Pteridine. Teil LXXXII. Synthese und Reaktivität von Lumazin‐7‐sulfensäuren

Synthesis and Reactivity of Lumazine‐7‐sulfenic Acids The chemical synthesis of the pteridine‐7‐sulfenic acids 13 – 16 is described ( Scheme 1 ). The 1,2,3,4‐tetrahydro‐1,3,6‐trimethyl‐2,4‐dioxopteridine‐7‐sulfenic acid ( 14 ) was isolated as a stable crystalline solid. Its chemical reactivity was investigated and the physical properties determined. In the solid state, the S ‐oxide form 14A predominates, but in protic solvents the S‐OH tautomer 14 exists most likely. In basic medium, the pteridine‐7‐sulfenate species is stable, whereas a low pH gives rise to a disproportionation to the disulfide 10 and the corresponding pteridine‐7‐sulfinic acid 37 ( Scheme 4 ). Reaction of 14 with ethyl propiolate leads, under cis ‐addition, to 36 , oxidation with KMnO 4 forms 1,2,3,4‐tetrahydro‐1,3,6‐trimethyl‐2,4‐dioxopteridine‐7‐sulfonic acid ( 38 ) and NaBH 4 reduction the corresponding 7‐mercaptopteridine dione 18 ( Scheme 4 ).