Synthesis of 3-pyrazolinyl chlorins related to chlorophyll by 1,3-dipolar cycloaddition reaction from methyl pheophorbide-a

Article abstract of DOI:10.1080/00397911.2010.525776

The synthesis of a series of 3-pyrazolinyl-substituted chlorins, possessing different basic skeletons of chlorophyll degradation products such as pheophorbide-a, pyropheophorbide- a, purpurin-18, purpurin-7, purpurin-5, chlorin-p₆, and chlorin-e₆, was fulfilled from methyl pheophorbide-a by chemical modification and 1,3-dipolar cycloaddition with diazomethane. The structures of new chlorins were characterized by ultraviolet (UV), infrared (IR), ¹H NMR, and mass spectra and elemental analysis. Taylor & Francis Group,LLC.

Full text of DOI:10.1080/00397911.2010.525776

Synthetic Communications1, 42: 487–496, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.525776
SYNTHESIS OF 3-PYRAZOLINYL CHLORINS RELATED
TO CHLOROPHYLL BY 1,3-DIPOLAR CYCLOADDITION
REACTION FROM METHYL PHEOPHORBIDE-a
Jin-Jun Wang, Chun-Lin Liu, and Jia-Zhu Li
Science and Engineering College of Chemistry and Biology,
Yantai University, Yantai, Shandong, China
GRAPHICAL ABSTRACT
Abstract The synthesis of a series of 3-pyrazolinyl-substituted chlorins, possessing different
basic skeletons of chlorophyll degradation products such as pheophorbide-a, pyropheophor-
bide-a, purpurin-18, purpurin-7, purpurin-5, chlorin-p6, and chlorin-e6, was fulfilled from
methyl pheophorbide-a by chemical modification and 1,3-dipolar cycloaddition with diazo-
methane. The structures of new chlorins were characterized by ultraviolet (UV), infrared
(IR), 1H NMR, and mass spectra and elemental analysis.
Keywords Chemical modification; chlorophyll-a derivative; 1,3-dipolar cyclicaddition;
methyl pheophorbide-a; photodynamic therapy (PDT)
INTRODUCTION
Photodynamic therapy (PDT) is an experimental cancer treatment modality that
selectively destroys cancer cells by interaction of light with a photosensitizing dye, pre-
sumably due to the formation of singlet oxygen.[1] In continuing efforts to develop
new photosensitizers for photodynamic therapy, the design and synthesis of chlorin
derivatives having high selectivity for removal of tumor cells from healthy cells are
important challenges in the PDT field. In these earlier works, chlorophyll and its deri-
vatives have been the preferred precursor for the synthesis of new photosensitizers
Received April 21, 2010.
Address correspondence to Jin-Jun Wang, Science and Engineering College of Chemistry and
Biology, Yantai University, Yantai, Shandong 264005, China. E-mail: wjj1955@163.com
487

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J.-J. WANG, C.-L. LIU, AND J.-Z. LI
used in PDT. A variety of photosensitizers related to natural chlorins have been
synthesized and evaluated for PDT efficiency.[2–6] Many naturally occurring (bacterio)
chlorophylls have a vinyl group attached directly to their chlorin p-systems at the
3-position such as the most common chlorophyll-a. This landmark structure was
widely utilized for the modifications and reconstructions of chlorins related to chloro-
phyll in which almost all chemical reactions of alkene were included. The relevant
research of quantitative structure–activity relationship (QSAR) showed that different
C3-functional groups of chlorins profoundly influenced their effects on PDT. Recently,
chlorophyll derivatives containing heterocyclic substituents at the 3-position have
received a great deal of attention because these heterocyclic components characterize
their structural, spectroscopic, and potential biological properties. Several kinds of
C3-heterocycle substituted chlorophyll-a derivatives, such as thienyl, triazolyl, indoyl,
pyrazolyl, and quinazolyl groups, have also been synthesized, among which
C3-pyrazolyl-substituted chlorins show excellent anticancer properties in photody-
namic therapy.[7–9] To investigate systematically C3-heterocycle-substituted chlorins
and search for effective photosensitizers for use in PDT, the synthesis of novel
3-pyrazolylchlorins with a basic carbon frame of chlorophyll-a was completed in the
present work.
