Synthesis and selected immunological properties of 10-substituted 1,8-diazaphenothiazines

Abstract

A new type of tricyclic azaphenothiazines—1,8-diazaphenothiazines—was obtained in the reaction of 2,3- and 3,4-disubstituted pyridines. The reaction ran as the Smiles rearrangement. The 1,8-diazaphenothiazine system was determined using NOE experiment and 2D NMR spectra (COSY, HSQC, HMBC). 10H-1,8-diazaphenothiazine was transformed into 10-derivatives with alkyl, aminoalkyl, amidoalkyl, sulfonamidoalkyl, and nitrogen half-mustard groups. The compounds were tested for their effects on phytohemagglutinin A-induced proliferative response of human peripheral blood mononuclear cells (PBMC) and lipopolysaccharide-induced tumor necrosis factor alpha production by human whole blood cultures. The compounds exhibited differential, dose-dependent inhibitory activities in these tests. All the compounds were low toxic against PBMC. The compounds showing the highest antiproliferative activity strongly inhibited the growth of leukemia L-1210 and colon cancer SW-948 cell lines, similarly as cisplatin, a reference drug.

Introduction

Tricyclic phenothiazines attract considerable attention because of their significant biological activities and interesting chemical features. Classical phenothiazines with aminoalkyl substituents at the nitrogen atom are the source of valuable drugs exhibiting neuroleptic, antihistaminic, antitussive, and antiemetic activities (Gupta and Kumar, 1988). The structure modifications of these compounds were carried out by introduction of new substituents, mainly at the thiazine nitrogen atom, and substitution of one or two benzene rings with homoaromatic and heteroaromatic rings. The modifications with azine rings lead to formation of azaphenothiazines. New phenothiazines can contain not only the tricyclic ring system but also tetra and pentacyclic ones with up to four additional nitrogen atoms in the aromatic rings (Silberg et al., 2006; Pluta et al., 2009, 2011). Such modifications can change potency and type of activities of the basic structures. Recent reports describe very promising anticancer, antibacterial, and anti-inflammatory activities, reversal of multidrug resistance and a potential benefit in treatment of Alzheimer’s, Creutzfeldt-Jakob’s and AIDS-associated diseases for the modified phenothiazines (Motohashi et al., 2000, 2006; Dasgupta et al., 2008; Sadandam et al., 2009; Aaron et al., 2009; Tandon et al., 2009; Pluta et al., 2011).

Our strategy for modification of the phenothiazine structure is based on the introduction of two pyridine rings instead of the benzene ones to form dipyrido[1,4]thiazines. Among ten theoretically possible dipyridothiazines types only four have been known before introduction of our research strategy, i.e., 1,6- (Maki, 1957; Takahashi and Maki, 1958a, b; Rodig et al., 1966), 1,9- (Rath, 1957), 2,7- (Kopp et al., 1963; Kopp and Strell, 1962), and 3,6-diazaphenothiazines (Okafor, 1967). Three nomenclature systems of phenothiazines with different atom numbering, valid in the sixties and seventies, were confusing. 2,7-Diazaphenothiazines described by Kopp and co-workers were in fact 3,7-diazaphenothiazines (Pluta et al., 2009). Correct 2,7-diazaphenothiazines were obtained by us and their ring system was confirmed by X-ray analysis (Morak et al., 2002; Morak and Pluta, 2007). The parent compound, 10H-2,7-diazaphenothiazine, was found to be a universal, low-toxic immunosuppressant, inhibiting both humoral and cellular immune responses, and antioxidant property (Zimecki et al., 2009; Morak-Młodawska et al., 2010; Pluta et al., 2010).

In continuation of our studies, we have worked out an efficient synthesis of a new type of dipyridothiazines, 10H-1,8-diazaphenothiazine and its 10-substituted derivatives, possessing alkyl, arylalkyl, aryl, heteroaryl and aminoalkyl, amidoalkyl, sulfonamidoalkyl, and nitrogen half-mustard type substituents. In this work, we discuss their synthesis and structures and test their activities in selected biological assays.

Results and discussion

Chemistry

It is well known that the synthesis of phenothiazines and azaphenothiazines may proceed via cyclization of diphenyl sulfides, phenyl azinyl sulfides, or diazinyl sulfides directly as the Ullmann cyclization or with the Smiles rearrangement of the S → N type depending on the reaction conditions. In the last case, the phenyl or azinyl part migrates from the sulfur atom to the nitrogen atom forming amine and subsequently phenothiazine or azaphenothiazine. The rearrangement proceeds most often under basic but also under acidic and neutral conditions. Sometimes it is impossible to state if a reaction runs with or without the rearrangement because the Ullmann and Smiles products are the same or very similar (Pluta et al., 2009).

We started the synthesis with a reaction of sodium 3-aminopyridinothiolate (1) with 2-chloro-3-nitropyridine (2) in refluxing DMF. After isolation and purification of the products we found dipyridothiazine (2,6-diazaphenothiazine 3 or 1,8-diazaphenothiazine 4) as the major product in 88 % yield and 3′-amino-3-nitro-2,4′-dipyridyl sulfide (5) in 9 % yield as the minor product (Scheme 1). The mass spectrum confirmed the diazaphenothiazine structure (M = 201) but the ¹H NMR spectrum does not point at the structure 3 or 4 as both compounds are built of the 2,3- and 3,4-pyridinediyl units giving a singlet (7.90 ppm), two doublets (7.18, 8.07 ppm), and three doublets of doublet (6.90, 7.26, 8.09 ppm) of the proton signals. To unquestionably determine the diazaphenothiazine structure, we transformed the product into the N-methyl derivative (vide infra). The differentiation between 1,8- and 2,6-diazaphenothiazine system was based on the NOE experiment of this derivative. Irradiation of the methyl protons at 3.44 ppm (Scheme 2) gave an enhancement only of one proton, the singlet signal at 7.90 ppm by 7.06 % what pointed at the 1,8-diazaphenothiazine system and the derivative 7 (Scheme 3).

