Full text of DOI:10.1070/MC2002v012n02ABEH001536

Mendeleev Commun., 2002, 12(2), 77–78
Synthesis of chlorin e6 amide derivatives
Dmitrii V. Belykh, Lyudmila P. Karmanova, Leonid V. Spirikhin and Aleksandr V. Kutchin*
Institute of Chemistry, Komi Scientific Centre, Urals Branch of the Russian Academy of Sciences,
167982 Syktyvkar, Russian Federation. Fax: +7 8212 43 6677; e-mail: chemi@mail.komisc.ru
10.1070/MC2002v012n02ABEH001536
The reactions of methylpheophorbide a with primary and secondary amines have been investigated as a means for the synthesis of
sensitizers used in the photodynamic therapy of tumors.
It was found earlier that the exo cycle E of methylpheophorbide
3(2)
3(1)
3
3(2)
3(1)
3
7(1)
7(1)
a 1 can be easily opened by simple primary amines (methyl-
amine1 and ethylamine2) with the formation of amides 2 and 3
(Figure 1), respectively. The analogous interaction of 1 with
secondary amines has not been reported, although it is interest-
ing for the synthesis of sensitizers for the photodynamic therapy
of tumors.3,4
It is well known that the insertion of a hydroxyl group
increases the hydrophilicity of porphyrin and the selectivity
of its accumulation in tumors.3 Nucleophilic substitution with
ethanolamine at C-13(1) in the exo cycle E of 1 may be a
convenient method for the insertion of a hydroxyl group into
the porphyrin molecule. In this work, secondary and tertiary
chlorin e6 amides 4–6 (Figure 1) were synthesised using the
reaction of nucleophilic substitution at C-13(1) in the exo cycle
E of 1.†
Chlorin e6 13(1)-N-(2-hydroxyethyl)amide-15(2),17(3)-di-
methyl ester 4‡ was prepared by the treatment of 1 with ethanol-
amine in chloroform at room temperature. Valency vibration
band of C=O 13(1) keto group is absent from the IR spectrum
of the substance obtained and bands ‘amide-I’ (at 1638 cm–1),
‘amide-II’ (at 1526 cm–1), valency vibration band of amide N–H
(weak band at 3100 cm–1) are present in this spectrum. The
5
5
7
7
6
6
8(1)
8(2)
8(1)
8(2)
2(1)
2
20
18
4
2(1)
2
4
A
A
B
B
8
8
N
N
NH
NH
9
9
1
1
10
10
20
19
19
11
11
18(1)
18(1)
N
HN
N
HN
12
12
D
D
C
C
16 14
16 14
18
17(1)
17(2)
12(1)
12(1)
13
13
13(1)
17
17
15
15
E
E
17(1)
13(1)
15(1)
13(2)
R
15(3)
13(4)
MeO2C
17(2)
O
O
17(4)
17(4)
MeO2C
15(2)
13(3)
MeO2C
MeO2C
17(3)
17(3)
–
2 6
1
1 Methylpheophorbide a
2 Chlorin e6 13(1)-N-methylamide-15(2),17(3)-dimethyl ester: R = NHMe
3 Chlorin e6 13(1)-N-ethylamide-15(2),17(3)-dimethyl ester: R=NHEt
4 Chlorin e6 13(1)-N-(2-hydroxyethyl)amide-15(2),17(3)-dimethyl ester:
R=NHCH2CH2OH
5 Chlorin e6 13(1)-N,N-dimethylamide-15(2),17(3)-dimethyl ester:
R=NMe2
6 Chlorin e6 13(1)-morpholinoamide-15(2),17(3)-dimethyl ester,
numbering:
†
1H and 13C NMR spectra were obtained in deuterochloroform solutions
at 300 and 75 MHz using a Bruker AM-300 spectrometer. Signals were
assigned by a comparison with the spectra of chlorin e6 13(1)-N-ethyl-
amide-15(2),17(3)-dimethyl ester 3.2 IR spectra were obtained in KBr
pellets on a Specord M80 spectrometer. UV-VIS spectra were obtained in
chloroform solutions using a Lambda 20 spectrometer (Perkin–Elmer)
in a range of 350–750 nm. HPLC analysis was carried out on a ‘Mili-
khrom 1’ chromatograph (column 2×64 mm; Silasorb 600, 5.0 µm).
Benzene–ethyl acetate in a ratio of 7:5 was used as an eluent for the
analysis of amide 5. Silica gel (La Chema, 40–100 mesh) was used for
column chromatography.
Figure 1 Chlorophyll derivatives.