RESULTS AND DISCUSSION
Methyl pheophorbide-a (1, MPa), as starting material separated from Spirulina
maxima alga, was treated with methanolic KOH in the presence of pyridine under an
inert atmosphere for 50 min followed by acidification with AcOH and methylation
and 1,3-dipolar cycloaddition with excess ethereal diazomethane for 24 h to give
3-pyrazolinylchlorin-p6 trimethyl ester (2) in 27% yield and 3-pyrazolinylpurpurin-18
methyl ester (3) in 36% yield, respectively. The 1,3-dipolar cycloaddition of
purpurin-5 dimethyl ester was carried out by an improved method, in which MPa
(1) was refluxed in the mixed solution of methanol and dimethylsulfoxide (DMSO)
containing KOH in the open and treated with CH2N2 for 48 h after acidification with
AcOH to give 57% of C3-pyrazolinyl-substituted purpurin-5 dimethyl ester (4). The
pheophorbide-a (1) was oxidized in propyl alcohol containing KOH in the presence
of pyridine by bubbling air for 2 h, acidizing it with concentrated HCl, and treating it
with excess ethereal diazomethane for 24 h to offer 3-pyrazolinylpurpurin-7 tri-
methyl ester (5) in 56% yield. These successive reactions included allomerization
and rearrangement of keto-ester on the exocyclic ring and 1,3-dipolar cycloaddition
at the 3-position.[10] 3-Pyrazolinylchlorin-e6 trimethyl ester (6) was prepared in 50%
yield by stirring in the mixed solution of methanol and pyridine containing KOH
under a nitrogen atomosphere and treatment with CH2N2 for 60 h after acidification.
These chlorins (2–6) were synthesized without separation from starting material 1
combining the functional group conversion on the E-ring and the cycloaddition with
diazomethane (Scheme 1).
The decarbomethoxylation of MPa (1) was carried out by refluxing in acetic acid
to give methyl pyropheophorbide-a (7, MPPa). Its E-cycloketone moiety was reduced
with NaBH4 in MeOH in the presence of trifluoroacetic acid to produce 132-
deoxo-MPPa (8) in yields of 56%. 20-Chlorochlorin (9) was obtained in 85% yield from
the starting material 7 by electrophilic substitution using N-chlorosuccinimide (NCS)

SYNTHESIS OF 3-PYRAZOLINYL CHLORINS
489
Scheme 1. Synthesis of C3-pyrazolylchlorins from pheophorbide-a by one-pot method.
as chlorinating agent in dichloromethane. The chlorination of pyroheophorbide-a (7)
was completed by the same method to afford chloro-substituted chlorin (10) in 80%
yield. MPPa (7) was stirred in saturated methanol with LiOH by bubbling air for
3 h and treated with AcOH and CH2N2 for acidification and methylation to give
132-oxopyro-pheophorbide-a (11, 32%) and purpurin-5 dimethyl esters (12, 15%) as
the main products.
The 1,3-dipolar cycloadditions of chlorins (8–10) with excess diazomethane
were performed to generate smoothly C3-pyrazolinyl-substituted chlorins (13–15)
in different yields and reaction times. The corresponding cyclization of compound
11 with diazomethane was ot successful because the a-diketon moiety on the E-ring
participated in a reaction to form a very complicated mixture. The chlorin (12) was
treated with ethereal diazomethane to give 3-pyrazolinyl purpurin-5 dimethyl esters
(16) in 58% yield (Scheme 2).
The structures of all pyrazolyl-substituted chlorins indicate that the 1,3-dipolar
cycloaddition with diazomethane has a particularly regioselective preference to produce
anti-Markovniko-type products; namely, the positive dipole end of diazomethane links
to the carbon atom at the 3a-position, and the negative dipole end connects with the
C3b-carbon. All pyrazolyl-chlorins are a mixture of two (R=S)-epimers in an approxi-
mate ratio of 1:1 due to the chiral center at the 3a-carbon atom. These isomeric mixtures
were clearly evident in their 1H NMR spectrum, showing splitting of the resonances for
the adjacent protons such as 5-meso-H, C2-methyl group or other functional group.
