New Di-(β-chloroethyl)-α-amides on N-(meta-Acylaminobenzoyl)- D,L-aminoacid Supports with Antitumoral Activity

Abstract

In order to obtain new compounds with antitumoural action the N-(meta-acylaminobenzoyl)-α-acylaminobenzoyl)-α-aminoacids 4-9 were prepared. These compounds were subsequently converted into the corresponding Δ²-oxazolin-5-ones 10-15, which in turn were submitted to a ring opening reaction with di-(β-chloroethyl)amine to afford the peptide supported N-mustards 16-21, which showed low toxicity and cytostatic activity similar to that of sarcolisine against the Ehrlich ascite and Walker 253 carcinosarcoma.

Introduction

The sensivity of tumours toward chemotherapic drugs varies widely in function of their biochemical characteristics, especially with regards to the metabolism of nucleic acids and the activity of the cell enzymatic equipment [1,2]. Among the chemotherapic agents used in the treatment of some malignant tumours the N-mustards are particularly important [3,4,5,6]. The cytostatic action of these compounds is exerted by the blocking alkylating effect on the components involved in the anarchic growth of the cancerous cells. The great disadvantage of the N-mustards used in treatment of certain cancer types is their rather high toxicity. By grafting the di-(β-chloroethyl)amino group on some compounds characteristic of living organisms, the transport of the cytostatic group to the cell level is facilitated, the toxicity lowered and the cytostatic action of these N-mustards by means of their antagonistic and alkylating effect increased [7,8,9,10].

Aminoacids and their derivatives are known to participate in animal metabolism decreasing the toxicity of some drug substances and facilitating the chemotherapic activity [4, 6, 9, 11,12,13,14]. Based on these considerations the present study is aimed to synthesize new N-mustards with the di-(β-chloro-ethyl)amino group supported by acylated derivatives of N-(meta-aminobenzoyl)-D,L-asparagic acid, N-(meta-aminobenzoyl)-D,L-asparagine and N-(meta-aminobenzoyl)-D,L-methionine, in order to follow their antitumour action by antagonist and alkylating effect.

Results and Discussion

The synthesis of the new di-(β-chloroethyl)amides with their active group supported by N-(meta-acylaminobenzoyl)-D,L-aminoacids was performed in several steps. First the N-(meta-acylamino-benzoyl)-L-aminoacids 4-9 were obtained by reaction of the previously obtained N-(meta-aminobenzoyl)-L-aminoacids 1-3 [15, 16] with formic acid when N-(meta-formylaminobenzoyl)-L-aminoacids 4-6 compounds have been obtained or acetic anhydride in acetic acid medium when N-(meta-acetylaminobenzoyl)-L-aminoacids 7-9 compounds have been obtained (Scheme 1).

Scheme 1. Synthesis of the N-(meta-acylaminobenzoyl)-L-aminoacids 4-9.

Scheme 1. Synthesis of the N-(meta-acylaminobenzoyl)-L-aminoacids 4-9.

The six N-acyl derivatives which had not been previously decribed in the literature were obtained as crystalline products melting within a narrow temperature range. The structures of these compounds were ascertained by means of elemental analyses and IR and ¹H-NMR spectral measurements. Absorption bands characteristic of these structures were noticed in their IR spectra, namely the amide I and amide II bands within 1635-1710 cm^-1 and 1520-1583 cm^-1, respectively. Every compound showed an absorption band characteristic of the meta-substituted benzene ring within the 685-830 cm^-1 range. In addition to that, the compound 6 and 9 also presented bands characteristic of the C-S valence bands at 728-754 cm^-1. The signal at 5.50 ppm in the ¹H-NMR of the compounds 1-3, was also presented in the spectra of the reaction products 4-9 between 5.70-6.30 ppm due to the conjugation effects with the >C=O group.

By heating the N-(meta-acylaminobenzoyl)-L-aminoacids 4-9 with acetic anhydride at 100°C the ring closure at the α-carboxyl group takes place, which results in the formation of Δ²-oxazolin-5-ones 10-15 (Scheme 2).

Scheme 2. Synthesis of the Δ²-oxazolin-5-ones 10-15.

Scheme 2. Synthesis of the Δ²-oxazolin-5-ones 10-15.

