propyl (4S)-4-ethyl-3,4-dihydroxy-8-methoxy-1,3-dihydropyrano[3,4-c]pyridine-6-carboxylate

propyl (S)-4-ethyl-3,4-dihydro-4-hydroxy-8-methoxy-3-oxo-1H-pyrano[3,4-c]pyridine-6-carboxylate