore 11 produced a large bathochromic shift (Δλ = 96 nm) in
space interaction with both signals associated with the 12-
methyl and 13 -methoxyl groups (Figure 2). By UV/near-IR
2
spectroscopy, bacterioverdin 14 has a Q absorption band
y
remarkably shifted into the near-IR region (891 nm, ε = 51,800
−1
−1
−1
−1
the Q absorption (850 nm, ε = 89,800 M cm ). The intense
M
cm ). When compared to 5, this represents a bath-
y
−1
−1
Q -band was also shifted to 553 nm (ε = 39,200 M cm ).
Presumably, bacteriochlorin 11 was formed as an autooxidized
byproduct (allomer) during the condensation process.
ochromic shift of Δλ = 137 nm, while the intensity of the Q
x
y
absorption is slightly decreased. The Q -band was shifted to
x
28
550 nm and the Soret (B and B ) bands were observed at 368
1
2
Using a similar synthetic methodology, condensation of
bacteriochlorin 8 with 1,9-diaminonaphthalene 12 in pyridine/
TFA gave perimidino-bacteriochlorin 13, which was isolated as
a sole product (79%) (Scheme 2). The annulated polycyclic
perimidine moiety caused a remarkably large hyperchromic
and 423 nm (Figure 3). To our best of our knowledge,
bacterioverdin 14 demonstrates the longest red-shifted Qy
absorption of any existing natural or synthetic bacteriochlorin
18
derivative.
−1
effect on the Q absorption band (829 nm, ε = 138,800 M
y
−1
cm ), which has an extinction coefficient almost twice as large
−1
−1
as its Soret band (398 nm, ε = 76,900 M cm ) in the
electron spectrum (Figure 1D). The exceptionally intense
absorption maximum in bacteriochlorin 13 is a unique optical
characteristic, which makes this chromophore very attractive for
use as a recording material in information-storage media, or a
dopant for nonlinear and luminescent optic materials. In
contrast to bacteriochlorins 10 and 11 which are red in
solutions, chromophore 13 displays broad absorption over
1
Figure 2. NOE interactions (selected) observed in 2D/ROESY H
NMR spectra of bacteriochlorins 14−16.
5
34−660 nm region, providing its solutions with a blue-green
color.
Bacterioverdins. In the search for novel near-IR absorbing
The major product of the diazomethane ring enlargement
reaction, isolated as the second fraction (42% yield), was
assigned as the 13 -methoxy-bacterioverdin (15). A H NMR
1
1
sensitizers, we were interested in exploring bacteriochlorins
with various six-membered conjugated ring systems. It is known
that the presence of a cyclohexenone (verdin) ring in chlorins
and porphyrins produces significant bathochromic shifts in the
of this product showed a 17-H resonance at 5.18 ppm, clearly
indicating the presence of a carbonyl function at the adjacent
3
1
3 -position, as had been seen with bacteriochlorins 11 and 13.
Additional evidence of its structure was provided by a 2D/
Q absorption spectra of the molecules, ranging from 50 to 60
1
y
ROESY H NMR experiment, which showed distinctive
30
31
nm for porphyrins and from 70 to 100 nm for chlorins. The
presence of the reactive a-diketone moiety in bacteriochlorin 8
provided an opportunity to introduce a verdin ring system to
the bacteriochlorin chromophore, using a recognized diazo-
1
interactions between resonances from the 13 -methoxyl group
1
and the 12-methyl substituent, as well as between the 13 -
2
methoxyl and the 13 -H signals (Figure 2). As with isomer 14,
bacterioverdin 15 displays a Q absorption shifted to the near-
y
3
2,33
methane ring-enlargement approach.
Utilizing this syn-
−1
−1
IR region (874 nm, ε = 78,500 M cm ), demonstrating a
significant bathochromic effect (Δλ = 120 nm).
2
thetic methodology, we found that treatment of 13 -oxo-
bacteriopyropheophorbide a (8) with excess diazomethane at
room temperature resulted in formation of three products
The third and slowest eluting product of the diazomethane
reaction was assigned as bacteriochlorin 16, isolated in 16%
1
(14−16) (Scheme 3), which were separated and purified
yield. The 2D/ROESY H NMR spectrum clearly shows that
1
chromatographically. Examination of the molecular weight for
the compounds showed that each product had the same
molecular ion at m/z 609.3, indicating that they were isomeric
in nature and all possessed an annulated methoxycyclohex-
enone (verdin) ring system. As a new subclass of
chromophores, we termed these compounds as bacteriovervins.
The structural assignment of bacterioverdins 14−16 was
the resonance of the 13 -methoxyl group exhibits strong
2
through-space interactions with the neighboring 17-H and 13 -
H atoms (Figure 2). The multiplet attributed to the proton at
the 17-position was observed at δ 4.78 ppm, indicating the
3
absence of a neighboring carbonyl functionality at the 13 -
32
position in the verdin ring. In contrast to bacterioverdins 14
and 15, the ketone functionality in bacteriochlorin 16 is located
1
1
made using detailed 2D/ROESY H NMR studies. The fastest
moving band on silica was assigned to be the 13 -methoxy-
bacterioverdin (14), isolated in 29%. A 2D/ROESY H NMR
spectrum of 14 shows that the 13 -H exhibits a strong through-
at the 13 -position; thus this product was termed as
2
bacterioisoverdin. Bacterioisoverdin 16 has a Q absorption at
y
1
−1
−1
865 nm (ε = 48,600 M cm ), while the Q band occurred at
x
1
596 nm. In contrast to bacterioverdins 14 and 15, which are red
1
0263
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Figure 3. UV/near-IR absorption spectra (in CH Cl ) of bacteriochlorins: (A) bacteriopyropheophorbide a 5; (B) bacterioverdin 14; (C)
2
2
bacterioverdin 15; (D) bacterioisoverdin 16.
in solution, this compound has a characteristic deep-green color
in solution (Figure 3).
and produce ring enlargement by incorporating the methylene
group between the 13 - and 13 -carbon atoms in the exocyclic
1
2
An X-ray crystallographic determination of bacterioverdin 14
provided an unambiguous identification of its structure, in
accord with independent 2D/ROESY H NMR studies, and
ring E to give compound 20, while ring enlargement between
1
2
the 13- and 13 , as well as 15-meso and 13 -positions, should
produce isomers 19 and 21. The cyclohexanedione derivatives
19 and 20 should quickly enolize to produce verdins 21−23,
which on methylation via diazomethane should afford
bacterioverdins 14−16. Interestingly, the product 24 was not
found among the isolated reaction products. Apparently, the
absence of 24 indicates that the initial diazomethane attack
1
presents the first stereochemical parameters for this new class
of bacteriochlorin. The compound crystallizes with three
independent molecules in the unit cell, which display subtle
differences in conformation and orientation of the side chains.
Theoretical calculations based on the X-ray coordinates predict
3
4
a range of 792−872 nm for the Q transition. A view of the
1
y
takes place regioselectively at the 13 -carbonyl function to form
conformer that yields the best calculated agreement with the
experimental value of 891 nm and presumably resembles most
closely the conformation in solution is shown in Figure 4.
the only intermediate 17, presumably due to the steric
hindrance from the neighboring 17-propionic side chain.
These data are consistent with earlier reports on the higher
1
29
reactivity of the carbonyl at the 13 -position.