The cyclization reaction may be considered to take place according to a mechanism similar to that described in literature for other 2,4-disubstituted-Δ²-oxazolones [11, 15, 17,18,19]. The products 10-15 were obtained in 62-99% yields as crystalline compounds with sharp melting points. The oxazolone structures were elucidated by means of elemental analysis data and IR and ¹H-NMR spectral measurements. The IR absorption bands characteristic of the >C=O group are to be found at 1630-1820 cm^-1. The NH group vibrations give a single wide band within the 3080-3500 cm^-1 range. The C=N bond is made evident by an absorption maximum at 1610-1625 cm^-1 and the C-S bond at 654-725 cm^-1. The ¹H-NMR spectra are indicative of the cyclization realization by the disappearance of the signal characteristic of the acylated amine group at 5.50-6.50 ppm as well as by the heterocyclic proton descreening in virtue of its neighborhoods.

The high reactivity of Δ²-oxazolin-5-ones towards numerous nucleophilic reagents [11, 17, 18, 20] prompted us to perform the reaction between the newly obtained oxazolones 10-15 and di-(β-chloroethyl)amine to obtain new N-mustards 16-21 with possible higher activity and lower toxicity; the electron of the nitrogen atom being involved in an amidic conjugation system (Scheme 3).

The N-mustards are solid compounds with fixed melting points and stable to long preservation in a moistureless medium. Their structures were elucidated by means of elemental analyses and spectral measurements (IR, ¹H-NMR). The IR spectra of the compounds 16-21 show the amide I and II bands as well as intense absorption maxima within the 670-800 cm^-1 range corresponding to the C-Cl valence bond. The spectra of the compounds 18 and 21 show an additional band at 718-771 cm^-1 attributable to the C-S group. The ¹H-NMR spectra also reveal the oxazolone ring opening. Some spectra of the synthesized compounds are presented in Figure 1, Figure 2, Figure 3 and Figure 4.

Scheme 3. Synthesis of the N-mustards 16-21.

Scheme 3. Synthesis of the N-mustards 16-21.

Figure 1. IR spectrum of the N-(meta-formylaminobenzoyl)-L-methionine (6)

Figure 1. IR spectrum of the N-(meta-formylaminobenzoyl)-L-methionine (6)

Figure 2. IR spectrum of 2-(meta-formylaminophenyl)-4-(β-methylthio-ethyl)-Δ²-oxazolin-5-one (12).

Figure 2. IR spectrum of 2-(meta-formylaminophenyl)-4-(β-methylthio-ethyl)-Δ²-oxazolin-5-one (12).

Figure 3. IR spectrum of the α-[N-di-(β-chloroethyl)-amide] of N'-(meta-formylaminobenzoyl)-D,L-methionine (18).

Figure 3. IR spectrum of the α-[N-di-(β-chloroethyl)-amide] of N'-(meta-formylaminobenzoyl)-D,L-methionine (18).

Figure 4. ¹H-NMR spectrum of the α-[N-di-(β-chloroethyl)-amide] of N'-(meta-acetylaminobenzoyl)-D,L-methionine (21).

Figure 4. ¹H-NMR spectrum of the α-[N-di-(β-chloroethyl)-amide] of N'-(meta-acetylaminobenzoyl)-D,L-methionine (21).

Biological activity

The six synthesized N-mustards 16-21 were tested for their toxicity (DL₅₀ – median lethal dose) and an experimental study on their antitumoural activity was performed. The antitumor activity was studied using two experimental tumours frequently used in experiments with functionalized aminoacids: Ehrlich ascite and Walker 256 carcinosarcoma. The data in Table 1 reveal the inhibitory effect of the synthesized N-mustards on the experimental tumors. At the same time the inhibition values on the liquid tumors were noticed to be higher than on the solid ones, meaning that the Ehrlich ascite is more sensitive to the action of the tested substances. The compounds 16-21 containing a p‑acetylamino moiety in their structure show the highest inhibition values, especially on the liquid tumor. The di-(β-chloroethyl)amino group grafted on N-(meta-aminobenzoyl)-aminoacids 1-3 is seen to be much less toxic and the obtained di-(β-chloroethyl)-amides 16-21 are selective enough toward the neoplastic cells.

Table 1. DL₅₀ values and inhibition (%) induced by the N-mustards 16-21 on some experimental tumors.