1H NMR spectrum shows a triplet of amide group NH proton
(at 6.88 ppm) and doublets of 15(1)-methylene group protons
[5.58 (d, 1H, J 18.4 Hz) and 5.31 (d, 1H, 18.4 Hz)]. The singlets
of 5-, 10- and 20-protons in the amide spectrum are downfield
shifted with respect to analogous signals of methylpheophorbide
a spectrum, and a difference between their chemical shifts is
smaller. The downfield shifts of 5-, 10- and 20-proton signals
and a decrease of the chemical shift difference between 5- and
10-protons may be explained by an increase in ‘ring current’
and the leveling of this proton shielding caused by exo ring
opening.
The interaction of 1 with secondary amines (dimethylamine,
morpholine) was carried out by the same way. The structures
of tertiary amides 5§ and 6¶ were determined by IR and NMR
spectroscopy. The ‘amide-I’ bond in IR spectra of compounds
obtained and 15(1)-methylene group signals in 1H NMR spectra
show that exo cycle E recovering and amide formation occur.
An NMR and HPLC study of compounds 5 and 6 shows that
each of these substances exists as two isomers in the ratio 2:1.
We suppose that the 13(1)-amide group and a chlorin ring are
in different planes, and tertiary amide isomers differ in the
General procedure for the synthesis of chlorin e6 13(1)-amides-
15(2),17(3)-dimethyl ester. A solution of 1 in chloroform (3 ml) was stirred
with an amine (0.3 ml; for dimethylamine, 0.5 ml of a 33% aqueous
solution) at room temperature until the absence of the starting material
(TLC). The reaction mixture was diluted with chloroform (50 ml), washed
with water (3×100 ml), dried (Na2SO4) and evaporated to dryness at 30–
40 °C under reduced pressure. The product was purified by column
chromatography on silica gel (eluent: tetrachloromethane–acetone) and
reprecipitated from chloroform–pentane.
‡
Chlorin e6 13(1)-N-(2-hydroxyethyl)amide-15(2),17(3)-dimethyl ester.
Compound 4 (222 mg, 63%) was obtained from 322 mg of 1. Amide 4
was eluted with CCl4–acetone (3:1, v/v). 1H NMR, d: 9.69 (s, 1H, 10-H),
9.64 (s, 1H, 5-H), 8.81 (s, 1H, 20-H), 8.10 [dd, 1H, 3(1)-H, J 17.7 and
11.6 Hz], 6.37 [dd, 1H, 3(2)-H (trans) J 17.7 and 1.4 Hz], 6.15 [dd, 1H,
3(2)-H (cis), J 11.6 and 1.4 Hz], 6.88 [br. t, 1H, 13(1)-NH (amide), J
5.7 Hz], 5.58 [d, 1H, 15(1)-CH2(B), J 18.4 Hz], 5.31 [d, 1H, 15(1)-
CH2(A), J 18.4 Hz], 4.47 (m, 1H, 18-H), 4.40 (m, 1H, 17-H), 3.75 [s, 3H,
15(3)-Me], 3.61 [s, 3H, 17(4)-Me], 3.57 [s, 3H, 12(1)-Me], 3.50 [s, 3H,
1(1)-Me], 3.31 [s, 3H, 7(1)-Me], 3.81 [q, 2H, 8(1)-CH2, J 7.5 Hz], 2.2–
2.6 [m, 4H, 17(1)-CH2, 17(2)-CH2], 1.71 [d, 3H, 18(1)-Me, J 7.0 Hz],
1.72 [t, 3H, 8(2)-Me, J 7.5 Hz], 3.80–3.95 [m, 2H, 13(2)-CH2], 4.02 [t,
2H, 13(3)-CH2, J 5 Hz]. 13C NMR, d: 174.37, 173.53, 170.48, 168.94,
166.63, 154.34, 149.06, 144.82, 138.99, 136.10, 134.92, 134.61, 130.26,
129.77, 129.43, 127.72, 121.68, 102.02, 101.47, 98.84, 93.65, 62.09, 53.03,
52.27, 51.59, 49.18, 43.55, 37.98, 31.06, 29.72, 17.68, 12.13, 11.99, 11.32.
IR (KBr, n/cm–1): 1740 (ester nC=O), 1638 (‘amide-I’), 1610 (‘chlorin
band’), 1526 (‘amide-II’). UV-VIS [CHCl3, l/nm (lg e)]: 663.7 (4.76),
608.1 (3.76), 557.9 (3.34), 529.0 (3.69), 500.5 (4.21), 401.6 (5.13).
