Macroheterocyclic compound of ABBB-type containing 2N-Alkyl substituted 1,2,4-thiadiazoline fragment: synthesis and acid-base properties Текст научной статьи по специальности «Химические науки»

Порфиразины

Porphyrazines

iVJaKporaTepoLii/JKj-JbJ

Статья

Paper

http://macroheterocycles.isuct.ru

DOI: 10.6060/mhc180166d

Macroheterocyclic Compound of ABBB-Type Containing 2N-Alkyl Substituted 1,2,4-Thiadiazoline Fragment: Synthesis and Acid-Base Properties

Yu. V. Butina, E. A. Danilova,@ T. V. Kudayarova, and A. S. Malyasova

Dedicated to Professor Oleg A. Golubchikov on the ocassion of his 70th Birthday

Ivanovo State University of Chemistry and Technology, Research Institute ofMacroheterocycles, 153000 Ivanovo, Russian Federation

@Corresponding author E-mail: danilova@isuct.ru

The synthesis of ABBB-type macroheterocyclic compound containing both the 5-amino-2-dodecyl-3-imino-1,2,4-thia-diazoline fragment (fragment A) and three residues of 1,3-diiminoisoindoline (fragment B) is described in this work. The purification of target compound was carried out by column chromatography and by silica gel plate eluting with CH2Cl2:MeOH:Cfl14 mixture. The structure of the resultant compound was determined by data of UV-Vis, IR, H and 13C NMR spectroscopy, and mass spectrometry. It was shown that the target product possesses unique stability in acid medium and can belong to the class of "molecular chameleons" due to its ability postsynthetic modification of the optical properties of molecule. A bathochromic shift of the absorption maximum at 459-555 nm and emergence of new inflection points at 692 and 721 nm in trifluoroacetic acid and a shift to 716 nm in sulfuric acid were observed in the UV-visible spectrum. Acid-base behavior has been studied by spectrophotometric titration method in two solvent systems: CH2Cl2-CF3COOH and C.H5OH-H.SO4. The study ofprotonation in the first solvent system shows an interaction between one molecule of the macroheterocycle with one molecule of the acid. Investigations of the second medium demonstrated the presence of one non-protonated (1=478 nm) and two protonated (1=550 nm, 1=716 nm) forms. The most possible position of protonation was determined by quantum chemical calculations at the DFT level.

Keywords: Macroheterocycle of ABBB-type, 1,2,4-thiadiazoline, 1,3-diiminoisoindoline, spectroscopy, molecular

Макрогетероциклическое соединение ABBB-типаr содержащее фрагмент 2Ы—алкилированного 1,2,4-тиадиазолина: синтез и кислотно—основные свойства

Ю. В. Бутина, Е. А. Данилова, @ Т. В. Кудаярова, А. С. Малясова

Посвящается профессору О. А. Голубчикову по случаю его 70-летнего юбилея

Ивановский государственный химико-технологический университет, НИИ химии макрогетероциклических соединений, 153000 Иваново, Российская Федерация @Е-таИ: danilova@isuct.ru

В работе описывается синтез макрогетероциклического соединения АВВВ-типа, содержащего фрагмент 5-амино-2-додецил-3-имино-1,2,4-тиадиазолина (фрагмент А) и три остатка 1,3-дииминоизоиндолина (фрагмент В). Очистку целевого соединения осуществляли колоночной с последующей препаративной хроматографией на пластинах силикагеля, элюируя смесью СН2С12:МеОН:СН14. Строение полученного соединения доказано данными электронной, ИК, 1Н и 13С ЯМР спектроскопии, масс-спектрометрии. Показано, что целевой продукт обладает уникальной стабильностью в кислой среде и может быть отнесен к классу

chameleon.