Compound	DL50 mg/Kg body	Inhibition (%)
		Ehrlich ascite			Walker 256 carcinosarcoma
mg/Kg body	-	400	200	40	400	200	40
16	770	35	32	28	27	21	18
17	810	42	38	32	36	30	23
18	898	46	41	35	40	36	31
19	986	56	49	42	48	42	35
20	1020	54	48	41	51	46	40
21	1270	58	52	47	53	47	41
Sarcolisine	223	56	52	48	50	48	40

Table 1. DL₅₀ values and inhibition (%) induced by the N-mustards 16-21 on some experimental tumors.

Compound	DL50 mg/Kg body	Inhibition (%)
		Ehrlich ascite			Walker 256 carcinosarcoma
mg/Kg body	-	400	200	40	400	200	40
16	770	35	32	28	27	21	18
17	810	42	38	32	36	30	23
18	898	46	41	35	40	36	31
19	986	56	49	42	48	42	35
20	1020	54	48	41	51	46	40
21	1270	58	52	47	53	47	41
Sarcolisine	223	56	52	48	50	48	40

In comparison with sarcolisine, a well-known antitumoural agent, the compounds 16-21 showed a similar inhibition on both Ehrlich ascite and Walker 256 carcinosarcoma. The great advantage of the tested compounds consists in their much lower toxicity (DL₅₀ values) than that of sarcolisine (Table 1). This could be explained by the presence of the peptide support involved in the cytotoxic group transport to the malignant cell level where it would inhibit the abnormal synthesis of some proteins and nucleoproteids by an alkylating mechanism. The cytostatic action of di-(β-chloroethyl)amines may be assumed to consist in the possibility of an intramolecular cyclization in aqueous solution affording the formation of an immonium cation consisting of a three-membered ethyleneiminic cation ring which is unstable and can be easily broken being thus able to act by means of the β-carbon atom as an alkylating reagent for the substances containing active groups such as –NH, -SH, etc. (Scheme 4).

Scheme 4. The alkylating mechanism of the di-(β-chloroethyl)-amines.

Scheme 4. The alkylating mechanism of the di-(β-chloroethyl)-amines.

The alkylating property of di-(β-chloroethyl)amines allow us to assume that the N-mustards 16-21 are linked by means of the di-(β-chloroethyl)-amino group to the active groups –NH, -SH etc. of proteins, nucleoproteids or desoxyribonucleic acid molecules which participate to the cell multiplication process, and thus the anarchical division of cancerous cells is blocked.

Conclusions

Six new di-(β-chloroethyl)-α-amides 16-21 were prepared by the ring opening reaction of the synthesized oxazolones 10-15 using di-(β-chloroethyl)-amine. The new Δ²-oxazolin-5-ones 10-15 in turn were obtained by the action of acetic anhydride on the N-(meta-acylaminobenzoyl)- α-aminoacids 4-9, which were prepared by the reaction of formic acid or acetic anhydride with the N-(m-aminobenzoyl)-α-aminoacids 1-3.

The structure of the final and intermediate synthesized compounds 4-21 was confirmed by elemental analysis and spectral measurements (IR and ¹H-NMR). The experimental study revealed the six N-mustards 16-21 to show low toxicity and significant antimour activity on the Ehrlich ascite and Walker 256 carcinosarcoma tumours, similarly to sarcolisine.

Experimental Section

General

All melting points were determined on a Melt-Temp R apparatus equipped with a digital thermometer and are uncorrected. C,H,N analyses were performed on an Elemental Exeter Analytical CE 440 Apparatus. The IR spectra were recorded with KBr pellets on a Digilab Scimitar Series spectrophotometer. The ¹H-NMR spectra were recorded on Bruker ARX-300 (300 MHz) or ARX-400 (400 MHz) spectrometers. Chemical shifts were recorded as δ values in parts per million (ppm). All chemical reagents were obtained from Aldrich Chemical Company.

General synthesis method of N-meta-(formylaminobenzoyl) aminoacids 4-6

N-(meta-aminobenzoyl)-L-aminoacid 1-3, (0.02 mol) was introduced in a reaction flask provided with a refluxing condenser, then 80% formic acid (10 mL) was added and the mixture heated on an oil bath for 30 minutes, at 115-120°C. After cooling, anhydrous acetone (20 mL) was added dropwise under stirring, when colorless crystalline products separated. The product was then filtered, dried in a vacuum oven at 45°C and finally recrystallized from an ethyl alcohol–acetone mixture.

