Cationic β-vinyl substituted meso-tetraphenylporphyrins:

Journal of Porphyrins and Phthalocyanines

J. Porphyrins Phthalocyanines 2012; 16: 101–113

DOI: 10.1142/S1088424611004373

Published at http://www.worldscinet.com/jpp/

Cationic b-vinyl substituted meso-tetraphenylporphyrins:

synthesis and non-covalent interactions with a short

poly(dGdC) duplex

Eduarda M.P. Silva, Catarina I.V. Ramos, Patrícia M.R. Pereira, Francesca Giuntini,

Maria A.F. Faustino, João P.C.Tomé^◊, Augusto C.Tomé^◊, Artur M.S. Silva, M. Graça

Santana-Marques*^◊, M. Graça P.M.S. Neves*^◊and José A.S. Cavaleiro^◊

Department of Chemistry, QOPNA, University of Aveiro, 3810-193 Aveiro, Portugal

Received 30 July 2011

Accepted 2 September 2011

ABSTRACT: Several cationic beta-vinyl-pyridinium and beta-vinyl-quinolinium-meso-tetraphenyl-

porphyrin derivatives were synthesized starting from 2-formyl-meso-tetraphenylporphyrin, and the

corresponding Zn(II) complex, and different N-alkyl derivatives of 2- and 4-methylpyridine and 2- and

4-methylquinoline. The new compounds were obtained in a one-step process via base catalyzed aldol-

type condensation reactions. Electrospray ionization mass spectrometry (ESI-MS) and ultraviolet-visible

(UV-vis) spectroscopy were used to investigate the binding mode of the synthesized cationic beta-vinyl-

pyridinium and beta-vinyl-quinolinium-meso-tetraphenylporphyrin derivatives with a short GC duplex

oligonucleotide. Analysis of the obtained mass spectrometry results indicates the probable occurrence of

outside binding. UV-vis spectroscopy data also points to non-intercalation. The potential photosensitizing

capacity of these compounds was also ascertained from preliminary photophysical studies.

KEYWORDS: cationic porphyrins, pyridinium salts, non-covalent adducts, electrospray mass

spectrometry.

irradiation with light of appropriate wavelength [4, 5].

INTRODUCTION

Recent studies demonstrated that PDT can also be very

The unique photophysical and chemical features

effective in the selective inactivation of microorganisms,

of tetrapyrrolic macrocycles are the main reasons for

indicating that it is a potential alternative tool for the

the continuous interest by the scientiﬁc community in

treatment and eradication of microbial infections [6–16].

such compounds. As it is well-known their potential

Ionic photosensitizers, especially those with an

or successful applications are important in a range of

asymmetricdistributionofthechargesinthemolecule, are

scientiﬁc areas, such as catalysis, advanced biomimetic

very promising for medicinal use since such compounds

modeling for photosynthesis, development of new

show an increased ability to accumulate in sub-cellular

electronic materials, sensors and also medicine [1]. In

compartments (enhanced membrane penetration) and

the biomedical ﬁeld, porphyrins and related compounds

to interact with the target [3]. In particular, cationic

are being employed successfully for the treatment of

porphyrins are able to induce photoinactivation of

cancer and several other diseases by photodynamic

microorganisms [8, 17], and/or to interact with DNA

therapy (PDT) [2, 3], a technique which relies on the

and also to cause its rupture upon irradiation [18]. In

administration of a photosensitizing agent and subsequent

a previous paper, we have shown that cationic b-vinyl

substituted meso-tetraphenylporphyrins are effective

in the photoinactivation of herpes simplex virus type

^SPP full member in good standing

1 (HSV-1) [19]. Such compounds were obtained by

condensation of 2-formylporphyrins with 1,2- and

1,4-dimethylpyridinium salts. Further investigations

*Correspondence to: M. Graça Santana-Marques, email:

santana.marques@ua.pt and M. Graça P.M.S. Neves, email:

gneves@ua.pt

102

E.M.P. SILVA ET AL.

carried out in our laboratory showed that this method has

a broad applicability and can be used to prepare a variety

of cationic porphyrin derivatives.

RESULTS AND DISCUSSION

Chemistry

Electrospray ionization mass spectrometry (ESI-MS)

and tandem electrospray ionization mass spectrometry

(ESI-MS/MS) have been previously used to differentiate

the 2- and 4-methylpyridyl isomers of free-base and

metalated cationic b-vinylpyridylporphyrins [20]. The

data acquired show that of all the studied compounds,

the free-base 2-methylpyridyl isomer, which was

operative in the in vitro photoinactivation of Herpes

simplex virus, has a different gas-phase behavior. Our

previous studies have shown that local distortion of the

macrocycle, due to the presence of the b-vinylpyridyl

substituent, occurs for all the compounds, but that a

different electron density distribution can account for the

observed gas-phase behavior of this potential antivirus

agent. In addition, these same techniques along with

UV-vis spectroscopy, have been previously used by us to

investigate the non-covalent interactions between small

oligonucleotide duplexes and a group of cationic meso-(1-

methylpyridinium-4-yl)porphyrins (four free-bases with

one to four positive charges, and the corresponding zinc

complexes) [21, 22]. The positive charges were located

in the meso-positions of the macrocycle. The results

obtained pointed to outside binding of the porphyrins,

with the binding strength increasing with the number of

positive charges.

Electron-poor alkyl-heterocycles (e.g. 2- and

4-alkylpyridines) undergo aldol-like condensations with

carbonyl compounds in the presence of strong bases or

Lewis acids, but in most cases such reactions have a

limited applicability because of the harsh requirements;

many chemical functions are not suited to such

conditions. However, when the corresponding N-oxides

or N-alkyl derivatives are used, the condensation occurs

in milder conditions, due to the increased acidity of

the side-chain protons induced by the strong electron

withdrawing effect exerted by the positive charge on the

ring [23, 24]. Bearing this in mind, we have undertaken

the synthesis of a series of b-monosubstituted cationic

meso-tetraphenylporphyrin derivatives, in a one-step

process, starting with 2-formyl-5,10,15,20-tetraphenyl-

porphyrin (2-formyl-TPP, 1a) and the corresponding

Zn(II) complex 1b and different cationic derivatives

of 2- and 4-methylpyridine (Scheme 1) and 2- and

4-methylquinoline (Scheme 4).

2-formyl-5,10,15,20-tetraphenylporphyrin was obtai-

ned by Vilsmeier formylation [25] of the copper complex

of 5,10,15,20-tetraphenylporphyrin (TPP), according to

the literature procedure [26]. The corresponding zinc

complex was obtained by metalation of the free-base

with zinc acetate [27]. The pyridinium and quinolinium

derivatives were prepared according to literature

procedures [28–30].

The promising features of the b-vinyl-

methylpyridinium porphyrins as virus photoinactivators,

led us to synthesize several related compounds and

to investigate the possibility of intercalation with a

GC-motif duplex oligonucleotides using electrospray

mass spectrometry.

The condensation reaction using 2-formyl-TPP

1a with either 1,2-dimethylpyridinium iodide 2 or

1,4-dimethylpyridinium iodide 4 [29] (Scheme 1) in the

5

Me

I^-

Me

4

3

6

Ph

+

2'

N

M

N

M

N

+

1''

CHO

N

Cl^-

2''

3''

2

1'

N

Me

(i), (ii)

Ph

1a, M = 2H

1b, M = Zn

3a, M = 2H

3b, M = Zn

X^-

+

3

6

+

R

Cl^-

2

Ph

N

R

Me

N

2'

N

1''

CHO

5

4-6

(i), (ii)

2''

3''

1'

N

M

N

M

N

7a, R = Me, M = 2H

7b, R = Me, M = Zn

Ph

8a, R = (CH₂)₉Me, M = 2H

9a, R = monosacharide unit, M = 2H

1a, M = 2H

1b, M = Zn

7, 8

Scheme 1. Reagents and conditions: (i) K₂CO₃, THF/MeOH; (ii) NaCl aq

J. Porphyrins Phthalocyanines 2012; 16: 102–113

CATIONIC b-VINYL SUBSTITUTED MESO-TETRAPHENYLPORPHYRINS

103

presence of K₂CO₃, at 30 °C, in a THF/MeOH mixture

Condensation of porphyrin 1a with 5, in the presence

of K₂CO₃, afforded porphyrin 8a in 30% yield, while

condensation of 1a with 6 gave porphyrin 9a in 53%

yield (Scheme 1). The unprotected galactose derivative

10a was obtained in 66% yield by acidic hydrolysis of

the isopropylidene moieties in porphyrin 9a (Scheme 3).

