2,7,8-Trimethyl-(S)-2-(beta-carboxyethyl)-6-hydroxy chroman (S-LLU-alpha) isolated from human uremic urine is apparently an oxidative side-chain degradation product of gamma-tocopherol. This compound exhibits natriuretic activity in vivo and it appears to mediate the inhibition of the 70 pS K+ channel in the apical membrane of the thick ascending limb of the nephron. The stereochemistry at the C-2 of LLU-alpha has been unequivocally established to be S(+) by X-ray crystallographic analysis of a diastereomeric amide derivative. It was also established that the chroman ring oxidation of S-LLU-alpha proceeded without racemization at C-2. This finding can be extended to nonepimerization at C-2 of alpha-delta tocopherols (Vitamin E) during side-chain oxidation and stereospecificity (retention or inversion) of oxidative opening of the chroman ring. The resolution of the enantiomers of the parent compound and derivatives was accomplished by chiral high-performance liquid chromatography. The stereospecific enzymatic hydrolysis by an array of commercially available enzymes of the racemic methyl ester of LLU-alpha was investigated. The lipase from Humicola languinosa appears to be the best enzyme for resolution by selective hydrolysis of the racemic methyl ester.