Synthesis of doubly locked 5Zs15Za-biliverdin derivatives and their unique spectral behavior

Article abstract of DOI:10.1246/cl.2009.602

Doubly locked 5Zs15Zb-biliverdin (BV) derivatives were synthesized toward the investigation of stereochemistry and function of the chromophore in bacteriophytochromes. The unique spectral behavior of the doubly locked 5Zs15Za-BV derivatives was observed b

Full text of DOI:10.1246/cl.2009.602

602
Chemistry Letters Vol.38, No.6 (2009)
Synthesis of Doubly Locked 5Zs15Za-Biliverdin Derivatives
and Their Unique Spectral Behavior
Liyi Chen, Hideki Kinoshita, and Katsuhiko Inomataꢀ
Division of Material Sciences, Graduate School of Natural Science and Technology,
Kanazawa University, Kakuma, Kanazawa 920-1192
(Received March 25, 2009; CL-090305; E-mail: inomata@cacheibm.s.kanazawa-u.ac.jp)
Me
Doubly locked 5Zs15Za-biliverdin (BV) derivatives were
O
Me
Et
synthesized toward the investigation of stereochemistry and
function of the chromophore in bacteriophytochromes. The
unique spectral behavior of the doubly locked 5Zs15Za-BV
derivatives was observed by UV–vis spectroscopy.
Me
A
Et
N
D
N
15
O
D
N
Za
5
Zs
NH
O
Za
C
N
N
C
B
CHO
Me
10
1, R = H
2, R = Allyl
CO2Allyl
3
STol
CO2R
Me
CO2R
Phytochromes are photoreceptive chromoproteins ubiqui-
tously present in plants and have also been found in bacteria
and fungi. They interchange reversibly by specific wavelengths
of light between two isomers, red light absorbing Pr form and
far-red light absorbing Pfr form, and it is known to cause the
photoreaction referred to as ‘‘red/far-red photoreversible reac-
tion.’’1 This photoreaction plays an essential role in many bio-
logical processes, such as seed germination, growth, and flower-
ing in plants; phototaxis, and pigmentation in bacteria. The
open-chain tetrapyrroles serve as a chromophore of phyto-
chromes, phytochromobilin (PꢀB) for land plants, phycocyano-
bilin (PCB) for cyanobacteria, and biliverdin (BV) for some
other bacteria. Recently, we revealed that BV covalently binds
to the apoproteins of Agrobacterium phytochromes Agp 1 and
Agp 2 via the A-ring vinyl side chain,2,3 and that the absorption
spectra of the locked 15Za-BV and 15Ea-BV adducts resemble
the spectra of Pr and Pfr, respectively.3
Hildebrandt and his co-workers proposed that a chromo-
phore in the plant phytochrome corresponding to Pr form has a
5Za15Za structure on the basis of DFT calculation of resonance
Raman spectra.4 On the other hand, we found that the chromo-
phore in the Pr form of Agp 1 and Agp 2 has a 5Zs15Za struc-
ture,3b which was also confirmed by X-ray crystallography for
other bacteriophytochromes.5 To investigate the structure and
function of the BV chromophores, we herein describe the syn-
thesis of doubly locked BV derivatives, which have 5Zs15Za
configuration and conformation corresponding to Pr form of
Agp 1 and Agp 2. A retrosynthetic analysis of the doubly locked
5Zs15Za-BV (1) is shown in Figure 1.
Compound 6 as the precursor of the B-ring was previously
prepared from allyl 4-oxobutanoate (7) obtained by the reaction
of ꢀ-butyrolactone (8) with sodium allyloxide and subsequent
oxidation.6 However, it was not easy to get reproducible high
yield of the key intermediate, allyl 4-hydroxybutanoate (9),
owing to the recyclization back to 8 under basic conditions.
Therefore, 8 was hydrolyzed with an equimolar amount of DBU,
followed by esterification with allyl bromide to avoid the recy-
clization to lactone 8. The initial hydrolysis completed within
1 h at rt. Yield of the following allylation was strongly affected
by stirring efficiency due to the heterogeneous reaction phase.