Scheme 1.

Synthesis if 10H-diazaphenothiazine 3 from disubstituted pyridines 2 and 3 and dipyridyl sulfide 5

Scheme 2.

The NMR experiments for compound 7: a NOE and COSY, b HSQC and HMBC

Scheme 3.

Synthesis of 10-dialkylaminoalkyl-1,8-diazaphenothiazines 7–19

The full ¹H NMR assignment of the proton signals came from the homonuclear ¹H–¹H correlation (COSY). Three most deshielded proton signals at 7.90, 8.07, and 8.09 ppm were considered as the α-pyridinyl proton signals. The doublet of doublet signal at 6.90 ppm, considered as the β-pyridinyl proton, was intercorrelated (ortho-coupling) with the signals at 8.09 ppm and at 7.26 ppm (γ-pyridinyl proton) with the coupling constants of 4.9 and 7.2 Hz, respectively. The signal at 7.26 ppm was weak intercorrelated (para-coupling) with the signal at 8.09 ppm with the coupling constant of 1.8 Hz. The protons were assigned as H₃, H₄, and H₂, respectively. The α-pyridinyl proton signal at 8.07 ppm was correlated with the signal at 7.18 ppm (β-pyridinyl proton) with the coupling constant of 5.4 Hz. These protons were assigned as H₇ and H₆. The proton signal assignment was presented in Scheme 2.

The new diazaphenothiazine system was also determined by the ¹³C NMR spectrum. The spectrum revealed eleven carbon signals: one primary, six tertiary, and four quaternary. The methyl group was observed at 32.8 ppm. The full assignment of carbon signals came from 2D NMR: HSQC (the tertiary carbon atoms connected with the hydrogen atoms) and HMBC (the tertiary and quaternary carbon atoms correlated with the hydrogen atoms via two and mainly three bonds). The proton-carbon correlation was presented in Scheme 2.

The product structure as 10H-1,8-diazaphenothiazine 4 is the evidence for the Smiles rearrangement of the S–N type of resulted dipyridinyl sulfide 5. Heating sulfide 5 in refluxing DMF gave 10H-1,8-diazaphenothiazine (4) in 88 % yield. The reaction run through the formation of dipyridinyl amine 6 which (not isolated) very easily cyclized to diazaphenothiazine 4 (Scheme 1). The 1,8-diazaphenothiazine ring system was confirmed by X-ray analysis of the nitropyridyl derivative 12 (obtained by independent way from appropriate sulfide containing three nitropyridyl moieties via the double Smiles rearrangement), published separately (Morak-Młodawska et al., 2012).

The parent 10H-1,8-diazaphenothiazine 4 was transformed into 10-derivative in one or three steps. The alkylation with alkyl (methyl, allyl, propargyl, benzyl), aryl (p-nitrophenyl) and heteroaryl (3-nitro-4-pyridinyl) halides and aminoalkyl (3-dimethylaminopropyl, 3-dimethylamino-2-methylpropyl, 2-diethylaminoethyl, 1-pyrrolidinoethyl, 1-piperidinoethyl, 1-methyl-2-piperidinoethyl, 1-morpholinoethyl) in DMF in the presence of sodium hydride or potassium tert-butoxide and in dioxane in the presence of sodium hydroxide gave derivatives 7–19 in good yields Scheme 3).

The substrate 4 was also transformed into compounds possessing aminopropyl derivative substituents. Reaction of compound 4 with the phthalimidopropyl bromide in toluene in the presence of sodium hydride gave the phthalimidopropyl derivative 20. The hydrolysis of this compound with hydrazine in ethanol led to aminopropyl derivative 21 which quickly (because of their instability) underwent reactions with acetic anhydride, methanesulfonyl chloride, and 2-chloroethyl isocyanate to give acetamidopropyl, methanesulfonamidopropyl, and chloroethylureidopropyl derivatives 22–24 in 63–80 % yield (Scheme 4).

Scheme 4.

Synthesis of 10-phthalimidopropyl-1,8-diazaphenothiazine 20 and transformations to the acetamidopropyl, methanesulfonamidopropyl, and chloroethylureidopropyl derivatives 22–24

Biological activities

10-substituted 1,8-diazaphenothiazines 4, 7–10, 12–20, and 22–24, possessing various substituents (hydrogen atom, alkyl groups with single, double, and triple bonds, arylalkyl, heteroaryl, alkylaminoalkyl, amidoalkyl, sulfonamidoalkyl and alkyl with a half-mustard-type group) were tested for their biological activities. The tests included the proliferative response of human peripheral blood mononuclear cells (PBMC) induced by phytohemagglutinin A (PHA), the cytotoxic effect on human PBMC and lipopolysaccharide (LPS)-induced production of tumor necrosis factor alpha (TNF-α). The combined results of the tests are presented in Table 1. The most promising compounds, selected on the basis of their strong antiproliferative effects, were tested for growth inhibition of leukemia L-1210 cells and colon carcinoma SW-948 cells in vitro.

Table 1.

Activities of 10-substituted 1,8-diazaphenothiazines in selected immunological assays

No.	Cytotoxicity against PBMC		Inhibition of PHA-induced PBMC proliferation			TNF-α inhibition
	10 µg/ml	50 µg/ml	1 µg/ml	10 µg/ml	50 µg/ml	5 µg/ml
4	6.7	21.4	5.0	74.4	78.6	50.4
7	0.8	1.7	9.6	22.9	45.6	76.4
8	−0.3	−6.0	19.0	26.0	55.6	89.3
9	−1.1	8.8	9.3	24.4	41.2	87.4
10	2.0	2.6	13.6	26.8	45.5	85.9
12	6.6	8.1	4.1	5.2	26.2	54.8
13	−3.6	15.0	5.7	20.9	81.1	86.7
14	−0.7	11.9	1.4	19.2	59.4	89.1
15	1.3	12.1	−6.8	−5.4	59.6	75.0
16	0.9	10.0	−0.9	−2.9	47.0	85.6
17	1.5	7.3	−0.9	−0.5	18.0	47.6
18	−1.4	18.7	−3.4	5.1	67.4	73.1
19	−4.5	4.8	−0.9	7.0	18.2	46.1
20	−2.0	−0.1	3.6	12.5	42.2	76.0
22	−5.0	6.7	8.9	16.2	62.5	5.8
23	−0.9	12.5	9.4	19.3	50.2	48.6
24	−1.6	4.5	8.4	12.4	46.8	7.3