Electrochemistry. The electrochemical properties of seven
bacterichlorins, 8, 10, 11, and 13−16, were examined in
CH Cl containing 0.1 M TBAP. Cyclic voltammograms are
2
2
shown in Figure 5, and the redox potentials for each oxidation
and reduction are listed in Table 1.
The investigated compounds undergo two reversible
reductions at E1/2 = −0.63 to −0.81 V and E = −0.97 to
1.2
−
1.14 V, respectively, to form the radical anion and dianion.
Two one-electron oxidations are also detected at E = 0.61−
1
/2
0
.81 V and E = 1.14−1.28 V to give the radical cation and
p
dication. The first oxidation is reversible, while the second
oxidation is quasi-reversible or irreversible due to the instability
of the dication generated. However, two reversible oxidations
can be observed at low temperatures, for these compounds and
examples of cyclic voltammograms at −70 °C are shown in
Figure 6 for compounds 10 and 14. As shown in this figure, the
second oxidation is located at E1/2 = 1.10 V (10) or E1/2 = 1.17
V (14), and side reactions are not observed after the second
oxidation as is the case at room temperature. In addition, the
first oxidation of 10 is split into two processes at the low
temperature, probably due to aggregation of this compound, to
a certain extent, under these experimental conditions.
Figure 4. X-ray structure of bacterioverdin 14. Peripheral substituents
have been omitted for clarity.
Single crystals of 14 (C H N O ) were grown from CH Cl /
3
6
40
4
5
2
2
MeOH. Details and results of the X-ray experiment are
included in CIF format in the Supporting Information. An
analysis of the structures from the ring enlargement reaction
sheds some light on the pathway of ring enlargement occurring
within ring E (Scheme 4). Theoretically, it is possible that
diazomethane reacts at both carbonyl functionalities to produce
intermediates 17 and 18. Both intermediates release nitrogen
1
0264
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
2
Scheme 4. Possible Mechanism for the Formation of Bacterioverdins (21−23) from 13 -Oxo-bacteriopyropheophorbide a (8)
An almost constant potential difference between two
reductions (Δred 1−2 = 0.33 ± 0.03 V) is observed for all
compounds (see Table 1), while the potential difference
between the first two oxidations is also similar for the examined
compounds (Δox 2−1 = 0.51 ± 0.05 V). The electrochemical
HOMO−LUMO gap of bacterichlorins in this series is 1.29−
has been described as a marker band for the radical anion of
35,36
bacteriochlorins and was predicted in MO calculations.
The
first two controlled potential reductions for compound 15 are
accompanied by reversible spectral changes in the thin-layer
cell, and these spectra are shown in Figure 7b. As the electron
transfer proceeds, the newly generated 628 and 1039 nm bands
disappear, accompanied by the appearance of a weak and broad
band at 564 nm, which is assigned to the bacteriochlorin
dianion.
1.50 V. A similar HOMO−LUMO gap of 1.40 ± 0.05 V has
been reported for other bacteriochlorin derivatives in our
3
5
previous study. These values are smaller than the gap of
3
6
1
.52−1.60 V for metal-substituted bacteriochlorophyll a and
Three moderate intensity Soret bands are seen at 360, 398
and 429 nm, and there is a weak NIR band at 896 nm in the
absorption spectrum of the radical anion for 15 (Figure 7c).
The NIR band at 896 nm can be used as a marker band of the
bacteriochlorin radical cation, and similar Soret bands were also
reported in the radical cation spectrum of other bacterio-
also much smaller than the gap of 1.90−2.10 V often seen for a
37
number of nonplanar porphyrins. It is worthy to point out
that bacterioverdins 14−16 having a fused cyclohexenenone
ring systems exhibit the smallest HOMO−LUMO gap (∼1.30
V). These three compounds also exhibit both the easiest
reduction and the easiest oxidation as compared to other earlier
studied compounds.
35,36
chlorophyll derivatives.
This is due to the chlorine structure
of the electrogenerated radical cation. A further oxidation of the
radical cation 15 leads to a disappearance of the 360, 398, and
896 nm bands and the appearance of a stronger band at 448 nm
when the controlled potential is switched to 1.30 V (Figure 7d).
Theoretical Study. Density functional theoretical (DFT)
calculations were performed using the Gaussian09 program (see
Experimental Section), and the structures were optimized at the
B3LYP/6-31+G(d,p) level of theory. The calculated HOMO−
LUMO gaps are summarized in Table 3. There is a linear
correlation between the HOMO−LUMO gaps obtained from
electrochemical measurements and theoretical calculations as
shown in Figure 8. The slope of the linear plot is 1.3, which
indicates that there are no significant contributions of solvation
to the redox behavior, due to the highly delocalized HOMO−
LUMO on the macrocycle.
Spectroelectrochemistry. The electroreductions and
electrooxidation of 8, 10, 11 and 13−16 were characterized
by UV−vis thin-layer spectroelectrochemistry and the spectral
data for the electrogenerated radical cations and radical anions
of these bacteriochlorins are listed in Table 2. The spectral
changes are reversible upon reversing the applied potentials,
consistent with a high stability of the oxidized and reduced
forms on the spectroelectrochemical time scale.
Examples of the UV−vis spectral changes obtained during
the first two oxidations and first two reductions of compound
1
−
8
5 are illustrated in Figure 7. Upon the first reduction of 15 at
0.90 V (Figure 7a), the 369 nm Soret band and the strong
72 nm near-IR band decreased in intensity, while two weak
bands grew in at 628 and 1039 nm. The NIR band at 1039 nm
1
0265
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Figure 6. Cyclic voltammograms of compounds 10 and 14 in CH Cl
2
2
containing 0.1 M TBAP at room temperature and −70 °C.
to the electron-transfer quenching of the singlet excited state by
the naphthylamine donor moiety of 13. The T-T absorption
decay of 8 obeys first-order kinetics (Figure 10a), and this
indicates that there is no contribution from the T-T
annihilation under the present experimental conditions. The
triplet lifetime was determined as 360 μs. The decay of the T-T
absorption of 8 in air-saturated PhCN (Figure 10b) was
enhanced significantly as compared with what is observed in
Figure 5. Cyclic voltammograms of compounds 8, 10, 11, and 13−16
−1
in CH Cl containing 0.1 M TBAP at the scan rate of 0.1 V s .
2
2
Time-dependent DFT calculations using the optimized
structure of DFT B3LYP/6-31+G(d,p) revealed the low-energy
transition with the strong oscillator strength. The strong Qy
band in the near-IR region arises from the delocalized π-orbitals
of the HOMO−LUMO. The near-IR transition obtained from
TD-DFT (hν(DFT)) exhibits a linear correlation with the Qy
transition observed in CH Cl (hν(obs)), as shown in Figure 9.
deaerated PhCN (Figure 10a) because of energy transfer from
3
the triplet excited state of 8 ( 8*) to O . The rate constant of
2
3
9
energy transfer from 8* to O was determined to be 1.5 × 10
2
−1
−1
M
s , which is smaller than the reported diffusion rate
37,38
constant in PhCN.
The rate constants of the triplet decay
and energy transfer to O2 for other near-IR absorbing
bacteriochlorins were determined similarly, and the results are
listed in Table 4.
2
2
The slope is close to unity (1.15).