There are several methods reported in the literature

to prepare porphyrin-carbohydrate conjugates. Those

conjugates are frequently used as neutral water-soluble

photosensitizers since they show a better biodistribution,

and are potentially more selective for cell targeting [36,

37]. In compound 10a, the simultaneous presence of a

carbohydrate unit and a positive charge may render this

compound as potentially useful as photosensitizer.

The mild conditions of our synthetic method show that

it can be applied for the synthesis of a range of cationic

vinylporphyrins bearing a diversity of groups linked to

the pyridyl nitrogen. However the applicability of our

synthetic method is not conﬁned to N-alkyl-pyridinium

salts. Both 1,2- and 1,4-dimethylquinolinium iodides (11

and 12) [30] also underwent condensation with the Zn(II)

complex of 2-formyl-TPP 1b, although under slightly

different conditions (Scheme 4).

has been previously published [19]. This reaction

allowed the preparation of the desired compounds 3a

and 7a (M = 2H) in 60% and 65% yields, respectively.

An attempt to improve these yields was performed

using the Zn(II) complex 1b. The new zinc complexes

3b and 7b (Scheme 1, M = Zn) were isolated by ﬂash

chromatography on silica gel, followed by washing

with brine (in order to assure the complete counter ion

exchange), and by subsequent crystallization. The zinc

complexes 3b and 7b (M = Zn) were obtained in 43%

and 40% yields, respectively. These results show that

the reactions carried out with the free-base 1a afforded

better yields than those in which the corresponding zinc

complex 1b was used. The position of the methyl group

on the pyridine ring seems not to affect the reaction; salt

2 proved to be only slightly less reactive than 4. The

synthesis of an analog of 7a (R = H) starting from 1a

has previously been reported in the literature [31–33].

However, the procedure described requires several steps,

namely reduction of the carbonyl function, halogenation

of the resulting hydroxymethyl group, its conversion

into the corresponding triphenylphosphonium salt and

then reaction with pyridine-4-carbaldehyde. This method

leads to the formation of both E- and Z-isomers of the

2-(4-pyridylvinyl)-substituted porphyrins, whereas with

our process only the E-isomer was formed.

Structural elucidation

1

The H NMR spectra of the new compounds show

In order to verify whether the presence of a bulkier

alkyl substituent at the pyridine nitrogen had any effect on

the course of the reaction, and to illustrate the scope of the

method, we prepared salts 5 and 6 (Scheme 2). 1-Decyl-

4-methylpyridinium iodide 5 was obtained in 86% yield

by alkylation of 4-methylpyridine with 1-iododecane.

Similarly, alkylation of 4-methylpyridine with 6-iodo-

1,2:3,4-di-O-isopropylidene-a-D-galactopyranose

afforded salt 6 in 96% yield [34, 35].

some common features (Table 1). The resonance due

to the H-3′′ proton is observed above 9 ppm, out of the

multiplet generated by the other beta protons (8.70–8.90

ppm), except for compounds 3b (vide infra). The vinylic

protons originate signals above 7 ppm for all compounds

except in the cases of 13b and 14b, in which the signals

of such protons fall within the multiplets generated by

the meta and para protons of the meso-phenyl rings.

The coupling constant values, for all compounds except

I

O

R¹

O

I

O

+

N

I

I(CH₂)₉Me

R²

N

Me

(CH₂)₉Me

Me

N

(i)

(ii)

O

5

6

O

(86%)

(96%)

Scheme 2. Reagents and conditions: (i) 80 °C, 6 h; (ii) 120 °C, 4 h

Cl^-

+

Ph

N

O

HO

O

N

H

N

H

O

H

(i)

O

OH

O

HO

N

H

N

H

N

Ph

9a

10a

Scheme 3. Reagents and conditions: (i) TFA/H₂O (9:1), rt, 30 min

J. Porphyrins Phthalocyanines 2012; 16: 103–113

104

E.M.P. SILVA ET AL.

6

7

5

8

4a

Ph

2'

4

N

M

N

1''

(i)

N

3

2''

3''

1'

+

1a or 1b

N

+

Me

+

Cl^-

N

Me

I^-

Me

Ph

11

13a, M = 2H, 2-yl (49%)

13b, M = Zn, 2-yl (38%)

6

7

5

8

4a

Ph

Me

2'

N

M

N

+

Cl^-

1''

(i)

3

2''

3''

1'

1a or 1b

N

2

+

N

I^-

Me

Ph

12

14a, M = 2H, 4-yl (22%)

14b, M = Zn, 4-yl (45%)

Scheme 4. Reagents and conditions: (i) pyridine, 60 °C, 60 h

for 3b, are higher than 15 Hz, conﬁrming the trans

stereochemistry of the vinylic system.

appear as an isolated singlet but instead it is found

within the multiplet generated by the remaining H-b,

as conﬁrmed by the HSQC spectrum. The resonances

of the vinylic protons appear slightly high-ﬁeld shifted

when compared with the remaining compounds, with

For the free-bases, the singlets generated by the inner

pyrrolic protons are observed, as expected, between -2.60

and -2.45 ppm. The ¹H NMR spectrum of each compound

bearing an N-methyl group shows a singlet between 3.55

and 4.75 ppm.

3

a J value (11.9 Hz) that does not allow to determine

unequivocally the trans conﬁguration. However, the

absence of correlation between H-1′ and H-2′ in the

NOESY spectrum clearly indicates that, in spite of

the relatively small value of the ³J, the stereochemistry of

the double bond is also trans.

1

Compound 3b shows a somewhat unusual H NMR

spectrum. The signal of H-3′′, for instance, does not

Table 1. Relevant common features (d, ppm and J, Hz) in the

NMR spectra of the synthesized compounds

Photostability of the compounds

H-3′′

H-2′

H-1′

J

Me

NH

The photostability of the compounds is an important

parameter to evaluate since it is necessary to certify that

the compounds do not undergo an extensive destruction

of the tetrapyrrolic macrocycle when exposed to UV-vis

light and oxygen [38]. In order to establish the rate of

photodegradation of the compounds, we performed

photostability studies at the same irradiation conditions

used in the biological assays (white light, 50 mW/cm²)

previously published for compounds 3a and 7a [19]. The

obtained values were calculated by the ratio between

the residual absorbance after irradiation for different

periods of time and the absorbance before irradiation.

The absorbances were measured at the corresponding

Soret band wavelengths. Under these conditions, all

compounds show a high photostability, between 98 and

100%, during at least the ﬁrst 15 min of irradiation.

3a^c9.09 (s) 7.47 (d)

7.33 (d)

15.6 4.67 -2.54

a

3b

7.27 (d)

6.97 (d)

11.9 4.09

—

7a^c9.09 (s) 7.49 (d)

7b 9.19 (s) 7.16 (d)

7.25 (d)

7.06 (d)

15.7 4.65 -2.52

15.2 3.55

—

8a

9a

9.09 (s) 7.46 (d)

9.09 (s) 7.49 (d)

7.25 (d)

7.24 (d)

7.41 (d)

16.0

15.4

16.0

—

-2.53

-2.59

10a 9.16 (s) 7.66 (d)

13a 9.30 (s) 7.71 (AB) 7.71 (AB) 15.5 4.61 -2.49

b

13b 9.38 (s)

—

4.29

—

14a 9.21 (s) 7.74 (d)

7.96 (d) 15.5 4.75 -2.51

b

14b 9.21 (s)

—

4.56

—

Singlet oxygen and ﬂuorescence quantum yields

^aThe signal of this proton lies within the multiplet generated by

the resonances of the other H-b. ^bThe COSY (¹H/¹H) spectrum

showed that the signals corresponding to these protons lie within

the multiplet generated by the Ph-H_meta/paraprotons. ^cThe structural

characterization of these compounds is described in Ref. 19.

The ability of the porphyrin derivatives to generate

singlet oxygen and its preferential location in tumor cells

or microorganisms, is the reason for their importance and

application in PDT. The basis for this use is dependent on

J. Porphyrins Phthalocyanines 2012; 16: 104–113

CATIONIC b-VINYL SUBSTITUTED MESO-TETRAPHENYLPORPHYRINS

105

energy transfer processes [39, 40]. In this particular case,

perhaps justify the signiﬁcant activity exhibited by

this compound that reached 99% of virus inactivation

after 15 min of photoactivation [19]. Compounds 7a

and 8a demonstrate behaviors comparable to TPP and

compounds 13a and 14a, which contain in their structure

the quinolinium moiety, do not produce singlet oxygen.