The table shows the degree of cytotoxicity against PBMC, effects on PHA-induced proliferative response of human PBMC and LPS-induced TNF-α production by these cells. The results are given in percentage inhibition as compared with appropriate DMSO controls. Positive values denote inhibition, negative stimulation

The proliferation test was performed at the concentrations of 1, 10, and 50 µg/ml. A strong activity (inhibition over 70 %) was exhibited by compound: 4 at 10 µg/ml and compound 13 at 50 µg/ml in comparison with the control cultures (culture medium containing appropriate dilution of DMSO). These compounds possess the hydrogen atom and dimethylaminopropyl groups at position 10. A moderate activity (inhibition about 60 % at 50 µg/ml) was exhibited by compounds: 14, 15, 18, and 22 (the dimethylamino-2-methylpropyl, diethylaminoethyl, 1-methyl-2-piperidinoethyl, and acetamidopropyl groups). Other compounds were weakly active or inactive.

In order to check whether the inhibitory effects of the compounds were not caused by cytotoxicity, the compounds were tested for their effects on viability of PBMC. All the compounds exhibited very weak cytotoxic properties with the inhibition of cell viability not exceeding 22 % even at 50 μg/ml. Because lack of toxicity at 1 μg/ml that concentration of the compounds was deleted in Table 1.

The compounds were also tested for their inhibitory effects on LPS-induced TNF-α production at the concentrations of 5 and 25 μg/ml. No further inhibition of TNF-α production was registered for 25 μg/ml and, therefore, not shown in Table 1. Compounds 8–10, 13, 14, and 16 showed inhibitions of over 85 % at 5 μg/ml.

The most promising compounds 4, 8, 13, and 22 (being strongly antiproliferative and low cytotoxic) were selected for evaluation of anticancer activities against the cancer cell lines at the concentrations of 0.1–50 µg/ml using cisplatin as the reference drug (Fig. 1). The most active was compound 4, exhibiting similar anticancer activity to cisplatin against colon carcinoma SV-948 cells at the concentration of 5 µg/ml and against leukemia L-1210 cells at 10 µg/ml (Table 2). Compounds 13 and 22 showed strong inhibition at 10 µg/ml. It is worth noting that cisplatin showed high toxicity killing of 50 % of granulocyte/macrophage progenitor cells already at 0.9 μg/ml after 1 h of culture (Umbach et al., 1984). The drug is also nephrotoxic (Yao et al., 2007). The ability of the compounds (in particular 4 and 13) to strongly inhibit TNF-α may be of additional advantage in anti-tumor therapy. Although TNF-α may have a dual role in tumor progression (Wajant, 2009) some anti-tumor strategies aim at inhibition of its activity (Guadagni et al., 2007).

Fig. 1.

The anticancer activities of selected compounds at concentrations of 0.1–50 µg/ml. L-1210 and SW-948 cell lines were used in the study. The results are presented as the mean optical density ± SE (*versus DMSO; ^#versus Control, p < 0.001)

Table 2.

Anticancer activity (IC₅₀) of selected compounds 4 and 13 and cisplatin as a reference drug against cancer lines SW-948 and L-1210

Compound	IC50 (μg/ml)
	SW-948	L-1210
4	5.47	7.41
13	14.95	6.03
Cisplatin	5.52	2.13

It is interesting that the most active was compound 4, possessing the hydrogen atom instead of the pharmacophoric aminoalkyl substituents at the thiazine nitrogen atom. It seems that compound 4 displays a different mechanism of action than that found for substituted phenothiazines and azaphenothiazines with the acylaminoalkyl and chloroethylureidoalkyl groups (Motohashi et al., 2000, 2006; Pluta et al., 2011).

Conclusion

We report here a few step synthesis and biological activity of novel tricyclic 10H- and 10-substituted 1,8-diazaphenothiazines. The synthesis was run through the Smiles rearrangement of S–N type. The structure diazaphenothiazine system was elucidated using the NOE experiment and 2D (¹H–¹H and ¹H–¹³C) spectra. Some 1,8-diazaphenothiazines exhibited antiproliferative, anticancer, TNF-α inhibitory activities with low cytotoxicity. The new diazaphenothiazine system was found to be pharmacophoric as 10H-1,8-diazaphenothiazine was the most active, with anticancer activities comparable to that of cisplatin. This compound seems to be a useful starting point for further study to found more potent anticancer agents by introduction of new substituents at the thiazine nitrogen atom.

Experimental

Chemistry

Melting points were determined in open capillary tubes on a Boetius melting point apparatus and are uncorrected. The ¹H NMR, COSY, NOE HSQC, HMBC spectra were recorded on a Bruker Fourier 300 and Bruker DRX spectrometers at 300 and 600 MHz in deuteriochloroform with tetramethylsilane as the internal standard. The ¹³C NMR spectrum was recorded at 75 MHz. Electron Impact mass spectra (EI MS) and Fast Atom Bombardment mass spectra (FAB MS, in glycerol) were run on a Finnigan MAT 95 spectrometer at 70 eV. The thin layer chromatography were performed on silica gel 60 F₂₅₄ (Merck 1.05735) with CHCl₃-EtOH (5:1 and 10:1 v/v) and on aluminum oxide 60 F₂₅₄ neutral (type E) (Merck 1.05581) with CHCl₃-EtOH (10:1 v/v) as eluents.

