The dehydrated surugatoxin framework was constructed by the following reactions. Oxidative acetylation of tetrahydropteridine 2 with Ac2O-pyridine to dihydropteridinediacetate 5, followed by reduction (NaBH3CN), gave a isatinylidene derivative 8. Acylation of 8 with pyruvoyl chloride in benzene gave pyruvoyl amide 9. Heating 9 in pyridine at 50°C resulted in a stereospecific ring closure to afford ethyl ester analogue 10 of dehydrated surugatoxin.