Thus, THF, acetone, or DMF was added to improve the yield.
Fortunately, the reaction mixture with a small amount of DMF
was kept homogeneous throughout the reaction to afford 9 in
3
Me
O
H
A
CN
CO2tBu
O
Ts
A
N
N
5
H
+
+
Zs
CO2Allyl
CO2tBu
EtNO2
+
N
B
Me
Me
tBuO2C
O
B
H
CO2Allyl
OHC
N
CO2Allyl
7
6
H
4
Figure 1. Retrosynthesis of doubly locked 5Zs15Za-BV (1).
94% yield, while the reaction with THF or acetone was still het-
erogeneous in the allylation stage. Compound 9 was oxidized to
the corresponding aldehyde 7, from which the B-ring precursor 6
was prepared according to our previous method (Scheme 1).6
Applying our original Wittig-type reaction (Scheme 2), 5-
tosylpyrrolinone 5 and formylpyrrole 6 were coupled to dipyr-
role 10 as a mixture of E and Z isomers, then E isomer was con-
verted to Z isomer with a catalytic amount of I2.7 (Z)-10 was
locked in Zs configuration and conformation with BrCH2CH2Br
in the presence of n-Bu4NBr. The vinyl group of compound 4
was introduced by the elimination of the tolylthio group via ox-
idation from the locked product 11. Compound 12, which was
produced by decarboxylation of 4 with TFA, was mixed with
compound 38 under acidic conditions to construct the doubly
locked 5Zs15Za-BV diallyl ester 2.9 5Zs15Za-BV (1)10 in free
acid form was furnished by treating 2 with sodium p-toluenesul-
finate (TsNa) in the presence of Pd catalyst.
When the UV–vis spectrum of 2 was measured as usual, in-
terestingly the color of the solution in methanol changed from
blue to green within a few minutes. As such phenomenon has
not been observed so far for other synthesized chromophores,
the UV–vis spectra of 5Zs15Za-BV diallyl ester 2 were carefully
investigated (Figure 2).
O
O
OAllyl
a
b
c
HO
O
6
H
CO2Allyl
O
8
9
7
Scheme 1. aH2O (13.0 equiv), DBU (1.0 equiv), DMF (0.28 mL/mmol),
rt, 1 h; then allyl bromide (1.5 equiv), rt, 4 h. 9, 94% from 8. b(COCl)2
(1.1 equiv), DMSO (2.0 equiv), Et3N (5.0 equiv), CH2Cl2, ꢁ78 ꢂC to rt,
c
1 h, 7, 85%. Ref. 6.
Copyright Ó 2009 The Chemical Society of Japan

Chemistry Letters Vol.38, No.6 (2009)
603
As described above, we successfully prepared the doubly
locked 5Zs15Za-BV derivatives 1 and 2 corresponding to the
chromophore in Pr form of Agp 1 and Agp 2, and found their
unique spectral behavior by UV–vis spectroscopy, which is
highly suggestive for our previous observation that the Agp 1
and Agp 2 adducts with the ‘‘15-syn chromophores’’ absorbed
in the blue spectral region only,3 probably due to the common
syn conformation at the C5- or C15-position of the bilin chromo-
phores.
Me
Me
Me
O
O
O
STol
c
STol
d, e
A
A
A
HN
N
N
5
+
6
a, b
g
h
1
Zs
Zs
2
(R = H)
HN
N
N
B
B
B
Me
Me
Me
tBuO2C
tBuO2C
R
CO2Allyl
CO2Allyl
CO2Allyl
f
10
11
4 (R = CO2tBu)
[12] (R = H)
Scheme 2. an-Bu3P (2.2 equiv), DBU (1.5 equiv), THF, 0 ꢂC to rt, 8 h. bI2
(0.2 equiv), CH2Cl2, rt, 4 h, (Z)-10, 90% in two steps. cNaH (7.0 equiv),
n-Bu4NBr (0.2 equiv), (BrCH2)2 (10 mL/mmol), THF, rt, 15 h, 11, 80%.
dmCPBA (1.0 equiv), CH2Cl2, 0 ꢂC, 0.5 h. eDBU (3.0 equiv), DMF,
The present work was financially supported in part by a
Grant-in-Aid for Scientific Research (B) (No. 19350082) from
Japan Society for the Promotion of Science (JSPS).
f
100 ꢂC, 1 h. 4, 85% in two steps. TFA (5 mL/mmol), rt, 40 min. g3 (1.0
equiv), TFA (4.0 equiv), MeOH, rt, 1 h; then mixed with 12, rt, 6 h. 2,
90%. h[Pd(PPh3)4] (0.2 equiv), TsNa (2.0 equiv), THF/MeOH (1/1), rt,
30 min, 1, 70%.