Synthesis of 10H-1,8-diazaphenothiazine (4)

From sodium 3-amino-4-pyridinethiolate (1) and 2-chloro-3-nitropyridine (2)

To a solution of 148 mg (1 mmol) sodium 3-amino-4-pyridinethiolate (1) in 10 ml dry DMF was added 158 mg (1 mmol) 2-chloro-3-nitropyridine (2). The mixture was stirred at rt 3 h and next was refluxed 3 h. After cooling, the reaction mixture was evaporated in vacuo. The dry residue was dissolved in CHCl₃ and purified by column chromatography (aluminum oxide, CHCl₃) to give

1. 10H-1,8-diazaphenothiazine (4) (0.125 g, 62 %) mp 135–136 °C.

¹H NMR (CDCl₃) δ 6.73 (dd, J = 7.5 Hz, J = 5.1 Hz, 1H, H₃), 6.84 (d, J = 5.0 Hz, 1H, H₆), 7.11 (dd, J = 7.5 Hz, J = 1.5 Hz, 1H, H₄), 7.69 (board s, 1H, N–H), 7.84 (dd, J = 5.1 Hz, J = 1.5, 1H, H₂), 7.89 (s, 1H, H₉), 7.95 (d, J = 5,0 Hz, 1H, H₇). ¹³C NMR (CDCl₃) δ 112.2 (C_4a), 118.9 (C₃), 120.5 (C₆), 128.9 (C_5a), 134.3 (C₄), 134.4 (C₉), 136.9 (C_9a), 143.1 (C₇), 145.9 (C₂), 152.1 (C_10a). EI MS m/z: 201 (M, 100), 174 (M-HCN, 30). Anal. Calcd for: C₁₀H₇N₃S, C 59.68, H 3.51, N 20.88; S 15.93. Found: C 59.49, H 3.53, N 20.80; S 15.79.

• (b)3-amino-3′-nitro-2,4′-dipyridinyl sulfide (5) (0.025 g, 9 %) mp 147–148 °C.

In cyclization of 3-amino-3′-nitro-2,4′-dipyridinyl sulfide (5)

The brown solution of 124 mg (0.5 mmol) 3-amino-3′-nitro-2,4′-dipyridinyl sulfide 5 in 5 ml dry DMF was refluxed for 4 h. After cooling, the reaction mixture was evaporated in vacuo. The dry residue was dissolved in CHCl₃ and purified by column chromatography (aluminum oxide, CHCl₃) to give 10H-1,8-diazaphenothiazine (4) (0.088 g, 88 %)

Synthesis of 10-substituted 1,8-diazaphenothiazines 7, 8, and 10–12

To a solution of 10H-1,8-diazaphenothiazine (4) (0.100 g, 0.5 mmol) in dry DMF (5 ml) NaH (0.024 g, 1 mmol, 60 % NaH in mineral oil was washed out with hexane) was added. The reaction mixture was stirred at room temperature for 1 h and then alkyl, aryl, and heteroaryl halides (methyl iodide, allyl bromide, benzyl chloride, 1-fluoro-4-nitrobenzene, 4-chloro-3-pyridine, 1.5 mmol) were added and the stirring was continued for 24 h. The mixture was poured into water (15 ml), extracted with CHCl₃ (3 × 10 ml), and dried using Na₂SO₄. The obtained product was purified by column chromatography (aluminum oxide, CHCl₃) to give

10-Methyl-1,8-diazaphenothiazine (7) (0.085 g, 79 %); mp 82–83 °C

¹H NMR (CDCl₃) δ 3.44 (s, 3H, CH₃), 6.90 (dd, J = 7.2 Hz, J = 4.9 Hz, 1H, H₃), 7.18 (d, J = 5.4 Hz, 1H, H₆), 7.26 (dd, J = 7.8 Hz, J = 1.8 Hz, 1H, H₄), 7.90 (s, 1H, H₉), 8.07 (d, J = 5.4 Hz, 1H, H₇), 8.09 (dd, J = 4.9 Hz, J = 1.8 Hz, 1H, H₂). ¹³C NMR (CDCl₃) δ 32.8 (NCH₃), 115.0 (C_4a), 118.2 (C₃), 120.8 (C₆), 131.9 (C_5a), 134.4 (C₄), 135.2 (C₉), 139.9 (C_9a), 143.9 (C₇), 145.8 (C₂), 154.3 (C_10a). EI MS m/z: 215 (M, 100), 200 (M-CH₃, 80). Anal. Calcd for: C₁₁H₉N₃S C 61.37, H 4.21, N 19.52. Found: C 61.22; H 4.23; N 19.41.

10-Allyl-1,8-diazaphenothiazine (8) (0.085 g, 70 %); an oil

¹H NMR (CDCl₃) δ 4.66 (m, 2H, N-CH₂), 5.32 (m, 2H, =CH₂), 5.96 (m, 1H, CH), 6.82 (dd, J = 7.5 Hz, J = 5.1 Hz, 1H, H₃), 7.04 (d, J = 5.0 Hz, 1H, H₆), 7.18 (dd, J = 7.5 Hz, J = 1.5 Hz, 1H, H₄), 7.89 (s, 1H, H₉), 8.02 (m, 2H, H_2, H₇₎. ¹³C NMR (CDCl₃) δ 47.6 (NCH₂), 113.0 (C_4a), 118.1 (C₃), 119.2 (C₆), 121.1 (CH₂=), 130.2 (C_5a), 131.2 (C₄), 134.5 (C₉), 137.9(–CH=), 138.8 (C_9a), 140.2 (C₇), 146.4 (C₂), 151.9 (C_10a). EI MS m/z: 241 (M, 50), 200 (M-CH₂CHCH₂, 100). Anal. Calcd for: C₁₃H₁₁N₃S C 64.70, H 4.59, N 17.41. Found: 64.58; H 4.58; N 17.31.