1
13(1)-amide group position relatively to a chlorin ring. The H
and 13C NMR spectra of the tertiary amides should be inter-
preted as a superposition of the spectra of two isomers (‘double
set of signals’). Each of superposed spectra has the same amount
of signals (for 1H and 13C NMR spectra) of the same multiplicity
(for 1H NMR spectra). The intensity ratio between isomer signals
1
in H NMR spectra of both tertiary amides is 2:1. HPLC data
are consistent with NMR data. The HPLC of 5 shows two peaks
in a ratio of 2:1 (by intensity).
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Mendeleev Commun., 2002, 12(2), 77–78
References.
It is possible that different positions of the 13(1)-amide group
relatively to the chlorin ring influence the electronic surrounding
of nearest protons and, therefore, the chemical shifts of their
signals. For example, the greatest chemical shift difference of
proton signals between isomers is observed for 15(1)-CH2 protons.
It indicates different influences of the amide group on the
electronic surroundings of these protons at different positions
relatively to the chlorin ring.
1 P. A. Ellsworth and C. B. Storm, J. Org. Chem., 1978, 43, 281.
2 L. Ma and D. Dolphin, Tetrahedron, 1996, 52, 849.
3 A. F. Mironov, Ross. Khim. Zh., 1998, no. 5, 23 (in Russian).
4 A. F. Mironov, SPIE Proceedings CIS Selected Papers ‘Laser Use in
Oncology’, 1996, vol. 2728, pp. 150–164.
Longwave bonds in the electron spectra of all amides are
in the range 663–664 nm. Thus, these compounds should be
interesting as potential sensitizers for the photodynamic therapy.
§
Chlorin e6 13(1)-N,N-dimethylamide-15(2),17(3)-dimethyl ester. Com-
pound 5 (35 mg, 54%) was obtained from 60 mg of 1. The amide was
eluted with CCl4–acetone (10:1, v/v). 1H NMR, d: major isomer: 9.75 (s,
1H, 10-H), 9.71 (s, 1H, 5-H), 8.88 (s, 1H, 20-H), 8.15 (dd, 1H, J 17.9
and 11.5 Hz), 6.40 [dd, 1H, 3(2)-H (trans), J 1.8 and 19.6 Hz], 6.18 [dd,
1H, 3(2)-H (cis), J 1.6 and 11.5 Hz], 5.88 [d, 1H, 15(1)-CH(B), J 19 Hz],
5.08 [d, 1H, 15(1)-CH(A), J 18.9 Hz], 4.4–4.6 (m, 2H, 18-H, 17-H),
3.84 [s, 3H, 15(3)-Me], 3.68 [s, 3H, 17(4)-Me], 2.78 [s, 3H, 13(1)-
NMe2], 3.4–4.0 [m, 14H, 12(1)-Me, 1(1)-Me, 7(1)-Me, 13(1)-NMe2,
8(1)-CH2], 2.1–2.7 [m, 4H, 17(1)-CH2, 17(2)-CH2], 1.75 [m, 6H, 18(1)-
Me, 8(2)-Me]; minor isomer: 9.73 (s, 1H, 10-H), 9.68 (s, 1H, 5-H), 8.83
(s, 1H, 20-H), 8.13 (dd, 1H, J 17.7 and 11.5 Hz), 6.40 [dd, 1H, 3(2)-H
(trans), J 1.8 and 19.6 Hz], 6.18 [dd, 1H, 3(2)-H (cis), J 1.6 and
11.5 Hz], 5.73 [d, 1H, 15(1)-CH(B), J 19.3 Hz], 5.16 [d, 1H, 15(1)-
CH(A), J 19.2 Hz], 4.4–4.6 (m, 2H, 18-H, 17-H), 3.80 [s, 3H, 15(3)-
Me], 3.70 [s, 3H, 17(4)-Me], 3.13 [s, 3H, 13(1)-NMe2], 3.4–4.0 [m, 14H,
12(1)-Me, 1(1)-Me, 7(1)-Me, 13(1)-NMe2, 8(1)-CH2], 2.1–2.7 [m, 4H,
17(1)-CH2, 17(2)-CH2], 1.75 [m, 6H, 18(1)-Me, 8(2)-Me]. 13C NMR, d:
major isomer: 173.45, 173.29, 170.64, 168.70, 167.28, 154.20, 149.32,
144.74, 138.79, 136.27, 134.76, 134.62, 133.77, 130.42, 130.09, 129.66,
127.09, 121.60, 102.46, 101.01, 98.91, 93.88, 52.96, 49.18, 51.92, 51.77,
37.04, 35.31, 31.36, 29.87, 23.10, 19.80, 17.58, 12.24, 11.86, 11.35;
minor isomer: 173.45, 173.29, 170.19, 168.96, 166.53, 154.20, 149.08,
144.74, 138.79, 136.18, 135.19, 134.52, 133.77, 130.42, 130.20, 129.66,
127.09, 121.60, 102.77, 101.01, 98.91, 93.65, 53.75, 49.53, 52.08, 51.77,
37.73, 35.27, 31.93, 29.87, 23.19, 19.80, 17.58, 12.24, 12.00, 11.35. IR
(KBr, n/cm–1): 1746 (ester nC=O), 1632 (‘amide-I’), 1613 (‘chlorin band’).
