Synthesis, Pharmacology, and Clinical Trial of the Riboflavine Analogue, Sodium-6,7-Dimethyl-9-(2′-Hemisuccinoxyethyl)-Isoalloxazine, U-6538

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Abstract
The synthesis of a riboflavine analogue, sodium-6,7-dimethyl-9-(2′-hemisuccinoxyethyl)-isoalloxazine, U-6538, is reported. Administered parenterally this compound produced inhibition of rat growth which could be reversed by riboflavine. The drug was capable of inhibiting the growth of a rat lymphosarcoma. Prolonged parenteral administration of 1-6538 was well tolerated by rats and dogs. A trial of U-6538 was conducted in 4 patients with malignant neoplasms. Drug dosage was limited by precipitation of a metabolite in the urinary tract. Some patients had signs of renal injury. No definite evidence was obtained of clinical riboflavine deficiency or antitumor effect. An explanation for this is based on the metabolism of the drug.