By Cleavage of Pteridines and Other Ring Systems

The preparation of 2-amino-3-carboxy-5-methylthio(and 5-benzylthio)pyrazines by saponification of 4-hydroxy-6-methylthio(and 6-benzylthio)pteridine with 5% sodium hydroxide has been described in Chapter II.5 (432,432a). Some additional references also describe these preparations (778, 780,783,786, 858). 2-Acetamido- 

3- amidinocarbamoyl-5-methylthio(and benzylthio)pyrazine has been prepared from 2-methyl-6-methylthio(and benzylthio)-4//-pyrazino[2,3-d][l,3]oxazin-4-one with guanidine and sodium methoxide (432) similar reactions were observed with aminoguanidine (463a). 

Bauer and Hirsch (764) found that 2,5-dimethylpyrazine 1-oxide refiuxed for 2 hours with propane-1-thiol in acetic anhydride gave 2,5-dimethyl-3-propylthio-pyrazine (5), and 2,5-dimethylpyrazine 1,4-dioxide similarly treated gave 2,5-dimethyl-3,6-dipropylthiopyrazine, but attempted reactions with benzenesulfonyl chloride instead of acetic anhydride (as in the pyridine series) were unsuccessful. 

The structure of 2-mercaptopyrazine (1, R = H) in aqueous solution has been examined by comparison of its ionization constants and ultraviolet spectra with 

IONIZATION CONSTANTS AND ULTRAVIOLET SPECTRA OF 2-MERCAPTOPYRAZINE AND ITS N- AND SJdETHYL DERIVATIVES 

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