2-sulfanylamido-pyrazine 1-or 4-oxide

We, SOCIFTA' FABMACEUTICI ITALIA, an Italian Joint Stock Company, of 1/2, Inigo Guido Donegani, feilano, Italy,

DO HEREBY DECLARE the nature of this invention and in whaf manner the same is to be performed to be particularly described and ascertained in and by the following sfafemenf:

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The invention relates to new pyrazine derivatives having antibacterial. activity.

The invention provides as new compounds 2-sulphanilamido-pyrazine-4-oxide (1) and 2-sulphanilamidopyrazine-l-oxide (11) which have the following structural formulae: Q

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The new compounds of the invention have a high antibacterial activity on gram-positive and gram-negative schizomycetes and a low toxicity such as to make them usefully employable in human and veterinary therapy. Besides having a high antibacterial activity and a toxicity lower than that of analogous compounds, the new compounds of the invention have a remarkable elimination ratio which makes them useful in sulphamidic therapy where the use of products having nondelayed action is recomended.

The new compounds of the invention are preferably administered by the oral route, for instance in the form of powders, tablets, pills or capsules, in the presence of a liquid or solid excipient or other pharmacologically acceptable substance.

The invention includes a process of preparing the new compounds (I) and (II) which comprises condensation of 2chloro-pyrazine-4-oxide or -1-oxide with sulphanilamide in the presence of a base, such as potassium carbonate, generally at about the melting point of the mixture, or with a sulpha-2i nilamide alkali metal salt in the presence of a solvent, such as acetamide, generally at a temperature of from 140° to 150°C.

On subsequent acidification the product precipitates and can be isolated and purified by separation, washing and recrystallization.

The following Examples illustrate the invention.

Example 2-Sulphanilamido-pyrazine-4-oxide (I) 1 mol of 2-chloro-pyrazine-4-oxide (L. Bernardi et al. Gazz. chim. ital. 91, (1961), page 1435) is mixed with 1.5 mols of sulphanilatnide and 0.82 mols of potassium carbonate. The mixture is kept at the melting point of 145°C for from 4 to 6 hours. When the reaction is over the mixture is diluted with 200 cc of water and acidified to pH 3.5 with 4N hydrochloric acid. The solid compound which precipitates is separated, by filtration, washed with water and dried. 2-Sulphanilamidopyrazine-4-oxide, melting at 235-240^oC, is obtained in a yield of 700 with respect to the starting 2-chloropyrazine-4-oxide. After recrystallization from ethanol the product melts at 240°-241°C. From the mother liquor unreacted 2-chloropyrazine-

4-oxide is recovered by extraction with chloroform.

Example 2-Sulphanilamido-pyrazine-l-oxide (II) Operating as in Example 1 but using 2-chloropyrazine-l-oxide (Bernardi et al. Gazz. Chim. Ital. 91., (1961), p. 1435) 2sulphanilamido-pyrazine-l-oxide melting at 22O°-221°C is obtained. After recrystallization from dioxan the product melts at 222°C,

The antibacterial activity of the new compounds of the invention has been determined and the results are reported below and compared with those for sulphamethopyrazine (2sulphanilamido-3-m'ethoxy-pyrazine: British Patent No.928,151).

Table 1 shows the values of the 50% inhibition dose (ΐΒ^θ), in vitro, expressed in ug per cc of liquid medium having the composition described by Capps et al. J. Bact. 55 , (1948), p. 869. The ID^q value indicates the concentration capable of reducing 50% of the development of the treated bacteria with respect to the controls.

TABLE 1

<td> Bacterial Strain</td><td> Sulphamethopyrazine</td><td>^ID50 I</td><td> (ug/cc) II</td>

<td> Staphylococcus aureus 114</td><td> 10</td><td> 25</td><td> 50</td>

<td> Staphylococcus aureus 153</td><td> 10</td><td> 25</td><td> 17</td>

<td> Escherichia coli</td><td> 5</td><td> 25</td><td> 22</td>

<td> Shigella flexneri var. Y</td><td> 10</td><td> 100</td><td> 10</td>

<td> Salmonella abortivo-equina</td><td> 28</td><td> 50</td><td> 25</td>

Tests of the therapeutical activity of the new compounds of the invention have been carried out bn mouse experimentally infected by the intraperitoneal route with Staphylococcus aureus Camp, Salmonella abortivo-equina and Plasmodium berghei The products were administered orally with one treatment daily

In Table 2 there are the following

LT״ (treated animals) ^LTR50 = -----------------LT,-״ (controls) טל

TD₅₀ = therapeutic dose, express figures:

wherein LT_C״ is the time טל within which 50$ of the animals die.

in mg/kg of body weight, which administration causes a recovery of 50% of the treated animals .