The ﬂuorescence quantum yields (F_f) measured

relatively to 5,10,15,20-tetraphenylporphyrin [F_ﬂ(TPP) =

0.11] [46, 47] are summarized in Table 2. For all deriva-

tives the introduction of cationic b-vinyl moieties led to

a weakening of ﬂuorescence emission. Moreover, the

derivatives 13a and 14a do not shown any ﬂuorescence

emission. Most likely these two compounds in their excited

formscandecaybyotherradiativeornon-radiativeprocesses

[4, 5] and to entirely understand the photophysical behavior

of these two compounds further studies are required.

a photosensitizer in its triplet state needs to interact with

the ground state triplet oxygen to produce the reactive

singlet oxygen species [41]. This active molecule can

oxidize important biomolecules in the cells leading to

cellular damage [40, 41]. Another important process

to assess, in what concerns energy transfer from the

photoexcited sensitizer, is the ﬂuorescence emission.

A sensitizer might discharge the excitation energy into

a radiative process and such release would allow its

location and in this way the sensitizer would act as a

marker. Therefore, in order to test the potential use of

these new porphyrin derivatives, preliminary evaluation

of the photosensitizing activity of these compounds was

performed through measurement of the singlet oxygen

and ﬂuorescence quantum yields.

The capability of the new porphyrin derivatives to

generate singlet oxygen was qualitatively estimated

by measuring the absorption decay of 1,3-diphenyli-

sobenzofuran (DPBF) at 415 nm in DMF [42–44]. The

Non-covalent interactions with d(GCGCGCGC) —

mass spectrometric results

1

yellow DPBF reacts with O₂in a [4+2] cycloaddition

Thenon-covalentinteractionsofthecationicporphyrins

3a, 7–9a, 13a and 14a (Scheme 1 and Scheme 4) with a

small DNA duplex with the GC-motif were studied by

electrospray mass spectrometry (ESI-MS), with several

stages of mass separation. At physiological pH the DNA

backbone is mostly deprotonated, thus all the spectra were

acquired in the negative ion mode using an ammonium

acetate buffer. The GC motif was chosen to maximize

the possible occurrence of interactions by intercalation,

of the positively charged porphyrins.

In this array of porphyrins one could point out two

distinct groups: (a) one group containing positional

isomers: compounds 3a/7a and 13a/14a where the

basic carbon skeleton remains unchanged but the

N-methylpyridinium and N-methylquinolinium rings are

either in an 4 or 2 position in relation to the vinyl group

being oxidized to colorless ortho-dibenzoylbenzene.

Since DPBF has an absorption maximum at 415 nm,

it is possible to follow the ability of the porphyrin to

1

generate O₂by measuring the absorption decay, at this

wavelength. Thus, a solution containing DPBF (50 mM)

and the porphyrin derivative (0.5 mM) was irradiated over

a period of 6 min using a white lamp with a cut-off ﬁlter

for wavelengths < 540 nm, at a ﬂuence rate of 50 mW/cm².

Given that the 5,10,15,20-tetraphenylporphyrin (TPP) is

knowntobeagoodphotosensitizeritwasusedinthisstudy

as reference [45]. The results obtained, summarized in

Fig. 1, show that the DPBF photodegradation is highly

enhanced in the presence of the photosensitizers 3a

and 9a, conﬁrming that they are good singlet oxygen

generators. The result obtained for compound 3a may

Fig. 1. Comparative photooxidation of DPBF (50 mM) in DMF with or without photosensitizer (0.5 mM); irradiation with white light

ﬁltered through a cut-off ﬁlter for wavelengths < 540 nm (50 mW/cm²)

J. Porphyrins Phthalocyanines 2012; 16: 105–113

106

E.M.P. SILVA ET AL.

Table 2. Fluorescence (F_ﬂ) quantum yields of compounds 3a,

7a, 8a, 9a, 13a and 14a in DMF

For porphyrin 13a (N-methylquinolinium-2-yl) the

adduct ion [ds+porphyrin-4H⁺]^3-was not observed. In

contrast the mass spectrum of its isomer, porphyrin 14a

(N-methylquinolinium-4-yl), does not show the triply

charged adduct ion [ds+porphyrin-3H⁺+CH₃COO^-]^3-. In

the spectrum of porphyrin 9a (N-sugar-pyridinium-4-yl)

(Fig. 2) the adduct [ds+porphyrin-3H⁺+CH₃COO^-]^3-is

also absent.

Compound

3a

7a

8a

9a

13a

14a

^aF_ﬂ

0.05 0.05 0.05 0.06 0.00 0.00

^aAbsorbance of all samples was 0.05 at l_exc= 532 nm.

and (b) a second group where different substituents on

the N-terminus are all present in position 4 in relation to

the vinyl group (Scheme 1 and Scheme 4).

The analysis of the mass spectra obtained at a cone

voltage of 45 V shows in general, a decrease in the

abundance of the adduct ions [ds+porphyrin-5H⁺]^4-and

[ds+porphyrin-4H⁺+CH₃COO^-]^4-and an increase in

the abundance of the triply charged adducts in special

the [ds+porphyrin-4H⁺]^3-adduct ions. This increase in the

abundance of the triply charged adducts may result from

two different factors. On one hand, we had observed in our

previous studies [21, 22] that duplex ions with a higher

number of negative charges are less stable at higher cone

voltages, the higher repulsion of the phosphate chains

leading to fragmentation by unzipping of the double

strand. On the other hand, the fragmentation in the source

of the adduct ions [ds+porphyrin-4H⁺+CH₃COO^-]^4-with

the formation of the [ds+porphyrin-4H⁺]^3-and CH₃COO^-

ions, is a probable process. An example of this behavior

is observed in the mass spectrum of the porphyrin 13a

(N-methylquinolinium-2-yl). At a cone voltage of 25 V

the ion [ds+porphyrin-4H⁺]^3-is absent and the adduct ion

[ds+porphyrin-4H⁺+CH₃COO^-]^4-is the most abundant

ion, but when the cone voltage is increased to 45 V,

the adduct ion [ds+porphyrin-4H⁺+CH₃COO^-]^4-has a

very low abundance and the [ds+porphyrin-4H⁺]^3-ion is

observed.

It is interesting to note that the observed behavior with

theincreaseinconevoltageoftheisomericpair,porphyrins

3a (N-methylpyridinium-2yl)/7a (N-methylpyridinium-

4-yl) and of porphyrin 8a (N-decylpyridinium-4-yl) is

similar: the [ds+porphyrin-4H⁺+CH₃COO^-]^4-adduct ion

is not present at 45V and the adduct [ds+porphyrin-4H⁺]^3-

is present with higher relative abundance. Although

we cannot distinguish between the positional isomers

3a and 7a it is apparent that the [ds+porphyrin-

4H⁺+CH₃COO^-]^4-adducts for this pair and for porphyrin

8a (N-decylpyridinium-4-yl), are less strongly bound

when compared with the same adduct ions of the other

In general, duplex DNA binding ligands with the

same binding mode display the same dissociation patterns

[48, 49]. Unknown duplex DNA binding modes may be

deduced by comparing the fragmentation of new duplex

DNA-ligand adduct ions, with those of known binders and

intercalators [50–56]. Possible ambiguities in the attribution

of binding modes by this procedure, can be eliminated

through the use of the same mass spectrometer and by using

adduct ions with the same charge states [57, 58].

To investigate the binding mode and stability of

the porphyrin-duplex adduct ions, different types of

experiments were undertaken. Initially the mass spectra

were obtained for all the electrosprayed oligonucleotide-

porphyrin solutions, at two different cone voltages (25

and 45 V) and following that, the product ion spectra

(precursor ion → productions, MS/MS or MS²) of chosen

adduct ions were acquired. Finally a different type of

experiments that can be considered as a pseudo MS³(ﬁrst

precursor ion → second precursor ion → product ions)

were undertaken. The designation pseudo arises from the

fact that, in this type of experiments, the ﬁrst precursor

ion is not mass selected but fragments in the source as a

result of an increase in the cone voltage.

Two types of adduct ions were observed in the mass

spectra, [ds+porphyrin-(n+1)H⁺]^n-and [ds+porphyrin-

nH⁺+CH₃COO^-]^n-(ds = double strand, n = 3 or 4), their

relative abundances varying with the porphyrin and with

cone voltage.

