Although three 6-aryl-substituted 7, 8-dihydro-8-thiopterins' were recently described in the literature4 and were found to be relatively stable, no corresponding data are available on the desired 6-alkyl-substituted 7, gdihydro-8-thiopterins. The stability and spectral characteristics of the 6-alkyl-and 6-aryl-substituted 7, 8-dihydro-8-thiopterins are expected to differ considerably due to the presence of extended conjugation in the structure of the ...