LD

T.I. = 50 = therapeutic index expressed by the ratio ^^D50 between the lethal dose 50 (LD^q), that is the dose in mg/kg able to cause the death of 50% of the treated animals, and the therapeutic dose 50 (TD^q).

TABLE 2

<td></td><td> Infection</td><td> Compound</td><td> Dose mg/kg</td><td> Days of treatme nt</td><td> ltr₅₀</td><td>^TD50 mg/kg</td><td> T.I.</td>

<td> 10</td><td> Staphylococcus</td><td> I</td><td> 200</td><td> 1</td><td> 2.41</td><td></td><td> —</td>

<td></td><td rowspan="2"> aureus Camp</td><td></td><td> 50-100-200</td><td> 5</td><td> —</td><td> 63</td><td> 103</td>

<td></td><td> Sulphametho-</td><td> 200</td><td> 1</td><td> 1.97</td><td> —</td><td> —</td>

<td></td><td></td><td> pyrazine</td><td> 50-100-200</td><td> 5</td><td> —</td><td> 49</td><td> 34.69</td>

<td></td><td> Salmonella</td><td> I</td><td> 200</td><td> 1</td><td> 2.12</td><td> —</td><td> —</td>

<td></td><td> abortivo-</td><td></td><td> 50-100-200</td><td> 5</td><td> י</td><td> 100</td><td> 65</td>

<td> 15'</td><td> -equina</td><td> II</td><td> 25-50-100</td><td> 5</td><td> -</td><td> 170</td><td> -</td>

<td></td><td></td><td> Sulphametho-</td><td> 200</td><td> 1</td><td> 1.94</td><td> —</td><td> —</td>

<td></td><td></td><td> pyrazine</td><td> 50-100-200</td><td> 5</td><td> —</td><td> 100</td><td> 17</td>

<td></td><td> Plasmodium</td><td> I</td><td> 25-100-400</td><td> 1</td><td></td><td> 80</td><td> 81.2</td>

<td rowspan="2"> 20</td><td> berghei</td><td></td><td> 6.25-25-100</td><td> 5</td><td> -</td><td> 10</td><td> 650</td>

<td></td><td> Sulphametho-</td><td> 25-100-400</td><td> 1</td><td> —</td><td> 75</td><td> 22.6</td>

<td></td><td></td><td> pyrazine</td><td> 6.25-25-100</td><td> 5</td><td> —</td><td> 6.25</td><td> 272</td>

<td></td><td> Plasmodium</td><td> II</td><td> 25-100-400</td><td> 1</td><td> —</td><td> 1200</td><td> —</td>

<td></td><td> berghei</td><td></td><td> 6.25-25-100</td><td> 5</td><td> -</td><td> 25</td><td> -</td>

<td></td><td></td><td> Sulphametho-</td><td> 25-100-400</td><td> 1</td><td> —</td><td> 400</td><td> 4.25</td>

<td></td><td></td><td> pyrazine</td><td> 6.25-25-100</td><td> 5</td><td> -</td><td> 12</td><td> 141.6</td>

<td> 25</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td>

The toxicity of 2-sulphanilamido-pyrazine-4-oxide intravenously determined in mouse, and expressed as LD^q, is 6.5 g/kg, while that of sulphamethopyrazine is 1.7 g/kg and that of sulphapyrazine is 0.630 g/kg.

In Table 3 are the values of therapeutical ac/tivity, r

(expressed as ratio LTR^q) of the new compounds of the invention in comparison to sulphapjflyrazine and to sulphamethopyrazine in the experimental infection of mouse with Diplococcus pneumoniae, by carrying out only one treatment with each product under exam!nation at the dose of 200 mg/kg. The infections were carried out at intervals of 8, 24 and 48 hours from the administration of the product.

TABLE 3

<td rowspan="2"> Compound</td><td colspan="3"> ltr₅₀</td>

<td> 8</td><td> 24</td><td> 48</td>

<td> I</td><td> 1.42</td><td> 1.05</td><td> 1</td>

<td> II</td><td> 1.57</td><td> 1</td><td> 1</td>

<td> Sulphapyrazine</td><td> 1.52</td><td> 1.05</td><td> 1.05</td>

<td> Sulphamethopyrazine</td><td> 2.10</td><td> 1.47</td><td> 1.44</td>

It appears from Table 3 that the elimination ratio of the two new products of the invention may be compared to that of sulphapyrazine but is higher than that of sulphamethopyrazine.

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HAVING NOW particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, . we declare that what we claim 1st**