N-(meta-Formylaminobenzoyl)-L-asparagic acid (4).White solid; yield 88 % (491 mg); m.p. 76-78°C. Anal. Calc. for C₁₂H₁₂N₂O₆: 51.42 % C, 4.32 % H, 10.00 % N; Found: 51.88 % C, 4.56 % H, 10.33 % N; IR (ν, cm^-1): 2500, 3340 (NH); 1525, 1670 (CO); 685 (CH); ¹H-NMR δ (CD₃CN): 2.30 (d, 2H, CH₂); 4.95 (t, 1H, CH); 6.20 (s, 1H, NH); 7.65 (t, 1H, Ar); 7.80 (d, 1H, Ar); 8.05 (d, 1H, Ar); 8.10 (s, 1H, Ar).

N-(meta-Formylaminobenzoyl)-L-asparagine (5). White solid; yield 78 % (434 mg); m.p. 156-158°C. Anal. Calc. for C₁₂H₁₃N₃O₅: 51.60 % C, 4.69 % H, 15.05 % N; Found: 51.38 % C, 5.06 % H, 15.33 % N; IR (ν, cm^-1): 2500, 3200 (NH); 1535, 1710 (CO); 685 (CH); ¹H-NMR δ (CF₃COOD, 300 MHz): 2.25 (d, 2H, CH₂); 4.90 (t, 1H, CH); 6.00 (s, 1H, NH); 7.60 (t, 1H, Ar); 7.85 (d, 1H, Ar); 8.0 (d, 1H, Ar); 8.15 (s, 1H, Ar).

N-(meta-Formylaminobenzoyl)-L-methionine (6). White solid; yield 72 % (426 mg); m.p. 195-196°C. Anal. Calc. for C₁₃H₁₆N₂O₄S: 52.70 % C, 5.40 % H, 9.45 % N, 10.81 % S; Found: 52.68 % C, 5.23 % H, 9.31 % N, 10.58 % S; IR (ν, cm^-1): 3339, 3136 (NH); 1706, 1635 (CO); 828 (CH); 754 (C-S); ¹H-NMR δ (DMSO-d₆, 400 MHz): 2.08 (s, 3H, CH₃); 2.50 (m, 4H, CH₂); 4.57 (t, 1H, CH); 6.26 (d, 1H, NH); 7.80 (t, 1H, Ar); 8.34 (d, 1H, Ar); 8.74 (s, 1H, Ar); 9.06 (d, 1H, NH); 9.80 (d, 1H, CH).

General synthesis method of N-(meta-acetylaminobenzoyl)-aminoacids 7-9

A reaction mixture consisting of N-(meta-aminobenzoyl)-L-amino acid 1-3, (0.02 mol), 96% acetic acid (10 mL) and acetic anhydride (4 mL) was refluxed for 4 hours in a reaction flask provided with a refluxing condenser. The reaction mixture was the passed into a crystallizer and allowed to stand for 24 hours at room temperature, when the crystalline products separated. It was filtered off, washed two-three times with acetone (5 mL each portion), dried in a vacuum oven at 45°C and finally purified by recrystallization from boiling ethyl alcohol.

N-(meta-Acetylaminobenzoyl)-L-asparagic acid (7). White solid; yield 69.5 % (398 mg); m.p. 120-122°C. Anal. Calc. for C₁₃H₁₄N₂O₆: 53.05 % C, 4.80 % H, 9.52 % N; Found: 53.54 % C, 5.03 % H, 9.86 % N; IR (ν, cm^-1): 2500, 3300 (NH); 1530, 1700 (CO); 690 (CH); ¹H-NMR δ (CD₃COCD₃, 300 MHz): 2.25 (d, 2H, CH₂); 4.50 (s, 3H, CH₃); 5.05 (t, 1H, CH); 5.70 (s, 1H, NH); 7.70 (t, 1H, Ar); 7.85 (d, 1H, Ar); 8.00 (d, 1H, Ar).