10-Benzyl-1,8-diazaphenothiazine (10) (0.095 g, 65 %); an oil

¹H NMR (CDCl₃) δ 5.34 (s, 2H, CH₂), 6.76 (dd, J = 7.2 Hz, J = 4.8 Hz, 1H, H₃), 6.87 (d, J = 5.0 Hz, 1H, H₆), 7.22 (dd, J = 7.2 Hz, J = 1.4 Hz, 1H, H₄), 7.29 (m, 5H, C₆H₅), 7.81 (s, 1H, H₉), 7.96 (m, 2H, H₂, H₇). EI MS m/z: 291 (M, 80), 200 (M-CH₂C₆H₅, 100). Anal. Calcd for: C₁₇H₁₃N₃S C 70.08, H 4.50, N 14.42. Found: C 70.00; H 4.52; N 14.29.

10-(4′-Nitrophenyl)-1,8-diazaphenothiazine (11) (0.120 g, 74 %); mp 171–172 °C

¹H NMR (CDCl₃) δ 6.88 (dd, J = 7.2 Hz, J = 5.0 Hz, 1H, H₃), 6.95 (d, J = 5.0 Hz, 1H, H₆), 7.21 (dd, J = 7.2 Hz, J = 1.6 Hz, 1H, H₄), 7.55 (m, 2H, 2H C₆H₄), 7.81 (dd, J = 5.0 Hz, J = 1.6 Hz, 1H, H₂), 7.96 (d, J = 5.0 Hz, 1H, H₇), 8.15 (s, 1H, H₉), 8.50 (m, 2H, 2H C₆H₄). EI MS m/z: 322 (M, 100), 276 (M-NO₂, 30), 200 (M-NO₂C₆H₄, 18). Anal. Calcd for: C₁₆H₁₀N₄O₂S C 59.62, H 3.13, N 17.38. Found: C 59.44; H 3.12; N 17.29.

10-(3′-Nitro-4′-pyridinyl)-1,8-diazaphenothiazine (12) (0.130 g, 80 %); mp 189–190 °C

lit. (Morak-Młodawska et al., 2012) mp 189–190 °C.

Synthesis of 10-propargyl-1,8-diazaphenothiazines (9)

To a suspension of 100 mg (0.5 mmol) 10H-1,8-diazaphenothiazine (4) in 10 ml DMF was added 80 mg (0.72 mmol) potassium tert-butoxide. The mixture was stirred at room temperature for 1 h. Then to the solution was added dropwise a solution of propargyl bromide 80 mg (0.64 mmol) in toluene. The solution stirred at room temperature for 24 h and poured onto water (20 ml), extracted with methylene chloride (20 ml), dried with Na₂SO₄, and evaporated to the brown oil. The residue was purified by column chromatography (silica gel, CHCl₃) to yield 85 mg (71 %) of 10-propargyl-1,8-diazaphenothiazine (9), mp 96–97 °C.

¹H NMR: δ 2.39 (t, J = 2.5 Hz, 1H), 4.61 (t, J = 2.5 Hz, 2H), 6.92 (dd, J = 7.5 Hz, J = 5.1 Hz 1H, H₃), 7.23 (m, 2H, H₄, H₆), 8.10 (d, J = 5.5 Hz, 1H, H₇), 8.13 (s,1H, H₉), 8.15 (dd, J = 5.1 Hz, J = 1.3 Hz, 1H, H₂). EI MS: 239 (M, 100), 200 (M-CH₂CCH, 85). Anal. Calcd for: C₁₃H₉N₃S C 65.25, H 3.79, N 17.56. Found: C 65.20; H 3.77; N 17.39.

Synthesis of 10-substituted 1,8-diazaphenothiazines 13–19

To a solution of 10H-1,8-diazaphenothiazine (4) (0.100 g, 0.5 mmol) in dry dioxane (10 ml) NaOH (0.20 g, 5 mmol) was added. The mixture was refluxed 1 and 5 h then the hydrochlorides of dialkylaminoalkyl chloride (3-dimethylaminopropyl, 2-diethylaminoethyl, 3-dimethylamino-2-methylpropyl) and hydrochlorides of cycloaminoethyl chloride (N-(2-chloroethyl)-pyrrolidine, 2-(1-methyl-2′-piperydinyl)ethylchloride, N-(2-chloroethyl)piperidine, N-(2-chloroethyl)morpholine, 1.5 mmol) were added. The reaction mixture was refluxed for 24 h. After cooling, dioxane was evaporated in vacuo and residue was dissolved in CHCl₃ (10 ml). The extracts were washed with water, dried with anhydrous sodium sulfate, and evaporated in vacuo. The obtained product was purified by column chromatography (aluminum oxide, CHCl₃-EtOH 10:1) to give

10-(3′-Dimethylaminopropyl)-1,8-diazaphenothiazine (13) (0.100 g, 70 %); an oil

¹H NMR: δ 2.00 (m, 2H, CH₂), 2.26 (s, 6H, 2CH₃), 2.44 (t, J = 7.5 Hz, 2H, NCH₂), 4.10 (t, J = 7.5 Hz, 2H, NCH₂), 6.73 (m, 1H, H₃), 6.89 (d, J = 4.8 Hz, 1H, H₆), 7.16 (d, J = 7.2 Hz, 1H, H₄), 7.99 (m, 2H, H₂, H₇), 8.08 (s, 1H, H₉). ¹³C NMR (CDCl₃) δ 24.2 (CH₂), 42.9 (CH₂), 45.5 (N(CH₃)₂), 57.13 (CH₂), 114.6 (C_4a), 118.1 (C₃), 120.8 (C₆), 131.8 (C_5a), 134.7 (C₄), 135.5 (C₉), 138.7 (C_9a), 143.6 (C₇), 145.6 (C₂), 153.6 (C_10a). FAB MS m/z: 287 (M+1, 100), 202 (M+1-C₃H₆NC₂H₆, 19). Anal. Calcd for C₁₅H₁₈N₄S C 62.91; H 6.33; N 19.56. Found: C 62.78; H 6.30; N 19.39.