In the mass spectra obtained at a cone voltage of

25 V, the adduct ions [ds+porphyrin-5H⁺]^4-, [ds+

porphyrin-4H⁺+CH₃COO^-]^4-, [ds+porphyrin-4H⁺]^3-and

[ds+porphyrin-3H⁺+CH₃COO^-]^3-were observed for

almost all the porphyrins (see Table 3), the exceptions

being discussed below.

Table 3. Mass to charge ratio and ionic current intensities of the observed adducts

[ds+porph-5H⁺]^4-[ds+porph-4H⁺+CH₃COO^-]^4-[ds+porph-4H⁺]^3-

[ds+porph-3H⁺+CH₃COO^-]^3-

Porph

m/z

I

I′

m/z

I

I′

m/z

I

I′

m/z

I

I′

3a

1387.05

1418.58

1444.07

1399.55

38

28

20

34

8

15

11

9

1402.55

1434.08

1459.57

1415.05

20

13

12

16

27

11

0

1849.73

1891.78

1925.76

1866.40

18

13

14

20

0

40

23

9

1870.06

1912.11

1946.10

1886.73

12

11

10

0

30

18

0

7a

8a

0

9a

10

11

13

10

15

13

20

15

25

0

13a

14a

16

0

27

21

15

11

I — ionic current intensities at a cone voltage of 25 V; I′ — ionic current intensities at a cone voltage of 45 V.

J. Porphyrins Phthalocyanines 2012; 16: 106–113

CATIONIC b-VINYL SUBSTITUTED MESO-TETRAPHENYLPORPHYRINS

107

In Fig. 3 the product ion spectrum of the

[ds+porphyrin-5H⁺]^4-adduct ion is shown for

porphyrin 3a (N-methylpyridinium-2-yl).

The same type of behavior was observed

by us for the [ds+porphyrin-5H⁺]^4-adduct

ions of the same duplex oligonucleotide, with

the monocharged compound 5-(1-methyl-

pyridynium-4-yl)-10,15,20-triphenylpor-

phyrin [21]. Thus, we may conclude that the

porphyrins are probably bound to the outside

of the duplex structure through coulombic

attractions with the phosphate ions. The

formation of duplex/porphyrin/acetate ion

adductsisalsoconsistentwithexternalbinding.

The acetate ion is probably electrostatically

bound to the nitrogen bearing the positive

charge in the substituent group.

Fig. 2. Mass spectrum of the solution of the oligonucleotide ds4GC and

porphyrin 9a at a cone voltage of 25 V

The similarity of the MS²spectra lead

us to acquire the pseudo MS³spectra,

[ds+porphyrin-5H⁺]^4-→ [ss+porphyrin-3H⁺]^2-

→ product ions, for all the porphyrins,

with the exception of porphyrin 13a

(N-methylquinolinium-2-yl), in order to obtain

furtherinformationonthe[ds+porphyrin-5H⁺]^4-

adduct ions.

The ﬁrst step was to increase the cone

voltage in order to generate in the source

the [ss+porphyrin-3H⁺]^2-ions, through the

Fig. 3. Product ion spectrum of the solution of the oligonucleotide ds4GC

and porphyrin 3a at a cone voltage of 25 V

unzipping of the [ds+porphyrin-5H⁺]^4-adduct ions.

Complete disappearance of the [ds+porphyrin-5H⁺]^4-

signal, with formation of the [ss+porphyrin-3H⁺]^2-and

[ss-2H⁺]^2-ions, was observed for porphyrins 3a, 7a and

14a for a cone voltage of 45 V. For porphyrin 9a the

complete disappearance of the [ds+porphyrin-5H]^4-ion

was observed for a cone voltage of 50V and for porphyrin

8a for a cone voltage of 55 V. This behavior can be

observed in Fig. 4 for porphyrin 7a. At the described cone

voltages, the [ss+porphyrin-3H⁺]^2-ions were formed with

relative abundances high enough to allow the acquisition

of their MS²spectra.

three porphyrins, since their adduct ions did not totally

disappear but their abundance decreases. As indicated

above the adduct ions [ds+porphyrin-4H⁺+CH₃COO^-]^4-

can be the main source of the [ds+porphyrin-4H⁺]^3-ions,

not only for porphyrin 13a (N-methylquinolinium-2-yl),

but also for porphyrins 3a and 7a. The differences in

behavior between the other pair of isomers 13a and 14a

are less easy to rationalize, specially the formation of the

[ds+porphyrin-3H⁺+CH₃COO^-]^3-adduct ion at a higher

cone voltage for porphyrin 14a.

The product ion spectra (precursor ion → product

ion, MS/MS or MS²) of the [ds+porphyrin-5H⁺]^4-adduct

ions were acquired by mass selecting them with the ﬁrst

analyzer, at the cone voltage value of 25 V for which

their relative abundances were higher. The exception

was porphyrin 13a (N-methylquinolinium-2-yl), due to

the low relative abundance of the [ds+porphyrin-5H⁺]^4-

precursor ion. However as, for this compound, the

adduct ion [ds+porphyrin-4H⁺+CH₃COO^-]^4-is formed

with higher relative abundance at this voltage, its MS²

spectrum was also acquired. Unzipping of the double

strand, with formation of the [ss+porphyrin-3H⁺]^2-

and [ss-2H⁺]^2-ions (ss = single strand, monoisotopic

mass = 2410.4399 Da) is the main feature in the MS²

spectra of the [ds+porphyrin-5H⁺]^4-adduct ions.

Similarly the [ds+porphyrin-4H⁺+CH₃COO^-]^4-adduct ion

of porphyrin 13a fragments with formation of the

[ss+porphyrin-2H⁺+CH₃COO^-]^2-and [ss-2H⁺]^2-species.

The [ss+porphyrin-3H⁺]^2-ions were then mass selected

and subjected to collisions with an inert gas (collision

energy of 50 eV). The spectra obtained were very similar

for porphyrins 3a, 7a, 8a and 14a. The signal of the

[ss+porphyrin-3H⁺]^2-ion for porphyrin 9a (N-sugar-

pyridinium-4-yl) was low and it was not possible to

perform the MS²experiments.

The overall results conﬁrm our previous hypothesis

that the positive charge is the main contributor for the type

and strength of porphyrin/duplex interactions [21, 22].

Nevertheless a general ranking of the binding strengths

can be proposed based on the cone voltages values

needed to completely unzip the [ds+porphyrin-5H⁺]^4-

adduct ions: 3a, 7a and 14a < 9a < 8a. The observed

trend points to a contribution of the more easily distorted

N-decylpyridinium-4-yl (8a) and N-sugar-pyridinium-

4-yl (9a) substituent groups in adduct formation.

J. Porphyrins Phthalocyanines 2012; 16: 107–113

108

E.M.P. SILVA ET AL.

analyses were performed in a Leco 999 CHN

analyzer. The UV-vis spectra were recorded

on an Uvikon 922 spectrophotometer using

DMSO as solvent. Column chromatography

was carried out using silica gel (Merck, 35–70

mesh). Analytical TLC was carried out on

precoated sheets with silica gel (Merck 60,

0.2 mm thick). All the chemicals were used

as supplied except 2- and 4-methylpyridine,

which were distilled from KOH under an

inert atmosphere and stored over KOH. Other

solvents were puriﬁed or dried according to

the literature procedures [64]. Both 1,2- and

1,4-dimethylpyridinium iodides (2 and 4) as

Fig. 4. Mass spectrum of the solution of the oligonucleotide ds4GC and

porphyrin 7a at a cone voltage of 45 V

well as 1,2- and 1,4-dimethylquinolinium iodides (11 and

12) were prepared according to the literature procedures

[29, 30].

UV-vis experiments

In an attempt to relate the behavior of the adducts

in the gas-phase to their behavior in solution, UV-vis

spectrophotometric experiments were performed for

all the cationic porphyrins. The alterations in the Soret

absorption band of the porphyrins were analysed when the

GC duplex was added. A general trend of hypochromism,

although modest, was observed for all the porphyrins in

0.5 M ammonium acetate solutions. However, it was

established that the ammonium acetate solutions on

its own produced the same sort of hypochromic shift.

Bathochromic shifts, which would be an indication of

the intercalative binding to the duplex [59–62], were

not observed. In the case of external or groove binding

the changes in the UV-vis absorption spectra are not

signiﬁcant, because of the less direct contact between

π-systems, when compared with intercalation [61, 63].

These data conﬁrms that intercalation does not occur for

the buffer concentrations (0.5 M) used to perform the

mass spectrometric experiments.