N-(meta-Acetylaminobenzoyl)-L-asparagine (8). White solid; yield 73.8 % (432 mg); m.p. 175-177°C. Anal. Calc. for C₁₃H₁₅N₃O₅: 53.22 % C, 5.16 % H, 14.33 % N; Found: 53.44 % C, 5.63 % H, 14.68 % N; IR (ν, cm^-1): 2600, 3300 (NH); 1520, 1680 (CO); 695 (CH); ¹H-NMR δ (CD₃COCD₃, 300 MHz): 2.30 (d, 2H, CH₂); 4.50 (s, 3H, CH₃); 5.00 (t, 1H, CH); 5.80 (s, 1H, NH); 7.75 (t, 1H, Ar); 7.90 (d, 1H, Ar); 8.05 (d, 1H, Ar); 8.25 (s, 1H, Ar).

N-(meta-Acetylaminobenzoyl)-L-methionine (9). Grey solid; yield 70.32 % (432 mg); m.p. 272-273°C. Anal. Calc. for C₁₄H₁₈N₂O₄S: 54.19 % C, 5.80 % H, 9.03 % N, 10.32 % S; Found: 53.98 % C, 5.63 % H, 9.07 % N, 10.18 % S; IR (ν, cm^-1): 2800, 3304 (NH); 1583, 1684 (CO); 830 (CH); 728 (C-S); ¹H-NMR δ (DMSO-d₆, 400 MHz): 1.90 (s, 3H, CH₃); 2.06 (s, 3H, CH₃); 2.12-2.60 (m, 4H, CH₂); 4.55 (t, 1H, CH); 7.38 (t, 1H, Ar); 7.66 (d, 1H, Ar); 7.80 (d, 1H, Ar); 8.35 (s, 1H, Ar); 9.05 (d, 1H, NH); 9.15 (s, 1H, NH).

General synthesis method of 2-(meta-acylaminophenyl)-4-(β-carboxymethyl-, β-amidomethyl-, β-methyl-thioethyl)-Δ²-oxazolin-5-ones 10-15

N-(meta-acylaminobenzoyl)-L-amino acid 4-9 (0.02 mol) and acetic anhydride (14 mL) were introduced in a flask provided with a reflux condenser and heated on an oil bath for 60 minutes at 140 °C. After cooling, a thin stream of the resulting solution was poured under stirring into a mixture of anhydrous ethyl ether (40 mL) and anhydrous petroleum ether (50 mL). The solvent mixture was then decanted and the remaining viscous mass washed repeatedly with anhydrous ethyl ether till it turned into a fine powder. It was filtered off, repeatedly washed on the filter with anhydrous ethyl ether and allowed to dry in a vacuum oven for 8 hours at 40-45°C. Finally it was purified by recrystallization from anhydrous dioxane.

2-(meta-Formylaminophenyl)-4-(β-carboxymethyl)-Δ²-oxazolin-5-one (10). Yellow solid; yield 67 % (351 mg); m.p. 180-182°C. Anal. Calc. for C₁₂H₁₀N₂O₅: 54.97 % C, 3.84 % H, 10.68 % N; Found: 54.08 % C, 4.24 % H, 10.12 % N; IR (ν, cm^-1): 3320, 3520 (NH); 1775, 1800 (CO); 1080 (C-O-C); 1620 (C=N); 710 (CH); ¹H-NMR δ (CD₃CN, 300 MHz): 2.90-3.00 (m, 2H, CH₂); 4.95 (t, 1H, CH); 6.60 (s, 1H, NH); 7.65 (t, 1H, Ar); 7.95 (d, 2H, Ar); 8.20 (s, 1H, Ar).

2-(meta-Formylaminophenyl)-4-(β-amidomethyl)-Δ²-oxazolin-5-one (11). Yellow solid; yield 69 % (360 mg); m.p. 198-200°C. Anal. Calc. for C₁₂H₁₀N₃O₄: 55.17 % C, 4.24 % H, 16.09 % N; Found: 55.41 % C, 4.54 % H, 16.61 % N; IR (ν, cm^-1): 3325, 3500 (NH); 1760, 1795 (CO); 1088 (C-O-C); 1625 (C=N); 715 (CH); ¹H-NMR δ (DMSO-d₆, 300 MHz): 2.90-3.00 (m, 2H, CH₂); 5.00 (t, 1H, CH); 6.60 (s, 2H, NH₂); 7.70 (t, 1H, Ar); 7.95 (d, 2H, Ar); 8.20 (s, 1H, Ar).

