Syntheses are described for N,N-dimethyl-2-[5'-(pyridin-2''-yl)-1',3',4'-thiadiazol-2'-ylthio]ethylamine; the homologous propylamine; the N,N-diethyl homologue; the 5'-phenyl analogue; and some substituted phenyl, pyrazinyl and pyrimidinyl analogues. Unlike the pyridin-4''-yl isomer previously described, these compounds proved but mediocre amplifiers of phleomycin-G in vitro against Escherichia coli. Testing in vivo against Ehrlich's tumour in mice was therefore confined to the pyridin-4''-yl compound and to N,N-dimethyl-2-(6'-methyl-2'-phenylpyrimidin-4'-ylthio)ethylamine: the first showed considerable amplifying power towards two phleomycins and a bleomycin; the second, only marginally less amplification towards the same phleomycins.
Synthetic routes are described to 5,6-diamino-2,4'-bipyrimidin-4-ones and thence to 2-(pyrimidin-4'-yl)purines and 2-(pyrimidin-4'-yl)pteridines, some of which bear a sulfur- or nitrogen-linked basic side chain; also reported are routes to a series of phenyl- and diphenyl-pyrimidines, to each of which is attached a similar sulfur-, nitrogen-, or oxygen-linked side chain. Members of all the above systems show activity as amplifiers of phleomycin in a bacterial screen but the phenylpyrimidines with a sulfur-linked side chain are especially active.