10-(3′-Dimethylamino-2′-methylpropyl)-1,8-diazaphenothiazine (14) (0.125 g, 83 %); an oil

¹H NMR: δ 1.02 (d, J = 6.5 Hz, 3H, CH₃), 2.39 (m, 9H, 2CH_3, CH₂, CH), 4.15 (m, 2H, CH₂), 6.80 (dd, J = 7.4 Hz, J = 5.2 Hz, 1H, H₃), 6.85 (d, J = 5.0 Hz, 1H, H₆), 7.20 (dd, J = 7.4 Hz, J = 1.4 Hz, 1H, H₄), 8.02 (dd, J = 5.2 Hz, J = 1.4 Hz, 1H, H₂), 8.09 (d, J = 5.0 Hz, 1H, H₇), 8.15 (s, 1H, H₉). FAB MS m/z: 301 (M+1, 100), 202 (M+1-C₂H₄NC₄H₁₀, 18). Anal. Calcd for: C₁₆H₂₀N₄S C 63.97; H 6.71; N 18.65. Found: C 63.80; H 6.73; N 18.42.

10-(2′-Diethylaminoethyl)-1,8-diazaphenothiazine (15) (0.113 g, 75 %); an oil

¹H NMR: δ 1.04 (t, J = 7.3 Hz, 6H, 2CH₃), 2.62 (q, J = 7.3 Hz, 4H, 2CH₂), 3.62 (t, J = 7.4 Hz, 2H, CH₂), 4.15 (t, J = 7.4 Hz, 2H, CH₂), 6.76 (dd, J = 7.2 Hz, J = 5.1 Hz, 1H, H₃), 6.83 (d, J = 5.0 Hz, 1H, H₆), 7.16 (dd, J = 7.2 Hz, J = 1.2 Hz, 1H, H₄), 7.96 (dd, J = 5.1 Hz, J = 1.6 Hz, 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.09 (s, 1H, H₉). FAB MS m/z: 301 (M+1, 100), 202 (M+1-C₂H₄NC₄H₁₀, 25). Anal. Calcd for: C₁₆H₂₀N₄S C 63.97; H 6.71; N 18.65. Found: C 63.81; H 6.73; N 18.41.

10-(2′-Pyrrolidinylethyl)-1,8-diazaphenothiazine (16) (0.110 g, 75 %); an oil

¹H NMR (CDCl₃) δ 1.90 (m, 4H, 2CH₂), 2.72 (m, 4H, 2CH₂), 3.09 (t, J = 7.2 Hz, 2H, CH₂), 4.35 (t, J = 7.2 Hz, 2H, NCH₂), 6.70 (dd, J = 7.6 Hz, J = 5.0 Hz, 1H, H₃), 6.83 (d, J = 5.0 Hz, 1H, H₆), 7.17 (dd, J = 7.2 Hz, J = 1.5 Hz 1H, H₄), 7.97 (dd, J = 5.0 Hz, J = 1.5 Hz, 1H, H₂), 8.04 (d, J = 5.0 Hz, 1H, H₇), 8.19 (s, 1H, H₉). FAB MS m/z: 299 (M+1, 100), 202 (M+1-C₂H₄NC₄H₈, 29). Anal. Calcd for: C₁₆H₁₈N₄S C 64.40; H 6.08; N 18.78. Found: C 64.25; H 6.05; N 18.55.

10-(2′-Piperydinylethyl)-1,8-diazaphenothiazine (17) (0.110 g, 70 %); an oil

¹H NMR (CDCl₃) δ 1.47 (m, 2H, CH₂),1.63 (m, 4H, 2CH₂) 2.54 (m, 4H, 2CH₂), 2.75 (t, J = 6.8 Hz, 2H, CH₂), 4.22 (t, J = 6.8 Hz, 2H, NCH₂), 6.73 (dd, J = 7.6 Hz, J = 5.0 Hz, 1H, H₃), 6.85 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.6 Hz, J = 1.6 Hz 1H, H₄), 7.97 (dd, J = 5.0 Hz, J = 1.6 Hz, 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.18 (s, 1H, H₉). FAB MS m/z: 313 (M+1, 100), 202 (M+1-C₂H₄NC₅H₁₀, 20). Anal. Calcd for: C₁₇H₂₀N₄S: C 65.35; H 6.45; N 17.93. Found: C 65.22; H 6.47; N 17.80.

10-(1′-Methyl-2′-piperydinylethyl)-1,8-diazaphenothiazine (18) (0.116 g, 72 %); an oil

¹H NMR (CDCl₃) δ 1.30–2.15 (m, 7H₎, 2.36 (s, 3H, NCH₃), 2.85 (m, 1H, CH), 4.0 (m, 2H, NCH₂), 6.73 (dd, J = 7.6 Hz, J = 5.1 Hz, 1H, H₃), 6.87 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.6 Hz, J = 1.6 Hz, 1H, H₄), 7.97 (dd, J = 5.1 Hz, J = 1.6 Hz, 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.06 (s, 1H, H₉). FAB MS. 327 (M+H, 80), 313 (M+1-CH₃ 100). Anal. Calcd for: C₁₈H₂₂N₄S C 66.22; H 6.79; N 17.16. Found: C 66.17; H 6.75; N 17.03.

10-(2′-Morpholinylethyl)-1,8-diazaphenothiazine (19) (0.106 g, 68 %); an oil

¹H NMR (CDCl₃) δ 1.67 (m, 4H, 2CH₂), 2.59 (m, 4H, 2CH₂), 2.82 (t, J = 6.6 Hz, 2H, CH₂), 4.22 (t, J = 6.6 Hz, 2H, NCH₂) 6.75 (dd, J = 7.2 Hz, J = 5.1 Hz, 1H, H₃), 6.88 (d, J = 5.0 Hz, 1H, H₆), 7.15 (dd, J = 7.6 Hz, J = 1.6 Hz 1H, H₄), 7.97 (dd, J = 5.1 Hz, J = 1.6 Hz, 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.16 (s, 1H, H₉). FAB MS m/z: 315 (M+1, 40), 202 (M+1-C₂H₄NOC₄H₈, 15), 114 (C₂H₄NC₅H₁₀, 100). Anal. Calcd for: C₁₆H₁₈N₄OS: C 61.12; H 5.77; N 17.82. Found: C 61.03; H 5.73; N 17.68.