2-(meta-Formylaminophenyl)-4-(β-methylthioethyl)-Δ²-oxazolin-5-one (12). Yellow solid; yield 62.2 % (345 mg); m.p. 182-183°C. Anal. Calc. for C₁₃H₁₄N₂O₃S: 56.11 % C, 5.03 % H, 10.07 % N, 11.51 % S; Found: 55.83 % C, 4.87 % H, 10.01 % N, 11.32 % S; IR (ν, cm^-1): 3429 (NH); 1751, 1631 (CO); 1610 (C=N); 1155 (C-O-C); 835 (CH); 654 (C-S); ¹H-NMR δ (DMSO-d₆, 300 MHz): 2.08 (s, 3H, CH₃); 2.50 (m, 4H, CH₂); 4.57 (t, 1H, CH); 6.22 (d, 1H, NH); 7.80 (t, 1H, Ar); 8.32 (d, 2H, Ar); 8.39 (d, 1H, Ar); 8.74 (s, 1H, Ar); 9.70 (d, 1H, CH).

2-(meta-Acetylaminophenyl)-4-(β-carboxymethyl)-Δ²-oxazolin-5-one (13). Yellow solid; yield 63.8 % (352 mg); m.p. 149-150°C. Anal. Calc. for C₁₃H₁₂N₂O₅: 56.52 % C, 4.38 % H, 10.14 % N; Found: 56.98 % C, 4.74 % H, 10.62 % N; IR (ν, cm^-1): 3084, 3210 (NH); 1730, 1770 (CO); 1084 (C-O-C); 1620 (C=N); 728 (CH); ¹H-NMR δ (CD₃CN, 300 MHz): 2.95 (d, 2H, CH₂); 4.50 (s, 3H, CH₃); 5.20 (t, 1H, CH); 6.50 (s, 2H, NH); 7.70 (t, 1H, Ar); 8.00 (d, 2H, Ar); 8.25 (s, 1H, Ar).

2-(meta-Acetylaminophenyl)-4-(β-amidoethyl)-Δ²-oxazolin-5-one (14). White solid; yield 61.5 % (337 mg); m.p. 168-170°C. Anal. Calc. for C₁₃H₁₃N₃O₄: 56.72 % C, 4.76 % H, 15.27 % N; Found: 56.91 % C, 4.95 % H, 15.43 % N; IR (ν, cm^-1): 3100, 3320 (NH); 1770, 1800 (CO); 1084 (C-O-C); 1620 (C=N); 705 (CH); ¹H-NMR δ (DMSO-d₆, 300 MHz): 2.80 (d, 2H, CH₂); 4.50 (s, 3H, CH₃); 5.05 (t, 1H, CH); 5.70 (s, 1H, NH); 6.60 (s, 2H, NH₂); 7.70 (t, 1H, Ar); 7.90 (d, 2H, Ar); 8.20 (s, 1H, Ar).

2-(meta-Acetylaminophenyl)-4-(β-methylthioethyl)-Δ²-oxazolin-5-one (15). Brown solid; yield 58.7 % (342 mg); m.p. 142-143°C. Anal. Calc. for C₁₄H₁₆N₂O₃S: 57.53 % C, 5.47 % H, 9.58 % N, 10.95 % S; Found: 57.18 % C, 5.21 % H, 9.24 % N, 10.81 % S; IR (ν, cm^-1): 3080, 3240 (NH); 1680, 1815 (CO); 1078 (C-O-C); 1615 (C=N); 820 (CH); 725 (C-S); ¹H-NMR δ (DMSO-d₆, 400 MHz): 2.07 (s, 3H, CH₃); 2.26 (s, 3H, CH₃); 2.57 (m, 4H, CH₂); 4.57 (m, 1H, CH); 5.73 (s, 1H, NH); 7.80 (t, 1H, Ar); 8.33 (d, 1H, Ar); 8.39 (d, 1H, Ar); 8.74 (s, 1H, Ar).