«молекулярных хамелеонов» из-за его способности к постсинтетической модификации оптических свойств молекулы. В среде трифторуксусной кислоты наблюдаются батохромный сдвиг максимума поглощения от 459 до 555 нм и появление небольших инфлексий при 692 и 721 нм, в среде серной кислоты - сдвиг до 716 нм. Кислотно-основные свойства изучены методом спектрофотометрического титрования в двух системах: CHCl-CFCOOH и C2H OH-H2SO4. Изучение протонирования в первой среде показало, что на первой стадии происходит взаимодействие одной молекулы макрогетероциклического соединения с одной молекулой кислоты. Исследования во второй среде продемонстрировало существование одной непротонированной (1=478 нм) и двух протонированных (1=550 нм, 1=716 нм) форм. Наиболее вероятное место присоединения протона определяли с использованием методов квантовой химии на уровне DFT.

Ключевые слова: Макрогетероцикл ABBB-типа, 1,2,4-тиадиазолин, 1,3-дииминоизоиндолин, спектроскопия, молекулярные хамелеоны.

Introduction

Recently, the development of methods of synthesis of hydrogenated derivatives of porphyrins is of special interest for researchers. These compounds, such as chlorins and bacteriochlorins, absorb light in the long-wave region of the spectrum due to changing of the symmetry upon the reduction of one or two double bonds while retaining of aromaticity. In the Russian Federation, sensitizers for photodynamic therapy of oncological diseases have been approved, i.e. Fotoditazin,[12] Radahlorin,[3] Photolon,[4] which are water-soluble chlorin e6 salts. The difficulty of synthesis of such compounds lies in the reduction of porphyrins, which results in the formation of a mixture of chlorins and bacteriochlorins.[5]

The syntheses of ABBB- and ABAB-type macroheterocyclic compounds, where A is a fragment of 2^-substituted 5-amino-3-imino-1,2,4-thiadiazoline, and B is the residue of 1,3-diiminoisoindoline, are of interest. Such products will possess tetrazachlorin- and tetrazabacteriochlorin-like structures (Figure 1) due to the presence of the 2^-substituted 1,2,4-thiadiazoline moiety. We have not found a description of these compounds in the literature. For our proposed

NH HN Л N ___ -

О

Tetraazaclorin-like compound

Bacteriochlorin

S— N

n^V^AsN 7 N

,NH

HN

Л N

Ч-Г

R

Tetraazabacteriochlorin-like compound

Figure 1. Chromophore system of conjugated double bonds in chlorin, bacteriochlorin and similar compounds.

syntheses, a decrease in the number of synthetic steps and the time of synthesis are expected. This phenomenon can be explained by the formation of a chlorin or bacterio-chlorin-like structure without the reduction of one or two double bonds in the macrocycle, which leads to the formation of a mixture of di- and tetrahydrogenated products.

It can be expected that the absorption maximum of such compounds will be shifted to the near-IR region in an analogous fashion as with chlorins and bacteriochlorins, which will allow them to be considered as photosensitizers. Therefore, this work attempts to synthesize of a chlorin-like mac-rocyclic compound containing a fragment of 2^-dodecyl-substituted 1,2,4-thiadiazoline.

Experimental

Methods

Research on the synthesized compound was carried out using the resources of the Center for Collective Use of Scientific Equipment of Ivanovo State University of Chemistry and Technology. UV-Vis spectra were measured using a HITACHI U-2001 spectrometer in quartz cells of thickness 2 and 10 mm. IR spectra were obtained with AVATAR 360 FT-IR spectrometer with a diffusion reflection attachment Tensor 27 Bruker Optics. The samples were prepared by carefully triturating of the synthesized compound with KBr and compression of the tablet. MALDI-TOF mass spectra were recorded on the AXIMA Confidence (SHIMADZU) instrument in the positive ion detection mode. Samples were prepared by dissolving of the synthesized compound in chloroform (C=10"4-10-6 molL-1). DHB is 2,5-dihydroxybenzoic acid, which was used as a matrix. Nuclear magnetic resonance spectra (1H and 13C) were registered using a Bruker DRX-500 and an AVANCE-300 spectrometers from Bruker, respectively. Working frequencies are 500 (1H) and 75.5 (13C) MHz. Samples were prepared by dissolving the explored compound in CDCl3. Thin layer chromatography (TLC) was carried out on aluminum plates coated with a 60 F254 (E. Merck) silica gel layer. Silica gel of 60 0.05-0.20 mm (Macherey-Nagel) was used for column chromatography.