Photophysical Properties. The dynamics of energy
transfer from the triplet excited states of near-IR absorbing
chlorines to dioxygen was examined by nanosecond laser flash
photolysis measurements. Figure 10 shows a triplet−triplet (T-
T) absorption band of 8 observed at 600 nm. Similar T-T
absorption bands were observed for 9-12. In the case of 13,
however, no T-T absorption band was observed probably due
CONCLUSIONS
■
The synthesis of a series of novel bacteriochlorins related to
bacteriochlorophyll a, possessing annulated heterocyclic
systems was achieved. Through the careful synthetic design of
introducing conjugated fused ring systems at the pyrrolic unit
Table 1. Half-Wave and Peak Potentials (V vs SCE) of Investigated Compounds (∼10− M) in CH Cl Containing 0.1 M TBAP
3
2
2
under RT
oxidation
reduction
2nd red
a
b
b
b
cmpd
Δox 2−1
2nd ox
1st ox
1st red
Δred 1−2
HOMO−LUMO gap
8
0.47
0.52
0.53
0.47
0.56
0.54
0.50
1.28
1.14
1.24
1.15
1.14
1.15
1.16
0.81 (0.07)
0.62 (0.08)
0.71 (0.06)
0.68 (0.08)
0.58 (0.06)
0.61 (0.06)
0.66 (0.08)
−0.69 (0.08)
−0.81 (0.08)
−0.63 (0.09)
−0.69 (0.06)
−0.72 (0.08)
−0.70 (0.07)
−0.63 (0.06)
−1.05 (0.07)
−1.14 (0.08)
−0.97 (0.10)
−1.00 (0.07)
−1.05 (0.06)
−1.05 (0.07)
−0.97 (0.07)
0.36
0.33
0.34
0.31
0.33
0.35
0.34
1.50
1.43
1.34
1.37
1.30
1.31
1.29
10
11
13
14
15
16
a
Epa at a scan sate of 0.1 V s . E (ΔE = E − Epc at a scan rate of 0.1 V s−1).
−1
b
1/2
p
pa
1
0266
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Table 2. Thin-Layer Near-IR Spectral Data of Radical Anions and Cations of Investigated Compounds (∼10− M) in CH Cl
3
2
2
Containing 0.1 M TBAP
radical anion
radical cation
λ, nm (ε × 10− M−1 cm−1
4
)
a
λ, nm (ε × 10−4 M−1 cm−1
)
a
cmpd
s
8
364 (5.5)
378 (5.6)
403 (6.5)
557 (2.1)
539 (2.8)
584 (1.7)
601 (2.1)
615 (2.4)
651 (3.1)
544 (2.5)
572 (1.6)
509 (1.4)
768 (1.7)
816 (3.9)
852 (2.4)
830 (2.3)
644 (2.5)
628 (2.3)
761 (1.8)
906 (1.5)
908 (1.1)
1017 (1.5)
1018 (1.4)
889 (1.5)
1039 (1.1)
867 (1.4)
348 (5.4)
365 (7.6)
364 (5.7)
353 (5.3)
353 (8.3)
360 (8.0)
370 (7.3)
396 (8.7)
406 (7.4)
397 (5.7)
413 (8.8)
398 (10.0)
398 (8.8)
392 (6.3)
518 (0.9)
582 (1.3)
434 (6.2)
589 (1.6)
434 (9.0)
429 (9.3)
641 (1.6)
770 (2.7)
730 (1.5)
584 (1.2)
833 (3.4)
800 (1.4)
769 (0.7)
766 (1.4)
836 (1.2)
817 (2.7)
895 (1.8)
885 (1.7)
885 (1.8)
896 (1.3)
866 (1.9)
1
1
1
1
1
1
0
1
3
4
5
6
363 (5.2)
376 (4.4)
363 (4.2)
365 (1.6)
374 (5.1)
369 (6.2)
s
381 (1.6)
398 (5.0)
400 (5.2)
a
Molar absorptivity (ε) of radicals is calculated by comparing the relative intensities of initial (neutral species) and final (radical) spectra, while the ε
of the neutral species was obtained by a regular near-IR measurement in a 1 cm cell; s = shoulder.
Figure 7. Near-IR spectral changes for (a) the first and (b) the second reductions, and (c) the first and (d) the second oxidations of compound 15 in
a thin-layer cell at indicated potentials in CH Cl containing 0.1 M TBAP.
2
2
Table 3. HOMO and LUMO Energies Determined from the
DFT B3LYP/6-31+G(d,p) Level of Theory
bands, accompanied by a significant hyperchromic effect in
several derivatives. Presumably the nature of bathochromic shift
could be explained as a result of a decrease in the energy gap
cmpd
HUMO, eV
LUMO, eV
HOMO−LUMO gap
38,39
between the HOMO and LUMO transitions.
8
−5.35
−5.02
−5.19
−5.13
−5.00
−4.96
−5.08
−3.35
−3.11
−3.39
−3.33
−3.23
−3.22
−3.26
2.00
1.91
1.80
1.80
1.77
1.74
1.82
The observed bathochromic effects in the absorption spectra
of these derivatives were largest in bacterioverdins 14−16,
which possess fused cyclohexenenone ring systems. These
10
11
13
14
15
16
bacteriochlorins have Q absorptions in the near-IR region
y
(
870−890 nm), potentially making them attractive candidates
as photosensitizers in the field PDT, especially for the
treatment of target cells deeply located within tissues. Energy
limitations in singlet oxygen generation likely make chromo-
phores with long-wavelength absorptions above 900 nm
C, we were successful in preparing near-IR absorbing dyes.
Spectroscopic data demonstrated that the outlined modifica-
4
0
nonpractical for PDT. Possibly, bacterioverdins 14−16
tions resulted in large bathochomic shifts in the Q -absorption
possess the longest near-IR shifted absorptions, which could
y
1
0267
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
Figure 8. Plot of HOMO−LUMO gaps determined from CV and
DFT calculations (B3LYP/6-31+G(d,p)).
Figure 10. (a) T-T absorption spectrum of 8 (3.0 × 10− M) obtained
by the laser flash photolysis in deaerated PhCN at 5.6 μs after laser
excitation (562 nm) at 298 K. (b) Decay curves of transient
5
absorbance at 610 nm of 8 (a) in the absence of O and (b) in air-
2
−3
saturated PhCN ([O ]) 1.7 × 10 M) at 298 K.
2
Table 4. Decay Rate Constants of the Triplet−Triplet
Absorption under Argon and Air Atmosphere and Rate
Constants of Energy Transfer from the Excited States to O2
in PhCN at 298 K
kobs(argon), s−
1
kobs(air), s−1
kEN, M−1 s−1
a
cmpd
Figure 9. Plot of the transition energies determined from TD-DFT
calculations (TDB3LYP/6-31+G(d,p)//B3LYP/6-31+G(d,p)) and
electronic absorption spectra.
1.4 × 104
2.3 × 10
1.6 × 104
2.5 × 106
2.5 × 10
1.9 × 106
9
9
9
8
8
8
8
1.5 × 10
1.5 × 10
1.1 × 10
8.8 × 10
8.2 × 10
6.5 × 10
4
6
1
1
1
0
1
4
4
6
4.8 × 10
1.5 × 10
be used to achieve a photodynamic effect. Photochemical
studies and biological testing of these novel bacteriochlorins are
currently under investigation and will be reported elsewhere.
The unique optical properties of the series of annulated
bacteriochlorins make them attractive for other applications,
15
16
4.8 × 104
1.5 × 104
1.4 × 106
1.1 × 106
a
−3
k
= (kobs(argon) − kobs(air)]/[O ]. [O ] under air is 1.7 × 10
EN
2
2
3
5
M.