General synthesis of α-[N-di-(β-chloroethyl)amides] of the N’-(meta-acylaminobenzoyl)-D,L-amino-acids 16-21

Δ²-Oxazolin-5-ones 10-15 (0.02 mol), di-(β-chloroethyl)amine hydrochloride (0.004 mol), anhydrous dioxane (20 mL) and triethylamine (0.556 mL) were introduced in a flask provided with a refluxing condenser, heated at 50-60°C for one hour and the resulting triethylamine hydrochloride removed by filtration. The dioxane was then removed by low pressure distillation at a temperature of 40-50°C and the viscous product remaining in the flask solved in absolute methyl alcohol (25 mL). After the vacuum distillation of the methyl alcohol, a sticky product resulted which turned into a solid product, after repeated washings with anhydrous ethyl ether. It was finally purified by recrystallization from boiling anhydrous methyl alcohol.

α-[N-di-(β-Chloroethyl)amide] of N’-(meta-formylaminobenzoyl)-D,L-asparagic acid (16). Light-yellow solid; yield 51.4 % (39 mg); m.p. 193-194°C. Anal. Calc. for C₁₆H₁₉Cl₂N₃O₅: 47.54 % C, 4.74 % H, 10.39 % N, 17.54 % Cl; Found: 47.22 % C, 4.50 % H, 10.24 % N, 17.68 % Cl; IR (ν, cm^-1): 3350, 3600 (NH); 1640, 1680 (CO); 770 (C-Cl); 705 (CH); ¹H-NMR δ (CD₃COCD₃, 300 MHz): 2.60 (d, 2H, CH₂); 4.20 (t, 2H, CH₂); 4.80 (t, 1H, CH); 5.10 (t, 2H, CH₂); 7.70 (t, 1H, Ar); 7.85 (d, 1H, Ar); 7.95 (d, 1H, Ar); 8.10 (s, 1H, Ar).

α-[N-di-(β-Chloroethyl)diamide] of N’-(meta-formylaminobenzoyl)-D,L-asparagic acid (17). Yellow solid; yield 50.5 % (40.5 mg); m.p. 198-200°C. Anal. calc. for C₁₆H₂₀Cl₂N₄O₄: 47.65 % C, 5.00 % H, 13.89 % N, 17.58 % Cl; Found: 47.85 % C, 5.15 % H, 14.11 % N, 17.92 % Cl; IR (ν, cm^-1): 3090, 3240 (NH); 1530, 1620 (CO); 745 (C-Cl); 710 (CH); ¹H-NMR δ (CD₃CN, 300 MHz): 2.90 (d, 2H, CH₂); 4.40 (t, 2H, CH₂); 4.95 (t, 1H, CH); 5.35 (t, 2H, CH₂); 6.60 (s, 2H, NH₂); 7.60 (t, 1H, Ar); 7.80 (d, 2H, Ar); 8.20 (s, 1H, Ar).

α-[N-di-(β-Chloroethyl)amide] of N’-(meta-formylaminobenzoyl)-D,L-methionine (18). Light brown solid; yield 56.38 % (47.30 mg); m.p. 177-178°C. Anal. calc. for C₁₇H₂₃Cl₂N₃O₃S: 48.57 % C, 5.47 % H, 10.00 % N, 16.90 % Cl, 7.61 % S; Found: 48.31 % C, 5.40 % H, 9.85 % N, 16.83 % Cl, 7.41 % S; IR (ν, cm^-1): 3065, 3472 (NH); 1700 (CO); 771 (C-S); 801 (C-Cl); 848 (CH); ¹H-NMR δ (DMSO-d₆, 400 MHz): 2.10 (s, 3H, CH₃); 2.56 (m, 4H, CH₂); 3.50 (t, 4H, CH₂); 3.82 (t, 4H, CH₂); 4.56 (t, 1H, CH); 6.20 (d, 1H, NH); 7.80 (t, 1H, Ar); 8.43 (d, 1H, Ar); 8.48 (d, 1H, Ar); 8.73 (s, 1H, Ar); 9.07 (d, 1H, NH); 9.68 (d, 1H, CH).