It was found that the rates and yields for the 1,3-dipolar cycliaddition of
chlorophyll-a degradation products depended on the electron-withdrawing groups

490
J.-J. WANG, C.-L. LIU, AND J.-Z. LI
Scheme 2. Synthesis of C3-pyrazolylchlorins from (pyro)pheophorbide-a by stepwise reaction.
linked in the periphery of chlorin chromophore. The more the electron-withdrawing
group linked with the terminal of C-D ring of chlorin, the faster the reaction rate
became with diazomethane. Comparatively speaking, the formation of chlorin (13)
in 40% yield, without any carbonyl group at 13- and 15- positions, required 4 days.
In contrast, the reaction time for purpurin (13), having a methoxycarbonyl group at
the 13-position and a formyl group at the 15-position, with CH2N2 needed just 24 h
to give 58% of cycloadduct (16).
CONCLUSIONS
An efficient methodology has been developed for the regioselective synthesis of
C3-pyrazolyl-substituted chlorins, related to chlorophyll-a, from methyl pheophor-
bide-a by the 1,3-dipolar cycloaddition with diazomethane in one-pot synthesis or

SYNTHESIS OF 3-PYRAZOLINYL CHLORINS
491
stepwise synthesis. The synthetic methodology utilizing 1,3-cycloaddition of vinyl-
substituted chlorins with diazomethane lays the groundwork for important
peripheral functionalization of tetrapyrrolic ring systems. The pyrazoline ring at
the 3-position can be used as a versatile building block that allows for subsequent
transformations into other special structures such as cyclopropane moiety. Such
reactions construct convenient five-membered heterocycles on the macrocycles,
and these modifications for the parent ring of chlorophyll-a derivatives may be
valuable in the generation of novel photosensitisers for PDT.
EXPERIMENTAL
The infrared (IR) spectra were measured with a Shimadzu Fourier transform
(FT) IR 8300 spectrophotometer. The ultraviolet–visible (UV-vis) spectra were taken
with a Unicam SP 800 spectrophotometer. The 1H NMR spectra were recorded with a
Varian 400 spectrometer. Mass spectra were recorded by JMX-DX300 in eV. The
elemental analyses were performed on a Perkin-Elmer 240 microanalyzer. Melting
points (mp) were determined with a WRS-1B melting-point apparatus and are uncor-
rected. Methyl pheophorbide-a (1) was obtained according to Smith’s method.[11]
Chlorine 8 and 10 were synthesized according to Ref. 12. Chlorine 9 was synthesized
according to Ref. 13. Chlorine 11 and 12 were synthesized according to Ref. 10.
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-chlorin-p6 Trimethyl Ester (2)
and 3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-purpurin-18 Methyl Ester (3)
Methyl pheophorbide-a 1 (160 mg, 0.264 mmol) was dissolved in 5 mL of pyri-
dine. To this solution, 80 mL of saturated methanol with KOH were added, and the
mixture was stirred in an open system in the dark for 2 h, poured into cool water,
adjusted pH to 3 with hydrochloric acid, and then extracted with dichloromethane
(2 ꢀ 50 mL). The combined extract was washed with water, dried over anhydrous
Na2SO4, and concentrated to 10 mL. The resulting solution was treated with excess
ethereal diazomethane, stirred in the dark for 24 h and with 25% acetic acid
(10 mL) to remove unreacted CH2N2. The mixture was poured into water (30 mL)
and extracted with dichloromethane (20 mL ꢀ 2). The extract was washed with water
(20 mL ꢀ 2) and dried over anhydrous Na2SO4. The evaporation residue was purified
by using chromatography on a silica-gel column with hexane–ethyl acetate (4:1) to
give 2 as a green solid (48 mg, 27%) and 3 as a red solid (59 mg, 36%), respectively.