41
including information-storage media and optical materials. In
addition, bacteriochlorin 8, which possesses a reactive a-
diketone functionality, could be useful also as a synthetic
building block for the preparation of linear porphyrinic arrays
carried out using the laser system. Measurements of the nanosecond
transient absorption spectrum were performed according to the
following procedure. A deaerated solution containing a compound was
excited by a laser. The photodynamics were monitored by continuous
exposure to a xenon lamp (150 W) as a probe light and a
photomultiplier as a detector. The solution was oxygenated by
nitrogen purging for 15 min prior to measurements. All new
compounds decomposed >150 °C.
Theoretical Calculations. Density functional theory (DFT)
calculations were performed with Gaussian09 (Revision A.02) The
calculations were performed on a 32-processor QuantumCube at the
B3LYP/lanl2dz level of theory. Graphical outputs of the computa-
tional results were generated with the GaussView software program
(ver. 3.09) developed by Semichem, Inc. Electronic excitation
energies and intensities were computed by the time-dependent (TD)-
DFT calculation at the B3LYP/lanl2dz level.
integration grid used for all calculations was 10. In each case, 40
excited states were calculated by including all one-electron excitations
38
and other photosynthetic models.
EXPERIMENTAL SECTION
Preparative thin-layer chromatography was performed on 1 mm silica
gel plates. Column chromatography was carried out using silica gel 60
■
(
70−230 mesh). Purity of the isolated products after preparative
4
2
chromatography was monitored using HPLC (RP-18 column) and
UV−vis spectroscopy on spectrophotometer. H NMR spectra were
1
4
3
recorded using deuterochloroform as a solvent. Chemical shifts are
reported in ppm downfield from tetramethylsilane as an internal
standard. The peak assignments of compounds 14−16 were confirmed
by two-dimensional (2D) (COSY, NOESY) methods. Fast atom
bombardment (FAB) low- and high-resolution mass spectra were
obtained on a double focusing, magnetic sector mass spectrometer.
Nanosecond time-resolved transient absorption measurements were
4
4
4
2,45
The size of the
1
0268
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
2
within an energy window of ±3 hartree with respect to the HOMO/
LUMO energies.
Condensation of 13 -Oxo-bacteriopyropheophorbide a
2
Methyl Ester (8) with 1,2-Phenylenediamine (9). 13 -Oxo-
Bacteriopheophorbide a Methyl Ester (4). Rb. sphaeroides
biomass (200 mL) was suspended in 1-propanol (1.5 L) and stirred at
room temperature, in the dark, with constant nitrogen bubbling for 12
h. The blue-green extract was filtered, and aq 0.5 N HCl (50 mL) was
added to the filtrate. The reaction mixture was diluted with aq 5%
NaCl (2 L) and extracted with dicloromethane (3 × 300 mL). The
combined extracts were washed with water (3 × 500 mL), dried, and
evaporated by rotary evaporation. The residue was precipitated from
hexanes to give bacteriopheophytine a (2) (590 mg) with purity
sufficient to proceed to the next step; UV−vis λ (Et O) nm 356,
bacteriopyropheophorbide a methyl ester 8 (100 mg) was dissolved
in pyridine (40 mL), and 1,2- phenylenediamine hydrochloride 9 (200
mg) was added. TFA (0.5 mL) was added, and the reaction mixture
was heated at reflux for 1 h, monitoring the progress spectroscopically.
The reaction mixture was diluted with water (500 mL) and extracted
with dichloromethane. The organic layers were washed with water,
dried over sodium sulfate, filtered, and evaporated in vacuum. The
residue was chromatographed on silica (eluent: dichloromethane−
acetone, gradient 2−5% acetone) to give two bands.
Quinoxalino-bacteriochlorin Methyl Ester (10). was isolated as
a faster moving orange-red band. Yield: 33 mg (29%). Red-brown
max
2
46
4
383, 527, 749; [lit.
λ
(Et O) nm (ε × 10 ) 356 (11.3), 383 (6.27),
max 2
5
25 (2.83), 750 (6.75)]. Compound 2 was dissolved in aq 80% TFA
crystals (from dichloromethane−hexane), UV−vis λmax (CH Cl ) nm
2 2
4
(
100 mL) and stirred in the dark at 0 °C for 2 h. The solution was
(ε × 10 ) 357 (7.36), 387 (8.52), 582 (2.87), 759 (1.48), 816 (10.76);
H NMR δ: 9.24 (s, 2H), 8.51 (s, 2H), 7.96 (m, 2H), 7.49 (m, 2H),
1
then diluted with ice/water (500 mL) and extracted with dicloro-
methane (3 × 200 mL). The combined organic extracts were washed
with water, treated with diazomethane, and evaporated to dryness. The
crude residue was chromatographed on silica (eluent: dichloro-
methane−acetone, gradient 3−5% acetone) to give two bands. The
minor, faster running band was 3-acetyl-3-desvinylpheophorbide a
5.03 (dd, 1H), 4.46 (q, 1H), 4.38 (m, 1H), 4.02 (m, 1H), 3.65 (s, 6H),
3.54 (s, 3H), 3.18 (s, 3H), 2.78 (m, H), 2.67 (m, H), 2.44−2.32 (m,
3H), 2.21 (m, 1H), 1.84 (m, 6H), 1.15 (t, 3H), 0.39 and −0.93 (each
br s, 2H); 13C NMR δ: 199.2, 174.0, 168.0, 167.0, 166.5, 164.2, 163.7,
154.8, 145.8, 141.3, 141.2, 141.1, 135.4, 134.2, 131.7, 131.0, 130.2,
129.4, 129.2, 128.2, 128.0, 125.0, 105.0, 100.3, 100.1, 97.3, 56.3, 52.4,
51.5, 48.4, 47.5, 33.3, 31.9, 31.4, 29.8, 23.9, 23.5, 13.5, 12.3, 10.8;
methyl ester (3) isolated as brown-green band (10 mg, 2%), UV−vis
4
λ
(CH Cl ) nm (ε × 10 ) 412 (11.9), 509 (1.13), 539 (0.98), 619
max
2
2
47
+
+
(
(
6
0.91), 678 (4.79); [lit. λmax (CH Cl ) 412, 510, 540, 620, 678
4.71)]. HRFABMS C H N O [MH] calcd 623.2869, obsd
23.2886.
The second major violet band was bacteriopheophorbide a methyl
ester (4) (350 mg, 91%). UV−vis λ (CH Cl ) nm (ε × 10 ) 362
10.5), 387 (5.19), 532 (2.76), 683 (1.12), 756 (6.27); [lit. λmax
CH Cl ) 362, 387, 503, 530, 628, 680, 755]. HRFABMS C H N O
MH] calcd 625.3026, obsd 625.3043.
Bacteriopyropheophorbide a Methyl Ester (5). Bacteriopheo-
FABMS m/z 653.3 ([MH] , 100%); HRFABMS C H N O [MH]
2
2
40 41 6 3
+
calcd 653.33240, obsd 653.3258.