Synthesis of the pyridinium salts

1-decyl-4-methylpyridinium iodide 5. 1-iododecane

(1.26 g, 4.70 mmol) was added to 4-methylpyridine (0.50

mL, 5.15 mmol) in a round bottomed ﬂask equipped with

a condenser, at room temperature while stirring. The

mixture was stirred at 80 °C for 6 h, then it was allowed to

cool at room temperature, and Et₂O was added. The sticky

precipitate formed was decanted and washed several

times with Et₂O. The desired product was obtained as a

pink oil (1.45 g, 84% yield) after puriﬁcation of the crude

by alumina column chromatography (eluent: CH₂Cl₂). ¹H

NMR (300 MHz, CDCl₃): d, ppm 9.17 (d, J = 6.5 Hz,

2H, H-2,6), 7.89 (d, J = 6.5 Hz, 2H, H-3,5), 4.86 (t, J =

7.4 Hz, 2H, N-CH₂R), 2.69 (s, 3H, 4-CH₃), 2.01 (quint,

2H, J = 7.4 Hz, N-CH₂CH₂R), 1.33–1.24 [m, 14H,

R(CH₂)₇CH₃], 0.87 [t, 3H, J = 6.7 Hz, R(CH₂)₉CH₃].

¹³C NMR (75 MHz, CDCl₃): d, ppm 159.0 (C-4), 143.9

(C-2,6), 128.8 (C-3,5), 61.5 (N-CH₂R), 31.8, 31.7, 29.4,

29.3, 29.2, 29.0, 26.0, 22.6 and 22.4 (C-decyl group

and 4-CH₃), 14.1 (N(CH₂)₉CH₃). ESI(+)-HRMS: m/z

C₁₆H₂₈N, calcd. 234.2216; found 234.2211.

EXPERIMENTAL

General

1-(1,2:3,4-di-O-isopropylidene-a-D-galacto-py-

ranos-6-yl)-4-methylpyridinium iodide 6. 6-iodo-1,2:3,

4-di-O-isopropylidene-a-D-galactopyranose (0.20 g, 0.54

mmol) was added to 4-methylpyridine (0.50 mL, 5.15

mmol), in a round bottomed ﬂask at room temperature

while stirring. The mixture was stirred at 120 °C for

4 h, then it was allowed to cool at room temperature and

light petroleum was added. The pale pink precipitate

formed was decanted and washed several times with Et₂O.

The desired product was obtained after crystallization

from CH₂Cl₂/petroleum ether (0.24 mg, 96% yield); mp

> 300 °C. ¹H NMR (300 MHz, CDCl₃): d, ppm 9.28

(d, J = 6.5 Hz, 2H, H-2,6), 7.75 (d, J = 6.5 Hz, 2H,

H-3,5), 5.68 (dd, J = 2.4 and 13.6 Hz, 1H, H-6′), 5.43

(d, J = 4.9 Hz, 1H, H-1′), 4.73 (dd, J = 1.6 and 7.9 Hz,

1H, H-4′), 4.67 (dd, J = 2.3 and 7.9 Hz, 1H, H-3′), 4.62

(dd, J = 9.5 and 13.6 Hz, 1H, H-6′), 4.36–4.32 (m, 1H,

Melting points were measured on

a Reichert

Thermovar apparatus ﬁtted with a microscope and are

1

uncorrected. H and ¹³C solution NMR spectra were

recorded on Bruker Avance 300 and 500 spectrometers

at 300.13/500.13 and 75.47/126.76 MHz, respectively.

DMSO-d₆, CDCl₃or a mixture of CDCl₃/MeOH-d₄

were used as solvent and TMS as internal reference;

the chemical shifts are expressed in d (ppm) and the

1

coupling constants (J) in Hertz (Hz). Unequivocal H

assignments were made with aid of 2D COSY (¹H/¹H),

while ¹³C assignments were made on the basis of 2D

HSQC (¹H/¹³C) and HMBC experiments (delay for long-

range J C/H couplings were optimized for 7 Hz). Mass

spectra and HRMS were recorded on VG AutoSpec Q

and M mass spectrometers using CHCl₃as solvent and

NBA as matrix (unless otherwise stated). Elemental

J. Porphyrins Phthalocyanines 2012; 16: 108–113

CATIONIC b-VINYL SUBSTITUTED MESO-TETRAPHENYLPORPHYRINS

109

H-5′), 4.32 (dd, J = 2.3 and 4.9 Hz, 1H, H-2′), 2.69 (s, 3H,

(m, 11H, H-Ph-m,p and H-3,5), 7.66 (t, 1H, J = 7.3 Hz,

H-20-Ph-p), 7.52 (t, 2H, J = 7.3 Hz, H-20-Ph-m), 7.16 (d,

1H, J = 15.2 Hz, H-2′), 7.06 (d, 1H, J = 15.2 Hz, H-1′),

6.88 (d, 2H, J = 6.2 Hz, H-2,6), 3.55 (s, 3H, N-CH₃).

¹³C NMR (75 MHz, CDCl₃/CD₃OD): d, ppm 154.5 (C-1),

152.1 (C-Ph), 152.0, 151.9 (C-Ph), 151.5 (C-Ph), 150.9

(C-Ph), 147.9, 146.7, 144.3, 144.0 (C-3,5), 143.9, 143.6,

139.5 (C-2′), 139.4, 135.3 and 135.2 (C-Ph-o), 133.2,

133.1, 133.0, 130.9, 132.8, 132.5 (C-3′′), 132.2, 128.8

(C-20′′-Ph-p); 128.4, 128.2 (C-5′′,10′′,15′′-Ph-m,p);

127.6 (C-20′′-Ph-m); 127.3, 127.2 (C-5′′,10′′,15′′-Ph-

m,p); 123.4 (C-2,6), 122.3 (C-1′), 121.8, 120.6, 46.8

(N-CH₃). UV-vis (CHCl₃): l_max, nm (%) 417 (100), 491

(57.3), 633 (22.4). ESI(+)-HRMS: m/z C₅₂H₃₆N₅Zn:

calcd. 794.2262; found 794.2282.

4-CH₃), 1.42, 1.40, 1.34 and 1.25 [4s, 12H, 2 × C(CH₃)₂].

¹³C NMR (75 MHz, CDCl₃): d, ppm 159.4 (C-4), 144.7

(C-2,6), 127.9 (C-3,5), 109.7 and 109.2 [2 × C(CH₃)₂],

96.1 (C-1′), 70.6, 70.45 and 70.40 (C-2′, 3′, 4′), 67.3 (C-5′),

60.6 (C-6′), 26.2, 25.9, 24.7 and 24.1 [2 × C(CH₃)₂], 22.4

(4-CH₃). FAB(+)-MS: m/z 336 [M - I + H]⁺. Elemental

analysis: calcd. for C₁₈H₂₆INO₅: C, 46.66; H, 5.66; N,

3.02; found (%) C, 46.55; H, 5.84; N, 2.98.

Synthesis of the (porphyrin-2-yl)vinylpyridinium salts

Typical procedure: zinc(II) complex of 1-methyl-

2-[2-(5,10,15,20-tetraphenylporphyrin-2-yl)vinyl]

pyridinium chloride 3b. 1,2-dimethylpyridinium

iodide (11.5 mg, 0.05 mmol) was added to a solution

of porphyrin 1b (15.7 mg, 0.02 mmol) in THF/MeOH

(2:1, 4.5 mL) containing K₂CO₃(20.6 mg, 0.14 mmol).

The reaction mixture was stirred for 1 h at 30 °C under

a N₂atmosphere. The mixture was then allowed to cool

at room temperature, and the solvents were evaporated

under reduced pressure. The crude was taken in CH₂Cl₂

and washed with water. The organic phase was dried

(Na₂SO₄) and the solvent was evaporated. The desired

product was obtained after ﬂash chromatography on

silica gel (eluent: CH₂Cl₂/MeOH, 95:5). The fraction

containing the desired product was concentrated and

washed several times with brine, the organic layer was

dried (Na₂SO₄) and the solvent was evaporated. The

porphyrin was crystallized from CH₂Cl₂/hexane (7.6

mg, 43% yield); some 2-formyl-TPP was recovered (4.7

1-decyl-4-[2-(5,10,15,20-tetraphenylporphyrin-

2-yl)vinyl]pyridinium

chloride

8a.