α-[N-di-(β-Chloroethyl)amide] of N’-(meta-acetylaminobenzoyl)-D,L-asparagic acid (19). Grey solid; yield 52.8 % (44 mg); m.p. 98-100°C. Anal. calc. for C₁₇H₂₁Cl₂N₃O₅: 48.82 % C, 5.06 % H, 10.05 % N, 16.95 % Cl; Found: 48.35 % C, 5.32 % H, 10.23 % N, 17.12 % Cl; IR (ν, cm^-1): 3340, 3500 (NH); 1640, 1660 (CO); 750 (C-Cl); 698 (CH); ¹H-NMR δ (CD₃CN, 300 MHz): 2.90-3.00 (m, 2H, CH₂); 4.95 (t, 1H, CH); 5.80 (s, 1H, NH); 7.65 (t, 1H, Ar); 7.95 (d, 2H, Ar); 8.20 (s, 1H, Ar).

α-[N-di-(β-Chloroethyl)diamide] of N’-(meta-acetylaminobenzoyl)-D,L-asparagic acid (20). Yellow solid; yield 53.8 % (44.8 mg); m.p. 168-169°C. Anal. calc. for C₁₇H₂₂Cl₂N₄O₄: 48.93 % C, 5.31 % H, 13.43 % N, 16.99 % Cl; Found: 49.10 % C, 5.88 % H, 13.70 % N, 17.40 % Cl; IR (ν, cm^-1): 3125, 3300 (NH); 1535, 1630 (CO); 740 (C-Cl); 698 (CH); ¹H-NMR δ (CD₃CN, 300 MHz): 2.75 (d, 2H, CH₂); 4.50 (t, 2H, CH₂); 4.90 (t, 1H, CH); 5.30 (t, 2H, CH₂); 6.60 (s, 2H, NH₂); 7.70 (t, 1H, Ar); 7.90 (d, 2H, Ar); 8.20 (s, 1H, Ar).

α-[N-di-(β-Chloroethyl)amide] of N’-(meta-acetylaminobenzoyl)-D,L-methionine (21). Light brown solid; yield 58.3 % (50.6 mg); m.p. 183-184°C. Anal. calc. for C₁₈H₂₅Cl₂N₃O₃S: 49.76 % C, 5.76 % H, 9.67 % N, 16.35 % Cl, 7.37 % S; Found: 49.58 % C, 5.62 % H, 9.46 % N, 16.17 % Cl, 7.28 % S; IR (ν, cm^-1): 3010, 3328 (NH); 1685 (CO); 718 (C-S); 670 (C-Cl); 855 (CH); ¹H-NMR δ (DMSO-d₆, 400 MHz): 2.11 (s, 3H, CH₃); 2.30 (s, 3H, CH₃); 2.56 (m, 4H, CH₂); 3.28 (t, 4H, CH₂); 3.85 (t, 4H, CH₂); 4.56 (t, 1H, CH); 6.02 (s, 1H, NH); 7.80 (t, 1H, Ar); 8.32 (d, 1H, Ar); 8.42 (d, 1H, Ar); 8.73 (s, 1H, Ar); 9.08 (d, 1H, NH).

Toxicity study

The acute toxicity, the DL₅₀ values respectively, was estimated by intraperitoneal administration of the compounds as a suspension in 1% methylcellulose to groups of four mice each, weighting 20±2 g, according to the classical laboratory procedure [21]. The methylcellulose was chosen in these experiments since it is chemically inert and inactive on the animal tissue [22]. The tested animals were carefully followed and the death rate registered seven days later.

Antitumour activity

The antitumour activity was estimated by using two experimental tumors: Ehrlich ascite and Walker 256 carcinosarcoma. Mice A₂G, weighing 25-30 g (± 2g) and Wistar rats, weighing 100-130 g (± 15 g), were used. The Ehrlich ascite tumors were transplanted to mice and the Walker 256 carcinosarcoma to rats. The ascite was transplanted intraperitoneally, from donors with 14 day old while the solid tumors was transplanted subcutaneously from donors with 21 day old tumors. The substances were administrated intraperitoneally, as suspensions in 1% methylcellulose. Single injection was made seven days after the transplantation with ascite and fourteen days after the transplantation with solid tumour. Concentrations of 400 mg, 200 mg and 40 mg/ kg body were taken and groups of 20 animals used with every concentration. The reference group of 20 animals with tumours was taken for every tumoural series. The inhibition induced by the compounds under study was estimated according to the literature method [9, 11, 23] after seven and fourteen days from their administration for the ascite and for solid tumour respectively.