compound 2: mp: 225–228 ꢁC; UV-vis (CHCl3) kmax: 405 (relative intensity, 1.00),
1
500 (0.12), 534 (0.05), 606 (0.06), 661 (0.38) nm; H NMR (CDCl3) d: ꢂ1.03, 0.33
(each br s, each 1H, NH), 1.68 (t, J ¼ 7.6 Hz, 3H, 8-CH3), 1.82 (d, J ¼ 7.4 Hz, 3H,
18-CH3), 2.00–2.82 (each m, 6H, 40-H þ 17a þ 17b-H), 3.72 (q, J ¼ 7.6 Hz, 2H,
8a-H), 4.23, 4.17, 3.91, 3.52, 3.27 (3.26), 3.18 (each s, each 3H or 1.5H, OCH3 þ CH3),
4.42 (q, J ¼ 7.0 Hz, 1H, 18-H), 5.17 (d, J ¼ 8.6 Hz, 1H, 17-H), 5.39–5.50, 4.67–4.82
(each m, each 1H, 50-H), 6.68 (t, J ¼ 8.6 Hz, 1H, 30-H), 9.71, 9.11, 8.70 (each s, each
=
1H, meso-H). IR (KBr) v: 3456 (N-H), 2960 (C-H), 1743, 1726, 1703 (C O), 1608
(C C), 1535 (chlorin skeleton) cmꢂ1. MS (70 eV) m=z (%): 667.3 (M þ þ 1, 100). Anal.
=
calcd. for C37H42 N6O6: C, 66.65; H, 6.35; N, 12.60. Found: C, 66.46; H, 6.48; N,
12.77. Compound 3: mp: 203–205 ꢁC; UV-vis (CHCl3) kmax: 410 (relative intensity,

492
J.-J. WANG, C.-L. LIU, AND J.-Z. LI
1.00), 477 (0.04), 506 (0.06), 542 (0.17), 642 (0.07), 696 (0.36) nm; 1H NMR (CDCl3) d:
ꢂ1.74, 0.42 (each br s, each 1H, NH), 1.55 (t, J ¼ 7.6 Hz, 3H, 8-CH3), 1.76 (d,
J ¼ 7.4 Hz, 3H, 18-CH3), 1.98–2.18 (m, 1H, 40-H), 2.20–2.15, 2.37–2.57 (each m, each
2H, 17a þ 17b-H), 2.71–2.84(m, 1H, 40-H), 3.55 (q, J ¼ 7.6 Hz, 2H, 8a-H), 3.06, 3.23
(3.22), 3.52 (3.54), 3.61 (3.62) (each s, each 3H or 1.5H, OCH3þCH3), 4.35–4.45 (m,
1H, 18-H), 4.77 (td, J ¼ 18.0, 8.9 Hz, 1H, 50-H), 5.14 (d, J ¼ 8.6 Hz, 1H, 17-H), 5.48
(dd, J ¼ 18.0, 9.8 Hz, 1H, 50-H), 6.57 (t, J ¼ 7.8 Hz, 1H, 30-H), 8.60, 8.95 (8.98),