Synthesis

2-Dodecyl-3,10,17,24-tetraimino-5,12,19,26-tetranitrilo-1-thiotribenzo[f,k,p](1,5,9,13)tetraazacyclohexadecene (1) was obtained by the reaction of 0.26 g (0.91 mmol) of 5-amino-2-dodecyl-3-imino-1,2,4-thiadiazoline (2), synthesized by method described in the literature,161 and 0.4 g (2.74 mmol) of 1,3-diiminoisoindoline in 3 mL of phenol with step-by-step heating during 1.5-2 hours.

R

The reaction mixture was stirred for 50 hours at temperature 100110 °C, then the product was washed by hot water and hexane in Soxlet apparatus while absence of phenol, which was determined by qualitative reaction with ferric chloride. The target product was purified by column chromatography with following preparative thin layer chromatography on plates of silica gel eluting with a mixture of CH2Cl2:Me0H:C6H14=10:1:3. A bright-burgundy band was collected, the target compound was washed with acetone for removed of silica gel, and the solvent was evaporated in vacuo.

The product is dark-cherry powder. Yield: 7 mg (3.7 %). M.p. >200 °C. m/z (MALDI-TOF) 690.6 [M+K]+. EM 651.3. C38H37N9S. IR (KBr) vmax cm-1: 3437, 2925, 2853 val (C-Halk), 1739, 1647, 1556 val (C=N), 1461 val (C-C"), 1378, 1264, 1091, 875, 713. UV-Vis (C2H50H, C=6.12T0"5 molL-1) Xmax (lge) nm: 263 (4.41), 480 (3.60); (benzene, C=3.0610"5 mol-L™)\max (lge) nm: 451 (3.70); (acetone, C=1.4910"3 molL-1) Xmax (lge) nm: 457 (2.85); (CH2Cl2, C=5.4310"4 molL-1) Xmsx (lge^nm: 453 (3.25); (CH3C00H, C=3.0610"5 mol L-1) Xma'ma(lge) nm: 478 (3.32); (2,2,2-CF3C00H, C=4.1610"4 molL-1) C (lge) nm: 555 (3.38), 692 (2.94), 721 (2.92). 1H NMR (CDCy SH ppm: 7.90-7.77 (m, 12HJ, 1.59-0.89 (25Halk). 13C NMR (CDCl3) 5C ppm: 170.33 (C14), 168.50 (C13), 134.3a0 (C15), 132.77 (C16), 1231.58 (C17), 121.49 (C18), 63.11 (C12), 50.82 (C11), 31.93 (C10), 31.81 (C9), 31.37 (C8), 30.53 (C7), 29.64 (C6), 29.62 (C5), 29.36 (C4), 25.80 (C3), 22.70 (C2), 14.13 (C1). The numbers of carbon atoms are shown in Figure 6.

Results and Discussion

Synthesis

To date, a number of macroheterocyclic compounds with an asymmetrical (ABBB-type) structure containing fragments of 3,5-diamino-1,2,4-triazoles[78] and 2,5-diamino-1,3,4-thiadiazoles[9] is known. However, the compounds that contain the 3,5-diamino-1,2,4-thiadiazole fragment remain insufficiently known. We obtained an ABBB-type macroheterocyclic compound containing the fragment of 2^-dodecyl substituted 5-amino-

3-imino-1,2,4-thiadiazoline. The synthesis of this product was performed according to the Scheme below.

,NH

S—N

Л^ N

✓ C12H25

J"1 +

2

Scheme. Synthesis of an ABBB-type macroheterocyclic compound containing 5-amino-2-dodecyl-3-imino-1,2,4-thiadiazoline fragment.

The product 1 was obtained by the reaction of 5-amino-2-dodecyl-3-imino-1,2,4-thiadiazoline with 1,3-diimi-noisoindoline in phenol at 100-110 °C over 50 hours. The reaction of the target compound was observed to be unselec-tive. The purification was not sufficient by a column method, and repeated use of this method was impossible because of the instability of the compound obtained. Therefore, product 1 was isolated using preparative chromatography.