Benzimidazolo-bacteriochlorin (11). 11 was isolated as the
second slower-eluting red-brown band. Yield: 59 mg (54%). Dark-
purple needles (crystallized from dichloromethane−hexane), UV−vis
3
6
38
4
6
4
max
2
2
4
8
4
(
(
[
λ
(CH Cl ) nm (ε × 10 ) 374 (8.86), 423 (3.54), 553 (3.92), 773
max
2
2
1
(0.98), 850 (8.98); H NMR δ: 9.26 (s, 2H), 8.71 (s, 1H), 8.59 (s,
1H), 8.06 (m, 1H), 7.86 (m, 1H), 7.30 (m, 2H), 5.43 (dd, 1H), 4.36
(m, 2H), 4.12 (m, 1H), 3.84 (s, 3H), 3.65 (s, 3H), 3.56 (s, 3H), 3.23
(s, 3H), 2.76 (m, 1H), 2.47 (m, 3H), 2.12 (m, 2H), 1.86 (m, 6H), 1.17
(t, 3H), −0.29 and −0.43 (each br s, 2H); C NMR δ: 198.5, 173.9,
173.0, 168.9, 167.8, 165.6, 164.2, 148.1, 145.4, 136.9, 135.9, 135.3,
135.1, 132.5, 132.3, 131.3, 130.8, 125.1, 125.0, 119.8, 116.2, 115.9,
102.4, 102.3, 98.5, 97.8, 56.8, 54.9, 51.5, 48.1, 46.9, 33.1, 32.4, 31.1,
2
2
36 40
4
6
+
phorbide a methyl ester, 4 (350 mg), was dissolved in collidine (20
mL) and refluxed under nitrogen for 2 h. The reaction mixture was
diluted with hexane (500 mL), and the precipitate was filtered off and
washed with hexane (100 mL). The residue was chromatographed on
silica (eluent: dichloromethane−acetone, gradient 2−4% acetone) to
separate a minor, faster-running brown band, identified as 3-acetyl-3-
13
+
29.8, 24.1, 23.4, 13.6, 12.6, 10.8; FABMS m/z 639.3 ([MH] , 100%);
HRFABMS C H N O [MH] calcd 669.3189, obsd 669.3173.
+
desvinyl-pyropheophorbide a methyl ester (6) (10 mg, 3%), UV−vis
40
41
6
4
4
2
λ
(
(CH Cl ) nm (ε × 10 ) 412 (11.9), 509 (1.13), 539 (0.98), 619
Perimidino-bacteriochlorin Methyl Ester (13). 13 -Oxo-
bacteriopyropheophorbide a methyl ester 8 (50 mg) was dissolved
in pyridine (20 mL), and 1,9-diaminonaphthalene hydrochloride (100
mg) was added. TFA (0.2 mL) was added, and the reaction mixture
was heated at reflux for 1 h, monitoring the progress spectroscopically.
The reaction mixture was diluted with water (300 mL) and extracted
with dichloromethane. The combined organic layers were washed with
water, dried, and evaporated in vacuum. The residue was chromato-
graphed on silica (eluent: dichloromethane−acetone, gradient 2−5%
acetone) to give the title product as dark-green crystals (from
max
2
2
48
0.91), 678 (4.79); [lit. λmax (CHCl ) 412, 510, 540, 620, 677].
HRFABMS C H N O [MH] calcd 565.2814, obsd 565.2803.
3
+
34
36
4
4
Bacteriopyropheophorbide a Methyl Ester (5). 5 was isolated
as the major product. It was recrystallized from dichloromethane−
hexane to give violet-black crystals (305 mg, 89%). UV−vis λ
max
4
(
(
7
CH Cl ) nm (ε × 10 ) 360 (10.2), 386 (5.23), 532 (2.69), 682
2
2
41
1.09), 754 (6.17); [lit. λ (CH Cl ) 361, 387, 503, 530, 628, 681,
54]. FABMS m/z 567.3 ([MH] , 100%); HRFABMS C H N O
max
2
2
+
34
38
4
4
+
[
MH] calcd 567.2971, obsd 567.2956.
2
1
3 -Oxo-bacteriopyropheophorbide a Methyl Ester (8).
dichloromethane−hexane). Yield: 44 mg (79%). UV−vis λ
max
4
Bacteriopyropheophorbide a methyl ester 5 (300 mg) was dissolved
in THF (100 mL), and a suspension of lithium hydroxide (0.5 g) in
water (4 mL) was added to the solution. The reaction mixture was
vigorously stirred overnight at room temperature and then poured into
water (0.5 L) containing acetic acid (5 mL). The product was
extracted with a dichloromethane−THF mixture (1: 1). The
combined extracts were washed with water, dried over sodium sulfate,
and briefly treated with excess ethereal diazomethane; the solvent was
evaporated in vacuum. The residue was separated on silica gel (eluent:
dichloromethane−acetone, gradient 5−8% acetone), and product 8
was isolated as yellowish-brown band (215 mg, 68%). Dark-brown
solid (from dichloromethane−hexane). UV−vis λ (CH Cl ) nm (ε
(CH Cl ) nm (ε × 10 ) 357 (6.63), 398 (7.69), 534 (2.13), 660
2
2
1
(1.38), 740 (2.28), 829 (13.68); H NMR δ: 9.28 (s, 2H), 8.76 (s,
1H), 8.63 (s, 1H), 8.17 (m, 1H), 7.34 (m, 5H), 5.46 (dd, 1H), 4.38
(m, 1H), 4.19 (m, 1H), 3.82 (s, 3H), 3.66 (s, 3H), 3.65 (s, 3H), 3.22
(s, 3H), 2.74 (m, 1H), 2.46 (m, 3H,), 2.10 (m, 2H), 1.83 (m, 6H),
13
1.18 (t, 3H), −0.69 and −0.83 (each br s, 2H); C NMR δ: 198.6,
173.9, 171.7, 168.7, 166.8, 166.0, 165.6, 146.6, 139.9, 136.0, 135.4,
134.8, 134.4, 134.2, 133.7, 132.7, 132.1, 130.3, 127.7, 127.1, 123.7,
122.7, 121.5, 119.1, 118.3, 115.5, 101.2, 101.1, 99.8, 97.7, 57.0, 54.8,
51.5, 48.0, 47.0, 33.2, 32.2, 31.5, 29.9, 24.2, 23.5, 13.6, 13.3, 10.8;
+
+
FABMS m/z 719.3 ([MH] , 100%); HRFABMS C H N O [MH]
44
43
6
4
calcd 719.3346, obsd 719.3338.
max
2
2
4
1
2
×
10 ) 346 (7.12), 385 (8.73), 518 (1.89), 676 (0.89), 768 (8.97); H
Diazomethane Ring-Enlargement Reaction. 13 -Oxo-bacter-
iopyropheophorbide a methyl ester 8 (100 mg) was dissolved in
dichloromethane (50 mL) and diazomethane, prepared from 2 g of N-
methyl-N-nitroso-p-tolunesulfonamide (Diazald), was added. The
reaction mixture was kept at room temperature in a sealed flask in
the dark overnight, after which the solvent was evaporated in vacuum.
Residue was chromatographed on silica (eluent: dichloromethane−
acetone, gradient 3−5% acetone) to give the three products. The
NMR δ: 9.05 (s, 1H), 8.51 (s, 1H), 8.45 (s, 1H), 5.06 (dd, 1H), 4.56
(
(
1
m, 2H), 4.02 (m, 1H), 3.65 (s, 3H), 3.52 (s, 3H), 3.44 (s, 3H), 3.18
s, 3H), 2.58 (m, H), 2.48 (m, H), 2.24−2.12 (m, 4H), 1.84 (d, 3H),
.78 (d, 3H), 1.13 (t, 3H), −0.29 and −1.03 (each br s, 2H); FABMS
+
+
m/z 581.3 ([MH] , 100%); HRFABMS C H N O [MH] calcd
34
36
4
5
5
7
81.2739, obsd 581.2744. Anal. C: 70.24, H: 6.14, N: 9.68; req. C:
0.32, H: 6.25, N: 9.65.