9.25 (each s, each 1H or 1.5H, meso-H). IR (KBr) v: 3440 (N-H), 2975–2850, 1749
(C O), 1639 (C N), 1617 (C C), 1552 (chlorin skeleton) cmꢂ1. MS (70 eV) m=z
(%): 621.4 (M þ þ 1, 100). Anal. calcd. for C35H36N6O5: C, 67.73; H, 5.85; N,
13.54. Found: C, 67.59; H, 6.08; N, 13.71.
=
=
=
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-purpurin-5 Dimethyl Ester (4)
Methyl pheophorbide-a 1 (168 mg, 0.277 mmol) was dissolved in methanol
saturated with KOH (10 mL) and DMSO (15 mL) and stirred in an open system
in the dark for 6 h. The resulting mixture was refluxed for 5 h, poured into cool
water, and extracted with dichloromethane (2 ꢀ 50 mL) after adjusting pH to 4 with
hydrochloric acid. The combined extract was washed with water, dried over anhy-
drous Na2SO4, and concentrated to dryness. The crude product was redissolved in
CH2Cl2 (5 mL), treated with excess ethereal diazomethane, and stirred in the dark
for 48 h. After adding acetic acid (5 mL) to remove unreacted CH2N2, the mixture
was evaporated under vacuum. The residue was chromatographed on a silica-gel
column with hexane–ethyl cetate (3:1) to give 4 (89 mg, 53%) as a green solid. Mp:
221–223 ꢁC; UV-vis (CHCl3) kmax: 399 (relative intensity, 1.00), 497 (0.11), 524
1
(0.06), 606 (0.05), 660 (0.48) nm; H NMR (CDCl3) d: 0.06, 0.86 (each br s, each
1H, NH), 1.71 (t, J ¼ 7.5 Hz, 3H, 8-CH3), 1.88 (d, J ¼ 7.1 Hz, 3H, 18-CH3),
2.07–2.28, 2.32–2.52, 2.55–2.65 (each m, 4H, 17a þ 17b-H), 2.68–2.82 (m, 2H,
40-H), 3.77 (q, J ¼ 7.5 Hz, 2H, 8a-H), 3.31, 3.25, 3.62, 3.82, 4.35 (each s, each 3H,
OCH3 þ CH3), 4.46–4.56 (m, 2H, 17-H þ 18-H), 4.77 (dtd, J ¼ 17.9, 9.8, 2.5 Hz,
1H, 50-H), 5.14 (d, J ¼ 8.6 Hz, 1H, 17-H), 5.48 (dd, J ¼ 17.9, 9.8 Hz, 1H, 50-H),
6.75 (t, J ¼ 9.8 Hz, 1H, 30-H), 8.77, 9.23, 9.77, 9.84 (each s, each 1H, meso-H). IR
ꢂ1
=
=
(KBr) v: 3446 (N-H), 1741, 1710 (C O), 1612 (C C), 1533 (chlorin skeleton) cm
.
MS (70 eV) m=z (%): 609.4 (M þ þ 1, 100). Anal. calcd. for C35H40N6O4: C, 69.06;
H, 6.62; N, 13.81. Found: C, 69.27; H, 6.76; N, 13.60.
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-purpurin-7 Trimethyl Ester (5)
A KOH solution in n-propanol (3 g dissolved in 20 mL) was added to a solution
of 1 (158 mg, 0.260 mmol) in a mixed solution of ether (100 mL) and pyridine (5 mL).
The mixture was stirred at room temperature by bubbling air for 2 h, acidized by 2%
aqueous HCl and extracted with CH2N2 (5 ꢀ 30 mL). The combined extract was
washed with 4% aqueous NaHCO3, dried over anhydrous Na2SO4, and concentrated
to dryness. The crude product was redissolved in CH2Cl2 (5 mL), treated with excess
ethereal diazomethane, and stirred in the dark for 24 h. The resulting mixture was
treated with acedic acid for moving unreacted CH2N2, and evaporated to dry.
The residue was chromatographed on silica gel by silica-gel chromatography with

SYNTHESIS OF 3-PYRAZOLINYL CHLORINS
493
hexane–ethyl acetate (4:1) to give 5 (105 mg, 58%) as a red-brown solid. Mp:
199–202 ꢁC; UV-vis (CHCl3) kmax: 402 (relative intensity, 1.00), 500 (0.09), 538
(0.08), 632 (0.06), 669 (0.27) nm; 1H NMR (CDCl3) d: ꢂ0.25, ꢂ0.15 (each br s, each
1H, NH), 1.66 (t, J ¼ 7.6 Hz, 3H, 8-CH3), 1.79 (d, J ¼ 7.3 Hz, 3H, 18-CH3), 1.71–1.83,
2.01–2.14 (each m, each 2H, 17a þ 17b-H), 2.32–2.42 (m, 1H, 40-H), 2.71–2.82 (m,
1H, 40-H), 3.67 (q, J ¼ 7.6 Hz, 2H, 8a-H), 3.12, 3.21, 3.53, 3.61, 4.15 (each s, each
3H, OCH3 þ CH3), 4.33 (q, J ¼ 7.2 Hz, 1H, 18-H), 4.68 (d, J ¼ 8.5 Hz, 1H, 17-H),
4.76 (ddd, J ¼ 18.0, 9.8, 2.6 Hz, 1H, 50-H), 5.46 (ddt, J ¼ 18.0, 9.8, 2.6 Hz, 1H,
50-H), 6.58 (t, J ¼ 9.7 Hz, 1H, 30-H), 8.53, 8.95, 9.62 (each s, each 1H, meso-H). IR
=
=
(KBr) v: 3334 (N-H), 2850 (C-H), 1733, 1708, 1703 (C O), 1616 (C C), 1585 (chlorin
skeleton) cmꢂ1. MS (70 eV) m=z (%): 695.3 (Mþ þ 1, 100). Anal. calcd. for
C39H42N6O7: C, 65.69; H, 6.09; N, 12.10; Found: C, 65.47; H, 6.10; N, 12.23.
