Synthesis of C14-Labeled L-Sorbose and L-Ascorbic Acid

A m ethod is prese nted for preparing C'4-l abeled L-ascorbi c acid (vi tamin C) from labeled banum D-gluconate or D-glucose. The process is adapted from t he commercial synthesis of vi tamin C t hrough sorbitol, L-sorbose and potassium di-O-isopropylidene-2kelo-L-guloll.ate. In .th e cyanohydrin . synt hesis of labeled D-glucose, barium D-gluconate is used as an lI1term ed~at~ . Fo: prepanng labeled L-ascorbic acid, t he gluconate is converted t o t he lactone. Th iS IS effi CIent ly redu ced, by m eans of odium borohydride di rectly to so rb ito l, obviating t he in term ediate preparation of D-glucose. ' . If labeled D-glucose is m ore readily available t ha n t he correspondin g glu coni c acid (as for lllstance D-glucose-6-CI4 or randomly labeled D-glucose), t he sugar is red uced t o sorbi tol by the sodi um borohydride m ethod ; t he y ield is nearly quantitative. In a p reparat ion of L-ascorbic acid-6-CI4 from barium D-glu conatel -CI4 t he yield was 41.5 percent, based on t he glu conate, or 67. percent, based on t he in te rm ediate L-sorbose. A mixture of Methyl Cell osol ve, ethylene dichloride, and hydrogen chloride was found to be effective in co nver t in g potas ium di-O-isopropylidenc-2-kelo-L-gulonate to L-asco rbic acid .