1
0269
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
2
fastest moving orange-red band was 13 -methoxybacterioverdin
methyl ester (14). Dark-red prisms (from dichloromethane−
methanol). Yield: 30 mg (29%). UV−vis λ (CH Cl ) nm (ε ×
Dichloromethane (CH Cl , 99.8%) was purchased from EMD
Chemicals Inc. and used as received.
2
2
Photophysical Measurements. Absorption spectra were re-
corded on a Hewlett-Packard 8453A diode array spectrophotometer.
Time-resolved fluorescence and phosphorescence spectra were
measured by a Photon Technology International GL-3300 with a
Photon Technology International GL-302 nitrogen laser/pumped dye
laser system equipped with a four-channel digital delay/pulse
generator (Stanford Research System Inc. DG535) and a motor
driver (Photon Technology International MD-5020). Excitation
wavelengths were from 538 to 551 nm using coumarin 540A (Photon
Technology International, Canada) as a dye. Fluorescence lifetimes
were determined by a single exponential curve fit. Nanosecond
transient absorption measurements were carried out using a Panther
OPO-pumped Nd:YAG laser (Continuum, SLII-10, 4−6 ns fwhm) at
430 nm with the power of 3 mJ as an excitation source. Photoinduced
events were estimated by using a continuous Xe lamp (150 W) and an
InGaAs-PIN photodiode (Hamamatsu 2949) as a probe light and a
detector, respectively. The output from the photodiodes and a
photomultiplier tube was recorded with a digitizing oscilloscope
(Tektronix, TDS3032, 300 MHz). The transient spectra were
recorded using fresh solutions in each laser excitation. All experiments
were performed at 298 K.
max
2
2
4
1
1
0 ) 360 (9.56), 424 (5.52), 550 (2.52), 799 (2.08), 891 (5.18); H
NMR δ: 8.93 (s, 1H, 5-H), 8.16 (s, 1H, 20-H), 8.15 (s, 1H, 10-H),
.89 (s, 1H, 13 -H), 4.79 (dd, 1H, 17-H), 4.06 (s, 3H, 13 -OCH ),
.98 (m, 1H, 7-H), 3.86 (q, 1H, 18-H), 3.77 (dd, 1H, 8-H), 3.62 (s,
H, CO CH ), 3.44 (s, 3H, 12-CH ), 3.18 (s, 3H, 2-CH ), 3.09 (s,
H, COCH ), 2.86 (m, H, 17 -H), 2.56 (m, 1H, 8-CH , 17 -H), 2.26
m, 3H, 8-CH , 17 -H,), 2.24 (m, 1H, 17 -H), 1.73 (d, 3H, J = 8.0
Hz, 7-CH ), 1.64 (d, 3H, J = 8.0 Hz, 18-CH ), 1.06 (t, 3H, J = 7.6 Hz,
-CH ), 0.49 and 0.22 (each br s, 2H, 21, 23-NH); C NMR δ:
1
2
6
3
3
3
3
2
3
3
3
1
2
3
a
2
b
1
2
(
2 a′ b′
3
3
2
13
8
1
1
5
1
3
98.3, 182.8, 174.5, 174.0, 168.7, 165.7, 162.8, 153.1, 141.4, 140.0,
33.6, 132.0, 130.7, 128.5, 127.6, 126.9, 104.0, 103.4, 101.8, 99.2, 57.6,
5.9, 55.7, 51.4, 46.1, 45.1, 32.9, 32.7, 30.1, 29.7, 28.9, 24.2, 23.4, 13.3,
+
0.8, 10.4; FABMS m/z 609.3 ([MH] , 100%); HRFABMS
+
C H N O [MH] calcd 609.3077, obsd 609.3054.
36
40
4
5
1
The second band was identified as 13 -methoxybacterioverdin
15) isolated as pink-red crystals. Yield: 45 mg (42%). UV−vis λ
(
(
(
8
3
8
max
4
CH Cl ) nm (ε × 10 ) 369 (10.43), 418 (5.12), 552 (3.72), 779
2
2
1
2.46), 874 (7.85); H NMR δ: 9.05 (s, 1H, 5-H), 8.46 (s, 1H, 10-H),
.37 (s, 1H, 20-H), 5.95 (s, 1H, 13 -H), 5.18 (dd, 1H, 17-H), 4.18 (s,
H, 13 -OCH ), 4.16 (m, 1H, 7-H), 4.05 (q, 1H, 18-H), 3.90 (dd, 1H,
-H), 3.65 (s, 3H, CO CH ), 3.54 (s, 3H, 12-CH ), 3.50 (s, 3H, 2-
CH ), 3.12 (s, 3H, COCH ), 2.76 (m, H, 17 -H), 2.52 (m, 1H, 8-
CH , 17 −H), 2.43 (m, 2H, 8-CH ), 2.14 (m, 2H, 17 -H, 17 -H),
.76 (d, 3H, J = 8.0 Hz, 7-CH ), 1.64 (d, 3H, J = 8.0 Hz, 18-CH ),
.06 (t, 3H, J = 7.6 Hz, 8 -CH ), 0.36 (br s, 2H, 21,23-NH); C NMR
δ: 198.5, 189.8, 174.1, 173.6, 167.3, 166.3, 166.2, 165.1, 139.3, 137.1,
34.2, 133.9, 132.2, 129.9, 129.3, 122.1, 103.7, 103.6, 102.3, 101.4,
7.9, 57.2, 55.8, 54.8, 51.4, 47.2, 46.2, 33.0, 32.6, 30.8, 29.5, 24.2, 23.4,
3.5, 12.4, 10.8; FABMS m/z 609.3 ([MH] , 100%); HRFABMS
C H N O [MH] calcd 609.3077, obsd 609.3066.
2
1
3
2
3
3
1
ASSOCIATED CONTENT
3
3
a
■
2
1
2
2
b
2
a′
b′
*
S
Supporting Information
1
1
1
H and 13C NMR spectra of compounds, their transient
3
3
2
13
3
absorption spectra and crystallographic details for compound
4 in CIF format and an ORTEP diagram of the conformer
1
1
9
1
shown in Figure 4, tables of atom coordinates and absolute
energies to document the theoretical calculations, transient
absorption spectra and full author list of ref 43. This material is
available free of charge via the Internet at http://pubs.acs.org.
+
+
36
40
4
5
3
The third product was identified 13 -methoxybacterioisoverdin
16) isolated as blue-green crystals (from dichloromethane−
methanol). Yield: 18 mg (16%). UV−vis λ (CH Cl ) nm (ε ×
(
max
2
2
AUTHOR INFORMATION
Corresponding Author
*ravindra.pandey@roswellpark.org (R.K.P.); kkadish@uh.edu
K.M.K.); fukuzumi@chem.eng.osaka-u.ac.jp (S.F.); akozyrev@
4
1
■
1
0 ) 371 (8.94), 395 (4.69), 596 (2.13), 766 (2.56), 865 (4.86); H
NMR δ: 8.95 (s, 1H, 5-H), 8.56 (s, 1H, 10-H), 8.36 (s, 1H, 20-H),
.05 (s, 1H, 13 -H), 4.78 (dd, 1H, 17-H), 4.22 (s, 3H, 13 -OCH ),
.18 (m, 1H, 7-H), 4.06 (q, 1H, 18-H), 3.92 (dd, 1H, 8-H), 3.74 (s,
H, 12-CH ), 3.65 (s, 3H, CO CH ), 3.51 (s, 3H, 2-CH ), 3.16 (s,
H, COCH ), 2.56 (m, H, 17 -H), 2.46 (m, 3H, 8-CH , 17 -H), 2.24
1
3
6
4
3
3
3
(
nanosyn.com (A.K.)
