Mercapto heterocyclic carboxylic acids, analogues of 3-mercaptopicolinic acid

3-Mercaptopicolinic acid (3-MPA), a potent hypoglycemic agent in fasted rats, provided the impetus for substituting this compound with a 5-mercapto group (1), a 6-carboxyl group (2), and a 5-mercapto and 6-carboxyl group (3) and for replacing the pyridine ring with other heterocycles: quinoline (4), thiazole (5), pyrazine (6), isoquinoline (7), and indole (8). The methyl sulfoxide (9) and sulfone (10) of 3-MPA were also prepared. The new compounds 1-10, with the exception of 8, did not lower blood glucose levels in 48-h fasted rats. 8 was toxic at doses which were hypoglycemic.