Compound 1 was characterized by mass spectrometry, UV-Vis, IR, 1H and 13C NMR spectroscopy. The mass spectrum of 1 contains a signal with m/z 690.6 Da corresponding to molecular ion in form [M+K]+. The isotopic distribution corresponds to the theoretically calculated: 690.3-100 %, 691.3-41.1 %, 692.3-7.2 % (Figure 2).

In the IR spectrum bands at 2925 and 2853 cm-1 can be assigned to stretching valence C-H vibrations of the alkyl group, with bands at 1556 and 1481 cm-1 characterized as stretching valence C=N and C-C bonds of the heterocyclic fragments.

Figure 2. The fragment of mass spectrum of compound 1.

3

There is an absorption maximum at X=263 nm in the UV-Vis spectrum recorded in ethanol, which indicates the presence of the thiadiazole ring. The nature of the spectrum in the visible region with X =480 nm is similar to that

° max

of the ABBB-type macroheterocyclic compounds containing the 1,3,4-thiadiazole moiety.[10] A hypsochromic shift of the absorption maximum occurs with a decrease in the polarity of the solvent. Thus, the absorption maximum appears in the region of 457, 453, 451 nm in acetone, dichlo-romethane, and benzene, respectively.

Figure 3 shows, that broadening of the long-wave absorption band occurs in the UV-Vis spectrum recorded in acetone upon dilution of a solution of 1. The dependence of the absorption intensity on the solution concentration is linear (Figure 4). Consequently, the Lambert-Bouguer-Beer law is observed within the limits of concentrations (5.77-14.9)10-4 molL-1. The same dependence is also observed for solutions in dichloromethane and ethanol.

In the 1H NMR spectrum of compound 1, recorded in deuterochloroform, there is a multiplet in the range

A 1,2

1,0

0,

0,6

0,4

0,2

0,0

457

i_

. 9 10 1 1 1 1 1 1 1 1 1 1

400

450

500

550

600 X, nm650

Figure 3. UV-Vis spectra of 1 (acetone, C-104, molL-1): 1 -2 - 13.4; 3 - 12.1; 4 - 10.8; 5 - 9.76; 6 - 8.79; 7 - 7.91; 8 -9 - 6.41; 10 - 5.77.

A 1,00,90,80,70,6-

■ 14.9; 7.12;

0,50,4

I | I | I

5 6 7

9 10 11 12 13 14 15 C104 molL-1

Figure 4. Dependence of optical density on concentration of 1 (acetone, A,max=457 nm). Squares are an experiment, the line is the least-squares calculation (±0.005, probability P 0.99).

of 7.90-7.77 ppm, which characterizes the resonance of the protons from the aromatic fragments. Theoretically, the signals of the protons of the isoindole residue should be observed in the form of 2 doublets, which are formed due to the spin-spin interaction of protons Ha and Hb (Figure 5). The presence of a multiplet can be explained by the asymmetry of molecule 1, because of which the protons of aromatic fragments are unequal. The overlapping of several doublets forms a complex system of multiplets, whose type couldn't be determined and calculation of the spin-spin coupling constant wasn't possible. Signals in the region of 1.59-0.89 ppm correspond to the resonance of the protons of the alkyl substituent. In the region of 11.5-12.5 ppm signals are not observed, which indicates the absence of protons at the intracyclic nitrogen atoms of isoindole fragments.[11] This phenomenon is also confirmed experimentally: when interacting with nickel acetate, compound 1 does not coordinate the metal atom. Therefore, our expectations of obtaining a compound similar hydrogenated por-phyrazine were unsuccessful.

The 13C NMR spectrum of 1 reveals the signals in the region 170.33, 168.50 ppm, which characterize the resonance carbon atoms of thiadiazole fragment. The signals in the region 134.30, 132.77, 123.58, 121.49 ppm can be assigned to carbon atoms of isoindole residue. The signals at 63.11, 50.82, 31.93, 31.81, 31.37, 30.53, 29.64, 29.62, 29.36, 25.80, 22.70, 14.13 ppm confirm presence of twelve carbon atoms of alkyl group (Figure 6).

