PubMed · 14938990
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H SOBOTKA, F E STYNLER. Isotopically labeled nirvanol.. https://pubmed.ncbi.nlm.nih.gov/14938990/
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An efficient and straightforward two-step approach toward N3,N'3-polymethylene-bis-hydantoins was developed. As a first step, a pyroglutamate is reacted with a diisocyanate to produce a bis-carbamoyllactam. The second step is a double-ring transformation by treatment of this bis-carbamoyllactam with KOtBu in ethanol. In this fashion N3,N'3-polymethylene-bis-hydantoins are produced in two quantitative steps and under very mild conditions. When properly derivatized, these compounds can be converted to their macrocyclic derivatives upon treatment with 5 mol % of second-generation Grubbs' catalyst. These macrocyclic derivatives are so far not described in the literature. It was proven that exclusively (E)-isomers are formed.
[reaction: see text] A fluorous synthesis of hydantoins is introduced. The reaction of perfluoroalkyl (Rfh)-tagged amino esters with an isocyanate is followed by the cyclization of ureas and simultaneous cleavage of the fluorous tag to afford hydantoins. The product purification is performed by solid-phase extraction over FluoroFlash cartridges, and no fluorous solvent is involved in either the reaction or the separation processes. The same method applies to synthesis of thiohydantoins.
USP/NF 2000 [The United States Pharmacopeia, Rockville USA, 24th ed., 2000, p. 1868, The National Formulary, 19th ed. 2000] and PH. EUR. 1997 [European Pharmacopoeia, third ed., Council of Europe, Strasbourg, 1997, pp. 63-64] determine the iodine values according to Hanus with iodine monobromide in glacial acetic acid. This reagent can be replaced by a solution of 1,3-dibromo-5,5-dimethylhydantoin (DBH) and potassium iodide or iodine in the same solvent. Both reagents yield equivalent results by means of method comparison according to Passing and Bablok [J. Clin. Chem. Clin. Biochem. 21 (1983) 709; 22, (1984) 431] in relation to the official method of PH. EUR.