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-chlorin-e6 Trimethyl Ester (6)
Methanolic potassium hydroxide (5%, 100 mL) was added to a solution of
methyl pheophorbide-a 1 (120 mg, 0.198 mmol) in pyridine (10 mL), and the mixture
was stirred at room temperature in the dark for 30 min. It was then diluted with
water (ꢃ200 mL), neutralized with acetic acid, and extracted with dichloromethane
(2 ꢀ 50 mL). The combined organic extract was shaken with 5% hydrochloric acid
(3 ꢀ 100 mL), washed with water, dried over anhydrous Na2SO4, and concentrated
to dryness. The crude product was treated with excess ethereal diazomethane and
stirred in the dark for 60 h. After adding acetic acid (5 mL) to remove unreacted
CH2N2, the mixture was evaporated under vacuum. The residue was chromato-
graphed on a silica-gel column with hexane–ethyl acetate (3:1) to give 6 (67 mg,
50%) as a green solid. Mp: 200–203 ꢁC; UV-vis (CHCl3) kmax: 407 (relative intensity,
1
1.00), 500 (0.32), 534 (0.05), 606 (0.06), 661 (0.38) nm; H NMR (CDCl3) d: ꢂ1.59,
ꢂ1.33 (each br s, each 1H, NH), 1.70 (t, J ¼ 7.6 Hz, 3H, 8-CH3), 1.75 (d, J ¼7.1 Hz,
3H, 18-CH3), 2.05–2.15 (m, 1H, 40-H), 2.16–2.24, 2.52–2.62 (each m, each 2H,
17a þ 17b-H), 2.73–2.83 (m, 1H, 40-H), 3.87 (q, J ¼ 7.6 Hz, 2H, 8a-H), 3.23, 3.32
(3.30), 3.58, 3.63, 3.77, 4.26 (each s, each 3H or 1.5H, OCH3þCH3), 4.22–4.43
(m, 1H, 18-H), 4.38–4.52 (m, 1H, 17-H), 4.62–4.82 (m, 1H, 50-H), 5.42–5.52 (m,
1H, 50-H), 6.73 (t, J ¼ 9.6 Hz, 1H, 30-H), 8.77, 9.18 (9.16), 9.70 (each s, each 1H or
0.5H, meso-H). IR (KBr) v: 3344 (N-H), 2862, 2927 (C-H), 1749, 1747, 1703
(C O), 1629 (C C), 1591 (chlorin skeleton) cmꢂ1. MS (70 eV) m=z (%): 681.4
(Mþ þ 1, 100). Anal. calcd. for C38H44N6 O6: C, 67.04; H, 6.51; N, 12.34; Found:
C, 67.21; H, 6.38; N, 12.39.
=
=
3-Devinyl-132-deoxo-3-[3’(R/S)-(1’-pyrazolinyl)]-pyropheophorbide-a
Methyl Ester (13)
The excess ethereal diazomethane (approximately 15 mL) was added To
dichloromethane (2 mL) in 8 (55 mg, 0.103 mmol) and stirred at room temperature
in the dark for 96 h. The reaction mixture was treated with acetic acid to remove
unreacted CH2N2, poured into water, and extracted with CH2Cl2. After evapora-
tion in vacuo, the residue was purified by chromatography on a silica-gel
column with hexane–ethyl acetate (5:1) to give 13 (24 mg, 40%) as a green solid.