UV-VIS [CHCl3, l/nm (lg e)]: 663.7 (4.70), 608.0 (3.62), 559.7 (2.98),
528.7 (3.47), 500.6 (4.13), 402.1 (5.19).
¶
Chlorin e6 13(1)-morpholinoamide-15(2),17(3)-dimethyl ester. Com-
pound 6 (24 mg, 42%) was obtained from 50 mg of 1. The amide was
eluted with CCl4–acetone (4:1, v/v). 1H NMR, d: major isomer: 9.72 (s,
1H, 10-H), 9.67 (s, 1H, 5-H), 8.86 (s, 1H, 20-H), 8.11 (dd, 1H, J 17.0
and 11.6 Hz), 6.38 [dd, 1H, 3(2)-H (trans), J 17.9 and 1.5 Hz], 6.16 [dd,
1H, 3(2)-H (cis), J 11.6 and 1.6 Hz], 5.81 [d, 1H, 15(1)-CH(B), J 19.0 Hz],
5.09 [d, 1H, 15(1)-CH(A), J 19.0 Hz], 4.42–4.65 (m, 2H, 18-H, 17-H),
3.57 [s, 3H, 15(3)-Me], 3.66 [s, 3H, 17(4)-Me], 3.88 [s, 3H, 12(1)-Me],
3.51 [s, 3H, 1(1)-Me], 3.34 [s, 3H, 7(1)-Me], 3.7–4.2 [m, 10H, 8(1)-CH2,
13(2)-CH2, 13(3)-CH2], 2.2–2.7 (m, 4H), 1.6–1.8 [m, 6H, 18(1)-Me,
8(2)-Me]; minor isomer: 9.69 (s, 1H, 10-H), 9.64 (s, 1H, 5-H), 8.81 (s,
1H, 20-H), 8.11 [dd, 1H, 3(2)-H], 6.38 [dd, 1H, 3(2)-H (trans), J 17.9
and 1.5 Hz], 6.16 [dd, 1H, 3(2)-H (cis), J 11.6 and 1.6 Hz], 5.52 [d, 1H,
15(1)-CH(B), J 19.0 Hz], 5.25 [d, 1H, 15(1)-CH(A), J 19.0 Hz], 4.42–
4.65 (m, 2H, 18-H, 17-H), 3.54 [s, 3H, 15(3)-Me], 3.62 [s, 3H, 17(4)-
Me], 3.83 [s, 3H, 12(1)-Me], 3.50 [s, 3H, 1(1)-Me], 3.33 [s, 3H, 7(1)-
Me], 3.7–4.2 [m, 10H, 8(1)-CH2, 13(2)-CH2, 13(3)-CH2], 2.2–2.7 [m, 4H,
17(1)-CH2, 17(2)-CH2], 1.6–1.8 [m, 6H, 18(1)-Me, 8(2)-Me]. 13C NMR,
d: major isomer: 173.45, 173.29, 169.24, 168.78, 167.16, 154.39, 149.00,
144.73, 138.86, 136.15, 134.89, 134.55, 134.40, 133.60, 130.22, 130.03,
129.47, 125.54, 121.64, 102.23, 101.01, 98.78, 93.87, 67.00, 52.10, 51.59,
49.43, 42.51, 37.08, 31.19, 30.87, 29.65, 19.67, 17.67, 12.14, 12.11,
11.33; minor isomer: 173.61, 173.04, 169.00, 168.68, 166.55, 154.39,
149.19, 144.78, 138.93, 136.22, 134.97, 135.12, 134.61, 133.43, 130.28,
129.83, 129.47, 125.74, 121.64, 102.29, 101.22, 98.78, 93.65, 66.84,
52.24, 51.59, 49.13, 42.43, 37.79, 31.19, 30.87, 29.76, 19.67, 17.67,
12.22, 12.11, 11.33. IR (KBr, n/cm–1): 1742 (ester nC=O), 1636 (‘amide-I’),
1608 (‘chlorin band’). UV-VIS [CHCl3, l/nm (lg e)]: 663 (4.73), 608.7
(3.74), 557.1 (3.41), 528.5 (3.68), 500.5 (4.19), 402.2 (5.21).
Received: 4th December 2001; Com. 01/1862
– 78 –