1-decyl-4-

methylpyridinium iodide (30.3 mg, 0.08 mmol) was

added to a solution of porphyrin 1a (26.1 mg, 0.04 mmol)

in THF/MeOH (2:1, 4.5 mL) containing K₂CO₃(34.0 mg,

0.25 mmol). The reaction mixture was stirred at 60 °C,

under a N₂atmosphere, for 9 h (total time). New portions

of 1-decyl-4-methylpyridinium iodide were added to the

reaction mixture (additions after 3, 5 and 7 h, 4 equiv.

per addition). The mixture was then allowed to cool at

room temperature, and the solvents were evaporated

under reduced pressure. The crude was taken in CH₂Cl₂

and washed with water and with brine, the organic phase

was dried (Na₂SO₄) and the solvent was evaporated. The

desired product was obtained after ﬂash chromatography

on silica gel (eluent: CH₂Cl₂/MeOH 20/1). The fraction

containing the desired product was concentrated and

washed several times with brine, the organic layer was

dried (Na₂SO₄) and the solvent was evaporated. The

porphyrin was crystallized from CH₂Cl₂/hexane (12.1

1

mg, 30%); mp > 300 °C. H NMR (300 MHz, CDCl₃/

CD₃OD): d, ppm 8.81–8.76 (m, 5H, H-b), 8.75 (d, 1H,

J = 4.8 Hz, H-b), 8.66 (d, 1H, J = 4.8 Hz, H-b), 8.36–

8.14 (m, 9H, H-Ph-o and H-5), 8.03–7.73 (m, 15H,

H-Ph-m,p and H-3,4,6), 7.27 (d, 1H, J = 11.9 Hz, H-2′),

6.97 (d, 1H, J = 11.9 Hz, H-1′), 4.09 (s, 3H, N-CH₃).

¹³C NMR (75 MHz, CDCl₃/CD₃OD): d, ppm 152.6 (C-1),

152.55 (C-Ph), 152.51 (C-Ph), 151.3 (C-Ph), 151.2

(C-Ph), 151.1, 144.34, 144.26 (C-5), 143.94, 143.86

(C-3), 143.0, 142.0, 140.5 (C-2′), 139.8, 136.3 (C-2′′),

134.9 and 133.6 (C-Ph-o), 133.32, 133.27, 133.1, 132.8,

132.7, 129.7; 129.0, 128.3, 128.0, 127.7, 127.4, 127.0

(C-Ph-m,p); 126.3 (C-4,6), 122.0, 120.9, 119.5 (C-1′),

46.3 (N-CH₃). UV-vis (CHCl₃): l_max, nm (%) 415 (100),

402 (71.1), 568 (15.3), 629 (14.4). ESI(+)-HRMS: m/z

C₅₂H₃₆N₅Zn: calcd. 794.2262; found 794.2276.

1

mg, 30% yield); mp 275–278 °C. H NMR (500 MHz,

CDCl₃): d, ppm 9.09 (s, 1H, H-3′′), 8.99 (d, 2H, J = 6.4

Hz, H-3,5), 8.85–8.77 (m, 6H, H-b), 8.23–8.18 (m, 8H,

H-Ph-o), 8.03 (t, 1H, J = 7.4 Hz, 20′′-H-Ph-p), 7.91–7.74

(m, 11H, H-Ph-m and 5′′,10′′,15′′-H-Ph-p), 7.54 (d, 1H,

J = 6.4 Hz, H-2,6), 7.46 (d, 1H, J = 16.0 Hz, H-2′), 7.25 (d,

1H, J = 16.0 Hz, H-1′), 4.77 (t, 2H, J = 7.5 Hz, NCH₂R),

2.04–2.02 (m, 2H, NCH₂CH₂R), 1.38–1.25 [m, 14H,

R(CH₂)₇CH₃)], 0.86 [t, 3H, J = 6.5 Hz, N(CH₂)₉CH₃],

-2.53 (s, 2H, NH). ¹³C NMR (126 MHz, CDCl₃/CD₃OD):

d, ppm 154.2 (C-1), 143.7 (C-3,5), 141.94 (C-Ph), 141.92

(C-Ph), 141.7 (C-Ph), 141.5 (C-Ph), 138.3 (C-2′); 134.7,

134.6, 134.52, 134.50 (C-Ph-o); 129.4 (C-20′′-Ph-p);

128.2, 127.9, 127.7, 126.9, 126.8 (C-5′′,10′′,15′′–Ph-p

and C-Ph-m); 123.6 (C-3,5), 122.7 (C-1′), 121.0, 120.63,

120.57, 119.6, 61.0 (NCH₂R), 31.9 (NCH₂CH₂R), 31.8,

31.7, 26.1, 22.7, 22.6, 14.1 (N(CH₂)₉CH₃). UV-vis

(DMSO): l_max, nm (log e) 431 (4.14), 523 (2.77), 579

(2.30), 599 (2.17), 666 (1.22). ESI(+)-HRMS: m/z

C₆₁H₅₆N₅: calcd. 858.4530; found 858.4562.

Zinc(II) complex of 1-methyl-4-[2-(5,10,15,20-

tetraphenylporphyrin-2-yl)vinyl]pyridinium chloride

7b. The synthesis was accomplished according to the

procedure described for 3b. Yield 6.1 mg (40%); some

2-formyl-Zn-TPP was recovered (2.1 mg, 19%); mp >

1

300 °C. H NMR (300 MHz, CDCl₃/CD₃OD): d, ppm

9.19 (s, 1H, H-3′′), 8.86–8.82 (m, 4H, H-b), 8.80 (d, 1H,

J = 4.7 Hz, H-17′′ or 18′′), 8.70 (d, 1H, J = 4.7 Hz, H-17′′

or 18′′), 8.28–8.25 (m, 2H, H-Ph-o), 8.22–8.17 (m, 4H,

H-Ph-o), 8.00 (d, 2H, J = 7.3 Hz, H-20-Ph-o), 7.88–7.72

1-(1,2:3,4-di-O-isopropylidene-a-D-galactopyranos-

6-yl)-4-[2-(5,10,15,20-tetraphenylporphyrin-2-yl)-vinyl]

J. Porphyrins Phthalocyanines 2012; 16: 109–113

110

E.M.P. SILVA ET AL.

pyridinium chloride 9a. Compound 6 (34.3 mg, 0.07

mmol) was added to a solution of porphyrin 1a (24.8

mg, 0.04 mmol) in THF/MeOH (2:1, 4.5 mL) containing

K₂CO₃(32.7 mg, 0.24 mmol). The reaction mixture was

stirred at 60 °C, under a N₂atmosphere, for 3 h (total time).

New portions of 6 were added to the reaction mixture after

1 h and 2 h (2 equiv. per addition). The mixture was then

allowed to cool at room temperature, and the solvents

were evaporated under reduced pressure. The crude was

taken in CH₂Cl₂and washed with water and with brine,

the organic phase was dried (Na₂SO₄) and the solvent

was evaporated. The compound was puriﬁed by ﬂash

chromatography on silica gel (eluent: CH₂Cl₂/MeOH 9:1).

The fraction containing compound 9a was concentrated

and washed several times with brine. The organic layer

was dried (Na₂SO₄) and the solvent was evaporated.

The porphyrin was crystallized from CH₂Cl₂/hexane

7.89–7.84 (m, 12H, H-Ph-m,p), 7.75 (d, 1H, J = 6.3 Hz,

H-2,6), 7.66 (d, 1H, J = 16.3 Hz, H-2′), 7.41 (d, 1H, J = 16.3

Hz, H-1′), 6.73 (d, 1H, J = 6.9 Hz, Gal-H-1), d 5.08–4.91

and 4.86–4.54 (2m, 7H, Gal-H), -2.59 (s, 2H, NH). ESI(+)-

HRMS: m/z C₅₇H₄₆N₅O₅: calcd. 880.3493; found 880.3491.

Synthesis of (porphyrin-2-yl)vinylquinolinium salts

Typicalprocedure:1-methyl-4-[2-(5,10,15,20-tetraph-

enylporphyrin-2-yl)vinyl]quinolinium chloride 13a.

