Heretofore, radiochemical yields of sugars position-labeled with carbon-14 have been only 5 to 10 percent. This paper reports an improved cyanohydrin synthesis, and the preparation of D-glucose-1-C 14 and D-mannose-1-C 14 from D-arabinose in yields of about 50 percent. Low yields in prior syntheses appear to have been due to several inefficient steps, and to the fact that extension of the carbon chain yields a pair of epimeric sugar derivatives, the proportion of which may not favor the desired

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... epimer. In the classical cyanohydrin synthesis of glucose from D-arabinose only 30 percent of the product goes to the gluconic epimer. To increase the yield of glucose, a systematic study was made of the proportions of the epimers formed from D-arabinose under a variety of conditions. It was found that the ratio of the epimers depends upon the conditions under which the reaction of the sugar with cyanide takes place. Thus, D-arabinose and cyanide, in the presence of sodium bicarbonate and carbon dioxide, yield about three parts of mannonic nitrile to one part of gluconic nitrile, but, in the presence of sodium carbonate the proportion is approximately reversed.