Purine analogues as amplifiers of phleomycin. IX. Some 2- and 6-substituted Thiazolo[4,5-b]pyrazines, 2-substituted Thiazolo[4,5-c]- and Thiazolo[5,4-b]-pyridines and related compounds

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Abstract
Derivatives of the thiazolo[4,5-b]pyrazine system are reported including those with 2-phenyl substituents or fused benzene rings (as in thiazolo[4,5-b]quinoxalines) together with strongly basic N,N-dimethylaminoethylthio or N,N-dimethylaminopropylthio side chains. Series of thiazolo[4,5-c]- pyridines, thiazolo[5,4-b]pyridines and quinoxalines are also described. A new process for the preparation of 3-N,N-dimethylaminopropylthio derivatives of heterocycles by reaction of the mercapto compound with 3-chloro-N,N-dimethylpropylamine in ethanolic ammonia has been shown to give more reliable and improved results. Of the compounds examined for amplification of the activity of phleomycin, N,N-dimethyl- 3-(2-methylthiazolo[4,5-pyrazin-6-ylthio)propylamine and 3-[3-(3-N,N-dimethylaminopropylthio)- quinoxalin-2-ylthiol-N,N-dimethylpropylamine were the best, and showed four star activity at 1 mM and 0.5 mM respectively. A 2-phenyl substituent in, or a benzene ring fused to, thiazolo[4,5-b]- pyrazines did not increase amplification. The 2-substituted thiazolo[4,5-c]pyridines showed activity comparable to that of the 2-substituted thiazolo[4,5-blpyrazines whereas that of the thiazolo[5,4-b]pyrazines was lower.