Non-insulin-dependent diabetes mellitus (NIDDM) is typically characterized by peripheral insulin resistance, hyperglycemia, and obesity. In addition to exercise and modified diet, glycemic control often uses therapeutic agents like sulfonylureas, which suffer from primary or secondary failure as well as potentially fatal hypoglycemia due to persistent insulin-releasing properties even with low plasma glucose. Takeda reported a series of compounds (e.g., ciglitazone) in 1982 that apparently potentiate the action of insulin in the periphery with a reduced risk of hypoglycemic episodes. Most subsequent work explored replacements for the lipophilic tail or phenyl ether moieties of such compounds, but the acidic heterocyclic portion remained largely unexplored. We chose to examine derivatives of the potent oxazolylethoxy backbone described by Meguro in which the acidic heterocycle is attached to this side chain at a nonenolizable site. These compounds were prepared via Scheme I: aldehyde 4 was converted to the oxime with hydroxylamine hydrochloride, reduced to hydroxylamine 5 using NaBH₃CN in HCl/MeOH, treated with excess potassium cyanate in acetic acid/water to give hydroxyurea 6, which was readily converted into oxadiazoledione 3 with ethyl chloroformate and 3 equiv of NaOH or into carbonate derivatives 7-10 with 1 equiv of NaOH; N-methyl derivatives 11 and 12 were also synthesized. The compounds were evaluated in vivo for hypoglycemic activity in the ob/ob mouse model, showing that 3 (oxadiazoledione) and 7 (methyl carbonate) had potent activity (e.g., 3 had 97% glucose normalization at 25 mg/kg, 7 had 100% at 25 mg/kg relative to ciglitazone). In vitro assays in 3T3-L1 adipocytes revealed that 3, 6, and 7 upregulated GLUT 1 glucose transporter expression (3 was most potent, effecting an increase at 3 and 30 μM; 6 and 7 only at 30 μM). In summary, the in vivo hypoglycemic activity found in the oxazolidinedione analog 2 was retained when the epimerizable C-5 center was replaced with a nitrogen. This activity, as well as GLUT 1 glucose transporter upregulation, was further extended to the ring-opened carboalkoxylated hydroxyureas, the first acyclic non-carboxylic acid compounds to show this potent biological effect.