References and Notes
1
2
3
M. Wada, K. Shimazaki, M. Iino, Light Sensing in Plants, Springer-
Verlag, Tokyo, 2005.
T. Lamparter, N. Michael, O. Caspani, T. Miyata, K. Shirai, K.
Inomata, J. Biol. Chem. 2003, 278, 33786.
a) K. Inomata, M. A. S. Hammam, H. Kinoshita, Y. Murata, H. Khawn,
S. Noack, N. Michael, T. Lamparter, J. Biol. Chem. 2005, 280, 24491.
b) K. Inomata, S. Noack, M. A. S. Hammam, H. Khawn, H. Kinoshita,
Y. Murata, N. Michael, P. Scheerer, N. Krauss, T. Lamparter, J. Biol.
Chem. 2006, 281, 28162.
0.4
0.3
0.2
0.1
0
4
5
M. A. Mroginski, D. H. Murgida, D. von Stetten, C. Kneip, F. Mark, P.
Hildebrandt, J. Am. Chem. Soc. 2004, 126, 16734.
J. R. Wagner, J. S. Brunzelle, K. T. Forest, R. D. Vierstra, Nature 2005,
438, 325; J. R. Wagner, J. Zhang, J. S. Brunzelle, R. D. Vierstra, K. T.
300
400
500
600
700
800
I;
II;
Wavelengh (nm)
III;
IV
Figure 2. Absorption spectra of a solution of 2 in CHCl3/MeOH (1/4,
v/v). I, a freshly prepared solution of 2; II, I + one drop of 1 M HCl;
III, a solution of 2 kept for 24 h at rt; IV, III + one drop of 1 M HCl.
´
Forest, J. Biol. Chem. 2007, 282, 12298; X. Yang, E. A. Stojkovic, J.
Kuk, K. Moffat, Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 12571; L.-O.
Essen, J. Mailliet, J. Hughes, Proc. Natl. Acad. Sci. U.S.A. 2008, 105,
14709.
6
A. Ohta, D. Sawamoto, K. P. Jayasundera, H. Kinoshita, K. Inomata,
Chem. Lett. 2000, 492.
-
Cl
+
NH
N
NH
N
7
8
T. Kakiuchi, H. Kinoshita, K. Inomata, Synlett 1999, 901.
M. A. S. Hammam, H. Nakamura, Y. Hirata, H. Khawn, Y. Murata, H.
Kinoshita, K. Inomata, Bull. Chem. Soc. Jpn. 2006, 79, 1561.
2: Mp 180–183 ꢂC (from CH2Cl2/hexane). IR (KBr): 2964, 2924,
2873, 2855, 1735, 1682, 1618, 1580, 1455, 1424, 1385, 1353, 1275,
C
C
B
B
10
H
10
Me
Me
HCl
MeOH
H
2
MeO
CO2Allyl
– MeOH
9
CO2Allyl
CO2Allyl
CO2Allyl
1151, 1065, 985, 951, 933, 892, 845, 755 cmꢁ1 1H NMR (CDCl3,
.
Scheme 3.