Synthesis of 10-phthalimidopropyl-1,8-diazaphenothiazines (20)

To a stirred solution of 10H-1,8-diazaphenothiazine (4) (0.100 g, 0.5 mmol) in dry toluene (20 ml) NaH (0.12 g, 5 mmol, washed out with hexane) was added. The mixture was stirred for 20 min at rt, then refluxed for 1 h and a solution of 1.5 mmol, N-(3-bromopropyl) phthalimide 0.405 g, in toluene (10 ml) was added. The mixture was refluxed for 24 h. After cooling, the resulted solid was filtered off, toluene was evaporated in vacuo and the residue was purified by column chromatography (aluminum oxide, CHCl₃) to give 10-(3′-phthalimidopropyl)-1,8-diazaphenothiazine (20) (0.110 g, 70 %), mp 40–41 °C.

¹H NMR (CDCl₃) δ 2.39 (m, 2H, CH₂), 3.86 (t, J = 6.1 Hz, 2H, NCH₂), 4.13 (t, J = 6.0 Hz, 2H, NCH₂), 6.77 (dd, J = 7.1 Hz, J = 4.9 Hz Hz, 1H, H₃), 6.88 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.1 Hz, J = 1.4 Hz, 1H, H₄), 7.71 (m, 2H_phthalimide), 7.79 (dd, dd, J = 4.9 Hz, J = 1.4 Hz, 1H, H₂), 7.82 (m, 2H_phthalimide), 7.98 (s, 1H, H₉), 8.07 (d, J = 5.0 Hz, 1H, H₇). FAB MS m/z: 389 (M+H, 100), 201 (M+1-(CH₂)₃N(CO)₂C₆H₄, 30). Anal. calcd. For C₂₁H₁₆N₄O₂S: C 64.93, H 4.15, N 14.42. Found: C 64.82; H 4.14; N 14.29.

Hydrolysis of 10-phthalimidopropyl-1,8-diazaphenothiazine (20)

To a solution of 10-phthalimidopropyl-1,8-diazaphenothiazine (20) (0.388 g, 1 mmol) in EtOH (20 ml) 80 % aqueous solution of hydrazine (0.2 ml, 5 mmol) was added. The mixture was refluxed for 2 h. After cooling, the reaction mixture was acidified with conc. hydrochloric acid to pH 2. The solution was concentrated and the resulted solid was filtered off. The filtrate was alkalized with 10 % aqueous solution of sodium hydroxide and extracted with CHCl₃ (3 × 10 ml). The extracts were washed with water, dried with anhydrous sodium sulfate, and evaporated in vacuo. The obtained residue with 10-aminopropyl-1,8-diazaphenothiazine (21) was fast used in the synthesis of the amide derivatives of 1,8-diazaphenothiazines (22–24).

Synthesis of 10-(3′-acetamidopropyl)-1,8-diazaphenothiazine (22)

To a suspension with the oil of 10-aminopropyl-1,8-diazaphenothiazine (21)(0.129 g, 0.5 mmol) in pyridine (5 ml) acetic anhydride (1.48 ml, 1.5 mmol) was added and the mixture was stirred at rt for 2 h. After evaporation of pyridine in vacuo the residue was dissolved in CHCl₃ (10 ml). The solution was washed with water, dried with anhydrous sodium sulfate, and evaporated in vacuo. The residue was purified by column chromatography (aluminum oxide, CHCl₃) to give 0.120 g (80 %) 10-(3′-acetamidopropyl)-2,7-diazaphenothiazine (22), mp 120 °C.

¹H NMR (CDCl₃) δ 2.05 (s, 3H, CH₃), 2.07 (m, 2H, CH₂), 3.44 (m, 2H, NCH₂), 3.96 (t, J = 6.6 Hz, 2H, NCH₂), 5.99 (broad s, 1H, NH), 6.73 (dd, J = 7.2 Hz, J = 5.0 Hz, 1H, H₃), 6.85 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.2 Hz, J = 1.4 Hz, 1H, H₄), 7.97 (dd, J = 5.0 Hz, J = 1.4 Hz 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.18 (s, 1H, H₉). FAB MS m/z: 301 (M+H, 100), 202 (M+1–C₃H₅NHCOCH₃, 30). Anal. calcd. For C₁₅H₁₆N₄OS: C 59.98; H 5.37; N 18.65. Found: C 59.83; H 5.35; N 18.55.

Synthesis of 10-(3′-methanesulfonamidopropyl)-1,8-diazaphenothiazine (23)

To a stirred solution of oil with 10-aminopropyl-1,8-diazaphenothiazine (21) (0.129 g, 0.5 mmol) in a mixture of CH₂Cl₂ (5 ml) and 10 % aqueous Na₂CO₃ solution (5 ml) a solution of methanesulfonyl chloride (0.12 ml, 1.5 mmol) in CH₂Cl₂ (3 ml) was added. The solutions were stirred at rt for 24 h. The organic phase was separated and aqueous phase was extracted with CH₂Cl₂ (2 × 5 ml). The combined extracts were washed with water (10 ml) and dried with anhydrous sodium sulfate and evaporated in vacuo. The residue was purified by column chromatography (aluminum oxide, CH₂Cl₂) to give 0.125 g (74 %) 10-(3′-methanesulfonamidopropyl-1,8-diazaphenothiazine (23) as an oil.

¹H NMR (CDCl₃) δ 2.08 (m, 2H, CH₂), 2.94 (s, 3H, CH₃), 3.42 (m, 2H, NCH₂), 4.02 (t, J = 6.9 Hz, 2H, NCH₂), 5.57 (broad s, 1H, NH), 6.74 (dd, J = 7.2 Hz, J = 5.0 Hz, 1H, H₃), 6.84 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.2 Hz, J = 1.4 Hz 1H, H₄), 7.97 (dd, J = 5.0 Hz, J = 1.4 Hz 1H, H₂), 8.03 (d, J = 5.0 Hz, 1H, H₇), 8.18 (s, 1H, H₉). FAB MS m/z: 337 (M+1, 100), 202 (M+1-C₃H₅NHSO₂CH₃,30). Anal. calcd. For C₁₄H₁₆N₄O₂S₂: C 49.98; H 4.79; N 16.65. Found: C 49.88; H 4.74; N 16.39.