494
J.-J. WANG, C.-L. LIU, AND J.-Z. LI
Mp: 221–223 ꢁC; UV-vis (CHCl3) kmax: 396 (relative intensity, 1.00), 500 (0.10), 588
1
(0.05), 642 (0.30) nm; H NMR (CDCl3) d: ꢂ3.37 (br s, 1H, NH), ꢂ1.66 (br s, 1H,
NH), 1.74 (t, 3H, J ¼ 7.6 Hz, 8a-CH3), 1.85 (d, 3H, J ¼ 7.4 Hz, 18-CH3), 2.12–2.25,
2.27–2.41, 2.55–2.65, 2.72–2.85 (each m, 6H, 40-H þ 17aþ17b-CH2), 3.38, 3.40,
3.49, 3.57 (each s, each 3H or 1.5H, OCH3þCH3), 3.85(q, J ¼ 7.5 Hz, 2H,
8a-CH2), 4.02 (ddd, J ¼ 17.0, 6.9, 2.8 Hz, 1H, 15a-H), 4.08 (ddd, J ¼ 17.0, 6.9,
3.1 Hz, 1H, 15a-H), 4.49 (dt, J ¼ 8.8, 2.2 Hz, 1H, 17-H), 4.68 (q, J ¼ 7.2 Hz, 1H,
18-H), 4.77 (ddd, J ¼ 16.2, 6.9, 3.1 Hz, 1H, 13a-H), 4.81 (ddd, J ¼ 16.2, 6.9,
2.8 Hz, 1H, 13a-H), 4.93 (ddd, J ¼ 17.0, 9.6, 3.0 Hz, 1H, 50-H), 5.49 (ddt, J ¼ 17.0,
9.6, 2.6 Hz, 1H, 50-H), 6.93(t, J ¼ 9.8 Hz, 1H, 30-H), 8.96, 9.54 (9.52), 9.59 (each s,
each 1H or 0.5H, meso-H). IR (KBr) v: 3446 (N-H), 2960, 2927 (C-H),þ1737
=
=
(C O), 1674 (C C), 1542 (chlorin skeleton). MS (70 eV) m=z (%): 577.4 (M þ 1,
100). Anal. calcd. for C35H40 N6O2: C, 72.89; H, 6.99; N, 14.57. Found: C, 72.70;
H, 6.77; N, 14.51.
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-20-chloropheophorbide-a
Methyl Ester (14)
This compound was obtained as a red solid from compound 9 by reaction with
CH2N2 for 30 h in the yield of 56% according to the method for preparing compound
13. UV-vis (CHCl3) kmax: 414 (relative intensity, 1.00), 518 (0.10), 550 (0.14), 620
1
(0.07), 678 (0.46) nm; H NMR (CDCl3) d: ꢂ2.01 (br s, 1H, NH), ꢂ1.96 (br s,
1H, NH), 1.64 (1.63) (d, 3H, J ¼ 7.0 Hz, 18-CH3), 1.66 (t, 3H, J ¼ 7.6 Hz,
8a-CH3), 2.02–2.35, 2.40–2.66 (each m, 5H, 40-H þ 17aþ17b-CH2), 2.73–2.84 (m,
1H, 40-H), 3.15 (3.17), 3.49 (3.50), 3.54 (3.55), 3.68, 3.89 (3.90) (each s, each 3H or
1.5H, OCH3þCH3), 3.65 (q, J ¼ 7.6 Hz, 2H, 8a-CH2), 4.10–4.18 (m, 1H, 17-H),
4.22–4.30 (m, 1H, 18-H), 4.72–4.86 (m, 1H, 50-H), 5.50–5.61 (m, 1H, 50-H), 6.28
(6.25) (each s, each 0.5H, 132-H), 6.64(t, J ¼ 9.5 Hz, 1H, 30-H), 9.03 (9.02), 9.50
(9.53) (each s, each 0.5H, meso-H). IR (KBr) v: 3438 (N-H), 2986, 2870 (C-H),
1733 (C O), 1610 (C C), 1539 (chlorin skeleton) cmꢂ1. MS (70 eV) m=z (%):
683.4 (Mþ þ 1, 100). Anal. calcd. for C37H39ClN6O5: C, 65.05; H, 5.75; N, 12.30.
Found: C, 65.16; H, 5.70; N, 12.56.