Notes
The authors declare no competing financial interest.
3
2
3
3
1
2
3
a
2
b
1
2
(
m, 2H, 17 -H, 17 -H), 1.79 (d, 3H, J = 8.0 Hz, 7-CH ), 1.73 (d,
a
′
b
′
3
2
3
0
1
1
4
H, J = 8.0 Hz, 18-CH ), 1.09 (t, 3H, J = 7.6 Hz, 8 -CH ), 0.39 and
3
3
13
.32 (each br s, 2H, 21, 23-NH); C NMR δ: 198.4, 185.1, 173.6,
71.0, 169.9, 169.1, 168.9, 163.5, 136.7, 136.2, 134.0, 133.9, 133.8,
31.5, 122.0, 103.1, 102.6, 102.5, 101.4, 96.7, 56.4, 56.1, 54.6, 51.6,
8.5, 47.2, 33.1, 31.9, 31.8, 29.8, 29.6, 23.8, 23.0, 13.4, 12.2, 10.7;
ACKNOWLEDGMENTS
■
Support from the NIH (CA127369, CA55791, R.K.P.), Robert
A. Welch Foundation (Grant E-680, K.M.K.) and a Global
COE program from the Ministry of Education, Culture, Sports,
Science and Technology, Japan (to S.F.), and KOSEF/MEST
through WCU projects (R31-2008-000-10010-0), Korea is
gratefully acknowledged. We are thankful to Dr. Fajer,
Brookhaven National Lab (BNL) for X-ray analysis of one of
the bacteriochlorin analogues. The help rendered by Dr. Mark
Renner (ZINDO calculations) and Michael Becker for
crystallizing compound 14 is also appreciated. X-ray data and
were measured at beamline X25 of the National Synchrotron
Light Source and supported by the Center for Research
Resources of the NIH, and the Office of Biological and
Environmental Research and Basic Energy Sciences of the U.S.
Department of Energy, a Grant-in-Aid (No. 20108010 to S.F.
and 23750014 to K.O.). We thank Dr. Avinash Phadke
+
+
FABMS m/z 609.3 ([MH] , 100%); HRFABMS C H N O [MH]
3
6
40
4
5
calcd 609.3077, obsd 609.3078.
Electrochemical Measurements. Cyclic voltammetry was carried
out with an EG&G model 173 potentiostat/galvanostat. A homemade
three-electrode cell was used that consisted of a platinum button or
glassy carbon working electrode, a platinum wire counter-electrode,
and a saturated calomel reference electrode (SCE). The SCE was
separated from the bulk of the solution by a fritted-glass bridge of low
porosity which contained the solvent/supporting electrolyte mixture.
All potentials are referenced to the SCE. Low-temperature measure-
ments were carried out by immersing the cell using a dry ice−acetone
mixture bath.
Thin-layer UV−vis spectroelectrochemical experiments were
performed using a home-built thin-layer cell, which has a transparent
platinum networking electrode. Potentials were applied and monitored
with an EG&G PAR model 173 potentiostat. High-purity N from
2
(
Achillion Pharmaceuticals, Inc.) for valuable discussions, the
Trigas was used to deoxygenate the solution and was kept over the
solution during each electrochemical and spectroelectrochemical
experiment.
Tetra-n-butylammonium perchlorate (TBAP, ≥99%) was purchased
from Fluka Chemical Co., recrystallized from ethyl alcohol, and dried
under vacuum at 40 °C for at least one week prior to use.
late Dr. James L. Alderfer, RPCI, Buffalo, for 2D/ROSEY
measurements and Dr. James G. Pavlovich (UCSB) for help in
obtaining mass-spectra and Drs. A. A.Tsygankov and N. Zorin
(ISP, Puschino-on-Oka, Russian Federation) for a supply of Rh.
sphaeroides biomass. A part of the experimental chemistry/
1
0270
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271

The Journal of Organic Chemistry
Article
analysis was performed at the former Miravant Medical
Technology, Inc. Santa Barbara, CA 93117.
(27) (a) Pandey, R. K., Kozyrev, A. N.; Zheng, L. U.S. Patent
,147,840, 2006. (b) Fukuzumi, S.; Ohkubo, K.; Zheng, X.; Chen, Y.;
Pandey, R. K.; Zhan, R.; Kadish, K. M. J. Phys. Chem. B 2008, 112,
7
2
738.
REFERENCES
■
(28) Kozyrev, A. N.; Alderfer, J. L.; Srikrishnan, T.; Pandey, R. K. J.
Chem. Soc., Perkin Trans. 1 1998, 837.
29) Kozyrev, A. N.; Suresh, V.; Das, S.; Senge, M. O.; Shibata, T.;
Alderfer, J. L.; Dougherty, T. J.; Pandey, R. K. Tetrahedron 2000, 56,
353.
30) Pandey, R. K.; Shiau, F.-Y.; Ramachandaran, K.; Dougherty, T.
D.; Smith, K. M. J. Chem. Soc., Perkin Trans. 1 1992, 1377.
31) Morgan, A. R.; Rampersaud, A.; Keck, R. W.; Selman, S.
Photochem. Photobiol. 1987, 46, 441.
32) Kozyrev, A. N.; Alderfer, J. L.; Dougherty, T. J.; Pandey, R. K.
Chem. Commun. 1998, 1083.
33) Kozyrev, A. N.; Alderfer, J. L.; Dougherty, T. J.; Pandey, R. K.
Angew. Chem., Int. Ed. 1999, 38, 126.
34) ZINDO-S method. In HyperChem, release 7; HyperCube, Inc.:
Gainesville, FL, 2002.
35) Fukuzumi, S.; Ohkubo, K.; Chen, Y.; Pandey, R. K.; Zhan, R.;
Shao, J.; Kadish, K. M. J. Phys. Chem. A 2002, 106, 5105.
36) Geskes, C.; Hartwich, G.; Scheer, H.; Maentele, W.; Heinze, J. J.
Am. Chem. Soc. 1995, 117, 7776.
37) Kadish, K. M.; Caemelbecke, V.; E.; Royal, G. In The Porphyrin
(
1) Ethirajan, M.; Chen, Y.; Penny, J.; Pandey, R. K. Chem. Soc. Rev.
(
2
011, 40, 340−362.
(
2) Dolmans, E. J. G. J.; Kadambi, A.; Hill, J. S.; Waters, C. A.;
Robinson, B. C.; Walker, J. P.; Fukumura, D.; Jain, R. K. Cancer Res.
002, 62, 2151.
3
(
2
(
3) Pandey, R. K.; Herman, C. Chem. Ind. (London) 1998, 739.
4) Bonnett, R. Chem. Soc. Rev. 1995, 19 and references therein.
5) Wilson, B. C. CIBA Found. Symp. 1989, 52, 741.
(
(
(
(
(
6) Jasat, A.; Dolphin, D. Chem. Rev. 1997, 97, 2267 and references
therein.