1,2-dimethylquinolinium iodide (13.7 mg, 0.05 mmol)

was added to a solution of porphyrin 1a (30 mg, 0.03

mmol) in pyridine (2 mL). The resulting mixture was

left overnight at 60 °C under a N₂atmosphere. After that,

another portion of 1,2-dimethylquinolinium iodide (13.6

mg) wasadded and stirring wascontinued through another

day. The addition was repeated again and the reaction

mixture was left for an additional day. The solvent was

evaporated under reduced pressure, the crude was taken

in CH₂Cl₂and the desired product was obtained after ﬂash

chromatography on silica gel (CH₂Cl₂/MeOH 9:1). The

fraction containing the desired product was concentrated

and washed several times with brine, the organic layer

was dried (Na₂SO₄) and the solvent was evaporated. The

porphyrin was crystallized from CH₂Cl₂/hexane (18.7

mg, 49% yield); 2-formyl-TPP was recovered (24.4 mg,

81%); mp 195.1–197.8 °C. ¹H NMR (300 MHz, CDCl₃/

CD₃OD): d, ppm 9.30 (s, 1H, H-3′′), 8.87–8.76 (m, 6H,

H-b), 8.59 (d, 1H, J = 8.9 Hz, H-8), 8.53 (d, 1H, J =

9.0 Hz, H-5), 8.28–8.05 (m, 10H, H-3,6 and H-Ph-o),

7.91–7.75 (m, 12H, H-Ph-m,p), 7.71 (AB, 2H, J = 15.5

Hz, H-1′,2′), 7.31 (d, 1H, J = 8.9 Hz, H-7), 7.29 (d, 1H, J

= 8.3 Hz, H-4), 4.61 (s, 3H, N-CH₃), -2.49 (s, 2H, NH).

¹³C NMR (75 MHz, CDCl₃/CD₃OD): d, ppm 156.0 (C-1),

143.5 (C-8 and C-2′), 142.3 (C-Ph), 141.6 (C-Ph), 141.5

(C-Ph), 141.2 (C-Ph), 139.4 (C-4a), 136.6 (C-3), 135.9,

134.7 (C-b), 134.6 (C-b), 134.4 (C-3′′), 129.9 (C-6),

129.6 (C-b), 129.4 (C-b); 128.7, 128.3, 127.9, 127.7,

127.6, 127.5, 127.4, 126.9, 126.8, 126.7 (C-Ph-o,m,p);

126.6 (C-8a), 125.8, 122.0, 121.6 (C-4), 120.7, 120.5,

120.3 (C-7), 119.1 (C-5), 117.8 (C-1′), 40.4 (N-CH₃).

UV-vis (DMSO): l_max, nm (log e) 428 (4.13), 492 (3.57),

562 (4.07), 600 (4.13), 629 (3.67).

1

(20.5 mg, 53% yield); mp 266–268 °C. H NMR (300

MHz, CDCl₃): d, ppm 9.18 (d, 2H, J = 6.7 Hz, H-3,5), 9.09

(s, 1H, H-3′′), 8.86–8.77 (m, 6H, H-b), 8.25–8.19 (m, 8H,

H-Ph-o), 7.96 (t, 1H, J = 7.6 Hz, 20′′-H-Ph-p), 7.87–7.74

(m, 11H, H-Ph-m and 5′′,10′′,15′′-H-Ph-p), 7.491 (d, 1H,

J = 6.7 Hz, H-2,6), 7.489 (d, 1H, J = 15.4 Hz, H-2′), 7.24

(d, 1H, J = 15.4 Hz, H-1′), 5.64 (dd, 1H, J = 2.2 and 13.7

Hz, Gal-H-6), 5.50 (d, 1H, J = 4.8 Hz, Gal-H-1), 4.79 (dd,

1H, J = 1.4 and 8.0 Hz, Gal-H-4), 4.72 (dd, 1H, J = 2.3 and

8.0 Hz, Gal-H-3), 4.56 (dd, 1H, J = 9.4 and 13.7 Hz, Gal-

H-6), 4.39–4.37 (m, 1H, Gal-H-5), 4.35 (dd, 1H, J = 2.3

and 4.8 Hz, Gal-H-2), 1.49, 1.44, 1.38, 1.28 [4s, 12H, 2 ×

C(CH₃)₂], –2.53 (s, 2H, NH). ¹³C NMR (75 MHz, CDCl₃):

d, ppm 154.4 (C-1), 144.6 (C-3,5), 142.0, 141.7, 141.5,

138.5 (C-2′), 134.8, 134.6, 134.53, 134.51, 132.9, 131.2,

129.9, 129.85, 129.77, 129.3, 128.2, 127.9, 127.6, 127.5

126.9, 126.8, 122.8 (C-2,6 and C-1′), 121.0, 120.7, 120.6,

119.5, 109.6 [C(CH₃)₂], 109.3 [C(CH₃)₂], 96.1 (Gal-C-1),

70.7, 70.6, 70.5 (Gal-C-2,3,4), 67.6 (Gal-C-5), 60.3 (Gal-

C-6), 26.3, 25.9, 24.8 and 24.1 [C(CH₃)₂]. UV-vis (DMSO):

l

_max, nm (log e) 431 (4.89), 525 (4.11), 574 (3.86), 600

(3.86), 663 (3.72). ESI(+)-HRMS: m/z C₆₃H₅₄N₅O₅: calcd.

960.4119; found 960.4167.

1-(a,b-D-galactopyranos-6-yl)-4-[2-(5,10,15,20-

tetraphenylporphyrin-2-yl)vinyl]pyridinium chloride

10a. A solution of 9a (7.5 mg, 6.8 mmol) in TFA/H₂O

(9:1, 1.0 mL) was stirred for 30 min at room temperature.

The reaction mixture was then partitioned between CHCl₃

(10 mL) and an ice-cold aqueous Na₂CO₃saturated solution

(10 mL). The organic layer was washed with water, dried

(Na₂SO₄) and the solvent was evaporated. The desired

product was obtained after ﬂash chromatography on silica

gel using CH₂Cl₂/MeOH 9:1 as the eluent. The fraction

containing the desired product was concentrated and

washed several times with brine, the organic layer was dried

(Na₂SO₄) and the solvent was evaporated. The porphyrin

was crystallized from CH₂Cl₂/petroleum ether (4.6 mg,

66% yield); mp > 300 °C. ¹H NMR (300 MHz, DMSO-d₆):

d, ppm 9.16 (s, 1H, H-3′′), 8.92 (d, 2H, J = 6.3 Hz, H-3,5),

8.87–8.73 (m, 6H, H-b), 8.28–8.21 (m, 8H, H-Ph-o),

Zinc(II) complex of 1-methyl-2-[2-(5,10,15,20-tetra-

phenylporphyrin-2-yl)vinyl]quinoliniumchloride13b.

The synthesis was accomplished according to the

procedure described for 13a. Yield 10.0 mg (38%); mp

1

289–292 °C. H NMR (300 MHz, DMSO-d₆): d, ppm

9.38 (s, 1H, H-3′′), 8.85–8.70 (m, 6H, H-b), 8.44–7.41

(m, 24H, H-Ph and H-3 to H-8), 7.05 (d, 1H, J = 9.1 Hz),

4.29 (s, 3H, N-CH₃). ESI(+)-HRMS: m/z C₅₆H₃₈N₅Zn:

calcd. 844.2413; found 844.2414.

1-methyl-4-[2-(5,10,15,20-tetraphenylporphyrin-

2-yl)vinyl]quinolinium chloride 14a. The synthesis was

accomplished according to the procedure described for

13a. Yield 8.4 mg (22%); 2-formyl-TPP was recovered

1

(20.2 mg, 66%); mp 219.7–221.1 °C decomp. H NMR

J. Porphyrins Phthalocyanines 2012; 16: 110–113

CATIONIC b-VINYL SUBSTITUTED MESO-TETRAPHENYLPORPHYRINS

111

(300 MHz, CDCl₃/CD₃OD): d, ppm 10.27 (d, 1H, J = 6.2

relatively to 5,10,15,20-tetraphenylporphyrin in DMF

used as the reference; F_ﬂ(TPP) = 0.11 [47]. The

samples and the reference in DMF were excited at 532

nm (OD_{532 nm}= 0.05) and emission was monitored from

600 to 750 nm. The ﬂuorescence quantum yield (F_ﬂ) of

porphyrins were calculated by comparison of the area

below the corrected emission spectrum with that of

tetraphenylporphyrin (TPP) as a ﬂuorescence standard,

exciting at l = 532 nm [47].

