Pyridazine mercapto

The reactivity of halogens in pyridazine N- oxides towards nucleophilic substitution is in the order 5 > 3 > 6 > 4. This is supported by kinetic studies of the reaction between the corresponding chloropyridazine 1-oxides and piperidine. In general, the chlorine atoms in pyridazine A-oxides undergo replacement with alkoxy, aryloxy, piperidino, hydrazino, azido, hydroxylamino, mercapto, alkylmercapto, methylsulfonyl and other groups. 

Amino-4-mercapto-6-methylpyridazine (10) (pyridazine Sj CAS 18591-81-6) represents another newly discovered antipyretic, analgesic and antiinflammatory agent [72], It was the most effective compound among several mercaptopyridazines tested in the German Democratic Republic [73-75] the acute toxicity was found to be low (LD50 x 10 mmol/kg p.o. mouse) [74]. 

In West Germany pyridazinium compounds as represented by formula (120, R1 = halogen, alkyl, aryl R2 = H, alkyl R3 = substituted amino R4 = substituted alkyl, cycloalkyl) have been claimed as antibacterial agents [338]. In Australia, mercapto derivatives of several nitrogen heteroaromatics including pyridazine-derived compounds (121, R = CONH2, CH2NMe2) have been prepared in a search of amplifiers of phleomycin [339] however, only low activity has been observed in this series. 

Pyridazine 6-Mercapto-3-methyl-amino- E9a. 636 (Cl -< SH) Pyrrol 2-(Hydrazino-thiocarbonyl)-E5, 1297f. 

Pyridazin 1,2-Dimethyl-4-mercapto-hexahydro- E16a, 580 (N-COOR-Red.) Schwefeldiimid Diisopropyl- Ell, 589 (RN = SC12 + Amin)... 

Dicyanopyrazine with sodium methoxide in methanol with ammonia at reflux gave 5,7-diimino-6//-pyrrolo[3,4-i)]pyrazine (65) (1442) and 2,3-dicyano-5,6-dimethyl(and 5,6-diphenyl)pyrazine with hydrazine by the procedure of Patel and Castle (1339) gave 2,3-dimethyl(and 2,3-diphenyl)-5,8-diaminopyrazino[2,3-rfJ-pyridazine(s) (66) (1435). Fusion of 2-chloro-3-cyano-5,6-diphenylpyrazine with urea and thiourea was reported to give 4-amino-2-hydroxy(and mercapto)-6,7-diphenylpteridine (848). 

Studies on the tautomerism of pyridazines with potential tautomeric groups have continued. On the basis of recorded ionization constants and UV spectra of 3,4,5-trimercaptopyridazine and its derivatives, it is concluded that the compound exists as 3,4-dimercaptopyridazine-5(2f/)-thione. Tautomerism of hydroxy- and mercaptopyridazines was investigated with the aid of the corresponding anhydro bases as reference compounds. They exist predominantly in the -one or -thione forms. Similarly, the 3-mercapto-pyridazine-6(l/f)-thione structure in aqueous solution has been redeter-... 

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