Synthesis of 10-(3′-chloroethylureidopropyl)-1,8-diazaphenothiazine (24)

To a stirred solution of 10-aminopropyl-1,8-diazaphenothiazine (21) (0.129 g, 0.5 mmol) in dry EtOH (10 ml) at 0 °C 2-chloroethyl isocyanate (0.87 ml, 1 mmol) was added. The mixture was stirred at 0 °C for 0.5 h and at rt for 24 h. After evaporation of EtOH in vacuo the residue was purified by column chromatography (aluminum oxide, CH₂Cl₂) to give 0.120 g (63 %) 10-chloroethylureidopropyl-1,8-diazaphenothiazine (24), mp 103 °C.

¹H NMR (CDCl₃) δ 1.75 (m, 2H, CH₂), 2.10 (m, 2H, CH₂), 3.49 (m, 4H, 2CH₂), 4.46 (m, 2H, CH₂), 6.76 (dd, J = 7.2 Hz, J = 5.1 Hz, 1H, H₃), 6.84 (d, J = 5.0 Hz, 1H, H₆), 7.14 (dd, J = 7.2 Hz, J = 1.4 Hz 1H, H₄), 7.96 (dd, J = 5.1 Hz, J = 1.4 Hz 1H, H₂), 8.01 (d, J = 5.0 Hz, 1H, H₇), 8.17 (s, 1H, H₉). FAB MS m/z: 364 (M+1, 30), 202 (M+H-C₃H₆NHCONHCH₂CH₂Cl, 10), 185 (2gly + H, 100). Anal. calcd. for C₁₆H₁₈ClN₅OS: C 52.82, H 4.99, N 19.25. Found: C 52.77; H 4.97; N 19.11.

Biological assays

Preparation of the compounds for biological assays

The compounds were dissolved in DMSO (10 mg/ml) and subsequently diluted in RPMI-1640 cell culture medium (see below).

Isolation of the peripheral blood mononuclear cells

Venous blood from a single donor was withdrawn into heparinized syringes and diluted twice with phosphate-buffered saline. PBMC were isolated by centrifugation on Ficoll-uropoline gradient (density 1.077 g/ml) and centrifuged at 800×g for 20 min at 4 °C. The interphase cells, consisting of lymphocytes (20 %) and monocytes (80 %) were then washed three times with Hanks’ medium and re-suspended in a culture medium, referred to below as the culture medium, consisting of RPMI-1640, supplemented with 10 % fetal calf serum, l-glutamine, sodium pyruvate, 2-mercaptoethanol, and antibiotics, at density of 2 × 10⁶ cells/ml.

PHA-induced proliferation of human blood mononuclear cells

The isolated PBMC were distributed into 96-well flat-bottom plates in 100 µL aliquots (2 × 10⁵ cells/well). PHA was added at a concentration of 5 µg/ml. The compounds were tested at doses of 1, 10, and 50 µg/ml. DMSO at appropriate dilutions served as control. After a four-day incubation in a cell culture incubator, the proliferative response of the cells was determined by the colorimetric MTT method (Hansen et al., 1989). The results are given in percentage inhibition as compared with appropriate DMSO controls.

Cytotoxicity of the compounds against human blood mononuclear cells

PBMC at density of 2 × 10⁵/well, re-suspended in the culture medium, were cultured for 24 h in a cell culture incubator with the preparations at indicated concentrations. Cell survival was determined by MTT colorimetric method (Hansen et al., 1989). The results are given in percentage inhibition as compared with appropriate DMSO controls.

Lipopolysaccharide-induced TNF-a production in whole blood cell culture

Venous blood from a single donor was diluted 10× with RPMI-1640 medium and distributed in 1 ml aliquots in 24-well culture plates. The cultures were stimulated by addition of 1 µg/ml of LPS from E. coli, O111:B4. The compounds were added to the cultures at concentrations of 5 and 25 µg/ml. Higher concentrations of the compounds could not be used because of inhibitory effects on TNF-α production by corresponding DMSO (the solvent) dilutions. Appropriate dilutions of DMSO served as controls. After overnight incubation in a cell culture incubator, the supernatants were harvested and frozen at −20 °C until cytokine determination by a biological assay (Espevik and Nissen-Meyer, 1986). The results are given in percentage inhibition as compared with appropriate DMSO controls.

Growth inhibition of tumor cell lines

L-1210 lymphoma and SW-948 colon tumor cell lines derived from the Collection of Cell Lines of The Institute of Immunology and Experimental Therapy, Wrocław, Poland. The lines were re-suspended in the culture medium and distributed into 96-well flat-bottom plates. L-1210 was present at 1.5 × 10⁴ cells/well while SW-948 and at 2.5 × 10⁴ cells/well. The preparations were added to the wells at the concentration range of 0.1–50 µg/ml. Cisplatin was used as a reference drug in the same concentrations. After 3-day incubation in a cell culture incubator, the proliferation was determined using MTT colorimetric method. The data are presented as a mean OD value from quadruplicate wells ± SE.

Statistics

The results are presented as mean values ± standard error (SE) or percentage inhibition = [(control value − tested value)/control value] × 100. Brown-Forsyth’s test was used to determine the homogeneity of variance between groups. When the variance was homogenous, analysis of variance (One-way ANOVA) was applied, followed by post-hoc comparisons with the Tukey’s test to estimate the significance of the difference between groups. Nonparametric data were evaluated with the Kruskal–Wallis’ analysis of variance. Significance was determined at p < 0.05. Statistical analysis was performed using STATISTICA 6.1 for Windows.