Hz, H-3), 9.21 (s, 1H, H-3′′), 8.88–8.80 (m, 6H, H-b),

8.77 (AB, 2H, J = 4.9 Hz, H-12′′,13′′), 8.58 (d, 1H, J =

8.5 Hz, H-8), 8.32–8.29 (m, 2H, H-20′′-Ph-o), 8.23–

8.17 (m, 6H, H-5′′,10′′,15′′-Ph-o), 8.14–8.12 (m, 2H,

H-5,6), 7.96 (d, 1H, J = 15.5 Hz, H-1′), 7.98–7.90 (m,

1H, H-7), 7.88–7.72 (m, 12H, H-Ph-m,p), 7.74 (d, 1H,

J = 15.5 Hz, H-2′), 7.45 (d, 1H, J = 6.2 Hz, H-2), 4.75

(s, 3H, N-CH₃), -2.51 (s, 2H, NH). ¹³C NMR (126 MHz,

CDCl₃/CD₃OD): d, ppm 153.5 (C-1), 148.7 (C-3), 142.1

(C-Ph), 141.7 (C-Ph), 141.6 (C-Ph), 141.5 (C-Ph), 140.0

(C-2′′ and C-2′), 138.7 (C-4a), 135.0 (C-6), 134.7 (C-20′′-

Ph-o), 134.6 and 134.5 (C-5′′,10′′,15′′-Ph-o), 133.1

(C-12′′,13′′), 132.4 (C-3′′), 130.2 (C-b), 129.1 (C-7),

128.1 and 127.9 (C-5′′,10′′,15′′-Ph-m,p), 126.9 and 126.8

(C-20′′-Ph-m,p), 126.4 (C-8a), 125.9 (C-8), 120.9, 120.7,

120.5, 119.9, 119.0 (C-1′), 118.2 (C-5), 116.4 (C-2), 44.9

(N-CH₃). UV-vis (DMSO): l_max, nm (log e) 414 (4.42),

461 (4.24), 529 (3.69), 583 (3.47), 658 (3.12).

Mass spectrometry and UV-vis experiments

The single-stranded oligonucleotide GCGCGCGC

(ss4GC, monoisotopic mass = 2410.4399 Da) was

purchasedfromEurogentec(Liege,Belgium).Thedouble-

stranded oligonucleotide dsGCGCGCGC (ds4GC) was

formedfromastocksolution:100μMsolutionofthesingle

strand in ammonium acetate 0.5 M heated to 85 °C and left

to cool overnight. Seventy-ﬁve microliters of porphyrin

solution in methanol (approximately 1.0 × 10^-5M)

was then added to 25 μL of oligonucleotide solution.

Electrospray ionization mass spectra were acquired with

a Micromass Q-Tof 2 (Micromass, Manchester, UK),

operating in the negative mode, equipped with a Z-spray

source, an electrospray probe and a syringe pump. Source

and desolvation temperatures were 80 °C and 150 °C,

respectively. Capillary voltage was 2600 V. The spectra

were acquired at a nominal resolution of 9000 and at

cone voltages between 25 and 55 V. Nebulisation and

collision gases were N₂and Ar respectively. The samples

were introduced at a 10 μL.min^-1ﬂow. MS/MS spectra

were acquired by selecting the ion of interest with the

quadrupole and using the hexapole as collision cell with

energies from 25 to 55 eV.

Zinc(II) complex of 1-methyl-4-[2-(5,10,15,20-tetraph-

enylporphyrin-2-yl)vinyl]quinolinium chloride 14b.

The synthesis was accomplished according to the

procedure described for 13a. Yield 12.0 mg (45%); mp

> 300 °C. ¹H NMR (300 MHz, DMSO-d₆): d, ppm 9.39

(d, J = 6.5 Hz, 1H, H-3), 9.22 (s, 1H, H-3′′), 8.91–8.68

(m, 6H, H-b), 8.58 (d, 1H, J = 6.1 Hz, H-1′), 8.29–7.65

(m, 25H, H-Ph, H-2′ and H-5 to H-8), 7.37 (d, 1H,

J = 6.5 Hz, H-2), 3.88 (s, 3H, N-CH₃). ESI(+)-HRMS:

m/z C₅₆H₃₈N₅Zn: calcd. 844.2413; found 844.2428.

Photostability

In a typical experiment, 2 mL of a solution of the

porphyrin (1 μM) in DMF in a glass cuvette was irradiated

with white light (50 mW/cm²) at room temperature and

under gentle stirring for different periods of time. The

intensity of the Soret band was registered at different

intervals of time by UV-visible spectroscopy, and the

photostability was expressed as I_t/I₀(%) (I_t= intensity of

the band at given time of irradiation, I₀= intensity of the

band before irradiation).

UV-vis absorption spectra were obtained using an

Uvikon 922 spectrophotometer (Kontron Instruments

Ltd, UK) and scanning from 350 to 800 nm, a 1 cm path

length cuvette was utilised in all experiments. For the

UV-vis measurements, porphyrin samples were dissolved

in dimethylsulfoxide/methanol and added to solutions

of the double-stranded oligonucleotides in ammonium

acetate 0.5 M.

Oxygen singlet

A

solution containing DPBF (50 mM) and

CONCLUSION

photosensitizer (0.5 mM) in DMF was irradiated in a

glass cuvette at room temperature using a white light

with a ﬂuence rate at 50 mW/cm². The light beam was

ﬁltered using an appropriate cut-off ﬁlter (<540 nm) and

the absorption of the stirred solution was monitored at

415 nm at irradiation intervals of 10 sec for the 1st min

and of 30 sec for the remaining 5 min.

New cationic porphyrins with different substituents

on the N-terminus of pyridinium and quinolinium rings

were efﬁciently prepared in moderate yields. The results

obtained with the DPBF photooxidation indicated that

cationic derivatives 3a and 9a are efﬁcient singlet oxygen

generators, possibly justifying their signiﬁcant in vitro

activity against herpes simplex virus type 1 [19]. On the

contrary, compounds 13a and 14a, which contain in their

structures the quinolinium moiety, do not produce singlet

oxygen. The ﬂuorescence studies demonstrated that all

the studied derivatives have shown a weak ﬂuorescence

emission revealing that these compounds most likely

Fluorescence

The ﬂuorescence of the compounds was measured at

20 °C in 1 cm × 1 cm quartz optical cells with a computer

controlled Jobin Yvon FluoroMax-3 spectroﬂuorometer.

Fluorescence quantum yields F_ﬂwere determined

J. Porphyrins Phthalocyanines 2012; 16: 111–113

112

E.M.P. SILVA ET AL.

decay by other radiative or non-radiative processes.

Concerning the possible non-covalent interactions of the

synthesized porphyrins with d(4GC), the data indicate

that the porphyrins are probably bound to the outside

of the duplex structure through coulombic attractions

with the phosphate ions. The overall results conﬁrm our

previous hypothesis that the positive charge is a main

contributor for the type and strength of porphyrin/duplex

interactions. A general binding strength order is proposed

(porphyrins 3a, 7a and 14a < 9a < 8a).

13. Oliveira A, Almeida A, Carvalho CMB, Tomé JPC,

Faustino MAF, Neves MGPMS, Tomé AC, Cava-

leiro JAS and Cunha A. J. Appl. Microbiol. 2009;

106: 1986–1995.

14. Lembo AJ, Ganz RA, Sheth S, Cave D, Kelly C,

Levin P, Kazlas PT, Baldwin PC, Lindmark WR,

McGrath JR and Hamblin MR. Laser Surg. Med.

2009; 41: 337–344.

15. Carvalho CMB, Tomé JPC, Faustino MAF, Neves

MGPMS, Tomé AC, Cavaleiro JAS, Costa L, Alves

E, Oliveira A, Cunha A and Almeida A. J. Porphy-

rins Phthalocyanines 2009; 13: 574–577.

Acknowledgements

16. Tavares A, Carvalho CMB, Faustino MAF, Neves

MGPMS, Tomé JPC, Tomé AC, Cavaleiro JAS,

Cunha A, Gomes NCM, Alves E and Almeida A.

Marine Drugs 2010; 8: 91–105.

17. Neves MGPMS, Valdeira ML, Tomé JPC, Cava-

leiro JAS, Mendonça AF and Tomé AC. PT Patent

102572, 2002.

Thanks are due to the University of Aveiro, to the

PortugueseFoundationforScienceandTechnology(FCT)

and FEDER for funding the Organic Chemistry Research

Unit and the Portuguese National NMR Network. E.M.P.

Silva (Post-Doc grant SFRH/BPD/66961/2009), and

C.I.V. Ramos (PhD grant SFRH/BD/30755/2006) thank

FCT for their grants.

18. a) Kubát P, Lang K, Anzenbacher Jr. P, Jursíková K,

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Article Doi

Cationic β-vinyl substituted meso-tetraphenylporphyrins:

DOI: 10.1142/S1088424611004373

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Article abstract of DOI:10.1142/S1088424611004373

Full text of DOI:10.1142/S1088424611004373

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