6-Amino-2-thiouracil (1) was condensed with benzenesulfonyl chloride and p-toluenesulfonyl chloride in presence of pyridine as an acid binder to give sulfonamides 2a, b, which could be methylated in basic medium to give methylmercapto derivatives 3a, b, which in turn reacted with bromine in glacial acetic acid to yield 5-bromo derivatives 4a, b. On the other hand, compounds 2a, b were cyclocondensed with monochloroacetyl chloride, p-tolualdehyde in glacial acetic acid/pyridine, and ethyl bromoacetate to give the corresponding thiazolopyrimidines 5a, b, 6a, b, and 7a, b, respectively; also compounds 2a, b were hydrazinolyzed to compounds 8a, b, which could be cyclized to triazolopyrimidines 9a, b in presence of formic acid. They could also be condensed with p-anisaldehyde to give hydrazones 10a, b. In another pathway, compounds 2a, b were reacted with monochloroacetic acid in basic medium to give acetic acid derivatives 11a, b. It can be deduced from the preliminary screening results that the cell lines most sensitive to the antiproliferative activity of tested compounds are human liver HEPG2 and colon cancer HT-29. All selected compounds exhibited moderate to strong growth inhibition activity against the HEPG2 cell line with 50 % inhibitory concentration (IC50) ranging between 1 and 10 μg/ml. The most active compounds, which revealed antiproliferative activity also against human colon HT-29 and breast MCF-7 cell lines, were 3a, 3b, 4a, and 10a.