Acid-base behavior

Porphyrazines are multicenter conjugate bases due to the presence in their structure of donor centers: intra-cyclic and peripheral nitrogen atoms. The stability of porphyrazines is determined by the existence of a neutral or acidic form of these compounds in a proton-donor medium. The number of donor centers participating in the acid-base interaction depends on the proton-donor medium and on the structure of the protonated molecule.

We have studied the stability of product 1 in acidic media, which is similar in structure to hydrogenated porphy-razine 3, in which there are no hydrogen atoms in the inside cavity.

When solution of compound 1 is added to trifluoro-acetic acid, a bathochromic shift of the absorption maximum is observed from 459 nm in dichloromethane to 555 nm in CF3COOH. Moreover, small inflections appear at 692 and 721 nm (Figure 7). When dissolving of 1 in monohydrate, the absorption maximum is bathochromatically shifted to the region of 611 nm (Figure 8). All these phenomena support the protonation of compound 1.

A determination of the number of donor centers involved in acid-base interaction is possible when performing spectrophotometric titration in media with a known acidity function. However, to determine the concentration stability constants, an investigation of 1 was carried out using two mixtures: CH2Cl2-CF3COOH and C2H5OH-H2SO4, for which the acidity functions are unknown. In the absence of the latter, the titration data do not allow us to determine the number of donor centers, but only show the number of acid molecules participating in the protonation reaction.

Figure 5. 1H NMR spectrum of compound 1.

Figure 6. 13C NMR spectrum of compound 1. Макрогетер0циmbl /Macroheterocycles 2018 11 (1) 59-66

Figure 7. UV-Vis spectrum of compound 1: 1 - CH2Cl2 (C=1.4910-4 molL-1); 2 - CF3COOH (C=1.4910-4 molL-1).

Figure 8. UV-Vis spectrum of compound 1 (monohydrate, C=1.4910-4 molL-1).

When compound 1 is acidified in dichloromethane with trifluoroacetic acid (TFA) in the concentration range of CF3COOH 0.0013-0.6165 molL-1, characteristic changes are observed in the electronic absorption spectra accompanying the formation of acidified forms. In the first stage of this acid-base interaction (CTFA=0.0013-0.0588 molL-1),

the intensity of the absorption maximum at X=459 nm gradually decreases, and at the same time a new band appears at X=523 nm. This protonated form is kept to a concentration of CF3COOH equal to 0.0875 molL-1. The concentration stability constant of the resulting acidified form according to the transformed Hammett equation (pA"si=lg/-nlgCTFA) is equal to 1.84±0.01.

It is known that the number of acid molecules participating in the interaction is equal to the tangent of the slope angle of the linear relationship pA"si=/(lgCTFA). For this interaction, tga is equal to 1.26, which indicates the participation of one molecule of acid in the first stage of protonation. The value of tga is greater than 1 due to the homoconjuga-tion phenomenon, in which the CF3COO--anion is stabilized by the formation of conjugates with one or more acid molecules: =NH+... -OOCCF3(CF3COOH)n, as well as the solvation of the macroheterocyclic compound.

An increase in the amount of CF3COOH to 0.6165 molL-1 leads to a further bathochromic shift of the absorption maximum, which indicates a stronger acid-base interaction 1 in this medium, but a second isosbestic point could not be determined. Thus, the study of properties of 1 in the CH2Cl2-CF3COOH medium (Figure 9) made it possible to establish that in the first stage, interaction of 1 with one molecule of acid is observed.

Figure 9. Changes in the UV-Vis spectrum of compound 1 in the system CH2Cl2-CF3COOH.

e

2000015000100005000

478

400

500

600

700

800. 900 X, nm

Figure 10. Changes in the UV-Vis spectrum of compound 1 in the system C2H5OH-H2SO4.

Investigation of acid-base behavior of 1 was continued by spectrophotometry titration in media of C2H5OH-H2SO4 (Figure 10), which showed existence of a non-protonated (X=478 nm) and two protonated (X=550 nm, X=716 nm) forms.