(
(
7) Lash, T. D.; Werner, T. M.; Thompson, M. L.; Manley, J. D. J.
Org. Chem. 2001, 66, 3152.
(
(
8) Sessler, J. L.; Hemmi, G.; Mody, T. D.; Murai, T.; Burrell, A.;
Young, S. W. Acc. Chem. Res. 1994, 27, 43 and references therein.
9) Vogel, E.; Koch, P.; Hou, X.-L.; Lex, J.; Lausman, M.; Kisters, M.;
Aukauloo, M.; Richard, P.; Guilard, R. Angew. Chem., Int. Ed. Engl.
993, 32, 1600.
10) Kozyrev, A. N.; Efimov, A. V.; Efremova, O. A.; Perepyolkin, P.
Yu.; Mironov, A. F. Proc. SPIE-Int. Soc. Opt. Eng. 1994, 2325, 297.
11) Phadke, A. S.; Robinson, B. C.; Barkigia, K. M.; Fajer, J.
Tetrahedron 2000, 7661.
12) (a) Hynninen, P. H. In The Chlorophylls; Scheer, H., Ed.; CRC
(
(
(
1
(
(
Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.; Academic
Press: San Diego, CA, 2000; Vol. 8; pp 1−97.
(
(38) (a) Fukuzumi, S.; Suenobu, T.; Patz, M.; Hirasaka, T.; Itoh, S.;
(
Fujitsuka, M.; Ito, O. J. Am. Chem. Soc. 1998, 120, 8060. (b) Fukuzumi,
S.; Ohkubo, K.; Imahori, H.; Guldi, D. M. Chem.Eur. J. 2003, 9,
Press: Roca Baton, FL, 1991; pp 146−209. (b) Chen, Y.; Li, G.;
Pandey, R. K. Curr. Org. Chem. 2004, 8, 1105. (c) Yang, E.; Kirmaier,
C.; Krayer, M.; Taniquchi, M.; Kim, H. J.; Diers, J. R.; Bocian, D. F.;
Lindsey, J. S.; Hollen, D. J. Phys. Chem. B 2011, 115, 10801. (d) Kim,
H. J.; Lindsey, J. S. J. Org. Chem. 2005, 70, 5475. (e) Tamiaki, H.;
Miyatake, T.; Tanikaga, R.; Holzwarth, A.; Schaffner, K. Angew. Chem.,
Int. Ed. Engl. 1996, 35, 772 and references therein. (f) Sasaki, S.;
Tamiaki, H. J. Org. Chem. 2006, 71, 2648.
1
2
585. (c) Kawashima, Y.; Ohkubo, K.; Fukuzumi, S. J. Phys. Chem. A
012, 116, 8942.
(39) Noy, D.; Fiedor, L.; Hartwich, G.; Scheer, H.; Scherz, A. J. Am.
Chem. Soc. 1998, 120, 3684.
(
(
40) Frank, B.; Nonn, A. Angew. Chem., Int. Ed. Engl. 1995, 34, 1795.
41) Seidal, D.; Lynch, V.; Sessler, J. L. Angew. Chem., Int. Ed. 2002,
4
1, 1422.
(
13) Yon-Hin, P.; Wijesekera, T. P.; Dolphin, D. Tetrahedron Lett.
991, 32, 2875.
14) (a) Pandey, R. K.; Shiau, F.-Y.; Ramachandaran, K.; Dougherty,
T. D.; Smith, K. M. J. Chem. Soc., Perkin Trans. 1 1992, 1377.
b) Ethirajan, M.; Joshi, P.; William, W. H., Jr.; Ohkubo, K.; Fukuzumi,
S.; Pandey, R. K. Org. Lett. 2011, 13, 1956−1959.
15) Robinson, B. C.; Barkigia, K. M.; Renner, M. W.; Fajer, J. J. Phys.
Chem. B. 1999, 103, 7324.
16) Kay, C. W.; Conti, F.; Fuhs, M.; Plato, M.; Weber, S.;
(42) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
1
(
(43) Frisch, M. J.; et al. Gaussian 09, Revision A.02; Gaussian, Inc.:
Wallingford CT, 2009(see Supporting Information for the complete
reference).
(
(44) Dennington II, R.; Keith, T.; Millam, J.; Eppinnett, K.; Hovell,
W. L.; Gilliland, R. Gaussview, ver. 3.09; Semichem, Inc.: Shawnee
Mission, KS, 2003.
(
(
45) Ethirajan, M.; Joshi, P.; William, W. H.; Ohkubo, K.; Fukuzumi,
S.; Pandey, R. K. Org. Lett. 2011, 13, 1956.
46) Crossley, M. J.; Langford, S. J.; Parashar, J. K.; Burn, P. L. J.
Chem. Soc., Chem. Commun. 1998, 1921.
47) Hartwich, G. A.; Fiedor, L.; Simonin, I.; Cmiel, E.; Schafer, W.;
Noy, D.; Scherz, A.; Scheer, H. J. Am. Chem. Soc. 1998, 120, 3675.
48) Kozyrev, A. N.; Perepyolkin, P. Y.; Mironov, A. F. Proc. SPIE-Int.
Soc. Opt. Eng. 1993, 186.
(
Bordignon, E.; Carbonera, D.; Robinson, B. C.; Renner, M. W.; Fajer,
J. J. Phys. Chem. B 2002, 106, 2769.
(
(
(
17) Robinson, B. C. Tetrahedron 2000, 56, 6005.
18) Morgan, A. R.; Skalkos, D.; Garbo, G. D.; Keck, R. W.; Selman,
(
S. H. J. Med. Chem. 1991, 34, 2126.
19) (a) Pandey, R. K.; Goswami, L. N.; Chen, Y.; Grushuk, A.;
Missert, J. R.; Oseroff, A.; Dougherty, T. J. Lasers Surg. Med. 2006, 38,
45 and references therein. (b) Pandey, R. K.; Zheng, G. In The
(
(
4
Porphyrin Handbook; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press, San Diego, 2000; Vol. 6, pp 157−230.
(
20) Beems, E. M.; Dubbelman, T. M. A. R.; Lugtenberg, J.; Van
Best, J. A.; Smeets, M. F. M. A.; Boegheim, J. P. Photochem. Photobiol.
987, 45, 639.
21) Henderson, B. W.; Sumlin, A. B.; Owczarczak, B. L.; Dougherty,
T. J. J. Photochem. Photobiol. B 1991, 10, 303.
22) Kozyrev, A. N.; Zheng, G.; Dougherty, T. J.; Smith, K. M.;
Pandey, R. K. Tetrahedron Lett. 1996, 37, 6431.
23) (a) Kozyrev, A. N.; Dougherty, T. J.; Pandey, R. K. Chem.
1
(
(
(
Commun. 1998, 481. (b) Joshi, P.; Ethirajan, M.; Goswami, L. N.;
Srivatsan, A.; Missert, J. R.; Pandey, R. K. J. Org. Chem. 2011, 76, 8629.
(
24) Mironov, A. F.; Kozyrev, A. N.; Brandis, A. S. Proc. SPIE-Int. Soc.
Opt. Eng. 1992, 202.
(
(
25) Wasielewski, M. R.; Svec, W. A. J. Org. Chem. 1980, 45, 1969.
26) Fischer, H.; Lambrecht, R.; Mittenzwei, H. Z. Physiol. Chem.
1
938, 253, 1.
1
0271
dx.doi.org/10.1021/jo301895p | J. Org. Chem. 2012, 77, 10260−10271