400 MHz): ꢂ 1.11 (t, J ¼ 7:6 Hz, 3H), 2.07 (s, 3H), 2.11 (s, 3H), 2.12
(s, 3H), 2.39 (q, J ¼ 7:6 Hz, 2H), 2.53 (t, J ¼ 7:6 Hz, 2H), 2.58 (t,
J ¼ 7:6 Hz, 2H), 2.82 (br, 2H), 2.94 (t, J ¼ 7:4 Hz, 4H), 3.89 (br,
2H), 4.54 (d, J ¼ 5:5 Hz, 4H), 5.18 (dt, J ¼ 10:5, 1.4 Hz, 1H), 5.19
(dt, J ¼ 10:5, 1.4 Hz, 1H), 5.25 (dt, J ¼ 17:0, 1.4 Hz, 2H), 5.64 (dd,
J ¼ 17:6, 1.4 Hz, 1H), 5.67 (dd, J ¼ 11:5, 1.4 Hz, 1H), 5.81–5.91
(m, 2H), 6.18 (s, 1H), 6.28 (s, 1H), 6.66 (dd, J ¼ 17:6, 11.7 Hz, 1H),
6.94 (s, 1H). The protons of the ethylene bridge between the nitrogens
of A- and B-rings appeared around 4.30 ppm as a very broad signal.
UV–vis (0.1 M HCl in MeOH): ꢃmax ¼ 377 (" ¼ 28540 Mꢁ1 cmꢁ1),
709 (82210) nm. HRMS (FAB) [M + 1]þ, Found: m=z 703.35061.
Calcd for C42H47N4O6: 703.34956.
The freshly prepared solution of 2 in CHCl3/MeOH (1/4,
v/v) had absorptions at 387 and 621 nm, and they shifted to 385
and 718 nm by addition of one drop of 1 M HCl. On the other
hand, when the solution of 2 in CHCl3/MeOH (1/4, v/v) was
kept at rt, a spectral change was observed. The absorption around
621 nm was diminished and a new peak appeared around 425 nm
as the color turned green. After 24 h, the peak around 621 nm
disappeared completely, and the solution changed to yellow. It
was also observed that a methine proton at C10-position of 2 dis-
1
appeared in the H NMR spectrum of the residue obtained by
10 1 was isolated as HCl salt, a dark blue solid. Decomposed above
270 ꢂC. IR (KBr): 3450, 2969, 2931, 2865, 2556, 1696, 1615, 1590,
1459, 1418, 1397, 1355, 1305, 1281, 1179, 1132, 1062, 987, 954,
evaporation of the solvent of solution III (Figure 2), although
the spectrum became rather complicated. Very interestingly
the absorption bands around 385 and 718 nm appeared again
when one drop of 1 M HCl solution was added to the resulting
yellow solution III. These facts suggest that the ꢁ-conjugation
of tetrapyrrole was destroyed at the C10-position of 2 by the ad-
dition of methanol and recovered under the acidic conditions
(Scheme 3).
Almost the same spectral behavior was observed for the free
acid form 1, while the addition of methanol proceeded much
faster than in the case of 2 probably owing to the self-protonation
by the free acids onto the nitrogen atom of the C-ring.
883, 695 cmꢁ1
.
1H NMR (C5D5N, 400 MHz): ꢂ 1.01 (t, J ¼ 7:5 Hz,
3H), 1.83 (s, 3H), 1.93 (s, 3H), 2.03 (s, 3H), 2.28 (q, J ¼ 7:5 Hz, 2H),
2.83–2.90 (m, 6H), 3.16 (t, J ¼ 7:1 Hz, 2H), 3.23 (t, J ¼ 7:6 Hz, 2H),
3.98 (br, 2H), 5.58 (d, J ¼ 11:7 Hz, 1H), 5.59 (d, J ¼ 17:8 Hz, 1H),
6.25 (s, 1H), 6.54 (s, 1H), 6.75 (dd, J ¼ 17:8, 11.5 Hz, 1H), 7.56 (s,
1H). The protons of the ethylene bridge between the nitrogens of
A- and B-rings appeared around 4.48 ppm as a very broad signal and
CO2H protons were not observed clearly. UV–vis (0.1 M HCl in
MeOH): ꢃmax ¼ 379 (" ¼ 28020 Mꢁ1 cmꢁ1), 710 (83400) nm. HRMS
(FAB) [M + 1]þ (observed as a free chromophore without HCl),
Found: m=z 623.28643. Calcd for C36H39N4O6: 623.28696.
Published on the web (Advance View) May 23, 2009; doi:10.1246/cl.2009.602