Spectral changes in compound 1 were observed in the C2H5OH-H2SO4 system over the concentration range of H2SO4 equaled 0.35496-15.4098 molL-1. In the first stage of the acid-base interaction (CH2SO4=0.3596-2.8952 molL-1), the intensity of the absorption maximum decreases and its bathochromic shift is 72 nm. The intensity of the absorption maximum at X=478 nm gradually decreases, at the same time a new band appears at X=548 nm. This acidic form corresponds to a concentration of H2SO4 equal to 2.8952 molL-1.

An increase in the amount of H2SO4 to 15.4098 molL-1 leads to a decrease of intensity at X=548 nm, a further bathochromic shift of the absorption maximum on 166 nm, and the appearance of a broadened band at X=716 nm, indicating a stronger acid-base interaction 1 in the C2H5OH-H2SO4 medium as compared to CH2Cl2-CF3COOH.

We could not calculate the concentration and ther-modynamic stability constants for a given medium, since

already in the first stage of protonation at concentrations of sulfuric acid 0.3596-2.8952 molL-1, several processes occurred simultaneously, which can be related either with the phenomenon of homoconjugation, or with intermolecular and chemical interaction of solvents. This study allowed only to determine the intervals of acid concentrations at which acid forms appear.

It should be noted that compound 1 has unique optical properties that allow the position of the absorption maximum in the visible region of UV-Vis spectrum to be changed by adding an acid or base to the solution of the compound in an organic solvent, i.e. to convert a non-protonated form into a protonated form, and vice versa. It is important that destruction of 1 is not observed, which is not characteristic for compounds of this type.[12] Such acid-base interactions make it possible to classify this product as "molecular chameleon", i.e. a compound that has a unique potential for postsynthetic modification of the optical properties of the molecule (Figure 11).[13]

Theoretically, there are four intra-cyclic nitrogen atoms from the isoindole and thiadiazole fragments and four bridging meso-nitrogen atoms of the macrocyclic ring in compound 1 which can act as donor centers for proton addition. To determine of the most probable location of the proton addition, we performed a theoretical study of the model compound (4), the structural formula of which is shown in Figure 12, the numbers denote the places of probable addition

Figure 12. The structure of model compound 4.

Figure 11. Changes of the UV-Vis spectrum of compound 1 at adding of acid or base by solution: a) in CH2Cl2, b) in C2H5OH. Макрогетероцикnbl /Macroheterocycles 2018 11 (1) 59-66

0

of the proton. To simplify the calculations, methyl is chosen as the alkyl substituent.

As mentioned above, according to spectrophotometry titration, one molecule of acid participates in protonation in the first stage. In this regard, complete optimization of the geometric parameters of all possible monoproton-ated configurations by the semi-empirical AMI method with further refinement by the DFT method using the B3LYP hybrid functional and the 6-31G (d,p) basic set was carried out. According to the results of the calculations, the most energetically favorable configuration is the one in which the proton addition takes place at position 8, i.e. along the intra-cyclic nitrogen atom of the isoindole fragment located opposite the thiadiazole ring (Table 1).

Table 1. The calculated values of the total and relative energies of monoprotonated configurations.

ö

13 à 1) ■tí

•s

Ü " & Is

tí . 2 o

o ft ja

E—

Atom number E ,,, kcal-mol-1 total' AE, kcal-mol-1 4. 5.

1 2 -1209998.06 -1210023.62 59.51 33.96 6.

3 -1210033.06 24.51

4 -1210033.40 24.17 7.

5 -1210025.74 31.83 8.

6 -1210040.69 16.88

7 -1210055.04 2.54 9.

8 -1210057.57 0 10

9 -1210055.30 2.27

11.

Conclusions

Thus, we synthesized ABBB-type macroheterocyclic compound containing the 5-amino-2-dodecyl-3-imino-1,2,4-thiadiazoline fragment. This compound has unique acid-base properties and can be used as indicator of acid-base processes. It was shown by 'H NMR spectroscopy that

the target product did not form the expected tatraazachlorin similar structure.

Acknowledgments. The work was carried out by support of Russian Scientific Fund (agreement 14-23-00204P).

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Received 27.01.2018 Accepted 06.02.2018