=
=
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-20-chloropyropheophorbide-a
Methyl Ester (15)
This compound was obtained as a red solid from compound 10 by reaction
with CH2N2 for 30 h in the yield of 60% according to the method for preparing com-
pound 13. UV-vis (CHCl3) kmax: 414 (relative intensity, 1.00), 517 (0.09), 550 (0.14),
621 (0.06), 678 (0.46) nm; 1H NMR (CDCl3) d: ꢂ1.99 (br s, 1H, NH), 0.83 (br s, 1H,
NH), 1.61–1.69 (m, 6H, 8a-CH3 þ 18-CH3), 2.05–2.27, 2.40–2.63 (each m, 5H,
40-H þ 17aþ17b-CH2), 2.75–2.80(m, 1H, 40-H), 3.11, 3.48, 3.59, 3.60 (each s, each
3H or 1.5H, OCH3þCH3), 3.61(q, J ¼ 7.6 Hz, 2H, 8a-CH2), 4.24 (4.23)(d, J ¼ 8.7 Hz,
1H, 17-H), 4.76 (dq, J ¼ 8.9, 2.5 Hz, 1H, 18-H), 4.78–4.84 (m, 1H, 50-H), 5.23 (s, 2H,
132-H), 5.49–5.58 (m, 1H, 50-H), 6.28 (6.25) (each s, each 0.5H, 132-H), 6.63 (6.62) (t,
J ¼ 10.1 Hz, 1H, 30-H), 9.00(899), 9.46 (each s, each 0.5H, meso-H). IR (KBr) v: 3350
=
=
(N-H), 2964, 2869 (C-H), 1747, 1699 (C O), 1606 (C C), 1533 (chlorin skeleton)

SYNTHESIS OF 3-PYRAZOLINYL CHLORINS
495
cmꢂ1. MS (70 eV) m=z (%): 625.3 (Mþ þ 1, 100). Anal. calcd. for C35H37ClN6O3: C,
67.24; H, 5.97; N, 13.44. Found: C, 67.07; H, 6.12; N, 13.53.
3-Devinyl-3-[3’(R/S)-(1’-pyrazolinyl)]-15-formyl-purpurin-5 Dimethyl
Ester (16)
This compound was obtained as a red solid from compound 12 by reaction
with CH2N2 for 24 h in the yield of 58% according to the method for preparing com-
pound 13. UV-vis (CHCl3) kmax: 408 (relative intensity, 1.00), 504 (0.07), 538 (0.09),
1
635 (0.05), 687 (0.30) nm; H NMR (CDCl3) d: ꢂ0.32 (br s, 1H, NH), ꢂ0.05(br s,
1H, NH), 1.65 (t, J ¼ 7.6 Hz, 3H, 18-CH3), 1.80 (d, J ¼ 7.2 Hz, 3H, 8a-CH3), 1.93–
2.10(m, 2H, 40-H), 2.20–2.28, 2.32–2.42, 2.48–2.59, 2.66–2.79 (each m, 4H,
17aþ17b-CH2), 2.75–2.80(m, 1H, 40-H), 3.12, 3.20, 3.56, 3.58, 4.19 (each s, each
3H or 1.5H, OCH3þCH3), 3.65 (q, J ¼ 7.6 Hz, 2H, 8a-CH2), 4.42 (4.41) (q,
J ¼ 7.1 Hz, 1H, 18-H), 4.73 (dt, J ¼ 17.9, 9.6 Hz, 1H, 50-H), 5.06 (dt, J ¼ 9.3,
2.3 Hz, 1H, 17-H), 5.44 (dd, J ¼ 17.9, 9.6 Hz, 1H, 50-H), 6.28 (6.25) (each s, each
0.5H, 132-H), 6.55–6.61 (m, 1H, 30-H), 8.56, 9.01 (9.02), 9.61 (each s, each 0.5H or
1H, meso-H), 11.48 (s, 1H, CHO). IR (KBr) v: 3323 (N-H), 2956, 2850 (C-H),
1735, 1697 (C O), 1605 (C C), 1502 (chlorin skeleton) cmꢂ1. MS (70 eV) m=z
(%): 637.2 (Mþ þ 1, 100). Anal. calcd. for C36H40N6O5: C, 67.91; H 6.33; N,
13.20. Found: C, 67.77; H, 6.18; N, 13.24.
=
=
ACKNOWLEDGMENTS
This work was supported by the Natural Science Foundation of Shandong
Province of China (No. Y2008B49) and by the Open Project of State Key Labora-
tory Breeding Base of Green Chemistry–Synthesis Technology (Zhejiang University
of Technology).
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