n-Glucose-6-phosphate dehydrogenase (Zwischenferment) was discovered by Warburg and Christian in 1931 (1, 2). An active preparation was obtained then from horse erythrocytes and in 1932 from the Lebedev juice made from brewers’ yeast (3). Because of its extreme specificity, this enzyme has become an important analytical tool. Various preparations of it have been described, the first being those...

The syntheses of novel tricyclic pyrrolo[2,3-d]pyrimidine analogues of S6-methylthioguanine are described. The crystal structures and pKa values of these and related O6-methylguanine analogues are reported. All compounds display higher pKa values than O6-methylguanine with the sulfur-containing analogues being the more basic and exhibiting higher stability in aqueous solution. In a standard sub...